Biochemical and pathogenic differences between Kenyan and Brazilian isolates of pseudomonas syringae pv. garcae

Isolates of Pseudomonas syringae pv. garcae from Kenya and Brazil differed in pathogenic and biochemical characters. In inoculations on Coffea arabica var. SL28 from Kenya, only the Kenyan isolates were virulent. The Kenyan isolates were not bacteriocin producers while the Brazilian isolates were active producers comparable to P. s. syringae from lilac ( Syringa vulgaris ). Pigment production separated the two types of P. s. garcae isolates distinctly. The Kenyan isolates produced the UV fluorescent yellow-green siderophore while the Brazilian isolates produced a nonfluorescent brown diffusible pigment on King's B medium. API-20NE diagnostic kits were largely ineffective in distinguishing between biochemical reactions of P. s. garcae isolates from Kenya and Brazil or between these and P. s. syringae . Syringomycin activity on lemon and Geotrichum candidum distinguished P. s. syringae from P. s. garcae isolates. It is concluded that P. s. garcae (as represented by the seven cultures from the National Collection of Plant Pathogenic Bacteria, Harpenden, UK) exists in at least two strains, the Kenyan isolates comprising one strain while the Brazilian isolates comprise one or more distinct strains.     

Molecular Fingerprinting Suggests Two Primary Outbreaks of Witches' Broom Disease (Crinipellis perniciosa) of Theobroma cacao in Bahia, Brazil

Crinipellis perniciosa (Stahel) Singer is the causal agent of witches' broom disease in the Sterculiaceae, Solanaceae, and Bixaceae families. The disease is endemic to the Brazilian Amazon, and was first reported infecting Theobroma cacao (cocoa) in the State of Bahia, Brazil, in 1989. Random amplified polymorphic DNA (RAPD) analyses were performed on 46 isolates of C. perniciosa from cocoa that were collected from 15 counties in Bahia and the Brazilian Amazon. A total of 258 RAPD loci from 20 primers and three mixed primers were analyzed. Of these loci, 108 (42%) were polymorphic, with an average of 4.7 polymorphic loci per primer produced. Genetic similarities were estimated using Nei and Li's index and UPGMA clustering. Bootstrap analysis divided the phenogram into four significantly different clusters: two groups contained isolates from Ariquemes and from Ouro Preto, Rondônia, and the other two separated the isolates from Bahia into two major groups of C. perniciosa, classified as Group 1 (G1) and Group 2 (G2). The two groups of isolates from Bahia differed for their genetic similarity with the isolates from the Brazilian Amazon. The geographic distribution of the groups in Bahia suggests two independent focal points of introduction. Ongoing programs to screen for resistant cocoa genotypes should consider both groups of isolates.     

Host specialization of Verticillium dahliae, with emphasis on isolates from cocoa (Theobroma cacao)

Isolates of Verticillium dahliae from cocoa (four Brazilian and one Ugandan) were screened against cocoa, aubergine, tomato, cotton, and pepper. Isolates originating from hosts other than cocoa were also inoculated. In general, all inoculated crops were systemically invaded by isolates from cocoa. Isolates from each host tended to be more aggressive on their original host. All isolates from cocoa were pathogenic to cocoa, but exhibited various degrees of aggressiveness to other crops. They induced severe symptoms on aubergine, but few symptoms on tomato, although colonization occurred up to the stem apex in both cases. Likewise, symptomless invasion of pepper was found with some Brazilian isolates. The Ugandan isolate was significantly more aggressive on cotton and pepper than the Brazilian isolates.
A Brazilian isolate from cocoa from the State of Bahia was also used to inoculate 12 common weed species from the same geographical area. Four species showed wilt symptoms, while V. dahliae was readily recovered from the stems of a further four species. The role of alternative hosts on disease spread in cocoa growing areas is discussed.     

