Host suitability of selected South African maize genotypes to the root-knot nematode species Meloidogyne incognita race 2 and Meloidogynejavanica: a preliminary study
McDonald, Alexander Henrique
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Thirty-one commercial maize (Zea mays L.) hybrids and open-pollinated varieties (OPV's) were screened in separate greenhouse trials with a resistant inbred line MP712W as reference genotype for host suitability to Meloidogyne incognita race 2 and Meloidogyne javanica. Approximately 10 000 eggs and second-stage juveniles (J2) of the appropriate root-knot nematode species were inoculated on roots of each maize seedling 10 days after plant emergence. The numbers of eggs and J2 per root system were counted, while it was also calculated g-1 root. In addition, percentage resistance in relation to the most susceptible genotype and nematode reproduction factors (Rf) were calculated for the maize genotypes screened. Substantial variation existed among the maize hybrids and OPV's with regard to the nematode parameters evaluated. A number of genotypes could be regarded as highly resistant to M. incognita race 2 based on the fact that they supported less than 10% of the population of this root-knot nematode species, compared to that supported by the most susceptible genotype. Several hybrids and OPV's were identified with Rf values less than one for M. incognita race 2 and M. javanica respectively, indicating antibiosis resistance to these parasites. Screenings of maize genotypes in this study have provided a clear indication of the genetic variability within the maize genome, also with regard to susceptibility of the crop to root-knot nematodes. This substantiates the fact that maize could not be regarded as a non-host to root-knot nematodes on a generic basis, particularly in terms of commercial hybrids. It is suggested that commercial maize hybrids are screened on a continuous basis against root-knot nematodes, which would facilitate selection of hybrids that are less susceptible to both nematode species but that would perform optimally in soils conducive to root-knot-nematode infestation.