Fungus Verticillium Dahliae Kleb Research Articles

The genomes of two Australian isolates of Verticillium dahliae recovered from cotton fields

Verticillium wilt is a major disease in a wide variety of crops and is caused by the fungus Verticillium dahliae Kleb. In Australian cotton growing regions two pathotypes of V. dahliae are described, namely non-defoliating and defoliating, classified on their ability to cause defoliation in cotton (Gossypium hirsutum) as well as okra (Abelmoschus esculentus) and olives (Olea europaea). Herein we report the genomes of two isolates of V. dahliae, one predicted to be non-defoliating and the other predicted to be defoliating. Phylogenomic analysis places each isolate into separate clades, but the highly aggressive, predicted defoliating, strain lacks the genomic features reported as important for causing defoliation on cotton in other regions.

Predicting the Risk of Verticillium Wilt in Olive Orchards Using Fuzzy Logic

Developing models to understand disease dynamics and predict the risk of disease outbreaks to facilitate decision making is an integral component of plant disease management. However, these models have not yet been developed for one of the most damaging diseases in Mediterranean olive-growing areas (verticillium wilt (VW), caused by the fungus Verticillium dahliae Kleb.), although there are parameters (e.g., level of V. dahliae inoculum in the soil, level of susceptibility of the olive cultivar, isothermality, coefficient of variation of seasonal precipitation, etc.) that have previously been correlated with the severity of the disease. Using the data from previous VW studies conducted in the Guadalquivir Valley of Andalusia (one of the most damaged areas worldwide), in this work, a set of fuzzy logic (FL) models is developed with the aforementioned disease and climatic parameters, and the results are compared with machine learning (ML) models, of known effectiveness, to predict the risk levels of VW appearance in an olive orchard. Under these conditions, both groups of models were less effective than those previously studied with simpler models or models used under controlled conditions. However, the accuracy achieved with the most efficient FL model (60%; classification system based on fuzzy rules using the Ishibuchi method with a weighting factor) was somewhat greater than the efficiency achieved with the most efficient ML model (59.0%; decision tree classifier), in addition to being more appropriate (from a practical point of view) for the incorporation into a decision support system by allowing the risk of appearance of each observation to be known by providing rules for each of the combinations of the different parameters with similar precision. Therefore, in this study, we propose the FL methodology as suitable to act as an expert system for the future creation of a decision support system for VW in olives.

Effect of 1-aminocyclopropane-1-carboxylic acid accumulation on Verticillium dahliae infection of upland cotton

BackgroundVerticillium wilt of cotton is a serious disease caused by the infection of soil borne fungus Verticillium dahliae Kleb, and the infection mechanisms may involve the regulation of phytohormone ethylene. The precursor of ethylene biosynthesis is 1-aminocyclopropane-1-carboxylic acid (ACC), whose biosynthesis in vivo depends on activation of ACC synthase (ACS). Here, we investigated how ACS activation and ACC accumulation affected the infection of V. dahliae strain Vd991 on cotton (Gossypium hirsutum L.) cultivar YZ1.ResultsPreliminary observations indicated that ACC applications reduced the disease incidence, disease index and stem vascular browning by impeding fungal biomass accumulation. Transcriptome and qRT-PCR data disclosed that Vd991 induced GhACS2 and GhACS6 expression. GhACS2- or GhACS6-overexpressing transgenic YZ1 lines were generated, respectively. In a Verticillium disease nursery with about 50 microsclerotia per gram of soil, these ACC-accumulated plants showed decreased disease indexes, stem fungal biomasses and vascular browning. More importantly, these transgenic plants decreased the green fluorescent protein-marked Vd991 colonization and diffusion in root tissues. Further, either ACC treatment or ACC-accumulating cotton plants activated salicylic acid (SA)-dependent resistance responses.ConclusionsThe GhACS2- and GhACS6-dependent ACC accumulations enhanced the resistance of cotton to V. dahliae in a SA-dependent manner, and this lays a foundation for cotton resistance breeding.

