The Effect of Malformed Fruit Thinning at Different Times on Fruit Yield and Quality of Kiwifruit (Actinidia deliciosa) cv. 'Hayward'

Document Type : Full Paper

Authors

• Rasool Barzegar ¹
• Mahmood Ghasemnezhad ¹
• Bahman Sharifzadeh ²
• Alireza Mehregan Nikoo ³

¹ Department of Horticultural Science and Engineering, Faculty of Agriculture, University of Guilan, Guilan, Iran

² Department of Engineering Sciences, Faculty of East Guilan Technical and Engineering, University of Guilan, Guilan, Iran

³ Department of Food Industry Science and Engineering, Faculty of Agriculture, University of Guilan, Guilan, Iran

Abstract

Keywords

• Ascorbic acid
• Qualitative grading
• taste index
• vine yield

Main Subjects

• Fruit Science

Extended Abstract

Introduction

The production of misshapen fruits in Hayward kiwifruit, due to genetic potential or environmental conditions, is the main factor for reducing exportable and marketable fruits. To solve this problem and uniformity in the produced fruits, it is recommended to thin the malformed fruits immediately after setting. Fruit thinning is one of the most important plant management techniques during the kiwifruit growing period, which enables producers to adjust the amount of the product and, as a result, achieve high fruit yield and superior fruit taste for consumers.

Materials and Methods

This study was conducted as a randomized complete block design with four replications. The experimental treatments included thinning all of the small, flat, fan-shape and misshapen fruits at four different times; 15, 30, 45 and 60 days after fruit set (DAFS) in the whole vine. Fruits were harvested when reached at maturity stage, and characteristics such as fruit yield per vine, fruit grading according to size, fruit firmness, dry matter percentage, soluble solids content, titratable acidity, TSS/TA, pH and ascorbic acid content were measured.

Results and Discussion

The results showed that there is no significant difference between thinned and control vines for fruit yield. Fruit thinning times caused a significant increase in the percentage of extra grade fruits, so that the highest extra fruit percentage was found when fruit thinning carried out 15 days after fruit set (49.01%), which showed an increase of about 25 percent compared to control (24.71%). Different thinning times showed a significant difference in fruit volume, so that the maximum fruit volume was observed in 15 DAFS (89.48 cm³) and the minimum in the control (69.75 cm³). The results of comparing the averages showed that the treatment 15 DAFS had the lowest amount of flesh firmness among the treatments with a rate of 8.73 kg/cm². Also, the highest percentage of dry matter was obtained in the treatment 45 and 60 DAFS (16.62% and 16.15%, respectively) and the lowest amount was observed in the control (15.56%). The highest amount of soluble solids was observed in the 15 DAFS (7.39° Brix) and the lowest amount in the control with malformed fruits (5.84° Brix). The highest amount of titratable acid was in the control with malformed fruits (2.18%), which showed a significant difference compared to other treatments. The taste index (TSS/TA) was at the highest and lowest amount in the 15 DAFS (4.97) and the control with malformed fruits (2.68), respectively. The variance analysis of the pH of fruit juice showed that the effect of different thinning times was significant at the 1% level and the pH decreased during the thinning times. The highest pH was in the treatment 15 DAFS (3.31) and the lowest in the control treatment with malformed fruit (3.08). The highest and lowest amount of ascorbic acid was observed in the control treatment with malformed fruits and the 30 DAFS by 53.99 and 31.36 mg/100 g FW, respectively. The results showed that the fruit yield was not affected by fruit thinning time. Fruit thinning significantly increased the volume of the fruit compared to the control. However, the trend of increasing the fruit volume slowed down with delay in the thinning time of the fruits. This indicates that cell division and cell growth occurred in high amount in the fruit of vines thinned 15 days after fruit set compared to other treatments. Competition between the fruits remained on the tree and other reservoirs for the absorption of photosynthetic substances were also reduced by fruit thining. The thinning of kiwifruit, particularly a few days after fruit formation, enhanced the content of soluble solids in the fruit. This suggests that thinning the fruits shortly after their formation of the fruit increased the rate of accumulation of compounds resulting from carbon assimilation in the fruit, therefor, they reached the harvest stage earlier than other treatments used in this study.

Conclusion

Overall, early fruit thinning; 15 days after fruit set, with increasing extra fruit size and reducing grade 2 and out-of-grade fruit sizes could improve marketable and exportable fruits.