Ultrastructure of the infection of sorghum bicolor and zea mays by pythium species

Abstract

The practice of cultivating mixed crops is common in Tropical Africa and elsewhere especially in areas of high population density. The practice of mixed cropping can promote disease spread especially in multi-host pathosystems. Pythium is a soil borne oomycete with a wide host range affecting both cereal and legumes. In this paper we examine pathogenesis by Pythium species in maize and sorghum, crops commonly included as intercrops in south western Uganda. In this study, both electron and light microscopy were used to study infection process using bean derived Pythium species-Pythium ultimum (MS 61) and Pythium irregulare (DFD 47) on beans, maize and sorghum. Electron microscopy revealed that on maize P.irregulare hyphae remained extracellular while P. ultimum hyphae in epidermis underwent necrosis after 9 days. In sorghum on the contrary, P. ultimum and P. irregulare extensively colonised both the epidermis and endodermis. In this study, P. ultimum also had two types of hyphae which mediated infection thus making it more virulent than P. irregulare. The results of this study confirm that Pythium spp. are pathogenic on sorghum and therefore the role of sorghum in Pythium inoculum build-up in bean fields cannot be precluded.