Studies on biological control of fusarium diseases of tomato and spinach by plant growth promoting fungus, Fusarium equiseti

Tomato and spinach are economically important vegetable crops in Japan. Although the continuous commercial production of tomato and spinach has been developed, soil-borne diseases such as Fusarium crown and root rot of tomato (FCRR) caused by Fusarium oxysporum f. sp. radicis-lycopersici (FORL) and Fusarium wilt of spinach (FWS) caused by caused by F. oxysporum f. sp. spinacisae (FOS) are appeared and become the maim limiting factor for their production. In recent years, as for the greenhouse tomatoes, the production has begun to shift from soil cultivation to various hydroponic culture systems such as rock wool system. However, a severe outbreak of FCRR was also occurred in the rock wool system. The most effective method of control Fusarium diseases has been soil disinfection using methyl bromide, but since that caused severe environmental problems its use was outlawed in 2005. Thus, further alternative control measures need to be made available as soon as possible. The objective of this study was to control FCRR and FWS throughout the growing period by plant growth promoting fungus (PGPF), Fusarium equiseti. Six isolates of PGPF, non-pathogenic Fusarium oxysporum, and five isolates of bacteria were tested in hydroponic rock wool systems as potential biocontrol agents of FCRR. PGPF F. equiseti GF191 proved the most effective organism in controlling FCRR. In short-term experiment (71 days after pathogen inoculation), the protection effect of F. equiseti was 100%, higher than those of other antagonists. In long-term experiments (117-140 days after pathogen inoculation), the protection effects of F. equiseti were also high (63-85%). A combination of F. equiseti and biodegradable pots (BPs) was tested for its ability to control FCRR in soil during long-term cultivation. The protection effect of F. equiseti with BPs was 58% 131 days after transplanting when using BPs to grow seedlings. When BPs were used at the time of transplanting to pathogen-infested soil in order to extend the separation time of tomato roots from the pathogen, the protection effects of F. equiseti and BPs further increased, reaching 81 and 87% 149 and 135 days after transplanting, respectively. FORL populations in soil and roots treated with F. equiseti wiyh BPs were lowered during the 135 days after transplanting, being only 0.6 - 31.9% and 4.3 - 16.7%, respectively, compared to those of control. Populations of F. equiseti in soil treated with F. equiseti in BPs were higher than those in soil treated with F. equiseti alone throughout the experiment. BPs were effective in maintaining the population of F. equiseti in rhizosphere soil and in suppressing the multiplication of FORL in roots and soil as they were able to shield plant roots from the pathogen during the early stage of transplanting. FORL populations in stems treated with F. equiseti were reduced by 93.2-99.9% relative to the pathogen-infested control in rock wool system 97-117 days after pathogen inoculation. FORL populations in stems treated with F. equiseti with BPs and F. equiseti only, were reduced by 97.0% and 98.9%, respectively, relative to the pathogen-infested control in soil system 135 days after transplanting. Spore germination was inhibited in stem extracts of F. equiseti-treated plants compared with those of untreated plants. The stem extracts treated with F. equiseti and unchallenged with pathogen inhibited the production of new budding-cells of FORL compared with those of untreated and unchallenged plants, and the rates of budding-cell formation were reduced by 33% throughout the experiment. F. equiseti GF183 was tested for its ability to control FWS in transplanting systems. Spinach plants treated with F. equiseti had less disease than pathogen-control plants in three experiments, and the protection effects were 51.5 - 91.8%. Three applications of F. equiseti which were single application at seeding, single application one day before transplanting, and double application at both seeding and one day before transplanting, were tested to compare the effectiveness against FWS. The single application at seeding and double application at both seeding and one day before transplanting significantly (P<0.05) reduced disease severity by 52.5% and 58.1%, respectively, compared to the pathogen control. The single application one day before transplanting was not effective for controlling FWS. In another experiment, the protective effect of the double application was higher than that of the single application at seeding and the protection effect was 87.3% compared to the pathogen control. FOS populations in roots treated with the F. equiseti were reduced by 85.3%, relative to the pathogen control. The root extracts from spinach plants treated with F. equiseti and unchallenged with pathogen inhibited the production of new budding-cells of FOS compared with those of untreated and unchallenged plants, and the rates of budding-cell formation 3, 5 and 7 days after inoculation were reduced by 19.7%, 24.1% and 30.9%, respectively. Futhermore, the root extracts from spinach plants treated with F. equiseti and challenged with pathogen also inhibited the production of new budding-cells of FOS compared with that of untreated and unchallenged plants 3, 5 and 7 days after inoculation, and the rates of budding-cell formation were reduced by 67.9%, 48.8% and 53.8%, respectively. In the present study, pre-inoculation of tomato and spinach seedlings with F. equiseti not only suppressed the diseases but also reduced pathogen populations in the stems of tomato and roots of spinach. We also observed such inhibitory effects of stem or root extracts from F. equiseti - treated plants on pathogen germination and proliferation, suggesting that F. equiseti might induce physiological changes in the composition of plant extracts. In this study, PGPF F. equiseti could effectively control FCRR both in hydoroponic and soil systems and FWS in soil system. Futhermore, combinations of F. equiseti and BPs or paper pots were more effective for control FCRR and FWS throughout the growing periods of tomato and spinach in field.