Chemotaxis of larval soybean cyst nematode,Heterodera glycines Race 3, to root leachates and ions
Second-stage larvae of the soybean cyst nematodeHeterodera glycines Race 3 were attracted in an in vitro bioassay to pooled leachates of soybean roots that were expressed as root gram-hours (1 g of root/hr/vol). Their responses were dosage dependent with maximal attraction to a 5 root g-hr/ml source. Optimal bioassay conditions used 24 hr for gradient formation and 1.5 hr for larval movement. Individual plants produced leachate with little variation in biological activity. Production was constant for five days of preparation. The attractive activity of root leachate declined with storage at 4 °C and heating over 30 °C, but loss of activity was reduced by freezing. Extraction and Sep-Pak fractionation indicated that the attractions(s) was water-soluble. Larvae were attracted also to several ionic solutions.
Factors Influencing Egg Hatching of the Soybean Cyst Nematode Heterodera glycines Race 3
Individual cysts of the soybean nematode Heterodera glycines contained an average of 323 eggs. Hatching increased linearly as the incubation temperature was raised during a 2-wk test. Insignificant differences in egg hatching were found over 25°C or after pre-exposure to —4°C tem- peratures for 3 wk prior to 25°C incubation. Optimal hatching rates were obtained with 25% soil moisture and pH 6.0. Increases or decreases in these values depressed egg hatching of//, glycines. Soybean root leachate at 4.86 root-g-hr/ml significantly elevated hatching when compared to the control, whereas Hoagland's solution, a plant nutrient, showed a tendency to reduce hatching. In- cubation in ionic solutions revealed various effects. Sodium, calcium, potassium, and chloride re- vealed no effect and, indirectly, osmotic influences may be negligible. Incubation in nitrate and ferric concentrations showed insignificant increases in hatching. In contrast, exposure of//, glycines eggs to zinc chloride gave a pronounced increase of egg hatching.
The location of the secretions that attract male Heterodera schachtii and H. rostochiensis to their females.
Females of H. schachtii and H. rostochiensis secrete male attractant all over the body, so it is probably produced by the hypodermis or distributed in the pseudocoelom rather than by special glands opening to the surface. More attractant is secreted around the tail of H. schachtii females than around the head, so the egg sac can act as a carrier of the pheromone whereas the small egg sac of H. rostochiensis does not. A correlation between the attractiveness of H. schachtii females and the presence of an egg sac suggests that a single mechanism may control secretions from several organs.