First Report of Colletotrichum Leaf Spot of Macadamia Caused by Colletotrichum siamense in China

Abstract

Macadamia (Macadamia integrifolia Maiden & Betche), growing in tropical and subtropical regions worldwide, is a high-value tree nut (Akinsanmi and Drenth 2017). In May 2018, the leaves of macadamia trees showed symptoms of anthracnose, with an incidence 10-15%, in Chongzuo (22°32′ N; 107°38′ E) (Guangxi province) in China. The disease begin to develop from the tip of leaf or the margin of leaf. Initially, the disease symptoms on leaves were water-soaked, black grey, light-yellow around, which enlarged and coalesced, the leaves appeared irregular, tawny or black lesions, ending in necrosis and defoliation. Abundant black little spots (acervuli) developed on the leaf surface, colonizing mainly the lesion zones. Under high humidity conditions, lots of mucilaginous masses of pink conidia were observed on the leaf surface. Symptomatic leaves were randomly sampled from different parts of the field and washed with tap water. Tissues from the margins of the lesions were surface sterilized with 75% ethanol for 20 s, 2% sodium hypochlorite solution for 2 min, rinsed in sterile distilled water, plated on potato dextrose agar (PDA) and incubated at 28℃ in constant light. After incubation for 5 days, the colonies of all isolates were white. After 10 days, a few aerial mycelia became greyish-green on the reverse side of plates. Fourteen days after incubation, many mucilaginous masses of pink conidia developed and monoconidial isolates were obtained by single-sporing. The nonseptate conidia were hyaline, cylindrical, obtuse at both ends, 14.4 to 21.4 μm (average 16.8 µm) × 5.4 to 7.0 μm (average 6.3 µm) (n = 100). These morphological characteristics were similar to the Colletotrichum gloeosporioides species complex (Weir et al. 2012). To confirm the pathogen’s identity, DNA sequencing of the internal transcribed spacer (ITS), β-tubulin (TUB), actin (ACT), glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and histone H3 (HIS3) genes were performed. The sequences have been deposited in GenBank under accession numbers MT219898, MT227807, MT227808, MT227810 and MT227811, respectively. A BLAST of the ITS, TUB, ACT, GAPDH, and HIS3 sequences revealed 99 to 100% identity with those of C. siamense (MG830368, MG830342, MH290847, MK863031 and MH370542). A phylogenetic tree generated using the method of maximum likelihood in MEGA7.0 (Kumar et al. 2016) revealed that our isolate MICS0319 falls within the C. siamense clade. For the pathogenicity test, 10 healthy leaves of macadamia were slightly punctured by a sterile pin and inoculated with 5 mm diameter mycelial plugs. The same number of leaves treated with PDA plugs served as controls. All plants were incubated at 28 °C and 100% relative humidity. After 4 days, the leaves inoculated with the mycelial, disc showed water-soaked, tawny necrotic lesions, whereas controls remained asymptomatic. The fungus was successfully reisolated from the symptomatic leaves, and the identity was confirmed by morphology and phylogeny as C. siamense on the basis of the methods described above, thus confirming Koch’s postulates. C. siamense has been reported on macadamia,chili, papaya and avocado (Prasannath et al. 2020; De Silva et al. 2017). To the best of our knowledge, this is the first report of C. siamense attacking leaf of macadamia in China. This research provides a basis for further research on the control of field disease.

First report of leaf spot caused by Colletotrichum siamense on Sophora tonkinensis

“…In China, various diseases caused by C. siamense can infect other hosts include Sterculia nobilis (Zhang et al 2020a, b), Sterculia lanceolata (Zhang et al 2020a, b), Hevea brasiliensis (rubber tree) (Cao et al 2019), Mallotus oblongifolius (Partridge tea) (Liu et al 2018), Macadamia sp. (Qiu et al 2020), Litchi chinensis (Ling et al 2019), and Camellia sinensis (Wang et al 2016). Although there have been other reports of Colletotrichum species on S. tonkinensis, namely C. gloeosporioides (Shivas and Alcorn 1996) and C. simmondsii (as an endophyte from roots) (Yao et al 2017), ours is the first known record of C. siamense on the plant of S. tonkinensis.…”

Pathogenicity and molecular phylogenetic analysis reveal Colletotrichum siamense as causal agent of leaf fall disease in rubber trees (Hevea brasiliensis) in southern Thailand

“…It can infect many plants and cause many diseases (Weir et al, 2012), such as crown rot in strawberries (Luo et al, 2021), as well as anthracnose disease and leaf disease in many plants, including Citrus spp., Piper nigrum, Artocarpus heterophyllus, Artocarpus sericicarpus, Coffea arabica, Coffea canephora, Eriobotrya japonica, Ficus carica, Mentha sp., Rosmarinus officinalis, Theobroma cacao, Jasminum sambac, Pongamia pinnata, Bauhinia forficata subsp. pruinose and Macadamia integrifolia, (Wikee et al, 2011;James et al, 2014;Larran et al, 2015;Dwarka et al, 2016;Qiu et al, 2020;Jian et al, 2021;Perez-Mora et al, 2021;Wang et al, 2021). Casas et al (2021a, b) reported that C. siamense can be endophytic and is used as a biological control in anthracnose disease.…”

Colletotrichum siamense leaf blight/spot: Characterization of a newly identified disease on Cinnamomum tamala

“…As such it can cause preharvest fruit anthracnose in Carica papaya L. [40], Litchi chinensis [18,41], Acca sellowiana [42], Fragaria ananassa Duch [43], Citrus spp. [44], Walnut (Juglans regia L.) [14], postharvest fruit anthracnose in Mangifera indica [45], crown rot and anthracnose in roots, runner of Fragaria ananassa Duch [43], leaf spot in rubber (Hevea brasiliensis) [37], Thai basil (Ocimum basilicum) [46], and Macadamia (Macadamia integrifolia) [27,30]. Recently Kumar et al [47] and Salunkhe et al [48] also reported C. siamense as the causal organism of Cliff Banana and cotton anthracnose in the neighboring country India.…”

“…In addition, the distinct leaf blight/spot symptom was also consistent with Colletotrichum Leaf Spot of Macadamia and Chrysalidocarpus lutescens (areca palm). In these hosts, the disease began to develop from the lea tip or the leaf margin as small spots, followed by coalescing into a large spot, then ending in necrosis and defoliation in severe cases [27, 28]. To the author's knowledge, no such symptoms (as described above) were reported for the C. tamala plant in Bangladesh or even in other countries.…”