Academic literature on the topic 'Seedbank persistence'

Effective weed seedbank management requires mechanistic understanding of ecological determinants of seed persistence in the soil seedbank. Chemical and physical defense of common lambsquarters, field pennycress, giant foxtail, kochia, velvetleaf, and yellow foxtail seeds were quantified in relation to short- and long-term seedbank persistence. Seed content ofortho-dihydroxyphenols (o-DHP), a class of putative seed defense compounds, varied more than threefold between the least protected species (common lambsquarters, 9.2 µg g seed−1) and the most protected species (kochia, 34.1 µg g seed−1). Seedo-DHP was inversely related (r= −0.77, P < 0.001) to seed half-life in the soil and to short-term seed persistence in burial assays (r= −0.82, P < 0.05). The relative importance of chemical seed protection in comparison to physical seed protection, as represented by the ratio of seedo-DHP concentration to seed coat thickness, decreased linearly with increasing short-term seed persistence (r= −0.96, P < 0.01) and nonlinearly with increasing long-term seed persistence in the soil seedbank (y = 0.16 + 0.21/(0.0432 + x),R2= 0.99, P < 0.001). Mechanical damage to the seed coat, via piercing, slicing, or grinding treatments, increased short-term mortality during burial for all six species. Mortality of pierced seeds was negatively associated (r= −0.35, P < 0.05) with seed phenol concentration and positively associated with seed half-life (r= 0.42, P < 0.01) and seed coat thickness (r= 0.36, P < 0.05). Seed phenolics, as a class, supported the results foro-DHPs. Overall, these findings suggest a potential weakness, with respect to seedbank management, in the way weed seed defenses are constructed. Weed species with transient seedbanks appear to invest more in chemical defense than those species with highly persistent seedbanks. As a result, seeds in the latter category are relatively more dependent upon physical seed protection for persistence in the soil seedbank, and more vulnerable to management tactics that reduce the physical integrity of the weed seed coat.

The ability to produce highly dense and persistent seedbanks is a major contributor to the successful widespread establishment of invasive plants. This study seeks to identify seed persistence and seedbank longevity for the invasive tussock grass Nassella trichotoma (Nees.) Hack. ex Arechav in order to recommend management strategies for preventing re-emergence from the seedbank. To determine the seedbank longevity and persistence, two experiments were conducted: (i) seeds were buried at four depths (0, 1, 2, and 4 cm) and collected and assessed for viability, seed decay, and in-field germination after 6, 9, 12, 15, and 18 months of field burial; and (ii) seeds were exposed to artificial ageing conditions (60% RH and 45 °C) for 1, 2, 5, 9, 20, 30, 50, 75, 100, and 120 days, and viability was determined through germination tests and tetrazolium tests. Less than 10% of the seeds collected after 12 months of in-field burial were viable. The artificial ageing treatment found germination declined to 50% after 5.8 days, further suggesting that N. trichotoma seeds are short lived. The results from both experiments indicate that N. trichotoma has a transient seedbank, with less than 10% of the seeds demonstrating short-term persistence. It is likely the persistent seeds beyond 12 months were exhibiting secondary dormancy as viable seeds did not germinate under optimal germination conditions. The “Best Practice Guidelines” recommend monitoring for seedbank recruitment for at least three years after treating N. trichotoma infestations. The results of this study support this recommendation as a small proportion of the seeds demonstrated short-term persistence.

