Chilling and heat requirements of grape cultivars under protected culture in Ningxia area

Abstract: 【Objective】China is the largest country for grape (Vitis vinifera L.) cultivation in the world. Grape can be grown in open field and in protected field, and the protected culture has become more pop- ular in recent years in China. Usually a chilling requirement is necessary for breaking the winter dor- mancy and a heat requirement is necessary for initiating bud burst of grape. Insufficient chilling require- ment and heat requirement would delay the bud burst, inflorescence degradation, and growth of new shoots, leading to poor production low quality of fruits. The experiment was designed to study the chill- ing requirement, heat requirement and the relationship between them of grape under protected culture in Ningxia, and to screen a suitable model for measuring the chilling requirement and heat requirements for grapes cultivated in protected condition in this region.【Methods】The experimental materials were six-year-old grape vines of‘Red Globe’‘Red October’‘Victoria’‘Thompson’‘Royal Rose’‘White Stone’‘6-12’‘August’in Ningxia, 3 models of estimation of chilling requirement (≤7.2 °C model, 0- 7.2 °C model and Utah model) were used to estimate the chilling requirement for breaking the dorman- cy, and 6 models of estimation of heat requirement (growing degree hours model, effective accumulated temperature model, maximum accumulated temperature model, maximum temperature accumulation model, average temperature accumulation model and heat model) were employed to estimate heat re- quirement for the bud burst after the dormancy. The chilling requirement and the heat requirement were estimated, in the past three years and the coefficients of the variations between the different estimation models were used to select the most suitable chilling requirement and heat requirement models for this region. At the same time, SPSS software were used to determine the correlation between the chilling re- quirements and the heat requirements estimated by different models【. Results】Through three consecu- tive years of estimation of the chilling requirements of grape under the protected culture via three mod- els, the smallest inter-annual coefficient of variation was obtained by the Utah model. A big difference in the chilling requirements among the 8 grape varieties in Ningxia was found.‘Thompson’had the highest chilling requirement, with 562-622 h (≤7.2 °C model), 535-582 h (0-7.2 °C model) and 518-544 CU (Utah model);‘White Stone’had the lowest chilling requirement, with 166-185 h (≤7.2 °C model), 162-179 h (0-7.2 °C model), 155-165 CU (Utah model). The comparison among three models showed that the Utah model had the lowest coefficient of variation with 5.66%, which should be more suitable for estimating the chilling requirement in the region. By comparing the temperature accumulation of the different heat requirement models in the same period of the three years, it was found the growing de- gree hours model had the smallest coefficient of variation. There was a little difference in the heat re- quirement among grape varieties. The growing degree hous model had the smallest variation coefficient among the six heat requirement estimation models for inter-annual three years, which was 3.83%, indi- cating that the growing degree hours model should be the most stable for the estimation of the heat requirement in the region. There was a negative correlation between the heat requirement and the chilling requirement. although the chilling requirement and the heat requirement of grape was not inevitability related to the fruit maturity period.【Conclusion】In conclusion, the Utah model and the growing degree hours model would be most suitable for estimating the chilling requirement and the heat requirement of the grape cultivars under protected culture in Ningxia, and there was a negative correlation between the chilling requirement and the heat requirement.