Fruit set and seed traits affected by N-phenyl-phetalamic acid in four grapevine (<i>Vitis vinifera</i> L.) cultivars
Keywords:grapevine cultivars, PPA, auxin synergistic, cluster, berry, seedlessness
Grapes are an important horticultural crop that is popularly consumed in a variety of different forms; the fruit is eaten in at its immature stage, as ripe fruit and dried as raisins and vine leaves are also consumed. Therefore any research on ways to improve production of Iranian grapes in terms of quality and quantity is valuable. The main purpose of this study was to test the use of Phenyl Phetalamic Acid (PPA) to improve fruit set and quality. The experiment was designed as a factorial for four grapevine cultivars; 'Razeghi', 'Askari', 'Sefidaly' and 'Rishbaba' and three concentrations of PPA (0, 500, 1000 mg∙L-1). Treatments were arranged in a completely randomized design with three replications. The experiment was done in the Kashmar vineyard (Khorasan Razavi province) during 2010 spring. PPA treatment was applied by foliar spraying at the stage of 50 % anthesis. Results showed that PPA levels had a significant effect on evaluated cluster traits (weight, length and number) and berry (number, weight, length and diameter). Fruit set index (number of berries per cluster) was 263.11 for 'Sefidaly' followed by 113, 109.89 and 76.11 for 'Askari', 'Razeghi' and 'Rishbaba', respectively. 'Askari' and 'Razeghi' cultivars showed similar and insignificant reactions but their difference was significant compared to 'Rishbaba'. The effect was significant for interactions of traits for cluster, berry and seed except for number of berries per cluster. Based on these results, cluster characters were significantly and positively affected by PPA treatment at the concentration of 1000 mg∙L-1. This concentration increased fruit set by 26.2 % compared to the control in all cultivars except for Askari. The PPA concentration 500 mg∙L-1, observed as the most effective treatment for improved berry characters, provided its non-significant difference with 1000 mg∙L-1. Seed number per berry decreased significantly in 'Askari' and 'Rishbaba' at 500 mg∙L-1, which was considered positive in terms of quality. In summary, results determined that PPA had a positive effect on fruit as an auxin synergist. These improved berry characteristics are hypothesized to occur through a decrease in the dominance of apical buds that would allow more metabolites to be directed to development of fruit clusters, although further research is required.
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