Spray Application of Nonpathogenic Fusaria onto Rice Flowers Controls Bakanae Disease (Caused by Fusarium fujikuroi) in the Next Plant Generation

Abstract

Bakanae disease, caused by Fusarium fujikuroi, is an economically important seed-borne disease of rice. F. fujikuroi is horizontally transmitted to rice flowers and vertically transmitted to the next generation via seeds. The fungus induces typical symptoms such as abnormal tissue elongation and etiolation. Sanitation of seed farms and seed disinfection are the only effective means to control bakanae disease at present; however, the efficacy of these methods is often insufficient. Therefore, alternative and innovative control methods are necessary. We developed a novel method for applying non-pathogenic fusaria as biocontrol agents by spraying spore suspensions onto rice flowers to reduce the incidence of seed-borne bakanae. We visualized the interaction between F. commune W5, a non-pathogenic fusarium, and F. fujikuroi using transformants expressing two different fluorescent proteins on/in rice plants. W5 inhibited hyphal extension of F. fujikuroi on/in rice flowers and seedlings, possibly by competing with the pathogen, and survived on/in rice seeds for at least six months. Importance We demonstrated that a spray-treatment of rice flowers with the spores of non-pathogenic fusaria mimicked the disease cycle of the seed-borne bakanae pathogen Fusarium fujikuroi and effectively suppressed the disease. Spray treatment of non-pathogenic fusaria reduced the degree of pathogen invasion of rice flowers and vertical transmission of the pathogen to the next plant generation via seeds, thereby controlling the bakanae disease. The most promising isolate, F. commune W5, colonized seeds and seedlings via treated flowers and successfully inhibited pathogen invasion, suggesting that competition with the pathogen was the mode of action. Seed-borne diseases are often controlled by seed treatment with chemical fungicides. Establishing an alternative method is a pressing issue from the perspectives of limiting fungicide resistance and increasing food security. This work provides a potential solution of these issues using a novel application technique to treat rice flowers with biocontrol agents.

Genome editing using a versatile vector-based CRISPR/Cas9 system in Fusarium species

“…These isolates were cultured on potato dextrose agar (PDA; 200 g/L potato broth, 0.5% (w/v) glucose, 1.5% (w/v) agar or Nissui Pharmaceutical Co.) or YG agar medium (0.5% (w/v) yeast extract, 2% (w/v) glucose, 1.5% agar) and stored in 25% (v/v) glycerol at − 80 °C. PCR and sequencing analyses were performed using standard procedures 8,15,[35][36][37] . The primers and oligonucleotides used in this study are listed in Table S1.…”

“…Nonpathogenic Fusarium strains are often isolated from asymptomatic crop plants and are capable of colonizing plant roots without inducing any disease symptoms. Recently, a novel technique to control Bakanae disease, caused by F. fujikuroi , using the nonpathogenic F. commune isolate W5 was reported 8 . Spray treatment with W5 reduced pathogen invasion of rice flowers, and W5 was transmitted to the next plant generation via seeds.…”

Various Methods for Controlling the <i>Bakanae</i> Disease in Rice

“…strain NR-L645 reduced bakanae disease incidence to 2-6% [74]. Recently, a non-pathogenic Fusarium commune strain W5 was reported as an effective biocontrol agent for bakanae disease [75]. Hyphal extension of F. fujikuroi was inhibited on/in rice seedlings and flowers by spray application of strain W5, which survived on/in rice seeds for at least 6 months [75].…”

Targeted deletion of three CYP51s in Fusarium fujikuroi and their different roles in determining sensitivity to 14α‐demethylase inhibitor fungicides

“…Prochloraz (N-propyl-N-[2- (2,4,6-trichlorophenoxy) ethyl] imidazole-1-carboxamide), a member of 14⊍-demethylase inhibitors (DMIs), has been widely applied since the late 1990s as the main fungicide controlling RBD. [5][6][7][8] Moreover, this chemical is also extensively applied as a foliar spray to manage Fusarium graminearum on wheat, Rhynchosporium secalis on barley, Magnaporthe oryzae on rice, Colletotrichum spp. on apple, strawberry, banana, and litchi, as a postharvest treatment to control citrus greening and blue mold caused by Penicillium spp., and as a seed treatment to control Fusarium spp.…”