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Title: Suppression of zoospore cyst and sporangial germination of Phytophthora infestans by treatments that might interfere with calcium-mediated functions
Author: Grayson, David Edward
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1998
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In laboratory experiments, Ca2+, other divalent cations and various Ca2+-modulating treatments were tested for effects on germination of zoospore cysts and of sporangia of three isolates of Phytophthora infestans and sometimes for an isolate of P. palmivora. The aim was to determine whether manipulation of Ca2+ or Ca2+-mediated events has the potential for control of potato late blight caused by P. infestans. This work was based on previous evidence for a central role of Ca2+ in the infection sequence from zoospores of phytopathogenic Phytophthora, Pythium and Aphanomyces spp. Zoospore cyst germination of both P. infestans and P. palmivora was suppressed by early post-encystment addition of the chelators EGTA or BAPTA, indicating a requirement for external Ca2+ or other polyvalent cations, by calcium channel blockers (La3+, Gd3+, verapamil) or by amiloride, indicating a requirement for flux of Ca2+ or other ions across the cyst membrane, by calmodulin antagonists (calmidazolium, dibucaine, trifluoperazine) and by intracellular calcium antagonists (caffeine, TMB-8), indicating a role for both calmodulin and for Ca2+ release from intracellular stores. Supplements of Ca2+ or other divalent cations (Ba2+, Mg2+) also suppressed cyst germination, but sometimes partly or completely overcame the suppression by other treatments if applied early as post-treatments. Germination of sporangia of P. infestans by hyphal outgrowth (direct germination, at c. 20°C) or zoosporogenesis (indirect germination, at c. 12°C) was suppressed by the same treatments as applied to zoospore cysts. These treatments sometimes caused rapid sporangial death, assessed microscopically by irreversible changes in cytoplasmic organisation. Their suppressive or toxic effects were generally more pronounced when sporangia were incubated to induce indirect rather than direct germination. The suppression caused by Ca2+-modulating treatments could be rescued only partly by simultaneous or early post-application of divalent cations. Even potentially mild chemical treatments (0.1% pectin or 5 mM orthophosphate) caused rapid (20-30 min) death of sporangia (especially when incubated for indirect germination). Simultaneous or early post-treatments with divalent cations could only partly reverse the suppression.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available