First Report of Glomerella Leaf Spot of Apple Caused by Glomerella cingulata in China

Abstract

A new destructive apple disease, causing black spots and necrotic lesions on leaves and defoliation on cvs. Gala and Golden Delicious (Malus × domestica Borkh.), was observed in August 2011 in Fengxian, Jiangsu Province, China. More than 90% of trees of those cultivars in the area were defoliated by the disease and almost no leaves were left on trees before harvest. The disease was similar to Glomerella leaf spot reported first in Brazil in 1988 (2) and in the United States in 1998 (1) on cvs. Gala and Golden Delicious. The initial symptom was small black lesions on leaves. Above 30°C, the lesions developed quickly and grew to 2 to 3 cm, with a blurred edge. Diseased leaves became dark and were shed. At lower temperatures, the black lesions stopped enlarging after 5 to 6 days and formed large necrotic spots with clear edges; these leaves gradually grew yellow and were shed. When incubated at 30°C and 100% relative humidity for 1 to 2 days, the black lesions produced a mass of saffron-yellow conidia. On fruit, the pathogen only caused circular, necrotic, sunken, red-bordered lesions 2 to 3 mm in diameter, which was different from bitter rot. Three monospored cultures were isolated from diseased leaves and new conidia were obtained from isolates. The colony, with abundant mycelium, was white but turned gray to black. Conidia were 12 to 17 × 5 to 7 μm, and were cylindrical with rounded ends. After germination, conidia formed appressoria, oval, or circular cells with black thick walls 7 to 12 × 5 to 7 um. Based on morphological characteristics, the pathogen was putatively identified as Glomerella cingulata. The conidia were inoculated in vitro on leaves of cvs. Gala and Fuji by dripping a suspension of about 104 conidia/ml of water onto upper leaf surfaces. Dark necrotic lesions were observed on all inoculated Gala leaves, which were similar to those observed in orchards, after 4 days incubation in a chamber at 30°C with 100% humidity. Only small black lesions, about 1 to 2 mm in diameter, were observed on Fuji leaves. No symptoms developed on leaves inoculated with distilled water. The internal transcribed spacer (ITS) region of ribosomal DNA and part of the 18S and 28S ribosomal RNA of the three isolates were amplified with the universal primers ITS1 (5′-TCCGTAGGTGAACCTGCGG-3′) and ITS4 (5′-CCTCCGCTTATTGATATGC-3′). The amplified ITS sequences confirmed that the three isolates belonged to the same species, with only one base pair variation among sequences. The nucleotide sequence of isolate 1 and 2 was deposited in GenBank (JN714400 and JN714401). BLAST analysis showed that the sequence had 99% homology with the sequence of G. cingulata (EU008836), the causal agent of Glomerella leaf spot. However, the sequence of isolate 1 had 100% homology with that of G. cingulata (HQ845103.1) isolated from walnut in Shandong, China, while the sequence of isolate 2 had 100% homology with that of G. cingulata (HM015004.1) isolated from sweet pepper in Taiwan. Results suggested the disease is Glomerella leaf spot and the causal agent is G. cingulata. The disease will eliminate sensitive apple cultivars, such as Gala, from wet, warm production areas if effective control measures are not developed within a few years. To our knowledge, this was the first finding of the disease in China and will provide useful information for developing effective control strategies. References: (1) E. González and T. B. Sutton. Plant Dis. 83:1074, 1999. (2) T. B. Sutton and R. M. Sanhueza. Plant Dis. 82:267, 1998.

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

“…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 , ). Recently, the disease was discovered in commercial apple orchards in Japan and the southern part of Uruguay (Casanova et al , ; Yokosawa et al , ).…”

Salicylic acid confers enhanced resistance to Glomerella leaf spot in apple

“…& H. Schrenk is an emerging disease and has become a serious problem in China (Wang et al, 2012(Wang et al, , 2015a. In China, GLS was first noticed in August 2011 in Fei-xian, Jiangsu Province (Wang et al, 2012), and currently, the disease has disseminated almost all of the apple producing areas (Wang et al, 2015a).…”

“…On leaves, the disease is first manifested by lots of small black spots and these expand rapidly causing premature defoliation within a few weeks (Wang et al, 2012;Moreira and May De Mio, 2015). Infected fruits show many small brown to black lesions that range from 1 to 5 mm in diameter.…”

“…Under these conditions, a large number of conidia are produced on diseased leaves within 3e5 days and disseminated by wind-blown rain. Due to the short incubation period, it is particularly difficult to control GLS after the pathogen infection (Wang et al, 2012(Wang et al, , 2015a.…”

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

“…The disease was finally confirmed as Glomerella cingulata (Wang et al. ). Currently, the disease has the potential to spread to other apple production areas (Wang et al.…”