Comparison of Visual and Normalized Difference Vegetation Index (NDVI) Assessments to Predict the Yield Tolerance of Wheat Genotypes to Root-Lesion Nematode Pratylenchus thornei

Wheat breeding programs have selected genotypes that are tolerant to the root-lesion nematode Pratylenchus thornei by measuring grain yield in field plots on infested sites. However, quicker methods are desirable to increase the capacity to assess more breeding lines for tolerance without harvesting grain. Two field experiments, time of sowing 1 (TOS1) and time of sowing 2 (TOS2), were conducted in the subtropical grain region of eastern Australia each year for eight years (sixteen experiments total) to characterize 396 wheat genotypes for tolerance when grown on high population densities of P. thornei. For each experiment, up to two visual tolerance ratings (TRs) and two normalized difference vegetation index (NDVI) readings were recorded using a Greenseeker™ during crop growth, and grain yield was obtained at crop maturity. The results showed that both TR and NDVI were predictive of tolerance based on the grain yield of the wheat genotypes. Generally, higher genetic correlations between grain yield and each vegetative assessment method were obtained with TOS2 than with TOS1 each year. The vegetative methods for assessing P. thornei tolerance proved to be valuable surrogates when grain yield was unreliable for germplasms that were agronomically unadapted to the regional environment. Our study established that at high population densities of P. thornei only, NDVI is a high-throughput phenotypic measurement of tolerance that can be used to screen a range of genetically diverse genotypes.