University of Hawai'i at Mānoa Honolulu, Hawaii, United States
Abstract Text: Plant-pathogenic fungi pose a serious threat to food security, and growers in Hawaii are especially challenged by disease pressure caused by fungi all year round. Additionally, a rising cost of agriculture production inputs is pushing food producers in Hawaii to adopt sustainable pest management tactics using local resources. Papaya seeds are an agricultural waste in Hawaii, and contain precursors to the volatile, biocidal compound benzyl isothiocyanate (BITC). This study aimed to 1) assess the toxicity of BITC to pathogenic fungal species isolated in Hawaii, and 2) examine the susceptibility of various fungi to ground papaya seed (PGS) biofumigation. Two in vitro bioassay methods were evaluated using either synthetic BITC or biofumigation with PGS on half-strength potato dextrose agar plates. Six true fungi (Fusarium oxysporum, F. oxysporum f.sp. cubense, F. solani, F. commune, Rhizoctonia solani, and Setophoma sp.) and two oomycete (Phytophthora cinnamomi and P. palmivora) isolates were tested against two concentrations of BITC (0.1 mM, 0.5 mM) and PGS (0.025 g/mL, 0.05 g/mL) and measured for growth suppression after incubation for 48 hours. Seven out of eight isolates reached 100% suppression of mycelia growth when using 0.5 mM BITC, and six out of eight isolates showed significant reduction in growth when using 0.05 g/mL PGS. Two isolates (F. commune and P. cinnamomi) were not suppressed by either PGS concentration. Based on observed results, PGS biofumigation has potential for future in-field applications as an alternative control against a range of pathogenic fungi.
