Organically based strategies used by small-scale farmers in Lesotho for the sustainable management of soilborne diseases

[摘要] English: Damping-off of vegetable seedlings caused by Rhizoctonia solaniKuhn., Pythium ultimum Trow. and Fusarium oxysporum Schlecht. causeserious losses in seedbeds in Lesotho. Composts prepared from poultry,cattle, pig and sheep manure and commonly used by Lesotho farmers wereshown to decrease disease severity and increase plant biomass. Cattle, pigand poultry manure composts gave the best disease suppression andstimulated the growth of vegetable seedlings. Composted sheep manurehowever, did not suppress damping-off nor increase seedling biomass. Seedgermination was also significantly suppressed in this compost. Highconcentrations of phytotoxic elements were possibly responsible for thisphenomenon. Disease suppression was also investigated in field studies.Composted cattle, pig and poultry manures significantly suppressed seedlingdamping-off. Sheep manure compost was also able to reduce damping-offseverity under field conditions but to a lesser extent than the other threecomposts.General microbial activity in field soil including fungal populationspresent in the four tested composts was evaluated in the laboratory usingFOA. Composted cattle, pig and poultry manure displayed a significantlyhigher level of microbial activity and consequently yielded more fungalcolonies. The lowest microbial activity was observed in composted sheepmanure.Research conducted on the suppression of R. so/ani, P. ultimum and F.oxysporum with crude extracts of Rhamnus prinoides L. Herit, Artemisia afraJacg. ex Willd., Leucosidea sericea Eckl. & Zeyh and Melia azedarach L,confirmed their ability to suppress these pathogens. Mycelial growth of R.so/ani, F. oxysporum and P. ultimum was inhibited in vitro by extracts of R.prinoides, L. sericea and A. afra. The growth of these pathogens washowever not significantly suppressed by extract of M. azedarach. The plantextracts were also able to suppress damping-off of seedlings when added tosoil. Populations of R. solani, F. oxysporum and P. ultimum in soils treatedwith these extracts were also significantly reduced. Disease reduction washighest 7 and 14 days after treatment with the extracts.The combination of composted animal manures with plant extractsresulted in a reduction of general soil microbial activity, especially fungi.Microbial activity was most reduced in cattle, pig and poultry manurecomposts while the microbial activity in composted sheep manure was notaffected by plant extracts. In fact in some cases, the application of plantextracts resulted in an increased microbial activity in sheep manure. Diseasesuppression in greenhouse studies was not negatively or positively affectedby the addition of plant extracts.The present study confirms that composted manure of cattle, poultryand pig as used by Lesotho farmers, can be effectively used to controldamping-off of vegetable seedlings in seedbeds. The use of sheep manure ishowever still questionable due to its negative effect on seed germination andgeneral plant growth. Extracts of L. sericea, A. afra, R. prinoides and M.azedarach as used by Lesotho farmers, also have the potential to suppresssoilborne pathogens. They can be used to control soilborne diseases eitherindividually or in combination with animal manure composts.

[发布机构] University of the Free State