This work was supported by Biotech Risk Assessment Grant Program competitive grand no. 2006-39454-17438 to A. Snow, K. Mercer, and H. Alexander from the United States Department of Agriculture, National Institute of Food and Agriculture. Experiments using this method were conducted at and supported by the University of Kansas Field Station, a research unit of the Kansas Biological Survey and the University of Kansas. The authors would like to thank P. Jourdan and E. Regnier for helpful reviews on earlier versions of this manuscript. Additionally, this work was aided by the contributions of the staff at the University of Kansas Field Station, Waterman Farm at the Ohio State University (OSU), the USDA Ornamental Plant Germplasm Center at OSU, and the Seed Biology Lab in the Department of Horticulture and Crop Science at OSU, especially E. Renze, S. Stieve, A. Evans, and E. Grassbaugh, for technical support.

1. Gather Seed from Multiple Species or Controlled Crosses of a Single Species
Note: This example used seed from 15 cross types within the species Helianthus annuus (sunflower) using wild, hybrid, and crop types as the maternal (seed producing) parent.
<ol>
	<li>At the end of the growing season, collect mature seed heads in labeled bags. Clean seed from chaff and place seed in envelopes labeled with parental cross type in standard format (i.e., maternal x paternal).</li>
	<li>Bulk seed together in large envelopes using equal amounts of seed from an equal number of identical parental cross types. For example, 100 seeds from 10 cross types with the same maternal and paternal parents. Label the envelopes with identifying (cross type) information. These large envelopes are seed masters for use in filling burial strips in Section 2.</li>
</ol>
<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td></td>
			<td colspan="3">Maternal Parent</td>
		</tr>
		<tr>
			<td>Paternal Parent</td>
			<td>Wild: WxW</td>
			<td>F1: WxC</td>
			<td>Crop: CxC</td>
		</tr>
		<tr>
			<td>Wild: WxW</td>
			<td>0% WxW</td>
			<td>25% F1xW &#8224;</td>
			<td>50% CxW &#8224;</td>
		</tr>
		<tr>
			<td>BC: WxF1 or F1xW</td>
			<td>12.5% WxBC</td>
			<td>37.5% F1xBC</td>
			<td>62.5% CxBC</td>
		</tr>
		<tr>
			<td>F1: WxC</td>
			<td>25% WxF1 &#8224;</td>
			<td>50% F1xF1</td>
			<td>75% CxF1 &#8224;</td>
		</tr>
		<tr>
			<td>F2: F1xF1</td>
			<td>25% WxF2</td>
			<td>50% F1xF2</td>
			<td>75% CxF2</td>
		</tr>
		<tr>
			<td>Crop: CxC</td>
			<td>50% WxC &#8224;</td>
			<td>75% F1xC &#8224;</td>
			<td>100% CxC</td>
		</tr>
	</tbody>
</table>
Table 1. Parental cross types produced from hand pollination. Sunflower crop-wild hybrid cross types were produced with hand-pollination for use in seed burial experiment. For all cross types, the maternal parent listed first and the paternal parent listed second. Cross types marked with &#8224; are part of reciprocal cross type pairs with the same % crop alleles but different maternal parents. Table has been previously published in: Pace, B. A. et al. (2015)15.
2. Create Custom Seed Burial Strips
NOTE: For this example, we had three removal date treatments and 15 replicates, so we required 45 strips total. This example uses 15 compartments per strip so, we required enough fine-meshed polyester fabric or mosquito netting to house 15, 7 x 10 cm compartments. See Figure 1.
<ol>
	<li>Start by cutting a 20 x 105 cm strip of fabric for each seed strip.</li>
	<li>Measure and mark compartments, then fold the fabric in half. Using a high-temperature glue gun, seal one short (10 cm) end. Once the glue cools slightly, but not completely, press the fabric sides together to create a seal. 
	CAUTION: High-temperature glue and glue gun tips can cause burns if contact with skin is prolonged.</li>
	<li>Glue lines from the folded edge to the open short end at each compartment mark. Press the two fabric sides together along the glue lines to ensure seals without holes between compartments. Seeds migrating between compartments contribute to experimental error. 
	NOTE: Now that the compartments have been created, the unfolded edge should remain open and ready to receive seed and their identifying information (cross type name).</li>
	<li>Randomly assign seed cross types to compartments for each strip.
	<ol>
