An investigation of some causes of die-back disorder of pistachio trees and its control through balanced fertilization in Iran.

摘要

The incidence of dieback in pistachio (Pistacia vera) occurs extensively in pistachio orchards of Iran where it has caused yields to be low. To evaluate the spread percent occurrences and to determine the causative factor(s) of this incidence, some 203 pistachio orchards located in Rafsanjan, Kerman, Yazd and Khorasan regions of Iran were visited during 2002-04. It was noted that 4-90%, or on average, 28% of the trees had been affected and that this incidence rate had increased by 60% from 1994 to 2004. Soil samples from profile depths of 0-40, 41-80 and 81-120 cm were collected in 31 randomly selected orchards for physicochemical analysis. Likewise, leaf samples and samples of irrigation water were collected in those orchards for chemical analysis. Then, correlations between the incidence of dieback and the examined factors were calculated. It was noted that the incidence of dieback in pistachio was positively correlated with soil EC, Na, K, SAR, Na/Ca and Na/K values. On the basis of our research and reports by others, the fungus Paecilomyces variotii was found to be a causative agent of dieback in pistachio. Twenty-four 25-five-year-old trees of the pistachio cv. Fandoghi, of which 40% was affected by the dieback problem, were investigated to determine the effect of balanced fertilizer application on preventing this incidence. The treatments included T1=the growers' conventional method (ammonium sulfate+triple superphosphate at 3 kg each per tree); T2=T1+potassium at 3 kg potassium sulfate per tree; T3=T2+calcium applied as gypsum at 40 kg/tree; and T4=T3+zinc applied as zinc sulfate at 1500 g/tree. The direct fungal inoculation of the trees followed two years of the fertilizer treatments. The results showed a significant decrease (at 1% level) in the incidence of dieback with treatments T2, T3 and T4 compared with the farmers' conventional fertilization method. In other words, the application of potassium, calcium and zinc fertilizers reduced this problem by 63%..