Two new species of Calonectria (Hypocreales, Nectriaceae) causing Eucalyptus leaf blight in Brazil

Abstract

In recent decades, commercial Eucalyptus plantations have expanded toward the warm and humid regions of northern and northeastern Brazil, where Calonectria leaf blight (CLB) has become the primary fungal leaf disease of this crop. CLB can be caused by different Calonectria species, and previous studies have indicated that Calonectria might have high species diversity in Brazil. During a disease survey conducted in three commercial plantations of Eucalyptus in northeastern Brazil, diseased leaves from Eucalyptus trees with typical symptoms of CLB were collected, and Calonectria fungi were isolated. Based on phylogenetic analyses of six gene regions (act, cmdA, his3, rpb2, tef1, and tub2) and morphological characteristics, two new species of Calonectria were identified. Five isolates were named as C.paragominensis sp. nov. and four were named as C.imperata sp. nov. The pathogenicity to Eucalyptus of both species was confirmed by fulfilling the Koch's postulates.

Keywords: Cylindrocladium; GCPSR; phylogenetic network analysis; phylogeny.

Figure 1.

Phylogenetic tree based on maximum likelihood analysis of concatenated act, cmdA, his3, rpb2, tef1 and tub2 gene regions. Bootstrap support values ≥ 80% for maximum parsimony (MP), Ultrafast bootstrap support values ≥ 95% for maximum likelihood (ML), and posterior probability (PP) values ≥ 0.95 from BI analyses are presented at the nodes (MP/ML/PP). Bootstrap values below 80% (MP), 95% (ML) and posterior probabilities below 0.80 are marked with “-”. Ex-type isolates are indicated by “▲”, isolates highlighted in bold were sequenced in this study, and novel species are in blue and orange. C.gracilipes was used as outgroup. The scale bar indicates the number of nucleotide substitutions per site.

Figure 2.

Results of the pairwise homoplasy index (PHI) test for C.paragominensis and C.imperata. Phylogenetic networks constructed using the LogDet transformation and the NeighborNet method and displayed with the EqualAngle algorithm. Bootstrap support values > 80% are shown. Φw < 0.05 indicate significant recombination. New species described in this study are highlighted in bold, with blue (A) and orange (B) lines.

Figure 3.

CalonectriaparagominensisA, B macroconidiophore C lateral stipe extensions D, E conidiogenous apparatus with conidiophore branches and doliiform to reniform phialides F, G globose to sphaeropedunculate vesicles H, I one, two, and three-septate macroconidia. Scale bars: 20 μm.

Figure 4.

CalonectriaimperataA–C macroconidiophore D–G ellipsoidal to narrowly obpyriform vesicles H–J conidiogenous apparatus with conidiophore branches and doliiform to reniform phialides K, L macroconidia. Scale bars: 20 μm.

Figure 5.

Pathogenicity tests on leaves of Eucalyptus genotypes A, B surface and reverse of C.paragominensis on MEA plates after 14 days grown at 25 °C C, D surface and reverse of C.imperata on MEA plates after 14 days grown at 25 °C E, I lesions on leaves of E.grandis × E.brassiana induced by C.paragominensis 72 h after inoculation F, J lesions on leaves of E.urophylla induced by C.imperata 72 h after inoculation G, H, K no disease symptoms on leaves inoculated with sterile water (negative controls). Scale bars: 5 cm (E–K).