		<li>Fill seed compartments with a uniform number of seeds (20 for each compartment are used in this example). For labels, use industrial permanent markers on cut-to-fit plastic garden darts so that they are able to withstand burial. 
		NOTE: Alternative labeling methods may be used.</li>
		<li>After each compartment is filled with seed and its label, seal the compartment immediately with the high-temperature glue gun. Proceed until the entire seed strip is completely sealed. Label overall strip in the first compartment with replicate, block and/or treatment information. 
		NOTE: For our study, since we had temporal removals, blocks, and replicate strips within blocks, we included all of this information.</li>
		<li>Check for gaps between compartments and spot glue as needed before moving on to the next strip.</li>
	</ol>
	</li>
</ol>
<img alt="Figure 1" src="/files/ftp_upload/54663/54663fig1.jpg" /> 
Figure 1. Burial seed strip schematic. Example of burial strip showing cross type identification for individual compartments. Maternal parent is listed first with the paternal parent listed second. Colors indicate different maternal parentage, with yellow for wild, blue for F1 hybrid, and red for crop. <a href="http://cloudfront.jove.com/files/ftp_upload/54663/54663fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
3. Bury Seed Strips in the Field
<ol>
	<li>Dig plots to the specified depth to house strips. Assign strips to individual blocks in which strips are randomly arranged to allow for removal date to be used as the main plot and compartment identity (in this example, cross type) as the subplot in analysis.</li>
	<li>Cover strips with earth. Cut metal mesh hardware cloth to be 10 cm larger than plots and place over buried strips. Use U-pins to secure edges and cover cloth edges with earth. 
	NOTE: This covering is for excluding burrowing seed predators. As another option, Mercer et al.13 constructed and buried boxes of hardware cloth that surrounded the seed strips due to intense gopher pressure in their field location.)</li>
	<li>Place colored surveyor&#39;s flags to distinguish strip location and removal dates to complement clear written records.</li>
</ol>
4. Excavate Strips and Evaluate Seed
<ol>
	<li>Dig up seed strips assigned to a given removal date. Maintain the strips in a cool moist environment until they reach the laboratory where seed evaluation will take place. This can be accomplished by wrapping the strips in wet newspaper and placing them in a cooler for transport or overnight shipping.</li>
	<li>Rinse mud and soil from strips in water until strips are clean enough that external debris will not obscure seeds.</li>
	<li>Use scissors to cut open one compartment at a time. Count germinated seeds and remove them. Count clearly dead seeds (e.g., rotting, or putrefied seeds). Place ungerminated seeds on labeled, wet Petri-sized blotter paper to further distinguish ungerminated, dormant, and dead seeds.
	<ol>
		<li>Place Petri dishes with ungerminated seeds into a growth chamber set for standard germination conditions: 25 &#176;C /10 &#176;C 12 hr day/night. Allow seeds one week to germinate. Any that do, count these as viable, but ungerminated since they did not germinate under field conditions.</li>
	</ol>
	</li>
	<li>After the growth chamber treatment, test remaining ungerminated seeds for viability using Tetrazolium chloride (TZ)13. To accomplish this, make up a percent solution of TZ appropriate for the study species using the AOSA Tetrazolium Testing Handbook14. For this example, a 1% solution is used.
	<ol>
		<li>Cut the ungerminated seeds in half and place one half were the embryo and endosperm are visible in a Petri dish containing enough TZ solution to cover the seed (seeds may float, this is okay).</li>
		<li>Place TZ Petri dishes into an incubator set at 30 &#176;C and wait 3 hr. Note: Higher temperatures will result in a faster reaction, if desired, but overstaining is a risk.</li>
	</ol>
	</li>
	<li>Remove Petri dishes from the incubator and evaluate. Seeds that have stained red in their embryos are germinable, while unstained seeds are dead. Consult the AOSA Tetrazolium Testing Handbook for more detail on distinguishing marginal cases and particular species.</li>
</ol>

