ABSTRACT
Lines from a cross between two wheat (Triticum aestivum) cultivars with contrasting resistance phenotypes to Pratylenchus thornei (Nematoda) were investigated to determine the stage at which resistance occurs. Host resistance was examined at nematode attraction to and penetration of roots and nematode motility, maturation, and reproduction within roots. There was no significant difference in the rate at which P. thornei was attracted toward or penetrated resistant or susceptible roots. However, suppression of migration, juvenile maturation, and reproduction in and near resistant roots was evident, suggesting that resistance acts post penetration. No preferential root penetration zone was observed in contrast to other studies. The inhibitory compounds from resistant wheat plants appeared to be constitutively expressed and water soluble because nematode migration was suppressed in roots and root exudates of unchallenged seedlings. The effects of these compounds were reversible and affected P. thornei but not P. neglectus. Apart from migration, nematode multiplication was greatly inhibited by resistance because only a few juveniles (10%) developed past stage three in roots of resistant compared with susceptible plants. Earlier in the life cycle, egg deposition and hatch of P. thornei were also significantly reduced in resistant roots and root exudates, suggesting the presence of hatching inhibitors.
