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Breeding
bean cultivars resistant to angular leafspot and root rots in Eastern
and Central Africa
P.M. Kimani, R. Buruchara,
R.Otsyula & G. Rachier
Angular leaf spot, caused by Phaeiosariopis griseola, and root rots caused by a complex of
pathogens, are probably the most important diseases of the common bean
in East and Central Africa. Angular leaf spot is ranked as the most
important fungal disease causing annual losses of more than 384,000 MT
per year in Africa. Losses due to root rots are estimated at 221,000 MT
year. Breeding cultivars resistant to the two diseases is considered the
most cost effective component of an integrated management strategy for
resource-poor farmers. The East and Central Africa Bean Research Network
(ECABREN) member countries are implementing a market-led breeding
strategy focusing on seven most important bean market classes.
The objective of the program is to develop and disseminate
well-adapted, high-yielding bean cultivars with resistance to two or
more biotic and abiotic constraints and with seed and cooking
characteristics acceptable to local, domestic, regional and
international markets. Multi-parent crosses were made from 56
genetically diverse lines from Andean and Middle American gene pools.
The parents included lines with resistance to angular leaf spot,
Anthracnose, common bacterial blight and tolerance to low soil
fertility. Fifty-two segregating populations from these crosses were
advanced to F4 generation and their seed separated into seven
market classes (red mottled, dark red kidneys, small reds, yellow and
brown, sugars, carioca and pintos).
Seed of each market class was divided into four sets. The first
set was screened for tolerance to angular leaf spot under artificial
inoculation at Kawanda; the second set was screened in a field plot
heavily infested with root rots in Sabatia, Vihiga District, in Western
Kenya. The third set was grown in a low soil phosphorus test site in
Kakamega. The fourth set was evaluated for yield and other agronomic
characteristics at Kabete, Thika, Juja and Ol Jorok for two seasons.
Results showed that 6.7% of the 267 red mottled lines and 14.6 % of the
233 red kidney lines were moderately resistant to Pythium spp in screen house tests. NM 12646-3-1, a red kidney type
was resistant to Pythium spp. Twenty-three
red kidney, 23 red mottled lines, 9 small red and 26 navy were tolerant
to low phosphorus at Kakamega. Pinto lines showed only intermediate
tolerance to low phosphorus. Several
lines combined tolerance to two or more stresses and high grain yield.
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