Abstract— The aim of this study was to elucidate the effect of hydrogen cyanamide (HC) and thiourea on dormancy release and carbohydrates metabolism in floral, vegetative buds and bark tissues of pear (Pyrus pyrifolia Nakai) cultivar ‘Wonhwang’. Selected cutting were immersed in appropriate solutions of HC, thiourea and dH2O as a control while cultured in forcing condition for 5 weeks. Our results showed that both the treatments were more effective in dormancy release of both floral and vegetative buds as compared to control. However, the cuttings treated with HC started the floral and vegetative budbreak after 5 and 7 days of treatment followed by thiourea 7 and 9 days and control 13 and 13 days respectively. 50% floral budbreak was observed after 18, 22 and 30 days of treatment during forcing, on cutting treated with HC, thiourea and control while 50% vegetative budbreak was noted on cuttings treated with HC and thiourea after 22 and 26 days treatment during forcing. For control, 49.3% vegetative budbreak was observed after five week during forcing. Mean time to budbreak (MTB) for both floral and vegetative buds was less for HC followed by thiourea and control. HC and thiourea application caused an abrupt increase in starch hydrolysis and a transient accumulation of soluble sugars in buds and bark tissues during the first five and ten days after treatment. These variations, which happened shortly after HC and thiourea application, seemed to be linked with a process leading to endo-dormancy release. In fact, as budbreak started, we observed a rapid decline in sucrose, glucose and fructose concentrations in all treated tissue, while these concentrations remained high in untreated tissues and then decreased when starch concentration started to increase. Sorbitol concentration increased in treated and untreated floral buds up to 20 days in the same trend and then decreased. Our data suggest that the difference in the timing of soluble sugars accumulation/consumption process between HC, thiourea applications and control cuttings may account for the differences in the timing of growth resumption and budbreak growth.
Keywords— Carbohydrates; Dormancy; Dormancy breaking agents; Pyrus pyrifolia; Stem cuttings.
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