Abstract:
Hot pepper (Capsicum annuum L.) is the most important vegetable crop grown in Ethiopia.
However, the production and productivity of the crop is seriously constrained by both biotic and
abiotic factors. Among biotic factors, wilt complex disease incited by multiple pathogens, recently
has become a major hot pepper production bottleneck in the study areas. The disease could
destructively affect the quality and quantity of the crop. The study comprised of a field survey,
laboratory and fieldworks (variety evaluation and integrated disease management) with the
following specific objectives to: (1) assess the biophysical factors influencing the geographic
distribution and epidemic development of the hot pepper wilt complex disease in northwestern
Ethiopia; (2) isolate, identify, and characterize the hot pepper wilt complex disease causal pathogens
and prioritize them according to their frequency of occurrence; (3) evaluate hot pepper varieties for
resistant reactions to wilt complex disease and agronomic performances; and (4) evaluate the effect
of integrated use of compost application, host resistance and fungicidal seed and seedling treatments
against the development of wilt complex disease epidemic on hot pepper and yield performance at
Jabi Tehena district during the 2020 and 2021 main cropping seasons. Descriptive statistics were
employed to determine the distribution and frequency of hot pepper wilt complex disease across
locations and variable classes. The associations among disease variables and biophysical factors
were determined using logistic regression analyses. A variety evaluation experiment against the wilt
complex disease was carried out using a randomized complete block design (RCBD) with three
replications; whereas the integrated wilt complex disease management experiment was conducted
using a split-split plot design with three replications. The survey results showed that out of the total
assessed fields, 233(76.6%) fields were affected by the wilt complex disease. The survey results also
exhibited significant variation in hot pepper wilt complex disease intensity across the study districts.
The highest mean disease incidence (72.4%) and severity (70.1%) were recorded in the Jabi Tehena
district, while the lowest incidence (17.1%) and severity (14.9%) were recorded in the Guagusa
Shekudad district. District, altitude, year, plant growth stage, weeding frequency, previous crop, wilt
management practice, cropping system, and disease-aggravating factor exhibited highly significant
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(P 0.001) associations with disease incidence and severity. The highest (≥ 50%) incidence and
severity of wilt complex disease in hot pepper were strongly associated with Bure, Dembecha, Jabi
Tehena, and Wenberma districts in the 2020 cropping season, where the altitude was < 2000 m a.s.l.,
wilting began at the seedling growth stage, the weeding frequency was 1–3 times, and the previous
crop was a vegetable crop. The results of the laboratory work confirmed that Fusarium oxysporum
f.sp. capsici, Fusarium solani, Rhizoctonia solani, Pythium spp. and Ralstonia solanacearum
pathogens were identified as being associated with infected roots and stems of hot pepper. Among
them, Fusarium oxysporum f.sp. capsici was found to be the most frequently occurring isolate in all
the surveyed districts, whereas Pythium spp. was found to be the least frequently isolated pathogen.
In the meanwhile, the results revealed that fungal and bacterial pathogens associated with wilted hot
pepper samples showed variability in their cultural and morphological characteristics. Variety
evaluation experiment exhibited that there were differences among varieties in disease resistance
reactions and agronomic performances. The local check had the highest disease incidence (58.04%),
severity (56.33%), area under the disease progress curve (1471.67%-days), and the fastest disease
progress rate (0.0157 units day–1
). The results revealed that out of a total of fourteen varieties, eight
hot pepper varieties were considered susceptible, while six varieties were grouped as moderately
susceptible. However, there was no hot pepper variety that was resistant to the wilt complex disease.
The results also showed that Melka Zala, Melka Dera, and Melka Oli hot pepper varieties gave better
fruit yield than the rest varieties evaluated. As a result, the highest number of fruits per plant
(133.80), marketable dry fruit yield (2.13 t ha–1
), and total dry fruit yield (2.30 t ha–1
) were obtained
from Melka Zala. In the integrated management experiment, the minimum (23%) disease severity,
AUDPC (478.33%-days), and disease progress rate (0.0034 units day–1
) were obtained when Melka
Zala seed and seedlings were treated with Apron Star fungicide and seedlings transplanted into
compost treated plots. Conversely, the maximum (54%) disease severity, AUDPC (1426.67%-days)
and disease progress rate (0.0114 units day–1
) values were computed from Mareko Fana seedlings
transplanted into compost untreated and control plots. The results also showed that Melka Zala seed
and seedlings treated with Apron Star fungicide and seedlings transplanted into compost treated
plots yielded higher marketable fruit yield (2.42 t ha–1
) and total fruit yield (2.47 t ha–1
) than other
treatment combinations. In conclusion, it was found that proper crop husbandry practices and
cultural wilt management techniques minimized wilt complex disease epidemic development and
sustained hot pepper production and productivity in the survey areas. Additionally, those high yielding hot pepper varieties combined with other management options served as a short-term
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solution for sustainable production and productivity of hot pepper. Furthermore, integrated
management consisting of compost, host resistance and fungicide increased hot pepper yield and
suppressed the pressure of wilt complex disease. It is recommended that Melka Zala treated with
Apron Star fungicide and transplanted into a compost treated plot relatively suppressed the spread of
hot pepper wilt complex disease. Hence, farmers better use these treatment combinations in the study
areas and other places having similar agro-ecologies. Further verifications of the current findings in
various hot pepper-producing locations are suggested.