Abstract
Sugarcane smut caused by Sporisorium scitamineum is a severe, global sugarcane disease with severe economic losses and is difficult to prevent. To explore more effective control techniques for smut, the effects and physiological mechanism of silicon (Si) on smut resistance in two smut-susceptible cultivars, ROC22 and Badila, were investigated. The results show that Si application significantly enhances smut resistance in ROC22 and Badila, and the incidence of sugarcane smut decreased by 11.57–22.58% (ROC22) and 27.75–46.67% (Badila). The incidence of smut is negatively correlated with the amount of Si applied and the Si content in sugarcane leaves, stems, and roots (highly significantly negatively correlated with stem Si content). Under S. scitamineum stress, the activities of pathogenesis-related enzymes, chitinase and β-1,3-glucanase, secondary metabolism-related enzymes such as polyphenoloxidase (PPO) and phenylalanine-ammonia-lyase (PAL), and the contents of secondary metabolites, total soluble phenol, and lignin in sugarcane leaves treated with Si were significantly higher than those without Si (CK). The results also demonstrated that the content of malondialdehyde (MDA) and hydrogen peroxide (H2O2), the superoxide dismutase (SOD) activity of sugarcane leaves treated with Si increased in the seedling and tillering stages, and the peroxidase (POD) activity decreased in the seedling stage, which caused the accumulation of reactive oxygen species (ROS) that in turn triggered defense responses. Moreover, MDA and H2O2 levels decreased, and the activities of SOD and POD increased at the jointing stage, which was beneficial to the removal of excessive ROS. Collectively, these results suggest that Si modulates pathogenesis-related protein activity, secondary metabolism, and active oxygen metabolism of sugarcane that positively regulate resistance to smut. This study is the first to reveal the physiological mechanism of Si in improving smut resistance in sugarcane, and the results provide a theoretical basis for the development of Si fertilizers to control sugarcane smut.
Highlights
Sugarcane (Saccharum spp. hybrids) is an important sugar crop and a renewable biomass energy crop with great development potential
In the 2017 experiment (Badila), the incubation period of the four treatments was 60–∞ days, that of CK2 was 60 days, that of Sis30 was longer than that of Sis15, and that of Sis45 did not exhibit smut whip, indicating that the incubation period of Si treatment was longer than that of non-Si treatment, and the incubation period was prolonged with increasing of Si application (Table 1)
Smut incidence of Sis15, Sis30, and Sis45 was significantly (P ≤ 0.05) lower than that of CK2; the highest incidence was observed in CK2 (46.67%), the lowest in Sis45 (0), and the incidence of Sis15 and Sis30 were, TABLE 1 | Effect of silicon on disease latency, disease incidence, and control effect under Sporisorium scitamineum stress
Summary
Sugarcane (Saccharum spp. hybrids) is an important sugar crop and a renewable biomass energy crop with great development potential. Sugarcane smut caused by Sporisorium scitamineum is an important global sugarcane fungal disease. In the past 20 years, smut has become one of the most economically harmful sugarcane diseases in mainland China. The main sugarcane cultivars in China are infected with smut, and the incidence in the field ranges from 10% to 20%, severely affecting yield and quality (Que et al, 2012, 2014; Shen et al, 2014a). Due to the pathogenicity or physiological race differentiation of S. scitamineum and sugarcane being an allopolyploid with complex inheritance and long breeding cycle, it is not easy to succeed in sugarcane breeding for smut resistance (Shen and Deng, 2011; Que et al, 2012; Su et al, 2016). It is necessary to establish a novel and effective method to manage sugarcane smut
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