Publication: Farmers’ perceptions and coping strategies with sweet potato weevil and characterization of sweet potato genotypes for diversity and resistance to cylas puncticollis boheman in kenya
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2018
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NACOSTI
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Abstract
Sweet potato (Ipomoea batatas (L.) Lam.) contributes significantly to food security and
income of subsistence farmers in Kenya. However, productivity of the crop is
constrained by several biotic, abiotic and socio-economic factors. Amongst the biotic
constraints, insect pests such as the sweet potato weevil (Cylas spp.) cause significant
yield losses. However, in Kenya, there is limited information on farmers’ perception
and management of Cylas spp. and on diversity among cultivated sweet potato
genotypes. The objectives of this study were to: (i) Assess farmers’ perceptions and
coping strategies to the sweet potato weevil; (ii) Analyze variation among selected
sweet potato genotypes using agro-morphological, molecular and nutritional characters,
and; (iii) Screen selected sweet potato (Ipomea batatas L.) genotypes for resistance to
the sweet potato weevil. Firstly, participatory rural appraisal approach was conducted in
the year 2012 in Homa Bay County where 269 farmers were interviewed on farmers’
perceptions and coping strategies against the sweet potato weevil (Cylas spp.). This
study revealed that Cylas spp. was the most problematic (93.3%) pest. Many farmers
(90.7%) were not aware of sweet potato genotypes that had field resistance to Cylas
spp. The most commonly used methods by farmers to manage Cylas spp. were reridging during weeding (21.2%) followed by covering exposed roots with soil (12.6%).
Secondly, field experiments were conducted on-station in 2014 at two sites (ATC -
Miyare and -KALRO Embu) using 68 sweet potato genotypes arranged in a
Randomized Complete Block Design. Data were recorded on variation in agromorphological, molecular and nutritional characters. On the basis of quantitative agromorphological traits, Analysis of variance revealed significant (p≤0.05) differences
among sweet potato genotypes. Genotypes Nyautenge (16.82 t/ha) and Kemb 10 (17.04
t/ha) had the highest average root yield at ATC Miyare and KALRO Embu respectively
while, genotypes 56682-03 (0.84 t/ha) and K/KA/2004/215 (1.07 t/ha) had the least
average root yield at ATC -Miyare and KALRO -Embu respectively. The genotypes
were variable in respect to all qualitative traits studied. Both quantitative and qualitative
based dendrograms did not group the genotypes according to geographical area of
origin or shared names. On molecular approach, 13 simple sequence repeat (SSR)
markers were used to determine genetic relationship among the sweet potato genotypes.
The SSR markers were highly polymorphic (0.2723) and cluster analysis divided the
genotypes into two major groups. However, the genotypes did not form specific groups
according to geographic regions or shared names. Nutrionally, the genotypes
significantly (p≤0.0001) differed in dry matter, root protein, root carotenoids, root
sucrose and root starch contents but dendrograms did not group the genotypes in
relation to their origin or shared names. Genotype Nyautenge had a stable high yield
(16.82 t/ha at ATC -Miyare and 15.23 t/ha at KALRO -Embu) and high dry matter
content (40.14% at ATC -Miyare and 32.26% at KALRO -Embu) at both sites.
However, the same genotype rated very low in other equally important nutrients like
total carotenoids and sucrose contents at ATC -Miyare and KALRO -Embu. Genotypes
Kenspot 1, Saly boro, 91/2187, 9 Nduma, Kenspot 3 and Kenspot 2 had high dry matter
contents at both sites and hence recommended for inclusion in future breeding
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programmes. Thirdly, fifty-one selected sweet potato genotypes were evaluated for their
resistance to Cylas punticollis Boheman (Coleoptera: Brentidae) in a controlled
experiment of no-choice arena from November, 2015 to February, 2016. The 51
evaluated genotypes were significantly (p≤0.0001) different in their resistance to C.
puncticollis damage. The study revealed that no genotype was completely resistant to
weevils but genotypes Obugi (5.00 adults) and 5 Nyandere (5.00 adults) were the highly
resistant to C. puncticollis while genotypes Tainung (25 adults), Naspot 1 (24.33
adults), Kenspot 5 (22.67 adults) and Fundukhusia (22.67 adults) were the most
susceptible to C. puncticollis damage. Resistance to weevils was negatively correlated
(-0.71) to dry matter content and positively correlated to starch (0.46) and sucrose
(0.48) contents. In conclusion, genotype Obugi is a stable high yield performer (9.21
t/ha and 9.55 t/ha in ATC -Miyare and KALRO -Embu respectively) and has a high
resistance to C. puncticollis as compared to Naspot 1 (susceptible check) and Santo
Amaro (resistant check). Other genotypes rated in this study as medium resistant to C.
puncticollis and had earlier recorded high yields at KALRO -Embu are Santo Amaro
(11.49 t/ha) and Wera (9.22 t/ha). However, these genotypes recorded low yields in
ATC -Miyare and thus may not be suitable for ATC -Miyare site and its surrounding.
Genotype Tainung was found to be the most inadequate since it was the most
susceptible (25 adults) to weevils, low performing in yield (1.44 t/ha at ATC -Miyare
and 5.70 t/ha at KALRO -Embu) and was low in dry matter content (21.40% at ATC -
Miyare and 24.39% at KALRO -Embu) as compared to others. All the above-mentioned
traits can make the genotype not to be preferred by many farmers. Nonetheless, the
genotype has got a high carotenoid content (27.55 µg/g at ATC Miyare and 30.57 µg/g
at KALRO Embu) as compared to other genotypes and thus suitable for addressing
vitamin A defficiency in the society.
Description
Phd Thesis
Keywords
sweet potato, to cylas puncticollis boheman, pest control