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Investigating pollen compatibility of commercial sweet cherry cultivars by DNA analysis

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posted on 2023-05-28, 12:10 authored by Lomax, JMH
Sweet cherries (Prunus avium L.) are largely self-incompatible, which is determined by a gametophytic self-incompatibility system that is controlled by a multi-allelic S-locus. Commercial cherry orchards select cross-compatible cultivars based on synchronous flowering and cross-compatible S-alleles to maximise pollination success. My project evaluated molecular approaches to: 1) determine the unknown S-allele profile in three sweet cherry cultivars (Simone, Sweet Georgia and Reid Fruits in-house cultivar; SLK) by DNA sequencing and 2) identify the pollinisers of Kordia and Regina that are notorious for below average fruit set (<20%) using S-locus genes and microsatellite markers (SSRs). These molecular techniques have been tested in other plant models, however, there are limited examples in commercial sweet cherry orchards. DNA sequencing unequivocally identified that the previously unknown S-alleles of Simone and Sweet Georgia are S1 and S4'. Interestingly, this is consistent with industry reports that both Simone and Sweet Georgia are self-compatible. SLK, had S1 and S3 alleles, supporting suggestions that it could be a mutation of the Regina cultivar. This new information means that producers can utilise these cultivars with confidence in their genetic compatibility. Primers targeting specific alleles of the SFB gene (S\\(_1\\), S\\(_3\\), S\\(_4\\), S\\(_4\\)', S\\(_6\\), S\\(_9\\), S\\(_{12}\\), S\\(_{13}\\) and S\\(_{36}\\)), revealed the pollen donor candidates for Kordia and Regina seeds in the open-pollinated orchard, but failed to discriminate among candidates that shared S-alleles. Five out of thirteen microsatellites were identified to amplify small size differences between candidate pollen donors but require accurate sizing using a DNA sequencer to be practical as agarose gel electrophoresis did not provide reliable discrimination. This was beyond the resources available for this project. The primers we designed can be developed into a multiplex PCR to make this technique even faster and cheaper. Orchardists can use these methods, which are also applicable to other Prunus crops, to optimise their orchard design and assist in the selection and introduction of new cultivars.

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