Variability and correlative interdependence of red clover and Italian ryegrass seed quality depending on varieties during the multi-year storage period

Seed quality is crucial for achieving the desired number of plants in the mixture, as well as the ratio of grass-legume components. Seeds of red clover and Italian ryegrass can be placed on the market with germination of 70 % and more. In this experiment, the seeds of six varieties of red clover and four varieties of Italian lily were examined. Seeds up to four years of age were tested. Seed quality was examined by monitoring the following parameters: germination energy, amount of hard-dormant seed, total germination and amount of abnormal seedlings. The tested varieties of red clover and Italian ryegrass seeds showed the best quality after one and two years of storage. After four years of storing seeds, out of six tested varieties of red clover, two did not meet the criteria for marketing in Serbia, according to the current rulebook on seed quality. In the case of Italian ryegrass, out of four tested varieties, two did not meet the criteria for placing seeds on the market.

Seed Dormancy in Hairy Vetch (Vicia villosa Roth) Is Influenced by Genotype and Environment

Seed dormancy complicates the agricultural use of many legume species. Understanding the genetic and environmental drivers of seed dormancy is necessary for advancing crop improvement for legumes, such as Vicia villosa. In this study, we quantify the magnitude of genetic and environmental effects on physical dormancy among 1488 maternal V. villosa plants from 18 diverse environments. Furthermore, we explore the relationship between physical dormancy and environmental conditions during seed development. Additive genetic variance (h2) accounted for 40% of the variance, while the growing environment explained 28% of the variance in physical dormancy. Maternal lines showed complete variance in physical dormancy, as one line was 100% dormant, and 56 lines were 0% dormant. Distributions of physical dormancy varied widely among seed production environments, with some site-years strongly skewed toward physically dormant seed, while other site-years exhibited little dormant seed. Twenty-three weather variables were associated with environmental and error effects of physical dormancy. High mean and minimum relative humidity, low mean and maximum temperature, and high precipitation weakly grouped with low physical dormancy. Weather variables calculated from fixed time windows approximating seed maturity to seed harvest at each site-year tended to be less predictive than biological seed drying windows calculated based on seed maturity of each maternal line. Overall, individual and cumulative effects of weather variables were poor predictors of physical dormancy. Moderate heritability indicates that breeding programs can select against physical dormancy and improve V. villosa for agricultural use. Marker-based approaches would maximize selection for physical dormancy by reducing the influence of unpredictable environmental effects.

Depauperate seed banks in urban tropical seagrass meadows

Seagrasses need to be resilient if they are to persist in the long term. Being able to build up a dormant seed bank in sediments is a key strategy that some species employ to regenerate from large-scale degradation. Much of the research on seed banks has focussed on temperate species, and little is known regarding the status of seed banks in tropical meadows. In the present study, we examined the seed bank status of three common seagrass species at six sites in Singapore and attempted to identify potential drivers of seed abundance. Our results indicated depauperate seed banks with few species setting viable seed and low seed densities. Halophila ovalis seeds were found at four sites and Halodule uninervis seeds at two sites, but Cymodocea rotundata seeds were absent from all six sites. Whereas H. ovalis seed viability ranged from 20% to 68.8%, none of the H. uninervis seeds was viable. Halophila ovalis seed densities (33–334m–2) were much higher than those of H. uninervis (9–21m–2). Of the variables examined, only H. ovalis cover was positively correlated with the number of seeds. Our study has highlighted the vulnerability of seagrass meadows in Singapore’s urban waters to future disturbances.

Conditional dormancy of Stipa lagascae (Poaceae) bulk-harvested on seed increase plots in South Tunisia: a reassessment and a surprise

Background and aims – With the perspective to reseed degraded drylands, grass seeds are often stocked for several years. This common practice overlooks conditional dormancy and the necessity to preserve it. This paper reports on the germination ecology of Stipa lagascae Roem. & Schult., which is a circum-Mediterranean winter-growing bunch grass of high grazing value. However, the published record on its germination ecology is scarce and inconsistent.Methods – This record was reassessed through a series of germination trials in combination with dormancy breaking treatments on seeds that were mainly harvested on a seed increase plot in South-Tunisia.Key results –The surprise finding was that Stipa lagascae exhibits a particular kind of conditional dormancy for many months after harvest. Whereas dormant seeds barely germinate at 10°C in classical Petri dishes or on germination tables, they germinate massively (but not fully) when allowed full contact with a water-saturated substrate at 7–10°C in boxes. Dehulling provokes fast germination of near 100% of the seeds, thus showing that the substrate effect at low temperatures breaks most but not all dormancy in a particular seed lot. This remaining or residual dormancy is not conditional, as it can only be broken through dehulling. There are thus two distinct germination windows: a very broad one for non-dormant seed and a narrow one for conditionally dormant seed.Conclusions – A pattern is suggested whereby each seed lot evolves through a continuum from full over conditional to non-dormancy and finally mortality. However, only the state of conditional dormancy times germination optimally with regard to the start of the winter growing season in South-Tunisia. Its ecological significance should be interpreted in combination with its trypanocarpy. Reseeding for restoration purposes and to render grazing value to depleted drylands should thus use conditionally dormant seed.

