Exploring the potential of RNA interference technology for the control of phytophthora palmivora

Abstract

Phytophthora palmivora is one of the most devastating plant pathogens of tropical crops, particularly on papaya and cacao in Hawaii, manifesting through symptoms such as fruit rot, stem rot and leaf damage. In papaya, traditional management methods involve the use of resistant cultivars, fungicides like phosphonates, metalaxyl, or copper hydroxide, and cultural practices. In addition to these conventional management techniques, double-stranded RNA (dsRNA) has emerged as a promising management approach, offering specificity in targeting mRNA sequences of the pathogenic genes of a pathogen while minimizing the environmental impact. Ppal15kDa, a protein secreted by P. palmivora, was previously shown to play an important role in the infection structure development and pathogenicity. In this thesis, the effect of Ppal15kDa dsRNA treatment on the pathogenicity of P. palmivora and development of infection structures was assessed using several assays. Co-incubation of fluorescein-labeled Ppal15kDa dsRNA and P. palmivora zoospores demonstrated the uptake of Ppal15kDa dsRNA by the zoospore cells. Experiments investigating the effect of Ppal15kDa dsRNA on germination tube length and appressorium formation showed that treatment with Ppal15kDa dsRNAs resulted in shorter germination tubes and reduced appressoria formation. Additionally, zoospores treated with Ppal15kDa dsRNA showed reduced lesion formation and smaller lesion diameters in papaya fruits and leaves. Lastly, Ppal15kDa dsRNA was shown to reduce the expression of Ppalk15kDa gene using reverse transcription quantitative PCR (RT-qPCR). Thus, this research demonstrated the promising effects of dsRNA treatment against P. palmivora on papaya.