**4. Fruit set and yield**

Webster et al. [27] reported that application of paclobutrazol @ 1.6 g a.i. tree <sup>−</sup><sup>1</sup> in 'Early Rivers' sweet cherry doubled the floral buds per unit shoot length in 1982 and trebled the number in 1983. Both the number of floral buds per fruiting spur and the number of flowers per floral bud increased by 26.8 and 5.6%, respectively. However, Webster and Quinlan [46] applied paclobutrazol to European plum trees and noticed reduction in yield and this effect was partially alleviated by sprays of 75 mg GA3 + 10 mg 2, 4, 5-TP at fruit set. Gaash [28] stated that the application of 1000–4000 ppm of paclobutrazol on 'Canino' apricot cultivar increased the yield. Increased number of vegetative and floral buds in 'Flavorcrest' peach was noticed by Martin et al. [47] by the application of 1.32 g a.i. paclobutrazol. Blanco [30] stated that paclobutrazol increased the average fruit size and yield of 'Crimson gold' nectarines. Stan et al. [48] revealed that foliar and soil application of paclobutrazol enhanced the flower bud formation and fruit set in high density planting of sweet cherry, peach and plum. In avocado, paclobutrazol enhanced the fruit set by increasing the partitioning of dry matter to fruits [49]. Kaska et al. [31] observed that application of paclobutrazol decreased flower bud formation in cherries when applied on the vegetative and reproductive parts. Kuden et al. [33] observed that 250 ppm of paclobutrazol increased the number of fruit buds in 'Canino' and 'Precoce de Colomer' apricot cultivars. Jindal and Chandel [50] reported that the application of paclobutrazol increased fruit set in 'Santa Rosa' plum and they further observed that maximum fruit set was observed by the application of 20 ppm TRIA followed by 500 ppm paclobutrazol. Arzani et al. [51] reported that paclobutrazol application advanced flowering of 5-year-old vigorous 'Sundrop' apricot trees by 2–4 days and also increased the fruit set, final fruit number, crop density and yield efficiency. Pant and Ratan [36] reported maximum number of fruit spurs, bloom per branch and yield with cultar @ 1000 ppm in 'Red Delicious' apple. Increased flowering by paclobutrazol application is because of the fact that paclobutrazol acts as inhibitor of gibberellin biosynthesis which changes the sink-source relationship by reallocating carbohydrate to other organs. Davenport [52] reported that more gibberellins were exported from apple fruit to spurs in biennial bearing cultivars than in regular flowering cultivars, concluding that endogenous gibberellins have inhibitory effect on flowering. Increased flowering by application of paclobutrazol was also reported by Wani [37] in sweet cherry and Pant and Ratan [36] in 'Red Delicious' apple. Application of paclobutrazol initiates flowering in fruit plants by the decrease of gibberellins levels and increase of auxins and cytokinins levels in shoot tip [53]. They also observed that flowering date was advanced slightly with application of paclobutrazol. Similar results were recorded by [8, 54–57] in mango. Carreno et al. [58] reported that the application of paclobutrazol before blooming increased fruit set in grapes. The higher fruit set by paclobutrazol application may be attributed to increased partitioning of dry matter to fruits [49]. Abdel Rahim et al. [54] observed that paclobutrazol application advanced off season flowering of regular bearing mango cultivars, Baladi Abu Zaid (26.7%) and Baladi Burai (30.7%) by almost 60 and 70 days, respectively, as compared to the control. They also reported that the flowering percentage in the paclobutrazol treated trees were 50%, and 100% at 60, and 90 days, respectively for all tested cultivars. Similar results on the positive effects of paclobutrazol on mango

