| dc.description.abstract | Common bean in Kenyans are predominantly grown by subsistence, resource-poor
farmers who use little or no soil amendment chemicals. Production is limited by
infertile soils with inherently low P and N, diseases, pests, use of unimproved cultivars
and poor general agronomic practices.
Eight common bean (Phaseolus vulgaris L.) cultivars, their 28 F, progenies derived
from a half-diallel cross were evaluated under P and N stress (-) and non-stress (+)
conditions at two locations (Kabete and Thika) in 2000 long rain season. Data were
recorded on basal root length, root dry weight; number of nodules per plant, mid-leaf
area, leaf area per plant, leaf dry weight, ,shoot dry weight, day to 50% flowering and
maturity, pods per plant, seeds per plant, 100-seed mass and grain yield. The
experimental design was a randomized complete block design (RCBD) with three
replications at each location. Analysis of variance and combining ability analysis were
performed for genotypes according to Griffing's (1956a) Method 2 Modell, while the
GCA: SCA ratio "vascalculated as suggested by Baker (1978).
Analysis of variance (ANOVA) showed highly significant differences (P = 0.01)
among the genotypes for all the traits studied under both P stress and non-stress
conditions at Kabete and Thika.
General combining ability analysis of variance indicated that at Kabete and Thika,
both the GCA and SCA mean squares were highly significant (P = 0.01) for all the
characters studied under both P stress and non-stress conditions.
Root traits, especially the basal root length, were well developed in crosses
involving the efficient parents. These generally had good yields thus indicating
improved tolerance to P stress at Kabete and Thika. CIM 9314-36 and CAL 143 were
the best performers in grain yield under both P stress conditions and locations. In
general a marked response of yield to P application of 21.1 % at Kabete and 15.3 % at
Thika was observed.
The general combining ability was more important than the specific combining
ability for all the traits studied for both P stress conditions and locations. This in effect
implies that the fixable additive genetic effects were more important than the
interactions in controlling inheritance of these traits.
The combining ability analysis showed highly significant differences for all the
traits studied at both N stress and non-stress conditions and locations.
Root traits especially the basal root length for both parents and F1 progerues
influenced tolerance to N stress as indicated by higher yields for both locations. CIM
9314-36 and CAL 143 performed well again in grain yield under non-stress conditions
at Thika. The overall response to N application for yield was 28.7 % at Thika and 17 %
at Kabete.
The general combining ability was more important than the specific combining
ability for all the traits studied for both N stress conditions and locations in controlling
the inheritance of tolerance to low soil N. | en |
