Differential effects of type and quantity of leaf damage on growth,reproduction and defence of lima bean (Phaseolus lunatus L.)

Folivores are major plant antagonists in most terrestrial ecosystems. However, the quantitative effects of leaf area loss on multiple interacting plant traits are still little understood. We sought to contribute to filling this lack of understanding by applying different types of leaf area removal (complete leaflets versus leaflet parts) and degrees of leaf damage (0, 33 and 66%) to lima bean (Phaseolus lunatus) plants. We quantified various growth and fitness parameters including above‐ and belowground biomass as well as the production of reproductive structures (fruits, seeds). In addition, we measured plant cyanogenic potential (HCNp; direct chemical defence) and production of extrafloral nectar (EFN; indirect defence). Leaf damage reduced above‐ and belowground biomass production in general, but neither variation in quantity nor type of damage resulted in different biomass. Similarly, the number of fruits and seeds was significantly reduced in all damaged plants without significant differences between treatment groups. Seed mass, however, was affected by both type and quantity of leaf damage. Leaf area loss had no impact on HCNp, whereas production of EFN decreased with increasing damage. While EFN production was quantitatively affected by leaf area removal, the type of damage had no effect. Our study provides a thorough analysis of the quantitative and qualitative effects of defoliation on multiple productivity‐related and defensive plant traits and shows strong differences in plant response depending on trait. Quantifying such plant responses is vital to our understanding of the impact of herbivory on plant fitness and productivity in natural and agricultural ecosystems.     

Effect of seed size and plant growth on nodulation and nodule development in lima bean (Phaseolus lunatus L.)

Lima bean (Phaseolus lunatus L.) cultivars vary widely in their growth habit and seed size. Preliminary experiments indicated that a large-seeded pole cultivar (King of the Garden) formed many more nodules than a small-seeded bush cultivar (Henderson). The relative importance of seed size and shoot mass in determining nodule number and mass was assessed in five lima bean cultivars differing in seed size and growth habit. Between cultivars, significant positive correlations between initial seed mass, plant weight and nodule number and mass were observed during the first four weeks after planting. Comparisons within cultivars indicated a strong correlation between nodule mass and shoot dry weight. The influence of plant morphology on nodule formation and mass was secondary to the effects of seed and shoot mass. As plants matured, the increase in nodule mass paralleled the increase in plant mass, while nodule number was relatively stable after day 18. These results suggest that the highly regulated process of nodule formation was under the influence of seed derived factors, while the continued accumulation of nodule tissue was related to shoot growth.     

Inheritance of partial resistance to bean rust in the common bean (Phaseolus vulgaris L.)

The inheritance of partial resistance within eight bean cultivars to a single-pustule isolate of bean rust was studied by means of a F₁ diallel test. General combining ability (GCA) and specific combining ability (SCA) were very highly significant over two seasons and in interaction with seasons. The partitioning of the sums of squares indicated the greater importance of GCA in the inheritance of the resistance. Reciprocal effects were not significant. The estimates of narrow-sense heritability in the two seasons were 0.899 ± 0.056 and 0.603 ± 0.065.     

Morphological and molecular screening of French bean (Phaseolus vulgaris L.) germplasm using SCAR markers for Colletotrichum lindemuthianum (Sacc. and Magn.) Scrib. causing anthracnose resistance

This study was carried out to screen Phaseolus vulgaris L. germplasm accessions for anthracnose resistance genes to the fungus Colletotrichum lindemuthianum. (Sacc. and Magn.) Scrib. This fungus is made up of many pathogenic races which poses a challenge in developing resistant plant varieties; however, screening for and selection of resistant plant sources plays an important role in developing resistant plant lines. This screening work involved examining 69 accessions consisting of two resistant lines (D-line, L-line) and two susceptible varieties (Kanchana and Jwala). Fourteen SCAR primers specific to anthracnose disease resistance in the French bean were used. Of these 14 SCAR primers, 5 of them, SAS13, SF10, SC08, SZ04 and SBB14, produced amplification with good monomorphic bands.     

