EPIDEMIOLOGY AND MANAGEMENT OF HOT PEPPER (Capsicum annuum L.) WILT COMPLEX DISEASE IN NORTHWESTERN ETHIOPIA

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 xvi (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 xvii 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.