The rice sl mutant showed two types of responses to Magnaporthe grisea infection by light treatments. One was an sl‐mutant‐type response characterized by Sekiguchi lesion expression under light waves of 400–700 nm, and the other was a wild‐type response characterized by blast and/or necrotic spot lesion expression in the dark or at wavelength between 290 and 330 nm. There was a large difference in the resistance to M. grisea infection between the mutant‐ and wild‐type responses in the rice sl mutant. When the mutant‐type response was induced in the rice sl mutant, the disease resistance was enhanced relative to that in the wild‐type response. Enhanced resistance was demonstrated by two components: (a) the number of Sekiguchi lesions was reduced relative to that of blast or necrotic lesions; (b) sporulation of M. grisea was not induced in Sekiguchi lesions. The enhanced resistance was dependent on light of 400–700 nm.
The effect of pyroquilon. an inhibitor of melanin synthesis, on the sporulation and secondary infection of Magnaporthe grisea spores was investigated. Spore formation of M. grisea was significantly inhibited on the pyroquilon-containing medium, but myceliat growth was not impaired. Moreover, aUhough the colour of the spore suspension obtained from control medium without pyroquilon was black, the suspension prepared from spores which had grown on the pyroquiloncontaining medium was red-brown. The cell walls of the spores consisted of two layers, the outer of which was highly electron-dense and saw-like in cross section, regardless of treatment. Both the outer and the inner layers of the ceil walls of spores which had grown on pyroquiloncontaining medium were thin compared with those of control spores. When M. gri.tea spores which had formed on the pyroquilon-containing medium were inoculated onto rice leaf sheaths, red brown appressoria were formed. Compared with the control, appressorial penetration and hyphal growth in the host cells were inhibited. The inhibitory effect pyroquilon exerted upon the infection behavior of M. grisea spores was dependent on the dose of the chemical.
Zusammenfassung
Wirkung des Meliuiinsyntti^e-lntaibitors Pyroquilon auf die Sponilation von Magnaporthe grisea und die seJiundiire Infektion durch den PilzDie Wirkung des Melaninsynthese-Inhibitors Pyroquilon auf die Sporulation von Magnaporthe grisea und die sekundare Infektion durch Sporen des Pilzes wurde untersucht. Auf pyroquilonhaltigem Medium war die Sporenbildung von M. grisea signifikant gehemmt. wahrend das Myzelwachstum nicht beeintrachtigt wurde. Von pyroquilonfreiem Kontrollmedium gewcnnene Sporensuspensionen waren schwarz, von pyroquilonhahigem Medium erhaltene Sporensuspensionen dagegen rotbraun gefarbt. Die Zellwande der Sporen bestanden aus zwei Schichten, deren auBere unabhangig von der Behandlung hochgradig elektronendicht war und im Querschnitt ges^gt erschien. Die aufleren und inneren Zellwande der auf pyroquilonhaltigem Medium gehildeten Sporen waren dQnner als die Zellwande der Sporen der KontroUvariante. Wurden auf pyroquilonhaltigem Medium gewachsene M.-grisea-Sporea auf Reisblattscheiden inokuiiert, bildeten sie rotbraune Appressorien. Appressorienpenetration und Hyphenwachstum in den Wirtszellen waren im Vergleich zur KontroUvariante gehemmt. Die Hemmwirkungvon Pyroquiton auf das Infektionsverhalten der A/.-^ruea-Sporen war dosisabhangig.
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