Submitted to: Journal of Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/17/2008
Publication Date: 8/1/2009
Citation: Olanya, O.M., Plant, A.B., Larkin, R.P., Honeycutt, C.W. 2009. Infection Potential of Hairy Nightshade (Solanum sarrachoides) by Phytophthora Infestans and Late Blight Implications of the Alternate Host. Journal of Phytopathology. 157:427-437. Interpretive Summary: Hairy nightshade is a common weed that can serve as a host for potato late blight disease. To evaluate its potential significance, we assessed the importance of environmental (temperature and relative humidity), pathogen (inoculum load and isolates), and host factors (weed growth stage and the ability of disease plants to produce inoculum) in controlled experiments in comparison to potato and tomato hosts. Late blight infection was greater on potato and tomato than on hairy nightshade. Disease level on hairy nightshade varied with inoculum level and weed growth stage. Because hairy nightshade occurs in a similar agro-ecosystem where potato is cultivated, and has similar environmental requirements for blight infection, proper controls are required to minimize its potential impact in serving as a refuge or source of inoculum.
Technical Abstract: Infection of hairy nightshade (Solanum sarrachoides Sendt) by Phytophthora infestans has been reported; however, the epidemiological significance of hairy nightshade to potato late blight is not well known. Disease development and infection rates of P. infestans were quantified on hairy nightshade relative to tomato (cv Bellstar) and potato (cv Shepody) hosts to evaluate infection potential at 14, 18, 22 and 26 C and 72, 82, 87, and 92% relative humidity (RH). The susceptibility of hairy nightshade to inoculum levels, weed ontogeny, and sporangia production potential were also investigated. Late blight development varied among hairy nightshade, tomato and potato hosts. Pathogen infection rates ranged from 0.0325 to 0.4674 gompits/day, and were significantly (P<0.05) greater on potato and tomato than on hairy nightshade. Late blight severity was variably affected by RH. Disease levels on hairy nightshade varied with inoculum load; and ranged from 9-26% and 26-37% at low and high sporangia concentrations, respectively. Late blight was recorded irrespective of hairy nightshade ontogeny, and was significantly greater on 8-10 than 4-6 wk-old plants. These results indicate that pathogen, environmental and host factors affect late blight development on hairy nightshade.