Identification of new phylogenetic lineage of Lasiodiplodia causing leaf spot and tip necrosis causing agent on Aloe vera in Sri Lanka and screening eco-friendly control measures

Abstract

Aloe vera, a member of the Asphodelaceae family, is renowned globally for its medicinal properties and widespread applications in cosmetics, pharmaceuticals, and food production. In Sri Lanka, both cultivated and wild A. vera are susceptible to leaf spot and tip necrosis. The present aims to identify the causative agent of this disease and screen the effectiveness of various natural substances in disease control. Disease incidence was assessed in both cultivated fields and wild habitats, and the results showed a higher percentage in the wild. Isolates obtained from symptomatic leaves were identified as members of Lasiodiplodia based on morphological studies. The phylogenetic analysis, which combined sequences from the Internal Transcribed Spacer (ITS) region and a segment of the calmodulin (cmdA) gene, suggested that the isolates might represent a new lineage within the genus Lasiodiplodia. These isolates appeared to share a common ancestor with Lasiodiplodia hormozganensis. Koch's postulates validated the pathogenicity of the isolates. Natural substances, namely marine algal extracts, plant extract and cell-free supernatants (CFSs) of bacteria, were tested against the isolates. CFSs of Pseudomonas fluorescens and Bacillus megaterium showed significantly higher inhibition on conidial germination compared to the tested commercial fungicide. Further, CFS of P. fluorescens revealed the notable effectiveness on the development of leaf spot and tip necrosis on the leaf compared to the tested fungicide. These findings underscore the potential of P. fluorescens CFS in managing A. vera diseases caused by the isolates of Lasiodiplodia in Sri Lanka.