RESUMEN
Mango anthracnose, caused by Colletotrichum spp., is the most significant disease of mango (Mangifera indica L.) in almost all production areas around the world. In Mexico, mango anthracnose has only been attributed to C. asianum and C. gloeosporioides. The aims of this study were to identify the Colletotrichum species associated with mango anthracnose symptoms in Mexico by phylogenetic inference using the ApMat marker, to determine the distribution of these species, and to test their pathogenicity and virulence on mango fruits. Surveys were carried out from 2010 to 2012 in 59 commercial orchards in the major mango growing states of Mexico, and a total of 118 isolates were obtained from leaves, twigs, and fruits with typical anthracnose symptoms. All isolates were tentatively identified in the C. gloeosporioides species complex based on morphological and cultural characteristics. The Bayesian inference phylogenetic tree generated with Apn2/MAT intergenic spacer sequences of 59 isolates (one per orchard) revealed that C. alienum, C. asianum, C. fructicola, C. siamense, and C. tropicale were associated with symptoms of mango anthracnose. In this study, C. alienum, C. fructicola, C. siamense, and C. tropicale are reported for the first time in association with mango tissues in Mexico. This study represents the first report of C. alienum causing mango anthracnose worldwide. The distribution of Colletotrichum species varied among the mango growing states from Mexico. Chiapas was the only state in which all five species were found. Pathogenicity tests on mango fruit cultivar Manila showed that all Colletotrichum species from this study could induce anthracnose lesions. However, differences in virulence were evident among species. C. siamense and C. asianum were the most virulent, whereas C. alienum and C. fructicola were considered the least virulent species.
Asunto(s)
Colletotrichum , Mangifera , Filogenia , Teorema de Bayes , Colletotrichum/clasificación , Colletotrichum/genética , Colletotrichum/patogenicidad , Colletotrichum/fisiología , ADN de Hongos/genética , Mangifera/microbiología , México , Filipinas , Enfermedades de las Plantas/microbiología , VirulenciaRESUMEN
The State of Michoacán, México cultivates approximately 100,000 ha of avocados (Persea americana M.) (4). During a survey from 2006 to 2007 in cv. Hass avocado groves in Tingambato County, in the State of Michoacán, deep yellow spots and streaks, which sometimes became necrotic or reddish, were observed on the skin of fruits and the pulp of the fruit also showed big yellow spots. Some young shoots developed fine, yellow streaks, and leaves of symptomatic trees sometimes showed irregular, white-to-yellow spots. These symptoms were similar to those recorded for Avocado sunblotch viroid (ASBVd) (3). To determine if ABSVd was associated with these symptoms, total RNA extracted (1) from the skin and pulp of symptomatic and asymptomatic fruits and also from leaves and bark of shoots from five trees collected in a commercial plot in Tingambato County was tested by a one-step reverse transcription (RT)-PCR protocol using one primer pair to amplify specifically the complete ASBVd genome sequence (3). All 30 samples of skin and pulp of fruits, leaves, and cortex of shoots from symptomatic trees yielded two PCR fragments with estimated sizes of 250 and 500 base pairs (bp) corresponding to the putative monomeric and dimeric forms of ASBVd, respectively. The 500-bp RT-PCR fragments obtained from the different samples were purified from an agarose gel and cloned. The 249-bp nucleotide sequence of the ASBVd genomic monomer was determined using the clones from the fruit skin from sample Arb No. 3 (GenBank Accession No. EU888588), pulp from sample Arb No. 5 (GenBank Accession No. EU888590), leaves from samples Arb No. 15 (GenBank Accession No. EU888589) and Arb No. 8 (GenBank Accession Nos. EU888591 and EU888592), and cortex of shoots from sample Arb No. 16 (GenBank Accession Nos. EU888593, EU888594, EU888595, EU888596, and EU888597). BLAST analysis of the ASBVd sequences showed a range of 98 to 100% nucleotide identity to ASBVd sequences (GenBank Accession Nos. AF404064, AF404051, or AF229821). A clone of the Michoacán ASBVd (GenBank Accession No. EU888593) was used to synthesize a Dig-High Prime-UTP-T7 (Roche, Mannheim, Germany) fluorescent riboprobe complementary to the ASBVd plus strand to perform a dot-blot analysis as described previously (2). All ASBVd samples positive by RT-PCR gave a strong signal in the dot-blot analysis. This riboprobe will be used to index the ASBVd in other commercial avocado groves in Michoacán. To our knowledge, this is the first report of ASBVd in Michoacán, México. References: (1) D. J. Mackenzie et al. Plant Dis. 81:222, 1997. (2) J. A. Sánchez-Navarro et al. Plant Pathol. 47:780, 1998. (3) R. J. Schnell et al. Plant Dis. 81:1023, 1997. (4) D. Téliz and A. Mora. El aguacate y su Manejo Integrado. Mundiprensa, Mexico City, 2007.