Characterization of Monilinia species associated with brown rot in stone fruit in Brazil

Fungi of the Monilinia genus occur worldwide and affect a wide range of economically important stone fruits. Several Monilinia species are responsible for brown rot. Although this disease is common in Brazil, Monilinia sp. genetic variability in Brazilian orchards has generally been poorly characterized. The present study represents the first report on the genetic diversity of Monilinia sp. from Brazilian orchards. The genetic structure of the Brazilian population was also compared to isolates from other countries, together with some morphological characteristics and aggressiveness. Sixty‐one isolates belonging to the Monilinia genus were obtained from different orchards in Brazilian states. Ten Monilinia fructicola isolates from the United States and one isolate from a fruit imported into Brazil were also evaluated. Phylogenetic analysis of the ITS1‐5.8S‐ITS2 region (internal transcribed spacer) clustered most Brazilian and American isolates with M. fructicola authentic strains from Q‐Bank. Two isolates (one from an imported fruit) clustered as Monilinia laxa. The results revealed M. fructicola as the prevalent species associated with brown rot in Brazilian orchards. To evaluate the intraspecific diversity of M. fructicola and M. laxa, multigene sequence analysis was performed using ITS1‐5.8S‐ITS2 and TEF1 (elongation factor 1). Whilst TEF1 is the most phylogenetically informative gene for intraspecific studies of M. fructicola, RPB2 (RNA polymerase II gene) displayed low variation in intraspecific analysis, but was an informative locus for assigning isolates to M. fructicola or M. laxa species. The amova suggests that Brazilian isolates from the States of the main producing regions belong to a single genetic population, which is genetically distinct from the US (Californian) population of M. fructicola.     

Hypovirulence detected in Brazilian isolates of Cryphonectria cubensis

A single 3 kb segment of double-stranded (dsRNA) was present in three of 30 Brazilian isolates of Cryphonectria cubensis . These dsRNA-containing isolates showed morphological characteristics suggestive of hypovirulence and were significantly less virulent than dsRNA-free isolates. One isolate, however, with morphological characteristics suggestive of hypovirulence, showed reduced virulence, but was free from dsRNA. Conversion of virulent isolates with normal morphology to a morphology associated with hypovirulence was achieved by pairing hypovirulent and virulent isolates of the same vegetative compatibility group (VCG). This suggests that dsRNA can be transmitted to isolates of the same vegetative compatibility group by hyphal anastomosis. Converted isolates exhibited the same hypovirulence-associated traits as those of the original dsRNA-containing hypovirulent isolates. These studies suggest that a single 3 kb segment of dsRNA alters both morphology and virulence by conferring hypovirulence on the pathogen; the first such report for Brazilian isolates of C. cubensis .     

Morphological and molecular characterization of the sudden-death syndrome pathogen of soybean in Brazil

Brazilian Fusarium isolates causing soybean sudden death syndrome (SDS) were characterized by comparing them with other Fusarium isolates associated with soybean root rot, as well as F. solani f.sp. glycines isolates associated with the disease in the USA, using molecular (mitochondrial and nuclear rDNA), morphological, cultural and pathogenic characteristics. On the basis of pathogenicity data, and restriction fragment length polymorphism and sequence analysis of the rDNA internal transcribed spacer (ITS) regions, isolates formed a group distinct from nonSDS F. solani isolates, as well as other Fusarium species. ITS sequence analysis also revealed that Brazilian isolates were distinct from the majority of SDS pathogens from the USA ( Fusarium virguliforme ) and conformed to Fusarium tucumaniae .     

Morphological and molecular characterization of Colletotrichum spp. from citrus orchards affected by postbloom fruit drop in Brazil

Brazilian isolates of Colletotrichum spp. from citrus orchards affected by postbloom fruit drop were examined for colony colour, mycelial growth, benomyl-resistance, pathogenicity, and genetic variability by random amplified polymorphic DNA (RAPD) analysis. All isolates were obtained from flowers and persistent calyxes from different citrus hosts from Sao Paulo, Brazil. DNA polymorphisms detected after amplification with random 10-mer primers were used to classify the isolates into two groups. Group I isolates grew rapidly on potato-dextrose agar (PDA) and were sensitive to benomyl, and group II isolates grew slowly on PDA and were benomyl-resistant. Colletotrichum acutatum was analyzed by RAPD and had high genetic similarity with group II isolates of Colletotrichum from citrus. Probably, the group I is C. gloeosporioides and group II is C. acutatum.     

