Effects of different water treatments during veraison to ripening period on leaf photosynthetic characteristics and fruit quality traits of Shine Muscat grapes

Abstract: 【Objective】At present, more than 66.7 thousands hectare of Shine Muscat grape has been planted in China. The root zone restricted cultivation of table grape is one of very important cultivation method for Shine Muscat grape. Compared with conventional cultivation methods, the grapevine is much easier to lose soil water under root restriction. This study evaluated the photosynthetic parameters and berry quality indicators of the Shine Muscat grapes under the root restriction model with different soil water content ranges(45%-<85%) in Hunan province to obtain the most suitable range of soil water content during the veraison to ripening period.【Methods】During the veraison to the maturity period(60 to 110 days after full flowering), four soil moisture content range treatments were made on the Shine Muscat grapevines by the temperature and humidity sensor to detecting the soil moisture contents to determine and compare the photosynthetic characteristics, water use efficiency(WUE) and fruit quality indicators. The treatments were 75%-85%(T1, adequate water supply), 65%-<75%(T2, mild water stress), 55%-<65%(T3, moderate water stress) and 45%-<55%(T4, severe water stress) of field moisture capacity of soil water moisture. The soluble solid substances and chromatic aberrations of grape berries with four treatments were compared.【Results】Under water stress, the fruit soluble solid content of the berries increased, accompanied by the obvious change of the berry color from green to yellow and the formation of many rust on pericarp. In the ripening period(110 days after full flowering), there was a higher significant linear relationship(Sig. < 0.01) between the soluble solids of each treatment and the peel chromatic aberration value a*(which could approximately represent red and green color values of berry pericarp). The linear equation was: Y=1.239 X + 18.953, coefficient of determination R2=0.326.while there was no significant linear relationship(sig. >0.05) with b* value(which could approximately represent yellow and blue color values of berry pericarp). The T2 treatment significantly increased the soluble solid substances of the mature fruits by 8.0%, significantly reduced the fruit titratable acids by9.1%, significantly increased the solid-acid ratio by 18.8%, significantly reduced the peel thickness by25.6%, significantly increased the fruit firmness by 14.59%, and significantly increased the content of malondialdehyde by 15.35%. Compared with T2 treatment, T3 and T4 treatments did not significantly improved the fruit quality, but, significantly reduced the pedicel tension.From the veraison(70 days after full flowering) to ripening period(110 days after full flowering), the photosynthetic indexes of the leaves at the clusters position were measured with a photosynthetic instrument every 10 d. The results showed that most of the photosynthetic parameters such as Pn, Trand Gsof T1, T2, were higher tha those of T3, T4. And with the increase of water stress, the Pn, Trand Gsof the leaves at the clusters position gradually decreased. The photosynthetic parameters of each treatment from veraison to the ripening period showed a“V”-shaped trend. In the early stage of the stress(60-90 days after full flowering), Pn, Trand Gsshowed an overall downward trend, the decrease of Pnand Trof leaves at this stage was mainly affected by the decrease of Gs. As the water stress time prolonged(after 90 days after flowering), Pn, Trand Gs were all showed a continued downward trend, while Ci showed an upward trend. The decrease of Pnand Trat this stage was due to the other non-stomatal conductance factors hindering the consumption of CO2,meanwhile leading to CO2enrichment. In the case of water stress(T2, T3, T4 treatment), the heavier the water stress was, the higher the water use efficiency was(T4 > T3 > T2). Within 15 days after the treatment, the WUE trend was T4 > T3 > T2 > T1, after 15 days of the treatment, the WUE trend was T1 > T4 > T3 > T2.【Conclusion】Under the condition of root restriction cultivation in Hunan province, mild water stress(T2 treatment) improved mature fruits quality,without affecting photosynthetic parameters. Therefore, during the veraison to the maturity period, the optimum soil water ratio(soil water content of field water holding rate) of Shine Muscat grape would be 65%-<75%.