Development of a Technique for Assessing Late Leaf Spot (Cercosporidium personatum) Using an Unmanned Aerial System in Large Mapping Populations of Peanut (Arachis hypogaea L.).

Recombinant inbred line (RIL) populations of peanut (Arachis hypogaea L.) are being used to develop markers for resistance to several diseases, including late leaf spot, caused by Cercosporidium personatum. In efforts to develop molecular markers to assist in selection for resistance to late leaf spot, several populations have been developed from parents with varying levels of resistance. Breeding programs are faced with the challenge of phenotyping large numbers of genotypes in a timely manner with a limited number of people. Unmanned aerial systems (UAS) may have potential to help overcome this challenge. Through the use of a UAS, imaging techniques, and ground truthing we developed an analysis method to quickly and easily assess late leaf spot severity in the field. This experiment utilized 72 RILs with varying levels of susceptibility to late leaf spot and seven parental lines. With adequate ground truthing, late leaf spot can be differentiated from other diseases in the field by the necrotic lesions on all above ground plant parts and defoliation. By testing vegetative indices (VIs) in ArcMap (ESRI, Redlands, CA 92373 USA) we could determine the percent change of each VI over the course of the season. This percentage was then used to determine the correlation with visual ratings. Analyses show a positive correlation between the normalized difference vegetation index and final visual ratings with a correlation coefficient of 0.676 (p-value < 0.05). Results suggest that through the use of a UAS equipped with a multispectral camera, the percent change in VIs can be positively correlated to visual ratings. This technique could greatly increase the efficiency of peanut breeding programs.