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United States Department of Agriculture

Agricultural Research Service

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Research Project: Identifying Sources of Resistance to Wood-canker Diseases in Pistachio Germplasm

Location: Crops Pathology and Genetics Research

2013 Annual Report

1a. Objectives (from AD-416):
Screen pistachio cultivars with the causal agents of Panicle and Shoot Blight of Pistachio.

1b. Approach (from AD-416):
Planting disease-resistant cultivars is a time-tested and sustainable approach to disease management. Based on field observations and published research on resistance to wood-canker diseases, we know that a range of resistance exists among commercial cultivars of almond and grape. We propose to improve screening assays for evaluating both commercial cultivars and USDA germplasm repositories for sources of disease resistance. In pistachio, the entire acreage of which consists of a single, suceptible cultivar, newly-released cultivars offer an opportunity for identifying new sources of resistance. Our approach is to screen plant materials from both commercial nurseries and the USDA-ARS National Clonal Germplasm Repository.

3. Progress Report:
This project was established in support of objective 1 of the in-house project, which is to develop sustainable disease control practices for grapevines. The goal of this project is to screen pistachio cultivars with the causal agents of Panicle and Shoot Blight of Pistachio. We have tested five pistachio cultivars for resistance to canker causing Botryosphaeriaceae species. Lost Hills was the cultivar most resistant to Botryosphaeria shoot blight, although it was not significantly better than the widely planted Kerman. Kalehghouchi and Aria were the most susceptible cultivars. From 300 isolates from pistachio trees in California collected from 1998 to the present, we identified eight species of Botryosphaeriaceae (Botryosphaeriaceae dothidea, Diplodia seriata, Dothiorella iberica, Dothiorella sarmentorum, Lasiodiplodia citricola, Lasiodiplodia gilanensis, Neofusicoccum mediterraneum, Neofusicoccum vitifusiforme) and one species of Diaporthe (Diaporthe rhusicola). Neofusicoccum mediterraneum, which was widely distributed, was found in 19 counties in California where pistachios are grown. Ten commercial almond cultivars were also tested for susceptibility to Botryosphaeriaceae. In a previous study, we found seven different species attack almonds and cause band canker (cankers develop in the tree trunk), cankers initiated from pruning wounds, and cankers in the canopy starting from lenticels or natural wounds (growth cracks, limb breaking, cracks created by winds, etc.). Ten cultivars of almonds were inoculated with two of the most aggressive Botryosphaeriaceae isolated from almond cankers: Neofusicoccum nonquaesitum and Neofusicoccum parvum. The results showed, regardless of the pathogen used, some of the cultivars, i.e. Carmel and Padre, were more susceptible than the Butte and Peerless. These initial results indicate considerable differences in the resistance of almond germplasm to canker-causing fungal pathogens.

4. Accomplishments

Last Modified: 05/28/2017
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