Biology and control of bean anthracnose in Ethiopia

[摘要] English: Common bean (Phaseolus vulgaris L.) is an important food legume for millions ofEthiopian people. However, diseases are major constraints in bean productionwith anthracnose, caused by Colletotrichum lindemuthianum (Sacc. & Magn.)Briosi and Cav. (teleomorph = Glomerella cingulata (Stonem.), being of particularconcern. Anthracnose is the most important disease of bean in Ethiopia and cancause complete yield losses on susceptible cultivars when contaminated seedare planted. The impact of epidemics is further enhanced when favourableenvironmental conditions prevail. The main objective of this study was toprovide information that can be used as part of an integrated control program foranthracnose in Ethiopia.Field surveys were conducted in the foremost bean growing areas of Ethiopia toacquire information on the geographical distribution of anthracnose. Similar tobean rust, anthracnose is favoured by high moisture and relative humidity. Insurveys of the different agro-ecological zones (AEZ) anthracnose was foundsevere at Ambo (08°58'N, 03r26'E), Meki (08°05'N, 038°51 'E), Arsi-Negele(OrOO'N, 038°35'E), Areka 0 and Bako (09°06'N, 37°09'E), intermediate atAwassa (06°52'N, 038°27'E), Jimma (07°28'N, 035°37'E), and Metu (07°02'N,35°63'E), and slight to absent at Melkassa (08°23'N', 039°19'E). Other diseasesobserved included bacterial blight, angular and floury leaf spot and rust.The success rate in breeding for resistance depends to a large extent on thedegree of variability in a pathogen. Using the standard differential cultivar setand binomial system proposed by CIAT (Centro Internacional de AgricultutraTropical), eight races of C. Iindemuthianum, viz. 65, 73 128, 296, 511, 589, 961,and 1027, were identified from Ethiopia and compared to races 3, 6, 81,323,390and 593 from Southern Africa. Races 128 and 511 constituted more than 50% ofall isolates characterised. Considering the differential cultivars, G 2333 wasresistant to all races in Ethiopia, and AB 136, G 2333, Kaboon, Cornell 49-242 toall races in Southern Africa.Field studies were conducted at Ambo and Bako (Ethiopia) to evaluate resistantand susceptible cultivar mixtures as a means of anthracnose control. Resultsshowed that disease incidence and severity were consistently lower in mixturescontaining 50%, 67% and 80% of the resistant component at both locations.Disease progress curves and disease gradients indicated that diseasedevelopment and spread were slower or reduced in all treatments that containedan increased proportion of the resistant cultivar. It was thus found thatanthracnose could be controlled by growing cultivar mixtures containing at least60% of a resistant cultivar. In an assessment of the efficacy of chemical controlof anthracnose, a benomyl seed dressing followed by a foliar difenoconazolespray, or difenoconazole application alone, showed the most promising results.Finally, greenhouse and multi location field experiments were carried out toidentify bean genotypes as possible sources of resistance to Ethiopian isolates ofC. lindemuthianum. The study established that cultivars Widusa, GLP X 1132, A482, A 193, G-7, HAL 5 and G 2333 were valuable sources of anthracnoseresistance.

[发布机构] University of the Free State