Reproductive Variability of Field Populations of Meloidogyne spp. on Grape Rootstocks

Variability in penetration, development, and reproduction of two resistance-breaking field pathotypes (pt.) of Meloidogyne arenaria, M. incognita, and a population of mixed Meloidogyne spp. virulent to grape hosts were compared on two resistant Vitis rootstocks ''Freedom'' and ''Harmony'' in separate tests. ''Cabernet Sauvignon'' was included as a susceptible host to all four nematode populations. Secondstage juveniles (J2) of the mixed population failed to penetrate Freedom roots. By contrast, 6% of J2 in the M. incognita population penetrated Freedom roots but did not develop beyond the swollen J2 stage. The two resistance-breaking populations of M. arenaria differed in their virulence except on susceptible roots of Cabernet Sauvignon. More J2 of M. arenaria pt. Freedom penetrated Freedom roots and reached adult stage than did M. arenaria pt. Harmony. Later life stages of M. arenaria pt. Freedom occurred earlier and in greater numbers in Harmony roots than did M. arenaria pt. Harmony. Reproduction of M. arenaria pt. Freedom was greater in Freedom and Harmony roots than M. arenaria pt. Harmony. Thus, one population of M. arenaria is highly virulent and the other is moderately virulent.     

The Natural Host Range of Steinernema and Heterorhabditis spp. and Their Impact on Insect Populations

The natural host range of entomopathogenic nematodes of the genera Steinernema and Heterorhabditis can be defined as the range of insects which indigenous nematode populations use for propagation. Information on the natural host range is rare. However, based on records of insects found to be naturally infected with nematodes, some conclusions regarding the natural host range of some Steinernema spp. and Heterorhabditis spp. are presented. Reports of indigenous nematode populations impacting on insect populations can be divided between relatively balanced, long-lasting nematode-host associations and unbalanced, short-lasting epizootics. Examples of the augmentation and inoculative introduction of nematodes in agriculture and forestry ecosystems are presented. Based on current knowledge, nematode reproduction strategies are discussed and indications of the risk involved in the release of non-indigenous nematodes are given.