Development of a Rapid Phenotyping Method to Screen for Didymella arachidicola Resistance in Peanuts

Net or web blotch (NB), caused by Didymella arachidicola, is an emerging threat causing significant reduction in yield to peanuts in cooler production regions globally, including Australia, China and southern Africa. Host resistance against NB is poorly understood, with field screenings reliant upon favorable climatic conditions. A rapid and effective phenotyping method is essential to differentiate between resistant and susceptible breeding lines and improve selection accuracy. In this study, a greenhouse screening method using mycelium as inoculum to determine host response to D. arachidicola was developed. A liquid-culture mycelia suspension of the pathogen was sprayed onto 9-week-old peanut plants and one disease assessment was made between 14 and 17 days after inoculation. Lesion growth in the greenhouse was found to correlate to disease response assessed under field conditions (r = 89%). The phenotyping method developed in this study can facilitate the identification of NB resistance lines and assist in identifying regions of genetic resistance within the peanut host.