Host Leaf Research Articles

Unraveling the Complexity of Coffee Leaf Rust Behavior and Development in Different Coffea arabica Agroecosystems.

Crop health management systems can be designed according to practices that help to reduce crop losses by restricting pathogen development and promoting host plant growth. A good understanding of pathogen and host dynamics, which are interdependent, is therefore needed. In this article, we used a holistic approach to explain the behavior of coffee leaf rust (CLR), a major coffee disease. We monitored coffee plant and CLR dynamics simultaneously in plots under different disease management and agroforestry systems. Diseased leaves were also collected to characterize inoculum stock and rust life stages (latent rust area, area with uredospores, necrosis due to rust) through picture analysis. We used structural equation modeling to obtain an overview of CLR pathosystem functioning on a plant scale. This overview integrates processes such as disease dilution by host leaf renewal, direct and indirect effects of fruit load on CLR development, antagonistic effects of shading depending on rust life stages, the tonic effect of copper-based fungicides on leaf retention, and effects on rust life stages depending on fungicide types. From our results, we also deduced that the inoculum stock could be calculated in unsprayed plots from the rust area with uredospores, with uredospores at 58 × 103 cm-2, on average.

Histopathological study of resistant (Vitis labrusca L.) and susceptible (Vitis vinifera L.) cultivars of grapevine to the infection by downy mildew

ABSTRACT Plasmopara viticola (Berk. & M. A. Curtis) Berl & de Toni is a biotrophic oomycete responsible for downy mildew on grapevine. This study aimed to compare the development of P. viticola between a resistant interspecific hybrid of Vitis labrusca (‘Ives’, synonym ‘Bordô’), and a susceptible V. vinifera (‘Cabernet Sauvignon’) cultivars at different times after inoculation with the pathogen. The host leaf tissues were analysed at 0, 6, 12, 24, 48, 72, 96 and 120-h post-inoculation (hpi), by means of light optical microscopy and scanning electronic microscope (SEM). Light optical microscopy was used to analyse the pathogen development in the mesophyll intercellular spaces, as well as the histochemical changes occurring at host level during the infection. Structural differences were observed in stomata, and in the shape of mesophyll cells in the resistant cultivar after infection. SEM analysis showed differences in the pathogen development between both cultivars. All the stages of pathogen development were observed on the leaf surface of cv. ‘Cabernet Sauvignon’, but not in the cv. ‘Ives’. The results showed that cv. ‘Ives’ and ‘Cabernet Sauvignon’ display structural and histochemical differences to the downy mildew infection. Implications of these differences to the plant–pathogen interactions are discussed.

Morphological characterization of <em>Plasmopara viticola</em>, the inciting agent of grapes downy mildew

Grapes downy mildew is incited by the most destructive pathogen called P. viticola is a major bottleneck for grapevine production. The morphological and ultra structural analysis of the pathogen plays a significant role inorder to take precautionary management strategies. For morphometric analysis the downy mildew infected leaf samples were collected from eight different locations in Coimbatore and Theni districts. The collected samples were subjected to morphoplogical analysis under light microscope at 40 X magnification. The length and breadth of the sporangia vary from 19.94 - 22.73 µm and 14.58-17.69 µm. The scanning electron microscopic analysis of P. viticola shows the developmental stages of the pathogen on the host leaf surface. The Pathogenicity of the pathogen was confirmed through detached leaf assay. The characteristic sporulation of the fungus was observed at 7th day after post inoculation.

Host identity and phylogeny shape the foliar endophytic fungal assemblages of Ficus.