Vilt resistance of cotton varieties while inoculation with various isolates of the fungus Verticillium dahliae kleb. in an artificial climate of Uzbekistan

This article addresses the studies on the resistance of cotton varieties to Verticillium dahliae Kleb on an artificial infectious background. It is shown that resistance indicators depend on the origin of varieties. V.dahliae isolates isolated from varieties C-6524, Namangan-77, Barkhayot, Shodiyona, Omad and C-8290 showed different virulence; isolates allocated from varieties C-6524, Namangan-77, Barkhayot, Shodiyona and Omad showed the highest virulence.

Metabolomics reveals differential mechanisms of toxicity of hyperbranched poly(ethyleneimine)-derived nanoparticles to the soil-borne fungus Verticillium dahliae Kleb

There is a consensus on the urge for the discovery and assessment of alternative, improved sources of bioactivity that could be developed as plant protection products (PPPs), in order to combat issues that the agrochemical sector is facing. Based on the recent advances in nanotechnology, nanoparticles seem to have a great potential towards the development of the next generation nano-PPPs used as active ingredients (a.i.) per se or as nanocarriers in their formulation. Nonetheless, information on their mode(s)-of-action (MoA) and mechanisms of toxicity is yet largely unknown, representing a bottleneck in their further assessment and development. Therefore, we have undertaken the task to assess the fungitoxicity of hyperbranched poly(ethyleneimine) (HPEI), quaternized hyperbranched poly(ethyleneimine) (QPEI), and guanidinylated hyperbranched poly(ethyleneimine) (GPEI) nanoparticles to the soil-born plant pathogenic fungus Verticillium dahliae Kleb, and dissect their effects on its metabolism applying GC/EI/MS metabolomics. Results revealed that functionalization of HPEI nanoparticles with guanidinium end groups (GPEI) increases their toxicity to V. dahliae, while functionalization with quaternary ammonium end groups (QPEI) decreases it. The treatments with the nanoparticles affected the chemical homeostasis of the fungus, altering substantially its amino acid pool, energy production, and fatty acid content, causing additionally oxidative and osmotic stresses. To the best of our knowledge, this is the first report on the comparative toxicity of HPEI, QPEI, and GPEI to filamentous fungi applying metabolomics. The findings could be exploited in the study of the quantitative structure-activity relationship (QSAR) of HPEI-derived nanoparticles and their further development as nano-PPPs.

Use of RGB Vegetation Indexes in Assessing Early Effects of Verticillium Wilt of Olive in Asymptomatic Plants in High and Low Fertility Scenarios

Verticillium Wilt of Olive, a disease caused by the hemibiotrophic vascular fungus Verticillium dahliae Kleb. presents one of the most important constraints to olive production in the world, with an especially notable impact in Mediterranean agriculture. This study evaluates the use of RGB vegetation indexes in assessing the effects of this disease during the biotrophic phase of host-pathogen interaction, in which symptoms of wilt are not yet evident. While no differences were detected by measuring stomatal conductance and chlorophyll fluorescence, results obtained from RGB indexes showed significant differences between control and inoculated plants for indexes Saturation, a*, b*, green Area (GA), normalized green-red difference index (NGRDI) and triangular greenness index (TGI), presenting a reduction in plant growth as well as in green and yellow color components as an effect of inoculation. These results were contrasted across two scenarios of mineral fertilization in soil and soil amended with two different olive mill waste composts, presenting a clear interaction between the host-pathogen relationship and plant nutrition and suggesting the effect of V. dahliae infection during the biotrophic phase was not related to plant water status.

