Cereal Cyst Nematode (Heterodera avenae) on Oats. II. Early Root Development and Nematode Tolerance.

The effect of Heterodera avenae infestation on early seminal and lateral root growth was examined in four oat genotypes differing in tolerance to H. avenae. Recently emerged seminal roots were inoculated with a range of H. avenae larval densities, then transferred a hydroponic system to remove the effect of later nematode penetration on root development. Intolerance to H. avenae was assessed in terms of impairment of seminal root extension resulting in fewer primary lateral roots emerging from the seminal root below the zone of juvenile penetration. Tolerant plants infested with H. avenae had longer lateral root systems than infested intolerant plants. The decline in lateral root growth below the penetration zone was partly offset by increased growth above. This did not contribute to tolerance, however, as there were no differences between cultivars for this feature. Nematodes induced earlier nodal root emergence in all cultivars. Nodal root development was most advanced on the most tolerant cultivar.