Document Type : Original Article
Authors
1
Plant Pathology Department, Faculty of Agriculture, Damanhour University, Damanhour, Egypt
2
Plant Pathology Department, Faculty of Agriculture, Alexandria University, El-Shatby, Alexandria, Egypt
Abstract
Thirteen isolates of Erwinia carotovora subsp. carotovora (Ecc) (Jones) Bergy et al., were isolated from potato tubers exhibiting soft rot symptoms in a survey conducted in Behera governorate during 2006-2007 growing seasons. The isolates were monomorphic for the different morphological and physiological characteristics tested. All isolates were short rods, non-spore forming, gram negative, motile and exhibited positive reaction for catalase activity, gelatin liquefaction, growth on NaCl 6%, growth at 36°C, production of acid from arabinose, lactose, mannose, raffinose and sorbitol. However, the isolates showed negative reaction for hydrolysis of starch, sensitivity to erythromycin, and production of acid from maltose, adonitol and dextrin. More variations between isolates were recorded for their virulence on potato tubers. Four isolates out of the l3 tested were classified as highly virulent (rot covered ≥75% of potato tuber diameter) while 7 isolates were intermediate (rot 25%) and 2 isolates were weakly virulent. Meantime, the isolates differed in virulence for the host range and even for the same isolate on the different host species studied. The virulent isolates were found to be polygalacturonase (PG) and pectatelyase (PL) active producers. These could be the major factors in the development of soft rot in potato tubers. cv. Nicola of potato was most tolerant to Ecc isolates recovered from Behera governorate. Cvs. Diamant and Sponta, however, were highly susceptible while cv. Cara was moderately susceptible. The tests performed on aerial stems of the tested potato cultivars confirmed the obtained results on tubers. A relationship between soft-rot incidence and soil extracts of the four regions surveyed was revealed. Soil extract prepared from Abou El-Matameer region was highly conducive for the population growth of Ecc while soil extracts of the other regions (South El-Tahrir, Nubaria and Banger El-Sukar) were not. This could explain the often-observed high soft rot bacterial incidence in Abou El-Matameer compared to the other regions in the conducted survey. A high bactericidal inhibition (>90% reduction) was obtained in vitro. with 100 ppm magnesium sulfate, 200 ppm potassium sulfate, 100 ppm calcium sulfate, 0.3 ppm zinc sulfate, and 0.3 ppm copper sulfate, four days after inoculation. Also, the antibiotics were of significant effect to control Ecc isolates affecting potato in Behera governorate. Streptomycin and Ampicillin exhibited a considerable in vitro inhibitory effect (16-21%) on Ecc particularly at 200 ppm. The integration between such control measures could be the way for a sustainable potato soft rot control in Behera governorate, Egypt.
Keywords
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