Early stage effects of Verticillium wilt of olive (WVO) on nutrient use in young olive trees grown in soils amended with compost and mineral fertilisation

Verticillium wilt, caused by the soil-borne pathogenic fungus Verticillium dahliae (Kleb), is one of the most severe diseases of olive trees in Mediterranean agriculture. At present, the use of organic amendments is considered an effective means to combat certain soil-borne plant diseases while in turn supplying plants with nutrients. The aim of this study was to determine the early stage effects of Verticillium wilt of olive (VWO) on macronutrient uptake and in planta mobility by analysing nutrients in young olive trees. Young olive trees were grown in unamended as well organically amended soils (employing two distinct olive mill waste composts, C1 and C2) in the presence or absence of mineral fertilisation. Half of the soils were inoculated with Verticillium dahliae (Vd) defoliating (D) pathotype, leaving the other half non-inoculated. At 22 and 100 days after inoculation, nutrient content (N, P, K, S, Ca, and Mg) was analysed in mature and young leaves. Olive mill compost enhanced N, P, K and S availability but did not prevent Verticillium infection in young olive trees. Pathogen inoculation affected nutrient content in mature and young leaves and reduced leaf nutrient input during the early stages of host colonization. Stronger effects were observed in pathogen inoculated plants grown in soil amended with C2, coinciding with high N and P and transiently low S availability. Leaf K input showed the highest sensitivity to V. dahliae inoculation. In high N conditions, deleterious effects caused by Vd on young olive trees may be overcome by promoting the growth of new shoots. We present evidence that Vd requires S during the initial stages of host colonization, in which plant-pathogen competition for this element is key, and that low levels of S in foliage during such early stages may enhance Verticillium wilt development.

Bacillales Members from the Olive Rhizosphere Are Effective Biological Control Agents against the Defoliating Pathotype of Verticillium dahliae

The use of biological control agents (BCAs) is of interest within an integrated management strategy of Verticillium wilt of olive (VWO) caused by the soil-borne fungus Verticillium dahliae Kleb. Previous studies have shown that the root/rhizosphere of healthy olive plants is an important reservoir of microorganisms displaying biocontrol activity against VWO (i.e., Pseudomonas strains PICF7 and PIC141). Moreover, these BCAs are already adapted to the ecological niche where they are deployed. Three novel bacteria (strains PIC28, PIC73 and PIC167) from nursery-produced olive plants were in-depth characterized using a previously implemented approach consisting of in situ isolation, in vitro antagonism tests, in planta bioassays, phenotypic and metabolic characterization, genome analyses and in silico identification of traits involved in plant-bacteria interactions, and multi-locus sequence analyses. All strains displayed in vitro growth inhibition of different olive pathogens and biocontrol effectiveness against Verticillium dahliae, with strain PIC73 being the most effective BCA. Strains PIC73 and PIC167 were identified as Paenibacillus polymyxa (Prazmowski) Ash et al. and Paenibacillus terrae Yoon et al., respectively. Strain PIC28 belongs to the Bacillus genus. Some of these Bacillales members showed in vitro compatibility with previously characterized BCAs (Pseudomonas spp. strains) also originating from the olive rhizosphere, paving the way for the future development of tailored bacterial consortia effective against VWO.

Plant genotype-specific archaeal and bacterial endophytes but similar Bacillus antagonists colonize Mediterranean olive trees.

Endophytes have an intimate and often symbiotic interaction with their hosts. Less is known about the composition and function of endophytes in trees. In order to evaluate our hypothesis that plant genotype and origin have a strong impact on both, endophytes of leaves from 10 Olea europaea L. cultivars from the Mediterranean basin growing at a single agricultural site in Spain and from nine wild olive trees located in natural habitats in Greece, Cyprus, and on Madeira Island were studied. The composition of the bacterial endophytic communities as revealed by 16S rRNA gene amplicon sequencing and the subsequent PCoA analysis showed a strong correlation to the plant genotypes. The bacterial distribution patterns were congruent with the plant origins in “Eastern” and “Western” areas of the Mediterranean basin. Subsequently, the endophytic microbiome of wild olives was shown to be closely related to those of cultivated olives of the corresponding geographic origins. The olive leaf endosphere harbored mostly Proteobacteria, followed by Firmicutes, Actinobacteria, and Bacteroidetes. The detection of a high portion of archaeal taxa belonging to the phyla Thaumarchaeota, Crenarchaeota, and Euryarchaeota in the amplicon libraries was an unexpected discovery, which was confirmed by quantitative real-time PCR revealing an archaeal portion of up to 35.8%. Although the function of these Archaea for their host plant remains speculative, this finding suggests a significant relevance of archaeal endophytes for plant–microbe interactions. In addition, the antagonistic potential of culturable endophytes was determined; all isolates with antagonistic activity against the olive-pathogenic fungus Verticillium dahliae Kleb. belong to Bacillus amyloliquefaciens. In contrast to the specific global structural diversity, BOX-fingerprints of the antagonistic Bacillus isolates were highly similar and independent of the olive genotype from which they were isolated.