<ol>
	<li>Walck, J. L., Baskin, J. M., Baskin, C. C., Hidayati, S. N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Defining+transient+and+persistent+seed+banks+in+species+with+pronounced+seasonal+dormancy+and+germination+patterns.">Defining transient and persistent seed banks in species with pronounced seasonal dormancy and germination patterns.</a> Seed Sci Res. 15 (3), 189-196 (2005).</li><li>Alexander, H. A., Schrag, A. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Role+of+soil+seed+banks+and+newly+dispersed+seeds+in+population+dynamics+of+the+annual+sunflower.+Helianthus+annuus.">Role of soil seed banks and newly dispersed seeds in population dynamics of the annual sunflower. Helianthus annuus.</a> J Ecol. 91, 987-998 (2003).</li><li>Burnside, O. C., Wilson, R. G., Weiseberg, S., Hubbard, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Seed+longevity+of+41+weed+species+buried+17+years+in+eastern+and+western.">Seed longevity of 41 weed species buried 17 years in eastern and western.</a> Weed Sci. 44 (1), 74-86 (1996).</li><li>Baskin, C. C., Baskin, J. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Seeds: Ecology, biogeography, and evolution of dormancy and Germination. , (2001).</li><li>Finch-Savage, W. E., Leubner-Metzger, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Seed+dormancy+and+the+control+of+germination.">Seed dormancy and the control of germination.</a> New Phytol. 171, 501-523 (2006).</li><li>Baskin, J. M., Baskin, C. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+classification+system+for+seed+dormancy.">A classification system for seed dormancy.</a> Seed Sci Res. 14 (1), 1-16 (2004).</li><li>Donohue, K., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Environmental+and+genetic+influences+on+the+germination+of+Arabidopsis+thaliana+in+the+field.">Environmental and genetic influences on the germination of Arabidopsis thaliana in the field.</a> Evolution. 54 (4), 740-757 (2005).</li><li>Roach, D. A., Wulff, R. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Maternal+effects+in+plants.">Maternal effects in plants.</a> Ann Rev Ecol Syst. 18, 209-235 (1987).</li><li>Pace, B. A., Alexander, H. M., Emry, J. D., Mercer, K. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Seed+fates+in+crop-wild+hybrid+sunflower:+crop+allele+and+maternal+effects.">Seed fates in crop-wild hybrid sunflower: crop allele and maternal effects.</a> Evol Appl. 8 (2), 121-132 (2015).</li><li>Alexander, H. M., Emry, D. J., Pace, B. A., Kost, M. A., Sparks, K. A., Mercer, K. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Roles+of+maternal+effects+and+nuclear+genetic+composition+change+across+the+life+cycle+of+crop-wild+hybrids.">Roles of maternal effects and nuclear genetic composition change across the life cycle of crop-wild hybrids.</a> Am J Bot. 101 (7), 1176-1188 (2014).</li><li>Stewart, N. C., Matthew, J., Halfhill, D., Warwick, S. I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Transgene+introgression+from+genetically+modified+crops+into+their+wild+relatives.">Transgene introgression from genetically modified crops into their wild relatives.</a> Genetics. 4, 806-817 (2003).</li><li>Mercer, K. L., Shaw, R. G., Wyse, D. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Increased+germination+of+diverse+crop-wild+hybrid+sunflower+seeds.">Increased germination of diverse crop-wild hybrid sunflower seeds.</a> Ecol Appl. 16, 845-854 (2006).</li><li>Delouche, J. C., Still, T. W., Rapset, M., Lienhard, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+tetrazolium+test+for+seed+viability.">The tetrazolium test for seed viability.</a> Mississippi Sta Uni Ag Exp Sta Techn Bull. 51, 1-63 (1962).</li><li>Association of Official Seed Analysts. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Tetrazolium Testing Handbook. , (2010).</li><li>Alexander, H. M., Emry, D. J., Pace, B. A., Kost, M. A., Sparks, K. A., Mercer, K. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Roles+of+maternal+effects+and+nuclear+genetic+composition+change+across+the+life+cycle+of+crop-wild+hybrids.">Roles of maternal effects and nuclear genetic composition change across the life cycle of crop-wild hybrids.</a> Am J Bot. 10 (7), 1176-1188 (2014).</li><li>Weiss, A. N., Primer, S. B., Pace, B. A., Mercer, K. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Maternal+effects+and+embryo+genetics:+germination+and+dormancy+of+crop-wild+sunflower+hybrids.">Maternal effects and embryo genetics: germination and dormancy of crop-wild sunflower hybrids.</a> Seed Sci Res. 23, 241-255 (2013).</li></ol>

