Introducing an Index to Selection Sunflower Genotypes for Second Planting Date

 Sunflower is a plant with high economic value and adapted to a wide range of climatic conditions. Spring cultivation is one of the ways to enhance in Iran the area under cultivation of this crop, which is usually accompanied by terminal low temperatures. In this regard, there is a need to identify and introduce indices for selecting tolerance to low temperatures in the reproductive stage.

This research was conducted in 2014 and 2017 as a split plot in the form of a randomized complete block design with three replications in Tarbiat Modarres University and Seed and Plant Improvement Institute, respectively. The main plots included planting dates in two levels and the subplots consisted of five inbred lines and three sunflower hybrids. Planting dates were adjusted to allow temperatures of 25± 2 °C and 15± 3 °C during and after anthesis. Single plant yield and physiological traits such as components related to remobilization from stem and receptacle base to seeds, dry weight of leaves and electrolyte leakage of receptacle tissue were evaluated on all treatments. Multivariate analyzes were performed on the measured traits.

The results of combined analysis of variance of the data showed that the interaction effects of experiment-planting date-genotype of all traits were not significant. The second planting date reduced grain yield in all genotypes. In both planting dates, the hybrids had the highest grain yield and the lowest electrolyte leakage. Low temperatures differentiated the yield behavior in the inbred lines. A significant negative correlation was observed between electrolyte leakage in the first planting date and grain yield in the second planting date. Also, the correlation between stem diameter in top of the stem in the first planting date was significant and positive with dry weight of the head and stem at anthesis, grain yield, 1000-seed weight and remobilization from receptacle base to the grain in second planting date. Stepwise regression analysis of plant yield in the second planting date on the measured traits in the first planting date showed a significant positive effect of head dry weight at maturity and stem diameter in top of the stem and a negative effect of electrolyte leakage. The first and second principal components, explaining 79% of the total data variance, were able to group genotypes based on differences in grain yield and its components, electrolyte leakage, stem diameter in top of the stem and resistance to assimilate transfer from storage to grain.

Increased cell membrane stability is an evolutionary mechanism by which some genotypes maintain their yield and performance to some extent under cold stress conditions. This trait along with the stem diameter in top of the stem can be used as indices for selecting inbred lines in segregating generations to withstand low temperature conditions in the second planting date.