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.
|
|
