Defense responses induced by ulvan in wheat against powdery mildew caused by Blumeria graminis f. sp. tritici.

Ulvan is a water-soluble sulfated heteropolysaccharide extracted from the cell walls of the green seaweeds Ulva spp. This polysaccharide is known to induce resistance and protect plants against a broad range of plant pathogenic fungi, such as Blumeria graminis f. sp. tritici (Bgt), the causal agent of powdery mildew in wheat. We aimed to study the defense mechanisms induced by ulvan against Bgt in susceptible wheat by investigating the defense-related gene expression, enzymes activity, accumulation of phenolic compounds and hydrogen peroxide (H2O2), as well as the development of Bgt infection structures in vitro and in planta. Symptoms were reduced by 42% in ulvan-treated plants. In vitro, ulvan did not inhibit conidial germination of Bgt but in planta, increased the appressorial germ tubes without haustorium. Ulvan increased the presence of fluorescent papillae and accumulation of H2O2 at the penetration sites of Bgt, as well as the content of phenolic compounds. POX, PAL and LOX activities were stimulated in ulvan-treated plants during the first 48 h after inoculation. However, few of defense-related genes studied were differentially expressed in infected plants after ulvan treatment. By contrast, in non-infected conditions, ulvan up-regulated the expression of genes involved in phenylpropanoid metabolism, i.e. PAL, CHS, COMT, ANS and FLS, genes encoding pathogenesis-related proteins, i.e. PR1, PR9, PR15, and LOX during the first 96 h after treatment. This study provides new insights about the multiple ulvan effects on wheat defense responses, and especially the elicitation of the phenylpropanoid pathway leading to phenolic compounds accumulation, which could be involved in cell wall reinforcement.

Reclassification of the Main Causal Agent of Glomerella Leaf Spot on Apple into Colletotrichum chrysophilum in Southern Brazil and Uruguay.

Glomerella leaf spot (GLS) is one of the most important diseases of apple, affecting a wide range of economically important cultivars, particularly Golden Delicious and its descendants. Caused mainly by species of the Colletotrichum gloeosporioides species complex (CGSC), C. fructicola has been described as the most prevalent and aggressive species associated with GLS and apple bitter rot (ABR) in Brazil and Uruguay. Recently, new CGSC species, closely related to C. fructicola, have been identified causing ABR. To verify the accuracy of species identification within the CGSC, we aimed to reevaluate the identity of representative GLS-causing isolates from Brazilian and Uruguayan populations, previously identified as C. fructicola. Multilocus phylogenetic analysis based on APN2, ApMAT, CAL, GAPDH, GS, ITS, and TUB2 allocated these isolates in a monophyletic clade with C. chrysophilum. This species was first described as the causal agent of anthracnose in banana fruits in Brazil, and recent reports indicate its association with ABR in the United States. This is the first report of C. chrysophilum causing GLS disease on apple worldwide.

A Laminarin-Based Formulation Protects Wheat Against Zymoseptoria tritici via Direct Antifungal Activity and Elicitation of Host Defense-Related Genes.

The present study aimed to evaluate the potential of the laminarin-based formulation Vacciplant to protect and induce resistance in wheat against Zymoseptoria tritici, a major pathogen on this crop. Under greenhouse conditions, a single foliar spraying of the product 2 days before inoculation with Z. tritici reduced disease severity and pycnidium density by 42 and 45%, respectively. Vacciplant exhibited a direct antifungal activity on Z. tritici conidial germination both in vitro and in planta. Moreover, it reduced in planta substomatal colonization as well as pycnidium formation on treated leaves. Molecular investigations revealed that Vacciplant elicits but did not prime the expression of several wheat genes related to defense pathways, including phenylpropanoids (phenylalanine ammonia-lyase and chalcone synthase), octadecanoids (lipoxygenase and allene oxide synthase), and pathogenesis-related proteins (ß-1,3-endoglucanase and chitinase). By contrast, it did not modulate the expression of oxalate oxidase gene involved in the reactive oxygen species metabolism. Ultrahigh-performance liquid chromatography-mass spectrometry analysis indicated limited changes in leaf metabolome after product application in both noninoculated and inoculated conditions, suggesting a low metabolic cost associated with induction of plant resistance. This study provides evidence that the laminarin-based formulation confers protection to wheat against Z. tritici through direct antifungal activity and elicitation of plant defense-associated genes.