High-resolution airborne hyperspectral and thermal imagery for early detection of Verticillium wilt of olive using fluorescence, temperature and narrow-band spectral indices

Verticillium wilt (VW) caused by the soil-borne fungus Verticillium dahliae Kleb, is the most limiting disease in all traditional olive-growing regions worldwide. This pathogen colonizes the vascular system of plants, blocking water flow and eventually inducing water stress. The present study explored the use of high-resolution thermal imagery, chlorophyll fluorescence, structural and physiological indices (xanthophyll, chlorophyll a+b, carotenoids and blue/green/red B/G/R indices) calculated from multispectral and hyperspectral imagery as early indicators of water stress caused by VW infection and severity. The study was conducted in two olive orchards naturally infected with V. dahliae. Time series of airborne thermal, multispectral and hyperspectral imagery was acquired in three consecutive years and related to VW severity at the time of the flights. Concurrently to the airborne campaigns, field measurements conducted at leaf and tree-crown levels showed a significant increase in crown temperature (Tc) minus air temperature (Ta) and a decrease in leaf stomatal conductance (G) across VW severity levels, identifying VW-infected trees at early stages of the disease. Higher Tc−Ta and G values measured in the field were associated with higher VW severity levels. At leaf level, the reduction in G caused by VW infection was associated with a significant increase in the Photochemical Reflectance Index (PRI570) and a decrease in chlorophyll fluorescence (F). The airborne flights enabled the early detection of VW by using canopy-level image-derived airborne Tc−Ta, Crop Water Stress Index (CWSI) calculated from the thermal imagery, blue/blue–green/blue–red ratios (B/BG/BR indices) and chlorophyll fluorescence, confirming the results obtained in the field. Airborne Tc−Ta showed rising values with a significant increase of ~2K at low VW severity levels, and was significantly correlated with G (R2=0.76, P=0.002) and PRI570 (R2=0.51, P=0.032). Early stages of disease development could be differentiated based on a CWSI increase as VW developed, obtaining a strong correlation with G (R2=0.83, P<0.001). Likewise, the canopy-level chlorophyll fluorescence dropped at high VW severity levels, showing a significant increase as disease progressed. These results indicate the potentials of an early detection of V. dahliae infection and discrimination of VW severity levels using remote sensing. Indicators based on crown temperature such as CWSI, and visible ratios B/BG/BR as well as fluorescence were effective in detecting VW at early stages of disease development. In affected trees, the structural indices PRI, chlorophyll and carotenoid indices, and the R/G ratio were good indicators to assess the damage caused by the disease.

Complete genome sequence of a novel dsRNA mycovirus isolated from the phytopathogenic fungus Verticillium dahliae Kleb.

A novel double-stranded RNA (dsRNA) mycovirus, designated Verticillium dahliae partitivirus 1 (VdPV1), was isolated from a strain of the fungus Verticillium dahliae. The VdPV1 genome has two dsRNA genome segments. The larger segment (1768bp) has a single open reading frame (ORF) with a conserved RNA-dependent RNA polymerase (RdRP) domain. The smaller segment (1587bp) contains a single ORF encoding a putative coat protein. Analysis of its genomic structure indicated that VdPV1 is a new member of the genus Partitivirus. We report the full-length sequence of this partitivirus that infects Verticillium dahliae, the causal agent of verticillium wilt of cotton.

