马唐种子萌发及幼苗建成对不同环境因子的响应

马唐是我国常见的旱田杂草之一,然而近年来在部分地区直播稻田危害十分严重.本研究测定了马唐种子萌发和幼苗建成过程中对不同环境因子的响应特征,以期为直播稻田马唐综合防控提供科学依据.结果表明:马唐在 L//D=12 h//12 h,光照/黑暗阶段温度分别为40℃/30℃、35℃/25℃、30℃/20℃、25℃/15℃、20...     

Within‐population variation in resistance of Digitaria sanguinalis to Ustilago syntherismae resulting from different modes of seed germination and environment

In annual plants affected by inflorescence‐invading smut pathogens, avoidance of infection is crucial, while in the event of infection, the existence of different degrees of tolerance could also affect the interaction dynamics. Two experiments were performed with Digitaria sanguinalis spikelets vacuum inoculated with ustilospores of Ustilago syntherismae. In the first experiment, they were sown in pots and mature plants were checked to detect internal hyphae. Observations revealed the presence of symptomless mycelium in a few plants. In the second experiment the spikelets, from two different lots, were grown in a chamber. The objective was to explore the importance of two factors in the degree of seedling infection, one genotypic – type of germination (TG; radicular or coleoptilar) and one environmental – 48 h dark treatment (DT) applied just after germination. Analysis of the infection frequency showed that all the main effects (seed lot origin, TG and DT) were significant, while interactions were not. For TG, the estimated least square mean infection percentages were 66% for radicular germination and 46% for coleoptilar germination. Darkness increased seedling infection by 25%. Differences between TG, DT and their relationship with mesocotyl length exposed to the germinating spores are discussed.     

Suppression of Digitaria sanguinalis and Amaranthus palmeri using autumn-sown glucosinolate-producing cover crops in organically grown bell pepper

Experiments were conducted to compare growth characteristics, biomass production and glucosinolate content of seven autumn‐planted glucosinolate‐producing cover crops that were terminated the following spring. The control of Digitaria sanguinalis and Amaranthus palmeri following cover crop incorporation into soil was characterised and fruit yields of bell pepper transplanted into cover crop‐amended soil were determined. Differences in glucosinolate concentration and composition were noted between cover crop roots and shoots and among cover crops. Total biomass production by cover crops ranged from 103 g m⁻² for garden cress to 894 g m⁻² for Indian mustard (F‐E75), but cover crop biomass was not correlated with D. sanguinalis and A. palmeri control. D. sanguinalis and A. palmeri control in bell pepper varied by cover crop. D. sanguinalis control by cover crops ranged from 38% to 79%, and A. palmeri control was 23% to 48% at 4 weeks after transplanting (WATP) bell pepper in 2004. D. sanguinalis control was positively correlated with total glucosinolate production, but A. palmeri control was not. D. sanguinalis control in 2005 ranged from 0% to 38% at 2 WATP. In the absence of weeds, cover crops did not negatively affect fruit yields which were often higher than in the absence of a cover crop. Glucosinolate‐producing cover crops are not a stand‐alone weed management strategy, but some will provide early season control of D. sanguinalis and A. palmeri without having a negative effect on transplanted bell pepper.     

Phalaris minor seedbank studies: longevity, seedling emergence and seed production as affected by tillage regime

Studies were conducted to investigate seed longevity, seedling emergence and seed production of the weed Phalaris minor in wheat in northern India. The longevity of P. minor seeds buried in bags in the field was often limited to less than 1 year, although many seeds buried at 30 cm depth in a rice–wheat rotation remained viable for longer. The application of direct seeding in wheat reduced the seedling emergence rate of P. minor , when compared with conventional ploughing and sowing. However, a larger P. minor seedbank in the upper soil layer in plots under direct seeding partly reversed this positive effect in one of the two studies. Besides differences in relative distribution of weed seeds through the soil profile, it was likely that other factors such as reduced soil disturbance and soil characteristics associated with the application of direct seeding were also involved in regulating the emergence rate. Mature P. minor plants in wheat were found to invest a stable part (27%) of their aboveground biomass in seed, so that total seed weight was strongly linearly correlated with the aboveground biomass of the mother plant. Individual seed weight, however, was little affected by the weight of the mother plant.     

