Hatching of Globodera pallida juveniles by diffusate of potato genotypes, differing in tolerance to G. pallida

Hatching induced by root diffusate, obtained from various potato genotypes, and by standard potato root diffusate, was determined in vitro. The used potato genotypes differed considerably in tolerance to Globodera pallida. A three parameter logistic model was used to describe the numbers of hatched juveniles in relation to time of exposure to root diffusate. Clear differences in hatching characteristics between genotypes were found. Some tolerant genotypes induced hatching of G. pallida juveniles relatively slowly, compared to intolerant genotypes. Other tolerant genotypes, however, induced hatching as fast as intolerant genotypes, and no significant correlation between hatching parameters and tolerance was found.     

Indirect sperm transfer and male mating strategies in soil invertebrates

Summary

Many soil invertebrates transfer their sperm indirectly by means of spermatophores. Among the different taxa there is great variation in spermatophore architecture, auxiliary structures and behaviour. The behaviour, ranging from elaborate courtship rituals to seemingly indifferent scattering of spermatophores, can roughly be classified as association and dissociation. Which of the two is adaptive depends on many factors which can be summarized in a simple functional response model showing that in some cases the best choice depends on density.     

The effect of the potato cyst nematode Globodera pallida on in vitro root growth of potato genotypes, differing in tolerance

Roots of eighteen potato genotypes, differing in tolerance of G. pallida, were grown from tuberpieces on agar in Petri dishes. Juveniles of G. pallida were inoculated directly onto root tips. Root length was measured at various times after inoculation. Inoculation reduced root growth within one day. At later stages, genotypes differed strongly in growth of inoculated roots. Between four and seven days after inoculation, growth of inoculated roots was not significantly correlated with growth of untreated roots, and was only poorly correlated with tolerance assessed in the greenhouse or in the field. However, multiple regression analysis revealed that the tolerance of the tested genotypes was associated with both the rate at which they induced hatching and the growth of roots after inoculation. The combination of these two variables accounted for high percentages explained variance.