Field evaluation of selected introgression clones for their resistance to root-knot nematodes

Sugarcane nematodes, root-knot (RKN) and root-lesion (RLN), cause an estimated loss of over $80 million per year to the Australian sugar industry. In particular, RKN is a major problem if sugarcane is planted in sandy soil. No effective control method is available for sugarcane nematodes in Australia. Crop rotation and fallowing provide only short-term control and nematode populations usually bounce back within 12 months after these control methods. The use of nematicides is restricted due to inconsistent results, difficulty in application and the highly toxic nature of the chemicals to humans and the environment. No commercial cultivars are resistant to sugarcane nematodes. Recent glasshouse trials in Australia suggested that clones from introgression populations, originating from crossing between commercial canes and Saccharum spontaneum or Erianthus arundinaceus, possessed good resistance to root- knot nematodes. Field trials were established to determine the reliability of glasshouse resistance-screening results. Eight introgression clones that showed resistance to RKN in glasshouse trials were evaluated in a field in Wallaville, north of Childers. Test clones were planted in plots with high and low nematode populations and maintained up to the second- ratoon crop. Trial plots were assessed for nematodes each year 6 weeks after planting and ratooning. Three years of results showed that 7 of 8 introgression clones consistently maintained low numbers of RKN until the end of the trial period, and significantly (P<0.05) lower numbers of RKN (195 nematodes per kg of soil) compared to commercial standards (1500 nematodes per kg of soil). There was no difference in numbers of nematodes high and low nematode treatments after the second ratoon. These results suggested that the glasshouse-screening trials are reliable and can predict the field resistance of clones for RKN, and that introgression clones are a valuable source of resistance to these important pathogens/pests. Commercial cultivars Q208 A and Q240 A maintained high yield despite very high numbers of RKN, suggesting that these clones might be tolerant to RKN. Key words Sugarcane nematodes, root-knot nematode, Meloidogyne javanica, Saccharum spontaneum, Erianthus arundinaceus, nematode resistance