Oliver, O., Muthomi, J., Narla, R., Ojiem, J., Nderitu, J mechanisms contributing to poor crop emergence and establishment of common beans after lablab incorporation Oliver, O., Muthomi, J., Narla, R., Ojiem, J., Nderitu, J University of Nairobi

Introduction Green manuring is practice of ploughing or turning into the soil undecomposed green plant tissues for the purpose of improving soil fertility However, undecomposed plants residues have been reported to reduce crop establishment and increase incidences of pests and diseases. Reduced emergence of about 30 -40% have been reported Decomposition of plant residues results in metabolites that are toxic to other plants. Thee chemicals can either be inhibitory or stimulatory to crop growth, yield and microorganisms in the soil The chemicals released alter the plant surrounding which may result in either poor crop germination or reduced growth Therefore, there is need to determine the mechanism that may contribute to poor crop establishment.

MATERIALS AND METHODS Treatments – extracts from lablab, bean, soybean and groundnut Compost preparation – legume resides chopped and piled in a container with small layer of soil added to obtain microorganism for decomposition Extracts preparation –fresh legume residues were macerated with sterile distilled water and ethanol (80%) ratio 1:10 to obtain crude extracts Solvent (ethanol) was evaporated at lower temperature under reduced pressure in rotary flash evaporator to get the crude extracts Both fresh and compost extracts were tested on bean germination, mycelial growth, spore germination and bacterial growth Data collected - % germination, % spore germination, mycelial growth inhibition

MATERIALS AND METHODS Percentage germination = Seeds germinated in extracts Seeds used in bioassay ×100, Percentage spore germination= germinated spores total of spores ×100 Saprophytic fungi were tested for antagonistic activities against root rot pathogens Percent inhibition of radial growth (PIRG) PIRG = Radius in control −Radius of fungi in the direction of antagonists Radius in control ×100

RESULTS - Effect of different legume extracts on germination of common beans Seeds treated with lablab extracts had the lowest germination percentage while the maximum was recorded with seeds treated with aqueous groundnut extracts (85%) ( Fig 1) Seeds treated with lablab ethanol extracts had the lowest germination percentage while maximum was recorded with seeds treated with soybean ethanol extracts (Fig 2) Seeds treated with sterile distilled water had highest germination percentage Fig. 1: effect of aqueous extracts on germination Fig. 2: effect of ethanol extracts on germination

Ethanol extracts had strong antifungal activity Effect of different legume extracts on radial growth of Fusarium oxysporum The inhibition of mycelial growth varies from legume to legume and with extraction medium used. Ethanol extracts had strong antifungal activity The extracts of soybean and groundnut showed a high antifungal activity after four days lablab extracts showed the least antifungal activity against Fusarium oxysporum Fig. 3: effect of aqueous extracts on mycelial growth Fig. 4: effect of ethanol extracts on mycelial growth

Effect of different legume extracts on spore germination of Fusarium oxysporum Among the tested extracts, ethanol legume extracts showed near complete inhibition of spore germination The lowest conidial germination was recorded in spores treated with lablab extracts while the highest inhibition was recorded with groundnut extracts Lablab aqueous extracts seemed less inhibitory against Fusarium oxysporum Fig. 5: effect of aqueous extracts on spore germination Fig. 6: effect of ethanol extracts on spore germination

Effect of different legume extracts on germtube elongation of spores of Fusarium oxysporum Among the tested extracts, ethanol extracts showed near complete inhibition of germtube elongation germination The shortest germtube length was recorded in spores treated with beans and groundnuts extracts while the longest germtube length was recorded with lablab extracts Lablab aqueous extracts seemed very stimulatory against Fusarium oxysporum Fig. 7: effect of aqueous extracts on germtube elongation Fig. 8: effect of aqueous extracts on germtube elongation

C. Lablab ethanol fresh extracts D. Soybean fresh extracts Figure 9: Germinated spores of Fusarium after 24 hours of incubation on different legume extracts. A. Lablab fresh extract, B. Bean fresh extracts C. Lablab ethanol fresh extracts D. Soybean fresh extracts B B C D

Effect of saprophytic fungi against activities of root rot pathogens of common beans All antagonists inhibited mycelial growth with varying efficiencies for different pathogens The radial growth values ranged from 26mm to 39mm Trichoderma and Paecelomyces were significantly the best in terms of inhibiting root rot pathogen growth

CONCLUSION The plant extract of lablab origin exhibited effect on Fusarium oxysporum spores causing increase in the size of germtube and rate of sporogenesis Incorporation of lablab extracts stimulates the population of root rot pathogens through enhanced mycelial growth and through germtube elongation Lablab extracts Plant extracts with a good antifungal activity generally have high concentrations of total polyphenolic content and are able to inhibit pathogens The effective use of this green manure wherein planting within plots incorporated with green manure could affect the growth of the economically viable plants through reduced germination and establishment .

Acknowledgement

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