On the Impact of Zucchini Yellow and Watermelon Mosaic Viruses on the Production Rhythms of Transgenic ZW-20 and Nontransgenic Squash (Cucurbita pepo L.)

Throughout the growing season the numbers of harvested young fruits that reached marketable size fluctuated per unit of time, depicting the production rhythm of the crop. Most studies on the impact of disease on a crop pertain to the extent of yield reductions caused, and not to perturbation or annihilation of the production rhythm. On the Crittenden Farm of the New York State Agricultural Experiment Station in Geneva, NY, field trials were conducted to study the impact of cucurbit viruses Zucchini yellow mosaic (ZYMV) and Watermelon mosaic (WMV) on production rhythms of transgenic ZW- 20 (H and B) and nontransgenic cv Pavo squash. Both, ZW-20H and ZW-20B were genetically engineered from cv Pavo and expressed virus-resistance evoked by coat protein genes of ZYMV and WMV. The nontransgenic cv. Pavo control did not contain virus resistance and was fully susceptible to ZYMV and WMV. Production rhythms were depicted by time series of successive average numbers of small fruits of marketable size, harvested at 2-3 day intervals between 31 and 49 days post planting (dpp). For both, virus-infected and virus-free transgenic ZW-20 ( H and B ), as well as for virusfree nontransgenic cv Pavo the trend was manifest that, at each harvest the number of fruits was higher than at the previous one; indicating the existence of autocorrelation between harvest rounds of these genotypes. In contrast, this trend of increasing numbers of fruits could not be identified with virus-infected nontransgenic cv Pavo. Consistent with these trends, Von Neumann’s Q confirmed the occurrence of significant autocorrelations between harvest rounds of ZW-20 (both, virusfree and infected) and of virus free nontransgenic cv Pavo. In contrast, Von Neumann’s Q did not detect autocorrelation between harvest rounds of virus-infected nontransgenic cv Pavo. These results reveal that autocorrelation between harvest rounds was retained in transgenic ZW-20 squash, irrespective if they were virus-infected or not, but was lost in infected virus-susceptible nontransgenic cv Pavo crops. The outcomes of this study sustain the hypothesis that ZYMV and WMV have no impact on the production rhythms of virus-resistant transgenic ZW-20 squash, but they do alter those of nontransgenic cv Pavo