**49**

*Response of Growth Inhibitor Paclobutrazol in Fruit Crops*

flowering were reported in many tropical and subtropical regions of the world [16,

obtained in treatment 750 ppm paclobutrazol +2 summer prunings in comparison to control in Red Delicious apples. Paclobutrazol (80 ml/tree) produced earlier flowers (125.79 days) with respect to panicle emergence in mango cv. Alphonso compared to control (165.04 days) [59]. Paclobutrazol is effective in enhancing the yield of several horticultural crops as it inhibits gibberellic acid (GA) biosynthesis which changes the sink-source relationship by reallocating carbohydrate to other organs [53]. Huang et al. [60] reported that soil application of paclobutrazol twice during the year 1989 and 1991 in spring at 1.5 g a.i and 0.75 g a.i., respectively increased the yield efficiency twice than control in apple cultivar 'Aki Fuji' (with average

compared with 13.95 kg tree<sup>−</sup><sup>1</sup>

George and Nissen [62] observed that the return bloom was increased in peach in the subsequent season of paclobutrazol application which may result in a large number of small fruit if a large percentage of flowers set. Asin et al. [63] observed that paclobutrazol and root pruning increased return bloom and yield in 'Blanquilla' pear. Asin et al. [39] reported that foliar application of paclobutrazol resulted in highest return bloom in 'Blanquilla' pear. Wani et al. [64] observed that the soil application of paclobutrazol increased the return bloom significantly in Red Delicious apples. Bill [65] noticed that paclobutrazol application increased the average number of flowers per shoot compared to the control in the 2010–2011 seasons. Flower numbers also increased linearly with an increase in paclobutrazol application rate and noticed that paclobutrazol application increased the return bloom. Application of paclobutrazol initiates flowering in fruit plants by the decrease of gibberellins levels and increase of auxins and cytokinins levels in shoot tip. An increase in return bloom is a common response to paclobutrazol treatment and its application has a carryover effect on return bloom as well which has been reported

for various fruit crops, such as peach [66], apple [67] and mango [10].

that application of paclobutrazol @ 0.5, 0.75, 1.0 and 2.0 kg ha<sup>−</sup><sup>1</sup>

Paclobutrazol (PBZ), one such GA inhibitor, is widely used to advance harvest maturity in various fruit crops including mango [68], peach [62] and persimmon [69]. Delayed fruit maturation and increased fruit weight was found in peach by the application of paclobutrazol [70]. Webster et al. [27] reported that application of 1.8 g a.i paclobutrazol per tree of 'Early Rivers' cherry applied at full bloom stage increased the fruit weight. Looney and Mckeller [29] observed that application of 1.15 g paclobutrazol per tree increased weight of individual cherry fruits in the year of application and for the following 3 years. Martin et al. [47] reported

peach increased the size of fruits significantly than control. Blanco [30] stated that paclobutrazol increased the average fruit size of 'Crimson gold' nectarines. Blanco [71] noticed that 2 g a.i. paclobutrazol dissolved in 1 litre of water and pouring the solution around the trunk of 'Crimson Gold' nectarine tree increased the weight of fruit though not significantly. Jindal and Chandel [50] applied paclobutrazol

increased respiration or activation of enzymes or growth promoting substances. Kumar et al. [61] reported that the application of paclobutrazol at 1.0 g in October

was

) which might be due to

in 'Flavorcrest'

55]. Ashraf et al. [43, 44] reported that the highest yield of 101.0 kg tree<sup>−</sup><sup>1</sup>

*DOI: http://dx.doi.org/10.5772/intechopen.92883*

fruit yield of 26.25 kg tree<sup>−</sup><sup>1</sup>

**5. Return bloom**

enhances yield and quality in mango.

**6. Fruit physical characteristics**

*Response of Growth Inhibitor Paclobutrazol in Fruit Crops DOI: http://dx.doi.org/10.5772/intechopen.92883*

flowering were reported in many tropical and subtropical regions of the world [16, 55]. Ashraf et al. [43, 44] reported that the highest yield of 101.0 kg tree<sup>−</sup><sup>1</sup> was obtained in treatment 750 ppm paclobutrazol +2 summer prunings in comparison to control in Red Delicious apples. Paclobutrazol (80 ml/tree) produced earlier flowers (125.79 days) with respect to panicle emergence in mango cv. Alphonso compared to control (165.04 days) [59]. Paclobutrazol is effective in enhancing the yield of several horticultural crops as it inhibits gibberellic acid (GA) biosynthesis which changes the sink-source relationship by reallocating carbohydrate to other organs [53]. Huang et al. [60] reported that soil application of paclobutrazol twice during the year 1989 and 1991 in spring at 1.5 g a.i and 0.75 g a.i., respectively increased the yield efficiency twice than control in apple cultivar 'Aki Fuji' (with average fruit yield of 26.25 kg tree<sup>−</sup><sup>1</sup> compared with 13.95 kg tree<sup>−</sup><sup>1</sup> ) which might be due to increased respiration or activation of enzymes or growth promoting substances. Kumar et al. [61] reported that the application of paclobutrazol at 1.0 g in October enhances yield and quality in mango.

