Geranium bronze tolerance in diploid and tetraploid ornamental geraniums

The ornamental geranium, Pelargonium × hortorum Bailey, is a traditional ornamental plant largely cultivated in Europe and Northern America. Recently, a lepidopteran pest, the geranium bronze (Cacyreus marshalli Butler), is threatening the popularity of geraniums in Europe. An inventory of ornamental geranium samples present in remote rural areas and National Parks is currently being established to build a national germplasm bank [the Spanish Pelargonium Germplasm Bank (SPG Bank)] of garden geraniums. The objective of this study was to analyse twenty representative taxa from the SPG Bank and seven commercial cultivars of Pelargonium × hortorum to assess their ploidy level and test them for potential resistance to the geranium bronze. The ploidy level was determined by flow cytometry. All commercial cultivars tested for geranium bronze tolerance had an elevated degree of susceptibility compared to the most tolerant SPG taxa. This study indicates that there is enough variability among the SPG Bank taxa to be used as potential sources for geranium bronze-tolerant germplasm for the development of commercial Pelargonium cultivars.