Shuichi Iwahori

Retardation of abscission of citrus leaf and fruitlet explants by brassinolide

Brassinolide (BR), a novel plant growth-regulating steroidal lactone, markedly retarded the abscission of leaf explants of Calamondin (Citrus madurensis Lour.), when dissolved in water and fed through the petiole. BR was effective at concentrations as low as 0.021 μM, and showed a stronger effect than IAA which also retarded abscission. Trifluoperazine (TFP), an inhibitor of the calmodulin-calcium complex, accelerated abscission, and this acceleration could be counteracted by a simultaneous addition of IAA or BR, the effect of IAA being stronger. BR in lanolin applied to the cut surface of the leaf blade of the explant showed a weaker abscission-retarding effect than that applied in water via the petiole. BR and IAA also markedly retarded the abscission of fruitlet explants of Calamondin.

Chemical thinning of ‘satsuma’ mandarin (citrus unshiu marc.) fruit by 1-naphthaleneacetic acid: Role of ethylene and cellulase

Abstract Experiments were conducted to find the effects of 1-naphthaleneacetic acid (NAA) on fruit thinning of ‘Satsuma’ mandarins, and to see whether it affected ethylene production and cellulase activity at the abscission zone. NAA at 300 p.p.m. sprayed 25 days after full bloom was found to thin fruit causing a 30% increase in fruit drop in 1973. The following year, however, the effect of spraying was not significant because the overall percentage of fruit set was low. Cellulase activity of abscission zones of NAA-treated fruit showed considerably increased values in 1973, whereas in 1974 cellulase activity of control and NAA-treated fruit showed similar high values reflecting a higher fruit drop from control trees. Yellow, ready-to-abscise fruit from NAA-treated and from control trees produced higher amounts of ethylene than did apparently healthy green fruit from both treated and control trees. Essentially NAA caused no leaf abscission nor any increase in cellulase activity in abscission zones. Ethylene production from the leaves also remained low. Spraying 500 p.p.m. ethephon (2-chloroethylphosphonic acid) caused severe leaf fall, markedly increased cellulase activity in abscission zones and ethylene production. The mechanism of fruit thinning by NAA is discussed in relation to the role of ethylene and cellulase.

Increase in first-flush flowering of ‘Meiwa’ kumquat, Fortunella crassifolia Swingle, trees by paclobutrazol

Abstract Paclobutrazol (PP 333) ((2RS, 3RS)-1-(4-chlorophenyl)-4,4-dimethyl-2-(1,2,4-triazol-1-yl-)pentan-3-ol) sprayed at 1000 mg l −1 on 23 April and also on 8 May, during the flower bud induction stage, remarkably increased the first-flush flowering of ‘Meiwa’ kumquat, Fortunella crassifolia Swingle. Flowering of the second flush was decreased by the paclobutrazol treatment. As a result, the total number of first- and second-flush flowers was also somewhat decreased by the treatment, although it was not significantly different from the control. The number of newly emerged shoots and new leaves was not affected by the treatment. Paclobutrazol slightly decreased the length of the shoots. Applications of 3000 mg l −1 daminozide, on the same dates, slightly decreased first-flush flowering, increased second-flush flowering, and somewhat reduced the length of the shoot. It was concluded that paclobutrazol induced flower bud differentiation. Paclobutrazol may be used commercially to increase early flowering of kumquat trees.

Alleviative effects of calcium acetate on defoliation and fruit drop induced by 2-chloroethylphosphonic acid in citrus.

Abstract Experiments were conducted to evaluate the effects of calcium acetate on defoliation and fruit drop of ponkan ( Citrus reticulata Blanco) and Meiwa kumquat ( Fortunella crassifolia Swingle) trees treated with 2-chloroethylphosphonic acid (ethephon). Ethephon at 200 or 300 p.p.m. caused about 20% defoliation of ponkan trees, while this defoliation was materially alleviated by an addition of 0.05 M calcium acetate to the ethephon solution. Acceleration effects on fruit color did not differ with ethephon or ethephon + calcium acetate treatments. Ethephon at 400 p.p.m. caused about 30% fruit drop in kumquat trees, and an addition of 0.05 M calcium acetate to the solution almost completely prevented the fruit drop. Fruit color of kumquat was most advanced by the use of ethephon alone, and the addition of calcium acetate decreased the effect slightly.

Ethychlozate accelerates colouration and enhances fruit quality of ponkan, Citrus reticulata Blanco

Abstract Experiments were conducted for six consecutive years to study the effects of ethychlozate (ethyl 5-chloro-1H-3-indazolylacetate) on the acceleration of colouration and enhancement of fruit quality of ponkan, Citrus reticulata Blanco. Spraying 67–200 mg 1 −1 ethychlozate twice at 15-day intervals between 65 and 125 days after full bloom enhanced colouration and Brix considerably. Citric acid contents were also increased. The best result was obtained when spraying was carried out at 90 days and again at 105 days. The treatment induced a deeper orange colour. This resulted in a higher percentage of fruit with more advanced colour at harvest in the middle of December. These findings are discussed in relation to the commercial application of the method on ponkan to allow an earlier harvest.