NEW HOSTS OF MACROPHOMINA PHASEOLINA IN IRAN

Abstract

The host range and geographical distribution of Macrophomina phaseolina, the causal agent of charcoal rot or ashy stem blight, was studied in different provinces of Iran during 2006-2008. Plants with signs and symptoms of charcoal rot showed leaf yellowing, blackening of the stem and root rot. Numerous black microsclerotia were observed on the rotted tissue. To isolate the pathogen, infected tissues were surface-disinfected and placed on potato dextrose agar plates Pure cultures were obtained from hyphal tips and maintained on sterile toothpicks at room temperature (Edmunds, 1964). The mycelium that was initially hyaline, turned grey with time and after 4 to 5 days incubation, produced minute, black, round to oblong or irregularly shaped microsclerotia with mycelial attachment. In 10-day-old cultures, microsclerotia ranged in size from 62 to 189×52 to 149 (116×93) μm. All the isolates were identified at the species level based on the amplification of the ITS region with species-specific primers (Babu et al., 2007). Fungal attacks were observed on marigold (Tagetes erecta), cantaloupe (Cucumis melo var. cantaloupensis), cumin (Cuminum cyminum), hemp (Cannabis sativa), mung bean (Vigna radiata), okra (Abelmoschus esculentus), tomato (Lycopersicon esculentum), turnip (Brassica rapa), and watermelon (Citrullus lanatus), which are reported as new hosts for M. phaseolina in Iran. Pathogenicity tests, repeated twice, were conducted in a greenhouse on each of the above host as described by Abawi and Pastor-Corales (1990). The outcome of inoculation assays was assessed after 2-6 months according to the host. Inoculated plants produced typical symptoms on the leaves, stem and roots, and the fungus was consistently re-isolated from them.