Seed dormancy in six cold desert Brassicaceae species with indehiscent fruits

Abstract

The dispersal unit of many species of Brassicaceae is an indehiscent fruit, but relatively few studies have tested the effect of the pericarp on seed germination in this family. Our aim was to determine the effect of the pericarp on seed dormancy in six species of Brassicaceae native to the cold desert of north-west China. Intact dispersal units and isolated seeds of Chorispora sibirica, Euclidium syriacum, Goldbachia laevigata, Spirorrhynchus sabulosus, Sterigmostemum fuhaiense and Tauscheria lasiocarpa were stored dry at ambient laboratory conditions for 0 -12 months and tested for germination in light and in dark at 5/2, 15/2 and 30/158C. The amount of water absorbed by fruits and by seeds within the fruits was determined. For four species, intact fruits, isolated seeds and isolated seeds plus the removed pericarps were used to test for the mechanical versus possible chemical role of the pericarp in seed dormancy. Fresh isolated seeds, which have a fully developed embryo, germinated to lower percentages and rates than afterripened seeds. Thus, seeds have non-deep physiological dormancy. The pericarp significantly reduced germination, but inhibition was not due to lack of water uptake by seeds or to chemical inhibitors. Afterripened seeds of the six species germinated to 0 -50% inside the fruits. We conclude that the pericarp plays a dominant role in seed dormancy of the six study species, and it does so by mechanically restricting embryo growth. Thus, the pericarp has the potential to spread germination over an extended period of time.

Factors affecting the seed germination and seedling emergence of muskweed (Myagrum perfoliatum)

“…Removing the siliques of turnipweed, which has a similar fruit morphology to that of M. perfoliatum , was very effective in breaking its seed dormancy (Cousens et al ; Chauhan et al 2006b; Ohadi et al ). Likewise, other researchers, by working on the effect of the pericarp on seed dormancy in some species of Brassicaceae, have demonstrated that the fruit wall restricts embryo growth, mainly because of its mechanical effects (Cousens et al ; Lu et al , ; Mamut et al ).…”

Delayed dehiscence of the pericarp: role in germination and retention of viability of seeds of two cold desert annual Brassicaceae species

“…The fruit, rather than the seed, is the dispersal/germination unit in many angiosperms, including quite a few species of Brassicaceae (Maun & Payne 1989;Liu & Tan 2007;Cousens et al 2010;Lu et al 2010Lu et al , 2015aOhadi et al 2011;Mamut et al 2014). Plants of Brassicaceae species produce siliques (dry two-valved capsule, three or more times longer than wide) or silicles (dry two-valved capsule, less than three times longer than wide), which differ in structure and size (Hall et al 2011;Zhou et al 2001).…”

“…(iv) Fruits separate into segments, each containing one seed, e.g. Chorispora sibirica (Lu et al 2015a) and Raphanus raphanistrum (Cousens et al 2010). (v) Fruits do not dehisce, but after several months, e.g.…”

“…(Barbour 1970;Hocking 1982;Maun & Lapierre 1986;Maun & Payne 1989;Zhang 1993), Coincya spp. (Copete et al 2005), Fezia pterocarpa (Bermejo & Munoz 1977) and Rapistrum rugosum (Cousens et al 1994); (iii) D. strictus (Lu et al 2010(Lu et al , 2015b; (iv) C. sibirica (Lu et al 2015a) and R. raphanistrum (MeKenian & Willemson 1975;Cousens et al 2010); and (v) C. sibirica, E. syriacum, G. laevigata (Lu et al 2015a), L. lehmannii (Mamut et al 2014), S. sabulosus, S. fuhaiense, T. lasiocarpa (Lu et al 2015a) and I. violascens (Zhou et al 2015). Retention of seed viability has been studied in pericarp variation 2 (R. rugosum; Ohadi et al 2011), pericarp variation 3 (D. strictus;Lu et al 2010Lu et al , 2015b and pericarp variation 5 (L. lehmannii; Mamut et al 2014;I.…”

“…Based on results from studies of indehiscent fruits of cold desert Brassicaceae (Lu et al 2010(Lu et al , 2015aMamut et al 2014;Zhou et al 2015), we hypothesised that the pericarp of L. filifolium and N. korolkovii can influence seed dormancy, germination phenology and retention of viability. To test this hypothesis, we compared dormancy-break via after-ripening in the laboratory and retention of viability and germination phenology in an experimental garden of seeds in intact siliques and isolated seeds.…”