Oxalic acid application to increase quality and disease resistance in postharvest kiwifruit

Oxalic acid (OA) is an abiotic elicitor that induces systemic resistance against disease caused by fungi, bacteria and viruses in plants. Postharvest application of OA is effective in decreasing disease incidences in fruits and vegetables such as mango, pear, artichokes. Recently, it has been found that pre-harvest application of OA increases fruit size, bioactive compounds, and antioxidant capacity in sweet cherries at commercial harvest without affecting the on-tree ripening process.

Scientists have investigated the effects of pre-harvest OA application on quality and disease resistance in kiwifruit, with special focus on its effect on blue mold decay and patulin contamination caused by Penicillium expansum.

For the study, kiwifruit (Actinidia deliciosa cv. Bruno) fruits were sprayed with 5 mM OA at 130, 137, and 144 days after full blossom, and then harvested at commercial maturity [soluble solid content (SSC) around 10.0%] and stored at room temperature (20 ± 1°C).

Results showed that pre-harvest application of OA led to fruit with higher ascorbic acid content at harvest, slowed fruit softening and ascorbic acid content decrease, increased SSC content during storage, and decreased the natural disease incidence, lesion diameter, and patulin accumulation in fruit inoculated with P. expansum, indicating that the OA treatment increased quality and induced disease resistance in kiwifruit.

For the first time, it was found that pre-harvest spraying of the natural compound of OA on kiwifruit plants increased the postharvest quality and disease resistance of the fruit, especially inhibited the blue mold rot and patulin accumulation by P. expansum. The effects of pre-harvest OA treatment on increasing the activities of defense-related enzymes and the levels of resistance-related substances might collectively contribute to the apparent induced resistance of kiwifruit against postharvest diseases such as blue mold.

Scientists conclude that further investigations are needed to test this treatment on additional cultivars and other postharvest fungi under large-scale conditions.

Work is available online since June 3rd 2015 at:
www.sciencedirect.com/science/article/pii/S0308814615008791
and it has been published on Food Chemistry.

Source: Yuyan Zhu, Jie Yu, Jeffrey K. Brecht, Tianjia Jiang, Xiaolin Zheng, 'Pre-harvest application of oxalic acid increases quality and resistance to Penicillium expansum in kiwifruit during postharvest storage', 2016, Food Chemistry, Vol. 190, pages 537–543.

Contacts:
Xiaolin Zheng
College of Food Science and Biotechnology, Key Laboratory of Fruits and Vegetables Postharvest and Processing Technology Research of Zhejiang Province, Zhejiang Gongshang University
Hangzhou 310018, PR China
Email: zheng9393@163.com