automating-citrus-budwood-processing-for-downstream-pathogen

Automating Citrus Budwood Processing for Downstream Pathogen Detection Through Instrument Engineering

Graft-transmissible, phloem-limited pathogens of citrus such as viruses, viroids, and bacteria are responsible for devastating epidemics and serious ...

University of California Riverside

Fluorescent pseudomonads have been associated, via diverse mechanisms, with suppression of root disease caused by numerous fungal and fungal-like pathogens. However, inconsistent performance in disease abatement, after their employment, has been a problem. This has been attributed, in part, to the inability of the biocontrol bacterium to maintain a critical threshold population necessary for sustained biocontrol activity. Our results indicate that a nitrogen stabilizer (N-Serve, Dow Agrosciences) selectively and significantly enhanced, by two to three orders of magnitude, the resident population of fluorescent pseudomonads in the amended (i.e., 25 microg ml(-1) nitrapyrin, the active ingredient) and recycled nutrient solution used in the cultivation of hydroponically grown gerbera and pepper plants. Pseudomonas putida was confirmed as the predominant bacterium selectively enhanced. Terminal restriction fragment length polymorphism (T-RFLP) analysis of 16S rDNA suggested that N-Serve selectively increased P. putida and reduced bacterial diversity 72 h after application. In vitro tests revealed that the observed population increases of fluorescent pseudomonads were preceded by an early growth suppression of indigenous aerobic heterotrophic bacteria (AHB) population. Interestingly, the fluorescent pseudomonad population did not undergo this decrease, as shown in competition assays. Xylene and 1,2,4-trimethylbenzene (i.e., the inert ingredients in N-Serve) were responsible for a significant percentage of the fluorescent pseudomonad population increase. Furthermore, those increases were significantly higher when the active ingredient (i.e., nitrapyrin) and the inert ingredients were combined, which suggests a synergistic response. P. putida strains were screened for the ability to produce antifungal compounds and for the antifungal activity against Pythium aphanidermatum and Phytophthora capsici. The results of this study suggest the presence of diverse mechanisms with disease-suppressing potential. This study demonstrates the possibility of using a specific substrate to selectively enhance and maintain desired populations of a natural-occurring bacterium such as P. putida, a trait considered to have great potential in biocontrol applications for plant protection.

Selective enhancement of the fluorescent pseudomonad population after amending the recirculating nutrient solution of hydroponically grown plants with a nitrogen stabilizer.

Rice blast, caused by the ascomycete Magnaporthe oryzae, is one of the most destructive rice diseases worldwide. Even though the disease has been present in California since 1996, there is no data for the pathogen population biology in the state. Using amplified fragment length polymorphisms and mating-type markers, the M. oryzae population diversity was investigated using isolates collected when the disease was first established in California and isolates collected a decade later. While in the 1990 samples, a single multilocus genotype (MLG) was identified (MLG1), over a decade later, we found 14 additional MLGs in the 2000 isolates. Some of these MLGs were found to infect the only rice blast-resistant cultivar (M-208) available for commercial production in California. The same samples also had a significant decrease of MLG1. MLG1 was found infecting the resistant rice cultivar M-208 on one occasion whereas MLG7 was the most common genotype infecting the M-208. MLG7 was identified in the 2000 samples, and it was not present in the M. oryzae population a decade earlier. Our results demonstrate a significant increase in genotypic diversity over time with no evidence of sexual reproduction and suggest a recent introduction of new virulent race(s) of the pathogen. In addition, our data could provide information regarding the durability of the Pi-z resistance gene of the M-208. This information will be critical to plant breeders in developing strategies for deployment of other rice blast resistance genes/cultivars in the future.

Genetic Structure of the Rice Blast Pathogen (Magnaporthe oryzae) over a Decade in North Central California Rice Fields.

High-throughput nucleic acid extraction is critical for the implementation of modern viroid detection assays. Successful large-scale nursery, field surveys, and other regulatory, quarantine, or research diagnostic programs are increasingly dependent on high-throughput tissue pulverization and nucleic acid extraction protocols. Magnetic bead-based approaches using semi-automated robotic equipment allow high-throughput extraction and purification of high-quality uniform total nucleic acids for each individual sample. Here, we describe a streamlined and optimized protocol for citrus tissue processing and RNA extraction that can be used for downstream applications such as viroid detection by reverse transcription-quantitative polymerase chain reaction.

Deborah Pagliaccia

Department of Microbiology and Plant Pathology,
California Agriculture and Food Enterprise (CAFÉ)

University of California Riverside

Automating Citrus Budwood Processing for Downstream Pathogen Detection Through Instrument Engineering

Deborah Pagliaccia

Department of Microbiology and Plant Pathology,California Agriculture and Food Enterprise (CAFÉ)

University of California Riverside

Automating Citrus Budwood Processing for Downstream Pathogen Detection Through Instrument Engineering

Department of Microbiology and Plant Pathology,
California Agriculture and Food Enterprise (CAFÉ)