Alleviation of dormancy in annual ryegrass (Lolium rigidum) seeds by hydration and after-ripening

The effect of hydration (priming) treatment on dormancy release in annual ryegrass seeds from two populations was investigated. Hydration duration, number, and timing with respect to after-ripening were compared in an experiment involving 15 treatment regimens for 12 wk. Seeds were hydrated at 100% relative humidity for 0, 2, or 10 d at Weeks 1, 6, or 12 of after-ripening. Dormancy status was assessed after each hydration treatment by measuring seed germination at 12-hourly alternating 25/15 C (light/dark) periods using seeds directly from the hydration treatment and seeds subjected to 4 d postpriming desiccation. Seeds exposed to one or more hydration events during the 12 wk were less dormant than seeds that remained dry throughout after-ripening. The longer hydration of 10 d promoted greater dormancy loss than either a 2-d hydration or no hydration. For the seed lot that was most dormant at the start of the experiment, two or three rather than one hydration event or a hydration event earlier rather than later during after-ripening promoted greater dormancy release. These effects were not significant for the less-dormant seed lot. For both seed lots, the effect of a single hydration for 2 d at Week 1 or 6 of after-ripening was not manifested until the test at Week 12 of the experiment, suggesting that the hydration events alter the rate of dormancy release during subsequent after-ripening. A hydrothermal priming time model, usually used for modeling the effect of priming on germination rate of nondormant seeds, was successfully applied to dormancy release resulting from the hydration treatments.

Effect of tillage, fungicide seed treatment, and soil fumigation on seed bank dynamics of wild oat (Avena fatua)

No-tillage offers potential for improved soil quality, reduced erosion, and equal or increased crop yields. We hypothesized that, compared with conservation tillage (CT), no-tillage (NT) offers conditions more conducive to microbial decay of weed seed. In NT systems seed remain at or near the soil surface where crop residues, moisture, and lack of disturbance create an environment with greater soil microbial diversity. In late fall of 1998 and 1999, dormant seed of wild oat, either individually glued to plastic toothpicks or mixed with soil and placed in mesh bags, were buried (mean seed depth of 2.5 cm) in replicated field plots managed by NT or CT since 1982. Treatments including fungicide seed treatment (thiram + metalaxyl + captan) and soil fumigation (propylene oxide) provided estimates of the contribution of microorganisms to observed mortality. Seed were retrieved in May and August, 1999 and 2000. Contrary to our original hypothesis, the proportion of dead seed was generally similar in NT and CT systems. Lack of tillage system by seed or soil treatments affecting the proportion of dead or decayed seed suggests that the contribution of microorganisms to seed fate is similar in these tillage environments. However, the proportion of dormant seed was consistently lower in the NT compared with CT treatments; there was a corresponding increase in the proportion of germinated seed. Overall, more than half of the wild oat seed bank losses could be directly attributed to germination whereas losses due to decay were relatively minor by comparison. Despite favorable distribution of seed and improved quality of the surface-strata of soil in NT systems, this study fails to provide evidence that enhanced microbial decay will contribute to a “weed-suppressive” capacity in such cropping systems.

INDUCTION OF SPROUTING IN DORMANT YAM (DIOSCOREA SPP.) TUBERS WITH INHIBITORS OF GIBBERELLINS

A reliable means to induce sprouting in dormant seed tubers of yams (Dioscorea species) is required to enhance flexibility in planting date and rate of propagation of the crop. Experiments were conducted to assess the potential of two gibberellin inhibitors, Uniconazole-P and Prohexadione-calcium, to induce sprouting in tubers from three varieties of D. rotundata and four of D. alata. Uniconazole-P and Prohexadione-calcium shortened the period of dormancy in tubers of some varieties. In others, they either had no effect or extended dormancy. The varietal responses were also influenced by whether the tubers were treated at harvest (before shoot senescence) or four weeks after harvest by which time shoots had senesced fully. Tubers stored in darkness at a constant temperature of 30 °C sprouted earlier but lost weight faster than did those stored under natural daylight and ambient temperature. The apparent slow action of Uniconazole-P and Prohexadione-calcium, and their variable effectiveness in relation to variety, would limit their usefulness in seed or breeding programmes, or in determining treatment timing and the best storage environment for the tubers after treatment.

Patterns in longevity of soil seedbanks in fire-prone communities of south-eastern Australia

Seed burial in nylon mesh bags over a 2-year period was used to examine seed longevity patterns in 12 shrub and two graminoid species in fire-prone habitats around Sydney, south-eastern Australia. Most species released a large fraction of their annual seed-crop in a dormant state and all species showed evidence for some form of persistent seedbank. However, regressions of seed persistence over time were in most cases poor predictors of seed decay (9 of 14 study species). Considerable variation in the degree and pattern of seed longevity was apparent in the study species. Three functional groupings of species are suggested. (1) Seed half-lives in the soil predicted to be greater than 2 years and evidence of imposed secondary dormancy (continuous, Kunzea spp. or seasonal, Grevillea caleyi). Only Kunzea capitata and G. caleyi showed significant seed decay in this group. (2) Seed half-lives in the soil predicted to be greater than 2 years and no evidence of secondary dormancy (nine species). Six species had high seed dormancy at release (only two of which showed significant seed decay). Three species had initial seed dormancy of 40–57%—two (Asterolasia elegans and Zieria involucrata) with significant decay only for the non-dormant seed fraction, and one (Comesperma ericinum) with significant decay of both the dormant and non-dormant seed fractions. (3) Two species (Darwinia biflora and Persoonia pinifolia) showed evidence of very short mean half-lives of seeds in the soil (0.4–1.0 years). The threatened species, D. biflora, had a rapid initial seed decay over 6 months followed by little decay for 18 months, and the half-life of seeds is likely to be a poor predictor of seed longevity. For P. pinifolia, maintenance of a soil seedbank is predicted to be dependent on continual inputs of seeds locally or dispersal of seeds from other sites.