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Analysis of the expression of partial self-incompatibility in almond (Prunus dulcis)

Martinez-Garcia, P. J., Ortega, E., Dicenta, F.
Journal of horticultural science & biotechnology 2011 v.86 no.3 pp. 284-290
Prunus dulcis, alleles, almonds, biotechnology, buds, cultivars, fruit set, fruits, horticulture, microscopy, parentage, phenotype, pistil, plant ovary, pollen, pollen tubes, polymerase chain reaction, progeny, reproductive behavior, ribonucleases, seedlings, seeds, self-pollination
Several pollination studies carried out on different, self-incompatible almond cultivars and seedlings have shown the presence of variable levels of fruit set following self-pollination that could be attributed to partial self-incompatibility (PSI). PSI is an intermediate reproductive behaviour, described in some angiosperm species, which indicates that selfincompatibility is a quantitative and plastic trait. The present study was performed to substantiate the occurrence of PSI in almond by studying ten cultivars that are traditionally considered to be self-incompatible (four of which had previously shown fruit set after self-pollination). These cultivars were analysed by microscopic observations of the progression of pollen tubes through the pistil following controlled self-pollination, determinations of fruit set after bagging flower buds, and molecular identification of the parentage of the fruits obtained using consensus PCR-primers for Prunus S-RNase alleles. The results showed that, in nearly all cases, the pollen tubes did not enter the ovary and, from a total of 5,349 bagged flower buds, only 17 fruits were obtained. In all cases, PCR analysis of the plants obtained after germination of these seeds showed a band corresponding to an S-RNase allele not present in the maternal progenitor, clearly indicating that they could only have arisen from cross-pollination.Therefore, the low fruit set values observed in some of the cultivars studied were not due to a breakdown in the self-incompatibility response that confers PSI, but to very low rates of contamination with foreign pollen. These results corroborate the selfincompatibility phenotype of the cultivars studied here, and highlight the importance of ascertaining the identity of the parentage in any progeny obtained after bagging.