Shigeto Tominaga

High chromosomal variability of mandarins (Citrus spp.) revealed by CMA banding

Fluorochrome staining with chromomycin A3(CMA) was used to characterize and compare the CMA banding patterns of chromosomes in 17 accessions of mandarins (Citrus spp.). All accessions had 2n = 18 chromosomes. These chromosomes were classified into six types based on the number and position of CMA positive bands; A: two telomeric and one proximal band, B: one telomeric and one proximal band, C: two telomeric bands, D: one telomeric band, E: without bands, F: one proximal band. Each accession possessed two to five types of chromosomes, and showed unique CMA banding patterns. Type D and E chromosomes were predominant in all accessions. Their numbers were generally higher in Chinese and Indian mandarins. Type F chromosome was present only in some mandarins originating in Japan, which could thus be distinguished from mandarins originating in other areas. This study is the first report of type F chromosome in citrus. The Vietnamese mandarins we studied were the only one shaving type A, B, C, D and E chromosomes.

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.

The effect of time of girdling on carbohydrate contents and fruiting in Ponkan mandarin (Citrus reticulata Blanco)

Seasonal changes of sucrose, glucose and fructose were monitored in the bark (phloem) and xylem in Ponkan mandarin (Citrus reticulata Blanco cv. Yoshida). Sucrose was the most abundant sugar. A decline in bark sucrose content coincided with the major fruit abscission period. Stem girdling was carried out at anthesis (May), end of June drop (July), start of autumn (September) and in early winter (November). Girdling in July and September slightly increased leaf sugar content. At peak starch content (in winter), the September girdled treatment had the highest starch content. May girdling increased fruit set significantly and also improved fruit color. July and September girdling improved fruit size, but late girdling (November) had no effect on fruit size. Flowering and fruit set in the following year were closely related to starch content in the previous winter: they were highest in September girdled trees and lowest in May girdled trees.

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.

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.