Efficiency of pyramiding of three quantitative resistance loci to apple scab

Abstract

Quantitative plant resistance is supposed to be more durable than qualitative resistance for the control of plant diseases. However, it has been experimentally shown that erosion of quantitative resistance can occur. Cumulation of quantitative resistance loci (QRLs) in the same cultivar is considered to improve the efficiency and durability of quantitative resistance, but the choice of QRLs to be combined is of crucial importance. This study investigated whether the combination of QRLs acting on different stages of pathogen development could improve the efficiency of resistance in the apple scab pathosystem. The efficiencies of three QRLs were evaluated against 10 isolates of Venturia inaequalis and the stages of pathogen development that were affected by the QRLs were defined microscopically. A gain in the efficiency of resistance was observed when QRLs were pyramided compared to when they acted alone. Thanks to the combined effects of the individual QRLs, the pyramiding of the three QRLs hindered fungal development at different stages: before the penetration of the plant cuticule, after the penetration with hypersensitivity reaction, and during the colonization and asexual reproduction. These effects were dependent on the V. inaequalis isolates. These results suggest that the gain in efficiency of resistance by pyramiding may derive from the combination of different and complementary molecular mechanisms underlying QRLs. Thus, the resistance achieved from pyramiding such a combination of QRLs should be durable.

Assessing the durability and efficiency of landscape-based strategies to deploy plant resistance to pathogens

“…We also envisage varying the mutation probabilities (τ g and τ w ), cost of infectivity (θ g ), cost of aggressiveness (θ w ), and number of steps to erode a trait for quantitative resistance (Q w ), to simulate various possible choices of major genes and traits for quantitative resistance. It would also be of interest to simulate and investigate the potential for combinations of several sources of quantitative resistance, whose performance on disease severity has been experimentally demonstrated [ 144 ]. Finally, we will also explore different spatiotemporal strategies to deploy plant resistance to pathogens.…”

Quantitative Resistance to Plant Pathogens in Pyramiding Strategies for Durable Crop Protection

“…QTL acting at different stages of plant development, corresponding to different stages of the pathogen infection cycle, were also identified in two wheat cultivars with durable resistance to yellow rust ( Dedryver et al, 2009 ). In apple, the pyramiding of three resistance QTL to scab was suggested to result in more durable resistance since the QTL were shown to act at different stages of the fungal infection cycle, from as soon as it penetrated the plant to a later stage during subcutaneous growth and sporulation ( Laloi et al, 2016 ). In pea NILs, combinations of resistance QTL individually acting on delaying symptom appearance and/or on slowing down root colonization by Aphanomyces euteiches had an increased action on the two pathogen life-history traits ( Lavaud et al, 2016 ).…”

Successful intergeneric transfer of a major apple scab resistance gene (Rvi6) from apple to pear and precise comparison of the downstream molecular mechanisms of this resistance in both species

“…Moreover, diversifying resistance mechanisms is expected to promote conflicting selection pressures on the pathogen populations, which should constrain them to an evolutionary compromise limiting their development. Indeed, Laloi et al [95] showed that the combination of QTLs acting on different stages of pathogen development, and thus probably based on different mechanisms, could improve the efficiency of resistance in the apple scab pathosystem.…”