Advances in understanding the mechanism of resistance to anthracnose and induced defence response in tea plants

The tea plant (Camellia sinensis) is susceptible to anthracnose disease that causes considerable crop loss and affects the yield and quality of tea. Multiple Colletotrichum spp. are the causative agents of this disease, which spreads quickly in warm and humid climates. During plant–pathogen interactions, resistant cultivars defend themselves against the hemibiotrophic pathogen by activating defence signalling pathways, whereas the pathogen suppresses plant defences in susceptible varieties. Various fungicides have been used to control this disease on susceptible plants, but these fungicide residues are dangerous to human health and cause fungicide resistance in pathogens. The problem-solving approaches to date are the development of resistant cultivars and ecofriendly biocontrol strategies to achieve sustainable tea cultivation and production. Understanding the infection stages of Colletotrichum, tea plant resistance mechanisms, and induced plant defence against Colletotrichum is essential to support sustainable disease management practices in the field. This review therefore summarizes the current knowledge of the identified causative agent of tea plant anthracnose, the infection strategies and pathogenicity of C. gloeosporioides, anthracnose disease resistance mechanisms, and the caffeine-induced defence response against Colletotrichum infection. The information reported in this review will advance our understanding of host–pathogen interactions and eventually help us to develop new disease control strategies.     

苹果炭疽叶枯病菌致病力分析及苹果种质抗病性鉴定

苹果炭疽叶枯病是由胶孢炭疽菌(Colletotrichum gloeosporioides)引起的一种真菌病害,现已上升为世界苹果生产中的主要病害之一。了解不同来源的苹果炭疽叶枯病菌致病力差异及明确苹果种质资源对苹果炭疽叶枯病的抗性,对品种选育、品种合理布局以及控制病害的流行具有重要的参考价值。本研究对不同来源的79株病原菌进行了室内致病力测定,获知该菌致病力差异明显,其中强致病力菌株所占比例大。同时,本研究也对327份苹果种质资源进行了室内抗病性鉴定,其中高抗资源160份,中抗资源6份,中感资源22份,高感资源139份。表明我国现保存的苹果种质资源中存在丰富抗病种质。进一步按苹果分类系统分析发现,抗病资源在当前栽培的主要品种群中均有分布,特别是红玉品种群、富士品种群抗病资源最为丰富。     

Azoxystrobin induces lignification-related enzymes and phenolics in rice (Oryza sativa L.) against blast pathogen (Pyricularia grisea)

Abstract

This study was conducted to analyse the induction of lignification-related enzymes and phenolic content in rice to blast disease caused by Pyricularia grisea using azoxystrobin. The severity of rice blast was reduced (70% over control) through treatment by azoxystrobin. This reduction in disease severity was mainly associated with induction of host defense mechanisms by azoxystrobin. Increased production of secondary metabolite – phenolic and lignification – related enzymes, namely, peroxidase (POD), polyphenol oxidase (PPO) and phenylalanine ammonia-lyase (PAL) were observed in rice plants treated with azoxystrobin.     

Plant and soil resistance to water flow in faba bean (Vicia faba L. major Harz.)

An experiment was conducted to determine soil and plant resistance to water flow in faba bean under field conditions during the growing season. During each sampling period transpiration flux and leaf water potential measured hourly were used with daily measurements of root and soil water potential to calculate total resistance using Ohm's law analogy. Plant growth, root density and soil water content distributions with depth were measured. Leaf area and root length per plant reached their maximum value during flowering and pod setting (0.31 m² and 2200 m, respectively), then decreasing until the end of the growing period. Root distribution decreased with depth ranging, on average, between 34.2% (in the 0–0.25 m soil layer) and 18.1% (in the 0.75–1.0 m soil layer). Mean root diameter was 0.6 mm but most of the roots were less than 0.7 mm in diameter. Changes in plant and soil water potentials reflected plant growth characteristics and climatic patterns. The overall relationship between the difference in water potential between soil and leaf and transpiration was linear, with the slope equal to average plant resistance (0.0165 MPa/(cm³ m^-1 h^-1 10^-3). Different regression parameters were obtained for the various measurement days. The water potential difference was inversely related to transpiration at high leaf stomatal resistance and at high values of VPD. Total resistance decreased with transpiration flux in a linear relationship (r=−0.68). Different slope values were obtained for the different measurement days. Estimated soil resistance was much lower than the observed total resistance to water flow. The change from vegetative growth to pod filling was accompanied by an increase in plant resistance. The experimental results support previous findings that resistance to water flow through plants is not constant but is influenced by plant age, growth stage and environmental conditions. A more complex model than Ohm's law analogy may be necessary for describing the dynamic flow system under field conditions. This revised version was published online in June 2006 with corrections to the Cover Date.     

