Planting climate causes of the style features for the chemical quality of flue-cured tobacco in Yunnan Province

Yunnan Province has a complicated geographical environment, in which altitude differences are larger from place to place and regional climate differences are significant. But the province has the largest tobacco leaves output in China, with its flue-cured tobacco growing areas being distributed in the altitude interval of 1000-2000 meters. In order to understand the internal relations between the chemical quality of flue-cured tobacco and planting climates, based on the field experiments and related climate data in 10 counties (districts) from 2017 to 2020 in Yunnan, the methods of systematic cluster and principal component analysis are used to analyze the effects of planting climate on the contents of nicotine, total nitrogen and protein inside local tobacco leaves. The results showed that the climates of tobacco-growing areas of Yunnan province in tobacco field growth period (from mid-April to late August) were divided into six types, which meant Yunnan had climate diversity in planting flue-cured tobacco. But most of the planting climate types had the main climatic feature of the low latitude plateau region of Yunnan, which manifested that lower average air temperature appeared in flue-cured tobacco field growth period with the average values of the hottest month being lower than 22.5℃. Simultaneously, there were higher average relative humidity (being higher than 78%), more rainfall (being greater than 5.5mm per day on average) and lesser sunshine duration (being less than 5.0 hours per day on average) in vigorous growth and mature period of flue-cured tobacco (mainly in summer, i.e., from June to August), while there were lower average relative humidity (being less than 66%), rare rainfall (being less than 1.8mm per day on average) and more sunshine duration (being more than 7.0 hours per day) in transplanting and root growth period (from mid-April to mid-May). That is to say, in most tobacco-growing areas of Yunnan Province, the characteristics of the phased climate changes during flue-cured tobacco field growth season were similar. Higher average relative humidity and more rainfall in tobacco field growth period (especially in the mature period from July to August) were conducive to increasing the contents of total nitrogen and protein inside tobacco leaves. And lower temperature conditions in field growth period (particularly in vigorous growth and mature period) were infavor of the accumulation of nicotine inside tobacco leaves. To sum up, the temperate, humid climate with inadequate sunlight in the vigorous growth and mature period of flue-cured tobacco were the main reasons for the relative higher contents of aforementioned three chemical compositions inside tobacco leaves in Yunnan. And the climatic characteristics of tobacco field growth season (showed as a temperate, humid climate with inadequate sunlight in summer while relatively dry, sunny warm climate in spring) had significant influences on the contents of main chemical components (including total sugar, reducing sugar, potassium, petroleum ether extract and aboved-mentioned three components) inside tobacco leaves and led to the formation of chemical quality style features of the tobacco leaves produced in most of the tobacco-growing areas in Yunnan. The analyzed results could be applied to the development of characteristic tobacco leaves according to different climatic conditions. They also would help to predict and evaluate the changes of chemical quality for tobacco leaves with climate conditions, and to provide scientific basis for tobacco industry to rationally deploy raw tobacco leaves from different places.