Effects of hydrogen cyanamide on physiological characteristics of dormancy release and comprehensive berry quality of three grape cultivars

Abstract: 【Objective】Natural dormancy is an insurmountable stage during the growth and development of deciduous fruit trees. Grapevine is a perennial deciduous vine of grapevine family. If the variet-ies cannot meet the chilling requirement, it often leads to low germination rate and irregular germina-tion, which seriously affects the yield and quality of berries. Therefore, breaking the natural dormancy and promoting early germination has become a key technology to be solved in forcing cultivation. The purpose of this experiment was to explore the effects of monocyandiamide treatment on the growth and development of different grapes, and to reveal the physiological and biochemical mechanism of break-ing dormancy of grapes.【Methods】Three grape cultivars Zaoheibao, Zaoxia Meigui and Shaoxing No.1 were selected as test materials and treated with sleeping breaking agent hydrogen cyanamide (H2CN2) and water as the control (CK). The budding stage, flowering stage, berry coloring stage and rip-ening stage of each grape cultivar were recorded, and the uniformity of germination, germination rate,berry setting rate, fruiting cane rate, diameter change of fruiting mother cane, bearing position, inter- node length, leaf length, leaf width and the growth dynamics of new buds, leaves and fruits were calcu-lated. The development of each grape bud after dormancy breaking treatment was observed by paraffin section. The content of H2O2, and the activity of POD and CAT were measured. The photosynthetic pig-ment of mature leaves was measured by ethanol extraction method. The length and width of grape bunch were measured by tape measure. The weights of grape bunch and berry grain were measured by an analytical balance. The vertical and horizontal diameters of berry grain and the thickness of berry peel were measured by a vernier caliper. The ratio of vertical to horizontal diameter of berry grains was fruit shape index. The hardness of berry was determined by a hardness index measure with a thermome-ter. The method for measuring soluble solids, total sugar and acid-base titration and vitamin C content was determined by 2,6-dichloroindophenol titration method; the relative content of total phenols and fla-vonoids was determined by hydrochloric acid methanol method; the relative content of total anthocya-nins in pericarp was determined by hydrochloric acid absolute ethanol extraction method. Combined with principal component analysis (PCA) and comprehensive evaluation index, the main influencing fac- tors of monocyandiamide on grape dormancy were screened, and the effects of monocyandiamide on the growth and development of different grape cultivars and their comprehensive berry quality were ex-plored.【Results】The effects of dormancy breaking treatment on the growth of all grape cultivars were similar as a whole, and the germination and berry ripening times were significantly earlier. After dorman- cy breaking treatment, the internal structure of each grape bud developed rapidly, the growth point gradually increased and elongated, the main axis was differentiated and filled with buds, the number of cells increased, the leaf primordium formed continuously, the inflorescence primordium developed continu-ously, and the flower meristem morphology was complete; however, after water treatment, the internal growth of bud was slow, the structures developed but did not take shape, and a small amount of leaf pri-mordium and inflorescence could be seen. There was no significant change in the whole primordium.The germination uniformity and germination rate, and the H2O2 content and POD activity were signifi-cantly higher than those of the control, while the CAT activity was significantly lower. The contents of chlorophyll b, total chlorophyll and carotenoid in mature leaves were significantly higher than those of the control, while the content of chlorophyll a was significantly lower. After breaking dormancy treat-ment, the appearance quality and internal quality of each grape berries were improved on the basis of maintaining the inherent level, and there was no significant difference in the appearance quality between the treatment and control. For the internal quality of berry, the soluble sugar, soluble protein and starch contents in Zaoxia Meigui grape berries treated by breaking dormancy was significantly higher than those of the control, while the other two kinds of grapes were improved, but there was no significant difference; the contents of soluble solid and vitamin C in Zaoheibao and Shaoxing No.1 grapes signifi-cantly increased, but there was no significant difference with Zaoxia Meigui. The relative contents of total phenols, flavonoids and anthocyanins in all grape cultivars increased after dormancy breaking treatment, and there was no significant difference except for the relative contents of total phenols in Shaoxing No.1. PCA was used to analyze the physiological and biochemical indexes of different grape cultivars after breaking dormancy. The three principal components with the highest eigenvalues were extracted, and the cumulative contribution rate reached 94.36%. Combined with comprehensive evalua-tion index, the order of grape comprehensive quality was as follows: Zaoheibao (H2CN2) > Shaoxing No.1 (H2CN2) > Zaoheibao (CK) > Zaoxia Meigui (H2CN2)> Shaoxing No.1 (CK) > Zaoxia Meigui (CK).【Conclusion】Germination uniformity, germination rate, H2O2 content, POD activity and CAT activity were the main influencing factors for breaking dormancy of grape. The comprehensive quality of Zaoheibao grape berries was better than that of Zaoxia Meigui and Shaoxing No.1 grape after treat-ment with H2CN2.