A new species of Calonectria causing leaf blight and cutting rot of three forest tree species in Brazil

RESEARCH ARTICLE ARTIGO

A new species of Calonectria causing leaf blight and cutting rot of three forest tree species in Brazil

Rafael F. Alfenas^I,III; Olinto L. Pereira^I; Vanessa L. Jorge^I; Pedro W. Crous^II; Acelino C. Alfenas^I

^IDepartamento de Fitopatologia, Universidade Federal de Viçosa, 36570-000, Viçosa, MG, Brazil

^IICBS-KNAW Fungal Biodiversity Centre, Uppsalalaan 8, 3584 CT, Utrecht, The Netherlands

^IIIClonar Resistência a Doenças Florestais, CENTEV, 36570-000, Viçosa, MG, Brazil

^{Author for correspondence}

ABSTRACT

Several species of Calonectria cause diseases on a wide range of forest tree species that are propagated either via seedlings or rooted cuttings. In nurseries these fungi cause damping-off, cutting and root rots, stem lesions, and leaf blights. Recently a Calonectria sp. was isolated from rooted cuttings of Anadenanthera peregrina (Fabaceae), Piptadenia gonoacantha (Fabaceae), and Azadirachta indica (Meliaceae) exhibiting leaf blight and cutting rot in a forest nursery at the Universidade Federal de Viçosa, Brazil. Morphological comparisons and DNA sequences of three loci containing partial gene sequences of β-tubulin (TUB2), calmodulin (CAL), and elongation factor (TEF-1α) indicated that these isolates represent an unnamed species of Calonectria, described here as C. hodgesii sp. nov. Sprayinoculated plants of all three hosts with a suspension at 1x10⁴ conidia mL^-1 induced leaf lesions, cutting rot, and intense defoliation as observed under natural conditions. Calonectria hodgesii was re-isolated from infected tissue, which fulfilled Koch's postulates and confirmed its status as a pathogen with a wide host range.

Key words: forest pathology, Hypocreales, pathogenicity, phylogeny, taxonomy, tropical fungi.

INTRODUCTION

In recent years there has been an increasing demand for planting forest tree species in Brazil, in part due to the government's initiatives to restore degraded areas and mitigate global warming. Anadenanthera peregrina (L.) Speg. (Angico Vermelho) and Piptadenia gonoacantha (Mart.) J.F. Macbr. (Pau-Jacaré) are among the most commonly used native species (Carvalho, 1994; Araújo et al., 2006). There has also been an increase in plantations of Azadirachta indica A. Juss. (Neem), which is native to India. The increased planting of A. indica is largely due to its multiple applications in the pharmaceutical industry, use in agriculture as a natural insecticide, and more recently for biodiesel production (Mossini & Kemmelmeier, 2005). Nevertheless, propagation of these species either via cuttings or seedlings is generally still done in nurseries with low technology, where appropriate management practices for disease control are not employed (Mafia et al., 2007).

Numerous pathogenic fungal species, especially species of Calonectria, have been described from forest nurseries and have been reported as pathogens of a wide range of plant hosts cultivated via seedlings or vegetative propagation (Crous, 2002). Among the major nursery diseases, damping-off, cutting rot, stem girdling and leaf blight caused by Calonectriaspp. are commonly encountered (Hodges & May, 1972; Lombard et al., 2010a). In recent years several new species of Calonectria have been newly described from hosts in forestry nurseries using a polyphasic approach incorporating morphological and molecular data (Lombard et al., 2010c; Alfenas et al., 2013).

Because of the importance of the genus Calonectria as plant pathogen in tropical and subtropical climates, we have for the past two years been collecting plant and soil samples from different hosts throughout Brazil to facilitate population biology studies of Calonectria spp.

During one these collecting in the Forest Nursery at the Universidade Federal de Viçosa, Brazil, in May 2011, we found rooted cuttings of A. peregrina, A. indica and P. gonoacantha exhibiting necrotic leaf blight, defoliation and cutting rot symptoms with brown and necrotic tissues at the stem base, covered by profuse white sporulation typical of Calonectria infection (Figure 1). The same symptoms were observed on all three hosts. The primary aim of this study was to identify the causal agent of this disease through a combination of morphological and molecular characterization, and pathogenicity tests.

MATERIAL AND METHODS

Isolates

Single conidial isolates of a Calonectria sp. were obtained from leaves and cuttings of infected plants of A. peregrina, A. indica and P. gonoacantha.

