Anti-fungal Efficacy of Carica papaya(Papaya) Leaves Crude Ethanolic Extract Against Magnaporthe oryzae, the Causal Pathogen of Rice Blast

Abstract

INTRODUCTION

Half of the world's human population relies on rice as a staple food. Asia, yielding more than 650 million tons of rice, accounts for 90% of the total rice produced. Biotic and abiotic stresses, however, instigate huge losses globally. Rice blast, caused by the fungus Magnaporthe oryzae, is responsible for roughly 30% of yield loss worldwide. The use of chemical fungicides has been widely utilized; however, these chemicals adversely affect human and environmental health. Thus, there is a need for an effective yet safe treatment using organic extracts as a promising alternative management control against rice blast.

METHODS

Carica papaya leaves extract (CPLE) was evaluated against Magnaporthe oryzae on both in vitro and in vivo assays. Spore germination and mycelial growth tests were conducted to assess the in vitro antifungal activity in concentrations of 1.5625, 3.125, 6.25, 12.5, 25, 50, and 100 Âμg/mL of CPLE. invivo, eradicative activities of the varying concentrations of CPLE were evaluated against M. oryzae on 14-day old rice plants by determining the percentage diseased-leaf area (%DLA).

RESULTS

Significant antifungal activity was observed starting from 1.5625 Âμg/mL with percentage germination mean of 47.65%. It was also assessed that CPLE was most active at 100 Âμg/mL and least at 0 Âμg/Ml, with percentage germination mean of 6.15% and 68%, respectively. However, despite its inhibitory effects in spore germination, suppression in mycelia growth was not observed in any of the CPLE concentrations tested. Then again, in vivo assay results showed the potent fungicidal activity of CPLE as it inhibited the growth and development of rice blast. Compared to negative control with 59.04% DLA, the significant drop rate of infection was observed starting at 1.5625 Âμg/mL with 37.3% DLA. Minimum infection was 1.65% at 100 Âμg/mL and the maximum was 59.04% at 0 Âμg/mL. It was determined that the suppressive effect of CPLE increased in parallel with its concentration.

DISCUSSIONS

Pathogenicity of most fungi starts from the germination of its spores. inline with the study conducted and to other relevant studies, CPLE could obstruct the process by which M. oryzae starts its pathogenicity in host plants, which was then confirmed further in the in vivo assay. The specific mode of action of CPLE against M. oryzae, however, was not fully understood. To fully intuit this, relevant studies using other high-end tests must be conducted.