First Report of Colletotrichum karstii Causing Glomerella Leaf Spot on Apple in Santa Catarina State, Brazil

Abstract

Glomerella leaf spot (GLS) is an emerging disease of apple (Malus domestica Borkh.) that has been reported in regions with a humid subtropical climate, such as southern Brazil, the southeastern United States, and more recently eastern China. GLS is favored by high humidity and temperatures between 23 and 28°C and can result in extensive defoliation when the severity is high. The disease was first reported 1988 in Brazil on cvs. Gala and Golden Delicious in orchards in Paraná State (3), but now is widespread in the country's producing areas. Two Colletotrichum species of different complexes have been associated with GLS, C. gloeosporioides (Penz.) Penz. & Sacc. and its sexual stage Glomerella cingulata (Stoneman) Spaulding & Scherenk, and C. acutatum J. H. Simmonds, although GLS is more commonly associated with the former. In the summer of 2012, necrotic spots were observed on apple leaves (cv. Gala) in Santa Catarina state, Brazil. The first symptoms were reddish-brown spots, evolving to small necrotic lesions 1 to 10 mm long at 7 to 10 days after symptoms were first noted. Pure cultures were obtained by monosporic isolation and grown on PDA at 25°C and with a 12-h photoperiod under fluorescent light. The color of the upper surface of the colony varied from white to gray and the reverse was pink. The conidia length and width ranged from 9.1 to 17.1 μm ([Formula: see text] = 12.8) and from 2.9 to 6.8 μm ([Formula: see text] = 4.9), respectively, and were cylindrical, hyaline, and straight. After germination, conidia formed oval or circular appressoria measuring between 4.0 and 10.0 ([Formula: see text] = 6.3) × 3.0 and 9.0 ([Formula: see text] = 5.7). To confirm pathogenicity, susceptible apple seedlings (cv. Gala) were inoculated with a suspension of 1 × 106 conidia.mL–1. Seedlings sprayed with sterile distilled water served as controls. Seedlings were incubated in a moist chamber at 25°C and 100% RH for 48 h. First symptoms appeared 4 days after inoculation and were similar to those observed in the field. The control treatment remained symptomless. The pathogen was reisolated from lesions, confirming Koch's postulates. Fungus was molecularly characterized by sequencing the internal transcribed spacer (ITS) rDNA and glyceraldehyde-3-phosphate dehydrogenase (GAPDH), and the nucleotide sequence was deposited in the GenBank database (KC876638 and KC875408). C. karstii, considered as part of the C. boninense species complex (1), was identified with 100% sequence homology. This species was previously reported in China (4), Thailand, and the United States, affecting Orchidaceae plants (2), and in Brazil it has been reported affecting Carica papaya, Eugenia uniflora, and Bombax aquaticum (1). To our knowledge, this is the first report of C. karstii causing GLS on apple in Brazil. The development of pre-harvest management practices may be warranted to manage this disease. References: (1) U. Damm et al. Stud. Mycol. 73:1, 2012. (2) I. Jadrane. Plant Dis. 96:1227, 2012. (3) T. B. Sutton. Plant Dis. 82:267, 1998. (4) Y. Yang. Cryptogamie Mycologie 32:229, 2011.

Histological and ultrastructural characterization of the leaf infection events of Colletotrichum fructicola on Malus domestica ‘Gala’

“…These histological observations demonstrate that C. fructicola causes GLS in a typical hemibiotrophic manner. Similarly, by electrolyte leakage assay, Velho et al (2016) indirectly revealed that C. fructicola serves as a hemibiotrophic fungus, with a biotrophic stage that lasts at least 24 hr. In the present study, ultrastructural results showed that the biotrophic stage could last at least 36 hr.…”

“…In the United States, the disease was first found in Georgia in 1970 and named in eastern Tennessee in 1998 (Taylor, ; González and Sutton, ). In Brazil, the disease was widely reported in the main apple‐producing areas of the country (Velho et al , ). In China, GLS was first reported in Jiangsu Province in 2011 (Wang et al , ) and thereafter has been documented in seven major apple production provinces, covering almost all apple‐producing areas (Wang et al , ).…”

“…Conidia are the primary infection source at the early stage of a GLS epidemic. After touching the apple leaf surface, conidia germinate and form melanized appressoria to penetrate epidermal cells (Rockenbach et al, 2015;Velho et al, 2016;Rockenbach et al, 2018).…”

“…To date, although several studies have characterized the aetiology, epidemiology, and preinfective process (i.e., appressoria formation) of GLS (Crusius et al, 2002;Rockenbach et al, 2015;Wang et al, 2015b;Velho et al, 2016), the histological details of the post-infective process of the pathogen remain unexamined. In this paper, the first detailed description of the post-infective process of C. fructicola is reported on apple leaves under field conditions, using light and electron microscopy.…”

Investigation and genetic mapping of a Glomerella leaf spot resistance locus in apple

“…, Velho et al. ). The disease resulted in up to 70% of leaf defoliation of ‘Gala’ (Camilo and Denardi ).…”