INTERACTIONS OF CROP LEVEL AND LATE-SEASON WATER-STRESS ON GROWTH ANDPHYSIOLOGY OF FIELD-GROWN CONCORD GRAPEVINES

The effects and interactions of late season soil water deficit and cro p level on the growth, yield, fruit quality, and physiology of four-ye ar-old Concord own-rooted grapevines in a loam soil in New York were e xamined. Soil moisture stress was induced in half of the vines by rain -shielding beginning after bloom, while natural and supplemental drip irrigation were used to maintain high water status of the other half. Within each stress plot crop levels were adjusted to give unthinned vi nes with a mean of 130 clusters/kg pruning weight versus 67 clusters/k g pruning weight giving about 18 and 9 t/ha, respectively. Thinning of the crop significantly decreased cluster number and yield, but increa sed shoot growth, juice degrees-Brix, and pruning weights as expected. Since significant soil water stress did not developed until about 10 to 20 days after veraison, the stress only significantly reduced net p hotosynthesis (Pn) and leaf conductance (g(l)) after veraison at leaf and pre-dawn soil water potential below -1.1 and -0.25 MPa. A signific ant water stress X crop level interaction occurred at harvest for juic e degrees-Brix and total soluble solids (TSS) per berry, indicating th at reduction of sugar accumulation due to water stress was aggravated in heavier cropping vines. No significant effects of crop level on lea f gas exchange or vine water use (i.e., soil water reduction in shield ed plots) were observed. The reduction of leaf function and earlier le af senescence in the unthinned stressed vines were not severe enough t o cause carry-over effects the following season.