Comparative Cytopathology and Immunocytochemistry of Japanese, Australian and Brazilian Isolates of Orchid fleck virus

Cytopathic effects in orchid leaf tissues infected with Australian, Japanese and Brazilian isolates of Orchid fleck virus (OFV) were indistinguishable and like those previously described in the literature. Cells had an electron-lucent viroplasm with unenveloped rod-shaped virions in the nucleus and cytoplasm, often associated with the inner membrane of the nuclear envelope and the endoplasmic reticulum. Antiserum raised against a Japanese isolate of OFV reacted with Brazilian and Australian isolates in ELISA, and when used for immuno-gold labelling, also reacted in situ with the rod-shaped virions and the intranuclear viroplasm of all three isolates. These results suggest that the viroplasm is where structural proteins accumulate and virions are formed. Received 13 December 2000/ Accepted in revised form 13 April 2001     

Development,characterization and application of genomic SSR markers for the oat stem rust pathogen Puccinia graminis f. sp. avenae

Oat stem rust, caused by Puccinia graminis f. sp. avenae (Pga), is one of the most severe diseases of oats worldwide. Population studies are scarce for this pathogen, mainly due to the lack of polymorphic molecular markers suitable for genetic analysis. In this study, an Australian Pga isolate was sequenced, the abundance of simple sequence repeats (SSRs) was determined and PCR‐based polymorphic markers suitable for genetic diversity analysis were developed. The amplification of 194 primer pairs was initially assessed using a set of 12 isolates of different cereal rust species and their formae speciales. A high frequency of cross‐species amplification was observed for most markers; however, 36 SSRs were diagnostic for P. graminis only. A subset of 19 genome‐derived SSRs were deemed useful for genetic diversity analysis of Pga and were assessed on 66 Pga isolates from Australia, Brazil and Sweden. Brazilian and Australian isolates were characterized by one and two predominant clonal lineages, respectively. In contrast, the Swedish isolates, previously shown to undergo sexual recombination, were highly diverse (nine distinct genotypes out of 10 isolates) and divided into two subpopulations. The genome‐derived SSR markers developed in this study were well suited to the population studies undertaken, and have diagnostic capabilities that should aid in the identification of unknown rust pathogen species.     

Genetic diversity and aggressiveness of Erwinia psidii on Eucalyptus spp. in Brazil

The genetic variability and aggressiveness of Brazilian Erwinia psidii isolates from Eucalyptus spp. was studied and compared with reference isolates from guava (Psidium guajava). Repetitive element sequence (rep)-based PCR markers of 101 isolates from Eucalyptus spp. and five from guava showed that the populations of E. psidii displayed a relatively low genetic variability. No correlation of genetic clustering based on rep-PCR analysis with geographic origin or host of origin was observed, indicating that genome rearrangements associated with adaptation to a particular host were not detected by these molecular markers. A higher genotypic richness was detected in the Mato Grosso do Sul population, probably reflecting a pathogen dissemination associated with the recent expansion in eucalypt plantations. Wilcoxon and ANOVA tests of disease severity data indicated differences in aggressiveness among isolates and an isolate × clone interaction. The area under the disease progress curve (AUDPC) and disease severity for some isolates were significantly different between two susceptible clones tested. Notably, isolate LPF681 from guava was not able to cause disease on a susceptible Eucalyptus urophylla clone, suggesting that some co-evolution between pathogen and host has taken place. The variability in aggressiveness and virulence among isolates of E. psidii observed in this study will be important for the establishment of appropriate screening approaches to select for disease resistance.     

