The investigation of cold resistance in different populations of Narcissus tazetta

Extended Abstract
 
Background and Objectives
The flower market is a globally active industry that has experienced significant growth over the past few decades. Narcissus tazetta (Daffodils), a key flowering plant, thrives in tropical and semi-tropical regions. It is used both as a cut flower and for planting in pots and green spaces. It is cultivated in some parts of Iran, including South Khorasan province, the North, North-East, and much of southern Iran, primarily for cut flower production. Farmers in South Khorasan province have experienced cold damage in specific years due to sub-zero temperatures. Therefore, this study was conducted to evaluate the cold resistance and assess the extent of damage in various populations of Narcissus tazetta collected from different regions of Iran.
 
Materials and Methods
A factorial experiment was conducted in the greenhouse of the Plant Production and Genetics Group, Agriculture and Natural Resources Paradise, University of Birjand from 2018 to 2019. Factor A included 13 populations of Narcissus tazetta (Azadshahr, Shahlai Shomal, Shastpar Shomal, Shiraz 1, Shiraz 2, Yasouj, Yasouj small perfume, Tabase Golshan, Khusf 1, Khusf 2, Behbahan 1, Behbahan 2, and Gachsaran). Factor B consisted of four temperature levels: environmental temperature (control), +5°C, 0°C, and -5°C. Five leaves were collected from each pot and exposed to refrigeration at +5°C, 0°C, and -5°C for 5 hours. Traits measured included relative leaf water content (RWC), ion leakage, chlorophyll a, chlorophyll b, total chlorophyll, carotenoid, chlorophyll a/total ratio, total chlorophyll/carotenoid ratio, and the percentage of chilling stress. Data analysis was carried out using SAS9.4 and SPSSv26 softwares and histograms were drawn using Excel 2010 software. Duncan's test was used to compare means. Pearson's correlation was applied to analyze correlations. Multivariate analysis (cluster analysis and principal component analysis) was conducted using all of the traits under both stress and normal conditions.
Results
Analysis of variance revealed significant differences of populations and cold stress treatments for all the traits except chlorophyll a. The population by clod stress interaction effect was significant for all the traits, suggesting that populations responded differently to various temperatures. The highest and lowest ion leakage values were observed at -5°C and the control treatment (22°C), respectively. The highest values of RWC, chlorophyll a, chlorophyll b, total chlorophyll, carotenoids, and the chlorophyll a/total ratio were observed at the control temperature, while the lowest values were observed at -5°C. Chilling stress was highest in February and lowest in December in the natural environment. As temperature decreased, ion leakage and chilling stress increased, while other traits declined. Correlation and regression analyses indicated that chlorophyll b and total chlorophyll were more strongly associated with chilling stress. Cluster analysis categorized the populations into three groups under both normal and stress conditions. The populations Yasouj, Tabase Golshan, Shiraz 1, small aromatic Yasouj, and Azadshahr formed the first cluster; Behbahan 2, Shiraz 2, Shahlai Shomal, Shastpar Shomal, Khusf 1, Khusf 2, Gachsaran, and Behbahan 1 formed the second and third clusters. The results showed no relationship between geographical proximity and chilling stress.
Conclusion
The study identified chlorophyll b and total chlorophyll as critical traits for assessing cold resistance. The populations Khusf 1, Khusf 2, Gachsaran, and Behbahan 1 were the most frost-resistant, while Yasouj, Tabase Golshan, Shiraz 1, and small aromatic Yasouj were the most frost-sensitive. Azadshahr, Behbahan 2, Shiraz 2, Shahlai Shomal, and Shastpar Shomal were intermediate in cold tolerance. Gachsaran was the most resistant, and Shiraz 1 was the most sensitive to chilling stress. The results showed significant diversity among populations regarding cold resistance, suggesting that researchers and farmers interested in Narcissus as an economic plant should focus on these frost-resistant populations.