Studies suggest that disturbance-induced reductions in soil seedbank density are diminished by periods of water scarcity after soil disturbance; however, this hypothesis has yet to be tested. The objectives of this study were (1) to determine the effects of increasing time between soil disturbance and flood irrigation on disturbance-induced reductions in soil seedbank density, and (2) to identify specific soil moisture levels that cause seedbank reductions under flood irrigation. Weed species in this study were junglerice, Palmer amaranth, and yellow foxtail. For Objective 1, artificial seedbanks with known numbers of seeds were disturbed 10, 3, or 0 d prior to flood irrigations under field conditions. For Objective 2, seeds were buried in soil mesocosms that were hydrated to specific soil water potentials (flooded, 0 kPa, −30 kPa, −60 kPa, and −180 kPa) and placed in laboratory conditions favorable for germination. For both objectives, seeds were recovered to determine the percentages of buried seeds that survived the disturbance or moisture treatments. Results for the field study indicated that soil disturbances reduced seedbank persistence of Palmer amaranth but did not affect seedbank persistence of junglerice and yellow foxtail. Disturbance-induced reductions in seedbank density were greatest when soil was disturbed 0 and 3 d prior to flood irrigations. For the laboratory study, results showed that waterlogged soil was not required for seedbank losses because rates of seedbank persistence were greater in saturated soils (0 kPa and flooded) compared to the lower moisture levels. These studies indicate that delays in irrigation can reduce the seedbank reduction potentials of soil disturbance events. Further, irrigation timing effects on disturbed soil seedbanks are likely to occur in all irrigation systems, including those that reduce the amount of water applied compared to flood irrigation.

Poor pasture persistence and ingress of weedy species are major concerns for farmers The seedbank gives an indication of what weedy species may establish in pastures and compete with sown species It was hypothesised that the aboveground composition reflects the seedbank The seedbank was sampled and botanical assessments were undertaken during OctoberNovember 2009 in Northland Waikato Taranaki and North Canterbury Aboveground botanical composition did not reflect the weed seedbank composition in any of the regions assessed While cover of grasses was greater than legumes and herbs aboveground weedy herbs were most dominant in the seedbank followed by grasses then legumes There was no emergence of sown grass from the seedbank highlighting the lack of a persistent sown grass seedbank which may contribute to poor pasture persistence

In western Canada, little is known about the seedbank ecology of volunteer canola. Therefore, integrated recommendations for the management of this weed are limited. In this study, we investigated the seedbank persistence and seedling recruitment of two spring canola genotype groups with different secondary seed dormancy potentials under contrasting tillage systems. The study was conducted at two locations with different soils in the Mixed Moist Grassland ecoregion of Saskatchewan. A single cohort seedbank was established in 1999 and was followed for 3 yr in successive wheat crops. In a separate laboratory study, the six canola genotypes examined were classified as those with high and those with medium potentials for the development of secondary seed dormancy (HD and MD, respectively). After one, two, and three winters, maximum persistence of 44, 1.4, and 0.2% of the original seedbank was observed among the treatments, respectively. In 2001, HD canola genotypes tended to exhibit 6- to 12-fold greater persistence than MD canola genotypes, indicating lower seedbank mortality in HD canola. Seedling recruitment of HD canola also was higher than MD canola when differences were observed between these genotype groups. Therefore, long-term seedbank persistence of canola can be reduced by growing genotypes with low inherent potential for the development of secondary seed dormancy. The proportion of persisting seeds tended to be higher under conventional tillage than under zero tillage because of lower seedbank mortality, but no clear distinction in seedbank persistence in terms of absolute time could be made between these two tillage systems. Volunteer canola seedling recruitment followed the pattern of a typical summer-annual weed, where seedling emergence was observed only during May and June.

Frequent cultivation is often used to control weeds in crops such as lettuce. The efficacy of this technique on weed populations has been evaluated, but the effect on weed emergence and seedbanks is less documented. Studies in mineral soil indicate that soil disturbance can increase both weed emergence and seed persistence depending on where seeds are redistributed in the soil profile. Evaluations done in muck soil are scarce. This study evaluated the effect of two and four repetitive shallow (3.4 to 7.1 cm deep) cultivations on weed emergence and the weed seedbank in muck soil. Cultivation treatments (0, 2, and 4 cultivations using a inter-row rototiller) were done in lettuce plots from 2017 to 2019. Weed density was evaluated by species before each cultivation date and after crop harvest. Viable seedbanks were evaluated by collecting soil samples before and after each growing season and placing them in greenhouse flats. Statistical analyses were based on mixed models. Results showed that shallow cultivation modified the emergence patterns of weeds but did not reduce total emergence during the subsequent years or viable seedbanks. After two seasons without seed inputs, total emergence was reduced by 46.6% and the seedbank was reduced by 31.7% regardless of the cultivation treatment. However, the seedbank of the very abundant common purslane (Portulaca oleracea) remained high.

