Resistance Induction by Salicylic Acid Formulation in Cassava Plant against Fusarium solani

Fusarium root rot caused by the soil-borne fungus Fusarium solani is one of the most important fungal diseases of cassava in Thailand, resulting in high yield losses of more than 80%. This study aimed to investigate if the exogenous application of salicylic acid formulations (Zacha) can induce resistance in cassava against Fusarium root rot and observe the biochemical changes in induced cassava leaf tissues through synchrotron radiation based on Fourier-transform infrared (SR-FTIR) microspectroscopy. We demonstrated that the application of Zacha11 prototype formulations could induce resistance against Fusarium root rot in cassava. The in vitro experimental results showed that Zacha11 prototype formulations inhibited the growth of F. solani at approximately 34.83%. Furthermore, a significant reduction in the disease severity of Fusarium root rot disease at 60 days after challenge inoculation was observed in cassava plants treated with Zacha11 at a concentration of 500 ppm (9.0%). Population densities of F. solani were determined at 7 days after inoculation. Treatment of the Zacha11 at a concentration of 500 ppm resulted in reduced populations compared with the distilled water control and differences among treatment means at each assay date. Moreover, the SR-FTIR spectral changes of Zacha11-treated epidermal tissues of leaves had higher integral areas of lipids, lignins, and pectins (1,770–1,700/cm), amide I (1,700–1,600/cm), amide II (1,600–1,500/cm), hemicellulose, lignin (1,300–1,200/cm), and cellulose (1,155/cm). Therefore, alteration in defensive carbohydrates, lipids, and proteins contributed to generate barriers against Fusarium invasion in cassava roots, leading to lower the root rot disease severity.