Verticillium dahliae's VdNEP acts both as a plant defence elicitor and a pathogenicity factor in the interaction with Helianthus annuus

The soil-borne fungus Verticillium dahliae Kleb. causes a serious wilt disease in many economic crops worldwide, including sunflower. We investigated the role of V. dahliae's necrosis and ethylene-inducing proteins (VdNEP) in the interaction with sunflower. We inoculated two highly and two weakly aggressive V. dahliae isolates onto moderately resistant and susceptible sunflower hybrids. We also synthesized VdNEP protein in vitro and infiltrated it into sunflower control plants to compare its effects with those of the fungus. VdNEP induced wilting symptoms, i.e. chlorosis, necrosis and vascular discoloration but also triggered host defence responses, i.e. hypersensitive response in Nicotiana benthamiana leaves and sunflower cotyledons. It activated the production of reactive oxygen species and the accumulation of fluorescent compounds in sunflower leaves, as well as pathogenesis-related genes (Ha-PR-3 and Ha-PR-5), two defensin genes (Ha-PDF and Ha-CUA1) and those encoding Ha-ACO, Ha-CHOX, Ha-GST and Ha-SCO. The latter suggested that more than one signalling pathway may be involved in the V. dahliae-sunflower interaction. Two other genes (Ha-PAL and Ha-NML1), related to the salicylic acid pathway, were slightly downregulated by VdNEP, suggesting a possible involvement of VdNEP in affecting sunflower defences. The phenotypic changes induced by VdNEP indicate that this protein acts both as a defence elicitor and a pathogenicity factor.

Genomic characterization of a novel dsRNA virus detected in the phytopathogenic fungus Verticillium dahliae Kleb.

Four novel double-stranded RNA segments were detected in a Verticillium dahliae Kleb. strain ( V. dahliae isolate 0-21), a causal fungal agent of Verticillium wilt disease of cotton. Each dsRNA genome segment contains a single large open reading frame (ORF) that encodes a distinctive protein with modest levels of sequence similarities to the corresponding putative proteins in the genus Chrysovirus. These include an RNA-dependent RNA polymerase (RdRp), a coat protein, an undefined replication-related protein and an ovarian tumor domain peptidase. Phylogenetic analysis of the four putative proteins unanimously indicated that they are evolutionarily related to viruses in Chrysovirus. The 5′- and 3′-untranslated regions of the four dsRNAs share highly similar internal sequence and contain conserved sequence stretches of UGAUAAAAAA(/U)UG(/U)AAAAA- (in the 5′-UTR) and -UUUACUACU (in the 3′-UTR), indicating that they have a common virus origin. Indeed, isometric virus-like particles (VLPs) with a diameter of approximately 34 nm were extracted from the fungal mycelia, and the four dsRNA segments were also detected in the virus-like particle (VLP) fraction. These results suggest that the mycovirus with four different dsRNA genome segments from the fungal isolate 0-21 is a new member of the genus Chrysovirus. We named the virus Verticillium dahliae chrysovirus 1 (VdCV1).

Reactions of selected eggplant cultivars and lines to verticillium wilt caused by Verticillium dahliae Kleb.

