RELATIONSHIP BETWEEN LEAF WATER POTENTIAL AND GAS-EXCHANGE ACTIVITY AT DIFFERENT PHENOLOGICAL STAGES AND FRUIT LOADS IN PEACH-TREES

Relationships between midday (Psi(md)) and predawn (Psi(pd)) leaf wate r potential, stomatal conductance (g(s)), and net CO, assimilation rat e (A) mere determined at different fruit growth stages and for 2 years with different fruit loads in a 'Sudanell' peach [Prunus persica (L) Batsch] plot subjected to two regulated deficit irrigation (RDI) strat egies plus a control irrigation treatment. A postharvest RDI (PRDI) tr eatment was irrigated at 0.35 of the control after harvest, The second treatment (SPRDI) applied RDI during Stage II, the lag phase of the f ruit growth curve, at 0.5 of the control and postharvest at 0.35 of th e control, The control treatment and the PRDI and SPRDI when not recei ving RDI were irrigated at 100% of a modified Penman crop water use ca lculation (ET0) in 1994, a full crop year, and 80% in 1995, a year of nearly zero crop, In 1995, with 80% of the 1994 irrigation rate and no crop, the Psi(md) was higher, probably because of the lower crop load , while Psi(pd) was lower, probably because less water was applied to the soil, The relationship of g(s) and A with Psi(nd) during Stage II was steeper than during postharvest. Low Psi(md) was not indicative of a depression in g(s) and A in Stage Iii, Osmotic leaf water potential at turgor loss (Psi(x)(0)) as derived from pressure-volume curves was more negative during Stage III and postharvest (about -2.9 MPa) than in Stage II (about -2.7 MPa), The Psi(md) measurements together with P si(pi)(0) determinations seemed to be more useful to characterize peac h tree water status than Y-pd under soil water deficits because of the ir better relationship to midday stomatal closure.