Effects of after-harvest period and environmental factors on seed dormancy of Amaranthus species

The effects of seven constant temperatures (10–40°C at 5°C intervals) and seven after‐harvest periods (30–540 days after harvest) were evaluated on seed germination of nine Amaranthus species (A. albus, A. blitoides, A. cruentus, A. deflexus, A. graecizans, A. hybridus, A. lividus, A. retroflexus and A. viridis). Seeds of A. blitoides and A. viridis were also tested at alternating temperatures of 10/30°C (12/12 h thermoperiod) in continuous darkness and in an alternating 12/12 h dark/light photoperiod. With the exception of A. blitoides and A. viridis, germination increased as temperature increased from 20 to 35°C; the latter representing the optimum temperature (70–100% germination). At 10 and 15°C constant temperatures, no significant seed germination occurred in A. albus, A. deflexus, A. graecizans and A. lividus, while in A. cruentus, A. hybridus and A. retroflexus there was no germination at 10°C, but at 15°C more than 60% germination occurred. Germination was influenced strongly by after‐ripening period in A. cruentus, A. hybridus and A. retroflexus, partially in A. deflexus, and barely in A. graecizans and A. lividus. Seeds of A. blitoides and A. viridis required alternating temperatures and light to achieve high germination percentage (>90%). Primary dormancy in Amaranthus plays a fundamental role in extending germination over a longer period, so that the probability of seedling survival is maximised. The present study adds to the understanding of the environmental control and germination ecology of Amaranthus species and provides data that can contribute to predicting weed emergence dynamics.     

不同贮藏条件下龙葵种子的季节性休眠特性

龙葵是农田恶性杂草?为明确龙葵种子休眠与季节温度的关系, 研究了室内和室外不同贮藏条件下其种子萌发对温度的响应规律?结果表明, 室外贮藏条件下的龙葵种子萌发呈季节性变化, 从10月到翌年5月, 龙葵种子萌发率均在95%以上, 随着夏季温度的升高, 萌发率从6月开始下降, 9月达到最低值(25.4%), 由此进行年际间休眠和非休眠周期的循环?夏季6月-9月的高温可诱导龙葵种子进入休眠状态, 而秋冬季的相对低温有利于解除种子休眠, 使种子恢复萌发状态?龙葵种子休眠和非休眠状态之间的切换受季节性温度变化的影响?室内贮藏的种子, 由于环境温度较为稳定, 其萌发率年际变化较小, 在20%~50%之间?本文明确了龙葵种子休眠的周期性变化规律, 有助于精准预测其出苗时间, 研究结果可为阐明龙葵种子休眠萌发机制和制订基于萌发调控的绿色防控策略提供依据?     

Seed production and subsequent seed germination of Senecio vulgaris (groundsel) grown alone or in autumn-sown crops

Senecio vulgaris is a common weed of agriculture in the UK, but is also of food value to invertebrates and birds. Thus, it may be beneficial to retain it within agricultural ecosystems to enhance overall biodiversity. A less intensive approach to weed management requires a sound understanding of weed population dynamics so as to avoid unacceptable population growth. Experiments were carried out in 2003 and 2004 to assess seed production, and subsequent germination, by S. vulgaris growing alone, in winter wheat, or in winter field beans. Plant and seed samples were collected during May and June. There was a strong allometric relationship between capsule number and plant weight, irrespective of the year or the presence of crop competition. Numbers of seeds/capsule varied slightly from 51 to 66 seeds per capsule. Plants growing alone were estimated to produce 8471 to 12 887 seeds per plant, whilst those in wheat only 923 to 2156. Germination tests in Petri dishes in incubators showed that virtually all seeds were viable and germinated under daily alternating light:dark conditions within 10 days. Seeds in continuous dark germinated less readily, reaching only 30% after 21 days. On the basis of this and other published work, it would appear that the retention of S. vulgaris in arable fields will not pose a major threat to the long-term viability of crop production.     

Effects of individual plant phenology on dormancy of Rumex obtusifolius seeds at dispersal

In 1998–2000, the relationship was investigated between the time of bolting of shoots and the percentage of germinability in seeds from individual plants of Rumex obtusifolius . Each year, the date of bolting of shoots was recorded in 30–108 plants, which were then grown intact until maturation, and their seeds were collected before dispersal. The proportion of germinable seeds increased with the date on which the shoots bolted. The timing of shoot bolting and seed germinability for individual plants persisted over the years of observation. To discriminate between the effect of mother plant and timing of seed maturation, shoot bolting of another 40 (1998) and 50 (1999) plants was recorded, and their shoots were then cut in late June The shoots of cut plants regrew and matured nearly simultaneously, later than in intact plants, whereas overall seed germinability decreased. In individual plants, the seed germinability was still significantly correlated with the date when plants originally bolted.     

Ecological aspects of seed dormancy-break and germination in Heteranthera limosa (Pontederiaceae), a summer annual weed of rice fields

Summary Heteranthera limosa seeds were buried in flooded and in non-flooded soil and exposed to natural seasonal temperature changes in Lexington, Kentucky, USA. Seeds exhumed after various periods of burial ranging from 2 to 36 months were tested for germination under both flooded and non-flooded conditions. Seeds were dormant at maturity in September and became non-dormant during winter. Seeds buried in non-flooded soil during winter germinated to higher percentages and over a wider range of temperatures when tested under flooded conditions (in light) during spring and summer, than did those buried in flooded soil during winter. Thus, the water regime associated with rice culture (non-flooded in winter and flooded in summer) is optimal for dormancy-break and germination of H. limosa seeds. A portion of the buried seeds exhibited an annual dormancy/non-dormancy cycle, whereas others had a conditional dormancy/non-dormancy cycle. Regardless of the type of cycle, seeds buried in non-flooded soil retained the ability to germinate in light at high temperatures under flooded conditions throughout the summer. Thus, seeds potentially can germinate at any time during the growing season, whenever rice fields are flooded. Flooding fields during winter and/or sowing rice relatively early in the growing season may help in establishing rice before seeds of H. limosa germinate.     

