Influence of atmospheric humidity on sporulation of Sphaerotheca pannosa (Wallr.) Lev. var. rosae Wor. Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/cz30px62n

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  • The influence of atmospheric humidity on three aspects of sporulation of Sphaerotheca pannosa (Wallr.) Lev. var. rosae Wor., which causes rose powdery mildew, was studied on leaf disks of susceptible Rosa cultivar Samantha. To study conidiophore production, leaf disks were inoculated on the adaxial (upper) surface with conidia of S. pannosa race 2 and incubated at 21 C for 24 hours, then exposed to 20, 50, 80, and 95% relative humidity (RH). RH was maintained with glycerol solutions inside insulated chambers held at 21 C. After six days the disks were removed and the number of conidiophores per disk was determined with an epi-illuminating microscope. At 80 or 95% RH the number of conidiophores produced per disk was significantly greater than at 20 or 50% RH. It v/as noted that the incidental occurrence of mycoparasites reduced sporulation on disks exposed to 95% RH, so that it was not significantly different from that on disks exposed to 20 or 50% RH. To study the effect of atmospheric humidity on the latent period of S. pannosa, leaf disks were inoculated on the adaxial surface with conidia of S. pannosa race 2 and incubated for 24 hours at 21 C, then exposed to RH of 20, 50, 80, and 95%. After 48 hours, disks were removed from the humidity chamber at 24- hour intervals, and examined under epi-illumination to determine the earliest day that conidiophores and conidia appeared on each disk. The occurrence of conidiophores and conidia was significantly earlier at 80 or 95% RH than at 20 or 50% RH. To study the effect of atmospheric humidity during conidial production on conidial viability of S. pannosa , leaf disks excised from infected plants were exposed to 20, 50, 80, and 95% RH for two days. Percent germination of conidia produced during the RH treatments was evaluated on uninfected leaf disks. There were no differences in percent germination of conidia produced at any of the four RH treatments. Results suggest that the quantity and rate of sporulation of S. pannosa is favored by high RH, but that RH conditions during sporulation do not affect conidial viability. Also, the presence of fungal antagonists may inhibit sporulation of S. pannosa significantly at high RH.
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