Performance responses of strawberry seedlings to the sublethal effects of non-fumigated soils

Nine selected strawberry genotypes (Fragaria x ananassa Duch.) from the University of California, Davis, strawberry improvement program were intercrossed and their seedling offspring evaluated for five production traits, Plants were evaluated in annual hill culture, with and without preplant soil fumigation using a mixture of 67 methyl bromide : 33 chloropicrin (wt/wt, 392 kg/ha). Plant mortality was <1% for seedlings grown in either soil environment, indicating that the main effects of fumigation treatment in this experiment were due to the consequences of sublethal soil organisms, Plants grown in nonfumigated soils measured from 74% to 77% of the diameter of those grown in fumigated soils and yielded 59% as much fruit, Significant cross x fumigation interactions were not detected for fruit yield, fruit size, and weighted fruit appearance. Moreover, genetic correlations for these three traits calculated by comparing seedling performance in fumigated and nonfumigated soil environments were at or near unity, suggesting that the same genes condition genetic variability for these traits in both soil environments, Together, these findings demonstrate that strawberry fruit yield and vigor are increased substantially by fumigation, even in the absence of an identifiable major pathogen problem. Further, there may be little promise for developing cultivars with genetic adaptation specific to the sublethal effects of nonfumigated soils, as selection in either soil fumigation environment is likely to affect the same sets of genes.