DISTRIBUTION OF COMMON BEAN (Phaseolus vulgaris L.) DISEASES AND ITS MANAGEMENT THROUGH HOST RESISTANCE AND SEED TREATMENT IN ETHIOPIA

Abstract

The common bean (Phaseolus vulgaris L.) is an economically important legume consumed as a source of food and used as a cash crop in Ethiopia.However, biotic and abiotic factors affected its production and productivity. Among the biotic factors, diseases caused by fungi, bacteria, and viruses represent major limitations and most destructive factors resulting in significant yield and quality losses. Of the diseases, common bacterial blight (CBB), angular leaf spot (ALS), anthracnose, and rust are the major and frequently occurring diseases of common bean in Ethiopia. Therefore, the study was conducted with the major objective of determining the distribution and management of common bean diseases through host resistance and seed treatment in Ethiopia with the following four specific objectives: (1) To determine the distribution, current status and importance of CBB and anthracnose diseases and the association of factors influencing epidemic development in major common bean growing areas in Ethiopia,(2) To evaluate common bean genotypes resistance to CBB, ALS, anthracnose, and rust diseases and their agronomic performances, (3) To manage CBB and anthracnose diseases using common bean varieties as host resistance and seed treatment, and (4) To determine the integrated effect of common bean varieties and seed treatment on grain yield, yield component, and seed health in eastern Ethiopia. A field survey was conducted in the 2019 main cropping season to determine the distribution of CBB and anthracnose diseases. A total of 180 common bean fields were assessed in 12 districts across six zones. The magnitude and the associations of disease parameters with biophysical factors were determined using a logistic regression model. Moreover, field experiments were conducted to evaluate the genetic resistance reactions of 25 common bean genotypes to CBB and ALS diseases and their agronomic performances at Haramaya and Melkassa, Ethiopia, during the 2019 and 2020 main cropping seasons. The experiment was arranged in a 5 x 5 triple lattice design with three replications. Another separate field experiment was carried out to evaluate 16 small-seeded common bean genotypes for xv sources of multiple disease resistance and agronomic traits at Haramaya and Melkassa, Ethiopia, during the 2019 and 2020 main cropping seasons. The experiments were laid out in a randomized complete block design (RCBD) with three replications. Furthermore, field experiments were conducted at Haramaya and Hirna, Ethiopia, during the 2019and 2020 main cropping seasons to determine the effect of common bean varieties and seed treatments on CBB and anthracnose epidemic progression, growth, grain yield, yield components, and seed health in eastern Ethiopia.Treatments were factorial arranged in RCBD with three replications. Survey results revealed that all the inspected fields were 100% infected with CBB and anthracnose diseases with severe CBB. Incidence and severity of CBB and anthracnose were significantly associated with biophysical factors with variable magnitudes. High CBB incidence (>70%) at Ambo, Shashemene-zuriya and Arsi-Negele, and high severity (>30%) at Sidama, Ambo and Shahsemene-zuriya were significantly associated (P<0.001) with sole cropping, sowing at July, poor weeding practices, maturity growth stage, and use of own saved seeds. On the other hand, anthracnose incidence (>50%) and severity (>30%) had high probability of associations with zone, sole cropping system, own saved seeds, variety, poor weed management practices, and maturity growth stages. Analysis of variance indicated that significant (P<0.05) differences observed among diseases and agronomic data collected. Large seeded common bean genotypes NUA-225, NUA-517, DAB-388, NUA-577, DRKDDRB-81, DRKDDRB-70, DAB-478, and NUA 536 attained low severity, low AUDPC and slow disease progress rate next to checks. However, genotype DAB-525 showed moderately resistant reaction to CBB and ALS diseases, and other genotypes demonstrated variable disease resistance reaction at both locations in the two cropping seasons. Similarly, genotypes NUA-225, NUA-517, DAB-388, and NUA-577 relatively performed well for growth, yield components, and grain yield. Additionally, small seeded common bean genotypes RAZ-11, RAZ-42, SCR-11, SCR-15, SSLN-1309, and SSLN-939 including check SER-119 showed resistant reaction to CBB, ALS and rust diseases. Check Awash-1 is found to be moderately resistant to CBB, ALS and rust diseases. Conversely, the small seed common bean genotypes, SSLN-1309 and SSLN-939 provided the highest grain yield. Furthermore, the third experiments consisted of eight common bean varieties (Awash-1, Awash 2, Awash-Melka, Ayenew, Chercher, Gofta, Haramaya, and Hirna) moderately resistant to CBB and anthracnose and susceptible Mexican-142 variety, seed treatment fungicide mancozeb, xvi bactericide streptomycin, and mancozeb and streptomycin combination (MS) including untreated control. The results showed that integration of common bean varieties and seed treatments significantly (P<0.0001) reduced CBB and anthracnose diseases parameters, enhanced grain yield, yield components, seeds health and reduced yield loss. Haramaya variety with mancozeb and streptomycin combined seed treatment resulted lower CBB severity (29.2%) and AUDPC (343.5%-days) at Haramaya, and CBB severity (23.8%) and AUDPC of 245.9%-days at Hirna than other treatments. Similarly, Chercher variety had low anthracnose severity (22.9%) and AUDPC (271.4%-days) and (20.4%) and (239.5%-days) at Haramaya and Hirna, respectively. High grain yields of 5.71 t ha–1 at Haramaya and 5.38 t ha–1 at Hirna obtained from Gofta variety on mancozeb and streptomycin combined seed treated plots. On the contrary, the highest grain yield losses of 27.4% and 29.9% were computed from untreated plots of Mexican-142 variety at Haramaya and Hirna, respectively. Seed treatment brought higher net economic benefit with higher marginal rate of return in each variety. The wide distribution and occurrence of CBB and anthracnose diseases requires proper agronomic practices and effective management options to reduce their impact. Thus, use of resistant genotypes, and integration of host resistance with seed treating chemicals could reduce diseases epidemics, enhance growth, yield components, grain yield, bring economic advantages, and seed health. Therefore, these approaches should become common place and practiced in common bean growing areas in Ethiopia.