To obtain single conidial cultures, pathogen structures observed under a stereoscopic microscope (45 x) were deposited on Petri dishes containing water agar medium [WA, 1.5% (w/v) agar]. Subsequently 2 mL of sterile distilled water were added to each WA dish, and shaken manually. Excess water was removed by inverting the Petri dish, and under a stereomicroscope (45 x) a single conidium was transferred to a Petri dish containing malt extract agar (MEA). Plates were maintained at 26ºC for 5 days to promote fungal growth. One representative isolate from each host was selected for further studies. To maintain viable isolates strains were stored in a glycerol solution (10%) at -80ºC.

DNA extraction and amplification

Mycelia of the respective isolates were scraped from colonized MEA plates, and placed separately in 2 mL microtubes for genomic DNA extraction using the Wizard Genomic DNA Purification (Promega) kit. For PCR, the DreamTaq Master Mix (Fermentas) was used, following the manufacturer's protocol.

Three loci, including fragments of the β-tubulin (TUB2), calmodulin (CAL), and elongation factor (TEF1α) gene regions were amplified using the primers T1 (O'Donnell & Cigelnik, 1997) and CYLTUB1R (Crous et al., 2004) for TUB2, CAL-228F and CAL-737R (Carbone & Kohn, 1999) for CAL, and EF1-728F (O'Donnell et al., 1998) and EF-2 (Carbone & Kohn, 1999) for TEF-1α. Amplification was performed with an initial denaturing at 96ºC for 5 min followed by 35 cycles of denaturation at 96ºC for 30 s, annealing at 52ºC for 30 s, extension at 72ºC for 1 min and a final 4 min extension at 72ºC. The PCR product was visualized on a 2% agarose gel to determine fragment size and purity. PCR products were prepared for sequencing with the ExoSAP-IT kit (Affymetrix) according to the manufacturer's protocol.

Sequencing and phylogenetic analyses

Sequencing was performed at the Laboratory of Genomics of the Instituto de Biotecnologia Aplicada à Agropecuária (BIOAGRO) at the Universidade Federal de Viçosa, Brazil. Sequence quality was checked via Sequence Scanner Softwarev.1.0(AppliedBiosystems),andeditedusing the software package Seqman from DNAStar Inc. Consensus regions of edited sequences were compared in the NCBI GenBank nucleotide database (www.ncbi.nlm.nih.gov) using the nucleotide collection (nr/nt) optimised for highly similar sequences (megablast). Calonectria sequences generated in this study were deposited in GenBank (Table 1). All sequences were assembled in MAFFT v. 6 (Katoh & Toh, 2010), using the FFT-NS-i (Slow; iterative refinement method) alignment strategy with the 200PAM/K=2 scoring matrix and a gap opening penalty of 1.53 with an offset value of 0.0. Aligned sequences were then manually corrected when necessary using MEGA v. 5 (Tamura et al., 2011).

PAUP (Phylogenetic Analysis Using Parsimony, v. 4.0b10; Swofford, 2002) was used to analyse the DNA sequence datasets. A partition homogeneity test (Farris et al., 1994) was applied to determine whether the data sets were consistent and combinable. Phylogenetic relationships were estimated by heuristic searches based on 1,000 random addition sequences and tree bisection-reconnection, with the branch swapping option set on 'best trees' only. All characters were weighed equally and alignment gaps were treated as missing data. Measures calculated for parsimony included tree length (TL), consistency index (CI), retention index (RI) and rescaled consistence index (RC). Bootstrap analyses (Hillis & Bull, 1993) were based on 1,000 replications.

Analysis of Bayesian Inference (BI) was performed with MrBayes v. 3.1.1 (Ronquist & Heulsenbeck, 2003) using the algorithm of Markov Chain Monte Carlo (MCMC) with two sets of four chains (one cold and three heated) with 10 million random generations. The sample frequency was set to 1,000 and the first 25% of trees were removed as burnin. Likelihood values were calculated and the best model of nucleotide substitution for each gene was selected according to the Akaike Information Criterion (AIC) using MrModeltest v. 2.3 (Posada & Buckley, 2004).

The convergence of the log likelihood was analysed using TRACER v. 1.5 (Rambaut & Drummond, 2009) and no indication of lack of convergence was detected. Calonectria chinensis (Crous) L. Lombard, M. J. Wingf. & Crous was used as outgroup in the analysis.

Morphological characterization

For morphological characterization single conidial cultures were grown in synthetic nutrient-poor agar (SNA) at 26ºC for 7 days. Fungal structures were mounted in clear lactic acid for morphological examination, and 30 measurements of each structure determined at 1,000 × magnification using a Zeiss Axioscope-2 microscope with differential interference contrast (DIC) illumination. The 95% confidence levels were determined and extremes of conidial measurements are given in parentheses. For other structures, only extremes are presented.

