Phytophthora capsici Zoospore Infection of Pepper Fruit in Various Physical Environments

Phytophthora capsici is a pathogen on several economically important crops including pepper. The fungus attacks the roots, stems, leaves and fruit of the plant. Experiments were conducted to determine environmental conditions that may affect infection of pepper fruit by zoospores of P. capsici. Two techniques were used to inoculate the mature green pepper fruit. First, the blossom end of the fruit was submerged in an aqueous suspension of zoospores. This technique attempted to simulate dispersal of zoospores by flood irrigation. The second technique involved placing water drops of the zoospore suspension on the fruit. Disease incidence and severity were greater for the first technique than for the second technique. In addition, 100% of fruit were infected when immersed in the zoospore suspension for 10 min. Disease incidence and lesion length were greatest at 27 °C. Drop sizes of 10, 50, and 100 µl with identical zoospore content (5000 zoospores/drop) did not significantly affect lesion size. Disease incidence, however, was significantly greater when a 100-µl drop was used for inoculation, compared to the 10- and 50-µl drops. These data suggest that the most severe infection occurs when peppers are in contact with a large volume of inoculum (i.e. flood irrigation), in contrast to a small droplet with the same concentration of zoospores.