Foliar endophytic fungi (FEF) are diverse and ubiquitously associated with photosynthetic land plants. However, processes shaping FEF assemblages remain poorly understood. Previous studies have indicated that host identity and host habitat are contributing factors, but these factors are often difficult to disentangle. In this study, we studied FEF assemblages from plants grown in a botanical garden, enabling us to minimize the variation in abiotic environmental conditions and fungal dispersal capacity. FEF assemblages from 46 Ficus species were sequenced using next‐generation methods, and the results indicated that closely related host species had clearly differentiated FEF assemblages. Furthermore, host phylogenetic proximity was significantly correlated with the similarity of their FEF assemblages. In the canonical correspondence analysis, eleven leaf traits explained 32.9% of the total variation in FEF assemblages, whereas six traits (specific leaf area, leaf N content, leaf pH, toughness, latex alkaloid content, and latex volume per leaf area) were significant in the first two dimensions of ordination space. In the multiple regression on distance matrix analysis, 21.0% of the total variance in FEF assemblage was explained by both host phylogeny and leaf traits while phylogeny alone explained 7.9% of the variance. Thus, our findings suggest that both evolutionary and ecological processes are involved in shaping FEF assemblages.

Congeneric mutualist ant symbionts (Tetraponera, Pseudomyrmecinae) differ in level of protection of their myrmecophyte hosts (Barteria, Passifloraceae)

AbstractBarteria fistulosa and B. dewevrei, central African rain-forest trees, provide nesting cavities for Tetraponera aethiops and T. latifrons ants, respectively, which protect them against herbivores. To compare protection efficiency between these two symbioses, for 20 plants of each species in two sites in Gabon we measured the time elapsed before ants reached a focal leaf, for host leaves that were undisturbed, damaged (cut with scissors) or subjected to slight vibration (mimicking such damage), and for damaged leaves of the non-host Barteria species. Tetraponera aethiops displayed stronger protective behaviour than did T. latifrons. Time to reach a damaged host leaf (4.5 ± 2.6 min, mean ± SD) did not differ significantly from time to reach a leaf subjected to slight vibration (5.2 ± 3.0 min) for T. aethiops, but response to a leaf subjected to slight vibration (9.5 ± 1.9 min) was significantly slower than that to a damaged leaf (7.8 ± 1.9 min) for T. latifrons. The faster response of T. aethiops to slight vibration may have masked a response of this species to chemical signalling. Both ants reached damaged host leaves faster than damaged leaves of the non-host Barteria sp., indicating host plant specificity in ant responses.

Xanthomonas citri subsp. citri and Xanthomonas arboricola pv. pruni: Comparative analysis of two pathogens producing similar symptoms in different host plants.

Comparative studies in Xanthomonas have provided a vast amount of data that enabled to deepen in the knowledge of those factors associated with virulence and Xanthomonas plant interaction. The species of this genus present a wide range of host plants and a large number of studies have been focused to elucidate which mechanism are involved in this characteristic. In this study, comparative genomic and phenotypic analysis were performed between X. citri subsp. citri (Xcc), one of the most studied pathogens within Xanthomonas, and X. arboricola pv. pruni (Xap), a pathogen which has aroused great interest in recent time. The work was aimed to find those elements that contribute to their host divergence despite the convergence in the symptoms that each species cause on Citrus spp. and Prunus spp., respectively. This study reveals a set of genes that could be putatively associated with the adaptation of these pathogens to their hosts, being the most remarkable those involved in environmental sensing systems such as the case of the TonB-dependent transporters, the sensors of the two-component system and the methyl accepting chemotaxis proteins. Other important variants were found in processes related to the decomposition of the cell wall as could be appreciated by their dissimilar set of cell-wall degrading enzymes. Type three effectors, as one of the most important factors in delineating the host specificity in Xanthomonas, also showed a different array when comparing both species, being some of them unique to each pathogen. On the other hand, only small variations could be connected to other features such as the motility appendages and surface adhesion proteins, but these differences were accompanied by a dissimilar capacity to attach on host and non-host leaf surface. The molecular factors found in this work provide the basis to perform a more in-depth functional analyses that unveil those actual factors associated with pathogenesis and host specificity in Xcc and Xap.

