2019 ASHS Annual Conference

Genetic gains for cumulative fruit yield have been significant in strawberry (Fragariax ananassa) over the last 50 years, especially among hybrids selected for production in coastal California environments. From commercial production statistics, we estimate that strawberry yields have increased 10-fold since 1970 despite a stable production acreage. However, common garden experiments have not been conducted to quantify realized genetic gains for yield or to study the effect of intense selection for increased yield on the underlying genetic diversity. Moreover, we hypothesized that heterosis might have played a significant role in driving strawberry yields upwards. To explore these questions, we developed and studied 545 hybrids among elite short-day and long-day parents developed using a factorial mating design, in addition to studying 72 hybrids developed over a 15-year period—parents and hybrids were genotyped with high-density SNP arrays. Genetic diversity appears to be comparatively narrow among the hybrids studied. Heterozygosity ranged from 0.25 to 0.32 among the 72 era-study hybrids and 0.18 to 0.45 among the 545 factorial-study hybrids and was not correlated with fruit yield in either study. High-parent heterosis for cumulative fruit yield was virtually non-existent and was only statistically significant for 34 of the 545 hybrids tested (6.2%). Consistent with these results, we found no evidence for heterotic groups in the population under study, which includes public germplasm that has played an important role in the expansion of strawberry industry worldwide. We speculate that interactions among genes in homeologous genomes, so-called fixed heterosis, might underlie genetic gains for yield in strawberry.