11 Plant protection using natural defence systems of plants

Inhibition of Blumeria graminis f. sp. tritici Germination and Partial Enhancement of Wheat Defenses by Milsana

ABSTRACT The prophylactic efficiency of Milsana against powdery mildew was evaluated on wheat (Triticum aestivum). A single short spraying on 10-day-old plantlets reduced the infection level by 85% and two long sprayings led to the total restriction of the disease. Although microscopic studies showed that Milsana treatments enhance hydrogen peroxide accumulation at the fungal penetration site, biochemical analysis did not allow us to correlate this accumulation with the activation of several enzyme activities involved in active oxygen species (AOS) metabolism. Only lipoxygenase activity, which is involved in both AOS metabolism and lipid peroxidation, showed a 26 to 32% increase 48-h posttreatment in leaves infiltrated with Milsana. This weak effect of Milsana on wheat lipid metabolism was confirmed at the lipid peroxidation level, which surprisingly, was shown to decrease in treated plants. In order to explain the high efficacy of Milsana, the fungistatic effect on conidia germination was also examined. In planta, we showed that a Milsana treatment resulted in a higher proportion of abnormally long appressorial germ tubes, whereas in vitro, it dramatically inhibited fungal conidia germination. The partial activity of Milsana in terms of defense response induction in the wheat/powdery mildew pathosystem and its newly described direct fungistatic activity are discussed.

Trehalose induces resistance to powdery mildew in wheat

• Reduction in the degree of powdery mildew infection of wheat leaves is observed after treatments with trehalose, a nonreducing disaccharide commonly found in a wide variety of organisms, including fungi. • Wheat (Triticum aestivum) cv. Sideral plants grown in phytotrons were inoculated with Blumeria graminis f.sp. tritici. In addition to degree of infection, the effect of trehalose solution was further investigated using light and fluorescence microscopy and enzyme assays. • Infection in wheat leaves was reduced by 50 and 95% with trehalose solution (15 g l^-1 ) following a single spraying and three sprayings, respectively; in a detached leaf assay, trehalose was effective at concentrations as low as 0.01 g l^-1 . Trehalose did not inhibit conidial germination and differentiation of appressoria (in vitro or on the leaf epidermis), but enhanced papilla deposition in epidermal cells. Trehalose also enhanced phenylalanine ammonia-lyase (PAL) and peroxidase (PO) activities; both markers of plant defence responses. However, the level of three cinnamyl alcohol dehydrogenase (CAD) activities (conyferyl, p-coumaryl and sinapyl alcohol dehydrogenase) was unchanged. • Trehalose treatment of wheat confers resistance to B. graminis infection by activating plant defence responses (e.g. papilla deposition, PAL and PO activities).