Evidence for a race-specific resistance factor in some lettuce (Lactuca sativa L.) cultivars previously considered to be universally susceptible to Bremia lactucae regel

Summary Previously undetected race-specific resistance to Bremia lactucae (downy mildew) was located in many lettuce cultivars hitherto considered to be universally susceptible to this disease. This resistance factor(s) may also be widely distributed in other cultivars known to carry combinations of already recognised factors R1 to R11. Specific virulence to match this resistance is almost invariably present in pathogen collections. This situation may be either a relic of the evolutionary history of the B. lactucae — L. sativa asssociation or may reflect a rare mutation in B. lactucae for avirulence on all but a few specialised L. sativa genotypes.     

Combining a host gene and a tobacco vein mottling virus coat protein gene for broad and effective resistance to potyviruses in tobacco (Nicotiana tabacum L.)

Over 100 transgenic tobacco lines in five genetic backgrounds were transformed with the tobacco vein mottling virus (TVMV) coat protein (CP) gene. Transgenic lines were initially tested for their reaction to inoculation with a TVMV systemic strain (TVMV-S) and a potato virus Y common strain (PVY-O). Of the 104 TVMV CP lines 60% were classified as resistant to PVY-O, whereas only 30% of these same lines were resistant to TVMV-S. A subset of six PVY-O-resistant transgenic lines and four control lines were tested for their reaction to a local isolate of TVMV, tobacco etch virus (TEV) and five isolates of PVY. The same ten lines were also tested for responses to a serial dilution of inoculum for two PVY isolates, PVY-KY1 and PVY-NN. Transgenic lines carrying an endogenous resistance gene known as Virgin A mutant (VAM) had greater resistance and a broader spectrum of resistance than did transgenic lines without the VAM gene. This additive effect of the endogenous resistance gene and coat protein-mediated resistance (CPMR) was not overcome by the highest inoculum concentration. The results indicate that the additive effect of the VAM gene and CPMR could extend the effectiveness of CPMR in controlling potiviruses. These findings could have important implications for plant improvement programs using CPMR against potyvirus diseases.     

Lack of correlation between constitutive and induced resistance to a herbivore in crucifer plants: real or flawed by experimental methods?

The correlation between constitutive and induced resistance to herbivores in plants has long been of interest to evolutionary biologists, and various approaches to determining levels of resistance have been used in this field of research. In this study, we examined the relationship between constitutive and induced resistance to the diamondback moth, Plutella xylostella (L.) (Lepidoptera: Plutellidae), in 11 closely related species of wild crucifers. We assessed the survival, development, and reproduction of the test insects and calculated their intrinsic rate of increase as an indicator of constitutive and induced resistance for the plants. We used larvae of P. xylostella and jasmonic acid as elicitors of the induced response. We failed to find a correlation between constitutive and induced resistance in these crucifer plants when the induction of resistance was initiated by either herbivory or jasmonic acid application. Analysis of the results suggests that the failure to detect a relationship between the two types of resistance could be caused by flaws in measuring constitutive resistance, which was apparently confounded with induced resistance. We discuss the difficulties and pitfalls in measuring constitutive resistance and ways to improve the methodology in investigating the relationships between constitutive and induced resistance in plants.     

Wounding and pathogen infection induce a chloroplast-targeted lipoxygenase in the common bean (<Emphasis Type="Italic">Phaseolus vulgaris</Emphasis> L.)

Chloroplastic LOXs are implicated in the biosynthesis of oxylipins like jasmonic acid and C₆ volatiles among others. In this study, we isolated the cDNA of a novel chloroplast-targeted Phaseolus vulgaris LOX, (PvLOX6). This gene is highly induced after wounding, non-host pathogen infection, and by signaling molecules as H₂O₂, SA, ethylene and MeJA. The phylogenetic analysis of PvLOX6 showed that it is closely related to chloroplast-targeted LOX from potato (H1) and tomato (TomLOXC); both of them are implicated in the biosynthesis of C₆ volatiles. Induction of PvLOX6 mRNA by wounding ethylene and jasmonic acid on the one side, and non-host pathogen, salicylic acid on the other indicates that common bean uses the same LOX to synthesize oxylipins in response to different stresses. PvLOX6 accession number: EF196866.     

