OCCURENCE, DIVERSITY AND BOTANICAL MANAGEMENT OF ANTHRACNOSE PATHOGEN (Colletotrichum lindemuthianum) IN FARM-SAVED BEAN SEED IN WESTERN KENYA.
Common bean (Phaseolus vulgaris L.) crop plays an important role in human nutrition and poverty alleviation in Western Kenya. Most farmers use farm saved seed. However, seed borne anthracnose Colletotrichum lindemuthianum disease lowers the quality of farm-saved bean seed resulting in low bean yields. Host plant resistance and environment friendly fungicides are among the most affordable, appropriate and effective control measures of the disease. Unfortunately, C. lindemuthianum is highly variable resulting in breakdown of resistance in bean cultivars. The objective of this study was to investigate the occurrence, diversity and botanical management of C. lindemuthianum in farm-saved bean seed in western Kenya. The study was done in Bungoma, Kakamega, Trans Nzoia, Nandi, Busia, Kisii and Siaya regions of Western Kenya between December 2008 and July 2010. One hundred and ninety six farmers’ farm-saved seed accessions and 122 infected bean pod samples in the field were collected from the study area using systematic random sampling. Disease incidence on the seed was determined using blotter and growing-on test. Virulence on the 12 common bean differential cultivars and BOX-AIR marker were used to assess the physiological and genetic diversity of C. lindemuthianum isolates from the infected pods. Eight plants extracts; Allium cepa L., Allium sativum, Aloe vera, Azadirachta indica, Datura stramonium, Eucalyptus globules, Lantana camara and Cleome gynandra were screened for antifungal activity against C. lindemuthianum. Data collected was analyzed by analysis of variance and means separated using Turkey’s test at p≤0.05. Diversity data was analyzed using Numerical Taxonomy and Multivariate Analysis System for personal computer (NTSYS-pc) ®. Different seed varieties from different regions had high and significantly different (p≤0.05) anthracnose incidences. GLP 585 variety had the highest incidence (53.1%) whereas GLP 2 had the lowest (28.7%). Seventy four races of C. lindemuthianum were identified among 122 isolates showing high virulence diversity. Race 0 was the most frequent race and occurred frequrntly. The most virulent races were less frequent and occurred in single region only. The isolates were virulent to all bean differential cultivars with 14 races breaking the resistance of the most resistant cultivar G2333. Seventy three new races were obtained as they did not conform to the races previously obtained in Kenya. Sixty races grouped into eight clusters revealing that C. lindemuthianum was a highly variable pathogen. No associaton was observed between the genetic diversity and race classification of the isolates. All the in vitro tested water extracts were active against C. lindemuthianum at inhibitory concentration of 30% though A. vera had the highest (90.6%) whereas L. camara had the lowest (28.7%). In vivo tests showed that plants treated with A.vera extracts had a lower anthracnose incidence and severity (23% and 15% respectively) and compared well with disease reductions due to the application of the Mancozeb at 2 gm l -1 (11.1% and 10% respectively). It was concluded that in Western Kenya C. lindemuthianum was highly variable and 73 new races had been obtained in addition to those from previous studies in Kenya. The use of A. vera plant extract as foliar treatment by farmers could offer alternatives for anthracnose management for resource-poor, small holder farmers
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