Abstract
Potato virus Y (PVY) is a major pathogen in potato production that is spread through vegetative propagation of tubers and is the most common defect resulting in downgrading or rejection of seed lots. Implementation of seed certification practices has been a global response in attempt to limit the spread of viruses through seed distribution. The overall goal for this research was to provide methods for seed certification agencies to continue ensuring that available seed for distribution is of quality and further understand the impact of PVY on potato production. To accomplish this goal three major objectives were conducted for this project. The first objective was to understand distribution of PVY within a seed lot and to determine yield impact of seedborne PVY under commercial-like production conditions. The second objective was to identify post-harvest methods to hasten sprout development in freshly harvested tubers. The final objective was to facilitate the development of direct tuber testing as a means to estimate PVY levels in seed lots. Determining PVY distribution within a seed lot was carried out by planting seed pieces from several different mother tuber size categories in field plots and evaluating for PVY incidence. The effects of seedborne PVY on yield were assessed by planting seed from certified lots with various levels of seedborne PVY infection of Russet Burbank (0, 2 and 10% PVY), Ranger Russet (3 and 34% PVY), and Russet Norkotah (2 and 11% PVY) and evaluating final yield and grade. Objective two was conducted by applying several post-harvest treatments (cold temperature and temperature fluctuations, cold aerosol smoke, gibberellic acid, and combination treatments) to Russet Burbank, Clearwater Russet, and Umatilla Russet potato tubers four, eight, or ten weeks after harvest and evaluating for sprout development. Objective three was conducted on Ranger Russet, Clearwater Russet, and Umatilla Russet. Treatments were applied to break dormancy soon after harvest (untreated, smoke, or Rindite) and evaluated for sprout development. PVY detection via ELISA was conducted on tissue directly from a non-dormant tuber and compared to PVY levels from leaf tissue samples in the winter grow out and subsequently compared to the directly tested seed planted in a field the following spring.
Major findings from this study were as follows. For objective one, distribution of PVY within a seed lot appeared to be uniform regardless of the mother tuber size used to produce a successive plant and the response was consistent with cultivar, PVY infection level, and year. Results indicate that selecting for tuber size, whether for the winter grow out or in commercial plantings, does not influence the level of PVY observed. Effects of seedborne PVY infection on yield and grade were dependent upon cultivar. Russet Burbank and Russet Norkotah yields had an inverse relationship with seedborne PVY infection, as PVY infection increased, yields decreased. Although yield reduction was not a linear function for Russet Burbank. Ranger Russet yield or grade was not significantly impacted by seedborne PVY infection in the current study. These results align with previous studies indicating seedborne PVY can impact yield, but the response is cultivar dependent.
For objective two, efficacy of treatments at promoting early sprout development were dependent upon treatment timing, cultivar, and year. The efficacy of most treatments at inducing sprout development increased with time after harvest, with the exception of temperature treatments, which resulted in equal or less sprout development compared to the untreated control. Aerosol smoke and gibberellic acid based treatments increased sprout development compared to the untreated control. The combination of aerosol smoke plus gibberellic acid hastened dormancy break and had the greatest sprout development in all treatment timings, years, and cultivars. Umatilla Russet was more responsive to gibberellic acid treatment, whereas Clearwater Russet and Russet Burbank were more responsive to 1h 20h smoke treatment in promoting sprouting. A novel method of breaking dormancy using cold aerosol smoke was identified and can be used alone or in combination with gibberellic acid to promote dormancy break and enhance sprout development to help facilitate direct tuber testing for PVY detection.
For objective three, treatments to enhance sprouting prior to direct tuber testing showed Rindite consistently produced the greatest sprout development. The smoke treatment encouraged sprout development more than the untreated control. This established three levels of sprout development at the time of direct tuber testing for PVY. In general, utilizing direct tuber testing was comparable to the winter grow out for PVY detection in three russet cultivars (15% versus 14%). To observe PVY infection in a subsequent crop and further confirm accuracy of PVY infection in seed lots that were direct tuber tested after artificial dormancy break, a spring grow out of tested seed was conducted. Direct tuber testing of samples provided accurate PVY incidence results for three seed lots of russet cultivars 47 days earlier on average than the winter grow out results could be obtained. Findings from this research directly benefit potato seed certification agencies in determining proper management strategies for PVY detection in commercial seed lots.