The relationship between greenhouse and field performance of diverse cultivars of summer squash and watermelon grown under moisture stressed conditions
Date
2019
Authors
Ray, Deborah Kay, author
Uchanski, Mark, advisor
Qian, Yaling, committee member
Byrne, Patrick, committee member
Journal Title
Journal ISSN
Volume Title
Abstract
Drought stress poses a major threat to the global food supply, and most domestic vegetable growers lack cultivar-specific information that would allow them to adopt best management practices to limit the impacts of these stressors. Summer squash (Cucurbita pepo) and watermelon (Citrullus lanatus) are two crops in the Cucurbitaceae family that are commonly grown and consumed in the U.S. Heirlooms and modern cultivars of these crops with reports of "drought resistance" are currently available on the market without concomitant recommended modifications to irrigation management. Many published greenhouse experiments have been used to screen cultivars and breeding lines for drought resistance, but often lack paired field trials to confirm results. We conducted a greenhouse dry-down study on nine summer squash and 10 watermelon cultivars, and sustained deficit irrigation (SDI) field trials on a selected 13. Our objective was to determine if crop characteristics identified in the greenhouse studies could be predictive of season-long field success under drought conditions. Colorado-bred conventional hybrids were used as control cultivars in both studies, and were hypothesized to have a more drought-sensitive response than cultivars with reports of drought resistance. Parameters evaluated in the greenhouse study included: days to death, percent soil moisture at death, root:shoot ratio, and root system characteristics. The cultivars that were then evaluated in the field study received one of three sustained deficit irrigation treatments: control, deficit, or drought, using a drip irrigation system in a split-plot design with three replications. Control treatments were reduced to approximately half the average recommended number of acre-inches of water per season for each crop, averaging 5.9 and 4.8 inches for summer squash and watermelon, respectively. Deficit and drought irrigation treatments were reduced 50% beyond the control during the treatment interval, which began after flowering and extended over the course of 12 weeks for the squash, and six weeks for watermelon. The deficit treatment plots received irrigations of equal frequency to the control, in half the amount, and the drought treatment plots received irrigations at half the frequency of the control, with the same volume of water as the control applied at each irrigation event. Squash were grown under rain exclusion and watermelons were grown in an open field with rainfall amounts factored into total water application calculations. Soil moisture and environmental conditions were monitored, and yield and quality measures were taken in both crops. Photosynthetic activity was also evaluated twice each season in the summer squash plot using a MultispeQ. Our results revealed that greenhouse performance was often not indicative of field performance, and that almost all squash cultivars produced acceptable levels of marketable yield under severe water deficits in the field. Watermelon cultivars produced marketable fruits in both years, but performance was inconsistent from year to year, and yield was low across all cultivars and treatments. Modern cultivars and heirlooms with reports of drought resistance, such as 'Desert King' watermelon and 'Desert F1' zucchini, did not necessarily out-perform hybrids or open-pollinated cultivars without such reports, such as 'Amiga' watermelon, and 'Jasper' and 'Dark Star' summer squash. By imposing a sustained deficit of more than 50% below recommended season-long rates, we identified five best-performing cultivars of summer squash that experience an approximate yield penalty of 30% under these conditions. The results of this study offer a prescriptive weekly method of irrigation management combined with recommendations for currently available cultivars that can be readily adopted by local, fresh-market growers to enable significant water savings without reductions in quality.