Pratylenchus thornei populations reduce water uptake in intolerant wheat cultivars

Pratylenchus thornei is a major pathogen of wheat crops in the northern grain region of Eastern Australia with an estimated annual yield loss of $38 million. Damaged crops show symptoms of water and nutrient stress that suggest uptake is significantly affected. In order to understand the mechanisms involved in reducing water uptake and consequently plant yield, detailed measurements of water extraction and leaf area were conducted on a range of wheat cultivars with differing levels of tolerance and resistance to P. thornei. Planting wheat into high populations of P. thornei reduced the extraction rate (kl) in the intolerant cultivars; this in turn caused a delay in the root extraction velocity and effectively changed the crop lower limit. The early season stress applied by the reduced extraction rate impeded canopy development that consequently reduced demand for water and nutrients, growth and yield potential. The resulting yield loss was consistent across both a wet and a dry wheat growing season with the intolerant cultivar yielding 34% less than the tolerant cultivar. Understanding the mechanism with which P. thornei reduces yield allows the impact of P. thornei to be included in simulation models to better understand how to manage this constraint to the Australian grain industry