A new Fusarium lineage within the Gibberella fujikuroi species complex is the main causal agent of mango malformation disease in Brazil

Mango malformation is a serious disease in tropical and subtropical areas of the world and has been attributed to various Fusarium spp., including F. mangiferae , F. proliferatum , F. sacchari , F. sterilihyphosum and F. subglutinans . Isolates of Fusarium associated with mango malformation from Brazil, Egypt, India, South Africa and the United States were evaluated through amplified fragment length polymorphisms (AFLPs) and partial DNA sequences of the genes encoding β-tubulin ( tub2 ) and translation elongation factor 1-α ( tef1 ). These techniques were used to delimit species and to estimate the genetic and phylogenetic relatedness of the isolates. In the AFLP analysis, most of the Brazilian isolates formed a unique cluster. Additionally, one small cluster was formed by isolates of F. sterilihyphosum from Brazil and South Africa, and another by isolates of F. mangiferae from Egypt, India, South Africa and the United States. In the phylogenetic analysis, most of the Brazilian isolates represented a new phylogenetic lineage in the Gibberella fujikuroi species complex, where they formed a sister clade to F. sterilihyphosum. Representatives of both clades were pathogenic to mango (cv. Tommy Atkins) and Koch's postulates were completed for isolates belonging to the new lineage and to F. sterilihyphosum . Thus, most of the mango malformation disease in Brazil is due to a distinct phylogenetic lineage of Fusarium , and to a lesser extent by F. sterilihyphosum. The new phylogenetic lineage identified in this study, together with F. mangiferae and F. sterilihyphosum , are the only known taxa of Fusarium proven to be capable of causing mango malformation.     

Growth and pathogenicity of isolates of the fungus Metarhizium anisopliae against the parasitic mite, Psoroptes ovis: effects of temperature and formulation

Psoroptes mites (Acari: Psoroptidae) are important ectoparasites of mammals, and are of particular economic significance as the agents of mange in sheep. To be effective against mites, putative fungal biocontrol agents must be able to operate at the relatively high temperatures and humidities found at the sheep skin surface. To consider this, the growth rates of different isolates of the entomopathogenic fungus Metarhizium anisopliae (Metschnikoff) Sorokin (Deuteromycotina: Hyphomycetes) were compared and the pathogenicity of these isolates against Psoroptes derived from rabbits (Psoroptes ovis Hering, syn P cuniculi) were evaluated at temperatures between 28 degrees C and 40 degrees C, and when formulated in either Tween 80 or silicone oil. For this study four multi-conidia, arthropod-derived, isolates of M anisopliae were used: from the USA, France, Denmark and Brazil. One single-conidia culture derived from the US isolate was also included in the investigation. Fungal growth was higher at the lower temperatures and none of the isolates grew at 40 degrees C. The growth of the US and single-conidia isolate declined markedly with temperature. In contrast, the Danish, French and Brazilian isolates grew almost as well at 32 degrees C and 35 degrees C as at 28 degrees C and 30 degrees C. The French and Brazilian isolates showed some growth at 37.5 degrees C but the Danish and US isolates did not. The number of fatal infections which resulted from exposure of mites to the fungal isolates was also strongly influenced by temperature. At 30 degrees C all isolates gave between 70 and 90% infection. The number of infections declined with increasing temperature and no infections were seen at 40 degrees C. However, the French and Danish isolates of M anisopliae gave higher numbers of infections than the other isolates at elevated temperatures. When formulated in silicone oil, significantly higher levels of infection were obtained than when formulated in Tween 80, even at the relatively high temperature of 37.5 degrees C. It is suggested that high-temperature adapted isolates of M anisopliae formulated in silicone oil offer good candidates as control agents under the conditions found at the sheep skin surface.     

