Characterization, phylogenetic analysis and toxigenic potential of Fusarium incarnatum-equiseti species complex isolates associated with root rot disease in vegetables

Abstract

Fusarium incarnatum-equiseti species complex infects a wide variety of food crops. Six fungal isolates were isolated from rotted roots of Dolichos lablab (hyacinth bean), Trichosanthes dioica (pointed gourd), Momordica dioica (spiny gourd), Capsicum frutescens (chilli) and Pisum sativum (garden pea), and identified as Fusarium spp., belonging to Fusarium incarnatum-equiseti species complex (FIESC), through conidial morphology, sporodochia on carnation leaf agar medium and sequencing of nuclear ITS-rRNA and transcription elongation factor 1α gene. Multilocus phylogenetic analysis demonstrated their inclusion within the Incarnatum clade of FIESC. All of them were self-incompatible and failed to pair with other isolates. Vegetative incompatibility affected their pathogenicity and host specificity. The isolates secreted extracellular cell wall degrading enzymes cellulase (0.033 ± 0.002–0.403 ± 0.020 U.mL⁻¹), polygalacturonase (0.005 ± 0.0001–0.392 ± 0.010 U.mL⁻¹) and pectin-lyase (0.015 ± 0.001–0.407 ± 0.012 U.mL⁻¹) for direct penetration to root tissue. They also secreted toxic metabolites that inhibited germination of Cicer arietium (chickpea) and Pisum sativum (garden pea) seeds. The isolates exhibited complete pathogenicity on their original hosts (death due to root rotting, Disease Severity Index- 100%) but less pathogenicity in other non-host plants (yellowing of lower leaves without sign of root rot, Disease Severity Index- <20%). This study reported the production of plant cell wall degrading enzymes and toxic metabolites by some pathogens belonging to FIESC and three new hosts of the pathogen such as hyacinth bean, spiny gourd and garden pea, from the Indian subcontinent.