Studies on the hatching factors of the cyst nematode are important since they contribute to not only elucidation of the hatching mechanism but also establishment of the control method. The present study was undertaken to elucidate hatching factors and their role in the hatching mechanism in the soybean cyst nematode, Heterodera glycines Ichinohe.
The results obtained are as follows:
(1) Hatching rate of the eggs used in hatching experiments
The eggs used in the present experiments were obtained from the cysts in the soil samples taken from the soybean fields at Memuro, Hokkaido, infested with the soybean cyst nematode in October every year, and the soil samples had been stored at about 5°C before use. The hatching rate of the stored eggs was low in winter, high from April to June, and low again from September onwards. The low rate in winter can be explained from the ‘diapause’ which is reported even in the case of the potato cyst nematode, etc. On the other hand, hatching rate tended to be lower substantially in the first two years of the storage and slightly in the subsequent three years.
(2) Effect of environmental factors on hatching
The optimum environmental conditions for hatching were investigated. The optimum temperature for hatching in distilled water was 25°C followed by 20°C, but it was 25-30°C in host root diffusate after pre-soaking in water at 25°C. Concerning the eggs stored at about 5°C, a higher hatching rate was obtained when they were exposed to the root diffusate after pre-soaking than when directly exposed to the root diffusate without pre-soaking. The pre-soaking appears to have contributed to the cumulative temperature necessary for hatching. The optimum term of pre-soaking was 1-2 weeks at 25°C and 4-7 days at 30°C insofar as it was tested. Adverse effects of oxygen deficiency on hatching were removed by supplying test solution with enough amount of air and adjusting population density of eggs and hatched larvae to 200-300 individuals in one ml of the solution. At almost all values of pH, all of the buffer solutions themselves, which were used in the present experiments, had an adverse effect on hatching, although the effect was smallest at pH 5.0-5.5.
(3) Hatching-promoting substance (s) in host plants
The root diffusates were collected from soybean and kidney bean, during their most active vegetative growth period, concentrated under vacuum and the insoluble residues were filtered off. They were then stored at about 5°C after sterilization. The activity of hatching-promoting substance (s)(PSp) in the host root diffusate was found stable for a long term insofar as stored at about 5°C or during the hatching test for three weeks at 25°C. Initially, it became higher with dilution of the diffusate concentrate but when over the maximum point, it lowered with further dilution. It also depended upon physiological conditions of the eggs. The inhibitory effect of the root diffusates at higher concentrations was considered due to the high amounts of impurities. Although the differences of chemical constitution and property of root diffusates among host plants are not yet revealed, the lower larval hatching in the root diffusates of soybean and adzuki bean in comparison with kidney bean root diffusate can be partly explained from the differences of kinds or amounts of impurities in each diffusate.
(4) Artificial hatching agents
Effects of some compounds having been reported as artificial hatching agents for the soybean cyst nematode were tested by the present methods, and it was ascertained that all the effective compounds contained Zn⁺⁺ or Fe⁺⁺.

View full abstract