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Longevity of high-temperature embryo dormancy in Medicago murex and trifolium Subterraneum

M.J. Blumenthal and R.L. Ison

School of Crop Sciences, University of Sydney, NSW 2006

The presence of high temperature dormancy in seeds of subterranean clover has been recognised for some years. Although rare in medic, there is a suggestion that it may be present in M. murex (D. Gillespie pers. comm.). An experiment was carried out to examine the longevity of dormancy in both Medicago murex and Trifolium subterraneum.


Burrs of 2 lines of Medicago murex (CD26 and CD53) and four cultivars of Trifolium subterraneum (Woogenellup, Junee, Seaton Park and Dalkeith) were collected from plots in two blocks of a field experiment at Forbes, NSW (3323'S) on 9 December 1987. Sub-samples of 200 burrs from each plot were placed in an alternating temperature cabinet, set on a diurnal cycle of 60-15C, on 6 January 1988. Burrs were withdrawn after 2,8,16, or 32 weeks and hand threshed. From each sample 3 lots of 100 seeds were nicked and placed on two layers of moist Whatman No.1 filter paper in petri dishes which were placed in a constant temperature room at 20C and in germination cabinets set at either 24 and 30C. The filter paper was kept moist and the number of germinated seeds were counted daily for four days.

Results and discussion

Table 1. Germination percentages (retransformed data). Treatment time means not superscripted by the same letter (a- c) and temperature means not superscripted by the same letter (x-z) are significantly different (P=0.05).

After two weeks at 60/15C all lines displayed some degree of high-temperature dormancy. At 16 weeks (equivalent to one summer in the field) embryo dormancy was ranked in the order Junee = Seaton Park > Dalkeith = Woogenellup > CD26 > CD 53. Seeds of both murex lines became more high-temperature dormant with time beyond 8 weeks and had reverted to initial 2 week levels by 32 weeks.

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