Does Manganese Nutritional Status Affect the Resistance of Sugarcane to Orange Rust?

Abstract

Sugarcane cultivation has faced major phytosanitary challenges that might contribute to compromise the sustainability of crop production, such as the leaf orange rust (Puccinia kwenii (w. Fruger) E. J. Blutler). Therefore, understanding the factors that interfere in the sugarcane responses to this disease is critical to maintain crop yield, especially when interacting with other adverse factors occurring under field conditions (i.e., nutritional stresses). The proper mineral nutrition might influence the tolerance of crop plants to biotic stress conditions, and thus it might be considered as a complementary management strategy to improve plant tolerance to the diseases. In this context, even though manganese (Mn) can reduce the severity of fungal diseases in many cultures, there is a lack of informations about the effects of this nutrient in the responses of sugarcane to contamination with leaf orange rust. Accordingly, a study is being proposed with the following objectives: i) to verify how the variation in the availability of Mn interfere with the tolerance of sugarcane the leaf rust; ii) to add informations about the mechanisms that govern the differential resistance of sugarcane varieties to leaf orange rust by assessing leaf anatomy, photosynthesis and ultrastructure of varieties of sugarcane under varying availability of Mn. The varieties RB835054, RB855453, which are classified as resistant to rust orange and with differences tolerances to stress by Mn, and RB72454 which is susceptible to rust orange, will be grown in sand culture and fertigated with the following Mn treatments: deficient Mn (Mn = 0.1 mmol L-1), adequate (Mn = 10 mmol L-1) moderate excess (Mn = 100 mmol L-1) and highly excessive Mn (Mn = 500 mmol L-1). Next, the plants will be inoculated with the fungi causing leaf orange rust (Puccinia kwenii (w. Fruger) E.J. Blutler) and the disease progression will be weekly evaluated by a diagrammatic scale. Moreover, evaluations involving growth analysis, leaf photosynthesis, oxidative stress, ultrastructural and lignin will be also preformed in fully expanded leaves. Then, the plants will be harvested and analyzed for lead nutrient concentration and further correlation with disease severity. We believe that the results obtained in the present project will contribute to improve our understanding about the role played by a proper nutritional management in the resistance of sugarcane to leaf rust orange that is, verify if the resistance of sugarcane varieties to leaf rust is changed with the occurrence of stress by Mn (deficiency or excess). Thus, we expect the results of this study contribute to increase the sustainability of sugarcane production in tropical soils. (AU)