Changes in xylem morphology and activity of defense-related enzymes are associated with bean resistance during Fusarium oxysporum colonization.

Genetic resistance is the main strategy to control Fusarium wilt in common bean. Despite this, few studies have focused on defense mechanisms involved in bean resistance to Fusarium oxysporum f. sp. phaseoli (Fop). Thus, the present study aimed to investigate the changes in xylem morphology and involvement of phenylpropanoid compounds and their biosynthetic enzymes in bean resistance against Fop. Uirapuru and UFSC-01 genotypes characterized, respectively, as susceptible and resistant were used. In roots and hypocotyls, guaiacol peroxidase (GPX), phenylalanine ammonia-lyase (PAL), and polyphenol oxidase (PPO) activities were determined at 0, 1, 2, 3, 4, 5, and 6 days after inoculation (dai), and flavonoids, total phenolics, and lignin content were quantified at 0, 3, and 6 dai. Cross sections of taproots and hypocotyls were examined under epifluorescence (at 1, 3, and 6 dai) and transmission electron (at 6 dai) microscopic to analyze the morphology of xylem cell walls. Overall, there was an increase in the activity of all studied enzymes in resistant bean plants, mainly during advanced colonization stages. Modifications in xylem morphology were more intense in roots of resistant genotype resulting in an increase of occluded cells, organelles, and cell wall strengthening. This study provides evidence that bean resistance is associated with increased phenylpropanoid enzymatic activity and cell wall reinforcement of some xylem cells.

The Algal Polysaccharide Ulvan Induces Resistance in Wheat Against Zymoseptoria tritici Without Major Alteration of Leaf Metabolome.

This study aimed to examine the ability of ulvan, a water-soluble polysaccharide from the green seaweed Ulva fasciata, to provide protection and induce resistance in wheat against the hemibiotrophic fungus Zymoseptoria tritici. Matrix-assisted laser desorption/ionization-time-of-flight-mass spectrometry (MALDI-TOF-MS) analysis indicated that ulvan is mainly composed of unsaturated monosaccharides (rhamnose, rhamnose-3-sulfate, and xylose) and numerous uronic acid residues. In the greenhouse, foliar application of ulvan at 10 mg.ml-1 2 days before fungal inoculation reduced disease severity and pycnidium density by 45 and 50%, respectively. Ulvan did not exhibit any direct antifungal activity toward Z. tritici, neither in vitro nor in planta. However, ulvan treatment significantly reduced substomatal colonization and pycnidium formation within the mesophyll of treated leaves. Molecular assays revealed that ulvan spraying elicits, but does not prime, the expression of genes involved in several wheat defense pathways, including pathogenesis-related proteins (ß-1,3-endoglucanase and chitinase), reactive oxygen species metabolism (oxalate oxidase), and the octadecanoid pathway (lipoxygenase and allene oxide synthase), while no upregulation was recorded for gene markers of the phenylpropanoid pathway (phenylalanine ammonia-lyase and chalcone synthase). Interestingly, the quantification of 83 metabolites from major chemical families using ultra-high-performance liquid chromatography-mass spectrometry (UHPLC-MS) in both non-infectious and infectious conditions showed no substantial changes in wheat metabolome upon ulvan treatment, suggesting a low metabolic cost associated with ulvan-induced resistance. Our findings provide evidence that ulvan confers protection and triggers defense mechanisms in wheat against Z. tritici without major modification of the plant physiology.

First Report of Colletotrichum chrysophilum Causing Anthracnose on Blueberry in Brazil.

