Discovery of potential protein biomarkers associated with sugarcane white leaf disease susceptibility using a comparative proteomic approach

Sugarcane white leaf disease (SCWLD) is caused by phytoplasma, a serious sugarcane phytoplasma pathogen, which causes significant decreases in crop yield and sugar quality. The identification of proteins involved in the defense mechanism against SCWLD phytoplasma may help towards the development of varieties resistant to SCWLD. We investigated the proteomes of four sugarcane varieties with different levels of susceptibility to SCWLD phytoplasma infection, namely K88-92 and K95-84 (high), KK3 (moderate), and UT1 (low) by quantitative label-free nano-liquid chromatography-tandem mass spectrometry (nano LC-MS/MS). A total of 248 proteins were identified and compared among the four sugarcane varieties. Two potential candidate protein biomarkers for reduced susceptibility to SCWLD phytoplasma were identified as proteins detected only in UT1. The functions of these proteins are associated with protein folding, metal ion binding, and oxidoreductase. The candidate biomarkers could be useful for further study of the sugarcane defense mechanism against SCWLD phytoplasma, and in molecular and conventional breeding strategies for variety improvement.

The role of salicylic acid and benzothiadiazole in decreasing phytoplasma titer of sugarcane white leaf disease

The objective of this research was to study the effect of Benzothiadiazole (BTH) and Salicylic acid (SA) on the systemic acquired resistance (SAR) of sugarcane the phytoplasma associated with the sugarcane white leaf (SCWL) disease. The experiment was conducted on plants of the sugarcane variety Khon Kaen 3 (KK3) infected with SCWL phytoplasma using insect vectors. Biochemical changes related to the SAR such as SA and total phenolic compounds were followed according to 4 different timepoints: 7, 14, 21 and 28 days after inoculation. Together, phytoplasma were quantified by RT-qPCR using the secA gene of phytoplasma. According to our results, the spraying of BTH and SA tended to increase the amounts of SA, total phenolic compounds and a lower presence of phytoplasma in the plants in comparison with the inoculated control. Spraying BTH at a concentration of 2.4 mM and SA at a concentration of 2.4 mM exhibited the best efficiency to reduce the concentration of phytoplasma. According to RT-qPCR results, the inoculated plants sprayed with BTH displayed a significantly lower concentration of phytoplasma compared to the inoculated controls. Overall, our results indicated that the spray of BTH and SA could induce an efficient SAR response to the phytoplasma associated with the SCWL disease. We expect these results will give support to the development of new products for controlling white leaf disease in sugarcane.

Sugarcane white leaf phytoplasma (white leaf of sugarcane).

Losses due to sugarcane white leaf (SCWL) phytoplasma vary greatly depending on the susceptibility of the clones, the weather and other environmental conditions influencing sugarcane growth. In Taiwan, over 60 hectares of sugarcane were abandoned due to both high incidence and severity of SCWL disease whereas incidence of more than 10% occurred in 700 hectares. Also, crop losses of 33 and 74%, as well as a decrease of 30% in the sugar content in infected sugarcane plants compared to healthy ones, were recorded (Rishi and Chen, 1989). In Sri Lanka, the incidence of SCWL disease in some sugarcane-growing areas has reached 50-84%, where the yield and quality of infected plants were greatly affected (Chandrasene et al., 2003). In SCWL-affected sugarcane plants, the total chlorophyll content was reduced by 90% while the respiratory rate increased significantly (Chen and Chen, 1974). Affected plants usually die soon after the appearance of the first symptoms. SCWL is one of the most destructive diseases of sugarcane in Thailand (Wongkaew and Fletcher, 2004; Hanboonsong et al., 2006).