Weed seedling emergence in contrasting fodder crop systems following 30 years of cultivation in the lowlands of Northern Italy

Five fodder crop systems of different intensity (ranging from a double annual crop of Italian ryegrass + silage maize to a permanent meadow) were adopted for 30 years in the lowlands of Northern Italy under two input levels, differing mainly in their provision of organic fertiliser (manure). Herbicides were used in the maize crops included in all systems, except the meadow. After 30 years, the weed seedbank of all systems and input levels were assessed by the seedling emergence technique on soil samples from each plot. The cropping systems determined the abundance and composition of the weed assembly. Relatively few, frequent species made up the majority of the emerged seedlings in all systems, and there was no relationship between the total number of emerged seedlings and the mean number of species recorded in the different systems. Arabidopsis thaliana and Oxalis corniculata were abundant in the annual double crop and in the 3- and 6-year rotations that also comprised the annual double crop. These weeds, however, were unlikely to represent a major threat to the crops, due to their vigour and growth period. The permanent meadow tended to greater weed biodiversity than the other systems. The application of manure favoured the seedbank of species such as Lolium multiflorum, Digitaria sanguinalis and A. thaliana. Weed communities in the different systems were mainly determined by herbicide application, (through the ability of weeds to avoid its effects, determined by the weed life history and emergence period) and manure application (with its possible dual effect of spreading weed seeds and favouring nitrogen-responsive weeds).     

The dynamics of an interaction between Digitaria sanguinalis and Ustilago syntherismae at local scale is strongly influenced by environment and spatial distribution

A wild loose smut–summer annual grass interaction was studied to explore the relative importance of some local spatiotemporal patterns of variation for its existence. The prevalence-related variable measured was the proportion of diseased plants (PDP). The mean annual PDP of nine consecutive seasons (2009–2017) was analysed using a generalized linear model with a binomial distribution considering covariables related to rainfall. During the seasons 2013–2015, the precise location of each sample within the plot was taken into account. The PDP of these seasons was analysed in various ways by means of generalized linear models, searching for its spatial variation with plant density in a given season, and with sorus and seeded inflorescence densities of the previous season. Symptomless plants were estimated as 6.1% of the 2015 population. The mean annual PDP ranged from 0.08 to 0.42 and covaried positively with precipitation. Within the field, two zones could be repeatedly delimited among seasons: one in which high plant densities and high PDP co-occurred, and another with lower values of both in which PDP depended on the sorus density. The role played by differences in the encounter rate within and among seasons is discussed; lack of encounter could be as necessary as encounter for plant–pathogen coexistence over time.     

播种深度和种子来源对羊草种苗出土的影响

研究了5种播种深度下2种种子来源的羊草(野生和栽培)出苗情况.结果表明:播种深度和种子来源都显著影响羊草出苗率、出苗速率和种苗首次出土时间.羊草出苗率、出苗速率与播种深度成反比.播深1 cm时出苗最多,野生和栽培羊草的出苗率分别为84%和91%;覆土2 cm次之,分别为74.5%和84.5%;覆土6cm出苗最低,为33%和24.25%;不覆土与覆土1 cm的相比分别下降了50.25%和45.25%.野生和栽培羊草的出苗速率分别由覆土1 cm 时的6.46和8.46下降到覆土6 cm时的2.41和1.65.种苗首次出土时间随着播种深度的增加而延长,播种深度1～2 cm时,两种羊草9～10 d都可出苗;不覆土的处理种苗首次出土所需时间最长,分别需要21.25 d和21 d.总体上,栽培羊草的出苗率和出苗速率高于野生羊草的出苗率和出苗速率,栽培羊草首次出苗时间早于野生羊草.     