Highbush (Vaccinium corymbosum L.) and rabbiteye (V. ashei R.) blueberry are the most important export small fruit crops in southern Brazil. Anthracnose has been considered one of the most destructive disease and exclusively associated with C. karstii in Brazil (Rios et al. 2014). In November 2019, severe anthracnose symptoms including leaf spots but particularly twig blights and fruit rots were observed on all blueberry plants (V. ashei) in one organic orchard in Santa Catarina state, Brazil (27º43'48.96"S, 49º0'57.79"W). Four isolates were obtained from necrotic lesions and monosporic cultures were grown on potato dextrose agar at 25°C and with a 12 h photoperiod under near ultra violet light. After 15 days, colonies showed upper surface color varying from grayish-white to pale-orange and the reverse side pale-orange. Conidia were hyaline, cylindrical with rounded ends, and their length and width ranged from 9.5 to 15.5 µm (x ̅=11.8) and 6.5 to 3.5 µm (x ̅=4.9), respectively. The isolates were identified by multilocus phylogenetic analyses using nucleotide sequences of actin (ACT), ß-tubulin (TUB2), calmodulin (CAL), glyceraldehyde-3-phosphate-dehydrogenase (GAPDH), glutamine synthetase (GS), internal transcribed spacer (ITS) and the intergenic spacer between DNA lyase and the mating-type locus MAT1-2-1 (ApMAT). Nucleotide sequences exhibited from 95 to 100% sequence identity to Colletotrichum chrysophilum ex-type (CMM4268) and were deposited in GenBank database (MW868219 to MW868222, MW868211 to MW868214, MW868215 to MW868218, MW868223 to MW868226, MW868202 to MW868205, MW793353 to MW793356, and MW868207 to MW868210). C. chrysophilum belongs to the C. gloeosporioides species complex and was previously described as C. ignotum in banana and other tropical fruits in Brazil (Vieira et al. 2017; Veloso et al. 2018). In addition, this species was recently reported on apple fruit in New York, USA (Khodadadi et al. 2020). To confirm pathogenicity, one-year-old blueberry plants were inoculated by spraying a suspension of 1×106 conidia/ml, incubated in a moist chamber in the dark for 48 h and then kept in the greenhouse. Plants sprayed with sterile distilled water served as control. Additionally, fruits were immersed for 2 min in a conidial suspension (1×106 conidia/ml) and incubated at 25°C and 12 h photoperiod for 20 days. Inoculated plants exhibited first symptoms in twigs at 10 days after inoculation (dai). Infected twigs showed initially dark brown spots that coalesced and became necrotic. On leaves, reddish-brown lesions with less than 2 mm appeared at low intensity at 15 dai. On fruits, sunken areas associated with an abundant orange mucilaginous mass of acervuli and conidia were seen at 7 dai. Symptoms on plants were identical to those observed under field conditions, and the pathogen was re-isolated from lesions fulfilling Koch's postulates. To the best knowledge, this is the first report of C. chrysophilum causing anthracnose on blueberries in Brazil. The identification of this species causing blueberry anthracnose is crucial to improve the disease control strategies and resistance breeding.

First Report of Colletotrichum karstii Causing Anthracnose on Strawberry in Brazil.

