A mutation in 'Nonpareil' almond conferring unilateral incompatibility

'Jeffries', a mutant of 'Nonpareil' almond [Prunus dulcis (Mill.) D.A. Webb], showed "unilateral incompatibility" in that its pollen failed to fertilize cultivars in the 'Carmel' (CIG-V), 'Monterey' (CIG-VI), and 'Sonora' (GIG-VII) pollen cross-incompatibility groups (CIGs), as well as specific cultivars ('Butte', 'Grace', and 'Valenta') whose CIG group is unknown. 'Jeffries' is not self-compatible, but produced good set when pollinated by 12 almond cultivars representing the entire range of CIGs involving 'Nonpareil' parentage, as well as the parent 'Nonpareil'. It was concluded that the 'Jeffries' mutant--both gametophyte and sporophyte--expressed a loss of a single S allele of the 'Nonpareil' genotype