Fates of Setaria faberi and Abutilon theophrasti seeds in three crop rotation systems

Weed seeds in and on the soil are the primary cause of weed infestations in arable fields. Previous studies have documented reductions in weed seedbanks due to cropping system diversification through extended rotation sequences, but the impacts of different rotation systems on additions to and losses from weed seedbanks remain poorly understood. We conducted an experiment in Iowa, USA, to determine the fates of Setaria faberi and Abutilon theophrasti seeds in 2‐, 3‐ and 4‐year crop rotation systems when seed additions to the soil seedbank were restricted to a single pulse at the initiation of the study. Over the course of the experiment, seedlings were removed as they emerged and prevented from producing new seeds. After 41 months, seed population densities dropped >85% for S. faberi and >65% for A. theophrasti, but differences between rotation systems in the magnitude of seedbank reductions were not detected. Most of the reductions in seedbank densities took place from autumn through early spring in the first 5 months following seed deposition, before seedling emergence occurred, suggesting that seed predation and/or seed decay was important. For S. faberi, total cumulative seedling emergence and total seed mortality did not differ between rotation systems. In contrast, for A. theophrasti, seedling emergence was 71% lower and seed mortality was 83% greater in the 3‐ and 4‐year rotation systems than in the 2‐year system. Results of this study indicate that for certain weed species, such as A. theophrasti, crop rotation systems can strongly affect life‐history processes associated with soil seedbanks.     

Seed dormancy,germination, emergence and seed longevity in Galinsoga parviflora and G. quadriradiata

Galinsoga quadriradiata (hairy galinsoga) and Galinsoga parviflora (smallflower galinsoga, gallant soldier) are very troublesome weeds in many vegetable row crops in Europe. To optimise management strategies for Galinsoga spp. control, an in‐depth study of germination biology was performed. Germination experiments were conducted to evaluate the impact of light and alternating temperatures on germination of a large set of Galinsoga populations. Seedling emergence was investigated by burying seeds at different depths in a sandy and sandy loam soil. Dormancy of fresh seeds harvested in autumn was evaluated by studying germination response in light at 25/20°C with and without nitrate addition. Seed longevity was investigated in an accelerated ageing experiment by exposing seeds to 45°C and 100% relative humidity. Galinsoga spp. seeds required light for germination; light dependency varied among populations. Seedling emergence decreased drastically with increasing burial depth. Maximum depth of emergence varied between 4 and 10 mm depending on soil type and population. In a sandy soil, emergence percentages were higher and seedlings were able to emerge from greater depths than in a sandy loam soil. Freshly produced G. parviflora seeds, harvested in autumn, showed a varying but high degree of primary dormancy and were less persistent than G. quadriradiata seeds that lack primary dormancy. Lack of primary dormancy of freshly harvested G. quadriradiata seeds and light dependency for germination may be used to optimise and develop Galinsoga management strategies.     

Apera spica-venti population dynamics and impact on crop yield as affected by tillage, crop rotation, location and herbicide programmes

Apera spica‐venti is a winter annual grass and, increasingly, a severe weed problem in autumn‐sown crops. Non‐inversion tillage has become more common in Denmark in recent years, but may accentuate problems with A. spica‐venti. These problems may be avoided, if selected preventive and cultural weed management practices are adopted. To this end, we conducted a 4‐year field study investigating the effects of crop rotation, tillage method, location and limited herbicide input on A. spica‐venti population dynamics and crop yield. Additionally, detailed studies were performed on the fate of A. spica‐venti seeds when incorporated to different soil depths. The location with a lighter soil texture, cooler climate and higher rainfall favoured A. spica‐venti growth and consequently crop yield loss, especially in the crop sequence comprised only of autumn‐sown crops and with non‐inversion tine tillage. Incorporating A. spica‐venti seeds in the soil improved their survival, explaining the higher A. spica‐venti proliferation seen with tine tillage as opposed to direct drilling. The rotations including an even mixture of spring‐ and autumn‐sown crops did not lead to noteworthy changes in the A. spica‐venti population, irrespective of tillage method. Thus, in many regions, management of A. spica‐venti will require rotations that balance autumn‐ and spring‐sown crops.