Comparative analysis of salicylic acid levels and gene expression in resistant, tolerant, and susceptible cassava varieties following whitefly-mediated SLCMV infection

Abstract

Sri Lankan cassava mosaic virus (SLCMV), the primary pathogen responsible for cassava mosaic disease in cassava plantations, is transmitted via infected cutting stems and the whitefly vector, Bemisia tabaci. To obtain better insights into the defense mechanism of cassava against SLCMV, whiteflies were used to induce SLCMV infection for activating the salicylic acid (SA) signaling pathway, which triggers the innate immune system. The study aimed to investigate the specific interactions between viruliferous whiteflies and SA accumulation in resistant (C33), tolerant (Kasetsart 50; KU50), and susceptible (Rayong 11) cassava cultivars by infecting with SLCMV. Leaf samples were collected at various time points, from 1 to 7 days after inoculation (dai). The SA levels were quantified by gas chromatography-mass spectrometry and validated by quantitative reverse transcription polymerase chain reaction. The SA levels increased in KU50 and C33 plants at 2 and 3 dai, respectively, but remained undetected in Rayong11 plants. The expression of PR-9e, PR-7f5, SPS1, SYP121, Hsf8, and HSP90 increased in infected C33 plants at 4 dai, whereas that of KU50 plants decreased immediately at 2 dai, and that of Rayong11 plants increased at 1 dai but gradually decreased thereafter. These findings strongly indicate that SA plays a crucial role in regulating antiviral defense mechanisms, especially in SLCMV-resistant plants. Altogether, the findings provide valuable insights into the mechanisms underlying the activation of SA-mediated anti-SLCMV defense pathways, and the resistance, tolerance, and susceptibility of cassava, which can aid future breeding programs aimed at enhancing SLCMV resistance.

Figure 1

Comparison of the levels of SA in the leaves of the three different varieties of cassava infected with SLCMV (n = 3 per group).

Figure 2

Levels of SA in the leaves of the three different varieties of cassava collected at 1, 2, 3, 4, 5, 6, and 7 dai (n = 3 per group).

Figure 3

Analysis of the expression of genes related to the accumulation of SA. The PR-9e, PR-7f5, SPS1, SYP121, Hsf8, and HSP90 genes were detected in the C33, KU50, and Rayong11 genotypes. The SLCMV-infected leaves inoculated by whitefly infestation were collected at 1, 2, 3, 4, 5, 6, and 7 dai (n = 3 per group).