First Report of Leaf Spot and Stem Blight on Blueberry (Vaccinium corymbosum ‘Bluerain’) Caused by Calonectria pseudoreteaudii in China

Abstract

Blueberry has high nutritional value and is one of the five healthy fruits. In 2018, leaf spots and stem blights were observed on Vaccinium corymbosum cv. Bluerain in Guangzhou, Guangdong Province, China. Up to 80% of the plants were affected. Initial symptoms of affected leaves were red-brown, irregular, small spots, which gradually coalesced and formed larger irregular necrotic patches. The affected stems showed red-brown and irregular large lesions. Diseased tissues were surface sterilized with 75% alcohol for 15 s, followed by 2.5% NaClO for 30 s, and rinsing three times in sterile distilled water, placed on potato dextrose agar (PDA) and incubated at 25 C. Representative strains, ZHKUCC 21-0021 from diseased leaves and ZHKUCC 21-0073 from diseased stems, were selected for further studies. Colonies grew slowly at 25 C on malt extract agar (MEA) (average 5.68 mm/d), producing white aerial mycelium and red-brown color on the underside after 7 days. Macroconidiophores were hyaline, smooth, consisting of a stipe bearing fertile branches, and a stipe extension terminating in a vesicle. Each terminal branch produced 2–4 phialides, 8–13 × 3–6 μm, reniform or doliiform; Stipe extensions were septate, terminating in a narrowly clavate vesicle, 2–6 μm. Macroconidia were hyaline, straight cylindrical, round at both ends, 83–100 × 7–11 μm (average = 94 × 8 μm; n = 50), with 5 septa. These morphological characteristics were similar to the description of Calonectria pseudoreteaudii (Lombard et al., 2010). The partial calmodulin (cmdA), beta-tubulin (β-tubulin), and translation elongation factor 1-alpha (tef1-α) genes of the two isolates were respectively amplified using primers CAL-228F/CAL-737R (Carbone et al., 1999), EF1-728F/EF2 and T1/CYLTUB1R (Lombard et al., 2015), and sequences were deposited in GenBank (cmdA: MZ516854 and MZ516855; β-tubulin: MZ516858 and MZ516859; tef1-α: MZ516856 and MZ516857). BLAST analysis of three gene sequences showed 100% similarity to those of C. pseudoreteaudii. In the maximum likelihood (ML) tree of the concatenated sequences of the three genes, the two isolates from this study were clustered with C. pseudoreteaudii with 100% bootstrap support. Five-mm-diameter hyphal plugs of two representative isolates grown on PDA for five days were used in the pathogenicity test. Leaves were inoculated with ZHKUCC 21-0021, and stems were inoculated with ZHKUCC 21-0073 with five replicates. As controls, sterile PDA plugs were used. All inoculated plants were maintained at 25 C . After 7 days, inoculated leaves and stems developed symptoms similar to field samples, whereas the control plants remained asymptomatic. The pathogen was reisolated from inoculated plants and confirmed to be C. pseudoreteaudii by morphological characteristics. Five Calonectria species (C. canadensis, C. colhounii, C. ilicicola, C. kyotensis and C. pyrochroa), have been reported associated with blueberry (Farr and Rossman, 2022; Fei et al, 2017). Calonectria canadensis and C. ilicicola have been reported to cause stem blight and stem rot in Vaccinium spp. in China (Fei et al, 2017 and 2018). Calonectria colhounii has been reported to cause stem blight in V. angustifolium and V. corymbosum in the United States (Sadowsky et al, 2011). However, this is the first report of C. pseudoreteaudii causing leaf spot and stem blight on Vaccinium spp. worldwide. These results will provide a foundation for future research on prevention and control of this disease.

Identifying the Biological Characteristics of Anthracnose Pathogens of Blueberries (Vaccinium corymbosum L.) in China

“…Anthracnose fungi are ubiquitous pathogens in nature and represent significant phytopathogens of numerous economic crops, including Fragaria × ananassa Duch [55], Vitis vinifera L. [56], Malus pumila Mill [57], Mangifera indica L. [58], etc., resulting in negative impacts on plant growth and reduced yields, leading to substantial economic losses. Blueberry anthracnose is a significant disease in many countries, causing damage to blueberry production throughout the year by affecting leaves, branches, and fruits [14,31,59]. In previous reports, C. gloeosporioides and C. acutatum were confirmed as the main pathogens [60][61][62].…”

“…Examples include stem blight caused by Neofusicoccum vaccinii [8], anthracnose caused by Colletotrichum acutatum and C. gloeosporioides [9,10], anthrax caused by Pestalotiopsis spp. [11], Nigrospora oryzae [12], Diaporthe phoenicicola [13], and leaf spot disease caused by Calonectria pseudoreteaudii [14]. The diseases have resulted in significant economic losses to the blueberry industry.…”

Wide Distribution and Intraspecies Diversity in the Pathogenicity of Calonectria in Soil from Eucalyptus Plantations in Southern Guangxi of China

“…sp. in China and Laos [ 59 , 60 ] and caused leaf spot and stem blight in Vaccinium corymbosum L. in China [ 61 ]. The results of this and previous studies suggested that C. pseudoreteaudii is an important pathogen in many plant species with a wide geographic distribution.…”

Evidence of High Genetic Diversity and Differences in the Population Diversity of the Eucalyptus Leaf Blight Pathogen Calonectria pseudoreteaudii from Diseased Leaves and Soil in a Plantation in Guangxi, China

“…In addition to Eucalyptus in China, C. pseudoreteaudii has been isolated from Eucalyptus hybrids in Vietnam, India, and Indonesia; Macadamia sp. in Vietnam, Lao, and China; and blueberry in China [13,[15][16][17][18][19][20].…”