Temperature/light interactions and the effect of seed source on germination of annual ryegrass (Lolium rigidum Gaud.) seeds

Abstract

Germination of Lolium rigidum seeds, in the light (12 hr day length) and in the dark, was studied at constant and alternating (12/12 hr) temperatures in the range 8–35°C. Seeds had after-ripened for 22 weeks. Different constant temperature optima for germinability were found: 27° in light and 11° in dark. Germinability at alternating temperatures in darkness was determined solely by the minimum temperature of the alternation, and there was no response to thermoperiodicity per se. In contrast, light and alternating temperature appeared to interact to increase germinability, although the highest germinability occurred only when the maximum temperature was close to the optimum constant temperature, i.e. about 27°. Germination in both light and dark was most rapid where either the constant or the average temperature of an alternating regime was between 18 and 29°. Below 18° germination rates decreased markedly, and at 8°, rates were one-third of those at 18°. Seeds germinated more slowly in light than in darkness at all temperatures, but the differences were small relative to the effects of low temperatures.In another study, seeds collected from plants naturalized in eight different localities in the cereal belt of Western Australia and subsequently planted together in two contrasting environments were examined for germinability at 24/12°C in light and dark 18 weeks after harvest. Dark germinability differed between seed sources but not between planting sites, and ranged between 78 and 93%. Exposure of germinating seeds to light substantially alleviated dormancy in seeds from all sources.

An evaluation of the problem of volunteer ryegrass in seed production

“…The results indicate that this mediterranean grass species germinates best under cooler conditions and that optimum germination requires low alternating temperatures, which in fact, simulate the environmental conditions prevalent at autumn sowing time in regions of Natal where ryegrass is grown for seed production. Similar results were reported for L. rigidum (Gramshaw, 1976). (Table 1).…”

Seed dispersal in the dung of large herbivores: implications for restoration of Renosterveld shrubland old fields

“…Non-indigenous Mediterranean weeds are also shown to prefer cooler conditions for germination; for example, the seeds of Lolium and Avena did not germinate well above 26 and 20°C respectively (Quail and Carter 1968;Gramshaw 1976). The germination rate for the first collected samples was therefore greatest between March and June, ceasing in July (Figure 3), a period that also marks the end of winter season.…”

The biology and control of Lolium rigidum as a weed of wheat

“…Cocks & Donald (1973) showed that germinations with diurnal temperature fluctuations greater than 5°C were higher (mean 79% compared with 66%) than those with fluctuations less than 5°C for three temperature ranges: 15-20°C, 20-25°C and 25-30°C. However, Gramshaw (1976) found that in the dark there was close agreement between the percentage germination at any temperature alternation and the germination at a constant temperature equal to the minimum ofthe alternation. In the light, maximum temperature had the dominant eflect.…”

“…Germination at 24712°C in darkness of L. rigidum seed from diflerent field sources varied between 78 and 95%. These differences were not apparent in light where germination ranged from 95 to 100%-LSD 5-3% (Gramshaw, 1976).…”

“…L. rigidum seed will germinate at constant temperatures from 7°C (Cocks & Donald, 1973) to 35°C (Gramshaw, 1976), Gramshaw (1976) showed that the optimum temperature for germination was 11°C in darkness and 27°C in light. Germination rate increased as constant temperature increased from 5°C to 29°C (McWilliam, Clements and Dowling, 1970) and as alternating temperatures increased from 12°C/25°C to 20°C/25°C (Cocks & Donald, 1973),…”