Experimental Site The experiment was carried out at the Agroforestry farm and Environmental Science, Hajee Mohammad Danesh Science and Technology University, Dinajpur. The experiment was conducted from November 2014 to March 2015.
Plant Material Eight years old guava cv. Mukundapuri was chosen in the present investigation. The fruits of this cultivar are pear to round shape, nearly smooth and medium in sized. Crop husbandry and crop protection measures were taken according to Bangladesh Agricultural Research Institute (BARI) recommendation.
Application of Plant Growth Regulators Individual flowers were tagged on the day of anthesis and in the absence of hormone application the fruits were considered to be formed from natural pollination. To obtain parthenocarpic fruits, anthers were emasculated approximately 24 h before anthesis to prevent self-pollination, and flowers were then sprayed with the PGR to ensure fruit set. A hand sprayer was used to apply PGR and the flowers were tagged to show the date of application of the PGR. Application of PGR was performed in the morning between 8 to 9 am.
Design of the Experiment Two plant growth regulators: Gibberellic acid (GA) and β-naphthoxyacetic acid (NOA) were used. The concentration i.e., 200 ppm GA, 250 ppm GA, 50 ppm βNOA and 80 ppm β-NOA were applied, while naturally pollinated fruits were the control. The experiment was arranged in the randomized complete block design with four replications. The total numbers of plants were 4, representing 4 replications. For each treatment, 15 fruits were treated as per the experimental design. After fruitset, the diameter and length of the individual fruit were recorded at 30, 60 and 90 days after anthesis (DAA), and also at harvest. To avoid competition among fruits on the same branch only 2 to 3 fruits were allowed to set.
Harvest The fruits were harvested at their harvest maturity stage when those were green and medium hard in texture. Fruits were harvested at 110 days after anthesis, starting from mid February until mid March. Length of Fruit The length of fruit was recorded individually from the proximal end of the fruit (site of the calyx) to the distal end (point of abscission of the style) using a meter rule and recorded in centimeters. Length was measured at 30, 60, 90 days after anthesis and at harvest too. Fruit Diameter The diameter of individual fruit was recorded across the widest part of the fruit using an electrical digital caliper (ROHS, Germany) at 30, 60, 90 days after anthesis and at harvest. Weight of Fruits Individual fruit weight was measured in grams at harvest using an electronic balance (G & G, T100, Germany). TSS Fruits were peeled, and the pericarp (skin) and mesocarp tissues (flesh) were separated. Mesocarp tissue was then gently squeezed and a few drops of juice were used to determine the total soluble solids (TSS) with a digital refractometer (Hanna Instruments, Romania).
Analysis of Ascorbic Acid Ascorbic acid content (mg 100 g-1 fresh weight) was determined by the spectrophotometric procedure of Bajaj and Kaur (1981). The absorbance at 760 nm was measured with a UV/VIS spectrophotometer (PG Instrument Ltd. Model T60, UK). Ascorbic acid concentration was quantified using the standard curve of L-ascorbic acid and expressed as mg 100 g-1 fresh weight.
Analysis of Total Phenols: Total phenolic compounds were quantified using the Folin–Ciocalteu reagent (FC) and the colorimetric method of Singleton and Rossi (1965). Extraction was performed according to Velioglu et al. (1998) using a homogenizer (VELP Scientifica, Europe). The absorbance was measured at 765 nm using a UV/VIS spectrophotometer (PG Instrument Ltd. Model T60, UK). Phenol content was estimated from a standard curve of gallic acid and results were expressed as the mg of gallic acid equivalents (GAE) of 100 g-1 fresh fruit.
Statistical Analysis One factor analysis of variance (ANOVA) was conducted for all variables using the Statgraphics Plus Version 2.1 statistical program (STSC, Inc., 1987). The means were compared using Fisher’s Least Significant Difference (LSD), while the Student t-test was used to compare pairs of means.