Abstract:

The purpose of this study is to explore the effects of exogenous gibberellin and calcium amino acid on fruit cracking of ‘Asumi’, and provide theoretical basis and practical measures for the prevention of fruit cracking of citrus. Using 5-year-old ‘Asumi’ citrus with red orange as research material, 27 trees with the same growth potential and load were selected and treated with exogenous gibberellin and calcium amino acid at 60, 75 and 90 d after anthesis respectively. Samples were taken from 100 d after anthesis and once every 15 d, a total of 5 times. The fruit cracking rate, ultrastructure observation of pericarp cells, cell wall material content, water-soluble pectin content, ion binding pectin content, covalent binding pectin content, galacturonic acid content, cellulose, lignin content and fruit appearance quality were measured, compared and analyzed. The results showed that the content of water-soluble pectin increased at first and then decreased with the growth and development of fruit, and the content at the peak of fruit cracking was higher than that in other periods, and was greatly affected by gibberellin. The contents of ion-bound pectin, covalently bound pectin and cellulose decreased at first and then increased, and the contents at the peak of fruit cracking was lower than that in other periods, and the change of ion-bound pectin content was greatly affected by exogenous calcium. There was no significant difference in hemicellulose and lignin content among different treatments in different periods. The change of the content of different types of pectin in the pericarp was the main factor of fruit cracking of ‘Asumi’ citrus, and exogenous spraying gibberellin and calcium amino acid could significantly reduce the fruit cracking rate. Gibberellin and calcium amino acid can enhance fruit cracking resistance by affecting different types of pectin content in pericarp.

Key words: citrus, fruit cracking, gibberellin, exogenous calcium, cell wall, analysis of variance