Toshiki Asao

Effects of temperature and photoperiod on phytotoxic root exudates of cucumber (Cucumis sativus) in hydroponic culture

In order to elucidate the effects of temperature and photoperiod on the quality and quantity of plant root exudates, a Japanese cucumber (Cucumis sativus, cv. Shougoin-Aonaga-Fushinari) was grown hydroponically in growth chambers under controlled temperature and photoperiod conditions with or without the addition of activated charcoal (AC) to the nutrient solutions. Fresh AC was used to trap the organic compounds exuded from cucumber roots every two weeks. Cucumber plants without AC were severely retarded in root growth and in the accumulation of dry matter, especially at high temperature and long photoperiod, compared to those with AC. The growth inhibitors, adsorbed on the AC or accumulated in the nutrient solution without AC, were extracted by organic solvents and analyzed by GC-MS. Benzoic acid and its derivatives, cinnamic acid derivatives, and fatty acids were identified. The rate of root exudation in vegetative and reproductive stages for some of these organic acids increased with the elevation of temperature and the elongation of photoperiod, and the mean rate was two or more times higher than the minimum exudation at low temperature with short photoperiod. Some of the identified compounds significantly inhibited the germination and/or root growth of lettuce and cucumber.

Autotoxicity of root exudates from taro

Abstract Effects of chemicals exuded from taro roots in hydroponic culture on the growth and yield of taro were investigated. Taro plants grown in the nutrient solution without activated charcoal (AC) had significantly lower leaf numbers (90%) and shoot dry weights (67%) than those grown with AC. The corm yield per plant also decreased by 34% in the nutrient solution without AC. The allelochemicals adsorbed by the AC were extracted and analyzed by gas chromatograph coupled to a mass spectrometer (GC–MS). The identified compounds included lactic acid, benzoic acid, m-hydroxybenzoic acid, p-hydroxybenzoic acid, vanillic acid, succinic acid and adipic acid. The allelopathic potentials of these compounds were evaluated with taro plantlets as a test material. Results indicated that almost all the compounds were inhibitory to the growth of taro plantlets. But benzoic acid was the strongest inhibitor. All of these suggest that root exudates from the taro plant itself is one of the causes of problems in taro culture.

Autotoxicity of root exudates from strawberry in hydroponic culture

Summary The effects of exudates from strawberry roots on the growth of strawberries in hydroponic culture were investigated. Vegetative and reproductive growth in nutrient solution without activated charcoal (–AC) was lower than with AC (+AC). The root exudates adsorbed by the AC were extracted and analysed in a gas chromatograph coupled to mass spectrometer (GC-MS). The compounds identified included lactic, benzoic, succinic, adipic and p-hydroxybenzoic acids. The allelopathic potential of these compounds were evaluated on strawberry plantlets. The results indicated that benzoic acid significantly inhibited the fresh weights of shoots, the dry weights of shoots and roots, and the maximum root length, at all concentrations tested. These results suggest that root exudates from strawberry plants may cause growth inhibition, and that the greatest inhibition was caused by benzoic acid.

Mitigation of cucumber autotoxicity in hydroponic culture using microbial strain

Effects of a microbial suspension (bacterial strain) on the autotoxicity of cucumber plants grown by hydroponic culture with or without addition of 2,4-dichlorobenzoic acid (DCBA) to the nutrient solution were investigated. The growth and fruit yield of cucumber plants significantly decreased on the addition of DCBA (10 μmol/l) to the nutrient solution. The growth, however, recovered upon addition of the microbial strain. The yield reduction of cucumber plants for non-renewal of the nutrient solution was also checked when the strain was added to the nutrient solution at 2 weeks after the initial harvest. This result suggested that microorganisms, if added to the nutrient solution at the reproductive growth stage of cucumber, can catabolize autotoxic substances from root exudates into nontoxic substances and this results in an increase in fruit yield of cucumber plants.

