Symbiotic incompatibility induced callose deposition at the graft junction. A Twenty-five days after grafting, aniline blue staining was performed at the graft junction to observe the deposition of callose. Arrows indicate the phloem (ph) and the vascular bundles (vb). Scale bar: 100 μm. B Area of callose deposition of a single vascular bundle in A. C Callose content. D Callose synthase activity. E Callose hydrolase activity. F Expression of CmCalS1. Expression of the CmCalS1 gene was analyzed by qPCR in the rootstock of the grafted junction of different compatible combinations after grafting. Data represent the mean ± standard deviation (n = 3). According to Tukey’s test, means with the same letter did not differ significantly at P < 0.05. FW, fresh weight; NG, non-grafted; SG, self-grafted; CG, compatible combination; IG, incompatible combination.