| dc.description.abstract | Root nodules from bean plants and soil samples were
collected from several sites in farms located in Kiambu, Nakuru,
and Nyamira districts. In addition soil only was collected from
the botanical garden in Chiromo campus in Nairobi distr ict.
Beans had been cultivated for many years on most of the soils and
bean plants were well nodulated with the exception of those
sampled from Nyamira farms. The farmers grew different bean
varieties although some varieties such as Rose coco were grown
in all areas where the study was carried out. The soil physical
and chemical properties were determined for each of the 10 farm
soils. The soil properties varied from one farm to another and
their pH ranged from 5.5 to 7.4. Populations of Rhizobium
leguminosarum biovar Phaseoli in eadG-6f the 10 farm soils were
determined by MPN method. The numbers .ranged from 6.0 in the
botanical garden soil to 1x106 rhizobia cells/g soil in Limuru
soil.
A total of 23 bean nodulating strains were obtained after
authentication of the isolates obtained from the collected
nodules. Morphological and cultural characteristics of the
strains were studied under various cultural conditions. All the
str-a"inshad rod-shaped cells and were gram negative. Symbiotic
effectiveness of selected strains were studied using Rose coco
bean variety. The 45 days old inoculated plants showed increased
growth vigor with mean plant heights varying from 42.3-59 cm.
There were also variations in shoot dry weight (1.44-2. 64g) ,
shoot nitrogen content (0.7-1.68%) and nitrogen yield
(0.013-0.043g). Increases of 3.6-90% in shoot dry weight and
8.3-258.3% in nitrogen yield over the -N control plants were
obtained.
During the study of some selected Rhizobium stains using
Rose coco bean variety, increases of 15.5-83% and 14-122% in
shoot dry weight and nitrogen yield respectively over the -N
controls were observed. These 45 days old inoculated plants had
variations in shoot dry weight (3.13-4. 96g), shoot N content
(1.8-2.24%) and mean plant height (63.5-73 cm).
Studies on symbiotic effectiveness and competitiveness
indicated that among the selected Rhizobium strains S36, 6 and
84 were the best three strains in these parameters. Analysis
of variance at P = 0.05 for both shoot and nodule dry weight
indicated that the strains had significant differences in their
nitrogen fixation and competitiveness .
A study of the effect of inoculation time after planting,
Rhizobium strain and bean variety on nodulation and plant growth
was also carried out. The period taken for first nodule formation
reduced with a delay in inoculation time after planting. Plants
of all varieties nodulated at different periods even when
inoculation was performed at the same time using the same strain.
A bean 'Variety also nodulated at different periods when
inoculation was carried out at the same time using different
strains. When inoculation was carried out during planting or one
week after planting, Mwezi moja bean variety nodulated earliest
(between 4 to 13 days) with all the Rhizobium strains used while
Canadian wonder variety took longest (4 to 21 days) to nodulate.
Rose coco variety nodulated latest (7 to 8 days) with all the
strains when inoculation was delayed for 2 weeks after planting.
Strains 86 and 836 caused reduced or no nodulation in some
varieties when inoculation was delayed. The strains caused
varied nodule numbers, size and distribution and plant growth
characteristics (e.g shoot dry weight) among the varieties even
when inoculation was carried out at the same time and using the
same Rhizobium strain.
The effect of spectinomycin, streptomycin and a combination
of the two antibiotics at various concentrations on the growth
of the 23 Rhizobium isolates showed a range of resistance to the
antibiotics. The growth of all isolates was reduced with a few
of them growing at all concentrations used (250 to 750 pg/ml
spectinomycin and 40 to 120 pg/ml streptomycin).
On the basis of good nodulation , nitrogen content and
increase in shoot dry weight, Rhizobium.. strains 836 and S4 were .
found to be the most promising and should be studied further
under field conditions. | en |
