Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 5, 1996
Publication Date: N/A
Interpretive Summary: Soft rot organisms cause major losses to potatoes during the growing season and in storage. Good laboratory evaluations for tuber soft rot reactions are needed to enable potato breeders to screen germplasm for resistance to this important disease and identify resistant germplasm. Current laboratory evaluations of tubers for soft rot resistance are subject to tremendous variability, making conclusions about the relative soft rot resistance of cultivars difficult. This research examined different ways of measuring tubers for their soft rot resistance so as to minimize the variability present in the laboratory. The diameter of rotted tuber tissue and the square root transformation of one of the measures of relative weight loss were found to be the best measures of soft rot resistance. This research will benefit potato breeders involved in screening germplasm for resistance to soft rot.
Technical Abstract: Soft rot resistance in potato tubers can be determined by inoculating tuber slices with soft rot Erwinia species. The objectives of this study were to: 1) examine the statistical assumptions underlying the analysis of variance on different response variables; 2) determine the partial correlations among normally distributed variables after treatment effects were removed; 3) estimate necessary sample sizes to find significant differences between treatment means significant; and 4) choose the "best" variable for measuring resistance to soft rot. Slices from fifteen tubers from each of three cultivars were inoculated with Erwinia carotovora subsp. atroseptica, E. carotovora subsp. carotovora or E. chrysanthemi and incubated at two different temperatures (20C and 30C) for 48 hrs. The test was conducted on two dates. Tuber samples were sliced and weighed prior to inoculation and after the macerated tissue was removed following a 48 hr incubation period. The maximum diameter of macerated tissue on each slice was also measured. The "best" response variables for measuring resistance to soft rot by the tuber slice method were the diameter of the macerated tissue and a square root transformation of proportional weight loss.