Strawberry (Fragaria x ananassa Duch.) is one of the most important fruit crops worldwide. With increasing cultivated area in the last decades, Brazil has become the largest strawberry producer in South America. Anthracnose caused by Colletotrichum spp. has been considered one of the most destructive diseases in Brazil. In May 2019, irregular and circular dark brown leaf spots sometimes associated with chlorosis and petiole necrosis were observed on strawberry plants (cv. Pircinque) organically cultivated in Santa Catarina state, Brazil (27°45'40"S, 49°59'06''W). The Colletotrichum isolate was obtained from leaf, and monosporic culture was grown on potato dextrose agar at 25°C and 12-h photoperiod under near ultraviolet light. Colonies at the age of 15 days showed upper surface color varying from white to orange and the reverse side grayish to orange. Conidia were hyaline, cylindrical with rounded ends, 13.9 to 9.2 × 4.2 to 6.7 µm ((x ) ̅= 11.3 × 5.2, n = 100). Perithecia were produced in vitro and their diameter ranged from 265.2 to 142.5 µm ((x ) ̅= 198.4). Asci were 47.3 to 39.9 × 5.2 to 7.2 µm ((x ) ̅= 42.8 × 5.9, n = 50), and ascospores 12.6 to 8.1 × 4.3 to 2.1 ((x ) ̅= 10.3 × 2.9, n = 100). To confirm pathogenicity, 90-day-old plants of strawberry (cv. Pircinque) were inoculated by spraying a suspension of 1×106 conidia/ml, incubated in a moist chamber in the dark for 48 h and then kept in a greenhouse for further 30 days. Plants sprayed with sterile distilled water served as control. Additionally, detached leaves were inoculated with six drops of 10 µl (1×106 conidia/ml) onto abaxial surface and incubated in a moist chamber at 25°C and 12 h photoperiod for 15 days. Inoculated plants exhibited first symptoms in both leaves and petioles at 15 days after inoculation (dai). On leaf, irregular and circular dark brown spots evolved to necrotic lesions and were frequently surrounded by chlorotic halos. In petioles, lesions were reddish-brown, elongated, and depressed. Typical anthracnose symptoms on fruits at 6 dai showed as circular, slightly sunken lesions that enlarged over time and produced an abundant orange mucilaginous mass of acervuli and conidia, and after 20 days, fruits became mummified. In the detached-leaf-assay, symptoms appeared at 7 dai, with presence of circular dark brown lesions measuring 1 to 15 mm and then evolved to necrosis. The same pathogen was consistently re-isolated from the inoculated leaves, petioles, and fruits, and confirmed by morphological characterization and molecular assays as described in this note. A representative isolate (MANE189) was molecularly identified using genomic regions of actin (ACT), ß-tubulin (TUB2), calmodulin (CAL), glyceraldehyde-3-phosphate-dehydrogenase (GAPDH), glutamine synthetase (GS), and internal transcribed spacer (ITS). Nucleotide sequences exhibited 100% homology to the typical Colletotrichum karstii strains (CBS:127535, CBS:128500 and ML1792) and were deposited in GenBank database (MW396420, MW396430, MW396460, MW396440, MW396450, and MW331606). This species belongs to the C. boninense species complex (Damm et al. 2012) and was previoStrawberry (Fragaria x ananassa Duch.) is one of the most important fruit crops worldwide. With increasing cultivated area in the last decades, Brazil has become the largest strawberry producer in South America. Anthracnose caused by Colletotrichum spp. has been considered one of the most destructive diseases in Brazil. In May 2019, irregular and circular dark brown leaf spots sometimes associated with chlorosis and petiole necrosis were observed on strawberry plants (cv. Pircinque) organically cultivated in Santa Catarina state, Brazil (27°45'40"S, 49°59'06''W). The Colletotrichum isolate was obtained from leaf, and monosporic culture was grown on potato dextrose agar at 25°C and 12-h photoperiod under near ultraviolet light. Colonies at the age of 15 days showed upper surface color varying from white to orange and the reverse side grayish to orange. Conidia were hyaline, cylindrical with rounded ends, 13.9 to 9.2 × 4.2 to 6.7 µm ((x ) ̅= 11.3 × 5.2, n = 100). Perithecia were produced in vitro and their diameter ranged from 265.2 to 142.5 µm ((x ) ̅= 198.4). Asci were 47.3 to 39.9 × 5.2 to 7.2 µm ((x ) ̅= 42.8 × 5.9, n = 50), and ascospores 12.6 to 8.1 × 4.3 to 2.1 ((x ) ̅= 10.3 × 2.9, n = 100). To confirm pathogenicity, 90-day-old plants of strawberry (cv. Pircinque) were inoculated by spraying a suspension of 1×106 conidia/ml, incubated in a moist chamber in the dark for 48 h and then kept in a greenhouse for further 30 days. Plants sprayed with sterile distilled water served as control. Additionally, detached leaves were inoculated with six drops of 10 µl (1×106 conidia/ml) onto abaxial surface and incubated in a moist chamber at 25°C and 12 h photoperiod for 15 days. Inoculated plants exhibited first symptoms in both leaves and petioles at 15 days after inoculation (dai). On leaf, irregular and circular dark brown spots evolved to necrotic lesions and were frequently surrounded by chlorotic halos. In petioles, lesions were reddish-brown, elongated, and depressed. Typical anthracnose symptoms on fruits at 6 dai showed as circular, slightly sunken lesions that enlarged over time and produced an abundant orange mucilaginous mass of acervuli and conidia, and after 20 days, fruits became mummified. In the detached-leaf-assay, symptoms appeared at 7 dai, with presence of circular dark brown lesions measuring 1 to 15 mm and then evolved to necrosis. The same pathogen was consistently re-isolated from the inoculated leaves, petioles, and fruits, and confirmed by morphological characterization and molecular assays as described in this note. A representative isolate (MANE189) was molecularly identified using genomic regions of actin (ACT), ß-tubulin (TUB2), calmodulin (CAL), glyceraldehyde-3-phosphate-dehydrogenase (GAPDH), glutamine synthetase (GS), and internal transcribed spacer (ITS). Nucleotide sequences exhibited 100% homology to the typical Colletotrichum karstii strains (CBS:127535, CBS:128500 and ML1792) and were deposited in GenBank database (MW396420, MW396430, MW396460, MW396440, MW396450, and MW331606). This species belongs to the C. boninense species complex (Damm et al. 2012) and was previously reported causing anthracnose on strawberry leaves in Taiwan (Chung et al. 2020). To our knowledge, this is the first report of C. karstii causing anthracnose on strawberry in Brazil. The accurate identification of the pathogen will assist in the disease management and resistance breeding. usly reported causing anthracnose on strawberry leaves in Taiwan (Chung et al. 2020). To our knowledge, this is the first report of C. karstii causing anthracnose on strawberry in Brazil. The accurate identification of the pathogen will assist in the disease management and resistance breeding.

