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Potato cyst nematodes hatch in response to hatching factors (HF) present in potato root leachate (PRL). The much higher spontaneous hatch (hatch in the absence of potato plants or PRL) of both Globodera rostochiensis and Globodera pallida in sand (32.2 and 21.1%, respectively) compared to in vitro (6.0 and 4.8%) experiments suggested the presence of other hatching factor-producing organisms in the non-sterile sand. When sterile PRL (from aseptically cultured microplants) and non-sterile PRL (from aseptically cultured microplants grown in the presence of tuber washings) samples were collected and assayed for hatching activity, the in vitro hatch of both PCN species but particularly of G. pallida was greater in non-sterile PRL. When these samples were fractionated on Sephadex G-10 by low pressure liquid chromatography and the fractions tested for hatching activity, the non-sterile PRL produced more hatching factors (HF) than the sterile PRL; in the fractionated sterile PRL only one significant HF (active towards G. pallida) was observed, compared to six (towards G. pallida) and three (towards G. rostochiensis) HF from the non-sterile PRL, with two HF being active towards both species. The non-sterile PRL appeared to produce more hatching factor stimulants (HS) and fewer hatch inhibitors (HI) than the sterile PRL. These results suggest that soil micro-organisms play an important role in the production of hatching chemicals and it is proposed that the differences in HF profiles between sterile and non-sterile PRL were due, at least in part, to increased HS production in the non-sterile PRL. [ABSTRACT FROM AUTHOR]