STRESS AND STRESS RECOVERING BY GRAPEVINE S

Grapevines in natural environments are subjected to multiple stress du ring their life. Insufficient light during bud differentiation reduces fertility and bud burst in the following year. Reduced irradiance and hence a low supply of assimilates may induce inflorescence and bunch stem necrosis. Low temperature stress can cause direct crop loss becau se of poor pollination or fertilization, defective flower parts, or po or carbohydrate nutrition of the flower. Limiting light conditions and severe leaf removal during inflorescence initiation reduced bud ferti lity. Low temperature in autumn induces early leaf senescence and leaf fall mainly on overcropped vines. Crop load may under certain conditi ons affect photosynthesis. There was a clear trend towards lower photo synthetic rates on cluster thinned vines. Overcropped vines on the oth er hand bear lower quality grapes and accumulate insufficient reserves . These vines often show chlorosis in the following season. The grapev ine has a great potential for stress acclimation. Low-light stress str ongly enhances the number of new leaves and laterals. Plants bearing o nly main leaves compensate for absence of laterals by delaying leaf se nescence. Leaves are not the only source organs. Carbon as well as nit rogen can be mobilized from the permanent parts of the vine. Long-term survival of grapevines and therefore allocation to vegetative growth has priority over reproductive growth before pollination is completed and presemably after seed maturity is reached.