MonitoringPratylenchus thornei densities in SOCL and roots under resistant (Triticum turgidum durum) and susceptible (Triticum aestivum) wheat cultivars

Pratylenchus thornei densities were monitored in field plots of two winter wheat cultivars in a dry farming area of southern Spain. Samples were taken fortnightly during the wheat-growing season and from the following dry fallow. Under bread wheat cv. ‘Yecora’, densities ofP. thornei increased for 5 to 6 months and then were maintained or slightly decreased thereafter, surviving the summer dry fallow in an anhydrobiotic state (78.2% and 85.3% survival in soil and roots, respectively). Under durum wheat cv. ‘Donpedro’, nematode densities decreased over the growing season, although densities within the roots increased during the first 2 months of the wheat-growing period, indicating that nematodes could penetrate the roots of this cultivar but were unable to reproduce. These observations suggest resistance of wheat cv. Donpedro toP. thornei.     

Molecular breeding technologies and strategies for rust resistance in wheat (Triticum aestivum) for sustained food security

Wheat is an important cereal food crop providing key nutrients to humankind. Rusts are the most destructive pathogens of cereal crops, with the exception of rice, across the world and resistant cultivars have been widely employed to reduce the yield losses caused by them. The modern intensive monoculture of cultivars and changing climatic conditions has created congenial conditions for the emergence of new virulent races such as Ug99, which is a great concern for world food security. Conventional breeding efforts have not been effective in quickly developing new varieties with durable and broad‐spectrum resistance against the rapidly evolving rust pathogen races. However, in the last two decades, biotechnological methods such as marker‐assisted selection (MAS) and transgenic technology have provided novel strategies for enhancing resistance levels and durability in crop plants in a short span of time. Nevertheless, broad application of transgenics in agriculture is hindered by biosafety apprehensions. In recent years, improved versions of biotechnological breeding methods such as genomic selection, genome editing technologies, cisgenesis and intragenesis, RNA‐dependent DNA methylation (RdDM), agroinfiltration and reverse breeding are gaining popularity. These technologies provide a tremendous capability to manipulate crop plants more precisely than before and accelerate crop improvement efforts for sustained food production as well as overcoming safety concerns associated with food crops.     

Dissipation of propiconazole residues in and on wheat (Triticum aestivum L.)

In a 2-year investigation, the dissipation of residues of the fungicide propiconazole from winter wheat straw and leaves was measured by periodic sampling of the green plant material from several plots that had been sprayed with ‘Tilt 2.50EC’ at three different rates. The fungicide deposits on straw and leaves at day 0 were approximately one-quarter of the dose applied on all treatment plots, and this fraction did not differ significantly between three dosage rates. The fungicide residues disappeared rapidly, and the half-life of the fungicide on straw and leaves was approximately 5 days. At harvest time, the fungicide residues in grain and soil were negligible, but the residues remaining on straw and leaves were considerable, especially at higher spraying rates than the recommended dosage.     

Cropping systems modify soil biota effects on wheat (Triticum aestivum) growth and competitive ability

Plants alter soil biota which subsequently modifies plant growth, plant–plant interactions and plant community dynamics. While much research has been conducted on the magnitude and importance of soil biota effects (SBEs) in natural systems, little is known in agro‐ecosystems. We investigated whether agricultural management systems could affect SBEs impacts on crop growth and crop–weed competition. Utilising soil collected from eight paired farms, we evaluated the extent to which SBEs differed between conventional and organic farming systems. Soils were conditioned by growing two common annual weeds: Amaranthus retroflexus (redroot pigweed) or Avena fatua (wild oat). Soil biota effects were measured in wheat (Triticum aestivum) growth and crop–weed competition, with SBEs calculated as the natural log of plant biomass in pots inoculated with living soil divided by the plant biomass in pots inoculated with sterilised soil. SBEs were generally more positive when soil inoculum was collected from organic farms compared with conventional farms, suggesting that cropping systems modify the relative abundance of mutualistic and pathogenic organisms responsible for the observed SBEs. Also, as feedbacks became more positive, crop–weed competition decreased and facilitation increased. In annual cropping systems, SBEs can alter plant growth and crop–weed competition. By identifying the management practices that promote positive SBEs, producers can minimise the impacts of crop–weed competition and decrease their reliance on off‐farm chemical and mechanical inputs to control weeds, enhancing agroecosystem sustainability.     

