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
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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,
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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.