Evaluation of root-knot nematode resistance assays for sugarcane accession lines in Australia

Root-knot nematode (Meloidogyne javanica) is an important pathogen of sugarcane and can cause significant yield loss in sandy soil. Resistance to root-knot nematode is not common in commercial cultivars of sugarcane. In order to find new sources of resistance for root-knot nematodes, Sugar Research Australia (SRA) has screened new sets of accession lines derived from introgression breeding between wild relatives of sugarcane and commercial parents, and sugarcane accession lines from advanced stages of the core selection programs. This study aimed to determine the most suitable assessment parameter for comparing resistance of accession lines and cultivars. Eight screening trials were conducted from 2012 to 2019. Three parameters were measured on individual plants grown in pots inoculated with an initial population of M. javanica eggs, (i) number of eggs per plant, (ii) number of eggs per g of roots, and (iii) visual ratings of galls on roots. Resistance parameter, eggs per plant was repeatable among trials and had less variations within a trial than the other parameters. Eggs per g of roots was negatively correlated (r = -0.19 to -0.74, p < 0.05) with root biomass in seven out of eight trials, and with shoot biomass in four out of seven trials (r = -0.24 to -0.47, p < 0.001). Visual rating of galls showed inconsistent (positive or negative) correlations with shoot and root biomass. No significant correlations were found between number of eggs per plant and shoot or root biomass of test accession lines. Based on repeatability and variability of resistance parameters, eggs per plant was the most suitable parameter to compare and select sugarcane accession lines for resistance to M. javanica.