Competitiveness and yield impact of volunteer oilseed rape (Brassica napus) in winter and spring wheat (Triticum aestivum)

Journal of Plant Diseases and Protection - Volunteer oilseed rape is a relevant weed in many crop rotations due to seed persistence and dormancy. With the intro-duction of imidazolinone-tolerant...     

Greenhouse screening of the saprophytic resident microflora for control of leaf spots of wheat (Triticum aestivum)

Ten microorganisms of the epiphytic microflora of wheat leaves in Buenos Aires Province, Argentina, were evaluated under greenhouse conditions as potential biocontrol agents of the pathogensAlternaria triticimaculans, Bipolaris sorokiniana, Drechslera tritici-repentis andSeptoria tritici in two application sequences (prior to or together with the pathogens). The antagonists significantly reduced the expression of the diseases on wheat plants compared with control plants not inoculated with the antagonists. Maximum percentage of reduction of the necrotic lesion area (NLA) (40–55%) ofS. tritici resulted whenCryptococcus sp.,Rhodotorula rubra andPenicillium lilacinwn were sprayed on leaves prior to inoculations with the pathogen.Bacillus sp.,Cryptococcus sp.,Fusarium moniliforme var.anthophylium,P. lilacinum andR. rubra reduced significantly (34–52%) the NLA ofB. sorokiniana in both of the application sequences. The best antagonistic effect againstA. triticimaculans was shown byAspergillus niger, Bacillus sp.,Chaetomium globosum, F. moniliforme var.anthophylium andNigrospora sphaerica, with a NLA reduction from 21% to 35% in the co-inoculation or in the sequential application. All microorganisms exceptN. sphaerica performed better than the control againstD. tritici-repentis. The area under disease progress curve (AUDPC) of the pathogens appeared to progress similarly, but at lower values, in treated plants than in untreated controls. The two yeasts and the bacteria decreased AUDPC to 50–55% ofS. tritici andB. sorokiniana compared with the control in both application sequences, whereas the maximum efficacy againstA. triticimaculans was reached byN. sphaerica andA. niger for the sequential application and byF. moniliforme var.anthophylium for the co-inoculation. If the parasitism occurs also in nature, application of antagonists for biological control might provide the opportunity to compete with the pathogens and regulate their colonization in wheat leaves.     

Temperature induced changes in wheat (Triticum aestivum) growth and yield under salt affected environment of Indo-Gangetic Plains

An attempt has been made in the field conditions to evaluate the effect of atmospheric temperature rise on yield, ionic ratio (Na:K), and accumulation of antioxidative pigments in wheat in different growth stages under different soils. Five planting windows (PW) were classified, based on date of wheat sowing where the average temperature difference between a particular PW and PW-I varied from 1.33–4.24°C. Plant leaf area and root length density showed decreasing trend with increasing temperature. A low flag leaf water potential (?1.14?MPa) in sodic soil and high solute potential (?1.34?MPa) in saline-sodic soil was observed under PW-V, where high temperature difference (4.24°C) was recorded. The Na:K ratio was found to be highest in both straw and grain which were 1.802 and 1.126%, respectively, under saline-sodic conditions in PW-V. Proline and malondialdehyde concentration was highest under sodic conditions which varied between 2.82–2.95?mg?g^?1 fresh weight (FW) and 18.38–30.18 nmol g^?1 FW, respectively, under maximum temperature difference. An increase in temperature (>1°C) significantly reduced grain yield (>10%) that was negatively correlated with Na⁺ (r?=??0.78) but positively with K⁺ (r?=?+0.62) concentrations under saline-sodic conditions, however under sodic conditions, it was positively correlated with K⁺ (r?=?+0.63) concentration. Therefore, looking in to the climate change scenario, shifting planting window of wheat sowing may be helpful in mitigating the negative effects of heat and salt stress on wheat crop.     

