determination-self-inter-incompatibility-relationships-apricot

Determination of Self- and Inter-(in)compatibility Relationships in Apricot Combining Hand-Pollination, Microscopy and Genetic Analyses

Self-incompatibility in Rosaceae is determined by a Gametophytic Self-Incompatibility System (GSI) that is mainly controlled by the multiallelic locus S. ...

Instituto de Hortofruticultura Subtropical y Mediterránea La Mayora (IHSM La Mayora-UMA-CSIC)

In most flowering plants, pollen is dispersed as monads. However, aggregated pollen shedding in groups of four or more pollen grains has arisen independently several times during angiosperm evolution. The reasons behind this phenomenon are largely unknown. In this study, we followed pollen development in Annona cherimola, a basal angiosperm species that releases pollen in groups of four, to investigate how pollen ontogeny may explain the rise and establishment of this character. We followed pollen development using immunolocalization and cytochemical characterization of changes occurring from anther differentiation to pollen dehiscence.

Pollen development in Annona cherimola Mill. (Annonaceae). Implications for the evolution of aggregated pollen.

Pollen performance is an important determinant for fertilization success, but high variability in pollen behavior both between and within species occurs in different years and under varying environmental conditions. Annona cherimola, an early-divergent angiosperm, is a species that releases a variable ratio of bicellular and tricellular hydrated pollen at anther dehiscence depending on temperature. The presence of both bi- and tricellular types of pollen is an uncommon characteristic in angiosperms and makes Annona cherimola an interesting model to study the effect of varying environmental conditions on subsequent pollen performance during the final stages of pollen development. In this work, we study the influence of changes in temperature and humidity during the final stages of pollen development on subsequent pollen performance, evaluating pollen germination, presence of carbohydrates, number of nuclei, and water content. At 25 °C, which is the average field temperature during the flowering period of this species, pollen had a viability of 60-70 %, starch hydrolyzed just prior to shedding, and pollen mitosis II was taking place, resulting in a mixture of bi- and tricellular pollen. This activity may be related to the pollen retaining 70 % water content at shedding. Temperatures above 30 °C resulted in a decrease in pollen germination, whereas lower temperatures did not have a clear influence on pollen germination, although they did have a clear effect on starch hydrolysis. On the other hand, slightly higher dehydration accelerated mitosis II, whereas strong dehydration arrested starch hydrolysis and reduced pollen germination. These results show a significant influence of environmental conditions on myriad pollen characteristics during the final stages of pollen development modifying subsequent pollen behavior and contributing to our understanding of the variability observed in pollen tube performance.

Pollen performance, cell number, and physiological state in the early-divergent angiosperm Annona cherimola Mill. (Annonaceae) are related to environmental conditions during the final stages of pollen development.

The pawpaw, , is an underutilized fruit crop native to North America that belongs to the mainly tropical, early-divergent family Annonaceae.  is the only genus within the Annonaceae with species adapted to cold climates. A thorough analysis of its reproductive biology, specifically pollen-pistil interaction during the progamic phase, is essential to understand both its adaptation to cold climates and how to optimize its fertilization and fruit set.

Pollen-pistil interaction in pawpaw (), the northernmost species of the mainly tropical family Annonaceae.

The mango (Mangifera indica) is a woody perennial crop currently cultivated worldwide in regions with tropical and subtropical climates. Despite its importance, an essential process such as pollen development, and, specifically, cell wall composition that influences crosstalk between somatic cells and the male germline, is still poorly understood in this species and in the Anacardiaceae as a whole. A detailed understanding of this process is particularly important to know the effect of low temperatures during flowering on pollen development that can be a limiting factor for fertilization and fruit set. To fill this gap, we performed a thorough study on the cell wall composition during pollen development in mango. The results obtained reveal a clear differentiation of the cell wall composition of the male germline by pectins, AGPs and extensins from the early developmental stages during microsporogenesis and microgametogenesis reflecting a restricted communication between the male germline and the surrounding somatic cells that is very sensitive to low temperatures. The combination of the results obtained provides an integrated study on cell wall composition of the male germline in mango that reveals the crucial role of the sporophyte and the gametophyte and the vulnerability of the process to low temperatures.

Pollen wall development in mango (Mangifera indica L., Anacardiaceae).

Self-incompatibility (SI) is one of the most efficient mechanisms to promote out-crossing in plants. However, SI could be a problem for fruit production. An example is apricot (), in which, as in other species of the Rosaceae, SI is determined by an S-RNase-based-Gametophytic Self-Incompatibility (GSI) system. Incompatibility relationships between cultivars can be established by an -allele genotyping PCR strategy. Until recently, most of the traditional European apricot cultivars were self-compatible but several breeding programs have introduced an increasing number of new cultivars whose pollination requirements are unknown. To fill this gap, we have identified the -allele of 44 apricot genotypes, of which 43 are reported here for the first time. The identification of  in 15 genotypes suggests that those cultivars are self-compatible. In five genotypes, self-(in)compatibility was established by the observation of pollen tube growth in self-pollinated flowers, since PCR analysis could not allowed distinguishing between the  and ₈ alleles. Self-incompatible genotypes were assigned to their corresponding self-incompatibility groups. The knowledge of incompatibility relationships between apricot cultivars can be a highly valuable tool for the development of future breeding programs by selecting the appropriate parents and for efficient orchard design by planting self-compatible and inter-compatible cultivars.

Jorge Lora

Instituto de Hortofruticultura Subtropical y Mediterránea La Mayora (IHSM La Mayora-UMA-CSIC)

Determination of Self- and Inter-(in)compatibility Relationships in Apricot Combining Hand-Pollination, Microscopy and Genetic Analyses