ELISA-based quantification and role of callose in the development of banana Xanthomonas wilt disease in banana

Abstract

Xanthomonas vasicola pv. musacearum (Xvm) which causes banana Xanthomonas wilt (BXW) disease in banana shows incomplete systemic movement (ISM) in different banana organs and lateral shoots. This ISM phenomenon is yet understood. During pathogen infection, increased callose (a polysaccharide of β-1,3-glucan) deposition at the site of infection forms a permeability barrier to slow down microbial colonization and transmission. Whether callose is involved in the reported ISM of Xvm, is not known. Additionally, the current methods of callose quantification have several drawbacks which include subjectivity, noise-signal strength and sensitivity. The objectives of this study were to, i) assess the virulence of fresh Xvm ooze, ii) develop and optimize a new ELISA-based method for callose quantification, iii) investigate whether callose was involved in the reported ISM of Xvm, and iv) investigate the role of callose in the resistance of M. balbisiana to BXW. Completely randomized experimental design was conducted using two BXW susceptible banana cultivars (Kayinja and Mbwazirume) and the BXW resistant genotype (M. balbisiana). Plants were either inoculated with Xvm or sterile distilled water and samples of leaves, pseudostems, corms and roots were collected at 0, 1, 2, 7, 14 and 28 days post inoculation. The results showed that the virulence of fresh Xvm ooze was similar to pure Xvm infections. Additionally, a new ELISA-based method for callose quantification with high specificity, sensitivity and high throughput ability was developed. This study also reported differential callose production in banana organs with the corm producing significantly the highest (P < 0.0001) but there was no significant variation in callose production between the three banana genotypes (P = 0.079). Therefore, differential callose production in banana organs could be partly responsible for the reported ISM of Xvm. Additionally, the new ELISA-based method for callose quantification will enable reliable and quick quantification of callose in plant tissues. Thus, the findings of the current study could inform the breeding of BXW resistant cultivars through enhanced callose production in the aerial organs of banana leading to enhanced ISM of Xvm and subsequent BXW resistance. The use of callose-based resistant cultivars, the BXW cultural management practices and genetic engineering will ultimately eradicate BXW, increase banana production and subsequently contribute to the Sustainable Development Goals (SDGs) 2020/21 – 2024/25 which include SDG 1, SDG2 and SDG 3.