Response of wild barley (Hordeum spontaneum) and winter wheat (Triticum aestivum) to sulfosulfuron: The role of degradation

Wild barley (Hordeum spontaneum) is one of the most troublesome weed species in winter wheat (Triticum aestivum) in Iran. Two bioassay experiments were conducted in order to study the response of wild barley and wheat to different herbicides and to study the efficacy of pre‐emergence (PRE), postemergence (POST), and PRE followed by POST applications of sulfosulfuron on wild barely. Moreover, the degradation of sulfosulfuron was studied by liquid chromatography coupled with tandem mass spectrometry (LC‐MS/MS). The results showed that wild barley was highly tolerant to clodinafop‐propargyl and its dry weight was reduced by only 15%, compared to the control, at the recommended dose (64 g ai ha^?1). Sulfosulfuron reduced the wild barley biomass by ≤50% at the highest dose (90 g ai ha^?1) in the first bioassay but by not more than 20% and 12% at the recommended dose (22 g ai ha^?1) in the first and second bioassay, respectively. Significant differences were found among the application methods of sulfosulfuron, with the POST application being the least effective method. In contrast to the POST application, wild barley was severely injured by the PRE application of sulfosulfuron, with an ED₅₀ dose of 7.3 g ai ha^?1. The degradation study showed that wild barley can metabolize sulfosulfuron that is applied POST, but at a lower rate than wheat. By 4 h after application, wild barley had metabolized 26% of the sulfosulfuron, compared to 46% by wheat. In conclusion, wild barley can metabolize the recommended dose of sulfosulfuron that is applied POST; thus, the PRE application of sulfosulfuron or other integrated methods should be considered for the effective control of wild barley in wheat.     

Multispectral classification of grass weeds and wheat (Triticum durum) using linear and nonparametric functional discriminant analysis and neural networks

Field studies were conducted to determine the potential of multispectral classification of late‐season grass weeds in wheat. Several classification techniques have been used to discriminate differences in reflectance between wheat and Avena sterilis, Phalaris brachystachys, Lolium rigidum and Polypogon monspeliensis in the 400–900 nm spectrum, and to evaluate the accuracy of performance for a spectral signature classification into the plant species or group to which it belongs. Fisher’s linear discriminant analysis, nonparametric functional discriminant analysis and several neural networks have been applied, either with a preliminary principal component analysis (PCA) or not and in different scenarios. Fisher’s linear discriminant analysis, feedforward neural networks and one‐layer neural network, all showed classification percentages between 90% and 100% with PCA. Generally, a preliminary computation of the most relevant principal components considerably improves the correct classification percentage. These results are promising because A. sterilis and L. rigidum, two of the most problematic, clearly patchy and expensive‐to‐control weeds in wheat, could be successfully discriminated from wheat in the 400–900 nm range. Our results suggest that mapping grass weed patches in wheat could be feasible with analysis of real‐time and high‐resolution satellite imagery acquired in mid‐May under these conditions.     

Novel marine yeast strains as plant growth-promoting agents improve defense in wheat (Triticum aestivum) against Fusarium oxysporum

Journal of Plant Diseases and Protection - Yeasts are multilateral opportunistic plant symbionts that can cause intrinsic changes in the metabolism of host plants, thereby increasing plant growth...     

Roles of peroxidases and NADPH oxidases in the oxidative response of wheat (Triticum aestivum) to brown rust (Puccinia triticina) infection

