Recent studies into the soil biology of yield decline

Soil biology has been implicated as an integral part of the productivity constraint in sugarcane called yield decline (YD), which costs the Queensland sugar industry $200-$300 million each year. Known sugarcane root pathogens (Pachymetra chaunorhiza, Pythium arrhenomanes, P. myriotylum and nematodes) do not account for all the soil constraints associated with YD. Transmission experiments showed that addition of YD-affected roots alone may lead to the development of YD-root symptoms in pasteurised YD-soil or virgin rainforest soil. Soil sieving experiments suggested that unknown root pathogens may be concentrated in the smaller soil particle size fractions (20 and 38 f.lm). The general fungicide mancozeb controlled YD-type symptoms, while pathogenicity testing of over 200 fungal isolates has shown that dematiaceous fungi may depress growth. Further research is needed to identify previously unrecognised fungal root pathogens.