Abstract:

 Yunnan province has a complex geographical environment, where altitude differences are larger from place to place and regional climate differences are significant. However, the province has the largest tobacco leaf production in China, and its flue-cured tobacco growing areas are spread over an altitude interval of 1000-2000m. In order to understand the internal relations between chemical quality of flue-cured tobacco and planting climate conditions, based on the field experiments and related climate data in 10 counties（districts） of Yunnan province from 2017 to 2020, the methods of principal component analysis and correlation analysis were used to analyze the effects of planting climates on the contents of nicotine（Nt for short）, total nitrogen（Tn） and protein （Pt） inside local tobacco leaves. The results showed that 35 samples with above−mentioned three tobacco chemical composition indices (constituted a dependent variable field) and 13 climate factors for each of 5 growth stages (constituted five climatic variable fields) were obtained through the tobacco field trial at 10 sites from 2017 to 2020. The cumulative degree for the first two or three principal components of any of the variable fields to account for the total variance of the temporal and spatial variability of the corresponding original variables was more than 82%. In the climate variable fields, the third principal component (F3 for short) of flue−cured tobacco field growth period （from mid−April to late August） and the F3 of mature period （from July to August）, which reflected the air humidity and amount of precipitation, were significantly positively correlated with the first principal component (F1) of tobacco chemical components variables field（P<0.05）, which expressed the contents of Tn and Pt inside tobacco leaves. The second principal component (F2 for short) of field growth period for flue−cured tobacco and the F2 of vigorous growth and mature period （mainly from June to August）, which reflected the advantages and defects of heat conditions, together with the F2 of vigorous growth period （from late May to late June）, which represented minimum temperature, were significantly negatively correlated with the F2 of tobacco composition variables field （P<0.05）, which expressed the Nt content of tobacco leaves. All of the above five principal components of the climate variable fields indicated that certain climatic factors had a synergistic effect on the accumulation of certain chemical components inside tobacco leaves. Above these results indicated that the relatively large air humidity and the amount of precipitation during tobacco field growth period and mature period were favorable for increasing the contents of Tn and Pt  inside Yunnan tobacco leaves. The relatively abundant heat in tobacco field growth period and during the vigorous growth and mature period, together with the higher minimum temperatures during the vigorous growth period, were detrimental to the formation and accumulation of Nt inside tobacco leaves. Bacause Yunnan is located in the low latitude plateau region and affected by southwest monsoon, the climatic conditions of most local tobacco planting areas for the whole vigorous growth and mature period of flue−cured tobacco were as follows: the average temperature was not higher than 22.0℃, the mean daily amount of precipitation was more than 5.5mm·d⁻¹, the average relative humidity was bigger than 80%, the mean daily sunshine duration was lesser than 5.0h·d⁻¹ and the average diurnal temperature range was greater than 8.0℃. Such climatic conditions resulted in a weakening of transpiration and photosynthesis, an increase in the temperature effectiveness of tobacco, and a prolonged period of growth and development of flue−cured tobacco, which were the main reasons for the relatively higher contents of the above three chemical compositions inside the tobacco leaves in Yunnan. The conclusion about the influences of climatic factors on the chemical quality of flue−cured tobacco leaves was verified by the relevant data from several provinces which annually produce large quantities of tobacco leaves in China. In view of Yunnan's significant interannual climatic fluctuations, distinctive climate conditions and regional climate differences, the results of the analysis can be applied to the development of characteristic tobacco leaves based on different local climate conditions. They would also help to predict/assess the changes in the chemical quality of tobacco leaves on the basis of the climatic fluctuations, which was intended to provide a scientific basis for the tobacco industry to rationally deploy raw tobacco leaves from different producing areas.

Key words: Chemical quality of flue?cured tobacco, Meteorological conditions, Nicotine, Total nitrogen, Protein, Principal component analysis (PCA)