### **5. Return bloom**

Prunus

kaurenoic acid [15, 45].

**4. Fruit set and yield**

attributed to paclobutrazol, which is a triazol that inhibits gibberellin biosynthesis especially three steps in the oxidation of the GA precursors ent-kaurene to ent-

Webster et al. [27] reported that application of paclobutrazol @ 1.6 g a.i. tree <sup>−</sup><sup>1</sup> in 'Early Rivers' sweet cherry doubled the floral buds per unit shoot length in 1982 and trebled the number in 1983. Both the number of floral buds per fruiting spur and the number of flowers per floral bud increased by 26.8 and 5.6%, respectively. However, Webster and Quinlan [46] applied paclobutrazol to European plum trees and noticed reduction in yield and this effect was partially alleviated by sprays of 75 mg GA3 + 10 mg 2, 4, 5-TP at fruit set. Gaash [28] stated that the application of 1000–4000 ppm of paclobutrazol on 'Canino' apricot cultivar increased the yield. Increased number of vegetative and floral buds in 'Flavorcrest' peach was noticed by Martin et al. [47] by the application of 1.32 g a.i. paclobutrazol. Blanco [30] stated that paclobutrazol increased the average fruit size and yield of 'Crimson gold' nectarines. Stan et al. [48] revealed that foliar and soil application of paclobutrazol enhanced the flower bud formation and fruit set in high density planting of sweet cherry, peach and plum. In avocado, paclobutrazol enhanced the fruit set by increasing the partitioning of dry matter to fruits [49]. Kaska et al. [31] observed that application of paclobutrazol decreased flower bud formation in cherries when applied on the vegetative and reproductive parts. Kuden et al. [33] observed that 250 ppm of paclobutrazol increased the number of fruit buds in 'Canino' and 'Precoce de Colomer' apricot cultivars. Jindal and Chandel [50] reported that the application of paclobutrazol increased fruit set in 'Santa Rosa' plum and they further observed that maximum fruit set was observed by the application of 20 ppm TRIA followed by 500 ppm paclobutrazol. Arzani et al. [51] reported that paclobutrazol application advanced flowering of 5-year-old vigorous 'Sundrop' apricot trees by 2–4 days and also increased the fruit set, final fruit number, crop density and yield efficiency. Pant and Ratan [36] reported maximum number of fruit spurs, bloom per branch and yield with cultar @ 1000 ppm in 'Red Delicious' apple. Increased flowering by paclobutrazol application is because of the fact that paclobutrazol acts as inhibitor of gibberellin biosynthesis which changes the sink-source relationship by reallocating carbohydrate to other organs. Davenport [52] reported that more gibberellins were exported from apple fruit to spurs in biennial bearing cultivars than in regular flowering cultivars, concluding that endogenous gibberellins have inhibitory effect on flowering. Increased flowering by application of paclobutrazol was also reported by Wani [37] in sweet cherry and Pant and Ratan [36] in 'Red Delicious' apple. Application of paclobutrazol initiates flowering in fruit plants by the decrease of gibberellins levels and increase of auxins and cytokinins levels in shoot tip [53]. They also observed that flowering date was advanced slightly with application of paclobutrazol. Similar results were recorded by [8, 54–57] in mango. Carreno et al. [58] reported that the application of paclobutrazol before blooming increased fruit set in grapes. The higher fruit set by paclobutrazol application may be attributed to increased partitioning of dry matter to fruits [49]. Abdel Rahim et al. [54] observed that paclobutrazol application advanced off season flowering of regular bearing mango cultivars, Baladi Abu Zaid (26.7%) and Baladi Burai (30.7%) by almost 60 and 70 days, respectively, as compared to the control. They also reported that the flowering percentage in the paclobutrazol treated trees were 50%, and 100% at 60, and 90 days, respectively for all tested cultivars. Similar results on the positive effects of paclobutrazol on mango

