No abstract

Tan spot, caused by Pyrenophora tritici-repentis, and fusarium head blight (FHB), caused by the Fusarium graminearum species complex, are among the main wheat diseases worldwide. This 3-year field study evaluated the effect of soil incorporation of calcium silicate, a source of silicon (Si), to manage tan spot and FHB and improve grain yield and quality. The effect of Si was compared on two cultivars contrasting in disease resistance and associated with one or two fungicide sprays. Calcium silicate fertilization increased the Si concentration in the soil and wheat leaf and spike tissues. The increase of Si concentration in wheat tissues was associated with reduction in the severity of both tan spot and FHB, consequently increased the quality and grain yield of wheat. The reduction of disease severity conferred by Si was greater for tan spot than FHB. The greatest control of tan spot and FHB was obtained with the moderately resistant cultivar grown in soil amended with calcium silicate (+Si) and treated with two fungicide sprayings. On the other hand, the highest grain yield, under high disease pressure, was obtained in +Si plants, regardless of the cultivar, treated with two fungicide sprays. The results of this study show for the first time that the incorporation of Si in the soil complemented the effect of genetic resistance and fungicide treatments in controlling both tan spot and FHB. Furthermore, results indicate that calcium silicate fertilization is useful as part of integrated management of these wheat diseases.

Wheat (Triticum aestivum) is an annual crop, cultivated in the winter and spring and susceptible to several pathogens, especially fungi, which are managed with fungicides. It is also one of the most consumed cereals, and can be contaminated by mycotoxins and fungicides. The objective of this study was to validate an analytical method by LC-MS for simultaneous determination of mycotoxins and fungicide residues in wheat grains susceptible to fusarium head blight treated with fungicides, and to evaluate the relationship between fungicide application and mycotoxin production. All parameters of the validated analytical method were within AOAC and ANVISA limits. Deoxynivalenol was the prevalent mycotoxin in wheat grain and epoxiconazole was the fungicide residue found in the highest concentration. All fungicidal treatments induced an increase in AFB2 production when compared to the control (without application). AFB1 and deoxynivalenol, on the contrary, were reduced in all fungicide treatments compared to the control.

Tan spot caused by Pyrenophora tritici-repentis is a disease present in all wheat-producing countries and silicon (Si) treatment of wheat plants has been shown to increase plant resistance to tan spot. In this study, the effect of phenylpropanoid metabolism on resistance to tan spot was evaluated and some phenolic compounds that accumulated in response to P. tritici-repentis attack were identified. Furthermore, the effect of Si on phenylalanine ammonia-lyase (PAL) activity and phenolic compound accumulation were determined in situ. Antifungal activity of differentially accumulated phenolic compounds was also evaluated in in vitro tests. Results showed that the increase in concentration of phenolic compounds was greatest at the onset of infection, and that some compounds showed fungitoxic effects including fungal tip swelling, granulation of germ tube and hyphae, and hyphal hyperbranching. Silicon-induced reduction in both lesion size and tan spot disease progression were associated with activation of phenylpropanoid metabolism. PAL activity and accumulation of antifungal phenolic compounds were greater in pathogen-inoculated plants supplied with Si. In these plants, fluorescence indicative of accumulation of phenolic compounds occurred early in epidermal cells and its intensity increased during the evaluation period, showing higher numbers of fluorescent cells around infected cells. Thus, the combined responses of cell fluorescence at sites of infection, increased PAL activity and accumulation of phenols indicate that Si strengthened wheat defence responses to infection by P. tritici-repentis, reducing the severity of tan spot.

No abstract