Smooth barley has emerged as a problematic weed in cereal crops of South Australia. After the recent reports of herbicide resistance and increase in seed dormancy in smooth barley, it was considered important to determine the herbicide resistance status and seedbank behavior of field populations of this weed species. A field survey was undertaken in the Upper North and Eyre Peninsula regions of South Australia in October 2012. Of the 90 smooth barley populations screened for resistance to quizalofop, 15% exhibited some level of resistance and 85% were susceptible. Resistance to acetolactate synthase (ALS)-inhibiting herbicides was low, with only 3 and 12% of populations classified as developing resistance to imazamox + imazapyr and sulfosulfuron, respectively. No multiple resistance patterns were observed; however, two ALS-inhibiting herbicide-resistant populations had sulfonylurea-to-imidazolinone cross-resistance. At the start of the growing season, the majority of smooth barley populations emerged rapidly (median 50% time to emergence [T50] = 8 d). In contrast, some populations of smooth barley displayed an extremely slow emergence pattern, withT50of > 20 d. No direct linkage between seed dormancy and herbicide resistance was observed. However, two acetyl coenzyme A carboxylase-inhibiting herbicide-resistant populations were highly dormant and exhibited delayed emergence. The majority of smooth barley populations showed low-level or no seedbank persistence, but a few populations persisted for 1 yr. However, some weed populations had up to 20% seedbank persistence from 1 yr to the next. Overall there was a strong negative relationship between smooth barley seedling emergence and the level of seed persistence (R2= 0.84, P < 0.05). This association indicated that greater seed dormancy could be responsible for extended persistence of the seedbank of this weed species. The study provides valuable insights into the general pattern of herbicide resistance and the behavior of the seedbank of smooth barley populations on South Australian farms.

Despite efforts to eliminate weeds, they continue to thrive. Weed persistence is reliant upon the soil seedbank. Knowledge of the soil seedbank is continually expanding, but with the rising threat of herbicide-resistant weeds in agriculture, weed scientists have, in the past, focused their management tactics to more short-term solutions that tackle the aboveground problems, rather than long-term solutions. This article summarized the soil seedbank dynamics of weed seeds and derives management options, from a North American weed scientists’ perspective, that (i) favor the depletion of the seedbank, (ii) favor the germination of the seedbank, and (iii) reduce the possibilities of seed produced by the seedlings that germinated to return the soil. These options can potentially deter herbicide resistance and are successful in the short term for reducing field weed infestations, but are likely to take many years to affect recruitment to the weed seedbank, including recruitment of weed species with a high risk for resistance. The natural longevity of the seedbank suggests that alternative or additional weed management tactics are required to reduce the store of weed seeds in the active seedbank.

Models of weed population demography are critical to understanding the long-term viability of management strategies. The driving factors of weed seedbank persistence are often underrepresented in demographic models due to the cumbersome nature of seedbank research. Simplification of weed seedbank dynamics may induce substantial error in model simulations. A soil bioassay was conducted to determine whether growth of different crop species, including wheat (Triticum aestivum L.), canola (Brassica napus L.), and field pea (Pisum sativum L.), differentially impact seed mortality of kochia [Bassia scoparia (L.) A.J. Scott], wild oat (Avena fatua L.), and volunteer canola in seven burial environments in western Canada. Weed seed survival after the 7 week burial period varied widely among burial environments (from 8% to 88% when averaged among weed and crop species), whereas growth of the different crop species had negligible impact on seedbank persistence. Among environments, wild oat seed survived the greatest (79%), followed by kochia (20%), and volunteer canola (6%). Weed seed survival was associated with soil physical properties (texture) and seed microsite characteristics (temperature), but not crop species or soil chemical properties. Overall, these data support the need for greater integration of soil and environmental parameters into models of weed population demography.