The goal of this work was to establish which enzymes – peroxidases or NADPH oxidases – play the most important role in the resistance‐related oxidative burst response of wheat to infection by brown rust (Puccinia triticina). The expression of four peroxidases and two NADPH oxidases was analysed in the susceptible wheat cv. Thatcher and isogenic lines with different Lr resistance genes after pathogen inoculation. Of the peroxidases, TaPrx118 and TaPrx112 were induced several times more strongly than TaPrx103 and TaPrx107. The induction of peroxidases was more pronounced than that of NADPH oxidases. The patterns of peroxidase expression clearly differentiated moderately resistant from highly resistant lines and corresponded to oxidative response profiles. The possible involvement of peroxidases or NADPH oxidases was verified with enzyme‐specific inhibitors. The oxidative burst in the susceptible cv. Thatcher and in the lines TcLr24, TcLr25, TcLr9 was peroxidase‐dependent, while the response in line TcLr26 was NADPH‐oxidase‐dependent. It is postulated that class III peroxidases play a leading role in the formation of reactive oxygen species molecules during the response of wheat to pathogen infection. The results suggest a high level of redundancy of some peroxidase genes induced in biotic stress. The role of both enzyme systems in wheat response/resistance to brown rust is discussed in relation to the oxidative response, the efficiency of resistance, and the presence and origin of particular Lr resistance genes.     

Dissipation of the herbicide dithiopyr in soil and residues in wheat (Triticum aestivum L) grain under Indian tropical conditions

Dissipation of dithiopyr in soil was monitored after application to wheat crop as pre- or post-emergence applications at two rates, viz 100 and 200 g AI ha(-1). The level of dithiopyr in the soil was assessed by gas chromatography, and its disappearence was found to follow a first-order decay curve irrespective of rate or method of application. The half-life in soil ranged between 17.3 and 25.0 days and residues at harvest (150 days after application) ranged between 4.0 and 8.8% of amounts applied. Investigation of microbial degradation of dithiopyr was conducted in minimal salt and Czapek Dox media in which 80% of the compound degraded within 15 days. Residues were not detected in wheat grain at harvest.     

Defence responses in flag leaves and spikes of common wheat Triticum aestivum cultivars with contrasting levels of basal resistance to blast caused by Pyricularia oryzae

Wheat blast, caused by Pyricularia oryzae, can cause large yield losses in crops. This study aimed to investigate defence responses in flag leaves and spikes of wheat cultivars BR-18 (moderately resistant) and BRS-Guamirim (susceptible), which differ in their levels of basal resistance. In contrast to cultivar BRS-Guamirim, infected plants of cultivar BR-18 showed more pronounced increases in activities of β-1,3-glucanase and chitinase as well as higher concentrations of lignin-thioglycolic acid derivatives in the flag leaves and total soluble phenolics in the spikes. Polyphenoloxidase activity increased in both flag leaves and spikes in response to fungal infection, regardless of cultivar. Phenylalanine ammonia-lyase (PAL) activity increased in infected flag leaves of both cultivars, especially in BR-18. PAL activity was lower in spikes of infected compared to noninfected plants of both cultivars, although to a lesser extent in BR-18. Compared to BRS-Guamirim, the antioxidative system in both flag leaves and spikes of BR-18 was more efficient in removing reactive oxygen species, reducing cellular damage caused by fungal infection. The lower catalase and peroxidase activities, associated with high superoxide dismutase activity, in flag leaves and spikes of infected BR-18 culminated in a high hydrogen peroxide concentration. The increase in ascorbate peroxidase activity was higher in both flag leaves and spikes of infected plants of BR-18 than in infected BRS-Guamirim. It was concluded that wheat resistance to blast depended on the basal level of resistance of the cultivar, which was mainly associated with the activities of defence enzymes and a more effective antioxidative system.     

Effect of mecoprop on plant growth and distribution of photosynthate in wheat (Triticum aestivum L.) seedlings