Verticillium wilt caused by the fungus Verticillium dahliae Kleb. leads to decrease in the yield and quality of eggplant, an economically important vegetable in Turkey. To develop eggplant lines that are resistant to or tolerant to verticillium wilt, this study used cultivars K-1, K-2, K-3, K-4, K-5, K-6, K-7 and K-8 in the studies presented here. The wild species Solanum torvum and Solanum sodemeum ; the resistant cultivated forms DK-1, DK-2, DK-3, DK-4 and DK-6; and the cultivar DK-5 were also included in the study. For the pathogenicity tests, an isolate of V. dahliae used was identified by PCR at the Plant Protection Department of the Faculty of Agriculture, A. Menderes University. All the plant materials were tested with this isolate in 2004 and again in 2005. Results from the two years were similar; the lowest disease ratio was obtained from the DK-5 line in both years. F 1 plants were obtained through hybridisation of cultivar K-1 and line DK-5, which were determined to be respectively susceptible and tolerant to V. dahliae . Next, F 2 plants were obtained by selfing F 1 . In 2006, cultivar K-1, line DK-5, and F 1 and F 2 plants underwent pathogenicity tests. At the end of the pathogenity test, the disease severity in cultivar K-1 and line DK-5 was similar to that seen in previous years, whereas the yellowing and wilting values of F 1 plant leaves, as well as stem isolation and reisolation results, were higher than those of F 2 plants. Using a 0 to 5 scale and considering the yellowing area on leaves, the disease severity in F 1 plants was determined to be 38%; the severity value ranged from 2 to 6% in 55% of 200 F 1 plants and from 36 to 44% in the remaining 45%. Key words: Solanum melongena, Verticillium dahliae, resistance, hybridisation.

Verticillium wilt of olive: a case study to implement an integrated strategy to control a soil-borne pathogen

Olive (Olea europaea L.) is one of the first domesticated and cultivated tree species and has historical, social and economical relevance. However, its future as a strategic commodity in Mediterranean agriculture is threatened by diverse biotic (traditional and new/emerging pests and diseases) and abiotic (erosion, climate change) menaces. These problems could also be of relevance for new geographical areas where olive cultivation is not traditional but is increasingly spreading (i.e., South America, Australia, etc). One of the major constraints for olive cultivation is Verticillium wilt, a vascular disease caused by the soil-borne fungus Verticillium dahliae Kleb. In this review we describe how Verticillium wilt of olive (VWO) has become a major problem for olive cultivation during the last two decades. Similar to other vascular diseases, VWO is difficult to manage and single control measure are mostly ineffective. Therefore, an integrated disease management strategy that fits modern sustainable agriculture criteria must be implemented. Multidisciplinary research efforts and advances to understand this pathosystem and to develop appropriate control measures are summarized. The main conclusion is that a holistic approach is the best strategy to effectively control VWO, integrating biological, chemical, physical, and cultural approaches.

Analysis of bacterial communities in rhizosphere soil of healthy and diseased cotton (Gossypium sp.) at different plant growth stages

Bacterial communities in rhizosphere soil of healthy and diseased cotton (infected by the pathogenic fungus Verticillium dahliae Kleb.) were examined at different plant growth stages using T-RFLP and 16S rDNA clone library. At flowering and bolling, soil samples from the rhizosphere of healthy cotton had the highest richness, whereas the highest evenness was found in the rhizosphere of diseased cotton at boll opening. Acidobacteria and Proteobacteria were the main phyla in the cotton rhizosphere. Other phyla, including WS3, Deinococcus-Thermus, Verrucomicrobia, Firmicutes, Bacteroidetes, Actinobacteria, Thermomicrobia, Gemmatimonadetes, Planctomycetes, Proteobacteria, Cyanobacteria and unclassified bacteria were also found in cotton rhizosphere soils. Deinococcus-Thermus and Firmicutes were only present in diseased cotton rhizospheres. PCA analysis based on the 16S rDNA clone library demonstrated that six sampling resolved three groups of assemblages.

Assessing the Risk of Biological Control Agents on the Indigenous Microbial Communities: Serratia plymuthica HRO-C48 and Streptomyces sp. HRO-71 as Model Bacteria