Influence of Soilless Culture Substrate on Improvement of Yield and Produce Quality of Horticultural Crops

Soilless culture is the modern cultivation system of plants that use either inert organic or inorganic substrate through nutrient solution nourishment. Possibly it is the most intensive culture system utilizing all the resources efficiently for maximizing yield of crops and the most intense form of agricultural enterprises for commercial production of greenhouse vegetables [1-3]. Several studies suggested soilless culture in the greenhouse as an alternative to tradi‐ tional field production for high-value vegetable crops [4-7]. This protected cultivation system can control the growing environment through management of weather factors, amount and composition of nutrient solution and also the growing medium. Therefore, quality of horti‐ cultural crops grown through soilless culture improves significantly compared to conventional soil culture [8,9]. This artificial growing system provides plants with mechanical support, water and mineral nutrient for higher growth and development. Over the years, hydroponics has been used sporadically throughout the world as a commercial means of growing both food and ornamental plants. Now at days, it has also been used as the standard methodology for plant biological researches in different disciplines [10]. Various modification of pure solution culture has been taken place over time throughout the world. Primarily, gravel or sand was used in soilless culture system to provide plant support and retain mineral nutrient and water. Afterward, several substrates have been evolved due to their unique properties for holding moisture, aeration, leaching or capillary action, and reuse potentiality. Soilless growing media are easier to handle and it may provide better growing environment (in terms of one or more aspects of plant growth) compared to soil culture [11,12]. Organic substrates includes sawdust, coco peat, peat moss, woodchips, fleece, marc, bark etc. whereas, inorganic substrate of natural

Autotoxicity in Vegetables and Ornamentals and Its Control

Allelopathy comes from the Latin words allelon ‘of each other’ and pathos ‘to suffer’ refers to the chemical inhibition of one species by another. The ‘inhibitory’ chemical is released into the environment where it affects the development and growth of neighboring plants. Allelopathic chemicals can be present in any parts of an allelopathic plant. They can be found in leaves, flowers, roots, fruits, or stems and also in the surrounding soil. Around 300 BC, the Greek botanist Theophrastus was possibly the first person to recognize the allelopathic properties of plants when he observed and recorded that chickpea plants exhausted the soil and destroyed weeds. Later, Pliny the Elder, a Roman scholar and naturalist, noted that walnut trees were toxic to other plants, and that both chickpea and barley ruined crop lands for maize. The term allelopathy was first introduced by a German scientist Molisch in 1937 to include both harmful and beneficial biochemical interactions between all types of plants including microorganisms. Rice (1984) reinforced this definition in the first monograph on allelopathy. Research on the recognition and understanding of allelopathy has been well documented over the past few decades (Rice, 1984; Rizvi & Rizvi, 1992). These include the symptoms and severity of adverse effects of living plants or their residues upon growth of higher plants and crop yields, interactions among organisms, ecological significance of allelopathy in plant communities, replanting problems, problems with crop rotations, autotoxicity, and the production, isolation and identification of allelochemicals in agro ecosystem.

Low Potassium Content Vegetables Research For Chronic Kidney Disease Patients in Japan

1Department of Agriculture, Faculty of Life and Environmental Science, Shimane University, 2059 Kamihonjo, Matsue, Shimane 690-1102, Japan 2Department of Environmental Science, Bangabandhu Sheikh Mujibur Rahman Agricultural University, Gazipur 1706, Bangladesh 3Olericulture Division, Horticulture Research Center, Bangladesh Agricultural Research Institute, Gazipur 1701, Bangladesh 4Faculty of Home Economics, Otsuma Women’s University, Chiyoda-ku, Tokyo 102-8357, Japan 5Faculty of Medicine, Shimane University, 89-1, Izumo 693-8501, Japan 6Faculty of Agriculture, Tokyo University of Agriculture and Technology, Fuchu 183-8509, Japan

