Journal of Nuts (Oct 2024)
Occurrence of Root Gall Disease on Hazelnut (Corylus avellana L.) in Iran
Abstract
Hazelnut (Corylus avellana L.), one of the world's major tree nut crops, is widely produced in Iran, with an annual yield of more than 21,500 tons of hazelnuts. A survey of hazelnut orchards in Iran was conducted during 2021-2022, revealing the presence of root tumors on hazelnut trees in Guilan (northern Iran), Mazandaran (northern Iran), Qazvin (northwestern Iran), and Qom (north-central Iran) provinces. Samples of these root tumors were collected for further analysis. Isolations from fresh galls on SNA, D1M, IA, LB, and SC culture media yielded predominant colonies similar to Agrobacterium, which were subsequently purified and characterized. All 29 strains isolated were Gram-negative, rod-shaped, obligate aerobic, motile, and tested positive for oxidase, catalase, arginine dihydrolase, and urease. However, they did not hydrolyze starch, gelatin, or esculin, but did hydrolyze Tween-80 and urea. They exhibited growth on 2% NaCl and at 35°C, and were able to produce 3-ketolactose but not indole, DNase, pectinase, levan, or reduce nitrate. Furthermore, 11 representative strains were randomly selected for PCR amplifications of T-DNA genes using specific primers At1/At2, F8360/F8361, and tms2F1/tms2R2, resulting in 338, 453, and 617 bp amplicons, respectively. In pathogenicity tests, bacterial strains were inoculated into tomato, hazelnut, sunflower seedlings, and carrot discs, leading to the formation of tumors on plant stems and callus on carrot discs. Based on phenotypic, physiological, and biochemical properties, pathogenicity tests, and molecular methods, the bacterium responsible for causing root gall in hazelnut trees was identified as A. tumefaciens biovar 1. This bacterial root gall appears to be widespread among various local hazelnut cultivars (Gerd-e-Eshkavar, Alamout, Tarom, etc.), with a higher prevalence in old hazelnut orchards with stony soils. This study represents the first report of root gall on hazelnut trees grown in Iran. It was observed that the number of sites where tumors have developed and the number of galls present in old hazelnut orchards with stony soils are higher.
