First Report of Colletotrichum nymphaeae Causing Blossom Blight, Peduncle Rot, and Fruit Rot on Pyrus pyrifolia in Brazil

Abstract

Colletotrichum species belonging to the C. acutatum, C. gloeosporioides, and C. boninense complexes were reported in Pyrus spp. to cause lesions on fruits and leaves (Fu et al. 2019). In November 2017, diseased flowers and peduncles were observed in a Japanese pear (Pyrus pyrifolia) orchard cultivar Hosui in Campo Largo and Quatro Barras, Paraná, Brazil. On the surface of the decayed tissue, acervuli and orange conidial masses were found. Pure cultures were obtained following monosporic isolation and grown on potato dextrose agar (PDA) at 25°C with a 12-h photoperiod under fluorescent light for 7 days. The colony color was white to gray on the surface and orange on the bottom of the dish. The conidia were one-celled, hyaline, fusiform, and with a length and width ranging between 9 and 20 μm, and between 3 and 6.5 μm, respectively. These morphological characteristics correspond to Colletotrichum nymphaeae (Pass.) Aa and several other phylogenetically close species (Damm et al. 2012). In order to perform the pathogenicity test, a suspension containing 1 × 104 conidia/ml was prepared from the monosporic isolates (PpCnPR17_02 and PpCnPR17_03) with 1-week-old cultures growing on PDA medium at 25°C with a 12-h photoperiod under fluorescent light. An aliquot of 20 µl of the suspension was deposited on the surface of flower structures, peduncles, and wounded ripe fruits of P. pyrifolia cultivar Hosui. Sterile distilled water drops served as controls. Each isolate treatment was arranged in a completely randomized design with five replications for fruit and peduncles and 10 replications for flowers. The inoculated structures were maintained in moist chambers for 20 days at 25 ± 2°C with a 12-h photoperiod under fluorescent light. Only the inoculated structures showed symptoms. Lesions, after inoculation, were observed in 3 days on flower structures, in 11 days on peduncles, and in 3 days on wounded ripe fruits. The pathogen was reisolated from the lesions. Colony and conidia morphology were identical to those of the original isolates, confirming Koch’s postulates. Fungal isolates were also characterized by sequencing of the internal transcribed spacer (ITS) rDNA using ITS1/IT4 primers, glyceraldehyde-3-phosphate dehydrogenase (GAPDH) using GDF1/GDR1 primers, chitin synthase 1 (CHS-1) using CHS-354R/CHS-79F, and β-tubulin (TUB2) using BT2Fd/Bt-2b primers (Damm et al. 2012). Phylogenetic analysis was performed with the concatenated sequence alignment of four genes (ITS, GAPDH, CHS-1, and TUB2) using MEGA 6.0 software. The nucleotide sequences were deposited at GenBank (ITS, MK659663, MK659799; GAPDH, MK673275, MK673276; CHS-1, MK673273, MK673274; and TUB, MK681922, MK681923). A Bayesian inference phylogenetic tree showed that the isolates PpCnPR17_02 and PpCnPR17_03 from P. pyrifolia clustered in one separate clade with sequences of C. nymphaeae deposited at GenBank (CBS129928 and IMI370491). Isolates identified as C. nymphaeae are considered as part of the C. acutatum species complex (Damm et al. 2012). To our knowledge, this is the first report of C. nymphaeae causing symptoms in flowers, peduncles, and fruits of pear in South America.

Desirrê Petters-Vandresen

Postdoc in Genetics

My research interests include fungal genomics and evolution, fungal phylogeny and taxonomy and plant-pathogen interaction.