Abstract

BELTRAN SANCHEZ, Edgar; GILCHRIST RAMELLI, Elizabeth; JARAMILLO VILLEGAS, Sonia del Carmen  and  REYNALDI, Sebastián. INFLUENCE OF INCUBATION CONDITIONS ON THE ACTIVATION OF ZOOSPORES OF Spongospora subterranea, SEARCHING FOR AN INOCULUM TO THE STUDY OF THE POWDERY SCAB. Rev. Fac. Nac. Agron. Medellín [online]. 2009, vol.62, n.2, pp.5055-5062. ISSN 0304-2847.

The powdery scab is a disease that decreases potato production. It is caused by Spongospora subterranea f. sp. subterranea. This obligate parasite produces cystosori, which are groups of encysted zoospores. When these zoospores are active, they can infect roots and tubers initiating a new replication cycle. To investigate the influence of the incubation conditions on the zoospore activation, suspensions of cystosori in water were incubated under different conditions. The cystosori and the active zoospores were daily counted under microscope. The higher number of active zoospores was found after four days of incubation, meanwhile the lower number of cystosori was found after five days of incubation. This suggests that zoospores are active for a short period. The number of active zoospores per cystosorus was significantly (P<0.05) higher in tap water than in distillated water, and in presence of light than in dark. More zoospores per cystosorus were activated at 19 °C than at 5 °C, but potato roots did not have a significant (P<0.05) effect on zoospores activation. These results indicate that the incubation conditions may increase the zoospores activation. However, the number of active zoospores per cystosori was not higher than five. More active zoospores were expected, because a cystosorus is between 10 and 40 times bigger than a zoospore. This shows that a large number of cystosori are needed to ensure the presence of active zoospores in an inoculum

Keywords : Powdery scab; Spongospora subterranea f. sp. subterranea; cystosori; zoospores; potato.

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