A new meliolaceos foliicolous fungus from the Plio-Pleistocene of Arunachal Pradesh, eastern Himalaya

We report in this article, the in situ occurrence of a new species of Meliolinites (fossil Meliolaceae), Meliolinites neogenicus sp. nov. on the abaxial cuticular surface of fossilized leaf cuticle fragments of the angiosperm Litsea cf. salicifolia Khan et al. (Lauraceae) recovered from the upper part of the Siwalik succession of Neogene sediments (Kimin Formation: late Pliocene to early Pleistocene) of Arunachal Pradesh, eastern Himalaya, India. This Plio-Pleistocene melioloid foliicolous fungal morph features a well-preserved unique mycelium consisting of superficial, dark brown, thick-walled and branching hyphae with bicellular appresoria and unicellular phialides. The fungal colonies also include globose, dark brown perithecia, as well as one ellipsoidal, 5-celled, 4-septate, dark brown ascospore. The fossil leaf of Litsea, together with the foliicolous fungal remains indicates the prevalence of a warm, humid, climate in the Arunachal sub-Himalaya during the Plio-Pleistocene. The in situ evidence of Meliolinites on host leaf cuticle indicates the possible existence of a host–ectoparasite relationship in the ancient warm and humid tropical evergreen forest of this area during the Plio-Pleistocene. Based on present and earlier records it is suggested that Lauraceae has been a common host for meliolaceous fungi since the early Cenozoic. Meliolinites neogenicus sp. nov. might have thrived under a warm and humid climate with a mean annual temperature (MAT) from 21 to 26 °C and a mean annual precipitation (MAP) from 1000 to 2000 mm in the Plio-Pleistocene of Arunachal sub-Himalaya which is in conformity with our earlier published qualitative and quantitative climatic data.

Effects of Light Level and Nitrogen Supply on the Red Clover-Orobanche Minor Host-Parasite Interaction.

Infection by holoparasitic plants typically causes decreases in host mass, thought to be primarily as a result of resource abstraction. Inverse relationships have been noted between the number of Orobanche spp. parasites infecting a host and their mass, suggesting that the parasites compete for a shared resource pool, assumed to be recently fixed carbon (C). In clover, nitrogen (N) fixation requires a high proportion of daily photosynthate and represents a potential competitor for recently fixed C. We grew Trifolium pratense, either singly or parasitised by Orobanche minor, under high or low light levels, and with or without exogenous N supply. Low light and N deficiency led to decreased host biomass, while the damage caused by parasitism was proportionate to host mass. Parasitism caused reductions in host leaf mass, area, photosynthetic rates and shoot N concentration, but did not affect starch accumulation. Parasite mass as a proportion of system biomass was significantly higher when attached to plants grown at high light, which was attributed to higher photoassimilate supply, while the N supply had no effect. While both N limitation and parasitism caused reductions in host growth, little evidence of competition for C between N fixation and the parasites was noted.

Lignin biosynthesis as a key mechanism to repress Polystigma amygdalinum, the causal agent of the red leaf blotch disease in almond

The red leaf blotch (RLB) of almond, caused by the fungus Polystigma amygdalinum, is considered as one of the most important leaf diseases of this fruit tree. Differential cultivar susceptibility to the RLB has been described based on field observations, while its molecular and biochemical bases remain unknown to date. We aimed to explore the plant defence mechanisms related to the cultivar susceptibility by identifying some relevant physical and chemical strategies for the pathogen control. Thus, we studied the regulation of seven defence-related genes as well as the lignin deposition in two almond cultivars with highly differential response to RLB: the highly tolerant ‘Mardía’ and the susceptible ‘Tarraco’ cultivars. ‘Mardía’ displayed an up-regulation of the CAD and DFN1 genes at early stages of RLB symptom expression, with further lignin deposition in the fungal-colonized area that was visualized by microscopy. Thus, ‘Mardía’ uses both physical and chemical responses to effectively repress the pathogen. In contrast, ‘Tarraco’ triggered the up-regulation of HQT and LDOX genes, related to chlorogenic acid and anthocyanin biosynthesis pathways, respectively, while lignin deposition was not clearly noticed. This strategy recorded in ‘Tarraco’ at later stages of RLB symptoms failed to control the fungal infection and colonization. Our results suggested a major role of the phenylpropanoids pathway in the defence response against RLB, by showing that an early production of lignin might be a major mechanism to control the spread of P. amygdalinum within the host leaf tissues.