Foliar application of the phenoxy-acid herbicide, mecoprop, at four times normal field rate, caused decreases in root and shoot growth of wheat (Triticum aestivum L.). The shoot relative growth rate (RGR) was affected before that of the roots but subsequently the root RGR was significantly decreased. The roots of plants affected by mecoprop produced large numbers of short swollen laterals but the root system as a whole gradually recovered. Mecoprop treatment was associated with an immediate and lasting decrease in photo-synthetic ¹⁴CO₂ fixation. After a pulse of ¹⁴CO₂ in the light, the proportion of carbon moving to the roots in treated plants was always decreased but after a 24-h chase the proportion moving to the roots was initially decreased (2 days after spraying), then increased (9 days after spraying), but later became the same (17 days after spraying) as the water sprayed controls. Possible mechanisms involved with these mecoprop induced changes are discussed. Effets de l'herbicide mécoprop sur le développement végétatif et la répartition de produits photosynthétiques dans des plantules de blé (Triticum aestivum L.) Le mécoprop, acide phénoxypropionique, en application foliaire à quatre fois la dose conseillée, a amené une baisse dans la croissance des racines et des pousses du blé (Triticum aestivum L.). Le taux de croissance relative (RGR) des pousses a témoigné des effets plus tôt que les racines mais ultérieurement le RGR des racines a baissé de façon significative. Les racines des plantes touchées par le mécoprop ont produit de nombreuses ramifications courtes et renflées, mais le système racinaire s'est remis peu à peu. Les traitements au mécoprop sont associés à une baisse immédiate et prolongée dans la fixation du ¹⁴CO₂ photosynthétique. A la suite d'un marquage au ¹⁴CO₂à la lumière, la proportion de carbone qui s'acheminait vers les racines des plantes traitées a toujours fait voir une baisse mais au bout d'un intervalle de 24 h, la proportion qui s'acheminait vers les racines a d'abord diminué (2 jours après la pulvérisation) pour augmenter ensuite (9 jours après la pulvérisation). Plus tard (17 jours après la pulvérisation) cette proportion était semblable à celle des témoins ne recevant que de l'eau. Les mécanismea éventuellement enjeu dans ces changements provoqués par le mécoprop sont discutés. Wirkung von Mecoprop auf das Wachstum und die Verteilung von Assimilaten bei Jungpflanzen des Weizens (Triticum aestivum L.) Die Blattapplikation von Mecoprop in der 4 fachen Normaldosierung führte zu einer Abnahme des Wurzel-und Sprosswachstums des Weizens. Zunächst war das Wachstum des Sprosses, aber später auch das der Wurzeln herabgesetzt. Die Seitenwurzeln waren verkürzt und verdickt, aber nach und nach fand das Wurzelsystem zum normalen Wuchs zurück. Nach der Behandlung nahm die ¹⁴14C0₂-Assimilation für einige Zeit ab. 9 Tage nach der Behandlung nahm der Transport von Assimilaten in die Wurzeln wieder zu, so dass er 17 Tage nach der Behandlung dieselbe Höhe wie bei den Kontrollpflanzen erreichte. Der mögliche Mechanismus der von Mecoprop herbeigeführten Veränderungen wird diskutiert.     

Influence of sowing density and spatial pattern of spring wheat (Triticum aestivum) on the suppression of different weed species

To better understand the potential for improving weed management in cereal crops with increased crop density and spatial uniformity, we conducted field experiments over two years with spring wheat ( Triticum aestivum ) and four weed species: lambsquarters ( Chenopodium album ) , Italian ryegrass ( Lolium multiflorum ), white mustard ( Sinapis alba ), and chickweed ( Stellaria media ). The crops were sown at three densities (204, 449, and 721 seeds m⁻²) and in two spatial patterns (normal rows and a highly uniform pattern), and the weeds were sown in a random pattern at a high density. In most cases, the sown weeds dominated the weed community but, in other cases, naturally occurring weeds were also important. There were strong and significant effects regarding the weed species sown, the crop density, and the spatial distribution on the weed biomass in both years. The weed biomass decreased with increased crop density in 29 out of 30 cases. On average, the weed biomass was lower and the grain yield was higher in the uniform compared to the row pattern in both 2001 and 2002. Despite the differences in weed biomass, the responses of L. multiflorum , S. media , and C. album populations to crop density and spatial uniformity were very similar, as were their effects on the grain yield. Sinapis alba was by far the strongest competitor and it responded somewhat differently. Our results suggest that a combination of increased crop density and a more uniform spatial pattern can contribute to a reduction in weed biomass and yield loss, but the effects are smaller if the weeds are taller than the crop when crop–weed competition becomes intense.     

