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Growth responses of annual medics to temperature

M.H. Ababneh, J.H. Silsbury and E.D. Carter

The University of Adelaide Department of Agronomy, Waite Agricultural Research Institute Glen Osmond, South Australia 5064

The effects of temperature on the growth of a crop depend on the plant density, the amount of dry matter present, the solar radiation and the genotype. Since it is difficult to measure growth responses to temperature in the field due to associated variation in light flux density and temperature, controlled environment chambers are often used for this purpose. The experiment reported here aimed to quantify the effects of three contrasting temperatures (10, 15 and 20C) on the growth rates of two annual medic cultivars widely used in southern Australia namely M. scutellata cv. Sava and M. truncatula cv. Paraggio, also two annual medic genotypes from the colder areas of West Asia viz. M. rigidula Sel.#716 and M. rotata Sel.#1943 to see if these four medics differ in cold tolerance.

Methods

Small swards were established in pots (0.0225m-2), at 17.4g m-2 sowing rate. Seedlings were inoculated with appropriate Rhizobium meliloti and irrigated daily with a nutrient solution free of mineral N. Harvests were made every 7 days at first and later every 3 days. Growth curves were constructed by linear regression. The light flux density in the growth cabinet was 4O0 mole quanta m-2S-lwith a day length of 12h.

Results and discussion

Table 1. Growth rates (g m-2day-1) for medic genotypes grown at three temperatures for varying periods.

Growth rate was significantly influenced by temperature and genotype: however, there was a significant interaction between genotypes and temperature. Sel.#716 was depressed in growth rate by a temperature of 20C. While these results show that early growth of medic swards is generally favoured by moderate or high temperature (15C or 20C), it is clear that there is some variation between genotypes in response to temperature which indicates possible cold tolerance or a cold-escape mechanism. It is concluded that M. rigidula Sel.#716 is the most cold tolerant of these four medics and it may have a role in southern Australian farming systems.

1. Cocks, P.S. (1987). Annual Report: Pasture, Forage and Livestock Program, ICARDA, Syria, 288p.

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