PhD-Thesis
The work was undertaken to develop lines with multiple disease resistance incorporating
ALS, BCMNV and CBB and characterization of resistance to ALS from bean landraces to
improve yield of common bean in Tanzania. Single, double and three-way crosses were
made between the susceptible recurrent parent, Kablanketi and resistant parents (Mexico
54, Vax 4 and MCM 5001). The Fa were screened for the presence of resistance markers
through marker assisted selection using SNO2, SAP6 and ROC11 SCAR markers. Thirty
five Fa lines had a combination of genes for ALS, CBB and BCMV while 11 had a
combination of two genes for resistance which forms a good source for folia disease
resistance in breeding programmes. Those lines making 120 plants were validated for the
resistance by phenotyping with three pathogens (ALS, CBB and BCMV) in the screen
house and 31 plants were found resistant to the three pathogens (P. griseola, Xap and
BCMV). The performance of genotypes varied significantly for the disease reactions and
yields. Yield varied from 484 to 3305 kgha'1 with a mean of 2042 kgha'1. The genotypes
with combined resistance and high yields are recommended further for evaluation for
release as a variety. Results also demonstrated that the heritability for disease in this study
was moderate to higher indicating that the selection can be performed in early generation
for some of the pathogens like ALS and BCMV traits. The study confirmed further that
resistance of P. griseola is due to monogenic dominant gene for ALS and single recessive
gene for BCMV. The CBB resistance was found to be conditioned by one major gene
which had effects of partial resistance. The inheritance of ALS resistance in Beti-10,
Nanka, Nanavala and Nkanamna landraces indicated that one single dominant gene
controls the resistance. The heritability for ALS in the landraces was high indicating the
additive genetic effect for that trait. SSR marker Pv-ag004 was found to be linked to
resistance in Beti-10. This landrace can be used in pyramiding the ALS resistant genes iniii
the farmers preferred varieties. However, detailed investigation is needed for the
mechanisms of resistance of the four landraces.