The authors have nothing to disclose.

Here we present methods for using seed burial strips to observe seed germination, dormancy and mortality of diverse seed stocks at preselected time periods in the field. The advantages of using strips rather than individual packets lie in (1) the speed of strip and compartment construction over creation of individual packets; and (2) the ease and speed of removing multiple compartments in one motion without the danger of omitting a packet or removing one unintentionally. As two of the removal dates in the example present...

The overall goal of this method is to reliably assess seed survival over time under field conditions.
Soil seed banks are a reserve of dispersed, viable yet ungerminated seeds distributed either on the soil surface, within surface litter, or within the soil profile, which may persist transiently or for many years1,2. When seed burial methods similar to those presented here were applied to a 17-year study using several dozen species, viable seeds were found in many of the species tested3. Seed dormancy is a block to seed germination until the appropriate combination of conditions for seedling survival arise4. Remaining dormant can allow seeds to survive harsh conditions, such as low winter temperatures, nutrient limitation, or seasonal drought, until an external trigger for dormancy-release allows for germination. Triggers for dormancy-release can vary from exposure to extended cold, compounds left by fire, or physical attack on the seed coat through abrasion or contact with animal stomach acids5. As germination cues can be genera or species specific and often result from past natural selection, maladaptive seed germination is that which occurs at an inappropriate time, and may result in seed or seedling mortality or poor seedling growth. While dormancy has been classified into a number of types based on the mechanisms of dormancy release (e.g., physical dormancy, physiological dormancy),6 seed dormancy remains one of the least understood topics in plant biology. Thus, field studies that allow for assessment of the status of individual seeds or groups of seeds under relevant ecological conditions have higher explanatory power than those that simply rely on standard germination tests in the laboratory.
Exploitation of known seed characteristics can provide insight into the mechanisms of dormancy. Control of seed dormancy is complex, including genetic control of physiological and morphological factors. While a full understanding of the breadth of dormancy mechanisms has yet to be elucidated, a general model has emerged, involving a feedback relationship between the two plant hormones Gibberellic Acid (GA) and Abscisic Acid (ABA)7. In this generalized model for seeds with a physiological component to their dormancy, GA serves as signal for dormancy release, while ABA serves to maintain the dormant state. Maternal genetic effects as well as the maternal growth environment can influence dormancy and other seed traits, such as size, through maternally generated tissues and developmental signals8. Maternally generated external structures (or seed coverings) may maintain dormancy, at times in combination with physiological cues. Since maternally derived seed coverings are controlled by the mother plant&#39;s genes, they may not reflect the seed&#39;s actual nuclear genetic make-up. We have used the Helianthus annuus achenes from an array of crop-wild hybrid crosses to tease out these maternal vs. embryo genetic effects on seed characteristics9,10. Thus, study designs that include diverse species, cross types, or genotypes can glean information about the ecology and genetics of seed dormancy, germination and survival.
An important example of how seed germination and survival phenotypes can affect population dynamics can be seen in crop-wild hybrid zones. Selection during domestication of cultivated plants eliminates most dormancy and reduces a seed&#39;s ability to survive outside of the growing season. Yet gene flow, or hybridization, between the cultivated and wild types in crop-wild hybrid zones can reintroduce crop alleles (or genetic variants) into a wild population, with potential effects on seed bank dynamics. Hybrids between cultivated and wild relatives potentially found in crop-wild hybrid zones may possess a variety of intermediate dormancy phenotypes, with only a few phenotypes expected to survive conditions outside of cultivation (e.g., winter months)11.
The aim of this manuscript is to show how, using the seed burial strip method, we can evaluate germination, dormancy, and survival of a range of seed types at different time periods to investigate their natural variation under field conditions. In our example, we employed sunflower seeds from 15 crop-wild hybrid cross types since we are interested in maternal and embryo genetic effects on seed characteristics.

<table><tbody><tr><td>Small coin envelopes</td><td>Any</td><td></td><td></td></tr><tr><td>Large coin envelopes</td><td>Any</td><td></td><td></td></tr><tr><td>fine meshed polyester mosquito netting</td><td>Any</td><td></td><td></td></tr><tr><td>high-temperature glue gun</td><td>Any</td><td></td><td></td></tr><tr><td>high-temperature glue stick refills</td><td>Any</td><td></td><td></td></tr><tr><td>Industrial permenant markers</td><td>Any</td><td></td><td></td></tr><tr><td>plastic garden labels</td><td>Any</td><td></td><td></td></tr><tr><td>scissors</td><td>Any</td><td></td><td></td></tr><tr><td>Shovel</td><td>Any</td><td></td><td></td></tr><tr><td>Metal mesh hardward cloth</td><td>Any</td><td></td><td></td></tr><tr><td>Surveyor&#039;s flags, multiple colors</td><td>Any</td><td></td><td></td></tr><tr><td>Wet newspaper</td><td>Any</td><td></td><td></td></tr><tr><td>cooler</td><td>Any</td><td></td><td></td></tr><tr><td>blotter paper</td><td>Any</td><td></td><td></td></tr><tr><td>petri dishes</td><td>Any</td><td></td><td></td></tr><tr><td>Temp. controlled growth chamber</td><td>Any</td><td></td><td></td></tr><tr><td>razor blades</td><td>Any</td><td></td><td></td></tr><tr><td>Petri dishes</td><td>Any</td><td></td><td></td></tr><tr><td>Tetrazolium chloride</td><td>Any</td><td></td><td></td></tr><tr><td>water</td><td>Any</td><td></td><td></td></tr><tr><td>heat incubator</td><td>Any</td><td></td><td></td></tr></tbody></table>

reliable method for assessing seed germination, dormancy, and mortality under field conditions

We describe techniques for approximating seed bank dynamics over time using Helianthus annuus as an example study species. Strips of permeable polyester fabric and glue can be folded and glued to construct a strip of compartments that house seeds and identifying information, while allowing contact with soil leachate, water, microorganisms, and ambient temperature. Strips may be constructed with a wide range of compartment numbers and sizes and allow the researcher to house a variety of genotypes within a single species, different species, or seeds that have experienced different treatments. As opposed to individual seed packets, strips are more easily retrieved as a unit. While replicate packets can be included within a strip, different strips can act as blocks or can be retrieved at different times for observation of seed behavior over time. We used a high temperature glue gun to delineate compartments and sealed the strips once the seed and tags identifying block and removal times were inserted. The seed strips were then buried in the field at the desired depth, with the location marked for later removal. Burrowing animal predators were effectively excluded by use of a covering of metal mesh hardware cloth on the soil surface. After the selected time interval for burial, strips were dug up and seeds were assessed for germination, dormancy and mortality. While clearly dead seeds can often be distinguished from ungerminated living ones by eye, dormant seeds were conclusively identified using a standard Tetrazolium chloride colorimetric test for seed viability.

