Evaluation of pesticide effects on bean and sesbania rhizobia and their symbiotic relationship
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Date
1996
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Sokoine Univesirty of Agriculture
Abstract
Laboratory and glasshouse experiments were conducted at the Sokoine
University of Agriculture, Morogoro, to evaluate the effects of kocide 101 (77%
cupric
hydroxide)
a
fungicide
and
oxadiazon
[3-(2,4-dichloro-5(l-
methylethoxyphenyl)-5-(1 ,1 -dimethylethyl-1,3,4-oxadiazol-2(3 H)-one] a herbicide,
on the growth and symbiotic performance of bean (Phaseolus vulgaris L.) and
Sesbania rostrata rhizobia, respectively. The growth of the rhizobial strains in the
presence of the pesticides was evaluated in Yeast Mannitol Broth (YMB). The
\eg\i.vne-Rhizobium symbiosis was evaluated in the glasshouse using a sandy loam
soil (Typic Rhodustalf) for beans and a clay soil (Udic Ustifluvent) for Sesbania.
Kocide 101 in the broth medium inhibited growth of rhizobia. Of the three
strains tested for sensitivity to kocide 101, the local isolate was most tolerant
followed by the PV] strain, and the strain CI AT 899 was least tolerant. The growth
of Sesbania rhizobia in broth medium was unaffected by the addition of oxadiazon.
The application of kocide 101 at the recommended application rate
(equivalent to 1.7 mg/kg soil) had no harmful effect on growth, nodulation and
nitrogen fixation of bean plants. Kocide 101 applied at 2x and 4x the
recommended application rate (equivalent to 3.4, and 6.8 mg/kg soil) was
detrimental to the growth, nodulation and N2 fixation. The inhibition of nodulationiii
and N2 fixation in the presence of kocide 101 was mainly due to the direct effect
of the fungicide on the bean plants.
The application of oxadiazon at the recommended application rate, at 2x
and at 4x the recommended application rate (equivalent to 0.75, 1.50, and 3 mg/kg
soil, respectively) adversely affected the growth, nodulation and N2 fixation by
Sesbania rostrata plants, the inhibition increasing with increase in oxadiazon
concentration. The inhibition in nodulation and N, fixation in the presence of
oxadiazon was, to a large extent, due to adverse effects of the herbicide on plant
growth and development rather than on rhizobial viability.
Nodule formation and plant growth of both beans and Sesbania continued
to be curtailed by the pesticides residues four months after they were first applied
to the soil.
Description
Dissertation
Keywords
Symbiotic relationship, Glasshouse experiments, Pesticide effects, Sesbania rhizobia