Pathogenicity test

Single conidial cultures were transferred aseptically to Petri dishes (90 mm diam) containing Malt Extract Agar (MEA), and subsequently incubated at 26ºC for 10 days for pathogenicity studies. Healthy rooted cuttings (five per species) of A. peregrina, A. indica and P. gonoacantha were spray-inoculated with a conidial suspension of 1×10⁴ conidia mL^-1 of each isolate, as described by Graça et al. (2009). Five plants of each host species were treated with distilled water to serve as controls. The inoculated plants were maintained in a greenhouse under controlled conditions (25ºC±3ºC) and the development of symptoms was monitored daily for 10 days, after which time the fungus was re-isolated from the lesion margins.

RESULTS

Phylogenetic analysis

Amplicons of approximately 500 bases each for TUB2, TEF-1α, and CAL were generated. The 70% reciprocal bootstrap trees showed no conflict in tree topologies for the three gene regions separately, and therefore they were combined in a dataset consisting of 1,531 characters including gaps. Of these 1,100 were constant and parsimony uninformative and 431 were parsimony informative. Analysis of the 431 parsimony informative characters yielded three equally most parsimonious trees (TL = 1033 CI = 0.691, RI = 0.871, RC = 0.602). Evolution models HKY + G for TUB2, TEF, and CAL were selected and incorporated into the Bayesian analysis. The consensus tree obtained for the Bayesian analyses confirmed the tree topology obtained with parsimony. The isolates of Calonectria from A. peregrina, A. indica and P. gonoacantha formed a distinct, well-supported clade (PP=1,00) (Figure 2).

Taxonomy

Based on the DNA sequence data and morphological features, we conclude that the Calonectria isolates from A. peregrina, A. indica and P. gonoacantha represent a novel species, which is described below:

Calonectria hodgesii R.F. Alfenas, O.L. Pereira, Crous & Alfenas, sp. nov. MycoBank MB 803943 (Figure 3);

Etymology: Named after Dr. Charles S. Hodges, in honor of his contribution to forest pathology in the tropics;

Hosts: Anadenanthera peregrina, Azadirachta indica and Piptadenia gonoacantha;

Specimen examined: Brazil, Minas Gerais state, Viçosa, on Anadenanthera peregrina, May 2011, Rafael F. Alfenas (Holotype CBS H-21147, Culture ex-type CBS 133609).

Conidiophores containing a stipe bearing penicillate suites of fertile branches, stipe extensions, and terminal vesicles; stipe septate, hyaline, smooth, 40-82 × 5-7 µm; stipe extensions septate, straight to flexuous 136-196 µm long, 2-4 µm wide at the apical septum, terminating in pyriform to ellipsoidal or ovoid to sphaeropedunculate vesicles, 6-11 µm diam. Conidiogenous apparatus 4565 µm long, 61-72 µm wide at apex; primary branches aseptate, 18-27 × 4-5 µm; secondary branches aseptate, 1224 × 3-4 µm, and tertiary branches aseptate, 9-18 × 3-5 µm, each terminal branch producing 2-6 phialides; phialides doliiform to reniform, hyaline, 5-10 × 2-4 µm; apex with minute periclinal thickening and inconspicuous collarette. Macroconidia cylindrical, rounded at both ends, straight, (44)49-51(-55) × 3-5 µm (av. = 50 × 4.5 µm), 1-septate, lacking a visible abscission scar, held in parallel cylindrical clusters by colourless slime. Mega-and microconidia not seen.

Notes: Calonectria hodgesii is phylogenetically closely related to C. brasiliensis and C. sulawesiensis, but C. hodgesii can easily be distinguished from these species based on the size of its macroconidia, vesicle shape, number of macroconidiophore branches, and DNA sequence data.

Culture characteristics: Colonies sienna to umber on the surface and sepia to brown-vinaceous in reverse, with moderate aerial mycelium; chlamydospores moderate to extensive, occurring throughout the colony, forming microsclerotia; extensive sporulation on the aerial mycelium; moderate to rapid growth (50-65 mm) diam after 7 days at 25ºC on MEA.

Pathogenicity test

After 10 days spray-inoculated plants showed necrotic leaf blight, cutting rot with brown and necrotic tissues of the basal stem, and intense defoliation as observed under natural conditions in the nursery. Profuse sporulation was also observed on necrotic lesions of inoculated organs of all three host species.

