Association of mineral nutrients with vein reddening and necrosis in Thompson Seedless grape

Wide spread occurrence of reddening of veins and necrotic spots on the leaves of Thompson Seedless and its mutants leading to reduced fruitfulness and yield is observed in different grape growing regions of Maharashtra. The nutritional status of tissues (blades and petioles of varying age), chlorophyll content and fruitfulness of healthy and affected vines was studied during 2003-2007. The chlorophyll content was significantly lower in the symptomatic leaves. A significant and negative correlation (r = -0.72**) was observed between percent canes/vine having symptomatic leaves and percent fruitful canes/vine. The fruitfulness was reduced significantly in the affected vines. Among the nutrients, significantly lower NO3-N, P, K, and Na content was observed in the petioles of affected symptomatic/affected leaves. The stepwise regression analysis between the chlorophyll content and nutrients N, NO3-N, P, K, Ca, Mg, Na, and Cl revealed the revealed the involvement of K with the development of the symptoms. Petiole K content alone accounted for 82.6% (adjusted R-2 = 0.826) and 81.5% (adjusted R-2 = 0.815**) variations in the chlorophyll content of the blades when sampled at 45 days and during 70-75 days, respectively after foundation pruning. Nutrient composition of tissues of healthy and affected shoots within a vine was also studied. Significantly higher Mg content and lower K and chloride content were found in affected leaf blades compared to healthy leaf blades collected from different shoots of the same vine. The K content in the petioles from affected shoots was also significantly lower compared to petioles from the healthy shoots of the same vine. The micronutrients like Zn, Fe, Cu, Mn and Cl-1 were also not associated with the symptom. The yellowing of leaves could be corrected by application of K fertilizers. The symptomatic leaves showed enhanced sensitivity to powdery mildew disease.