Germination and dormancy states of seeds in the environmental weed Rumex vesicarius (Polygonaceae). II. Germination and dormancy of seeds enclosed within the fruit

Abstract

Rumex vesicarius (Ruby dock; subgenus Acetosa, section Vesicarii, family Polygonaceae) shows fascinating ways of controlling and staggering seed germination throughout the year. Seeds within the large inflated fruiting valves (fruits) display variations in their ability to germinate, which are related to the time of the year and depend on the presence of light. Perianth-imposed dormancy appears to undergo one distinct seasonal cycle under laboratory conditions. Our results suggest that germination is best during the autumn and winter months but poor during the rest of the year. In the natural environment (fruits either remain on the soil surface or are buried) dormancy release may be occurring several times during the year under appropriate light, temperature and moisture conditions. Preliminary experiments indicate that the fruiting valves produce chemical substances that inhibit seed germination, and their break down appears to be affected by light.

Studies on the soil seed bank of the environmental weed Rumex vesicarius (Fam.: Polygonaceae) at a rehabilitated mine site in semi-arid Western Australia

“…However, in most cases only one seedling emerged from each fruit and the soil still contained a large number of potentially viable Ruby Dock seeds. It is likely that the majority of the seedlings was produced by light seeds since usually light seeds germinate first, and only additional seedlings are produced by dark seeds (Schatral and Osborne, 2006b). Of a total of 120 fruits 53 fruits produced one seedling and eight fruits produced two seedlings during the three germination seasons.…”

“…Non-viable light seeds were frequently open, with shrivelled radicles emerging and therefore obviously died very soon after germination (perhaps due to a lack of sufficient moisture). During the experiments in the greenhouse mostly light seeds appeared to have germinated since (1) we found more dark than light seeds after the completion of the experiments, and (2) only a very small number of the fruits produced two seedlings (usually the light seed germinates first, additional seedlings are produced by dark seeds (Schatral and Osborne, 2006b)). Similarly, a study which compared Ruby Dock populations from several different semi-arid areas in Western Australia and the Northern Territory shows that potentially viable light seeds were significantly less common in the partly decomposed fruits collected in the soil than in intact fruits attached to or newly shed by maternal plants (Schatral and Osborne, 2006b).…”

“…During the experiments in the greenhouse mostly light seeds appeared to have germinated since (1) we found more dark than light seeds after the completion of the experiments, and (2) only a very small number of the fruits produced two seedlings (usually the light seed germinates first, additional seedlings are produced by dark seeds (Schatral and Osborne, 2006b)). Similarly, a study which compared Ruby Dock populations from several different semi-arid areas in Western Australia and the Northern Territory shows that potentially viable light seeds were significantly less common in the partly decomposed fruits collected in the soil than in intact fruits attached to or newly shed by maternal plants (Schatral and Osborne, 2006b). Finally, recent data collected during a study in the greenhouse demonstrate that light seeds still enclosed within the intact fruiting perianth and buried in the soil, produced seedlings significantly more often than dark seeds (Schatral, unpublished observation).…”

“…Germination was recorded for 3 weeks (after 21 days no significant germination occurs, see Schatral and Osborne, 2006a Fruits (gathered from waste rock at the Granite Gold mine site, Northern Territory, Australia in 2000) were sown in weed-free topsoil collected at the Granny Smith mine site in 2001 (Laverton, Western Australia). Since the number of seeds per fruit is related to fruit size, and small fruits are often empty (Schatral and Osborne, 2006b) only large fruits of light brown colour (mean weight: 0.05 g) were selected for the trials. The fruits were gently pressed in the soil and covered with a thin layer of soil.…”