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

Research PaperThe 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.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

The Role of mixed cropping systems on bean root rot epidemics in south western Uganda

Research PaperIn south western Uganda, beans are largely grown as intercrops with sorghum, maize, sweet potato and potato . Continuous cropping of beans, has increased bean root rot epidemics. Since some of the root rot causing organisms are known to affect other crops, there was need to investigate the role they may be playing in the current root rot epidemics. Surveys were carried out in Kabale district in order to establish the incidence of root rot on other crops grown in association with beans. Plant samples for isolation of Pythium, the main causative agent of root rot were also collected. Results indicated that potato had a high root rot incidence while maize had a low root rot incidence. Also, sorghum and peas had root rot symptoms. Out of the 142 Pythium isolates collected, 21 different Pythium species were identified by ITS-DNA sequencing. Fifteen new Pythium species not previously identified in the region were found. This study finds evidence that diverse crop species associated with beans may be playing a role in bean root rot epidemics.In south western Uganda, beans are largely grown as intercrops with sorghum, maize, sweet potato and potato . Continuous cropping of beans, has increased bean root rot epidemics. Since some of the root rot causing organisms are known to affect other crops, there was need to investigate the role they may be playing in the current root rot epidemics. Surveys were carried out in Kabale district in order to establish the incidence of root rot on other crops grown in association with beans. Plant samples for isolation of Pythium, the main causative agent of root rot were also collected. Results indicated that potato had a high root rot incidence while maize had a low root rot incidence. Also, sorghum and peas had root rot symptoms. Out of the 142 Pythium isolates collected, 21 different Pythium species were identified by ITS-DNA sequencing. Fifteen new Pythium species not previously identified in the region were found. This study finds evidence that diverse crop species associated with beans may be playing a role in bean root rot epidemics

Pathogenicity of pythium species on hosts associated with bean-based cropping system in south western Uganda

Research PaperA pathosystem is a subsystem of an ecosystem and is characterised by the phenomenon of parasitism. The bean-Pythium pathosystem consists of the host (bean), the pathogen (Pythium) and their host-pathogen relation. Of interest is how the pathogen causes pathogenicity on other crops and beans. To investigate this, screen house experiments were set up to test the pathogenicity of Pythium species derived from bean and other crops grown in association with beans. Pathogenicity was tested on maize (Zea mays), millet (Eleusine corcana), sorghum (Sorghum bicolor), peas (Pisum satium), susceptible bean variety (CAL 96) and resistant bean variety (RWR 719). The results indicated that distinct symptoms were observed in the roots and shoots of test crop species which are characteristic of Pythium infection. For instance peas had brownish watery stems and roots Also bean-derived pathogenic Pythium spp. were found to be more virulent than Pythium spp. derived from other crop species.Sorghum and peas had the highest disease scores upon infection by Pythium spp. We can conclude that there is cross pathogenicity among Pythium spp. especially affecting sorghum and peas. This phenomenon may account for the current root rot epiphytotics in south western Uganda and other similar agroecologies. An integrated disease management strategy that will deploy multi-non hosts to Pythium root rot is recommended.A pathosystem is a subsystem of an ecosystem and is characterised by the phenomenon of parasitism. The bean-Pythium pathosystem consists of the host (bean), the pathogen (Pythium) and their host-pathogen relation. Of interest is how the pathogen causes pathogenicity on other crops and beans. To investigate this, screen house experiments were set up to test the pathogenicity of Pythium species derived from bean and other crops grown in association with beans. Pathogenicity was tested on maize (Zea mays), millet (Eleusine corcana), sorghum (Sorghum bicolor), peas (Pisum satium), susceptible bean variety (CAL 96) and resistant bean variety (RWR 719). The results indicated that distinct symptoms were observed in the roots and shoots of test crop species which are characteristic of Pythium infection. For instance peas had brownish watery stems and roots Also bean-derived pathogenic Pythium spp. were found to be more virulent than Pythium spp. derived from other crop species.Sorghum and peas had the highest disease scores upon infection by Pythium spp. We can conclude that there is cross pathogenicity among Pythium spp. especially affecting sorghum and peas. This phenomenon may account for the current root rot epiphytotics in south western Uganda and other similar agroecologies. An integrated disease management strategy that will deploy multi-non hosts to Pythium root rot is recommended