Investigations into the chemoattraction of the potato cyst nematodes Globodera rostochiensis and G. pallida towards fractionated potato root leachate

The behaviour of stimulated second stage juveniles (J2) (i.e., hatched in root leachate from potato cv. Cara) and unstimulated J2 (spontaneously hatched in water) of Globodera rostochiensis and G. pallida in response to fractionated and unfractionated potato root leachate (PRL) was investigated in attraction assays. In PRL, fractionated by combined ion-exchange-gel permeation chromatography on Sephadex G-10, three classes of semiochemicals with activity towards J2 were distinguished: i) chemoattractants; ii) chemostats, and iii) chemorepellents. The motility of PRL-hatched G. rostochiensis J2 in one fraction (12) at 10 days after their removal from the root leachate was significantly greater than that of water-hatched J2 apparently due to sensitisation of PRL-hatched J2. PRL-hatched J2 of G. pallida were attracted to different fractions than those of G. rostochiensis, whereas the water-hatched J2 from the two species were attracted to common fractions, indicating that sensitisation by exposure to PRL was species selective. The attraction of PRL-hatched PCN J2 to unffactionated PRL appeared to be dependent on the ratio of chemoattractant to chemorepellent semiochemicals in the leachate. For both species there was no detectable correlation between hatching activity and either attractiveness of root leachates from 12 potato genotypes or chemoattraction in PRL fractions, indicating that hatching factors were not active chemoattractants.