Host reactions of sweetpotato genotypes to root-knot nematodes and variation in virulence of Meloidogyne incognita populations

Sweetpotato [Ipomoea batatas (L.) Lam.] genotypes were evaluated for resistance to North Carolina root-knot nematode populations: Meloidogyne arenaria (Neal) Chitwood races 1 and 2; M. incognita (Kofoid & White) Chitwood races 1, 2,3, and 4; and M. javanica (Treub) Chitwood. Resistance screening was conducted using 150-cm(3) Conetainers containing 3 sand : 1 soil mix. Nematode infection and reproduction were assessed as the number of egg masses produced by root-knot nematodes per root system. Host suitability for the root-knot nematode populations differed among the 27 sweetpotato, genotypes studied. Five genotypes ('Beauregard', L86-33, PDM P6, 'Porto Rico', and 'Pelican Processor') were selected for further study based on their differential reaction to the different root-knot nematodes tested. Two African landraces ('Tanzania' and 'Wagabolige') were also selected because they were resistant to all the nematode species tested. The host status was tested against the four original M. incognita races, and an additional eight populations belonging to four host races, but collected from different geographical regions. The virulence of root-knot nematode populations of the same host race varied among and within sweetpotato genotypes. 'Beauregard', L86-33, and PDM P6 were hosts for all 12 M. incognita populations, but differences in the aggressiveness of the isolates were observed. 'Porto Rico' and 'Pelican Processor' had different reactions to the M. incognita populations, regardless of the host race. Several clones showed resistance to all M. incognita populations tested. These responses suggest that different genes could be involved in the resistance of sweetpotato to root-knot nematodes. The results also suggest that testing Meloidogyne populations against several different sweetpotato hosts may be useful in determining the pathotypes affecting sweetpotato.