Penetration of Soybean Roots by Soybean Cyst Nematode at High Soil Water Potentlals

Abstract

AbstractSoil water is an important factor in the movement and development of soybean cyst nematode (Heterodera glycines Ichinohe). Plant growth and soybean cyst nematode (SCN) population density were measured to determine the effects of soil water potential (Ψ8) on root penetration by SCN of ‘Essex’, a suspectible cultivar of soybean [Glycine max (L.) Merrill]. Soybean seeds were planted in growth containers and subjected to constant Ψ8 of −5, −10, −20, −30, −40, and −50 kPa at SCN levels of 12 000 eggs and second‐stage juveniles (J2) per kg soil or no SCN for the controls for 16 d. The soil used was a Captina slit loam (fine‐silty, mixed, mesic Typic Fragiudult) with 23, 68, and 9% sand, silt, and clay, respectively. Soybean was inoculated with eggs and J2 at the cotyledon growth stage (VC). Average soil temperature during the study was 25.5 °C. Leaf water potential (Ψ1) and soil oxygen diffusion rate (ODR) were significantly affected by Ψ8 < (P > 0.01) after 16 d of exposure to SCN. In the infested treatments Ψ1 was reduced at a more rapid rate with decreasing Ψ8 than in the non‐inoculated controls. The increase in SCN penetration of the soybean root system corresponded positively to the increase in soil ODR and corresponding decrease in Ψ8. Recovery of SCN from the soil decreased with a decrease in Ψ1. A mechanistic, nonlinear mathematical model was used to describe the relationship between Ψ8 and SCN penetration of soybean roots. A quadratic regression model was used to describe the relationship between Ψ8 and SCN recovery from the soil.