INCOMPATIBILITY ALLELES OF HAZELNUT CULTIVARS

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Pollen-stigma incompatibility in hazelnut is sporophytic and under the control of a single locus with multiple alleles. To date, 33 alleles have been identified at the S-locus, and a designated pollen tester for each preserved in our collection. Hazelnut is diploid, and nearly all cultivars are heterozygous at the S-locus. Over the past 25 years, we have enlarged our collection by importing cultivars from several countries as scions. As the trees began to flower, we identified their S-alleles using florescence microscopy. In December, we bagged emasculated branches on trees growing in the field to protect the female inflorescences from wind-borne pollen. In January, we collected pollen from our tester trees. In February, females were collected from bagged branches and brought to the lab in petri dishes. The females were pollinated in the afternoon, one or two per tester pollen. The following day, the styles were squashed in aniline blue and observed under UV light. In compatible pollinations, pollen germination was excellent and tubes could be seen growing parallel down the style. In incompatible pollinations, germination was often reduced, pollen tubes were short and did not penetrate the stigmatic surface, and the tubes often ended in bulbs. Each pollination was scored as compatible or incompatible, and the testing of a tree required 1-3 years for completion. In this paper, we report the alleles of 170 cultivars for the first time, and summarize the alleles of 112 cultivars previously typed. Cultivars with different names often have identical microsatellite marker fingerprints and S-alleles. To reduce confusion, a list of cultivars with identical fingerprints is also included.