A protocol to perform mid-throughput phenotyping of plant resistance to the pollen beetle

Improving crop resistance to insect herbivores is a major research objective in breeding programs. Although genomic technologies have increased the speed at which large populations can be genotyped, breeding programs still suffer from phenotyping constraints. The pollen beetle is a major pest of oilseed rape for which no resistant cultivar is available to date, but previous studies have highlighted the potential of the white mustard as a source of resistance and introgression of this resistance appears as a promising strategy. Here we present a phenotyping protocol allowing mid-throughput acquisition of resistance data, which could then be used for genetic mapping of QTLs.Contrasted white mustard genotypes were selected from an initial field screening and then evaluated for their resistance under controlled conditions using a standard phenotyping method on entire plants. We then upgraded this protocol for mid-throughput phenotyping, by testing two alternative methods. We found that phenotyping on detached buds did not provide the same resistance contrasts as observed with the standard protocol, in contrast to the phenotyping protocol with miniaturized plants. This protocol was then tested on a large panel composed of hundreds of plants. A significant variation in resistance among accessions was observed, which validates the large-scale application of this new phenotyping protocol. The combination of this mid-throughput phenotyping protocol and of the white mustard as a source of resistance against the pollen beetle offers a promising avenue for breeding programs aiming at improving oilseed rape resistance.