The effect of high temperature pretreatments on germination of Townsville stylo seed material

Abstract

Townsville stylo cv. Gordon dehulled seed and intact pods were exposed to temperatures ranging from 40� to 11 5�C for between 12 and 48 hours in the expectation that a method of reducing hardseededness could be devised. Dry heat temperatures of 75� and 95�C markedly decreased the level of hardseededness in both dehulled seed and intact pods. A temperature of 11 5�C for 12 hours was sufficient to kill all seeds and pods. Fifty per cent germination was achieved after 2.5 days for dehulled seeds and after 5 days for pods exposed to a pretreatment of 95�C. Untreated scarified dehulled seeds took only 1.5 days to achieve 50 per cent germination. It was suggested that a suitable heat pretreatment on Townsville stylo pods should result in a seed material with a soft-seed level similar to dehulled scarified seed, yet with the pods still retaining considerable immunity from 'false starts' to the wet season.

Breaking dormancy of Stylosanthes humilis seeds with low pH solutions

“…By assum ing that pH of soil so lu tion is buf fered against dras tic changes un der short and me dium term, and that at the pH range shown by sa van nah soils germi na tion could be rel a tively high (Fig. 1), a large pro por tion of the mil lions of seeds shed to soil could ger mi nate and thus seed dor mancy might occur un per ceived, which is not usu ally men tioned in the lit er a ture (Cameron 1967, Holm 1972, Gardener 1975, McIvor 1976, Argel and Humphreys 1983. The other point is that cad mium, zinc and cu pric ions were shown to break dor mancy of seeds of Townsville sty lo (Delatorre and Barros 1996).…”

“…Any fac tor elic it ing eth yl ene pro duc tion breaks dor mancy of Townsville sty lo seeds. This in cludes chem i cals such as CEPA and ACC (Burin et al 1987, Vieira andBarros 1994), or con di tions such as high tem per a tures (Holm 1972) and flood ing (per sonal ob ser va tion). Stress ors such as heavy met als (Delatorre and Barros 1996) and selenomethionine Freitas 2000, 2001) are also good dor mancy-break ing agents, likely by trig ger ing eth yl ene biosynthesis.…”

Tratamento térmico para superação da dormência em sementes de Stylosanthes SW. (fabaceae papilionoideae)

“…Apesar de os tratamentos a 70ºC e a 60°C apresentarem praticamente o mesmo aumento de germinação (75% aproximadamente, em relação à testemunha), a temperatura de 70°C é recomendada, pois, de acordo com os resultados obtidos na análise de regressão, pode-se perceber que nesta temperatura o ponto máximo de inflexão foi alcançado mais rapidamente, às 12 horas aproximadamente, com 55,2% de germinação. Estes resultados corroboram com os resultados de Martins et al (1996) , 2004), B. brizantha (Martins e Lago, 1996) e ainda S. humilis (Holm, 1973).…”

Comparative evaluation of seed coat dormancy breaking treatments in Stylosanthes seabrana

“…High‐temperature drying capable of dealing with bulk samples of Stylosanthes species developed by Mott (1979) was not capable of giving uniform heating to the seed. Physiological dormancy due to inhibitors can be overcome by exposing the seeds to several stress factors, such as high temperature (Holm, 1972), a range of organic acids (Pelacani et al. , 2005), or thiourea (Delatorre and Barros, 1996), which can induce ethylene production by the seeds to counteract the inhibitors.…”