Identification and pathogenicity of Neophysopella species associated with Asian grapevine leaf rust in Brazil

Asian grapevine leaf rust (AGLR) causes severe crop losses in Brazilian viticulture, mainly in latitudes <25°S. The purpose of this study was to identify the pathogen(s) involved with AGLR in Brazil, based on phylogenetic and morphological analysis and pathogenicity tests. In total, 56 monouredinial isolates from six Brazilian states were identified using the internal transcribed spacer 2 and the large subunit rRNA gene D1/D2 regions. All 50 isolates from the south-central region were classified as Neophysopella tropicalis, and the other six isolates from the north-east region as Neophysopella meliosmae-myrianthae. This result provides evidence that two pathogen introductions from different sources may have occurred in the country. For both species, paraphyses were cylindrical, incurved, aseptate, and hyaline, while urediniospores were short-pedicellate, obovoid or obovoid-ellipsoid, with the wall colourless or pale yellowish, evenly echinulate. Representative isolates from both species caused typical AGLR symptoms on Vitis vinifera 'Merlot' and V. labrusca 'Niagara Rosada'. Overall, regardless of the Neophysopella species, isolates caused similar leaf disease severities. Higher disease severity was observed in Niagara Rosada (average of 40.3% of diseased leaf area) compared to Merlot (20.5%). This study reports, for the first time, the characterization of Neophysopella species associated with AGLR in Brazil.     

Pectobacterium spp. associated with bacterial stem rot syndrome of potato in Canada

Pectobacterium atrosepticum, P. carotovorum subsp. brasiliensis, P. carotovorum subsp. carotovorum, and P. wasabiae were detected in potato stems with blackleg symptoms using species- and subspecies-specific polymerase chain reaction (PCR). The tests included a new assay for P. wasabiae based on the phytase gene sequence. Identification of isolates from diseased stems by biochemical or physiological characterization, PCR, and multi-locus sequence typing (MLST) largely confirmed the PCR detection of Pectobacterium spp. in stem samples. P. atrosepticum was most commonly present but was the sole Pectobacterium sp. detected in only 52% of the diseased stems. P. wasabiae was most frequently present in combination with P. atrosepticum and was the sole Pectobacterium sp. detected in 13% of diseased stems. Pathogenicity of P. wasabiae on potato and its capacity to cause blackleg disease were demonstrated by stem inoculation and its isolation as the sole Pectobacterium sp. from field-grown diseased plants produced from inoculated seed tubers. Incidence of P. carotovorum subsp. brasiliensis was low in diseased stems, and the ability of Canadian strains to cause blackleg in plants grown from inoculated tubers was not confirmed. Canadian isolates of P. carotovorum subsp. brasiliensis differed from Brazilian isolates in diagnostic biochemical tests but conformed to the subspecies in PCR specificity and typing by MLST.     

Clarification of the Etiology of Glomerella Leaf Spot and Bitter Rot of Apple Caused by Colletotrichum spp. Based on Morphology and Genetic, Molecular, and Pathogenicity Tests

