Submitted to: Maine Potato Conference Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: December 15, 2005
Publication Date: January 25, 2006
Citation: Olanya, O.M., Plant, A.B., Larkin, R.P., Lambert, D.H. 2006. Late blight development on hairy nightshade and potential disease risks. Maine Potato Conference Abstracts. Page 20. Technical Abstract: The presence of alternate hosts of late blight can interfere with current disease management strategies by providing additional sources of inoculum, increased pathogen survival, and/or undetected refuges from which Phytophthora infestans may be disseminated to potato crops. To evaluate the significance of hairy nightshade as an alternate host of late blight and potential threat to potato production, we assessed the effects of infection rates, inoculum levels, plant growth stage, temperature, and relative humidity (RH) on late blight development on hairy nightshade. Sporangia production and viability potential of P. infestans on diseased nightshade leaves and seeds, respectively, were quantified. Parameter estimates for infection rates of hairy nightshade were significantly lower (P<0.05) than on tomato or potato hosts. Disease levels varied with inoculum amount. The susceptibility of hairy nightshade increased with plant age from 2 to 8 weeks. Late blight development on hairy nightshade was greater at 18 and 22 C than at 14 or 26 C, whereas foliage blight severity was similar at various relative humidity values (72 to 92%) at 22 C. Viable P. infestans was not detected from infected nightshade seeds. Variable growth stages of nightshade weeds were observed as well as a random spatial distribution in and around potato fields, although nightshade was often concentrated near field edges. These results imply that nightshade can be infected at various weed growth stages regardless of the inoculum amount. Disease development at various RH, temperature ranges, and low rates of progress suggest a longer duration for inoculum production and high late blight risk.