Effect of Leachates and Extracts from Different Parts of Jatropha curcas L. (Euphorbiaceae) On Soil Microorganisms

Abstract

Jatropha curcas L. is a potential source of biofuel because of its high oil content. Its broad scale propagation is advantageous in producing an alternative source of oil, however, the toxic substances that the plant contains may pose a threat on the soil microorganisms, especially when planted en masse. The study determined whether leachates from Jatropha-pianted soil and extracts from the different parts of Jatropha curcas L. affect the growth and population of selected soil microorganisms. Extracts from the different parts of Jatropha curcas L. (roots, stems, young leaf, old leaf, seed hull and pressed cakes) were tested for growth inhibition of soil bacteria (Bacillus subtilis, Rhizobium sp. and Azotobacter sp.) and fungi (Rhizoctonia solani, Trichoderma harzianum, Aspergillus niger, Fusarium oxysporum and Hansenula polymorpha). J. curcas extracts from roots, young leaf, and seed hull exhibited zones of inhibition with clearing only on Azotobacter sp. For the fungal species, T. harzianum showed zones of inhibition without clearing (stress zones) from the stem extract. Leachates were collected from a drum experiment to determine whether Jatropha- planted soil influenced the soil microbial population compared to non-planted soil. Populations of three major soil microorganisms (bacteria, fungi and actinomycetes) were counted from collected leachates of the Jatropha-planted and unplanted soil. Bacterial counts in Jatropha-planted soil for both Luisiana clay and Lipa clay loam were lower than the unplanted soils. In actinomycete counts, there was a small difference between Jatropha-p\anted and unplanted soil for Lipa clay loam, while the actinomycete count in Luisiana clay was higher. Increased fungal proliferation in Jatropha-planted soil for both Lipa clay loam and Luisiana clay was observed. J. curcas L. extracts slightly alter the growth response of some of the selected soil microorganisms and the bacterial count was the only one observed to be decreased by the plant. Due to the results obtained in the study, proper disposal by segregating or detoxifying of the seed hulls from the plant must be observed.

Jatropha curcas L. is a potential source of biofuel because of its high oil content. Its broad scale propagation is advantageous in producing an alternative source of oil, however, the toxic substances that the plant contains may pose a threat on the soil microorganisms, especially when planted en masse. The study determined whether leachates from Jatropha-pianted soil and extracts from the different parts of Jatropha curcas L. affect the growth and population of selected soil microorganisms. Extracts from the different parts of Jatropha curcas L. (roots, stems, young leaf, old leaf, seed hull and pressed cakes) were tested for growth inhibition of soil bacteria (Bacillus subtilis, Rhizobium sp. and Azotobacter sp.) and fungi (Rhizoctonia solani, Trichoderma harzianum, Aspergillus niger, Fusarium oxysporum and Hansenula polymorpha). J. curcas extracts from roots, young leaf, and seed hull exhibited zones of inhibition with clearing only on Azotobacter sp. For the fungal species, T. harzianum showed zones of inhibition without clearing (stress zones) from the stem extract. Leachates were collected from a drum experiment to determine whether Jatropha- planted soil influenced the soil microbial population compared to non-planted soil. Populations of three major soil microorganisms (bacteria, fungi and actinomycetes) were counted from collected leachates of the Jatropha-planted and unplanted soil. Bacterial counts in Jatropha-planted soil for both Luisiana clay and Lipa clay loam were lower than the unplanted soils. In actinomycete counts, there was a small difference between Jatropha-p\anted and unplanted soil for Lipa clay loam, while the actinomycete count in Luisiana clay was higher. Increased fungal proliferation in Jatropha-planted soil for both Lipa clay loam and Luisiana clay was observed. J. curcas L. extracts slightly alter the growth response of some of the selected soil microorganisms and the bacterial count was the only one observed to be decreased by the plant. Due to the results obtained in the study, proper disposal by segregating or detoxifying of the seed hulls from the plant must be observed.