ABSTRACT Morphological characteristics and vegetative compatibility groups (VCGs) of 486 isolates of Glomerella cingulata, Colletotrichum gloeosporioides, and C. acutatum collected from apple leaves with Glomerella leaf spot (GLS) symptoms and fruit with bitter rot symptoms in the United States and Brazil were studied. From this collection, 155 isolates of G. cingulata (93 from fruit, 61 from leaves, and 1 from buds), 42 isolates of C. gloeosporioides from fruit, and 14 isolates of C. acutatum (10 from fruit and 4 from leaves) were studied using mitochondrial (mt)DNA restriction fragment length polymorphism (RFLP) haplotypes. A subset of 24 isolates was studied by examining the sequence of a 200-bp intron of the glyceraldehyde 3-phosphate dehydrogenase (GDPH) nuclear gene. In addition, 98 isolates were tested for pathogenicity on leaves of cvs. Gala and Golden Delicious in the greenhouse, and 24 isolates were tested for pathogenicity on fruit of cv. Gala in growth chambers. In total, 238 and 225 isolates of G. cingulata were separated into four distinct morphological types and six VCGs, respectively. Five morphological types and six VCGs were identified among 74 and 36 isolates of C. gloeosporioides, respectively. Three morphological types and four VCGs were identified among 74 and 23 isolates of C. acutatum, respectively. Seven different mtDNA RFLP haplotypes were observed within isolates of G. cingulata, two within isolates of C. gloeosporioides, and two within isolates of C. acutatum. Phylogenetic trees, inferred based on maximum likelihood and maximum parsimony methods using the intron sequence, produced similar topologies. Each species was separated into distinct groups. All isolates tested were pathogenic on fruit, though only isolates with specific VCGs and haplotypes were pathogenic to leaves. Vegetative compatibility was a better tool than molecular characters for distinguishing isolates of G. cingulata pathogenic on both leaves and fruit from the ones pathogenic only on fruit. Isolates of G. cingulata capable of causing both GLS and bitter rot were included in haplotypes and groups based on the sequence analysis of the 200-bp intron that also included isolates capable of causing bitter rot only. Additionally, isolates of G. cingulata from the United States and Brazil which cause GLS were included in different haplotypes and sequence analysis groups. Therefore, one hypothesis is that isolates of G. cingulata from the United States capable of causing both GLS on foliage and bitter rot on fruit may have arisen independently of Brazilian isolates of G. cingulata capable of causing both GLS and bitter rot, and the two groups of isolates may represent distinct populations.     

Pathogenic and molecular comparison of Puccinia kuehnii isolates and reactions of sugarcane varieties to orange rust

Sugarcane orange rust, a disease caused by Puccinia kuehnii, was first reported in Brazil in 2009. There are no studies comparing the Brazilian P. kuehnii collections and the reaction of important sugarcane varieties under controlled conditions. This work compared the reaction of seven sugarcane varieties inoculated with six different P. kuehnii isolates from Brazilian sugarcane areas and verified the pathogenic and genetic variability of these isolates. The incubation (I) and latency (L) disease periods, disease severity (SEV), total number of lesions (TNL), total number of sporulating lesions (TNSL), and percentage of sporulating lesions (%SL) were evaluated. Furthermore, ITS1 and IGS ribosomal sequences of all P. kuehnii isolates used in this study were compared with pathogen sequences from 13 different countries. The disease incubation ranged from 7 to 10 days and the latency ranged from 10 to 21 days. SEV and TNL showed large variations and few significant differences between the reaction of the varieties to P. kuehnii, in contrast with the variables TNSL and %SL. The P. kuehnii isolates did not compose different virulent races, but the isolate from one site (Araras) was a more aggressive race. The ITS1 and IGS ribosomal sequences of six P. kuehnii isolates were identical with each other and to most P. kuehnii American sequences deposited at GenBank. The studied sequences of P. kuehnii isolates differed from the sequences from Asia, Tahiti and Oceania.     

Genetic diversity in the mango malformation pathogen and development of a PCR assay

Malformation is a destructive disease of mango, Mangifera indica . Its causal agent possesses the morphological features of Fusarium subglutinans , a species whose taxonomy and nomenclature has recently been in a state of flux. Genetic diversity was examined among 74 F. subglutinans -like isolates from malformed mango in Brazil, Egypt, Florida (USA), India, Israel and South Africa. With nitrate-nonutilizing ( nit ) auxotrophic mutants, seven vegetative compatibility groups (VCGs) were identified. Three of the VCGs were found in a single country, and VCG diversity was greatest in Egypt and the USA where, respectively, four and three different VCGs were found. RAPD profiles generated with arbitrary decamer primers were variable among isolates in different VCGs, but were generally uniform for isolates within a VCG. In PCR assays, a 20-mer primer pair that was developed previously to identify F. subglutinans from maize (mating population [MP]-E of the Gibberella fujikuroi complex) also amplified a specific 448 bp fragment for isolates of F. sacchari from sugarcane (MP-B) and what was probably F. circinatum (pine, MP-H). With the exception of three isolates from Brazil, it did not amplify the fragment from F. subglutinans -like isolates from mango. A second pair of 20-mer primers was developed from a unique fragment in the RAPD assays. It amplified a specific 608 bp fragment for 51 of 54 isolates from mango (all but the three Brazilian isolates). It also amplified a smaller, 550 bp fragment from isolates of F. nygamai (MP-G), but did not amplify DNA of isolates of any other taxon of Fusarium that was tested.     