A DNase from a Fungal Phytopathogen Is a Virulence Factor Likely Deployed as Counter Defense against Host-Secreted Extracellular DNA.

Histone-linked extracellular DNA (exDNA) is a component of neutrophil extracellular traps (NETs). NETs have been shown to play a role in immune response to bacteria, fungi, viruses, and protozoan parasites. Mutation of genes encoding group A Streptococcus extracellular DNases (exDNases) results in reduced virulence in animals, a finding that implies that exDNases are deployed as counter defense against host DNA-containing NETs. Is the exDNA/exDNase mechanism also relevant to plants and their pathogens? It has been demonstrated previously that exDNA is a component of a matrix secreted from plant root caps and that plants also carry out an extracellular trapping process. Treatment with DNase I destroys root tip resistance to infection by fungi, the most abundant plant pathogens. We show that the absence of a single gene encoding a candidate exDNase results in significantly reduced virulence of a fungal plant pathogen to its host on leaves, the known infection site, and on roots. Mg2+-dependent exDNase activity was demonstrated in fungal culture filtrates and induced when host leaf material was present. It is speculated that the enzyme functions to degrade plant-secreted DNA, a component of a complex matrix akin to neutrophil extracellular traps of animals.IMPORTANCE We document that the absence of a single gene encoding a DNase in a fungal plant pathogen results in significantly reduced virulence to a plant host. We compared a wild-type strain of the maize pathogen Cochliobolus heterostrophus and an isogenic mutant lacking a candidate secreted DNase-encoding gene and demonstrated that the mutant is reduced in virulence on leaves and on roots. There are no previous reports of deletion of such a gene from either an animal or plant fungal pathogen accompanied by comparative assays of mutants and wild type for alterations in virulence. We observed DNase activity, in fungal culture filtrates, that is Mg2+ dependent and induced when plant host leaf material is present. Our findings demonstrate not only that fungi use extracellular DNases (exDNases) for virulence, but also that the relevant molecules are deployed in above-ground leaves as well as below-ground plant tissues. Overall, these data provide support for a common defense/counter defense virulence mechanism used by animals, plants, and their fungal and bacterial pathogens and suggest that components of the mechanism might be novel targets for the control of plant disease.

Bucculatrix crataega sp. nov. (Lepidoptera: Bucculatricidae), a leaf miner on Crataegus, representing the first formally named species of the family from mainland China.

A new leaf-mining species of the genus Bucculatrix Zeller, 1839, B. crataega Liu, sp. nov., feeding on Crataegus pinnatifida Bunge is described herein, representing the first formally named species of Bucculatricidae from mainland China. Adult and genitalia of both sexes are described and illustrated. Host plant, leaf mine and cocoon are also illustrated. DNA barcode analysis supports the separation of B. crataega from related species.

Transcriptome profile of cup-shaped galls in Litsea acuminata leaves.

BackgroundInsect galls are atypical plant tissues induced by the invasion of insects. Compared to the host leaf, gall tissues lose photosynthetic ability, but have higher soluble sugar content. Although the physiological and biochemical regulation of gall tissues have been demonstrated, the mechanism of genetic regulation has only been analyzed in few studies.ResultsIn this study, the transcriptome of cup-shaped galls and its host leaf were de novo assembled. Cellular functional enrichment and differentially expressed gene groups in the gall tissues were analyzed. The genes associated with primary metabolism, including photosynthesis, cell wall turnover, and sugar degradation, were expressed differently in galls and leaves. The examination of gene expression demonstrated that the genes involved in brassinosteroid synthesis and responses exhibited a remarkable modulation in cup-shaped galls, suggesting a potential role of steroid hormones in regulating gall development.ConclusionsThis study revealed the genetic responses, including those involved in source-sink reallocation and phytohormone metabolism, of galls induced by a dipteran insect.

