Fruit Tree Physiology

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Prunus

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**Chapter 3**

**Abstract**

and anaerobic conditions.

**1. Introduction**

Response of Growth Inhibitor

Paclobutrazol (PBZ; IUPAC name: (2RS, 3RS)-1-(4-chlorophenyl)-4, 4-dimethyl-2-(1H-1, 2, 4-triazol-1-yl) pentan-3-ol) is a triazol derivative and an antagonist of gibberellins. It has been shown to inhibit shoot growth in various perennial fruit trees. Paclobutrazol application reduced the number of shoots, transforming trees into a more desirable, spur-type growth habit as the vegetative sink was reduced. This compound induces an early and intense flowering, diminishing vegetative growth and reducing the extension of buds, allowing for ripening and the initiation of apical buds inflorescence. Besides, it also increases fruit set, the years following application as a carryover effect. An increase in return bloom is a common response to paclobutrazol treatment and has been reported for various fruit crops. Paclobutrazol is widely used to advance harvest maturity in various fruit crops and it improves fruit quality in terms of accelerated colour development, delayed and synchronized fruit maturation and control of preharvest fruit drop. It is known to improve fruit physical and fruit chemical characteristics. Fruit calcium is increased for 2–3 years due to carry over effect. It helps in the maintenance of better fruit quality during storage and influences nutrient uptake in various fruit crops including stone fruits. It has been characterized as an environmentally stable compound in soil and water environments with a long half-life under both aerobic

**Keywords:** fruit set, paclobutrazol, flowering, shoot growth, fruit quality

One of the most important elements in fruit orchard management is growth control. Excessive vigour reduces light penetration, yield, fruit quality and an increase in cost of pruning and pest control [1]. On the other hand, many cultivars may set very large number of fruits with unacceptably smaller size and often serious reduction in return bloom and fruit set may occur in the following year leading

to biennial bearing. About 20–80% of the fruit which initially sets drop-off from the tree during various stages of development. Thus, various plant growth regulators are used for the control of vegetative growth, flowering of young trees, thinning of flowers and fruits, delaying fruit abscission, regulation of fruit ripening and improvement of fruit production and quality in bearing trees [2]. Various chemicals are used in horticulturally advanced countries to reduce the amount of pruning. Among the various growth control chemicals tested, paclobutrazol (PB) is one of the most successful and widely used in fruit trees that can retard tree

Paclobutrazol in Fruit Crops

*Naira Ashraf and Moieza Ashraf*
