Phenologic and growth responses to early and late season water deficits in Cabernet franc

Abstract

Phenologic and ontogenic responses to seasonal water deficits were investigated in the wine grape variety, Cabernet franc, in a California hillside vineyard. Water deficits were imposed by withholding irrigation water before or after the onset of veraison. In continually irrigated vines, midday leaf water potential (Ψ) declined from - 0.4 MPa to approximately -1.1 MPa between budbreak and veraison despite weekly irrigation at a rate which was 2 x the normal production practice for that commercial vineyard. Hence, water deficits may be a common component of grape production in hillside vineyards of California. When water was withheld until veraison, midday Ψ declined more rapidly and reached - 1.4 MPa at the time water was resupplied. For these vines, water status slowly recovered to the level of the continually irrigated vines. The water status of late deficit vines, (water withheld after veraison), decreased rapidly after veraison, reaching a minimum of - 1.6 MPa at harvest. These differences in vine water status had no effect on the major phenological indicators, i. e„ the timing (on basis of time or accumulation of degree days) of bloom, veraison, and harvest. However, early season deficits shortened the period of shoot elongation and node production, decreased the maximum rate of shoot elongation and node production, and accelerated periderm development on current season shoots. Possible ecological implications of accelerated periderm development are discussed. Shoot length and the number of nodes/shoot was reduced approximately 25 % by the early season water deficits. Radial shoot growth was also inhibited by early deficits but much less than axial shoot growth. Shoot growth had essentially ceased in all vines before late season deficits developed. The characteristic double-sigmoid growth pattern of berries was observed regardless of seasonal water deficits. Most fruit growth occurred during the first growth phase in all treatments. The rate of fruit growth was inhibited by early and late season water deficits. Yield was decreased more by early deficits than by late deficits.