The relationship between neutral lipid reserves and infectivity for hatched and dormant juveniles of Globodera spp.

A quantitative histochemical technique based on scanning microdensitometry has been used to investigate neutral lipid utilisation by hatched and dormant juveniles of Globodera rostochiensis and Globodera pallida. During storage in water at 20°C, hatched juveniles of the two species showed no statistical difference in their rate of lipid utilisation. A semi-logarithmic curve fitted to the pooled data suggests that 50% relative utilisation occurred after 36 ± 4 days of storage. Measurement of the neutral lipid reserves for unhatched juveniles of G. pallida dormant in field soils in Northern England for a maximum of 14 yr showed a reduced rate of metabolism with a 50% loss of neutral lipid reserves after 7·5 ± 1·1 yr. The use of neutral lipid reserves by the hatched, starved juveniles was correlated with their survival and with a loss of both locomotor activity and an ability to infect tomato seedlings. Furthermore, results suggest that a loss of mobility by juveniles from field populations of G. pallida immediately after hatching was more closely related to their neutral lipid reserves than the duration of their dormancy. Infection of plants was also reduced for one population. This suggests that measurement of the neutral lipid reserves of a population may be of value for modifying the economic threshold to take account of changes in infectivity during prolonged rotations.