Across Multiple Species, Phytochemical Diversity and Herbivore Diet Breadth Have Cascading Effects on Herbivore Immunity and Parasitism in a Tropical Model System.

Terrestrial tri-trophic interactions account for a large part of biodiversity, with approximately 75% represented in plant–insect–parasitoid interactions. Herbivore diet breadth is an important factor mediating these tri-trophic interactions, as specialisation can influence how herbivore fitness is affected by plant traits. We investigated how phytochemistry, herbivore immunity, and herbivore diet breadth mediate plant–caterpillar–parasitoid interactions on the tropical plant genus Piper (Piperaceae) at La Selva Biological station in Costa Rica and at Yanayacu Biological Station in Ecuador. We collected larval stages of one Piper generalist species, Quadrus cerealis, (Lepidoptera: Hesperiidae) and 4 specialist species in the genus Eois (Lepidoptera: Geometridae) from 15 different species of Piper, reared them on host leaf material, and assayed phenoloxidase activity as a measure of potential larval immunity. We combined these data with parasitism and caterpillar species diet breadth calculated from a 19-year database, as well as established values of phytochemical diversity calculated for each plant species, in order to test specific hypotheses about how these variables are related. We found that phytochemical diversity was an important predictor for herbivore immunity, herbivore parasitism, and diet breadth for specialist caterpillars, but that the direction and magnitude of these relationships differed between sites. In Costa Rica, specialist herbivore immune function was negatively associated with the phytochemical diversity of the Piper host plants, and rates of parasitism decreased with higher immune function. The same was true for Ecuador with the exception that there was a positive association between immune function and phytochemical diversity. Furthermore, phytochemical diversity did not affect herbivore immunity and parasitism for the more generalised herbivore. Results also indicated that small differences in herbivore diet breadth are an important factor mediating herbivore immunity and parasitism success for Eois at both sites. These patterns contribute to a growing body of literature that demonstrate strong cascading effects of phytochemistry on higher trophic levels that are dependent on herbivore specialisation and that can vary in space and time. Investigating the interface between herbivore immunity, plant chemical defence, and parasitoids is an important facet of tri-trophic interactions that can help to explain the enormous amount of biodiversity found in the tropics.

(2R,5S)-Theaspirane Identified as the Kairomone for the Banana Weevil, Cosmopolites sordidus, from Attractive Senesced Leaves of the Host Banana, Musa spp.

The principal active component produced by highly attractive senesced host banana leaves, Musa spp., for the banana weevil, Cosmopolites sordidus, is shown by coupled gas chromatography‐electroantennography (GC‐EAG), coupled GC‐mass spectrometry (GC‐MS), chemical synthesis and coupled enantioselective (chiral) GC‐EAG to be (2R,5S)‐theaspirane. In laboratory behaviour tests, the synthetic compound is as attractive as natural host leaf material and presents a new opportunity for pest control.

Taxonomic study of the leafmining genus Liocrobyla Meyrick, 1916 from China (Lepidoptera, Gracillariidae, Ornixolinae) with a description of one new species

Three species of the leafmining genusLiocrobylaMeyrick, 1916 from China are treated.Liocrobylaindigoferasp. n.feeding on the plant genusIndigoferais described as new to science.LiocrobylalobataKuroko, 1960 feeding on Puerariamontanavar.lobata is newly recorded in China.Lespedezabicoloris documented as a new host plant forL.desmodiellaKuroko, 1982. Photographs of adult habitus, male and female genitalia, as well as host plants, leaf mines and biology are provided.

The key gluconeogenic gene PCK1 is crucial for virulence of Botrytis cinerea via initiating its conidial germination and host penetration.

