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

Resistance and inheritance of common bacterial blight in yellow bean

Common bean (Phaseolus vulgaris L.) is the most important food legume among the pulses. It is a cheap source of protein, especially in Sub-Saharan Africa. However, bean production is constrained by bacterial diseases, of which common bacterial blight (Xanthomonas axonopodis p.v. phaseoli) is prevalent in Africa. The objective of this study was to transfer resistance to common bacterial blight and determine its inheritance in yellow beans. Sources of resistance were CIAT lines, Wilk 2 and VAX 6, which were crossed with susceptible Lusaka yellow and Pembla. The parents, F1, F2 and backcross progenies were inoculated with X. axonopodis and the resulting blight severity determined. Quantitative traits, including days to flowering, number of pods, and seed yield were also determined. The F1 and backcrosses to the resistant parents were all resistant, while the F2 and backcrosses to the susceptible parents segregated in 3:1 and 1:1 ratios, respectively. Additive genetic effects were observed in quantitative traits like days to flowering, plant height, days to maturity and yield. Therefore, resistance to common bacterial blight is controlled by a single dominant gene. The resistant parents Wilk 2 and VAX 6 could be used to improve bean varieties that are susceptible to common bacterial blight

Inheritance of resistance to angular leaf spot in yellow beans

Angular leaf spot (Phaeoisariopsis griseola (Sacc) is an important disease of common bean (Phaseolus vulgaris L.) in most parts of Africa, causing yield losses of 40-80%. This study was carried out to determine the inheritance of resistance to angular leaf spot in yellow beans. Biparental crosses were done between susceptible yellow bean genotypes and angular leaf spot resistant parents to generate F1, F2 and backcrosses. Resistance was evaluated in a screen house and field after inoculation with Phaeoisariopsis griseola. The F1 were resistant, indicating that resistance was dominant. There was no significant deviation from the expected 3:1 ratio for resistant to susceptible in the F2 population, confirming that resistance to angular leaf spot was both monogenic and dominant. The backcross to Lusaka Yellow showed a 1:1 segregation ratio, while the backcrosses to Mexico 54 were all resistant. Pembela was susceptible to angular leaf spot, while the F1 were resistant. The ratio of 3:1 represents resistant : susceptible F2 populations. All backcrosses to Mexico 54 were resistant, confirming that resistance to angular leaf spot in Mexico 54 is controlled by a single dominant gene. The results of the study showed that resistance to angular leaf spot in yellow beans is governed by a single dominant gene. This can be used to improve the local landraces by incorporating angular leaf spot resistance and high yield traits

Identification of Elsinoë phaseoli causing bean scab in Kenya and evaluation of sporulation using five adapted techniques

This research addresses the presence of Elsinoë phaseoli in Kenya, where information on the biology of this pathogen remains scarce. Employing a multifaceted approach, the study demonstrates the steps taken to isolate, identify, and characterize E. phaseoli as the pathogen responsible for scab on common bean. Field observations confirmed scab symptoms, particularly the prominent pod lesions. Elsinoë phaseoli was isolated from common bean using a targeted streaking method on older acervulus-bearing lesions. Morphological examinations revealed a notable diversity within E. phaseoli colonies, consistent with the characteristics of the genus. Molecular identification through ITS-rDNA sequencing confirmed isolate AscoSK1 obtained in this study as belonging to E. phaseoli, offering a robust species differentiation method. Assessing conidium production required the implementation of five different culture methods. An adaptation of the Scheper et al. (2013) method yielded the highest quantity of conidia from 25 colonies spaced at 1 cm apart, with a conidial yield of 5.0 × 106 conidia per 9-cm-diameter Petri dish. A higher conidial yield was attained after the colonies were pre-incubated on potato dextrose agar in the dark at room temperature for 28 days, followed by a transfer to corn meal agar for an additional 2 days at 20°C. This emphasizes the pivotal influence of incubation duration and pre-culture conditions on the process. This research provides insights into the biology of E. phaseoli and introduces an improved method for enhancing in vitro sporulation of the pathogen, setting groundwork for future research and handling

Application of superabsorbent polymers (SAP) as desiccants to dry maize and reduce aflatoxin contamination

The ability of superabsorbent polymers (SAP) in drying maize and controlling aflatoxin contamination was studied under different temperatures, drying times and SAP-to-maize ratios. Temperature and drying time showed significant influence on the aflatoxin formation. SAP-to-maize ratios between 1:1 and 1:5 showed little or no aflatoxin contamination after drying to the optimal moisture content (MC) of 13 %, while for ratios 1:10 and 1:20, aflatoxin contamination was not well controlled due to the overall higher MC and drying time, which made these ratios unsuitable for the drying process. Results clearly show that temperature, frequency of SAP change, drying time and SAP-to-maize ratio influenced the drying rate and aflatoxin contamination. Furthermore, it was shown that SAP had good potential for grain drying and can be used iteratively, which can make this system an optimal solution to reduce aflatoxin contamination in maize, particular for developing countries and resource-lacking areas