Development and implementation of a sequence-specific PCR marker linked to a gene conferring resistance to anthracnose disease in narrow-leafed lupin (Lupinus angustifolius L.)

Anthracnose caused by Colletotrichum gloeosporioides is the most serious disease of lupins (Lupinus spp). A cross was made between cultivars Tanjil (resistant) and Unicrop (susceptible) in narrow-leafed lupin (L. angustifolius). Analysis of disease reaction data on the F₂ population and on the resultant F₇ recombinant inbred lines suggested that Tanjil contained a single dominant gene (Lanr1) conferring resistance to anthracnose. The parents and the representative F₂ plants were used to generate molecular markers liked to the Lanr1 gene using the MFLP technique. A co-dominant MFLP polymorphism linked to the Lanr1 gene was identified as a candidate marker. The bands were isolated, re-amplified by PCR, cloned and sequenced. The MFLP polymorphism was converted into a co-dominant, sequence-specific, simple PCR-based marker. Linkage analysis by the computer program MAPMAKER indicated that the marker was 3.5 centiMorgans (cM) from the gene Lanr1. This marker is currently being implemented for marker assisted selection in the Australian National Lupin Breeding Program.     

Using virtual 3-D plant architecture to assess fungal pathogen splash dispersal in heterogeneous canopies: a case study with cultivar mixtures and a non-specialized disease causal agent

Background and Aims

Recent developments in plant disease management have led to a growing interest in alternative strategies, such as increasing host diversity and decreasing the use of pesticides. Use of cultivar mixtures is one option, allowing the spread of plant epidemics to be slowed down. As dispersal of fungal foliar pathogens over short distances by rain-splash droplets is a major contibutor to the spread of disease, this study focused on modelling the physical mechanisms involved in dispersal of a non-specialized pathogen within heterogeneous canopies of cultivar mixtures, with the aim of optimizing host diversification at the intra-field level.

Methods

Virtual 3-D wheat-like plants (Triticum aestivum) were used to consider interactions between plant architecture and disease progression in heterogeneous canopies. A combined mechanistic and stochastic model, taking into account splash droplet dispersal and host quantitative resistance within a 3-D heterogeneous canopy, was developed. It consists of four sub-models that describe the spatial patterns of two cultivars within a complex canopy, the pathway of rain-splash droplets within this canopy, the proportion of leaf surface area impacted by dispersal via the droplets and the progression of disease severity after each dispersal event.

Key Results

Different spatial organization, proportions and resistance levels of the cultivars of two-component mixtures were investigated. For the eight spatial patterns tested, the protective effect against disease was found to vary by almost 2-fold, with the greatest effect being obtained with the smallest genotype unit area, i.e. the ground area occupied by an independent unit of the host population that is genetically homogeneous. Increasing both the difference between resistance levels and the proportion of the most resistant cultivar often resulted in a greater protective effect; however, this was not observed for situations in which the most resistant of the two cultivars in the mixture had a relatively low level of resistance.

Conclusions

The results show agreement with previous data obtained using experimental approaches. They demonstrate that in order to maximize the potential mixture efficiency against a splash-dispersed pathogen, optimal susceptible/resistant cultivar proportions (ranging from 1/9 to 5/5) have to be established based on host resistance levels. The results also show that taking into account dispersal processes in explicit 3-D plant canopies can be a key tool for investigating disease progression in heterogeneous canopies such as cultivar mixtures.     

Effectiveness of resistance genes to the large raspberry aphid, Amphorophora idaei Börner, in different raspberry (Rubus idaeus L.) genotypes and under different environmental conditions

