Effect of gibberellic acid at different phenological stages on the quality of plum

The experiment was conducted at Agricultural Research Institute Tarnab, Peshawar, Pakistan during the year of 2017. Different concentrations of Gibberellic acid (GA3) i.e., 0, 20 and 30 ppm were sprayed at two different phenological stages i.e. at full bloom and after fruit set (80% petal fall) and the results were compared with control treatment. The experiment was laid out in two factors Randomized Complete Block Design with Split Plot arrangement having three replications. The results revealed that treatment of GA3 concentrations at different phenological stages had significant effect on the parameters having high total soluble solids (8.85), low fruit pH (4.49), maximum sugars (9.12 %), low acidity (0.18 %), high sugar: acid ratio (52.01) and high vitamin C content (5.54 mg/100g) with the application of GA3 after fruit set while, low total soluble solids (8.03), high fruit pH (4.86), minimum sugars (8.98 %), high acidity (0.21 %), low sugar: acid ratio (43.43) and high vitamin C content (5.34 mg/100g) were recorded with GA3 application at full bloom. Gibberellic acid at 30 ppm, resulted in highest total soluble solids (9.44), low fruit pH (4.03), maximum sugars (9.16 %), low acidity (0.17 %), high sugar: acid ratio (54.40) and high vitamin C (5.63 mg/100g) while, the lowest total soluble solids (7.23), high fruit pH (5.51), minimum sugars (8.88 %), high acidity (0.22 %), low sugar: acid ratio (40.41) and low vitamin C contents (5.22 mg/100g) were recorded in untreated control trees. From the current investigation it can be concluded that the treatment of GA3 at 30 ppm after fruit set found better in most of quality attributes of plum as compared to control.

In Pakistan, total area under plum cultivation was 7019 hectares (ha) which included 26 ha in Punjab, 2981 ha in Khyber Pakhtunkhwa and 4012 ha in Baluchistan.Total production was 54304 tonnes which represented production of 172, 26269 and 27863 tonnes in Punjab, KP and Baluchistan respectively [8].The plant growth regulators required in small quantities and at low concentrations to carry message from one part to another part of the plant for performing certain actions.Similarly, they are synthesized in one place and go to the other place to perform different functions.Moreover, plant growth regulators improve productivity by changing physiological and biochemical characteristics of a crop through rapid mobility inside plant [9, 10].Gibberellic acid has three important actions which include the ability of an organ to be used as a sink for the nutrients, the increase in synthesis of IAA in plant tissues and acceleration of hydrolytic enzymes synthesis in Aleurone cells [11,12].Gibberellic acid has great effect on plant physiological systems including fruit setting, leaf expansion, germination, breaking dormancy, increasing fruit size, improving fruit quality and many other aspects of plant growth and crop production [13].Gibberellic acid at 30 and 40 ppm was considered effective treatment when applied after berry set which resulted in improving quality of sharad seedless grapes [14,15].In view of these prospective, an attempt has been made to find out the suitable treatment which could improve the quality of plum.Therefore, the present research study "Effect of Gibberellic acid at different phenological stages on the quality of plum" was designed and conducted at Agricultural Research

Study parameters
The following bio-chemical parameters were studied.

Total Soluble Solids (TSS °Brix)
The total soluble solids of 10 fruits randomly selected, were measured by using hand Refractometer, according to method described in [17].The means were calculated.

Fruit pH
Fruit pH was described with the help of electronic pH meter before keeping the electrode of pH meter in plum juice, the pH meter was standardized by pH buffer solution and pH of the plum was determined by taking fruit sample from every treatment in each replication and their average was taken.

Total sugars (%)
Sugars content of 10 randomly selected fruits were determined by analyzing the sample in Food Technology lab, according to method described in [17].The average was counted.

Acidity (%)
Acidity of 10 randomly selected fruits were determined by analyzing the sample in Food Technology lab, according to method described in [17].The average was counted.

Sugar acid ratio
The ratio of sugar and acid was determined by sugar contents divided by acid contents of the fruits.

Vitamin C (mg/100gm)
Vitamin C content of 10 randomly selected fruits were determined by analyzing their sample in Food Technology lab, according to method described in [17].The average was counted.

Statistical analysis
All data were tested by the analysis of variance (ANOVA) for treatment effects on analyzed parameters.Means of the treatments were separated and compared by using the Least Significant Differences at 5% level of significance according to [18].The statistical analysis was performed by using Statistix 8.1 computer statistical Software.

Results and discussion
The results obtained of different parameters are discussed as below.

Sugars (%)
Mean (Table 3) shows that effect of GA3 concentration and phenological stages was found significant for percent sugars while interaction between them was found nonsignificant.Maximum sugars (9.12%) was recorded with GA3 application after fruit set, which was declined to (8.98%) with GA3 at full bloom.The mean data for GA3 concentrations revealed that the maximum sugars (9.16%) was observed with 30 ppm GA3, followed by (9.10%) with 20 ppm GA3, while minimum sugars (   6) revealed that different Gibberellic acid concentrations and phenological stages affected the Vitamin C significantly while their interaction was nonsignificant.Highest Vitamin C (5.54 mg/100g) was measured from the trees sprayed with Gibberellic acid, after fruit set while the lowest Vitamin C (5.34 mg/100g) was recorded at GA3 spray practiced at full bloom.In case of GA3 concentrations the fruits of maximum Vitamin C (5.63 mg/100g) were observed in trees sprayed with Gibberellic acid concentration at 30 ppm followed by (5.48 Introduction Plum (Prunus domestica L.) is a stone fruit of the family Rosaceae, locally known as Alocha and Alobukhara.The fruit develops with seed having a hard shell or stone.The inner part of the ovary wall develops into seed and the outer part into soft flesh [1].Different plum species are originated in different parts of the world such as Prunus domestica (European plum) in Europe, Prunus insititia (Damson plum) in Western Asia, Prunus salicina (Japanese plum) in China, Prunus cerasifera (cherry plum) in Western and Central Asia and Prunus americana (American plum) in North America [2, 3].There are fifteen cultivated species of plum in which Prunus domestica (European Plum) and Prunus salicina (Japanese plum) are commonly grown in Pakistan [4, 5].Plum is a rich source of vitamin A, vitamin C, iron and fibers.It is consumed in fresh, dry, canned, and also preserved into jams and jellies [6, 7].

Table 6 . Mean data for vitamin C (mg/100gm) as affected by Gibberellic acid concentrations and Phenological stages Phenological stages
mg/100g) at 20 ppm concentration while, in control treatment fruits of minimum Vitamin C (5.22 mg/100g) were produced.Vitamin C is an important part of human diet which helps to save the human from many serious diseases as it is a powerful antioxidant [27].Vitamin C was significantly influence by the GA3 concentrations and phenological stages as compared to control.According to Ingle [20] vitamin C increases in 'Nagpur' mandarin with the foliar application of GA3 at 25 ppm compared to control treatment.The results are similar to Saleem [22] who observed that application of GA3 in 'Blood Red' sweet orange has improved Vitamin C contents, and Wahdan [23] who observed that GA3 at 40 ppm after full bloom significantly increased vitamin C contents in mango fruits.Moneruzzaman [30] also reported that Vitamin C contents was significantly increased by GA3 application as compared to control in wax apple.
Majority of parameters are positively affected by phenological stages and had significant variation towards GA3 application.The application of Gibberellic acid at full bloom resulted significantly in maximum total soluble solids,