**48**

George and Nissen [62] observed that the return bloom was increased in peach in the subsequent season of paclobutrazol application which may result in a large number of small fruit if a large percentage of flowers set. Asin et al. [63] observed that paclobutrazol and root pruning increased return bloom and yield in 'Blanquilla' pear. Asin et al. [39] reported that foliar application of paclobutrazol resulted in highest return bloom in 'Blanquilla' pear. Wani et al. [64] observed that the soil application of paclobutrazol increased the return bloom significantly in Red Delicious apples. Bill [65] noticed that paclobutrazol application increased the average number of flowers per shoot compared to the control in the 2010–2011 seasons. Flower numbers also increased linearly with an increase in paclobutrazol application rate and noticed that paclobutrazol application increased the return bloom. Application of paclobutrazol initiates flowering in fruit plants by the decrease of gibberellins levels and increase of auxins and cytokinins levels in shoot tip. An increase in return bloom is a common response to paclobutrazol treatment and its application has a carryover effect on return bloom as well which has been reported for various fruit crops, such as peach [66], apple [67] and mango [10].

#### **6. Fruit physical characteristics**

Paclobutrazol (PBZ), one such GA inhibitor, is widely used to advance harvest maturity in various fruit crops including mango [68], peach [62] and persimmon [69]. Delayed fruit maturation and increased fruit weight was found in peach by the application of paclobutrazol [70]. Webster et al. [27] reported that application of 1.8 g a.i paclobutrazol per tree of 'Early Rivers' cherry applied at full bloom stage increased the fruit weight. Looney and Mckeller [29] observed that application of 1.15 g paclobutrazol per tree increased weight of individual cherry fruits in the year of application and for the following 3 years. Martin et al. [47] reported that application of paclobutrazol @ 0.5, 0.75, 1.0 and 2.0 kg ha<sup>−</sup><sup>1</sup> in 'Flavorcrest' peach increased the size of fruits significantly than control. Blanco [30] stated that paclobutrazol increased the average fruit size of 'Crimson gold' nectarines. Blanco [71] noticed that 2 g a.i. paclobutrazol dissolved in 1 litre of water and pouring the solution around the trunk of 'Crimson Gold' nectarine tree increased the weight of fruit though not significantly. Jindal and Chandel [50] applied paclobutrazol

in 'Santa Rosa' plum at 125, 250 and 500 ppm once at full bloom and again at pit hardening stage and reported maximum fruit weight of 24.33 g and fruit volume of 21.6 cc in fruits treated with 500 ppm of paclobutrazol. In persimmons, soil drench application of paclobutrazol accelerated ripening by 2–3 weeks [69]. The increase in fruit length and breadth was due to the reason that application of paclobutrazol reduced vegetative growth (sinks) which in turn, increased the partitioning of nutrients and dry matter towards fruits and thereby, increased the fruit size and weight [49]. Greene [72] reported that foliar application of paclobutrazol to Delicious apples produced fruits with higher flesh and less bitter pit, cork spot and senescence breakdown. Wani [37] reported that fruit acidity, vitamin C, percentage of bruised fruits, incidence of pitting and fruit cracking were reduced by the application of paclobutrazol in sweet cherry. Also, the organoleptic rating, total soluble solids, reducing sugars, total sugars and anthocyanin were increased. Pant and Ratan [36] studied the influence of different concentrations of paclobutrazol and chloromequat at 250, 500, 1000 and 5000 ppm on quality of apple cv. Red Delicious and observed that fruit weight and firmness was increased with both growth retardants. In contrast, in strawberries paclobutrazol application rate had no significant effect on fruit firmness [73]. Carreno et al. [58] found that grape berry size increased linearly with an increase in paclobutrazol application rate. Ashraf et al. [43, 44] observed that treatment 750 ppm paclobutrazol +2 summer prunings resulted in significantly improved fruit size (53.15 cm), weight (188.19 g), volume (188.12 cm3 ), colour change (3.40 score), firmness (11.98 kg cm<sup>−</sup><sup>2</sup> ), organoleptic rating in terms of taste (3.14 score), texture (3.24 score), flavour (3.12 score) and total soluble solids (14.47o B) whereas acidity (0.23%) was reduced in comparison to control and other treatments during both the years in apple cv. Red Delicious. The improvement in organoleptic rating of fruits may be attributed to the fact that more metabolites were translocated to the fruits in treated trees with paclobutrazol.
