Evaluation of two self-incompatibility alleles in three summer rape (Brassica napus L.) cultivars by UV fluorescence microscopy, seed set and outcrossing rates

Abstract

Evaluation of two self-incompatibility alleles in three summer rape (Brasica napus L.) cultivars by UV fluorescence microscopy, seed set and outcrossing rates. Can. J. Plant Sci. 80: 255-260. S-alleles W1 and T2 and an incompletely dominant white petal character were introgressed into the self-compatible (SC) summer rape (Brassica napus L. ssp. oleifera {Metzg.}) cultivars Global, Topas and Westar. The derived self-incompatible (SI) lines were evaluated for strength of incompatibility by ultraviolet fluorescence of pollen tubes, and by seed set. Pollen tube and seed set analyses showed the W1 and T2 alleles were strongly, moderately and weakly expressed in Topas, Global and Westar, respectively. Seed set data showed a significant difference between SI lines, but not between S-alleles, or between homozygous or heterozygous lines from the same SI cultivar. SI cultivar yellow petal (wild type) lines were field pollinated with SC white petal lines. Seed collected from the SI cultivars were evaluated for proportion of outcrossed progeny by recording the frequency of yellow petal and cream petal plants, which were the result of self-and cross-pollination, respectively. The proportion of outcrossed progeny (i.e., outcrossing rates) ranged from 23% to 79%. Topas SI lines had significantly higher outcrossing rates than Global SI lines, which corresponded to SI line seed set data. Environment, S-allele selection and genotype significantly affected outcrossing rates. In Brassicaceae (syn Cruciferae), molecular and classical genetic studies have determined that incompatibility is determined by a sporophytic system where pollen specificity is determined by the diploid pollen parent. In summer rape (Brassica napus L. ssp. oleifera (Metzg) 2n = 4x = 38, AACC), multiallelic S-loci are inherited from the progenitor species B. rapa L. (2n = 20, AA) and B. oleracea L. (2n = 18, CC). Whereas the allotetraploid B. napus is selfcompatible (SC), both ancestral species are self-incompatible (SI). Summer rape is a predominantly self-pollinating species (Olsson 1960a) with outcrossing rates of 20-45% under field conditions (Olsson