Dormancy in seeds of Hibbertia cuneiformis and H. huegelii (Dilleniaceae)

Abstract

Dormancy delays the germination of seeds in two species of the primitive angiosperm genus Hibbertia (H. cuneiformis and H. huegelii, family Dilleniaceae). After seed coat removal, germination increased in 18-month-old seeds of H. cuneiformis and 6- to 8-month-old seeds of H. huegelii. Hence, seeds of the two species exhibit seed coat dormancy. The removal of the seed coat may stimulate germination, as the result of increased water uptake, and/or the removal of mechanical and chemical inhibition. However, the occurrence of imbibitional injury and a reduced percentage of vigorous seedlings in decoated seeds suggest that embryo dormancy, as a second type of dormancy, impedes germination in H. cuneiformis. Embryo dormancy also delays the germination of seeds of H. huegelii, since a high percentage of seeds did not germinate after removal of the seed coat. Embryo dormancy appears to vary among individual seeds and between species. The germination experiments suggest a high percentage of non-dormant and weakly dormant embryos for 18-month-old seeds of H. cuneiformis. By contrast, many seeds of H. huegelii appear to contain deeply dormant embryos. In H. cuneiformis, the depth of the seed dormancy varied with the age of the seeds. Freshly harvested seeds did not germinate for 3 months. Treatment with gibberellic acid (GA3) (120 mg L-1) significantly enhanced germination of freshly harvested and 18-month-old, intact seeds of H. cuneiformis and the germination of decoated 18-month-old seeds of H. huegelii. The plant hormones kinetin and abscisic acid did not affect the final germination percentage in 18-month-old seeds of H. cuneiformis. For H. huegelii, germination was reduced in decoated seeds and seeds with cracked coats exposed to an 8 h day: 16 h night diurnal cycle compared with complete darkness.

Relationships between seed germination requirements and ecophysiological characteristics aid the recovery of threatened native plant species in Western Australia

“…This study also employed a number of these techniques to stimulate germination in threatened Western Australian taxa. Excision of seeds from the woody fruits of the Myoporaceae ( Myoporum and Eremophila ) as reported previously by Richmond & Ghisalberti (1994), and also for Hibbertia as reported by Schatral (1996) and Schatral et al (1997), produced high germination percentages in the study taxa. Fruit or seed coats may restrict oxygen and water exchange, and may create a physical barrier to radicle emergence (Beardsell et al 1993).…”

“…Dormancy takes many forms and includes both external (coat‐imposed) and internal (embryo) controls on germination (Bewley & Black 1994). No single set of conditions will give optimal germination in all species, and a wide range of environmental cues may be required for the breaking of dormancy and the initiation of germination (Langkamp 1987; Bell et al 1993; Richmond & Chinnock 1994; Dixon et al 1995; Plummer & Bell 1995; Plummer et al 1995; Schatral 1996; Schatral et al 1997; Bell 1999).…”

Sympatric species of Hibbertia (Dilleniaceae) vary in dormancy break and germination requirements: implications for classifying morphophysiological dormancy in Mediterranean biomes

“…Thus, the broadest range of temperatures for stimulating germination was achieved with dark conditions during stratification for H. racemosa. Schatral et al (1997) found that 6-to 8-month-old seeds of H. huegelii germinated to 32 % in darkness when the seed coat was removed but to 2 % in alternating light/dark conditions. Seeds of this species also germinated to higher percentages in darkness than in light/ dark when seed coats were cracked; no intact seeds germinated regardless of the light conditions.…”

“…The germination process in Hibbertia is slow -seeds of several species take on average 37-76 d for seedling emergence (Kullmann, 1981), a feature that means this genus is unreliable in propagation programmes and ecological restoration where broadcast seeding requires seed to be cued for germination (Merritt and Dixon, 2011). Germination is influenced by slow imbibition and seed ageing in the soil, and may be stimulated by exogenous application of GA 3 (Schatral, 1996;Schatral et al, 1997;Roche et al, 1997a;Allan et al, 2004). Application of smoke, as smoke water or as an aerosol, occasionally increases germination under ex situ conditions and enhances seedling emergence in the field (Dixon et al, 1995;Roche et al, 1997bRoche et al, , 1998Clarke et al, 2000;Tieu et al, 2001).…”

Alleviation of morphophysiological dormancy in seeds of the Australian arid-zone endemic shrub, Hibbertia glaberrima F. Muell. (Dilleniaceae)

“…Hibbertia is a large genus ( ca 225 species) of the family Dilleniaceae that is widely distributed throughout Australia, with a smaller number of species also occurring in Madagascar, New Guinea, New Caledonia and Fiji (Wheeler et al ., 1992; Horn, 2007). Previous studies investigating seed dormancy and germination characteristics in Hibbertia species from the south-west Western Australia (Mediterranean climate) and New Caledonia (tropical climate) have noted that their seeds are often deeply dormant, are slow to germinate, and possess MD or MPD (Schatral, 1996; Schatral et al ., 1997; Allan et al ., 2004; Hidayati et al ., 2012; Wulff et al ., 2012). For example, seeds of H. pancheri from New Caledonia only germinated after incubation for 50 days at 30°C, irrespective of whether seeds were exposed to a germination stimulant (Wulff et al ., 2012), while seeds of H. commutata from Western Australia did not germinate for at least 18 weeks, even under favourable temperatures (Hidayati et al ., 2012).…”