First Report of Botryosphaeria dothidea Causing Gray Mold on Tartary Buckwheat in Southwest China

First report of Botryosphaeria dothidea causing leaf spot of Camellia oleifera in China

Camellia oleifera Abel., a small evergreen tree or shrub, is mainly distributed in central and southern China with a larger scale of 4.5 × 106 hectares (Zhu 2020). In May 2021, severe leaf spots were observed in plantation located in Shuangfeng County (27°41'36" N, 111°56'60" E), Hunan Province, China. More than 60 C. oleifera plants were surveyed with over 80% disease incidence. The symptoms on leaves were initially small brown lesions from leaf margins or tips, developing to suborbicular or irregular-shaped dark brown lesions, leading to leaves withered. A total of 60 symptomatic samples were randomly collected. Lesion margins were surface sterilized in 2% sodium hypochlorite for 1 min, rinsed with sterile distilled water for three times, dried, placed on potato dextrose agar (PDA), and incubated at 25°C in the dark for 3 days. Hyphal sections from colony edges were transferred to new PDA plates. Three isolates of Botryosphaeria dothidea were obtained. Colonies of B. dothidea were initially white gradually turning dark-gray with dense aerial mycelium after 6 days. To induce sporulation, colonies of YCB17 were transferred to synthetic nutrient-poor agar (SNA) with sterilized leaves of C. oleifera. Cultures were initially incubated at 25°C in the dark for 3 days, then alternatively exposed to 12-hours near-UV light and 12-hours white light (CHU et al. 2021). After 5 days, conidia formed on leaves were examined microscopically. The conidia were unicellular, aseptate, hyaline, and fusoid, 20.9-25.5×4.7-6.4 µm (n = 50). Morphological characteristics of the isolates matched the description of B. dothidea (Slippers et al. 2014). DNA sequence was amplified using primer pairs ITS1/ITS4 (Tang et al. 2022), EF1-728F/986R (Slippers et al. 2004), and βt2a/2b (Glass & Donaldson. 1995) respectively. The sequences of three isolates (YCB2, YCB3, YCB17) were deposited in GenBank with accession numbers ON714603, MZ613350, MZ613349 (ITS), OM328342, OM328343, OM328344 (TEF-1α), and OM328345, OM328346, OM328347 (TUB2). A blast search of sequences showed the ITS, TEF-1α, and TUB2 sequences had >99% identity with homologue sequences from B. dothidea isolates IRNHM-KZ49 (MG198191.1), CAP288 (EF638732.1) and Mu1 (MK423987.1), respectively. For pathogenicity testing, healthy leaves of 2-year-old C. oleifera plants in the greenhouse were spray-inoculated with conidial suspension (2×106 conidia/mL) from YCB17. Ten surface-sterilized and wounded leaves per plant were sprayed with 30 µL suspension. The other ten wounded leaves sprayed with sterile distilled water served as control. All plants were kept in the greenhouse with temperature at 26 ± 2°C and 50% relative humidity. After 12 days, initial symptoms were observed on more than 80% leaves inoculated with conidial suspension, whereas no symptoms were observed on the control leaves. The test was repeated three times with similar results. It was found that B. dothidea could cause leaf spot of C. oleifera. The infected leaves showed same symptom as samples. Re-isolated fungi from infected leaves were morphologically identical to B. dothidea. Botryosphaeria dothidea has been reported causing leaf spot in a wide range of hosts, but has not previously been reported causing disease on C. oleifera. To our knowledge, this is the first report of B. dothidea causing leaf spot of Camellia oleifera in China. The information on identification of this fungus may be helpful to the control and prevention of the disease. References: 1. Chu Rui-Tian, et al. 2021. Mycosystema 40(3): 473. 2. Glass, N. L., and Donaldson, G. C. 1995. Appl. Environ. Microbiol. 61: 1323. 3. Slippers, B., et al. 2004. Mycologia 96:83. 4. Slippers, B., et al. 2014. Persoonia 33:155. 5. Tang, Y., et al. 2022. Plant Dis. 106: 765. 6. Zhu P.X. People's Daily. 2020.11.09. http://gz.people.com.cn/n2/2020/1119/c194844-34425098.html. *Indicates the corresponding author. Kaifa Guo, E-mail: andygkf@126.com.

