Ultrastructure of the Infection of Sorghum bicolor and Zea mays by Pythium species
Gichuru Virginia *
Faculty of Agriculture, Department of Crop Science, Makerere University, PO Box 7062, Kampala, Uganda, International Centre of Tropical Agriculture (CIAT-Kawanda), PO Box 6247, Kampala, Uganda and School of Pure and Applied Sciences, Department of Biological Sciences, Pwani University, P.O. Box 195-80108, Kilifi County, Kenya.
Okori Patrick
Faculty of Agriculture, Department of Crop Science, Makerere University, PO Box 7062, Kampala, Uganda.
Buruchara Robin
International Centre of Tropical Agriculture (CIAT-Kawanda), PO Box 6247, Kampala, Uganda.
Mahuku George
International Maize and Wheat Improvement Centre (CIMMYT), Apdo, Postal 6-641 06600, Mexico.
*Author to whom correspondence should be addressed.
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. Electron microscopy was used to study the 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. On the contrary, in sorghum P. ultimum and P. irregulare extensively colonised both the epidermis and endodermis. In this study, P. ultimum displayed two types of hyphae which mediated infection thus indicating that it might be more virulent than P. irregulare. The results of this study demonstrated that Pythium spp. are pathogenic on sorghum and therefore the role of sorghum in Pythium inoculum build-up in bean fields cannot be ruled out.
Keywords: Mixed cropping, Pythium ultimum, Pythium irregulare, electron microscopy, beans