Qualitative and Quantitative Resistance against Early Blight Introgressed in Potato

SIMPLE SUMMARY: Early blight is a disease of potato caused by the Alternaria fungus (notably A. solani). Fungicides that are commonly used to protect potato against the disease are losing their effectiveness and an alternative control method is desired. In this research, we identified several relatives of potato from Central and South America that have a high natural resistance against early blight. Although these plants belong to other species, it was possible to cross them with cultivated potato. The resistance was inherited in offspring plants, but, interestingly, the different species seem to contain distinct types of resistance. More detailed studies will help increase our knowledge of the mechanism(s) that cause resistance. Highly resistant offspring plants can be used to develop new potato varieties with a natural resistance to early blight. ABSTRACT: Early blight is a disease of potato that is caused by Alternaria species, notably A. solani. The disease is usually controlled with fungicides. However, A. solani is developing resistance against fungicides, and potato cultivars with genetic resistance to early blight are currently not available. Here, we identify two wild potato species, which are both crossable with cultivated potato (Solanum tuberosum), that show promising resistance against early blight disease. The cross between resistant S. berthaultii and a susceptible diploid S. tuberosum gave rise to a population in which resistance was inherited quantitatively. S. commersonii subsp. malmeanum was also crossed with diploid S. tuberosum, despite a differing endosperm balance number. This cross resulted in triploid progeny in which resistance was inherited dominantly. This is somewhat surprising, as resistance against necrotrophic plant pathogens is usually a quantitative trait or inherited recessively according to the inverse-gene-for-gene model. Hybrids with high levels of resistance to early blight are present among progeny from S. berthaultii as well as S. commersonii subsp. malmeanum, which is an important step towards the development of a cultivar with natural resistance to early blight.