小麦新品种川麦42抗条锈病性遗传分析

条锈病是我国小麦最重要的病害之一,严重威胁小麦生产。川麦42是利用硬粒小麦-节节麦人工合成的高抗条锈病小麦新品种。为明确川麦42抗条锈性遗传基础,将川麦42分别与高感条锈小麦品种绵阳26、绵阳335杂交和回交,获得杂交F1、F2、BC1群体,其中,川麦42×绵阳26、川麦42×绵阳335F2群体分别为208和337株,川麦42/绵阳26//绵阳26、川麦42/绵阳335//绵阳335BC1群体分别为171和216株用于抗性遗传分析。利用条锈菌小种条中32号(CYR32)对抗感杂交的F1、F2和BC1群体接种,结果显示,所有F1代对条中32都表现免疫或高抗,F2代群体中抗∶感分离比例均符合3R∶1S理论比例,BC1群体抗∶感分离比也符合1R∶1S理论比例,说明川麦42对条中32的抗性由1对显性基因控制。     

Herbicidal control of Cirsium arvense (L.) Scop,roots and shoots in no-till spring wheat (Triticum aestivum L.)*

Three herbicide treatments were applied each year over a period of 4 years to Cirsium arvense (L.) Scop, infestations in no-till spring wheat (Triticum aestivum L.) in North Dakota, USA. Both chlorsulfuron at 30 g ai ha^?1+a non-ionic surfactant and a mixture of clopyralid+2,4-D at 70+280 g ai ha^?1 gradually reduced Cirsium arvense shoot density, root biomass, and adventitious root buds over the 4-year treatment period in two trials. These two treatments did not merely induce adventitious root buds to become dormant. They virtually eliminated roots to a depth of 50 cm by year 4. Tribenuron methyl at 10 g ai ha^?1+ a non-ionic surfactant was less effective in reducing shoot density and root biomass. Lutte herbicide contre les racines et les tiges de Cirsium arvense (L.) Scop, dans du bli de printemps non laboure (Triticum aestivum L.) Trois traitements herbicides ont été appliqués chaque année pendant 4 ans, contre des infestations de Cirsium arvense (L.) Scop, dans du blé de printemps (Triticum aestivum L.) non labouré dans le Dakota Nord, USA. Tant le chlorsulfuron à 30 g m.a. ha^?+un surfactant nonionique qu'un mélange de clopyralide+2,4-D à 70+280 g m.a. h^? ont reduit progres-sivement la densité des pieds de Cirsium arvense, la biomasse racinaire, et les bourgeons racinaires adventices pendant les 4 années de traitements dans les 2 essais. Ces traitements ont à peu près éliminé les racines sur une profondeur de 50 cm en 4 ans. Ces deux traitements n'ont pas induit de dormance des bourgeons racinaires adventices. Le tribenuron methyl à 10 g m.a. ha^?+un surfactant non ionique a été moins efficace dans la réduction de la densité de plante et de la biomasse racinaire. Chemische Bekämpfung von Cirsium arvense (L.) Scop, in direktgesätem Sommerweizen (Triticum aestivum L.) In direktgesäter Sommerweizen (Triticum aestivum L.) wurdel in North Dakota. USA, Bestände von Cirsium arvense (L.) Scop, über 4 Jahre jährlich 3 Herbizidbehandlungen unterzogen. Sowohl Chlorsulfuron mit 30 g AS ha^?1 nichtionischem Netzmittel als auch eine Mischung von Clopyralid+2,4D mit 70+280 g AS ha^?1 verringerten die Sproßdichte der Acker-Kratzdistel, die Wurzelbiomasse und die Adventivknospen an den Wurzeln in 2 Ver-suchen graduell. Durch diese beiden Behand-lungen wurden nicht nur die Adventivknospen dormant, sondem auch die Wurzeln bis zu einer Tiefe von 50 cm bis zum 4. Jahr fast ganz elimi-niert. Tribenuron-methyl mit 10 g AS ha^?1 nichtionischem Netzmittel war hinsichtlich der Reduktion von Sproßdichte und Wurzelbiomasse weniger wirksam.     