Production of Low-Potassium Content Melon Through Hydroponic Nutrient Management Using Perlite Substrate

Chronic kidney disease patients are restricted to foods with high potassium content but our daily diets including melon are rich in potassium. Therefore, we investigated the production of low-potassium melon through hydroponic nutrient management in soilless culture using perlite substrate during autumn season of 2012, 2014 and spring season of 2016. In the first study, melon plants were supplied with 50% standard ‘Enshi’ nutrient solution until first 2 weeks of culture. In 3rd and 4th week, amount of applied potassium was 50, 75, 100, and 125% of required potassium nitrate for each plant per week (based on our previous study). It was found that, melon plants grown with 50% of its required potassium nitrate produced fruits with about 53% low-potassium compared to control. In the following study, four cultivars viz. Panna, Miyabi shunjuukei, Miyabi akifuyu412, and Miyabi soushun banshun309 were evaluated for their relative suitability of low-potassium melon production. Results showed insignificant difference in fruit potassium content among the cultivars used. Source of potassium fertilizer as potassium nitrate and potassium sulfate and their restriction (from 1 or 2 weeks after anthesis) were also studied. There were no influences on fruit potassium content and yield due to sources of potassium fertilizer and restriction timings. In our previous studies, it was evident that potassium can be translocated from leaves to fruits at maturity when it was supplied nutrient without potassium. Thus, we also studied total number of leaves per plant (23, 24, 25, 26, and 27 leaves per plant). It was evident that fruit potassium, yield, and quality were not influenced significantly due to differences in number of leaves per plant. These studies showed that restriction of potassium nitrate in the culture solution from anthesis to harvest could produce melon fruits with low-potassium (>20%) content compared to potassium content of greenhouse grown melon (340 mg/100 g FW). Quality testing and clinical validation of low-potassium melon also showed positive responses compared to greenhouse grown melon.

Effects of chitosan treatments on seedling growth, chitinase activity and ¯ower quality in Eustoma grandi¯orum (Raf.) Shinn. `Kairyou Wakamurasaki'

Summary The effects of chitosan treatments on seedling growth, chitinase activity, triphenyl tetrazolium chloride (TTC) reducing activity and flower quality of Eustoma grandflorum (Raf.) Shinn. ‘Kairyou Wakamurasaki’ were investigated. The application of a soil mix of chitosan (1% w/w) at sowing remarkably enhanced growth, whereas coating seed with 1% chitosan in lactate was rather ineffective. Chitinase activity and TTC reducing activity following treatment with chitosan soil mix were significantly higher compared with the untreated control or coating seed treatment. After transplanting, the chitosan soil treatment resulted in greater shoot length, stem diameter, weight of cut-flowers and increase in number of flowers than in the untreated control. Chemical name used: poly-(1Õ4)-b-0-glucoseamine (chitosan).

Differences in the Occurrence of Blossom-end Rot in Cherry and Large Fruit Tomatoes

ミニトマトと大型トマトを供試して, 高温期と低温期において水耕培養液濃度を変えて栽培することによって, 尻腐れ果発生の差異を比較するとともに, 尻腐れ果発生初期の小果柄の離層部周辺の維管束の様子を観察した.1.ミニトマトでは低温期には尻腐れ果が全く発生しなかったが, 高温期には16～18%の発生が見られた.大型トマトでは低温期, 高温期いずれも高濃度培養液で栽培すると多くの尻腐れ果が発生した.2.ミニトマトの果実縦径当たりの果実生長量は栽培時の気温や培養液濃度によって変化しなかったが, 大型トマトのそれは高温期において高濃度より低濃度の培養液で栽培するとやや大きかった.3.尻腐れ果発生初期の小果柄の離層部周辺の維管束を正常果のそれと比較した.ミニトマトでは両者に大きな差異はみられなかったが, 大型トマトでは維管束数が減少し, かつ導管の径が小さくなっていた.