The introduction into commerce of raspberry cultivars with major gene resistance to the large raspberry aphid, Amphorophora idaei, an important pest and virus vector on red raspberry in Europe, has been very effective both in decreasing pest numbers and greatly restricting infection with the viruses it transmits. However, biotypes of the aphid able to overcome these genes have developed in the field in recent years. Additionally, in field and laboratory tests, the response to aphid biotypes and recognised aphid strains of certain raspberry cultivars, such as Glen Prosen and Delight, differ markedly despite the fact that they are reputed to contain the same A. idaei‐resistance gene, A₁. In attempts to understand the reasons for this difference in response, analysis was made of the segregation of progeny seedlings from crosses between A. idaei‐resistant and ‐susceptible cultivars to two recognised strains of the aphid. These studies showed that, as expected, cv. Autumn Bliss contained the A. idaei‐resistance gene, A₁₀, and cvs Delight and Glen Prosen each contained the A. idaei‐resistance gene, A₁. When progeny seedlings were assayed in a heated glasshouse as young plants and in an unheated Tygan house as 1 m tall plants, the segregation ratios for resistance and susceptibility to A. idaei were largely unchanged. However, when the resistance of individual progeny plants was assessed, c. 37% of the putative gene A₁‐containing progeny and 9–23% of the putative gene A₁₀‐containing progeny, behaved differently in these two environments. Experiments involving an A. idaei‐resistant and ‐susceptible parent cultivar showed that shading plants increased their susceptibility to A. idaei colonisation. Whilst this shading effect has implications for experimentally detecting A. idaei‐resistant progeny in segregating raspberry seedlings, it does not explain the difference in field resistance to A. idaei of cvs Delight and Glen Prosen. Such differences in the field seem best explained by the presence in these cultivars of ‘minor’ genes for A. idaei resistance and/or susceptibility that influences the effectiveness of gene A₁.     

Isolation of a <Emphasis Type="Italic">Ve</Emphasis> homolog, <Emphasis Type="Italic">mVe1</Emphasis>, and its relationship to verticillium wilt resistance in <Emphasis Type="Italic">Mentha longifolia</Emphasis> (L.) Huds

As a step toward greater understanding of the genetics of verticillium wilt resistance in plants, we report the sequencing of a candidate wilt resistance gene, mVe1, from the mint diploid model species, Mentha longifolia (Lamiaceae). mVe1 is a putative homolog of tomato (Solanum lycopersicum L.) verticillium wilt (Ve) resistance genes. The mVe1 gene has a coding region of 3,051 bp. The predicted mVe1 protein contains a leucine-rich repeat domain, a common feature of plant disease resistance proteins. We compared 13 mVe1 alleles from three mint species. These alleles shared 96.2–99.6% nucleotide identity. We analyzed four M. longifolia populations segregating with respect to mVe1 alleles and wilt resistance versus susceptibility and found one association between mVe1 genotype and wilt phenotype. We conclude that mVe1 may play a role in mint verticillium wilt resistance, but variation for resistance in our segregating progenies is likely polygenic. Therefore, further investigations of mVe1 and identification of additional candidate genes are both warranted.     

Systemic acquired resistance in Cavendish banana induced by infection with an incompatible strain of Fusarium oxysporum f. sp. cubense

Fusarium wilt of banana is caused by the soil-borne fungus Fusarium oxysporum f. sp. cubense (Foc). The fact that there are no economically viable biological, chemical, or cultural measures of controlling the disease in an infected field leads to search for alternative strategies involving activation of the plant's innate defense system. The mechanisms underlying systemic acquired resistance (SAR) are much less understood in monocots than in dicots. Since systemic protection of plants by attenuated or avirulent pathogens is a typical SAR response, the establishment of a biologically induced SAR model in banana is helpful to investigate the mechanism of SAR to Fusarium wilt. This paper described one such model using incompatible Foc race 1 to induce resistance against Foc tropical race 4 in an in vitro pathosystem. Consistent with the observation that the SAR provided the highest level of protection when the time interval between primary infection and challenge inoculation was 10 d, the activities of defense-related enzymes such as phenylalanine ammonia lyase (PAL, EC 4.3.1.5), peroxidase (POD, EC 1.11.1.7), polyphenol oxidase (PPO, EC 1.14.18.1), and superoxide dismutase (SOD, EC 1.15.1.1) in systemic tissues also reached the maximum level and were 2.00–2.43 times higher than that of the corresponding controls on the tenth day. The total salicylic acid (SA) content in roots of banana plantlets increased from about 1 to more than 5 μg g⁻¹ FW after the second leaf being inoculated with Foc race 1. The systemic up-regulation of MaNPR1A and MaNPR1B was followed by the second up-regulation of PR-1 and PR-3. Although SA and jasmonic acid (JA)/ethylene (ET) signaling are mostly antagonistic, systemic expression of PR genes regulated by different signaling pathways were simultaneously up-regulated after primary infection, indicating that both pathways are involved in the activation of the SAR.