Aboveground botanical composition and seedling emergence from the soil seedbank were assessed in 30 Bay of Plenty dairy pastures in spring 2010 Pastures ranged in age (young 12 years medium 34 years old 56 years) and included those with and without forage herbs (chicory and/or plantain) As pastures aged there was an increase in the percentage of total dry matter of unsown weed grasses (3 8 27) and unsown herbaceous weeds (5 18 39) in young medium and old pastures sown with herbs respectively Unsown weed grasses dominated the seedbank and together with herbaceous weeds comprised more than 99 of seedlings that emerged from the seedbank Farm managers ranked insect pests and climate (eg droughts/floods) as the primary factors causing the decline of sown species while grazing management was perceived as the most important factor that can improve persistence of sown species

Chloris truncata and C. virgata, which are major weeds in cotton and grain crops in the sub-tropical region of Australia, have recently emerged as potential weeds of the future in southern Australia. Glyphosate, an inhibitor of 5-enolpyruvylshikimate-3- phosphate synthase (EPSPS), is the most widely used non-selective post-emergence herbicide globally. As a result of over-reliance on glyphosate combined with dominance of reduced tillage systems for weed control, glyphosate-resistant populations of C. truncata have already been reported in Australia. C. virgata is also considered hard to kill with glyphosate, but resistance has not been reported so far in the literature. Studies on growth, development and seed biology of C. truncata and C. virgata were conducted to better understand the biology of these emerging weed species. Under field conditions, C. truncata and C. virgata required 748-786 degree-days (Cd) and 1200 Cd respectively to progress from emergence to mature seed production. Freshly produced seeds of C. virgata were dormant for about 2 months, whereas 16-40% of seeds of C. truncata germinated within a week after maturation. Seed dormancy of C. virgata was released by the pre-treatment with 564 mM NaClO for 30 minutes. Exposure to light significantly increased germination of C. truncata seed from 0-2% in the dark to 77-84% in the light, and of C. virgata seed from 2-35% in the dark to 72- 85% in the light. Seeds of these two species could germinate over a wide temperature range (10-40oC), with maximum germination at 20-25oC for C. truncata and 15-25oC for C. virgata. The predicted base temperature for germination was 9.2-11.2oC for C. truncata and much lower 2.1-3.0oC for C. virgata. Seedling emergence of C. virgata (76% for seeds present on soil surface) was significantly reduced by burial at 1 (57%), 2 (49%) and 5 cm (9%), whereas seedling emergence of C. truncata was completely inhibited by burial of seed even at a shallow depth (0.5 cm). Under field conditions, both C. truncata and C. virgata seeds persisted in the soil for at least 11 months and seasons with below-average spring-summer rainfall increased seed persistence. Detailed studies were undertaken to identify glyphosate-resistant populations and to understand the mechanism of glyphosate resistance in C. truncata and C. virgata. Glyphosate resistance (GR) was confirmed in five populations of C. truncata and four populations of C. virgata. GR plants were 2.4 to 8.7-fold (C. truncata) and 2 to 9.7-fold (C. virgata) more resistant and accumulated less shikimate after glyphosate treatment than susceptible (S) plants. The differences in shikimate accumulation indicated that glyphosate did reach the target site but inhibited the EPSPS enzyme of each population differently. Glyphosate absorption and translocation did not differ between GR and S plants of either C. truncata or C. virgata. Two target-site EPSPS mutations (Pro-106-Leu and Pro-106-Ser) were likely to be the primary mechanism of glyphosate resistance in C. virgata but no previously known target-site mutations were identified in C. truncata. The C. virgata population with Pro-106-Leu substitution was 2.9 to 4.9-fold more resistant than those with Pro-106-Ser substitution. The primary mechanism of resistance to glyphosate in C. truncata was a combination of target-site EPSPS mutation (Glu-91-Ala) and amplification of the EPSPS gene. There were 16 to 48-fold more copies of the EPSPS gene in GR plants compared to S plants, with the number of EPSPS copies found to be variable both between and within populations.
Thesis (Ph.D.) -- University of Adelaide, School of Agriculture, Food & Wine, 2017