Cross types with varied maternal parentage and crop allele percentage (Table 1) differed across removal dates in percent germinated, ungerminated, and dead seed (Fig. 2 and 3). Using TZ testing of ungerminated seeds, we found some truly dormant seeds at the second removal (early spring) (Table 2), while all seeds ungerminated by the third removal (spring) were found to be truly dormant.
<p class="jove_content" fo:keep...

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Reliable Method for Assessing Seed Germination, Dormancy, and Mortality under Field Conditions

Here we present a protocol for assessing seed survivorship, germination and dormancy under field conditions using buried, labeled seed strips and tetrazolium chloride (TZ) viability testing.

We describe techniques for approximating seed bank dynamics over time using Helianthus annuus as an example study species. Strips of permeable polyester ...

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10.5K Views.  Ohio State University. Here we present a protocol for assessing seed survivorship, germination and dormancy under field conditions using buried, labeled seed strips and tetrazolium chloride (TZ) viability testing.

Video: Reliable Method for Assessing Seed Germination, Dormancy, and Mortality under Field Conditions

Protocols for Robust Herbicide Resistance Testing in Different Weed Species

Robust protocols to test putative herbicide resistant weed populations at whole plant level are essential to confirm the resistance status. The presented protocols, based on whole-plant bioassays performed in a greenhouse, can be readily adapted to a wide range of weed species and herbicides through appropriate variants. Seed samples from plants that survived a field herbicide treatment are collected and stored dry at low temperature until used. Germination methods differ according to weed species and seed dormancy type. Seedlings at similar growth stage are transplanted and maintained in the greenhouse under appropriate conditions until plants have reached the right growth stage for herbicide treatment. Accuracy is required to prepare the herbicide solution to avoid unverifiable mistakes. Other critical steps such as the application volume and spray speed are also evaluated. The advantages of this protocol, compared to others based on whole plant bioassays using one herbicide dose, are related to the higher reliability and the possibility of inferring the resistance level. Quicker and less expensive in vivo or in vitro diagnostic screening tests have been proposed (Petri dish bioassays, spectrophotometric tests), but they provide only qualitative information and their widespread use is hindered by the laborious set-up that some species may require. For routine resistance testing, the proposed whole plant bioassay can be applied at only one herbicide dose, so reducing the costs.

A robust and flexible approach to confirm herbicide resistance in weed populations is presented. This protocol allows the herbicide resistance levels to be inferred and applied to a wide range of weed species and herbicides with minor adaptations.

Robust protocols to test putative herbicide resistant weed populations at whole plant level are essential to confirm the resistance status. The presented ...

Quantification of Fungal Colonization, Sporogenesis, and Production of Mycotoxins Using Kernel Bioassays

The rotting of grains by seed-infecting fungi poses one of the greatest economic challenges to cereal production worldwide, not to mention serious risks to human and animal health. Among cereal production, maize is arguably the most affected crop, due to pathogen-induced losses in grain integrity and mycotoxin seed contamination. The two most prevalent and problematic mycotoxins for maize growers and food and feed processors are aflatoxin and fumonisin, produced by Aspergillus flavus and Fusarium verticillioides, respectively.
Recent studies in molecular plant-pathogen interactions have demonstrated promise in understanding specific mechanisms associated with plant responses to fungal infection and mycotoxin contamination1,2,3,4,5,6. Because many labs are using kernel assays to study plant-pathogen interactions, there is a need for a standardized method for quantifying different biological parameters, so results from different laboratories can be cross-interpreted. For a robust and reproducible means for quantitative analyses on seeds, we have developed in-lab kernel assays and subsequent methods to quantify fungal growth, biomass, and mycotoxin contamination. Four sterilized maize kernels are inoculated in glass vials with a fungal suspension (106) and incubated for a predetermined period. Sample vials are then selected for enumeration of conidia by hemocytometer, ergosterol-based biomass analysis by high performance liquid chromatography (HPLC), aflatoxin quantification using an AflaTest fluorometer method, and fumonisin quantification by HPLC.

The devastation of cereal crops by seed-infecting fungi has prompted numerous research efforts to better understand plant-pathogen interactions. To study seed-fungal interactions in a laboratory setting, we developed a robust method for the quantification of fungal reproduction, biomass, and mycotoxin contamination using kernel bioassays.

The rotting of grains by seed-infecting fungi poses one of the greatest economic challenges to cereal production worldwide, not to mention serious risks ...