反枝苋种子休眠解除方法研究

研究了光照和黑暗两种条件下氢氧化钠（NaoH）、盐酸（HC l）、赤霉素（GA3）和乙烯利（ETH）处理对反枝苋种子萌发的影响。结果表明,氢氧化钠、盐酸、赤霉素和乙烯利浸泡处理均可以明显提高反枝苋种子的发芽率,且随着试剂浓度的提高,发芽率表现出单峰变化曲线,浓度过低或过高均不利于种子的萌发。其中,赤霉素对解除反枝苋种子休眠最有效,且以200 mg/L浸泡处理24 h效果最好,发芽率可达90.8%,比对照提高了52.5百分点。其次为4%NaOH和6%HC l处理1 h,与800 mg/L ETH处理24 h的效果相当,发芽率在70%~75%之间。黑暗条件不利于反枝苋种子的萌发,发芽率略低于光照条件。     

Germination ecology of seeds of the annual weeds Capsella bursa-pastoris and Descurainia sophia originating from high northern latitudes

Low temperatures may inhibit dormancy break in seeds of winter annuals, therefore it was hypothesized that seeds of Capsella bursa‐pastoris and Descurainia sophia that mature at high latitudes in late summer–early autumn would not germinate until they had been exposed to high summer temperatures. Consequently, germination would be delayed until the second autumn. Most freshly matured seeds of both species collected in August and September in southern Sweden were dormant. After 3 weeks of burial at simulated August (20/10°C) and September (15/6°C) temperatures, 28 and 27%, respectively, of the C. bursa‐pastoris and 56 and 59%, respectively, of the D. sophia seeds germinated in light at 15/6°C. In contrast, in germination phenology studies conducted in Sweden, only a few seeds of either species germinated during the first autumn following dispersal. However, there was a peak of germination of both species the following spring, demonstrating that dormancy was lost during exposure to the low habitat temperatures between late summer and early autumn and spring. Nearly 100% of the seeds of both species subjected to simulated annual seasonal temperature changes were viable after 30.5 months of burial. In the burial study, exhumed seeds of C. bursa‐pastoris were capable of germinating to 98–100% in light at the simulated spring–autumn temperature regime (15/6°C) in both spring and autumn, while those of D. sophia did so only in autumn. In early spring, however, seeds of D. sophia germinated to 17–50% at 15/6°C. Thus, most seeds of these two annual weeds that mature in late summer do not germinate in the first autumn, but they may do so the following spring or in some subsequent autumn or spring.     

低温层积和室温干燥贮藏对4种蒺藜科草本植物种子萌发的影响

研究了低温层积和室温干燥贮藏对河西走廊骆驼蒿(Peganum nigellastrum)、骆驼蓬(P.harmala)、驼蹄瓣(Zygophyllum fabago)和蝎虎驼蹄瓣(Z.mucronatum)蒺藜科4种草本植物种子萌发的影响.结果显示,贮藏条件对4种蒺藜科植物种子萌发率和萌发速率有极显著的影响(P<0.0...     

Effects of maternal light environment on germination and morphological characteristics of Sicyos deppei seeds

The effect was studied of sunlight and far-red (FR) light during seed development, on seed quality and germination of Sicyos deppei G. Don. Seeds exposed to FR during development were lighter in colour and their weight, size and water content were significantly lower. Less than 10% of non-scarified freshly harvested seeds germinated. Scarified, freshly harvested seeds developed under sunlight had a partially negative photoblastic response; both red (R) and FR light inhibited germination. The highest and fastest germination occurred in darkness, probably due to the effect of the high photon flux densities on the phytochrome during seed development. Scarified seeds ripened under FR light, germinated well in FR light and in darkness, but R light inhibited germination. After 6 months of storage, the permeability of S. deppei seeds increased, the partially negative photoblastic response was lost and germination of scarified seeds increased. Specifically, in seeds developed under FR, germination in darkness was faster than for the other light treatments, but slow in darkness for seeds developed under sunlight. The physiological and morphological heteroblastic responses in S. deppei probably extend its seed germination and seedling recruitment periods.     

Seasonal changes in the germination of buried seeds of Monochoria vaginalis

This study investigates the seasonal variation of germination ability of buried seeds of Monochoria vaginalis (Burm.f.) Presl var. plantaginea Solms. The field-collected seeds were buried in a flooded or an upland field and then exhumed monthly. The exhumed seeds were germinated under four temperature regimes. The seeds exhumed from the flooded soil were dormant at the beginning of burial and proceeded into a conditional dormancy/non-dormancy/conditional dormancy cycle throughout the remaining period of the experiment. The seeds exhumed monthly from the non-flooded soil exhibited an annual dormant cycle, which is dormancy/conditional dormancy/non-dormancy/conditional dormancy/dormancy. At day and night temperatures of 25/20 °C, the exhumed seeds from both the flooded and the upland soil resembled each other in terms of seasonal variation of the germination percentage. In September and October, more seeds exhumed from upland soil failed to germinate under higher temperature than from flooded soil. Strictly avoiding exposure to light during seed exhuming and seed testing prevented the seeds from germinating. A short exposure of the exhumed seeds to light during preparation promoted dark germination when the seeds were at the non-dormant stage. The potential implications of our results for weed management strategies in rice production are discussed.