Molecular and biological characterization of Cowpea mild mottle virus isolates infecting soybean in Brazil and evidence of recombination

The biological and molecular characterization of six isolates of a new Cowpea mild mottle virus strain (CPMMV; Carlavirus, Betaflexiviridae) are reported. Soybean plants with mosaic and stem necrosis were collected in Bahia, Goiás, Mato Grosso and Minas Gerais states, Brazil. Complete genomes of the CPMMV isolates are 8180–8198 nucleotides (nt) long, excluding the 3′‐polyadenylated tail, and have 67–68% nt sequence identity with a Ghana isolate of CPMMV, the only CPMMV isolate for which the genome has previously been sequenced. The replicase has only 60–61% nt sequence identity with the Ghana CPMMV isolate, and the coat protein (CP) is highly conserved (79% nt sequence identity and 95–96% amino acid sequence identity). The high CP identity and the phylogenetic analyses supported the classification of the Brazilian isolates as CPMMV. Biological and molecular differences with the Ghana CPMMV isolate were found and indicated that the six isolates represent a distinct CPMMV strain denominated as CPMMV‐BR. Furthermore, it is shown that recombination occurred mainly in the polymerase gene, and may occur less frequently in other regions of the CPMMV genome.     

Brazilian Potato virus Y isolates identified as members of a new clade facilitate the reconstruction of evolutionary traits within this species

Potato virus Y (PVY) is a plant virus distributed worldwide that causes damage to several species of the Solanaceae family. It was established long ago that groups of PVY isolates defined by phylogenetic analyses correlate strongly with those demarcated by differential biological properties. Consequently, life‐history traits of this viral species can be inferred by phylogenetic analysis. In this study, characteristics of PVY isolates sampled in different tobacco fields in Brazil were analysed and most of the tested Brazilian PVY isolates were assigned to the recently described unconventional serogroup Y^U. The analysis of molecular diversity of the coat protein (CP) cistron from some Y^U isolates made it possible (i) to identify specific amino acid residues in the N‐terminal of the CP protein and (ii) to assign some Y^U isolates to a new PVY clade. The symptoms caused by isolates belonging to this new PVY ‘Brazilian’ clade and their ability to infect selected susceptible hosts led to the conclusion that neither veinal necrosis symptoms expressed on infected tobacco plants nor adaptation to potato or pepper hosts are ancestral characteristics of PVY. These observations suggest that PVY has gained a remarkable new biological property and broadened its host range over time.     

Assessing resistance to Crinipellis perniciosa using cocoa callus

Callus cultures from cocoa clones reported to have different susceptibilities to Brazilian isolates of Crinipellis perniciosa , causal fungus of witches' broom disease, including Catongo (susceptible). Scavina-6, CAB 64 and CAB 67 (resistant) were inoculated with basidiospores of C. perniciosa and the subsequent development of mycelia was assessed. Generally, on Catongo callus, mycelium similar to that found in green brooms (parasitic type), developed abundantly but on callus from Scavina-6 and the two CAB clones, mycelial growth was relatively poor and tended to be similar to that in dry brooms and on agar media (saprotrophic type). There was often considerable variation in fungal development on individual callus cultures from the same clone, but there was an overall consistency between successive experiments in ranking the callus material in terms of fungal development. However, growth of isolates from Colombia and Trinidad was similar on callus from Scavina-6 which in the field is known to reac differentially to these two isolates. Experiments with isolates from Colombia indicated that inoculum from basidiocarps produced on brooms which were kept for long periods in cabinets to induce fruiting had a decreased ability to colonize callus.