Immunology and Infection

A Direct and Simple Method to Assess Drosophila melanogaster's Viability from Embryo to Adult

In Drosophila melanogaster, viability assays are used to determine the fitness of certain genetic backgrounds. Allelic variations can result in partial or complete loss of viability at different stages of development. Our lab has developed a method to assess viability in Drosophila from embryo to fully mature adult. The method relies on quantifying the number of progeny present at different stages during development, starting with hatched embryos. After embryos have been quantified, additional stages are counted, including L1/L2, pupae, and mature adults. After all stages have been examined, a statistical analysis such as the chi-square test is used to determine if there is a significant difference between the starting number of progeny (hatched embryos) and later stages culminating in the observed number of adults, thus rejecting or accepting the null hypothesis (that the number of hatched embryos will be equal to the number of larvae, pupae, and adults recorded throughout the stages of development). The primary advantage of this assay is its simplicity and accuracy, as it does not require an embryo rinse to transfer them to the food vial, avoiding losses from technical errors. Although the protocol described here does not directly examine L2/L3 larvae, additional steps can be added to account for these. Comparing the number of hatched embryos, L1, pupae, and adults can help determine if viability was compromised during the L2/L3 stages for further studies (the use of colored food helps with visual identification of larvae). Overall, this method can help Drosophila researchers and educators determine when viability is compromised during the fly life cycle. Routine assessment of stocks using this assay can prevent accumulation of secondary mutations that may affect the phenotype of the originally isolated mutant, especially if the original mutations affect fitness. For this reason, our lab maintains multiple copies of each of our Dm ime4 alleles and routinely checks the purity of each stock with this method in addition to other molecular analyses.&#160;

A Direct and Simple Method to Assess Drosophila melanogaster's Viability from Embryo to Adult

This protocol is designed to assess the viability of Drosophila at every developmental stage, from embryo to adult. The method can be used to determine and compare the viability of different genotypes or growth conditions.

In Drosophila melanogaster, viability assays are used to determine the fitness of certain genetic backgrounds. Allelic variations can result in partial or ...

Developmental Biology

A Seed Coat Bedding Assay to Genetically Explore In Vitro How the Endosperm Controls Seed Germination in Arabidopsis thaliana

The Arabidopsis endosperm consists of a single cell layer surrounding the mature embryo and playing an essential role to prevent the germination of dormant seeds or that of nondormant seeds irradiated by a far red (FR) light pulse. In order to further gain insight into the molecular genetic mechanisms underlying the germination repressive activity exerted by the endosperm, a &#34;seed coat bedding&#34; assay (SCBA) was devised. The SCBA is a dissection procedure physically separating seed coats and embryos from seeds, which allows monitoring the growth of embryos on an underlying layer of seed coats. Remarkably, the SCBA reconstitutes the germination repressive activities of the seed coat in the context of seed dormancy and FR-dependent control of seed germination. Since the SCBA allows the combinatorial use of dormant, nondormant and genetically modified seed coat and embryonic materials, the genetic pathways controlling germination and specifically operating in the endosperm and embryo can be dissected. Here we detail the procedure to assemble a SCBA.

A Seed Coat Bedding Assay to Genetically Explore In Vitro How the Endosperm Controls Seed Germination in Arabidopsis thaliana

We present the procedure to assemble a seed coat bedding assay (SCBA) from Arabidopsis thaliana seeds. The SCBA was shown to be a powerful tool to explore genetically and in vitro how the endosperm controls seed germination in dormant seeds and in response to light cues. The SCBA is in principle applicable under any situation where the endosperm is suspected to influence embryonic growth.

The Arabidopsis endosperm consists of a single cell layer surrounding the mature embryo and playing an essential role to prevent the germination of ...

Biology

Standardized Method for High-throughput Sterilization of Arabidopsis Seeds

Arabidopsis thaliana (Arabidopsis) seedlings often need to be grown on sterile media. This requires prior seed sterilization to prevent the growth of microbial contaminants present on the seed surface. Currently, Arabidopsis seeds are sterilized using two distinct sterilization techniques in conditions that differ slightly between labs and have not been standardized, often resulting in only partially effective sterilization or in excessive seed mortality. Most of these methods are also not easily scalable to a large number of seed lines of diverse genotypes. As technologies for high-throughput analysis of Arabidopsis continue to proliferate, standardized techniques for sterilizing large numbers of seeds of different genotypes are becoming essential for conducting these types of experiments. The response of a number of Arabidopsis lines to two different sterilization techniques was evaluated based on seed germination rate and the level of seed contamination with microbes and other pathogens. The treatments included different concentrations of sterilizing agents and times of exposure, combined to determine optimal conditions for Arabidopsis seed sterilization. Optimized protocols have been developed for two different sterilization methods: bleach (liquid-phase) and chlorine (Cl2) gas (vapor-phase), both resulting in high seed germination rates and minimal microbial contamination. The utility of these protocols was illustrated through the testing of both wild type and mutant seeds with a range of germination potentials. Our results show that seeds can be effectively sterilized using either method without excessive seed mortality, although detrimental effects of sterilization were observed for seeds with lower than optimal germination potential. In addition, an equation was developed to enable researchers to apply the standardized chlorine gas sterilization conditions to airtight containers of different sizes. The protocols described here allow easy, efficient, and inexpensive seed sterilization for a large number of Arabidopsis lines.