Redox status regulation and action of extra- and intravascular defense mechanisms are associated with bean resistance against Fusarium oxysporum f. sp. phaseoli.

Genetic resistance is the main strategy to control one of the most destructive diseases of common bean (Phaseolus vulgaris L), i.e., the Fusarium wilt caused by Fusarium oxysporum f. sp. phaseoli (Fop). However, little is known on host defense reactions in Fop-bean interaction. Thus, this work examined the defense mechanisms in root and hypocotyl tissues of common bean against Fop. Resistant and susceptible bean plants were inoculated by dipping their roots in a conidial suspension. Cross sections of roots and hypocotyls were observed in light microscopy at 1, 3, 6, and 9 days after inoculation (dai) to monitor Fop colonization, and at 3 and 9 dai to detect callose, carbohydrates, lipids, phenolics, and protein, and under electronic microscopy at 9 dai to observe ultrastructural changes in xylem cells. The content of hydrogen peroxide (H2O2), lipid peroxidation, and activity of the antioxidant enzymes ascorbate peroxidase (EC 1.11.1.11) and catalase (EC 1.11.1.6) were monitored spectrophotometrically in roots and hypocotyls at 0, 1, 3, 6, and 9 dai. Fop colonized inter- and intracellularly the epidermis and cortex reaching the xylem vessels faster in susceptible genotype. Fop inoculation induced phenolics and carbohydrates accumulation, callose deposition, and formation of occlusion material inside xylem vessels mainly in resistant genotype. Lipid peroxidation occurred mainly in susceptible plants. In contrast, the antioxidant enzymes seem to have contributed to reducing damage caused by H2O2 accumulation in resistant plants. This study gives evidences that inter- and intracellular physicochemical mechanisms can act together to delay Fop colonization in resistant plants.

