Gummosis and leaf abscission in Yoshino cherry (Prunus yedoensis): relevance to hormonal regulation and chemical composition of gums

Gummosis is widely spread in the plant kingdom, especially in stone-fruit species of the Rosaceae, which resulted from an interaction with biotic and abiotic environmental factors. In this study, gummosis in shoots of 'Yoshino' cherry (Prunus yedoensis) was studied in relation to hormonal status, leaf abscission and chemical composition of gums. An ethylene-releasing compound, ethephon (1 to 2%, w/w in lanolin) substantially induced gummosis when it was applied in shoots as lanolin paste from the end of July to late August. Methyl jasmonate (JA-Me, 2.5%) had little effect on gummosis. Simultaneous application of ethephon with JA-Me caused total leaf abscission at 4 days after treatment and no gummosis. Our studies also showed that simultaneous application of ethephon (1.0%) with low concentrations of JA-Me (0.05 and 0.1%) in the first half of September greatly induced gummosis, but ethephon alone was not effective. On the contrary, ethephon (0.1 and 1.0%) and JA-Me (0.05, 0.1, 1.0 and 2.5%) applied independently on petioles in early August did not induce leaf abscission. Ethephon (0.1 and 1%) applied simultaneously with JA-Me induced almost total leaf abscission. Analyses of chemical composition of gums formed by ethephon revealed that gums were mainly polysaccharides consisting of ca. 85% of neutral sugars (Ara: ca. 55%; Gal: ca. 20%; Xyl: ca. 10%) and 15% of uronic acids. On the other hand, in sweet cherry (P. avium) gummosis was induced by the application of ethephon and JA-Me, their simultaneous application substantially enhancing gummosis. These results suggest that gummosis and leaf abscission in shoots of 'Yoshino'O cherry are regulated by a signal network and/or a crosstalk between ethylene and jasmonates, and that the presence of leaves plays an important role in gummosis.