Climatic variation in forage grasses. 2. Germination, flowering and leaf development in Mediterranean populations of Phalaris tuberosa.
8 Mediterranean populations of P. tuberosa covering the climatic range from Morocco and Israel (severe summer drought, growing season 5-6 months) to N. Italy and N. Greece (appreciable summer rainfall, growing season 9-10 months) grown at Canberra showed little difference in seed-germination characteristics at 4-5°C, but large differences in survival at high temperature. In populations from Morocco and Algeria, which have erratic summer rainfall, a high proportion of imbibed seed was 'dormant' at 38°C; this feature was less marked or absent in those from areas with adequate summer rains or none at all. Cold requirement for floral induction was closely related to winter temperature at the site of origin; material from N. Greece required 8 weeks at low temperature, whereas material from Morocco and Israel had little or no cold requirement. Time of flowering outdoors and time to heading after complete vernalization were closely related to the length of the potential growing season at the site of origin as determined by summer drought. Optimum temperature for expansion of leaf surface was about 24°C day/ 19°C night, but leaf length and leaf width responded differently to temperature; rate of leaf expansion at low temperature relative to that at 24/19°C was markedly greater in material from the S. (10-12°C winter temp.) than in that from the N. (3-7°C winter temp.); this was largely due to differences in leaf length. RGR in the early seedling stage was highly correlated with rate of leaf expansion and was greatest in the Moroccan forms with a short growing season; differences were maintained in older plants at lower temperatures but disappeared at higher temperatures as mutual shading developed.-R.B.