DISCUSSION

In the present study we describe a new species of Calonectria associated with necrotic leaf blight and cutting rot of A. peregrina, A. indica and P. gonoacantha in Brazil based on morphological and molecular data. Calonectria hodgesii formed a distinct and well-supported phylogenetic clade, closely related to C. brasiliensis and C. sulawesiensis, which belong to the C. morganii species complex. This complex, characterised by having uniseptate macroconidia and vesicles varying from pyriform to obpyriform or ovoid to ellipsoidal, includes C. cerciana L. Lombard, M.J. Wingf. & Crous, C. insularis C.L. Schoch & Crous, C. morganii, C. sulawesiensis, C. hawksworthii (Peerally) L. Lombard, M.J. Wingf. & Crous, C. leucothöes (El-Gholl, Leahy & T.S. Schub.) L. Lombard, M.J. Wingf. & Crous, C. variabilis Crous, B.J.H. Janse, D. Victor, G.F. Marias & Alfenas and C. brasiliensis (Peerally) L. Lombard, M.J. Wingf. & Crous (Schoch et al., 2001; Lombard et al., 2010c).

Calonectria hodgesii is characterised by having macroconidia larger than those of C. brasiliensis, C. morganii and C. sulawesiensis, but smaller than C. variabilis (Table 2). Superficially C. hodgesii resembles C. variabilis in having vesicles that vary in shape, and it is quite probable that many isolates previously identified as C. variabilis, were in fact representative of C. hodgesii. The two species can be distinguished, however, in that C. hodgesii has 1-septate conidia, while C. variabilis has (1-)3(-4)-septate conidia. Although the vesicle shape of C. hodgesii is also quite variable, it is mainly obpyriform to ellipsoidal, while those of C. variabilis vary from clavate to ellipsoidal. Interestingly, the new species shares morphological characteristics with phylogenetically distant species, such as Calonectria citri (H.S. Fawc. & Klotz) L. Lombard, M.J. Wingf. & Crous and Calonectria canadiana L. Lombard, M.J. Wingf. & Crous.

Species of the C. morganii complex are well-known pathogens of various hosts worldwide (Crous, 2002), and some, like C. brasiliensis, are known to be highly aggressive to Eucalyptus seedlings (Batista, 1951). Originally, C. brasiliensis was described as a variety of C. morganii Crous, Alfenas & M.J. Wingf. (as Cylindrocladium scoparium var. brasiliensis Batista & Ciferri) based on having macroconidia smaller than those of Calonectria morganii (Batista, 1951; Peerally, 1974). Based on morphological characteristics and total protein banding patterns however, Crous et al. (1993a) reduced C. brasiliensis to synonymy under C. morganii. By employing multigene DNA sequence data, Lombard et al. (2010b) recently showed that the ex-type culture of C. brasiliensis (CBS 230.51) is phylogenetically and morphologically distinct from C. morganii, and therefore reinstated it to species level.

Calonectria sulawesiensis Lombard et al. (2010c), described from Eucalyptus sp. in Indonesia, is another phylogenetically closely related species, but it is morphologically distinct, and presently nothing is yet known regarding its pathogenicity and host range.

In our studies all three selected isolates (CBS133608, CBS133609, and CBS133610) of C. hodgesii tested were pathogenic, and induced leaf blight, defoliation and cutting rot in A. peregrina, A. indica and P. gonoacantha similar to that observed in the nursery under natural conditions.

The occurrence of C. hodgesii sp. nov. causing leaf blight and cutting rot on these hosts represents an alert for nurseries that propagate these forest species either from seedlings or rooted cuttings.

ACKNOWLEDGMENTS

We thank the Departamento de Fitopatologia of Universidade Federal de Viçosa and CBS-KNAW Fungal Biodiversity Centre for financial and technical support to undertake this study. This work was also supported by Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES, Conselho Nacional de Desenvolvimento Científico e Tecnológico - CNPq, and Fundação de Amparo à Pesquisa de Minas Gerais -FAPEMIG. The first author is grateful to Dr. Lorenzo Lombard for advice regarding the morphological characterization of C. hodgesii, to Dr. Charles S. Hodges for reviewing the latest version of this manuscript, and to Drs. J.Z. (Ewald) Groenewald and Danilo Batista Pinho for advice regarding DNA sequence analyses.

Received 18 January 2013

Accepted 13 August 2013

TPP 2013-0005

Section Editor: Silvaldo Felipe da Silveira

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Publication Dates

• Publication in this collection
  17 Dec 2013
• Date of issue
  Dec 2013

History

• Received
  18 Jan 2013
• Accepted
  13 Aug 2013