Makoto Shinohara

Microbial mineralization of organic nitrogen into nitrate to allow the use of organic fertilizer in hydroponics

Hydroponics is an excellent technique for the cultivation of vegetable crops and other plants, but organic fertilizers cannot be used in conventional hydroponic systems, which generally use only inorganic fertilizers, because organic compounds in the hydroponic solutions generally have phytotoxic effects that lead to poor plant growth. Few microorganisms are present in hydroponic solutions to mineralize the organic compounds into inorganic nutrients. In this article a novel and practical hydroponic culture method that uses microorganisms to degrade organic fertilizer in the hydroponic solution has been developed. Soil microorganisms were cultured by regulating the amounts of organic fertilizer and inoculum, with moderate aeration. The microorganisms mineralized organic nitrogen via ammonification and nitrification into nitrate at an efficiency of 97.6%. The culture solution containing the microorganisms was usable as a hydroponic solution, and organic fertilizer could be directly added to it during vegetable cultivation. Vegetables grew well in the organic hydroponic system. Organic hydroponics based on this method is therefore a practical tool for the utilization of organic sources of fertilizer.

Suppression of Ralstonia solanacearum bacterial wilt disease by an organic hydroponic system

An organic hydroponic system that we developed has potential to control root diseases including bacterial wilt of hydroponically grown tomato. In inoculation tests with Ralstonia solanacearum during tomato plant cultivation in conventional inorganic hydroponics and in our organic system, many of the tomato seedlings in the conventional system wilted and died, but none of the seedlings in the organic hydroponics wilted or developed any symptoms, suggesting that the organic system can suppress this bacterial wilt disease. Interestingly, a rhizosphere biofilm, formed only on roots in the organic hydroponic system, may be responsible for the suppression of the bacterial wilt.

Effect of corn steep liquor on lettuce root rot (Fusarium oxysporum f.sp. lactucae) in hydroponic cultures

BACKGROUNDnRecent reports indicate that organic fertilisers have a suppressive effect on the pathogens of plants grown under hydroponic systems. Furthermore, microorganisms exhibiting antagonistic activity to diseases have been observed in organic hydroponic systems. This study evaluated the effect of corn steep liquor (CSL) on controlling lettuce root rot disease [Fusarium oxysporum f.sp. lactucae (FOL)] in a hydroponic system. The effect of CSL and Otsuka A (a chemical fertiliser) on the inhibition of FOL in terms of mycelial growth inhibition was tested in vivo.nnnRESULTSnAddition of CSL suppressed FOL infection rates. CSL inhibited FOL infection by 26.3-42.5% from 2 days after starting incubation. In comparison, Otsuka A inhibited FOL growth by 5.5-19.4%. In addition, four of 10 bacteria isolated from the nutrient media containing CSL exhibited inhibition zones preventing FOL mycelial growth.nnnCONCLUSIONSnWe found that CSL suppressed FOL in lettuce via its antifungal and biostimulatory effects. We suggest that activation of beneficial microorganisms present in CSL may be used to decrease lettuce root rot disease and contribute to lettuce root growth.

Organic hydroponics induces systemic resistance against the air-borne pathogen, Botrytis cinerea (gray mould)

Here, we propose that organic hydroponics trigger induced systemic resistance (ISR) in lettuce against air-borne Botrytis cinerea, which causes gray mold. We compared effects of organic and chemical hydroponics, assessed presence of ISR elicitors in the hydroponic nutrient solution, and investigated molecular mechanism of ISR. Organic hydroponics significantly reduced gray mold lesions in lettuce (cultivated hydroponically) and cucumber (cultivated in soil and foliar sprayed with nutrient solution). The 1-aminocyclopropane-1-carboxylic acid synthase gene in lettuce and lipoxygenase and ethylene receptor-related gene in cucumber showed heightened expression, suggesting that the jasmonic acid/ethylene (JA/ET)-signaling pathway was involved in ISR for both crops. Low salicylic acid β-glucoside levels confirmed role of the ISR signaling pathway. ISR in both lettuce and cucumbers indicated that elicitors in organic hydroponics were nonhost-specific and that the JA/ET pathway was activated without microbe–root interaction. Thus, organic hydroponics can be an effective method for both soil-borne and air-borne disease control.

Conversion factor (k factor) for estimation of soil microbial biomass potassium by the chloroform-fumigation extraction method

ABSTRACT The conversion factor, kK, for estimation of microbial biomass potassium (K) by the chloroform-fumigation extraction method was determined for some arable soils: upland field soils under different fertilization conditions, an upland field soil under a greenhouse condition, and a paddy field soil under a flooded condition. The kK value varied with land utilization (paddy or upland) or fertilization (chemical or organic fertilizer). Value of kK was different between paddy field soil (0.28–0.38) and upland field soil (0.41–0.73). This study indicates that the value could be useful for the estimation of microbial biomass K in soil by the chloroform-fumigation extraction method and further investigation of the amounts of biomass K in different types of soils under conditions with varied field managements will be necessary.

Draft Genome Sequence of Rhizobium sp. Strain TBD182, an Antagonist of the Plant-Pathogenic Fungus Fusarium oxysporum, Isolated from a Novel Hydroponics System Using Organic Fertilizer

ABSTRACT Rhizobium sp. strain TBD182, isolated from a novel hydroponics system, is an antagonistic bacterium that inhibits the mycelial growth of Fusarium oxysporum but does not eliminate the pathogen. We report the draft genome sequence of TBD182, which may contribute to elucidation of the molecular mechanisms of its fungistatic activity.