Does planting dirty potato seed really matter?

Certification schemes are in place to protect growers from planting disease containing potato seed; however, the role of seed borne inoculum and its effect on subsequent potato crop production is not fully understood. This study sought to define the role of three key soilborne pathogens, namely Streptomyces scabiei, Spongospora subterranea f.sp.subterranea and Rhizoctonia solani AG3.1 that cause common scab, powdery scab and black scurf of potato, respectively. The aim was to determine the importance of seed borne inoculum (as measured thru tuber peel pathogen DNA levels) of these key pathogens. Cultivars ‘Russet Burbank’ and ‘Innovator’ with varying levels of seed borne inoculum were grown in controlled pot experiments in clean soil. Disease parameters including root galling and necrosis were measured at ~60 days after planting (DAP) with tuber disease scored at plant senescence. The relationship between pathogen DNA levels on the parent tubers and subsequent disease status of the progeny daughter plants and tubers was quantified. For the pathogens S. scabiei and R. solani AG3.1, DNA levels in tuber peel provided a good measure (P<0.001) of subsequent tuber disease. For the pathogen, S. subterranea, DNA levels provided a good measure of potential galling in roots but not tuber symptoms. This suggests that seed borne inoculum is important in determining certain disease outcomes but other environmental factors are also important.