Possible involvement of salicylic acid in systemic acquired resistance ofCucumis sativus againstSphaerotheca fuliginea

Abstract

The possible involvement of salicylic acid in systemic acquired resistance of Cucumis sativus against Sphaerotheca fuliginea was studied. Cucumber plants were inoculated with tobacco necrosis virus on the cotyledons and the level of endogenous salicylic acid in the first true leaf was determined by gas chromatography. Salicylic acid increased continously from the second day after virus inoculation to the fifth day, when the same leaf was inoculated with Sphaerotheca fuliginea. In healthy plants, the efficiency of exogenous salicylic acid in inducing resistance was assayed by applying aqueous solutions at different times before Sphaerothecafuliginea inoculation. To evaluate the level of induced resistance, the following parameters were examined by light microscopy: percentage of conidial germination, length of the hyphae derived from single conidia, number of haustoria, percentage of epidermal cells with lignified walls and of necrotic cells underlying fungal hyphae. In treated plants conidial germination was reduced, the total length of the hyphae was shorter, the number of haustoria was lower and the haustoriumcontaining epidermal cells had more frequently lignified walls. Moreover, an evident increase in callose deposition was observed leading to the formation of oversized papillae around the penetration pegs. These results indicate that the application of salicylic acid before inoculation with Sphaerotheca fuliginea reduces the intensity of the infectious process and that salicylic acid is involved in the expression of systemic resistance in cucumber challenged by the biotrophic pathogen Sphaerotheca fuliginea.

Differential Activity of Peroxidase Isozymes in Response to Wounding, Gypsy Moth, and Plant Hormones in Northern Red Oak (Quercus rubra L.)

“…Isoform A3.9 activity was enhanced by treatment with SA (P = 0.055), a signal more associated with plant defense responses to microbes (Enyedi et al, 1992;Choi et al, 1994;Conti et al, 1996). It is possible, although unlikely, that our trees were incidentally infected by microbes during that particular treatment despite sterilizing the leaf punch, and that A3.9 is both wound-and microberesponsive.…”

Antifungal activity of salaceyin A against Colletotrichum orbiculare and Phytophthora capsici

“…Despite the ability to induce resistance against plant pathogens, it has been suggested that salicylic acid has no direct antifungal activity against several specific plant pathogens (Mills and Wood 1984). Other data have shown, however, that salicylic acid does alter various aspects of fungal development such as spore viability in S. cerevisiae (Romano and Suzzi 1985), reduction of conidial germination in Sphaerotheca fuliginea (Conti et al 1996), inhibition of sclerotial differentiation and growth in Sclerotium rolfsii and Sclerotina minor (Georgiou et al 2000), and the inhibition of Eutypa lata mycelia growth (Amborabe et al 2002).…”

Phytochemical analysis and insight into insecticidal and antifungal activities of Indian hawthorn leaf extract

“…While some studies have suggested that salicylic acid (SA) does not directly exhibit antifungal activity 48 , other research has indicated that SA can affect various stages of fungal development. For example, SA has been found to hinder conidial germination and hyphae development in Sphaerotheca fuliginea 49 and inhibit sclerotia differentiation and growth in Sclerotium rolfsii 50 . Therefore, SA can have an indirect impact on fungal growth and development.…”