Control of Bean Rust using Antibiotics Produced by Bacillus and Streptomyces species - Translocation and Persistence in Snap Beans

Antibiotic culture filtrates produced by Bacillus (CA5) and Streptomyces spp. were tested for translocation and persistence when applied on snap beans inoculated with rust ( Uromyces appendiculatus ) in greenhouse pot experiments. The antibiotics were applied on the first trifoliate leaves and translocation was assessed as the number of rust pustules on non-treated leaflets or trifoliates while persistence was assessed as the number of rust pustules on rust infected plants at different times after antibiotic treatment. The treatments were replicated three times, each replicate consisting of a pot containing three plants. Antibiotics from both Bacillus and Streptomyces were found to have up to 100% trans-lamina and leaflet-to-leaflet translocation but no significant trifoliate-totrifoliate translocation. The antibiotic culture filtrates also retained significant rust control for up to 10 days after application on the bean plant. However, no significant rust control was found on the plants after 16 days of treatment. The study indicated that the antibiotics produced by antagonistic Bacillus and Streptomyces species possess systemic activity that can persist within the plant for over one week. These metabolites are potential bean rust control products that could be incorporated in integrated disease management program

Control of Carnation Fusarium Wilt Using Antibiotics Culture Filtrate from Streptomyces Spp.

Streptomyces spp. isolated from soils collected from Kabete, Department of Crop Science, University of Nairobi isolates were screened for antibiosis against Fusarium oxysporum f. sp. dianthi in vitro. The culture filtrate of isolate 21, one of the antagonistic isolates was tested for activity and found to suppress growth of F. oxysporum f.sp dianthi in vitro. The culture filtrate was used to treat pathogen inoculated carnation cuttings and it reduced stem discolouration by 62.2% which was comparable to reduction by benlate that reduced stem discolouration by 78.3%. Different concentration levels of the culture filtrate (concentrated filtrate, normal filtrate, half strength filtrate and quarter strength filtrate) all effectively reduced discolouration of the carnation stems by 93.3, 73.1, 68.5 and 63.4%, respectively. Phytotoxicity that led to chlorosis and partial wilting during the first week of treatment was detected in the antibiotic treated plants especially when applied to young and tender cuttings. The chlorosis and partial wilting were significantly reduced when older and well established cuttings were used and when the culture filtrate was diluted to half or quarter strength

Control of Carnation Fusarium Wilt Using Antibiotics Culture Filtrate from Streptomyces Spp.

Streptomyces spp. isolated from soils collected from Kabete, Department of Crop Science, University of Nairobi isolates were screened for antibiosis against Fusarium oxysporum f. sp. dianthi in vitro. The culture filtrate of isolate 21, one of the antagonistic isolates was tested for activity and found to suppress growth of F. oxysporum f.sp dianthi in vitro. The culture filtrate was used to treat pathogen inoculated carnation cuttings and it reduced stem discolouration by 62.2% which was comparable to reduction by benlate that reduced stem discolouration by 78.3%. Different concentration levels of the culture filtrate (concentrated filtrate, normal filtrate, half strength filtrate and quarter strength filtrate) all effectively reduced discolouration of the carnation stems by 93.3, 73.1, 68.5 and 63.4%, respectively. Phytotoxicity that led to chlorosis and partial wilting during the first week of treatment was detected in the antibiotic treated plants especially when applied to young and tender cuttings. The chlorosis and partial wilting were significantly reduced when older and well established cuttings were used and when the culture filtrate was diluted to half or quarter strength

Survey, molecular detection and characterization of geminiviruses associated with cassava mosaic disease in Zambia

A survey was conducted from April to May 2014 in 214 farmers’ fields located across six major cassava-producing provinces (Western, Northwestern, Northern, Luapula, Lusaka, and Eastern) of Zambia to determine the status of cassava mosaic disease (CMD) and the species diversity of associated cassava mosaic geminiviruses (CMG). Mean CMD incidence varied across all six provinces but was greatest in Lusaka Province (81%) and least in Northern Province (44%). Mean CMD severity varied slightly between provinces, ranging from 2.78 in Eastern Province to 3.00 in Northwestern Province. Polymerase chain reaction discrimination of 226 survey samples, coupled with complete DNA-A genome sequence analysis, revealed the presence of African cassava mosaic virus (ACMV), East African cassava mosaic virus (EACMV), and East African cassava mosaic Malawi virus (EACMMV) as single or mixed infections of different proportions. Single-virus infections were predominant, occurring in 62.8% (ACMV), 5.8% (EACMMV), and 2.2% (EACMV) of samples relative to mixed-virus infections, which occurred in 19.5% (ACMV + EACMMV), 0.4% (ACMV + EACMV), and 0.9% (ACMV + EACMV + EACMMV) of samples. Phylogenetic analysis revealed the segregation of virus isolates from Zambia into clades specific to ACMV, EACMV, and EACMMV, further confirming the presence of all three viruses in Zambia. The results point to a greater diversity of CMG across major cassava-growing provinces of Zambia and implicate contaminated cassava cuttings in disease spread