Genetic analysis of strawberry root system traits in fumigated and nonfumigated soils I. Inheritance patterns of strawberry root system characteristics

Seedling offspring of crosses among 10 selected strawberry genotypes (Fragaria xananassa Duch.) from the University of California strawberry improvement program were established in annual hill culture. Soil treatments consisted of 1) preplant fumigation using a mixture of methyl bromide and chloropicrin or 2) no fumigation. Root systems of individual plants were sampled with a soil probe in January, April, and July 1994 to determine root mass (RM), secondary root mass (SRM), and a subjective root appearance score (RAS), For each trait, genetic analyses of partial diallels were performed to quantify sources of genetic, environmental, and interaction variance. Root trait values differed significantly between soil treatments only for the April sampling date, with all trait values greater in fumigated soils than in nonfumigated soils. For RM and SRM, variance due to general combining ability (GCA) was significant in April and July. Narrow-sense heritabilities (h(2)) for RR I increased between January (0.14) and July (0.40); SRM showed a similar trend with a higher h(2) on each sampling date. GCA variances were nonsignificant for RAS, however, significant fumigation x GCA interaction variance was detected for RAS in January. Specific combining ability (SCA) variances mere nonsignificant for all traits. To further quantify the extent of interactions, correlations (r(g)) between genotypic expressions in fumigated soils and nonfumigated soils were calculated for each root trait. These r(g) values were at or near unity (> 0.85) for RM and SRM on all sampling dates, implying that genetic variability for these traits is conditioned by genes with identical effects within each soil environment. Conversely, r(g) between soil environments was 0.52, 0.62, and -0.18, for January, April, and July RAS, respectively. These findings suggest that genetic variability exists within this germplasm base for strawberry root mass characteristics. Genetic variation also exists for January root appearance score, but it is not conditioned identically across fumigation treatments.