Bean bruchid resistance and genetic diversity of bruchid ecotypes from bean growing regions of Tanzania
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Date
2022
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Publisher
Sokoine University of Agriculture
Abstract
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.
Description
Dissertation
Keywords
Bean bruchid resistance, Genetic diversity, Bruchid, Bean bruchids, Zabrotes subfasciatus, Acanthoscelides obtectus ecotypes, Bean growing regions, Tanzania