The effect of Potato virus S infection on late blight severity in selected potato genotypes
Johnson, Dennis A.
Pappu, Hanu R.
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Late blight, caused by Phytophthora infestans, is an important disease of potato. Potato cv. Defender is the only cultivar with foliar resistance to late blight. However, this cultivar exhibited susceptibility to infection by Potato virus S (PVS). PVS infection is very common in commercial potato fields in the Columbia Basin of the Pacific Northwestern USA. To investigate the potential interactions between these two pathogens and the resulting response of various potato genotypes, ‘Defender’ and ‘Ranger Russet’ were inoculated with both P. infestans and PVS. The amount of sporulation and the extent of lesion expansion on inoculated leaves were measured to estimate the incidence of late blight. ‘Defender’ showed restricted spot lesions and had twenty times less amount of sporangia compared to ‘Ranger Russet’ when inoculated with P. infestans only. However, lesion expansion and sporulation increased significantly when ‘Defender’ was infected with PVS followed by inoculation with P. infestans. The increased late blight in PVS-infected ‘Defender’ suggests potential interaction between PVS and ‘Defender’ impacting the outcome to late blight infection.