Yield loss caused by Pratylenchus thornei on wheat in South Australia

A two-year field trial with 130 plots was conducted at Tanunda, South Austr alia. Ten cereal cultivars differing in susceptibility to Pratylenchus thor nei, two poor host crops (non-leguminous), and a bare fallow treatment were used to manipulate the numbers of nematodes in the plots in the first year . Initial and final densities were determined for each plot and varied from 0 to 9,400 nematodes/200 g oven-dried soil at the beginning of the second year. A highly susceptible wheat cultivar, Warigal, and two wheat lines kno wn to have some resistance to P. thornei, GS50A and AUS4930, were planted i n the second year. High densities of P. thornei caused more extensive lesio ns and severe cortical degradation in roots of Warigal than in GS50A or AUS 4930. There was a significant linear relationship between initial density o f P. thornei and Warigal grain yield (t/ha), with the estimated regression equation Y = 1.86 - 0.0000557x, where Y is the grain yield in t/ha and x is the number of P. thornei/200 g oven-dried soil. High initial densities (9, 000 P. thornei/200 g oven-dried soil) caused up to 27% yield loss of this c ommercial Australian wheat. In contrast, the yield of the two resistant lin es was not affected by initial density, suggesting that both were tolerant as well as resistant in the field.