The objective of this study was to determine the effects of bleach and chlorine gas sterilization on seed germination of a range of Arabidopsis genotypes grown on sterile media. Optimized sterilization protocols have been developed to prevent the growth of microbial contaminants while providing satisfactory seed survival.

Arabidopsis thaliana (Arabidopsis) seedlings often need to be grown on sterile media. This requires prior seed sterilization to prevent the growth of ...

Investigating Teliospore Germination Using Microrespiration Analysis and Microdissection

Smut fungi are the etiological agents of several devastating agricultural diseases. They are characterized by the production of teliospores, which are thick-walled dispersal agents. Teliospores can remain dormant for decades. The dormancy is characterized by low metabolic rates, paused macromolecular biosynthesis and greatly reduced levels of respiration. Upon receiving required environmental signals, teliospores germinate to produce haploid cells, which can initiate new rounds of infection. Teliospore germination is characterized by the resumption of macromolecular biosynthesis, increased respiration and dramatic morphological changes. In order to precisely measure changes in cellular respiration during the early stages of germination, we have developed a simple protocol employing a Clark-type respirometer. The later stages of germination are distinguished by specific morphological changes, but germination is asynchronous. We developed a microdissection technique that enables us to collect teliospores at distinct germination stages.

Smut fungi cause many devastating agricultural diseases. They are dispersed as dormant teliospores that germinate in response to environmental cues. We outline two methods to investigate molecular changes during germination: measuring respiration increase to detect metabolic activation and assessing changing molecular events by isolating teliospores at distinct morphological stages.

Smut fungi are the etiological agents of several devastating agricultural diseases. They are characterized by the production of teliospores, which are ...

Identification of Novel Regulators of Plant Transpiration by Large-Scale Thermal Imaging Screening in Helianthus Annuus

Plant adaptation to biotic and abiotic stresses is governed by a variety of factors, among which the regulation of stomatal aperture in response to water deficit or pathogens plays a crucial role. Identifying small molecules that regulate stomatal movement can therefore contribute to understanding the physiological basis by which plants adapt to their environment. Large-scale screening approaches that have been used to identify regulators of stomatal movement have potential limitations: some rely heavily on the abscisic acid (ABA) hormone signaling pathway, therefore excluding ABA-independent mechanisms, while others rely on the observation of indirect, long-term physiological effects such as plant growth and development. The screening method presented here allows the large-scale treatment of plants with a library of chemicals coupled with a direct quantification of their transpiration by thermal imaging. Since evaporation of water through transpiration results in leaf surface cooling, thermal imaging provides a non-invasive approach to investigate changes in stomatal conductance over time. In this protocol, Helianthus annuus seedlings are grown hydroponically and then treated by root feeding, in which the primary root is cut and dipped into the chemical being tested. Thermal imaging followed by statistical analysis of cotyledonary temperature changes over time allows for the identification of bioactive molecules modulating stomatal aperture. Our proof-of-concept experiments demonstrate that a chemical can be carried from the cut root to the cotyledon of the sunflower seedling within 10 minutes. In addition, when plants are treated with ABA as a positive control, an increase in leaf surface temperature can be detected within minutes. Our method thus allows the efficient and rapid identification of novel molecules regulating stomatal aperture.

Identification of Novel Regulators of Plant Transpiration by Large-Scale Thermal Imaging Screening in Helianthus Annuus

We provide a method for identifying modulators of foliar transpiration by large-scale screening of a compound library.

Plant adaptation to biotic and abiotic stresses is governed by a variety of factors, among which the regulation of stomatal aperture in response to water ...

Dry Root Rot Disease Assays in Chickpea: a Detailed Methodology

Dry root rot (DRR) disease is an emerging biotic stress threat to chickpea cultivation around the world. It is caused by a soil-borne fungal pathogen, Rhizoctonia bataticola. In the literature, comprehensive and detailed step-by-step protocols on disease assays are sparse. This article provides complete details on the steps involved in setting up a blotting paper technique for quickly screening genotypes for resistance to DRR. The blotting paper technique is easy and less expensive. Another method, based on the sick pot approach, is a mimic of natural infection and can be applied to study the interacting components&#8212;plant, pathogen, and environment&#8212;involved in the disease triangle.
Moreover, in nature, DRR occurs mostly in rainfed chickpea cultivation areas, where soil moisture recedes as crop growth advances. Drought stress is known to predispose chickpea plants to DRR disease. Pathomorphological and molecular understanding of plant-pathogen interaction under drought stress can pave the way for the identification of elite DRR-resistant varieties from the chickpea germplasm pool. This article provides a stepwise methodology for the preparation of a sick pot and subsequent disease assay. Overall, the information presented herein will help researchers prepare R. bataticola fungal inoculum, maintain this pathogen, set up the blotting paper technique, prepare sick culture and sick pot, and assess pathogen infection in chickpea plants.

