Plant parasitic nematodes and other organisms as a contributing factor to poor sugarcane root development in north Queensland

Large populations of parasitic nematodes can usually be detected in areas of poor sugarcane root development which display characters of what has been described as Northern Poor Root Syndrome (NPRS) (Egan et aI., 1984). Many symptoms associated with NPRS - small lesions, shortened secondary roots, poor lateral and fine root development - correspond with those described for nematode injury (Christie, 1959). Of the species commonly present, Pratylenchus zeae Graham (Khan, 1963; Santo and Holtzmann, 1970) and Meloidogyne javanica (Treub) Chitwood (Khurana and Singh, 1971) have been described as having some association with sugarcane root pathogens. Other species commonly present include Radopholus williamsi Siddiqi, and Helicotylenchus dihystera (Cobb) Sher. Early studies in North Queensland (Anon., 1960 and 1961) centred on reduction of nematode populations by fumigation with halogenated hydrocarbons. Treated plants had improved vigour initially but only small yield increases at harvest, this being attributed to the ability of all plants to outgrow any effects of nematodes during vigorous midsummer growth. In many of the areas displaying symptoms of NPRS, imbalances of calcium and magnesium nutrition and possibly of some trace elements have been shown to exist (Ridge, et aI., 1980). In a series of experiments with non-volatile nematicides, significant (P < 0.05) crop growth responses could be achieved after reductions in nematode popUlations (Chandler, 1978 and 1980). In many cases, these growth responses could only be achieved when nematicides were used in conjunction with calcium, magnesium and trace element additions to the soil. However, root decay remained prevalent in all treatments.