Field resistance to Orobanche crenata in pea (Pisum sativum L.) beyond strigolactones

Background  Orobanchaceae are parasitic weeds causing substantial yield losses in many crops, including pea (Pisum sativum L.). Within host species, genotypes that display enhanced resistance to Orobanchaceae often exude low levels of strigolactones (SLs) from their roots, in line with evidence that SLs stimulate the germination of Orobanchaceae. However, to which extent genetically determined low SL exudation contributes to field resistance to Orobanchaceae was poorly investigated. Here, we studied the relation between SL exudation and field response to Orobanche crenata Forsk. (Oc) in pea. Results  The screening of a germplasm panel identified three novel sources of field resistance to Oc and revealed an association between field resistance and low SL exudation. Although the SL-deficient mutants rms1 and rms5 were more resistant than their wild-type backgrounds, they still suffered substantial Oc parasitization. Genetic analysis and RNA-seq of recombinant inbred lines uncovered both SL-dependent and SL-independent mechanisms contributing to the near-complete resistance to Oc previously reported in the breeding line ROR12, and identified candidate genes possibly underlying resistance loci.
Conclusions  Besides identifying novel sources of resistance to Oc, our study indicates that reduced or absent SL exudation alone is not sufficient to confer complete field resistance to Oc in pea. This suggests the necessity of exploring SL-independent resistance mechanisms for breeding purposes. Further investigations are needed to clarify whether a similar scenario applies to other crops affected by Orobanchaceae, and to characterize genes causally related to Oc resistance.