Germination of guar (Cyamopsis tetragonoloba (L.) Taub.) genotypes with reduced temperature requirements
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2018, Southern Cross Publishing. Guar (Cyamopsis tetragonoloba (L.) Taub.) is an annual legume with a long crop cycle and high temperature threshold for seed germination (20-21C). In semi-arid Mediterranean areas, inadequate soil warmth delays guar planting to May/early June and harvest to October-November, when high rainfall hinders seed maturation and lowers gum quality. Nine world guar genotypes (from India, Pakistan, USA, South Africa) were tested for germination capability and speed in response to temperature. All source seeds were field grown in Sicily for use in germination assays. The following temperature regimes were imposed adopting a completely randomized design: A) seven constant temperatures from 5C to 35C (5C increments), and B) two alternating temperatures of 15/10C and 20/15C (6h/18h thermoperiod), each consisting of four replicates of 25 seeds. Optimal germination temperatures were always 30 and 35C, but Indian genotypes also demonstrated substantial germination percentages (33-43%) at constant temperatures as low as 15C. Mean germination time (MGT) of genotypes India2, Kinman, Lewis, and Monument were 1.1 to 1.7 days at 30 and 35C. At lower temperatures (15C), the germination percentage and MGT improved significantly when the seeds were exposed at 20C for 6 hours a day. In particular, Kinman, India2 and Monument gave good results, achieving 80%, 76% and 66% germination, respectively, with MGTs of 5 days. This alternating temperature regime is typical in soil during the Mediterranean spring. Results may be useful both for farmers to identify optimum timing for guar sowing, and for breeders to cross genotypes that tolerate low germination temperatures with high yielding genotypes.
