Effects of Ca, Mg and GA3 Spray on Bunch Stem Necrosis Disorder in Grape (Vitisvinifera cv. Bidaneh Sefid)

Late-season Bunch Stem Necrosis (BSN) is observed as a necrosis of the cluster stem (rachis) that leads to shriveling of berries on the affected portion of the cluster. The BSN symptoms include dark, necrotic lesions on the rachis or individual pedicels that may spread and eventually girdle the affected part of the cluster rachis. Berries distal to a lesion cease normal development, and the unripe berries either abscise or remain on the cluster in a withered condition. Frequently only the cluster tip or a shoulder is affected, while the rest of the cluster develops normally. Symptomatic and non-symptomatic clusters may be borne on the same vine. BSN has been correlated with numerous factors; however, no universal cause and effect relationships have been demonstrated. No pathogens are believed to cause this condition. Instead, certain weather conditions and vine nutrition seem to be associated with its occurrence. Low temperatures and high humidity around bloom or excessive rainfall after veraison may be related to its development. Imbalances between calcium and potassium as well as low levels of nitrogen in vines are other possible causes. Unaffected portions of clusters develop normal fruit quality.ʽBidaneSefidʼ or ʽKeshmeshiʼ is an important grape cultivar in Iran and is frequently affected by bunch stem necrosis disorder around country. The purpose of this study was to determine if mineral nutrition was associated with BSN of ʽBidaneSefidʼ grape cultivar under Urmia growing conditions.
To evaluate the effects of foliar sprays of Ca, Mg and GA3 on reduction of BSN incidence on ʽBidaneSefidʼ cultivar, and to examine the relationships between specific nutrients and the incidence of BSN this field experiment was performed based on randomized complete blocks design with eight treatments and three replicates on 2011in a vineyard around Urmia city. Vines were 8-year-old and were trained as bi lateral cordon. At the end of full bloom and a week after that the vines were sprayed two and five times with 2% MgSO4 and CaCl2 fertilizers alone and combined. GA3 also was sprayed at 70% of flowering with 20 ppm and replicated at fruit set with 40 ppm. Symptoms rate of BSN on bunches and minerals nutrient content(N, K, Ca, Mg and Ca㈏) of leaves and rachis were measuredin veraison phenological stage.
Results showed that in veraison stage the most and the least BSN incidence rate was recorded in control and the vines that were sprayed two times with 2% MgSO4, respectively. Leaf Ca content in vines treated two times with 2% CaCl2 and those sprayed five times with MgSO4ঠ was more than other treatments. Maximum amount of Mg was recorded in leaves of vines sprayed by 2% MgSO4, 5 times during growing season. These vines showed the least BSN rate, too. The most contentof K/Ca were in the leaves of control and GA3 treated vines and the least contentof those was in vines treated five times with MgSO4ঠ. Rachis tissue analysis for nutrient elements in veraisonstage did not consistently reveal any relationship between N, K, Mg, Ca and Mgয and bunch stem necrosis in bunches of studied vines of ʽBidaneSefidʼ cultivar in Urmia region. There are conflicting reports regarding the association of essential nutrients and the incidence of BSN. A high ratio of potassium to magnesium and/or calcium in affected tissues, and also the application of calcium and/or magnesium fertilizers effectively reduced the incidence of BSN in Europe. In California, BSN was not reduced by applications of calcium and magnesium. An increase in the incidence of BSN was reported with application of nitrogen fertilizers. Magnesium and calcium appeared to be involved in the disorder. The results illustrate that BSN-prone vineyards should be individually examined for nutrient imbalance or other stresses that may be contributing to BSN.
Results of this study suggest thecontrol of BSN incidence by fertilizer treatments. Foliar applications ofMg and Ca fertilizers appeared to have effect on BSN control and two times foliar applications of magnesium starting just before veraison minimize the problem. No apparent relationship was found between the petiole and/or rachis K/(Mg Ca) ratio and BSN incidence. External application of GA3 reduced the BSN incidence in comparison to control.