Aggressiveness of Phytophthora medicaginis on chickpea: Phenotyping method determines isolate ranking and host genotype-by-isolate interactions

Abstract

<p><i>Phytophthora medicaginis</i> causing Phytophthora root rot of chickpea (<i>Cicer arietinum</i>) is an important disease, with genetic resistance using <i>C. arietinum</i> × <i>Cicer echinospermum</i> crosses as the main disease management strategy. We evaluated pathogenic variation in <i>P. medicaginis</i> populations with the aim of improving phenotyping methods for disease resistance. We addressed the question of individual isolate aggressiveness across four different seedling-based phenotyping methods conducted in glasshouses and one field-based phenotyping method. Our results revealed that a seedling media surface inoculation method used on a susceptible <i>C. arietinum</i> variety and a moderately resistant <i>C. arietinum</i> × <i>C. echinospermum</i> backcross detected the greatest variability in aggressiveness among 37 <i>P. medicaginis</i> isolates. Evaluations of different components of resistance, using our different phenotyping methods, revealed that differential pathogen–isolate reactions occur with some phenotyping methods. We found support for our hypotheses that the level of aggressiveness of <i>P. medicaginis</i> isolates depends on the phenotyping method, and that phenotyping methods interact with both isolate and host genotype reactions. Our cup-based root inoculation method showed promise as a non-field-based phenotyping method, as it provided significant correlations with genotype–isolate rankings in the field experiment for a number of disease parameters.</p>