Diagnosis of nutrient imbalance in bunch stem necrosis affected Thompson Seedless grapevines grown on Dog Ridge rootstock using DRIS

A data bank of nutrient concentration vs incidence of late bunch stem necrosis (BSN) was established from survey of 73 commercial vineyards of Sangli district in Maharashtra. The diagnosis and recommendation integrated system (DRIS) was used for interpretation of results and diagnoses of nutrient imbalance in necrosis affected vineyards. The nutrient concentration in petiole, collected from the vineyards free of bunch stem necrosis, was made use for norm deriving exercise, while the indices were developed for vineyards having high incidence of necrosis for diagnosis of nutrient imbalance. The concentration of Mg, Na, Cu and Cl were significantly higher in healthy vineyards compared to unhealthy ones. Magnesium accounted for nearly 59% of the variation in the incidence of BSN. Among 44 necrosis affected vineyards, Mg was the most commonly deficient nutrient. Mn was found in excess with the highest positive indices in eight necrosis-affected vineyards, while K, Fe and Cl were high in five necrosis-affected vineyards. No major nutrient was found solely responsible for inducing BSN in grape. The DRIS indices for Ca showed a positive correlation (0.595**) with percentage bunch stem necrosis incidence while indices for Mg showed negative correlation (−0.380**) indicating that the relative balance of Ca and Mg rather than their absolute concentration governs the incidence of BSN. The overall imbalance of nutrients as reflected by sum of DRIS indices irrespective of sign showed a weak correlation with the incidence of BSN.