Effects of catechins and low temperature on embryonic development and hatching in Heterodera glycines and Meloidogyne incognita

Mimics of two natural influences, a chemical similar to one present in cyst nematodes and low temperature exposure of nematode eggs, were evaluated for their effects on quantitative and qualitative features of embryonic development and hatching. The polyphenol epigallocatechin gallate (EGCG), an analogue of a compound found in nematode cysts, reduced hatch from both Heterodera glycines and Meloidogyne incognita eggs. Reduction was by 22.7% in H. glycines and 68.5% in M. incognita at 14 days after exposure to 1.0 mM EGCG. Significant reductions in hatch were observed at 7 days after exposure in H. glycines eggs, and as early as 5 days in M. incognita. Half-maximal percentage hatch was delayed by 0.6 days in H. glycines and 1.1 days in M. incognita (16.2 and 18.3%, respectively). Decreased hatch was associated primarily with an increase in unhatched, but viable, second-stage juveniles (J2). Hatch levels could be completely restored by day 14 in both species if EGCG was replaced with water on day 3. Replacement on day 7 partially restored hatch in M. incognita but was not effective in H. glycines. Inhibition of chitinase activity by EGCG suggests one factor in J2 retention in the egg. Exposure to low temperature decreased hatch by ca 50% in both species but without accumulation of unhatched J2. This stage peaked on day 3 in H. glycines-treated eggs, and on day 7 in M. incognita. However, response to low temperature in each species was characterised by developmental arrest at the first-stage juvenile.