Evaluation of potato varieties and selections for resistance to bacterial soft rot

Potato varieties and selections were evaluated for resistance to bacterial soft rot caused by Erwinia carotovora subsp. carotovora and Erwinia carotov ora subsp. atroseptica in mist chamber. A randomized complete block design with a single treatment and 3 replications was used in this study. Potato l ines were inoculated with bacterial suspension (10 tubers/line) using the p uncture inoculation method and incubated for 4 days in a mist chamber at 21 C and 100% relative humidity in the dark. Although there were differences in incidence of soft rot and in amount of weight reduction, most of the pot ato lines were susceptible to tuber soft rot. Mean incidence (%) of soft ro t ranged from 10 to 100%. Mean reduction of tuber weight (%) ranged from 0. 13 to 16.43%. Among the varieties and selections tested, AF 522-5 was the m ost resistant to tuber weight loss, while AF 1424-7 was most susceptible. T here were also significant differences between years, and a variety by year interaction. Testing over a period of years is recommended. A significant correlation coefficient of soft rot incidence (%) and reduction of tuber we ight (%) was obtained (r=0.65; P=0.05), indicating that incidence was a fai r measure of soft rot potential. However, the greater variability in result s for incidence make weight loss a better measure of soft rot reaction. The re was a significant difference among varieties in the reduction of tuber w eight when potato lines were inoculated either 1 month or 2 months after ha rvest, but the interaction of time by year prohibits a conclusion as to whi ch time gives a better test reaction. Late maturing varieties had slightly less weight loss than earlier maturing varieties.