Theses and Dissertations Collection

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Browsing Theses and Dissertations Collection by Subject "Acanthoscelides obtectus ecotypes"

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    Bean bruchid resistance and genetic diversity of bruchid ecotypes from bean growing regions of Tanzania
    (Sokoine University of Agriculture, 2022) Mayunga Edina
    Bean bruchids Zabrotes subfasciatus and Acanthoscelides obtectus are the serious pests which cause serious damage to the stored beans. Damage is directly related to the time of bean storage, the longer storage time the greater the damage. Host plant resistance is a profitable and a safe alternative to control bruchids in common bean and is associated with biochemical, morphological, and molecular traits. These traits affect insect growth and development and in that way, reduce the losses by the pests. The aim of first objective was to evaluate the damage level of bruchids in resistant (AO-1012-29-3-3A) and susceptible (Njano gololi) bean genotypes associated with biotype variation. Bean bruchids were collected from different bean growing regions Songwe (Vwawa), Kilimanjaro (Mungushi), Karatu (Rhotia), Morogoro (SUA) and Arusha (Kimyaki) in Tanzania, then transferred to the laboratory for inoculation. . Experiment was conducted using a Completely Randomized Design (CRD) with a 2 x 5 factorial scheme, two bean cultivars (AO-1012-29-3-3A and Njano gololi), five bruchids ecotypes for each A. obtectus and Z. subfasciatus and 3 replications. The results of this study have reported that each bean bruchids from a specific region showed a significant difference at prob. = 0.001 on beans infestation. AO-1012-29-3-3A and Njano showed different results on the resistance to bean bruchids. It was observed that AO-1012-29-3-3A line was resistant to bruchids collected from many regions by experiencing less damage and Njano gololi was observed to have high population of emerged bean bruchids, high percentage weight loss, high Susceptibility index and severity hence susceptible. The purpose of second objective was to determine phenotypic characteristics of the emerged F 1 bruchid ecotypes resulted from crossing resistant (AO-1012-29-3-3A) and susceptible (Njano gololi) bean genotypes. To examine whether these traits are host induced or genetically determined. Resistant genotype was used to assess whether host-race morphological differences are genetically determined or due to phenotypic plasticity. There was significant difference in size of F 1 bruchids emerging from resistant genotype (AO-1012-29-3-3A) and susceptible genotype (Njano gololi). The results showed that the morphological change of F 1 bruchids from AO-1012-29-3-3A was due to phenotypic plasticity since morphological changes occurred due to feeding on resistant genotypes (environment factor). The purpose of third objective was to identify the genetic diversity of bean bruchid weevils (Acanthoscelides obtectus and Zabrotes subfasciatus) in bean producing regions in Tanzania using molecular taxonomy (12S rRNA and COI marker). The results obtained did not show genetic diversity (100% identity) of Acanthoscelides obtectus present in Tanzania. For Zabrotes subfasciatus some variations was observed (80.2% identity). The genetic diversity was observed between Acanthoscelides obtectus and Zabrotes subfasciatus in which there was difference in some sequence alignment. Better knowledge of bruchids diversity present in Tanzania will help breeders and farmers to propose effective control methods with impact on environmental changes.