Occurrence, biology, damage potential and management of Heterodera Schachtii (Nematoda: Heteroderidae) in small-scale farming in the Western Cape Province, South Africa

[摘要] ENGLISH ABSTRACT:During a survey in the greater Cape Flats Heterodera schachtii was found to bewidespread on cauliflower, Brussels sprouts, beetroot and cabbage. The numbers presentwere above two eggs and juveniles per gram of soil, generally regarded as the economicthreshhold level of infestation and requiring control.The damage potential of H schachtii on vegetables, as well as the ability of certainweeds to serve as a source of infection on subsequent crop plantings was studied undergreenhouse conditions and resulted in a reduction of yield and root weight of crops.Population densities of H schachtii increased significantly under favourable hosts likecabbage where densities of 198 eggs and juveniles per gram of soil were reached. Themost commonly occurring weeds maintained nematode development and increased theirpopulation densities. They can thus serve as alternative hosts in the absence ofsusceptible hosts and should be routinely controlled.The life cycle and biology of H schachtii was also studied. Penetration of plant tissueand subsequent development on vegetables, weeds and trap crops were observed.Penetration was successful on all crops tested reaching 37% and 52% at inoculum levelsof 22 and 11 juveniles per gram of soil, respectively. Subsequent development of Hschachtii on weeds and vegetables was similar, but in the case of cauliflower and blacknightshade as hosts, their life cycle was shorter in comparison to other crops.The possible existence of varying susceptibility of crops to different populations of Hschachtii was examined by comparing the rates of penetration in crops and reproductionof geographically isolated populations of H schachtii in the greater Cape Flats. Whenroot penetration, virulence and juvenile emergence were examined, populations fromLynedoch and Philippi were distinct from the other populations. Subsequently,representative individuals of these populations were subjected to PCR-RFLP, but withthese techniques real differences between the various populations could not be adequatelydetected.The environmental parameters such as soil texture, temperature and pH on H schachtiiwere investigated as to their influence on the root weight and yield of crops. Reductionsin the yield of beetroot and cabbage were observed with soil temperatures rangingbetween 15 to 30°C. Migration and penetration of H schachtii juveniles declined withan increase in clay and silt content of the soil. Above a 34% silt and clay content of soil,no migration and penetration took place. Root penetration levels of 30% and higher werereached with pH varying between 4.5 and 7.4. This resulted in a significant reduction inyield of crops.Crop rotation is an essential component of non-chemical control. In the case of Hschachtii, it required one host crop in four non-host rotational cycles to maintain thepopulation of the nematode in the soilless than three eggs and juveniles per gram of soil.The inclusion of a trap crop reduced the population densities to below two eggs andjuveniles per gram of soil. It therefore also forms an integral part of a control strategy.Solarization proved successful as a physical control method. Best results were obtainedin summer with clear polyethylene which led to a 97% reduction of infective juveniles.This method can be applied during the late summer in the greater Cape Flats, just beforethe onset of winter. This may safeguard future spring plantings. The need for effective control strategies in order to reduce the numbers of H schachtii isof the utmost importance to ensure vegetable production in the future. Small-scalefarmers should therefore be educated in this respect.

[发布机构] Stellenbosch University