Host range of tropical and sub-tropical isolates of Polymyxa graminis

The host range of Polymyxa graminis isolates originating from peanut clump- infested areas in India (Andhra Pradesh and Rajasthan), Pakistan and Senega l was studied on monocotyledonous and dicotyledonous cultivated species, us ing known quantities of sporosori as inoculum. Profuse multiplication occur red only on some graminaceous species, but the various isolates showed diff erent host specificity. All the isolates produced high infection on sorghum and pearl millet, and all but one isolate from Rajasthan infected maize. W heat, rye and barley were susceptible to some of the tested isolates. The i solates from Rajasthan and Pakistan produced moderate to severe infection o n at least one of these species. On rice, groundnut and sugar beet, only tr aces of infection by some isolates were detected, whereas no infection was observed on mustard and sunflower. Differences of susceptibility in Pennise tum spp. and Sorghum spp. were demonstrated. The variations in host specifi city among isolates from peanut clump-infested areas may result from an ada ptation of P. graminis populations to various biotopes. The implications of these results for the management of peanut clump disease are discussed. A comparison of the host ranges of isolates of P. graminis and P. betae from temperate areas demonstrated that distinct types of Polymyxa might be ident ified based on their relative ability to multiply on susceptible species. N evertheless, overlapping in the host ranges among the different Polymyxa ty pes, characterised by distinct ecological and genomic features, raises doub ts about the host range as a classification criterion for the Polymyxa genu s.