The phytopathogenic fungus Verticillium dahliae Kleb. causes high yield losses in strawberry production. As effective chemical control of this fungus is no longer available, biological control based on natural antagonists might provide new control strategies. The aim of this study was to assess the impact of the two biological control agents S. plymuthica HRO-C48 and Streptomyces sp. HRO-71 on the rhizosphere community of the Verticillium host plant strawberry in field trials at two different sites in Germany. Therefore, we determined the abundances of culturable bacteria and investigated the community structure of the total rhizosphere microbiota by PCR-single strand conformation polymorphism analysis of the 16S rRNA and fungal ITS1 region. The abundances of culturable rhizobacteria on R2A medium as well as the proportion of in vitro Verticillium antagonists did not differ significantly. Additionally, no treatment specific differences were obtained in the composition of species of the non-target antagonistic bacteria in the rhizospheres. The culture-independent analysis revealed only transient differences between the bacterial communities not due to the treatments rather than to the plant growth stage. Fungal and bacterial community fingerprints showed the development of a microbiota, specific for a field site. However, no sustainable impact of the bacterial treatments on the indigenous microbial communities was found using culture-dependent and -independent methods.

A hydrophobin gene, VDH1, is involved in microsclerotial development and spore viability in the plant pathogen Verticillium dahliae

The wilt fungus Verticillium dahliae Kleb. produces desiccation- and cold-tolerant resting structures, known as microsclerotia, which are the primary source of disease inoculum in the field. In an exploration of the molecular mechanisms involved in the development of these important structures, we have identified in V. dahliae a differentially expressed, class II hydrophobin gene ( VDH1). vdh1 mutants generated through targeted gene disruption show a severe reduction in microsclerotia production, indicating that the gene is important for this type of development. Although vdh1 mutants do produce normal conidiophores and spores, desiccation-tolerance of the spores is reduced. The VDH1 gene is not, however, needed for normal disease development in tomato. VDH1’s functions are multi-faceted, and seem generally relevant to long-term survival in V. dahliae.

Limitation to Photosynthesis in Pratylenchus penetrans‐ and Verticillium dahliae‐Infected Potato

Mechanism(s) responsible for decrease in photosynthetic rates of potato (Solanum tuberosum L.) leaves infected by the fungus Verticillium dahliae (Kleb) and the nematode Pratylenchus penetrans (Cobb, Sher, Allen) have not been fully researched. Two growth chamber experiments were undertaken to determine the factors contributing to the decrease in CO2 exchange rates of young, fully expanded leaflets of potato (cv. Russet Burbank) plants grown in pots infested with P. penetrans and/or V. dahliae Treatments were P. penetrans‐infested soil, V. dahliae‐infested soil, soil infested with both the nematode and the fungus, and a noninfested control. Leaf CO2 response curves were measured at early (16 d after inoculation [DAI]) and late (42 DAI) stages of infection for all treatments at saturating light (1500 μmol m−2 s−1 of photosynthetically active radiation [PAR] using a portable photosynthesis system. Carbon dioxide exchange rates were also measured at 1000, 400, and 200 μmol m−2 s−1 PAR to determine leaf light response. At ambient CO2 concentration, concomitant infection by both pathogens significantly reduced C assimilation rate (A) and light use efficiency (μmoles CO2 fixed per μmol of light used), and increased the intercellular CO2 (Ci ) of these young leaves at 42 DAI, but not at 16 DAI. Infection by either pathogen alone had little or no effect on the leaf gas exchange parameters. Analysis of the curve relating A and Ci showed that either treatment alone did not change the initial slope of the curve at 16 DAI. A significant reduction in both the initial slope of A vs. Ci curves and A at Ci = 500 μmol mol−1 in the jointly infected plants were noticeable at 42 DAI indicating that nonstomatal effects could explain the reduction in C assimilation rate at this late stage of disease infection. Leaf patchiness might also be a contributing factor to this phenomena in the leaves of the jointly infected plants.

Post-infectional changes in the phospholipids of the leaves of a cotton plant variety resistant toVerticillium dahliae

The class and fatty acid compositions of the phospholipids (PLs) of young leaves of healthy, cotton plants of the wilt-resistant variety 175-F and of plants of the same variety infected with the pathogenic fungusVerticillium dahliae Kleb. have been determined. The positional distributions of the fatty acids in the main classes of PLs have been established, and their possible molecular compositions have been calculated. The changes in the composition of the PLs taking place under the influence of infection have been elucidated.