Effect of alternating temperature regimes on seed germination of guar [Cyamopsis tetragonoloba (L.) Taub.]

Guar [Cyamopsis tetragonoloba (L.) Taub.] 2n=14, is an annual crop that belongs to the Fabaceae family and has a spring–summer growth cycle. This species has been assuming increasing importance among agro-industrial crops due to the high galactomannan content of its seeds for which a multitude of food and non-food applications have been developed. Guar is a viable rotation crop for growers in Mediterranean areas and can result in diversification in crop production systems. The effects of four alternating day/night temperature regimens on C. tetragonoloba seed germination were tested: (T1) 23/15 °C, (T2) 21/13 °C, (T3) 19/ 11 °C, and (T4) 17/09 °C with a 16/08 h light/dark photoperiod, respectively. Seeds from two guar cultivars (RGC-0936 and RGC-1066) were used. Treatments consisted of four replicates of 50 seeds each, arranged in a split-plot design with temperatures as the main plot and cultivars as the subplot. The results showed that lower temperatures reduced guar seed germination. The highest germination percentages were obtained at the 21/13 °C and 23/15 °C temperature regimens, while a significant drop in germination percentage occurred for the 19/11 °C treatment, and the lowest germination percentages were observed at 17/09 °C. No statistically significant differences were found between the two cultivars studied for seed germination percentages. The interaction effects among the different alternative temperature regimes on seed germination and guar cultivars were not statistically significantly different. The values obtained at the 21/13 °C temperature treatment allow us to conclude that this regimen is the minimum acceptable combination of temperatures to program the sowing date.