Ascospore Infection and Colletotrichum Species Causing Glomerella Leaf Spot of Apple in Uruguay.

Glomerella leaf spot (GLS) caused by Colletotrichum spp. is a destructive disease of apple restricted to a few regions worldwide. The distribution and evolution of GLS symptoms were observed for two years in Uruguay. The recurrent ascopore production on leaves and the widespread randomized distribution of symptoms throughout trees and orchard, suggest that ascospores play an important role in the disease dispersion. The ability of ascospores to produce typical GLS symptom was demonstrated by artificial inoculation. Colletotrichum strains causing GLS did not result in rot development, despite remaining alive in fruit lesions. Based on phylogenetic analysis of actin, ß-tubulin and glyceraldehyde-3-phosphate dehydrogenase gene regions of 46 isolates, 25 from fruits and 21 from leaves, C. karstii was identified for the first time causing GLS in Uruguay and C. fructicola was found to be the most frequent (89%) and aggressive species. The higher aggressiveness of C. fructicola and its ability on to produce abundant fertile perithecia could help to explain the predominance of this species in the field.

Extracellular enzymes of Colletotrichum fructicola isolates associated to Apple bitter rot and Glomerella leaf spot.

Colletotrichum fructicola causes two important diseases on apple in Southern Brazil, bitter rot (ABR) and Glomerella leaf spot (GLS). In this pathosystem, the Colletotrichum ability to cause different symptoms could be related to differences of extracellular enzymes produced by the fungi. Thus, the objectives of this study were to compare the production of these enzymes between ABR- and GLS-isolate in vitro and to evaluate their involvement on infected apple leaves with C. fructicola. In agar plate enzymatic assay, ABR- showed significantly higher amylolytic and pectolytic activity than GLS-isolate. In contrast, for lipolytic and proteolytic no significant differences were observed between isolates. In culture broth, ABR-isolate also had higher activity of pectin lyase (PNL), polygalacturonase (PG) and laccase (LAC). Notably, LAC was significantly five-fold higher in ABR- than GLS-isolate. On the other hand, in infected apple leaves no significant difference was observed between isolates for PNL, PG and LAC. Although differences in extracellular enzymes of ABR- and GLS-isolate have not been observed in vivo, these results contributed to highlight the importance to investigate such enzymes in depth.

Modulation of oxidative responses by a virulent isolate of Colletotrichum fructicola in apple leaves.

Apple bitter rot (ABR) and Glomerella leaf spot (GLS) can be caused by Colletotrichum fructicola. Although both diseases can occur simultaneously in orchards, some isolates show clear organ specialization. Thus, this work was aimed to compare microscopically the development of preinfective structures of ABR- and GLS isolates and their impact on the enzymatic oxidant defense system during the leaf infection process. On leaves, conidial germlings of GLS-isolate formed appressoria mostly sessile. In contrast, those of ABR-isolate were pedicellate and formed multiple melanized appressoria probably as a sign of unsuccessful infection attempts. Neither ABR- nor GLS isolate triggered hypersensitive response in apple leaves. In overall, the activity of scavenging enzymes was higher and long-lasting in leaves inoculated by GLS- than by ABR isolate and control. Guaiacol peroxidase, catalase, and glutathione reductase had activity peaks within 24 h after inoculation (HAI). Ascorbate peroxidase activity was higher only in GLS-infected leaves at 6 HAI, while superoxide dismutase remained unaltered. A lower level of hydrogen peroxide (H2O2) was determined in GLS-infected plants at 48 HAI, but the electrolyte leakage markedly increased. Disease symptoms in leaves were only caused by GLS-isolate. Results suggest that the virulent isolate coordinately downregulates the oxidative plant defense responses enabling its successful establishment in apple leaves.

Genetic Structure of Colletotrichum fructicola Associated to Apple Bitter Rot and Glomerella Leaf Spot in Southern Brazil and Uruguay.

