Exogenous Application of Plant Growth

Regulators Enhances Color and

Anthocyanin Content of Cherry Fruits

E.G. Nagpala, M. Noferini, L. Piccinini, G. Fiori, S. Vidoni, E. Bonora and G. Costa*

Department of Agricultural Sciences, University of Bologna,

Viale Giuseppe Fanin 46, 40127, Bologna, Italy

INTRODUCTION

Plant growth regulators (PGRs) are known to improve many quality aspects of fruit crops. Aside from improving the external quality parameters of fruits with PGRs, possibilities in increasing other traits (i.e antioxidative property) of fruits are also being investigated.

Both abscisic acid (ABA) and 1-aminocyclopropane-1-carboxylic acid (ACC) are involved in the synthesis of ethylene. In addition, the two PGRs also play a role in physiological processes such as the increase of soluble solid .

In the present study, the effects of exogenous applications of the two PGRs on the overall quality of cherry (Prunus avium L.) fruits were investigated. Indications of an enhanced fruit color as an effect of ABA and ACC were examined in relation to the fruit’s anthocyanin content to establish the antioxidative property of darker cherry fruits. The best application time of ABA and the optimum dosage of ABA and ACC were also determined. Differences on the effects of treatments were described using Cherry-Meter, a portable vis/NIR device that provides information on the ripeness of the fruit through the index of absorbance difference (IAD). Higher IAD value indicates a more advanced ripening stage.

MATERIALS & METHODS

The study was carried in the experimental station of the Department of Agricultural Sciences of the University of Bologna in Italy using seven-year old trees of Prunusavium ‘Lala Star’ grafted on Gisela 6. Three experiments were conducted to determine the effects of ABA and ACC on cherry fruits:

ABA application timeABA were applied on cherry trees at three different times: before veraison, during veraison, and after veraison at 300 ppm.

ABA optimum dosageAside from the concentration used for the application time trial (300 ppm), ABA was also applied on cherry trees at 400 and 500 ppm during veraison.

ACC optimum dosageFour treatments of ACC were tested on cherry fruits: 200 ppm, 400 ppm, 500 ppmand 200 ppm with repeated applications. Application of treatments were limited to branches only.

Diameter and IAD of cherry fruits were continually measured throughout the growing season. Incidence of phytotoxicity was also closely monitored. At harvest (69 days after full blomm (DAFB)), quality parameters such as fruit weight, firmness, elasticity, soluble solid content (SSC), titratable acidity (TA), pH, chroma and anthocyanin content were evaluated according to treatment.

The study was laid out in a Randomly Complete Block Design (RCBD). Data gathered were analyzed using the One-way Analysis of Variance. Differences between means were compared using the Duncan’s Multiple Range Test (DMRT) at 5% level of significance. Statistical analyses were performed using STATISTICA, version 7, StatSoft, Inc. (2004).

CONCLUSION

In summary, ABA and ACC were found to be effective in enhancing the color and functional properties of cherry fruits as reflected by the fruit anthocyanin content. The best time to apply ABA is during and after veraison taking into consideration the SSC, color and anthocyanin content of the fruits. Meanwhile, the optimum dosage of application for ABA is at 300 ppm. ABA applied at 400 ppm and 500 ppm caused phytotoxicity on the cherry trees and eventually, did not improve fruit quality in general. In the case of ACC, the optimum dosage is 200 ppm, applied during veraison with repeated applications on the seventh and 14th day after veraison.

Future studies to measure the ethylene production along the course of ripening of ABA and ACC treated fruits to determine the extent of the influence of the PGRs on the synthesis of ethylene could be conducted.

ACKNOWLEDGEMENT

Research funded by Misura 124 Apulia Region under the FRUTTINOVA: Ciliegia e Ortofrutta tipica. Due acknowledgement is also given to Valent Biosciences for providing the ABA and ACC formulates.

Table 1. Cherry fruits treated with 300 ppm ABA at different application times with their corresponding quality parameters. Means for the same quality parameter followed by the same letter do not vary significantly (p=0.05, DMRT).

ALMA MATER STUDIORUM

UNIVERSITÀ DI BOLOGNA

Figures1-3.The Cherry-Meter (top, left); IAD of ‘Lala Star’ monitored with the Cherry-Meter (top, right); application of treatments to the cherry trees (bottom).

RESULTS

In general, both PGRs significantly influenced the color of cherry fruits as reflected through the IAD and chroma. Darker fruits have higher IAD readings and lower chroma values, indicating a more intense color. This is further supported by the anthocyanin content measured from the fruits. Darker fruits consistently have higher anthocyanin content. Meanwhile, SSC were also noted to be higher in specific treatments against the control. Other quality parameters such as fruit diameter, weight, firmness, elasticity, TA and pH were not significantly influenced by ABA and ACC.

Fruits treated with ABA during and after veraison have higher IAD compared to the control and fruits treated before veraison. Meanwhile, significant influence of ABA on SSC is more evident on the fruits treated during and after veraison as compared tocontrol fruits and fruits treated before veraison. Chroma was found to be significantly lower in fruits treated during and after veraison compared to the control treatment and fruits treated before veraison in both upper and lower parts of the plant (Table 1).

Table 2. Cherry fruits as influenced by different dosages of ABA (400 and 500 ppm). Means for the same quality parameter followed by the same letter do not vary significantly (p=0.05, DMRT).

Meanwhile, high incidence of phytotoxicity was observed on trees sprayed with 400 and 500 ppm ABA. This was manifested by yellowing of leaves, followed by defoliation. In general, the two dosages of ABA had no positive effect on the quality of fruits, which implies that the concentration is rather high for cherries (Table 2).

Table 3. Cherry fruits as influenced by different dosages of ABA (400 and 500 ppm). Means for the same quality parameter followed by the same letter do not vary significantly (p=0.05, DMRT).

Results showed that ACC had a positive effect on the color enhancement of cherry fruits. Significantly higher IAD were noted on fruits treated with 400 ppm, 500 pmmand 200 ppm with repeated applications. The same treatments also gave fruits with most saturated color as indicated by the significantly lower chroma (Table 3). This was in accordance with the measured pulp and skin anthocyanin content from the three treatments, and was significantly higher compared to the anthocyaninsmeasured from the control fruits and fruits treated with 200 ppm ACC.

*Corresponding author. Email: guglielmo.costa@unibo.it