Abstract:
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.