Colletotrichum fructicola is the main species causing apple bitter rot (ABR) and Glomerella leaf spot (GLS) in southern Brazil, and ABR in Uruguay where GLS remains unnoticed. Thus, this work aimed to determine the genetic structure of C. fructicola isolates of both the countries. A total of 28 out of 31 Brazilian isolates (90.3%) caused typical symptoms of GLS, while only 6 of 25 Uruguayan isolates (24.0%) originating from fruits were able to infect leaves, but causing atypical symptoms. Both populations showed similar levels of Nei's gene diversity (h = 0.088 and 0.079, for Brazilian and Uruguayan populations, respectively), and Bayesian cluster analysis inferred two genetic clusters correlated with the geographical origin of isolates. A principal coordinates analysis scatter plot and an unweighted pair group method with arithmetic mean-based dendrogram also grouped Brazilian and Uruguayan isolates into two groups. By pairwise comparison of nitrate-nonutilizing (nit) mutants with a proposed set of testers, all Uruguayan isolates were grouped into a unique vegetative compatibility group (namely VCG 1), while Brazilian isolates were grouped into four VCGs (VCG 1 to 4). Brazilian and Uruguayan populations of C. fructicola were found to be genetically distinct. Our results suggest that isolates of C. fructicola from Brazil capable of causing GLS and ABR arose independently of those from Uruguay. Possible causes leading to the evolutionary differences between populations are discussed.

Ulvans induce resistance against plant pathogenic fungi independently of their sulfation degree.

The present work aimed to evaluate the defense responses induced by chemically sulfated ulvans in Arabidopsis thaliana plants against the phytopathogenic fungi Alternaria brassicicola and Colletotrichum higginsianum. Derivatives with growing sulfate content (from 20.9 to 36.6%) were prepared with SO3-pyridine complex in formamide. NMR and FTIR spectroscopic analyses confirmed the increase of sulfate groups after the chemical sulfation process. The native sulfated polysaccharide (18.9% of sulfate) and its chemically sulfated derivatives similarly reduced the severity of both pathogenic fungi infections. Collectively, our results suggest that ulvans induce resistance against both fungal pathogens independently of its sulfation degree.

New insights into the characterization of Colletotrichum species associated with apple diseases in southern Brazil and Uruguay.

Colletotrichum species are associated with Apple bitter rot (ABR) and Glomerella leaf spot (GLS). Whereas both apple diseases occur frequently in Brazil, only the former has been reported in Uruguay. This work was aimed at identifying and comparing morpho-cultural characteristics and pathogenic variability of thirty-nine Colletotrichum isolates from both countries. Sequencing of the internal transcribed spacer (ITS) rDNA, glyceraldehyde-3-phosphate dehydrogenase (GAPDH), and ß-tubulin (TUB2) allowed the identification of three species causing ABR and GLS in Brazil, i.e., Colletotrichum fructicola, Colletotrichum karstii, and Colletotrichum nymphaeae; and three species causing ABR in Uruguay, i.e., C. fructicola, Colletotrichum theobromicola, and Colletotrichum melonis. Six groups of colony colours were recorded with group 1 (mycelium white to pink and in reverse pinkish) and group 2 (mycelium white to grey and in reverse pinkish) the most frequent. Isolates of C. fructicola and C. theobromicola were sensitive to benomyl, while C. karstii, C. nymphaeae, and C. melonis were resistant. Conidia were predominantly cylindrical for C. fructicola and C. karstii, fusiform for C. nymphaeae and C. melonis, and obclavate for C. theobromicola. Brazilian isolates caused ABR in wounded fruits, but only five in non-wounded ones. Uruguayan isolates produced symptoms in fruits with or without previous wounding. All Brazilian isolates from GLS and twelve from ABR were able to cause GLS symptoms, while a sole Uruguayan ABR-isolate caused leaf spot symptoms. This study gives a better insight on the new species causing apple disease in both countries and discusses their pathogenic potential.