Disease development and enhanced susceptibility of wounded pepper roots toPhytophthora capsici

Greenhouse experiments were conducted to determine disease progression of p hytophthora root rot on nonwounded and wounded pepper plants (Capsicum annu um) and to determine whether susceptibility to Phytophthora capsici decreas es with wound aging. Two isolates of P. capsici were used in this study, on e less aggressive than the other. Trimming the roots immediately prior to i noculation with either isolate increased susceptibility significantly (P le ss than or equal to 0.05) compared with plant roots that were not trimmed. Both isolates caused a higher level of disease severity on disturbed/trimme d than on disturbed/nontrimmed roots. Disease also occurred earlier with th e more aggressive isolate on both wounded and nonwounded roots. Disease sev erity was three to four times more severe on plants treated with the aggres sive isolate (NM6011) than on those inoculated with the less aggressive iso late (NM6040), regardless of root treatment. In separate experiments, peppe r roots were wounded and allowed to age for up to 5 days before inoculation . Resistance to P. capsici increased as the wounds aged, resulting in signi ficantly (P less than or equal to 0.001) lower disease severity on plants w ith 3- and 5-day-old wounds than on those inoculated at the time of woundin g and the nondisturbed/nontrimmed controls. Wounding of the roots followed by immediate inoculation with zoospores resulted in significantly higher le vels of attachment than when roots were inoculated with zoospores 48 h afte r wounding. The 48-h postwounding inoculation treatment showed the same amo unt of zoospore attachment as nonwounded roots. Increase in plant resistanc e correlated (P less than or equal to 0.01) with an increase in total perox idase activity. Isoelectric focusing-polyacrylamide gel electrophoresis (IE F-PAGE) indicated increased band intensity of three acidic and one basic is ozyme as wounds aged. These data suggest that wound repair plays a role in decreasing infection and resultant disease symptoms of pepper to P. capsici .