Potato and Tomato Late Blight Caused by Phytophthora infestans: An Overview of Pathology and Resistance Breeding

Late blight (LB) caused by the oomycete Phytophthora infestans, is a major disease of potato and tomato worldwide and can cause up to 100% yield losses. The devastating economic impact of this disease intensified the related pathology and genetics research since the occurrence of Irish famine in 1840s, with a side gain of major scientific discoveries. For example, many of the crucial steps involved in LB defense response in host plants have been elucidated through the use of modern cytological and molecular biology techniques. Also, genetic and biochemical studies have revealed differences between oomycetes and pathogenic fungi, which has led to more selective use of chemicals for LB control. Furthermore, the discovery of P. infestans two mating types and the resultant generation of more aggressive lineages by sexual recombination stresses the need for an integrated and sustainable approach to LB control. These measures would include the use of cultural practices, selective fungicide applications, and genetic resistance. In potato at least a dozen major resistance genes and several quantitative trait loci (QTLs) for LB resistance have been identified, and most modern cultivars have been bred with one or more resistance genes. In tomato, though most commercial cultivars are susceptible to LB, a few major resistance genes and several QTLs have been identified and several breeding programs around the world are developing breeding lines and commercial cultivars with LB resistance. Most recently, a few fresh-market tomato hybrid cultivars with LB resistance were released by the North Carolina State University Tomato Breeding Program in the United States. There is, however, an insufficient number of potato and tomato cultivars with LB resistance, resulting in continued expensive as well as the hazardous and increasingly ineffective use of chemicals for disease control. In an era when both host plants and P. infestans genomes are sequenced and considerable genomic information is available, it is not unexpected that a more sustainable solution to controlling LB is on the horizon. In this review, we summarize the recent achievements in better understanding of the P. infestans pathogenesis, host-pathogen interactions, and the progress made in developing genetic resistance in potato and tomato.