Diversity of Asperisporium caricae (Speg.) Maubl. isolates causing papaya black spot disease

Abstract

Papaya black spot disease is an emerging concern in Karnataka, accompanied by a lack of knowledge regarding the associated pathogen. This study focuses on assessing the cultural and molecular variability of ten Asperisporium caricae isolates responsible for causing papaya black spot disease. The isolates underwent evaluation on twelve distinct solid media, with recorded observations on colony characteristics and sporulation. Among the ten isolates, three exhibited excellent radial growth, five displayed good growth, one had moderate growth, and one isolate demonstrated poor radial growth. All cultural media were subjected to sporulation testing, revealing that two isolates exhibited fair sporulation, five displayed sparse sporulation, and the remaining three showed no sporulation. PCR amplification using ITS 4 and ITS 5 resulted in a 590bp amplicon for all ten A. caricae isolates. Dendrogram clustering grouped the isolates into two clades, where the AcG isolate belonged to clade I, and AcH, AcKa, AcKu, AcMa, AcMU, AcMy, AcNa, AcR, and AcV formed clade II. Notably, the AcG isolate demonstrated lower similarity (62%) compared to other isolates. AcH and AcKu isolates exhibited the highest similarity (85%), followed by AcMa and AcMu (78.5%). The resemblance between AcH and AcKu was evident in certain cultural characteristics as well.