Response of winter wheat (Triticum aestivum L.) and weeds to tank mixtures of 2,4-D plus MCPA with clodinafop propargyl

Field and greenhouse experiments were conducted in 2004 and 2005 to study weed control and the response of winter wheat to tank mixtures of 2,4-D plus MCPA with clodinafop propargyl. The field experiments were conducted at Yazd and Oroumieh, Iran, with factorial combinations of 2,4-D plus MCPA at 0, 975, and 1300 g ai ha⁻¹ and with clodinafop propargyl at 0, 64, 80, 96, and 112 g ai ha⁻¹ in four replications. The greenhouse experiments further evaluated the effect of these tank mixtures on weed control, where each herbicide mixture was considered as one treatment and the experiment was established in a randomized complete block design with four replications. In the field experiments, the herbicides were applied at wheat tillering, while in the greenhouse experiments they were applied at the beginning of the tillering stage and at the four-leaf stage of the grass and broadleaf weeds, respectively. The results indicated antagonistic effects between 2,4-D plus MCPA and clodinafop propargyl. The best tank mixture with regard to weed control efficacy was 2,4-D plus MCPA at 975 g ai ha⁻¹ with clodinafop propargyl at 96 g ai ha⁻¹. The wheat grain yield was also increased by the tank mixture of clodinafop propargyl with 2,4-D plus MCPA. Generally, to inhibit clodinafop propargyl efficacy reduction due to tank-mixing with 2,4-D plus MCPA, it is recommended that the application dose of 64 g ai ha⁻¹ should be increased to 96 g ai ha⁻¹.     

干旱胁迫对两种辣椒叶片气体交换和叶绿素荧光特性的影响

试验研究了干旱条件下鸡爪×吉林和正椒13号两种辣撤叶片气体交换和叶绿素荧光参数的变化.结果表明,干旱处理5 d导致叶片相对含水量(RWC)、相对电导率(REC)、净光合作用(Pn)和暗适应下PSII最大光化学效率(Fv/Fm)下降,其中对鸡爪×吉林影响大于正椒13号.干旱处理下两辣椒品种的气孔导度(Gs)下降,而水分利用效率(WUE)、非光化学猝灭系数(NPQ)和光呼吸速率/净光合速率(Pr/Pn)均明显增加,其中正椒13号上升幅度高于鸡爪×吉林,这可能是正椒13号比鸡爪×吉林更耐旱的原因.     

Wheat (Triticum aestivum) Is Susceptible to the Parasitic Angiosperm Striga hermonthica, a Major Cereal Pathogen in Africa

ABSTRACT Striga hermonthica is a parasitic weed endemic to sub-Saharan Africa. It most commonly parasitizes sorghum, maize, pearl millet, and upland rice, lowering yields and affecting the welfare of over 100 million people, principally subsistence farmers. Cereal crops with complete resistance to this pathogen have not been reported. In southern and eastern Africa, where Striga spp. are endemic, 5.6 million ha of wheat are cultivated annually. Despite this, there are only isolated field reports of wheat infected with Striga spp. It is not clear whether this is due to resistance in this cereal or to environmental factors. In this article, we examined the ability of root exudates from five cultivars of wheat (Chablis, Cadenza, Hereward, Riband, and Brigadier) to trigger germination of S. hermonthica seed. A study of the development of S. hermonthica on two cultivars of wheat (Hereward and Chablis) and on a range of ancestral relatives of wheat (Triticum and Aegilops spp.) then was conducted. Last, the effect of Striga spp. on host growth and yield was examined using wheat cv. Chablis and compared with that of a highly susceptible sorghum cultivar (CSH-1). Wheat was able to support the germination, attachment, and subsequent development of Striga spp. All wheat cultivars and ancestral species of modern wheat (Triticum and Aegilops spp.) were susceptible to S. hermonthica. In addition, in wheat, infection severely lowered plant height (-24%) and biomass accumulation (-33%); a small parasite biomass elicited a large host response. In conclusion, wheat is highly susceptible to S. hermonthica and, in light of global climate change, this may have implications for wheat-producing areas of Africa.