Complex segregation analysis of day-neutrality in domestic strawberry (Fragaria ×ananassa Duch.)

Abstract

Thirty bi-parental progenies were generated using 45 genotypes from the University of California (UC) strawberry breeding population as parents. Both parent genotypes and their offspring were classified for photoperiod insensitivity, or day-neutrality, for flowering using a late-season flowering score and the number of inflorescences per plant recorded during late summer. Complex Segregation Analysis of these traits indicated that their distributions were best explained by a genetic model that postulates a single major locus with partial dominance for day-neutrality in combination with a background of polygenic and environmental variation. The frequency of the allele conferring day-neutrality was estimated as p = 0.59–0.62 in this experimental population. Genotypic values for the inferred major locus were estimated as a = 1.12 and d = −0.81 for the flowering score, and a = 4.93 and d = 2.41 for inflorescence number. Further resolution of inheritance patterns were obtained by comparing the phenotypic variance for each trait with estimates obtained by insertion of these genotypic class values and allele frequencies into standard quantitative genetic models, and by the comparing variance components estimated using a mixed model analysis with and without inferred genotypic classes as a fixed effect. These comparisons suggest that the major gene determines 80.5% and 73.9% of the additive genetic variance for flowering score and inflorescence number respectively. One complicating feature of the results obtained here is that a non-Mendelian model of segregation fit statistically better than a fixed Mendelian model. The genetic parameters estimated using this non-Mendelian model were essentially identical to those obtained with fixed segregation; hybrid and octoploid ancestry, selection affecting flowering response, and limited number of generations in the analysis are discussed as possible explanations of this result.