Efficacy of cultural methods in the control of Rhizoctonia solani strains causing tomato damping off in Kenya

Rhizoctonia damping off of tomato caused by Rhizoctonia solani can be a serious problem in most intensive production environments. Recent increase in smallholder vegetable production of 0.5-3.0 ha in Kenya has resulted in build up of the pathogen to above economic threshold levels. There is no effective chemical control or resistant varieties. Use of soil fumigants such as methyl bromide in the control of Rhizoctonia and other soil borne pathogens is not sustainable due to their high costs, and toxicity to man and environment. Cultural methods such as soil amendments, mode of planting and influencing soil moisture levels either alone or in combination with other methods are among the most likely substitutes to use of toxic fumigants for control of soil borne pathogens in agriculture. This study was undertaken to evaluate the effects of cow manure application, transplanting, planting on raised beds and varying watering interval on Rhizoctonia damping off of tomato as measured by percent seedling survival at 5-30 days after planting (DAP), disease severity at 30 DAP, percent crop stand at 60 DAP and fruit yield at maturity. The study was conducted in a field artificially inoculated with pathogenic strains of Rhizoctonia solani isolated from infected tomato plants and Rhizosphere soil sampled from the major production regions of Kenya. The efficacy of the various cultural strategies both singly and in combination on the Rhizoctonia damping off management was compared with the conventional disease control involving chemical fumigation with metham sodium and two chemical seed dressers (pencycuron, thiram, imidacloprid) and (captafol) as the standard. Cow manure application and shorter watering interval when used singly or in combination with other cultural methods produced lower disease control and yield. Transplanting, planting on raised beds and medium irrigation interval when used singly or in combination with other cultural strategies produced good disease control resulting in higher yield that compared favorably with the conventional disease control involving soil fumigation and seed dressing. The various cultural disease control methods documented in this study can be used alone and in integration with other compatible Rhizoctonia damping off of tomato control strategies. Furthermore the promising non-chemical strategies may form part of the urgently sought for alternative to use of hazardous fumigants in agriculture and since they are not specific, there is low risk of resistant development over time.Key words: Cultural disease control, Rhizoctonia solani, tomat

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 Streptomyceswere found to have up to 100% trans-lamina and leaflet-to-leaflet translocation but no significant trifoliate-totrifoliatetranslocation. 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 systemicactivity 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

Distribution of Turcicum leaf blight of maize in Kenya and cultural variability of its causal agent, Exserohilum turcicum

The causal agent of Turcicum leaf blight Exserohilum turcicum was isolated from infected maize samples collected during a survey in seven districts representing the main maize growing areas of Kenya. The cultural variability of the isolates was assessed in different types of media, temperatures and light conditions. Growth rates were measured at two-day intervals from the second day up to the sixteenth day. Potato Dextrose Agar, Leaf Decoction Agar, Malt Extract Agar and V8 juice Agar were the four types of media used at continuous light, continuous darkness and alternating 12 hours of light and darkness. Temperatures ranged from 5oC, 10oC, 15oC, 20oC, 25oC, 30oC, and 35oC up to 40oC. Disease prevalence in six out of the seven districts was 100% while it was 90% in Nakuru district. All the cultivars grown by farmers were susceptible with disease incidence and severity ranging from 10% to 90% and 0.11 to 1.54 respectively. Agro-ecological zones with moderate temperatures accompanied by reliable rainfall recorded higher disease incidence and severity than those zones characterized by dry conditions with low rainfall levels. Isolates from different agro-ecological zones showed variation in morphology, pigmentation, growth rate and sporulation rate in different media. The different light regimes had significant effect on the growth rate and sporulation of E. turcicum isolates. The type of media and incubation temperatures had a significant effect on the growth rate of different isolates. The optimum temperature was 25oC and only one isolate had minimal growth below 100C and no growth was observed in all the isolates at 400C. This study shows that E. turcicum has a wide distribution and isolates from different areas vary in cultural characteristics and parasitic fitness with isolates from the same locality showing less variation. Keywords: Exserohilum turcicum, growth rate, isolates, sporulation Journal of Tropical Microbiology and Biochemistry Vol. 4 (1) 2008: pp. 32-3

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 Streptomyceswere found to have up to 100% trans-lamina and leaflet-to-leaflet translocation but no significant trifoliate-totrifoliatetranslocation. 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 systemicactivity 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