Virulence of Colletotrichum Capsici (Syd. Buter and Bisby) in Pepper (Capsicum Spp) Varieties in Major Growing Areas of Ethiopia: Implications to Integrated Disease Management (Idm) Using Chemicals and Biological Control Agents
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Date
2017-05
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Addis Ababa Universty
Abstract
Hot pepper (Capsicum anuum L.) is the prominent type of Capsicum spp grown in Ethiopia, since
its introduction in the early 17th century by the Portuguese. It covers 67.98% of all the area under
vegetables in Ethiopia. Anthracnose is the most renowned pepper fungal disease in the south
western part of the country causing up to 100% loss. Total crop failure due to diseases has been
common in the region and farmers are sometimes forced to abandon their production due to
excessive infection pressure in the field. The present thesis probes a broad overview of the
disease in Ethiopia. The main aim of this study was; thus, to gather scientific information on
the characterization of the pathogen and management o f the disease it caused in the country.
The specific objectives of this study were to assess the magnitude of disease in main chili
growing areas of the country; and the level of pathogenesis of the strains of the pathogen using
cultural, pathological and morphological tools; evaluate different biological control agents, plant
extracts and fungicides in vitro; study the effect of seedling density and phonological stages on
development of anthracnose and yield parameters in chili; Search for variability and germplasm
tolerance among the existing chili/pepper varieties in Ethiopia; analyze and develop the
incidence-severity relationships model; identify economically effective timing and frequency of
fungicide spraying programs; and analyze the effect of integrated anthracnose disease
management on disease reactions, growth and yield parameters and economic profitability of chili
production.
Rigorous survey was conducted in anthracnose prone areas; and the highest and lowest disease
spread was observed in Alaba and Shashogo with cumulative incidence of 41.88% and 19.81%,
respectively. From the chili farms, the highest incidence was found in Arsi negelle followed by Alaba with the value of 31.66% and 28.66%, whereas the lowest incidence in farms was found in
Humbo and Maraqo with 13.63% and 14.89%. Nurseries with a highest incidence were observed
in Humbo and Alaba with values of 13.5% and 13.02%, respectively. The disease incidence was
low, 4.13% and 1.28%, in Shashogo and Arsi negelle. Prevalence was higher in upper-kolla agroecological
zones where the mean was recorded as 21.82% and 7.55% in farms and nurseries,
respectively.
The variability study indicated that colonies varied in their cultural behavior ranging from cottony
to fluffy, mostly suppressed with regular to irregular margins. Colletotrichum spp pathogen’s
color ranged between white to grey. Growth rate of isolates on PDA medium was between 22.0 -
69.5 mm. Morphological studies of isolates revealed variations in their color, size, shape, acervuli
production, setae size and shape of conidia. Average conidial size varied from 18.00 - 33.3 μm
and average setae size varied from 77.2 -181.2 μm. On the basis of disease reaction expressed by
differential hosts, eleven groups (races) of C. capsici were identified.
The evaluation of fungicides, plant extracts and antagonists showed that all test concentrations of
Tilt-250 EC significantly inhibited the mycelial growth of Colletotrichum capsici. Among the
tested plant extracts, garlic was the best both in reducing the radial mycelial diameter (72.33)
and mycelial dry weight (73.33) at the highest concentration of 15 %. There was s igni f icant
variation among isolates of Trichoderma spp and antagonistic activities ranged from 51% to
89% reduction of the mycelial radial growth of Colletotrichum capsici on the PDA medium.
Among the promising antagonists, the isolate Tri_3 of Trichoderma harzinum showed the highest,
89 %, inhibition of mycelial radial growth of Colletotrichum capsici Experiment on planting densities and seedling phonological stages showed that symptom
development was delayed one day in the youngest seedlings compared to the older ones. After the
appearance of symptoms, for four consecutive days, the level of leaf disease incidence and
severity was consistently lower on the youngest seedlings. Leaf wetness was highly reduced by
increasing seedling spacing by at least 15 cm. The highest plant population densities yielded the
highest weight of berries per plot.
In multi-locational germplasm screening trial, the majority of the genotypes were moderately
resistance to C. capsici and none of them was found to be immune at the two locations.
Significant variations were also obtained among the genotypes for all yield components, namely
percent establishment, dry fruit weight per plant, number of fruit per plant, pulp weight per plant,
unmarketable fruits weight per plant, fruit length and days to 50 percent maturity. Total yield per
plant was higher at Alaba than Maraqo high level of disease incidence at Alaba. Anthracnose leaf
incidence was consistently associated with leaf severity and their relationships can be estimated
using the linear function across locations, crop seasons, and genotypes. The economic implication
of the timing and frequency of Ridomil application in the current context of fungicide use on chili
in Ethiopia was also evaluated. Less frequent applications (3-7 times) starting from flushing
successfully prevented the disease development and significantly reduced the incidence of leaf
anthracnose.
The lowest plant infection (12.8%), leaf infection per plant (15.2%), percent diseased leaf
area(15.2%)and infected fruits per plot (17.4%) was observed on combined application of isolates
Trichoderma spp, plant extracts and Ridomil in Maraqo fana variety. Regarding the growth
parameters, viz. the highest Mean Percent establishment (81.67), mean days to 50% flowering (65.33), mean days to 50% maturity (82) days to first harvest (106.3) in was observed in T16, T4,
and T8, respectively. From the quality parameters, the highest mean number of branches per stem
(9), mean canopy diameter (24.8), mean number of flowers per plant (9.6) and mean plant height
(61.4) in T10, T15, T6 and T7, respectively. Both negative and positive control showed higher
incidence and severity as compared to single and combined application of isolates Trichoderma
spp, plant extracts and Ridomil. The combined application of Trichoderma, plant extracts and
Ridomil performed best in number of fruits/plant, number of seeds/pod, unmarketable fruit,
marketable fruit and total yield. This mix up gave a higher benefit-cost-ratio due to reduced
production cost indicating that a judicious combination of organic management practice is
environment friendly, healthy and sustainable.
Over and above, management o f pepper anthracnose disease through integrated me ans wa s
r e commended in Ethiopia.
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Keywords
Capsicum Spp