Takashi Hosoki

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.

Transformation and regeneration of ornamental kale (Brassica oleracea var. acephala DC) mediated by Agrobacterium rhizogenes

Abstract Transformation and regeneration of ornamental kale (Brassica oleracea var. acephala DC., cultivar ‘Shirohato’) was obtained using Agrobacterium rhizogenes. Hairy roots were induced from inoculated leaf tissue within 2 weeks. These roots grew well by adding Ri plasmid to the hormone-free Murashige-Skoog medium, while adventitious roots from uninoculated tissue stopped growth on the medium. The hairy roots produced adventitious buds when transferred to media supplemented with 5 mg l−1 zeatin plus 0.05 or 0.1 mg l−1 α-naphthaleneacetic acid. The transformation rate was 44%, as determined by the presence of mannopine, one of the opines produced by transformed tissue. Most of the transformants were normal in appearance. After rooting, they were transferred to a porous soil medium and grew well.

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.

Comparative study of Chinese tree peony cultivars by random amplified polymorphic DNA (RAPD) analysis

Random amplified polymorphic DNA (RAPD) analysis was applied to Chinese tree peony cultivars (Paeonia suffruticosa var. spontanea) to clarify their genetic relationships. Of 40 decamer primers tested, 11 produced 92 useful polymorphic DNA bands. Using these bands, 19 cultivars were distinguished and the similarity values among them were calculated. Although the values between cultivars were high, ranging from 0.722 to 0.928, a dendrogram produced by cluster analysis revealed that Chinese cultivars were largely divisible into four groups. These groups did not necessarily coincide with those classified based on flower and leaf types or petal color.

In vitro propagation of herbaceous peony (paeonia lactiflora pall.) by a longitudinal shoot-split method

A procedure for the clonal propagation ofPaeonia lactiflora Pall. cvs. Takinoyosooi and Sarah Bernhardt through shoot tip culture is described. Half strength Murashige and Shoog (1962) medium supplemented with 0.5 mg/l 6-benzylaminopurine plus 1 mg/l gibberellic acid promoted formation and growth of axillary buds. Continuous shoot multiplication was achieved by vertically splitting the shoot axis and subsequent division of elongated axillary shoots every 36 days. High frequency (57–100%) of rooting was obtained on paper-bridge liquid medium supplemented with 1 mg/l indole-3-butyric acid. Half of the rooted plantlets were established on porous soil. Thus, 700 and 300 plants of cv. Takinoyosooi and Sarah Bernhardt could be theoretically obtained from a single bud in one year.

Shoot regeneration from petioles of coral bells (Heuchera sanguinea Engelm.) cultured in vitro, and subsequent planting and flowering ex vitro

SummarySuccessful shoot regeneration from petioles, leaves, and petioles with leaves cultured in vitro is reported in Heuchera sanguinea. Petioles or petioles with leaves regenerated more shoots than leaves alone. For culture, the optimum hormonal concentrations were 0.19 μM α-naphthaleneacetic acid combined with 0.44 or 4.4 μM benzyladenine in Murashige and Skoog-based (MS) medium: the regenerating rate and the number of shoots per explant were 60% and 8.6–9.7, respectively. Histological study on petiole culture showed dividing cell clusters including vascular tissues after 1 wk, callus including several dividing cell clusters at the periphery after 3 wk and then apical meristems with immature leaves after 5 wk. Rooting from the regenerated shoots was highest (95%) on MS medium containing 4.9 μM indole-3-butyric acid. Seventy-three percent of rooted plants were successfully acclimatized in pots. When they were cultured in the field, the plants grew and most flowered the following year over winter.

MICROPROPAGATION OF SCABIOSA CAUCASICA BIEB. CV. CAUCASICA BLUE

SummaryMicropropagation of Scabiosa caucasica cv. Caucasica Blue was achieved by culturing, separating axillary and adventitious shoots, or node sectioning on Murashige and Skoog (MS) medium supplemented with benzyladenine (BA). The highest frequency of adventitious shoots regenerated from nodal or internodal explants and leaf blade (with or without petiole) appeared to occur on MS medium with 4.4 and 18 μM BA, respectively. Addition of 0.19 or 1.9 μM α-naphthaleneacetic acid to the BA-containing medium promoted callus formation and reduced shoot organogenesis. During micropropagation, shoot nodal explants derived from in vitro shoots cultured on MS medium supplemented with 4.4 μM BA yielded 8.9 shoots per explant within 40 d after culture initiation.

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).