Quantitative trait loci associated with resistance to a potato isolate of <i> <scp>V</scp> erticillium albo‐atrum </i> in <i> <scp>M</scp> edicago truncatula </i>

Abstract

V erticillium albo‐atrum is responsible for considerable yield losses in many economically important crops, among them alfalfa ( M edicago sativa ). Using M edicago truncatula as a model for studying resistance and susceptibility to V . albo‐atrum , previous work has identified genetic variability and major resistance quantitative trait loci ( QTL s) to V erticillium . In order to study the genetic control of resistance to a non‐legume isolate of this pathogen, a population of recombinant inbred lines ( RIL s) from a cross between resistant line F83005.5 and susceptible line A17 was inoculated with a potato isolate of V . albo‐atrum , LPP 0323. High genetic variability and transgressive segregation for resistance to LPP 0323 were observed among RIL s. Heritabilites were found to be 0·63 for area under the disease progress curve ( AUDPC ) and 0·93 for maximum symptom score ( MSS ). A set of four QTL s associated with resistance towards LPP 0323 was detected for the parameters MSS and AUDPC . The phenotypic variance explained by each QTL ( R 2 ) was moderate, ranging from 4 to 21%. Additive gene effects showed that favourable alleles for resistance all came from the resistant parent. The four QTL s are distinct from those described for an alfalfa V . albo‐atrum isolate, confirming the existence of several resistance mechanisms in this species. None of the QTL s co‐localized with regions involved in resistance against other pathogens in M . truncatula .