Incidence of pathogenic fungi on Scottish potato seed stocks derived from stem cuttings

Abstract

Families of tubers of up to 14 cultivars were produced from rooted stem cuttings in the glasshouse and multiplied for up to six years in Scotland on fields that had not grown potatoes for at least eight years. Samples of tubers were tested for the presence of tuber pathogens after lifting each year and the remaining tubers were treated with Agallol, benomyl or thiabendazole and planted in the following year. Incidence ofPolyscytalum pustulans andHelminthosporium solani on tubers during the years of multiplication was very low butRhizoctonia solani fluctuated and was not controlled by fungicide treatment of seed. When samples were uniformly wounded after lifting, gangrene lesions were equally common from all multiplication years butPhoma exigua var.foveata became the major cause of rots in fourth and fifth year stocks. Diseases remained scarce when samples of these stocks were grown at Rothamsted for one year and were much less common than in samples of commercial certified stocks.