Assessment of resistance to root-lesion and root-knot nematodes in Australian hybrid clones of sugarcane and its wild relatives

Root lesion nematode (Pratylenchus zeae) and root knot nematode (Meloidogyne javanica) are the two most important nematode pathogens of sugarcane in Australia. They cause significant yield loss but there are no known varieties with resistance. A research project commenced in 2011 to assess the level of nematode resistance in the progenies from clones derived from crosses between sugarcane (Saccharum spp.) and Erianthus spp. or Saccharum spontaneum Since standard methods of assessing nematode resistance in sugarcane clones were not available, the study aimed to develop rapid, effective and reliable methods for the screening of large numbers of clones for resistance to root lesion and root knot nematodes. A second objective was to determine the resistance of basic Saccharum spp., their wild relatives and some selected crosses to these two nematodes. Shoot and root biomass, reproduction factors (RF) and number of nematodes (or eggs) per g of roots were used to assess resistance levels. A visual rating of root galling was also used for root knot nematodes. The RF value, nematodes or eggs per g of roots, and visual rating (for root-knot nematode) were highly correlated. Resistant and susceptible clones were distinguished using any of these methods. It is concluded that the RF values can be used to detect nematode resistance in large numbers of clones. In the case of root-knot nematodes, visual gall ratings produced results that were similar to egg counts, and could be used as an alternative in future. For advanced clones, rating based on nematodes or eggs per g of root is likely to provide more accurate results. Basic S. spontaneum, E. arundinaceus clones and some progeny clones from crosses between these wild canes and commercial sugarcane clones, or from further backcrosses between these and sugarcane clones, were found to be resistant or moderately resistant to root-knot and root lesion-nematode. These clones are being further tested in the glasshouse and in the field, and should be useful sources of resistance for root-lesion and root-knot nematodes for sugarcane breeding programs.