Factors influencing the infectivity of the potato cyst nematodes, Globodera rostochiensis and G. pallida
Physiological and behavioural attributes were examined for juveniles (JJ2) of the potato cyst nematodes, Globodera rostochiensis and G. pallida, emerging from cysts either soon after stimulation by potato root diffusate (PRD) (early hatching JJ2) or following a delayed response (late hatching JJ2). There was little difference in the desiccation survival of the two groups but behavioural assays indicated that early hatching JJ2 travelled further than late hatching JJ2. Selection for early hatch was achieved by reproducing early hatching JJ2 over three generations. PRD increased lipid utilisation by unhatched individuals and late hatching JJ2 had a significantly reduced lipid content at eclosion which, in G.rostochlensis, was correlated with impaired infectivity and delayed development. Interspecific comparisons indicated that G. pallida is better adapted to hatch at lower temperatures and has a much slower initial rate of hatch. Motility and lipid depletion of both species were fastest at the inflection point of the moisture characteristic curve for sand. G. rostochlensis utilised lipid more rapidly than G. pallida at all sand moisture contents. Depletion of lipid reserves during storage had a significant adverse effect on motility and infectivity of hatched JJ2 of G. rostochiensis when reserves fell below about 65% of the initial level. Under optimal conditions for motility the infective life-span of juveniles was between 6 and 11 days. A novel plant growing technique allowed observations, using fluorescence microscopy, of the chronology and location of plant responses to invading JJ2 of both species in resistant and susceptible hosts. Differences among host-parasite combinations in nematode track lengths within roots and in the quantified fluorescence may be correlated with the degree of compatibility of the relationships. The extent of fluorescence also varied among cultivars tested. Analysis of the fluorescent tissues indicated the accumulation of phenylpropanoid compounds which may be involved in the expression of nematode resistance.