Current agricultural practices rely on crop varieties adapted to local biotic and abiotic conditions. If climate change alters precipitation, yields may decline for many reasons. Crops requiring cross-pollination and synchronous flowering to produce fruit may be most susceptible. Of great concern, then, are open-pollinated and monoecious crops. Monoecious plants have separate male and female flowers on a single plant and changes in flowering phenology may alter both pollination success and individual yield. Further, open pollinated (OP) crops tend to maintain more genetic variation than hybrid varieties, may exhibit more variation in phenology, and may be less susceptible to yield decline. In central Ohio in 2009, we manipulated soil moisture and monitored the response of flower phenology, relative to plants grown under control conditions, in two zucchini (Cucurbita pepo) varieties (hybrid and OP) grown in the field. The abiotic conditions mimic stressful conditions potentially associated with future climate change, including both wetter (irrigated) and drier conditions. Drier conditions were simulated by rain-out shelters that intercepted and removed 50% of the precipitation in the treatment plots. In addition to the un-manipulated control plots, we also compared the performance of plants grown in rain-out shelters with plants grown in rain-in shelters.
The two varieties (hybrid and OP) exhibited dramatically different flowering behavior. The OP produced 53% - 98% more male flowers (F1,12=62.14, P<0.0001) and 31%-64% less female flowers (F1,12=60.91, P<0.0001) than the hybrid variety. Water availability did not affect the amount of male flowers produced (F3,9=1.74, P=0.2292) by either variety, but drought reduced female flower production by 41% in the hybrid variety (P=0.0098). Further, drought shortened the season during which female, but not male flowers, were produced (Female: F3,10=3.876, P=0.044; Male: F3,9=0.585, P=0.640). The sequence of sex expression in hybrid plants differed from OP plants, but this difference depended on moisture conditions. In both drier and control environments, hybrid plants tended to produce female flowers first while OP plants tended to produce male flowers first (Control: P=0.0015; Rain-out: P=0.0112). However, the two varieties did not differ in flowering sequence under rain-in (male-first) and irrigation (female-first) treatment. These results suggest that the male and female flowering phenology of this important monoecious crop would shift under current predictions of climate change. Finally, drought reduced fruit production, which was possibly through the decrease in female flowers