Life Science Journal 2013;10(4) http://www.lifesciencesite.com 1278 Factors affecting on Sclerotinia sclerotiorum isolated from beans growing in Ismailia, Egypt Abdallah M. Elgorban 1,3 , Mohamed Elsheshtawi 2 , Basheer A. Al-Sum 1 , Ali H. Bahkali 1 1 Botany and Microbiology Department, College of Science, King Saud University, P.O. Box 2455, Riyadh 11451, Saudi Arabia, E-mail: aelgorban@ksu.edu.sa 2 Plant Pathology Department, Faculty of Agriculture, Mansoura University, Mansoura 35516, Egypt 3 Plant Pathology Institute, Agricultural Research Center, Giza, Egypt Abstract: Sclerotinia sclerotiorum, causal agent of white rot in bean (Phaseolus vulgaris, L.) are highly variable pathogens. This study was conducted on cultural and physiological characters. The data revealed that maximum mycelial growth, sclerotia and sclerotia dry weight was obtained in Potato dextrose agar as semi-solid media i.e. 78 mm, 29 sclerotium and 232 mg, respectively. While Potato dextrose broth as liquid broth media was the best suitable medium to growth of the fungus with 2.29 mg dry weight per flask. The optimum pH for growth of both S. sclerotiorum was 5.5 by 2.41 mg/flask, however the 5 degree was the best for sclerotia formation and sclerotia dry weight which produced 17 sclerotium/flask and 134 mg/flask, respectively. Alternating light and darkness and continuous light were found to be the most suitable for maximum growth of the fungus that giving 90 mm while alternating light and darkness (16 hours light+8 hours darkness) was the best for sclerotia formation and dry weight of sclerotia by 16 sclerotium/plate and 128 mg/plate, respectively. This study also revealed that a relative humidity of 98.6% was most suitable for the growth, sclerotia formation and sclerotia dry weight of the pathogen. [Elgorban A. M., Al-Sum, B. A., Elsheshtawi, M., Bahkali, A. H. Factors affecting on Sclerotinia sclerotiorum isolated from beans growing in Ismailia, Egypt. Life Sci J 2013;10(4):1278-1282] (ISSN:1097-8135). http://www.lifesciencesite.com . 169 Keywords: Sclerotinia sclerotiorum, relative humidity, lighting hours 1. Introduction Sclerotinia sclerotiorum (Lib.) de Bary, one of the most destructive soil borne pathogens has been reported to affect a wide range of wild and cultivated host plants infect over 400 species of plants (Boland and Hall, 1987) and causes considerable damage to the host under greenhouses and protected agricultural areas. The pathogen has been reported to hamper the cauliflower cultivation by causing stalk rot in different cauliflower growing areas such as United States during 1942-1943 (Snyder and Baker 1945). The fungus is classified within the genus Sclerotinia of the Sclerotiniaceae, an important family of Discomycetes of the class Ascomycetes (Kora, et al. 2003). Important crops affected include arrange of vegetable such as beans, lettuce, cabbage, carrot, potato and field crops such as oilseed rape, sunflower, and tobacco as well as a number of flower crops. The epidemiology of S. sclerotiorum has been investigated for number crops (Newton and Sequeira, 1972; Abawi and Grogan, 1979; Clarkson et al., 2001), where ascospores are the primary infection source. Ascospores are released by apothecia which develop following carpogenic germination of sclerotia at or near the soil surface. Bean (Phaseolus vulgaris, L.) is one of the most important vegetable crop in Egypt and many countries of the world. In Egypt, the cultivated area was 69921 feedan in 2011 season yielded approximately 305561 tons with average about 4.37 ton/feddan (FAO Stat. database, 2011). One of the major limitation in bean (Phaseolus vulgaris, L.) production and export in Egypt is the infestation by S. sclerotiorum which cause losses in the total yield and decreasing the quality of the exportable yield. There are a few studies on the effect of environmental factors on S. sclerotiorum growth and sclerotia formation, despite these being potentially important factors in life cycle of the pathogen. The present study aimed to study the effect of some factors on morphological and physiological characters of S. sclerotiorum. 2. Material and Methods Isolation of the pathogen Plant samples with blighted stems and branches, and displaying sclerotia and mycelium, were arbitrarily sampled from the affected field. The plants were placed in a plastic bag over ice in a cooler and transported to the laboratory for processing. Four sclerotia were collected from each of sample, wrapped in a piece of sterile cheesecloth and submerged in 1% NaOCl solution for 1 minute. Sclerotia were then removed from the cheesecloth and rinsed in sterilize distilled water, and blotted dry between two layers of sterilize paper towel. Each of the selected sclerotia was individually plated on acidified PDA (APDA; 40 g/liter of Difco PDA amended with 1 ml of 85% lactic acid after