The process of initiation of host invasion and survivalof some foliar phytopathogenic fungi in the absence of external nutrients on host leaf surfaces remains obscure. Here, we demonstrate that gluconeogenesis plays an important role in the process and nutrient-starvation adaptation before the pathogen host invasion. Deletion of phosphoenolpyruvate carboxykinase gene BcPCK1 in gluconeogenesis in Botrytis cinerea, the causative agent of grey mould, resulted in the failure of the ΔBcpck1 mutant conidia to germinate on hard and hydrophobic surface and penetrate host cells in the absence of glucose, reduction in conidiation and slow conidium germination in a nutrient-rich medium. The wild-type and ΔBcpck1 conidia germinate similarly in the presence of glucose (higher concentration) as the sole carbon source. Conidial glucose-content should reach a threshold level to initiate germination and host penetration. Infection structure formation by the mutants displayed a glucose-dependent fashion, which corresponded to the mutant virulence reduction. Exogenous glucose or complementation of BcPCK1 completely rescued all the developmental and virulence defects of the mutants. Our findings demonstrate that BcPCK1 plays a crucial role in B. cinerea pathogenic growth and virulence, and provide new insights into gluconeogenesis mediating pathogenesis of plant fungal pathogens via initiation of conidial germination and host penetration.

Maize Phyllosphere Microbial Community Niche Development Across Stages of Host Leaf Growth.

Background: The phyllosphere hosts a variety of microorganisms, including bacteria, which can play a positive role in the success of the host plant. Bacterial communities in the phylloplane are influenced by both biotic and abiotic factors, including host plant surface topography and chemistry, which change in concert with microbial communities as the plant leaves develop and age. Methods: We examined how the Zea mays L. leaf microbial community structure changed with plant age. Ribosomal spacer length and scanning electron microscopic imaging strategies were used to assess microbial community composition across maize plant ages, using a novel staggered experimental design. Results: Significant changes in community composition were observed for both molecular and imaging analyses, and the two analysis methods provided complementary information about bacterial community structure within each leaf developmental stage. Conclusions: Both taxonomic and cell-size trait patterns provided evidence for niche-based contributions to microbial community development on leaves.

Ecology and life history of Paratomapoderus brachypterus in Gabon (Coleoptera: Attelabidae)

On the base of data collected during four expeditions in Gabon (West Africa) from 2012 to 2016, the authors provide new information on trophic activity and reproductive behaviour of Paratomapoderus brachypterus (Voss, 1926) (Attelabidae: Apoderinae, Hoplapoderini), with emphasis on leaf-roll realisation; host plant, leaf roll, larva and pupa are illustrated for the first time.

Maize Phyllosphere Microbial Community Niche Development Across Stages of Host Leaf Growth

Background: The phyllosphere hosts a variety of microorganisms, including bacteria, which can play a positive role in the success of the host plant. Bacterial communities in the phylloplane are influenced by both biotic and abiotic factors, including host plant surface topography and chemistry, which change in concert with microbial communities as the plant leaves develop and age. Methods: We examined how the Zea mays L. leaf microbial community structure changed with plant age. Ribosomal spacer length and scanning electron microscopic imaging strategies were used to assess microbial community composition across maize plant ages, using a novel staggered experimental design. Results: Significant changes in community composition were observed for both molecular and imaging analyses, and the two analysis methods provided complementary information about bacterial community structure within each leaf developmental stage. Conclusions: Both taxonomic and cell-size trait patterns provided evidence for niche-based contributions to microbial community development on leaves.

Maize Phyllosphere Microbial Community Niche Development Across Stages of Host Leaf Growth

Background: The phyllosphere hosts a variety of microorganisms, including bacteria, which can play a positive role in the success of the host plant. Bacterial communities in the phylloplane are influenced by both biotic and abiotic factors, including host plant surface topography and chemistry, which change in concert with microbial communities as the plant leaves develop and age. Methods: We examined how the Zea mays L. leaf microbial community structure changed with plant age. Ribosomal spacer length and scanning electron microscopic imaging strategies were used to assess microbial community composition across maize plant ages, using a novel staggered experimental design. Results: Significant changes in community composition were observed for both molecular and imaging analyses, and the two analysis methods provided complementary information about bacterial community structure within each leaf developmental stage. Conclusions: Both taxonomic and cell-size trait patterns provided evidence for niche-based contributions to microbial community development on leaves.