Identification of Charcoal rot disease of bean seedlings in Kohgiluyeh and Boyerahmad province and evaluation of partial resistance of common bean (Phaseolus vulgaris) cultivars

Charcoal rot disease، caused by Macrophomina phaseolina has become a restrictive agent for annual crops in Iran. The disease incidence reaches up to 90 percent in some infested areas. High air temperature and drought stress associated with this disease، are the main factors for increasing the disease incidence and severity. In order to isolate the pathogenic agents، pieces of infected root and crown of bean were washed with tap water blotted dry and plated on potato dextrose agar (PDA). Twenty isolates of Macrophomina phaseolina، the cause of charcoal rot، were isolated from different parts of Kohgiluyeh and Boyerahmad province on bean. Phenotypic characteristics of the isolates were compared by growing on PDA at 35°C. Colony appearance، growth rate، production and amount of sclerotia and also the relationship between growth rate at 35°C and size of sclerotia were determined. Isolates were grouped in one phenotype that named fluffy with abundant sclerotia. Pathogenicity test of M. Phaseolina on different cultivars of bean were evaluated under greenhouse conditions. After two months root colonization was assessed by growing on PDA. The data were analyzed using MSTAT software. Disease indices including colonization of root and crown، and infected plants were measured. Comparative percentage of infected plants and root colonization showed that Khomain and Azna cultivars were the most susceptible and the most resistant tested varieties in reaction to M. phaseolina، respectively. The percentage of crown colonization showed that Khomain and Naz cultivars were the most susceptible and Azna cultivar was the most resistant in reaction to it.