Bacterial leaf spot of sweet pepper caused by Xanthomonads-. incidence, pathogen characterization, epidemiology and management options

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Sokoine University of Agriculture


A study was conducted in sweet pepper growing regions (Morogoro. Arusha, Tanga and Mbeya) in Tanzania to determine incidence and epidemiology of bacterial leaf spot disease (BLS), characterize bacterial spot-causing xanthomonad (BSX) strains and screen for resistance of the locally available sweet pepper varieties. One hundred sweet pepper fields were surveyed and diseased samples were collected for laboratory analysis. Bacterial isolates were identified based on physiological, biochemical, PCR and pathogenicity tests. Races were determined based on compatible or hypersensitive response on differential sweet pepper near-isogenic lines ECW-10R, ECW-20R and ECW- 30R. Results indicated that, BLS disease was wide-spread in farmers' fields in the surveyed regions. Disease incidence ranged between 10—100%, while the overall mean disease incidence was 69.3 %. Disease severity was statistically significant on village basis and the overall mean score was 4.6. High mean disease incidence (93.3 %) and disease severity score (6.5) were recorded in Lukozi and Kivulul villages, respectively. The lowest mean disease incidence (12 %) and severity (1.2) were recorded in Utengule village. Poor cultural practices and epiphytic survival of BSX on host and non-host plants were found to be the sources of inocula for successive crops. The RST2/RST3 primer sets detected 59 strains to genus level and the effector/avirulence gene primer sets detected 68 out of the 74 strains tested. The species-specific primer sets identified 63 out of 68 BSX to species level and were pathogenic on the susceptible cultivar Early Calwonder (ECW). The BSX were X. euvesicatoria (30), X. perforans (10) and X. gardneri (23). Xanthomonas euvesicatoria and X. perforans dominated in Tanga region whereas Xanthomonas gardneri dominated in Arusha region. Five strains were not pathogenic on cv. ECW. Seven sweet pepper races (P0 - P6) were identified. Race P3 (50 %) dominated the strains of BSX in Morogoro, Arusha and Tanga regions. Race P6 (27.9 %) dominated in Tanga and Morogoro regions. Frequencies of races PO, Pl, P2, P4 and P5 were considerably low. All the locally available sweet pepper varieties were susceptible to BLS disease. This is the first report to characterize BSX of sweet pepper in Tanzania.



Sweet pepper growing, Bacterial leaf spot of sweet pepper, Pathogen characterization, Tanzania, Sweet pepper