Application of remote sensing to identify adult plant resistance loci to stripe rust in two bread wheat mapping populations

Abstract

Phenotyping of wheat stripe rust in genetic studies has traditionally relied on quantifying disease by means of the modified Cobb Scale. This approach requires scoring of disease severity and response type, either on flag leaves or on a whole plot basis. The use of spectral crop sensors in wheat phenotyping has raised the question of whether this objective methodology is suitable for detecting stripe rust resistance loci in genetic studies. An Avocet S X Francolin#1 recombinant inbred population developed at the International Maize and Wheat Improvement Center (Centro Internacional de Mejoramiento de Maiz y Trigo—acronym CIMMYT), and a Kariega X Avocet S doubled haploid population developed in South Africa, both with available genetic maps, were used in this study. Field trials for stripe rust evaluation of these populations were planted at Greytown, South Africa in 2013 and 2014. Severe and uniformly distributed infection of Puccinia striiformis race 6E22A+ occurred in both years. Populations and parents were phenotyped according to the modified Cobb Scale and with a handheld Trimble GreenSeeker® crop sensor (model HCS-100). The sensing device emits red and infrared light and measures the reflectance of each wavelength in terms of the normalized difference vegetation index (NDVI). In both years, NDVI detected four previously characterized quantitative trait loci (QTL) on chromosomes 1BL, 2BS, 3BS and 6AL in the Avocet S X Francolin#1 population. The same QTL were detected with visual estimates in 2013 but only 2BS was significant in 2014. In the Kariega X Avocet S population, all stripe rust traits, including NDVI, mapped to previously described QTL on chromosomes 2BS, 4AL and 7DS. Remote sensing of infection levels thus consistently detected the same QTL regions as described by using visual ratings in earlier studies, indicating that a crop sensor can be easily applied in genetic mapping of stripe rust resistance in wheat.