RESUMEN
A new maize disease appeared in the State of Veracruz, Mexico during 2003-2004. Initial symptoms in the leaves were small, white-yellow, watery spots, which coalesced into dry necrotic stripes that were 0.3 wide and 8 cm long. Reddening sometimes developed on these leaves. Stems developed a rot in the crown. The flag leaf showed a rot and necrosis at the base, rolled inward, and dried out. Necrosis developed at the base of the corn ears and their growth was halted. A bacterium characterized by white colonies was consistently isolated from lesions on casamino acid peptone and glucose (CPG), King's medium B, and nutrient agar media. Ten isolates were chosen for further characterization. Pathogenicity was confirmed in the greenhouse (25 to 30°C) on 45-day-old ASGROW 7573 maize plants by injection of bacterial suspensions (107 CFU/ml) at the base of the stem. Control maize seedlings were injected with phosphate buffer. Symptoms similar to those observed in the field were observed after 3 days on all inoculated plants but were not observed on control plants. Koch's postulates were fulfilled with reisolation of the inoculated strain from the inoculated tissues and confirmation was fulfilled by phenotypic characters and 16S rDNA sequences. The white colonies on CPG were slightly convex, shiny, circular with entire margins, gram negative, lacked arginine dihydrolase, did not produce fluorescent pigment on Pseudomonas F medium, and grew aerobically. The strains were able to utilize l-arabinose, d-mannitol, and cellobiose, but unable to utilize d-maltose and l-rhamnose. Gel hydrolysis was positive but starch hydrolysis was not positive. Colonies grew at 40°C. These characteristics are the same as those described previously for Burkholderia gladioli (3). The identity of these isolates was confirmed by 16S analysis with two universal primers, FD1 and RD1, for Eubacteria (2), which generate a 1,600-bp fragment. Two primers specific for the genus Burhkolderia, RHG-F and RHG-R that generate a 500-bp fragment (1) were also used for amplification. Comparison of sequences using Clustal W and Megaline, DNAstar software showed 100% similarity among strains isolated from the three counties (GenBank Accession Nos. EU161873 to EU161878) and 99% similarity of field isolates with B. gladioli in the GenBank database. To our knowledge, this is the first report of B. gladioli causing leaf stripe and stem rot of maize in Mexico. References: (1) J. J. Lipuma et al. J. Clin. Microbiol. 37:3167, 1999. (2) L. M. Rodrigues et al. Appl. Environ. Microbiol. 69:4249, 2003. 3) N. W. Shaad et al., eds. 3rd ed. Laboratory Guide for Identification of Plant Pathogenic Bacteria. The American Phytopathological Society, St. Paul, MN, 2001.
RESUMEN
The coat protein gene of the papaya ringspot virus was cloned and sequenced in three Mexican isolates (two from Veracruz, and one from Chiapas). The sequences of these viral isolates were compared to those of eleven isolates from other parts of the world. They had higher similarity to isolates from Australia and the United States than to Asian isolates. A region of about one hundred nucleotides neighboring the putative aphid transmission triplet of the coat protein, contained repeats of an EK (glutamic acid-lysine) motif in all the sequences. The bearing of this region on the genetic relationships and geographical distribution of the isolates is analyzed and discussed.