This study presents methodologies to study the pathomorphological and molecular mechanisms underlying chickpea&#8211;Rhizoctonia bataticola interaction. The blotting paper method is useful to rapidly study chickpea genotype responses, while the sick pot-based method can be used to simultaneously impose drought and R. bataticola infection and screen for tolerant genotypes.

Dry root rot (DRR) disease is an emerging biotic stress threat to chickpea cultivation around the world. It is caused by a soil-borne fungal pathogen, ...

High-throughput, Robust and Highly Time-flexible Method for Surface Sterilization of Arabidopsis Seeds

Arabidopsis is by far the plant model species most widely used for functional studies. The surface sterilization of Arabidopsis seeds is a fundamental step required towards this end. Thus, it is paramount to establish high-throughput Arabidopsis seed surface sterilization methods to handle tens to hundreds of samples (e.g., transgenic lines, ecotypes, or mutants) at once. A seed surface sterilization method based on the efficient elimination of liquid in tubes with a homemade suction device constructed from a common vacuum pump is presented in this study. By dramatically reducing labor-intensive hands-on time with this method handling several hundreds of samples in one day is possible with little effort. Series time-course analyses further indicated a highly flexible time range of surface sterilization by maintaining high germination rates. This method could be easily adapted for surface sterilization of other kinds of small seeds with simple customization of the suction device according to the seed size, and the speed desired to eliminate the liquid.

A high-throughput protocol for the surface sterilization of Arabidopsisthaliana (Arabidopsis) seeds is provided, optimizing the liquid handling steps with a simple suction device constructed with a vacuum pump. Hundreds of seed samples can be surface-sterilized in one day.

Arabidopsis is by far the plant model species most widely used for functional studies. The surface sterilization of Arabidopsis seeds is a fundamental ...

Microscopy Techniques for Interpreting Fungal Colonization in Mycoheterotrophic Plants Tissues and Symbiotic Germination of Seeds

Structural botany is an indispensable perspective to fully understand the ecology, physiology, development, and evolution of plants. When researching mycoheterotrophic plants (i.e., plants that obtain carbon from fungi), remarkable aspects of their structural adaptations, the patterns of tissue colonization by fungi, and the morphoanatomy of subterranean organs can enlighten their developmental strategies and their relationships with hyphae, the source of nutrients. Another important role of symbiotic fungi is related to the germination of orchid seeds; all Orchidaceae species are mycoheterotrophic during germination and seedling stage (initial mycoheterotrophy), even the ones that photosynthesize in adult stages. Due to the lack of nutritional reserves in orchid seeds, fungal symbionts are essential to provide substrates and enable germination. Analyzing germination stages by structural perspectives can also answer important questions regarding the fungi interaction with the seeds. Different imaging techniques can be applied to unveil fungi endophytes in plant tissues, as are proposed in this article. Freehand and thin sections of plant organs can be stained and then observed using light microscopy. A fluorochrome conjugated to wheat germ agglutinin can be applied to the fungi and co-incubated with Calcofluor White to highlight plant cell walls in confocal microscopy. In addition, the methodologies of scanning and transmission electron microscopy are detailed for mycoheterotrophic orchids, and the possibilities of applying such protocols in related plants is explored. Symbiotic germination of orchid seeds (i.e., in the presence of mycorrhizal fungi) is described in the protocol in detail, along with possibilities of preparing the structures obtained from different stages of germination for analyses with light, confocal, and electron microscopy.

This protocol aims to provide detailed procedures for collecting, fixing, and maintaining mycoheterotrophic plant samples, applying different microscopy techniques such as scanning and transmission electron microscopy, light, confocal, and fluorescence microscopy to study fungal colonization in plants tissues and seeds germinated with mycorrhizal fungi.

Structural botany is an indispensable perspective to fully understand the ecology, physiology, development, and evolution of plants. When researching ...

Reliable Method for Assessing Seed Germination, Dormancy, and Mortality under Field Conditions

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Protocols for Robust Herbicide Resistance Testing in Different Weed Species

Quantification of Fungal Colonization, Sporogenesis, and Production of Mycotoxins Using Kernel Bioassays

A Direct and Simple Method to Assess Drosophila melanogaster's Viability from Embryo to Adult

A Seed Coat Bedding Assay to Genetically Explore In Vitro How the Endosperm Controls Seed Germination in Arabidopsis thaliana

Standardized Method for High-throughput Sterilization of Arabidopsis Seeds

Investigating Teliospore Germination Using Microrespiration Analysis and Microdissection

Identification of Novel Regulators of Plant Transpiration by Large-Scale Thermal Imaging Screening in Helianthus Annuus

Dry Root Rot Disease Assays in Chickpea: a Detailed Methodology

High-throughput, Robust and Highly Time-flexible Method for Surface Sterilization of Arabidopsis Seeds

Microscopy Techniques for Interpreting Fungal Colonization in Mycoheterotrophic Plants Tissues and Symbiotic Germination of Seeds