First report of Botryosphaeria dothidea as the causal agent of a new fruit rot disease of pepper in China

Pepper is an important and widely cultivated economic vegetable in the world (Yin et al., 2021). In June 2021, approximately 25% to 33.3% of the pepper plants had rot disease symptoms in Zhuanghang Comprehensive Experimental Base (30.894829 °N, 121.391374 °E), Fengxian district, Shanghai city, China. Water-soaked spots appeared on fruits that increased in size and leading to smelly fruit decay. To isolate the pathogen, three pepper samples with severe symptoms were collected. The samples were surface disinfected with 70% ethanol for 30 sec, 10% chlorine bleach for 10 min, rinsing with sterile water for three times and the rot tissues were cut and dried on sterile filter paper. The dried paper was later placed on potato dextrose agar (PDA) medium and incubated at 28°C (Tang et al., 2021). After 2-3 days, four types of colonies with different colony appearances were observed, in which only one can induce fruit rot phenotype (data not shown). Four isolates were cultured for molecular identification in each type. ITS1/ITS4, T1/βt-2b and EF1-526F/EF1-1567R primers were used to amplify the internal transcribed spacer region (ITS), the beta-tubulin (TUB2) and the translation elongation factor I alpha (EF1-α) genes, respectively (Chen et al., 2018) and corresponding sequences from the isolates were analyzed with BLAST. Sequences of the isolate which can induce pepper decay were submitted to GenBank under the accession numbers of OM663701 (ITS), OM720127 (TUB2) and OM720128 (EF1-α). The results showed that the pathogen had 99% sequence homology to most strains of Botryosphaeria dothidea (B. dothidea) and displayed the highest sequence similarity to strain LBSX-1 (ITS: KF55123), strain JGT01 (TUB2: MW202404) and isolate CZA (EF1-α: MN025271). Based on molecular characterization, the isolate was identified as B. dothidea isolate SH01. A phylogenetic tree was constructed using Maximum Parsimony (MP) methods by MEGA7, and showed that SH01 was closely related to isolate CMW9075. To confirm the pathogenicity, five healthy pepper fruits were surface sterilized, 500μl of conidial suspension (1×103 conidia/ml) were injected into pepper (sterilized distilled water as control). Six days post inoculation (dpi), fruit rot symptoms appeared and the pepper decayed at 12 dpi. Four days post inoculation with mycelium plugs (from a 4-day-old culture on PDA, PDA plugs as control), hyphae were observed in the inoculation site and B. dothidea was re-isolated from the symptomatic areas, thus fulfilling Koch's postulates (Back et al., 2021, Chen et al., 2020). The pepper rotted severely at 7 dpi. The colonies of SH01 were pale to white and gradually turned into gray in 4-6 days. Conidia of the pathogen were unicellular, aseptate, hyaline and fusiform to fusoid, with dimensions of 19.7-23.5 μm × 3.8-5.2 μm (average = 21.9 μm × 4.8 μm, n = 50). Hyphae were transparent, branched and composed of multiple cells. The characteristic was consistent with the descriptions of B. dothidea (Vasic et al., 2013). B. dothidea belongs to Botryosphaeriaceae, causing widespread diseases in many plant species, commonly associated with cankers and dieback of woody plants and economic crops, such as plumcot trees (Back et al., 2021), eucalyptus (Yu et al., 2009) and soybeans (Chen et al., 2020) in China and Korea. Our findings reported for the first time that B. dothidea (SH01) can induce the pepper rot disease and future work on its pathogenesis may provide strategies for disease control against this fungus.

Comprehensive Profiling of Tubby-Like Proteins in Soybean and Roles of the GmTLP8 Gene in Abiotic Stress Responses

Tubby-like proteins (TLPs) are transcription factors that are widely present in eukaryotes and generally participate in growth and developmental processes. Using genome databases, a total of 22 putative TLP genes were identified in the soybean genome, and unevenly distributed across 13 chromosomes. Phylogenetic analysis demonstrated that the predicted GmTLP proteins were divided into five groups (I-V). Gene structure, protein motifs, and conserved domains were analyzed to identify differences and common features among the GmTLPs. A three-dimensional protein model was built to show the typical structure of TLPs. Analysis of publicly available gene expression data showed that GmTLP genes were differentially expressed in response to abiotic stresses. Based on those data, GmTLP8 was selected to further explore the role of TLPs in soybean drought and salt stress responses. GmTLP8 overexpressors had improved tolerance to drought and salt stresses, whereas the opposite was true of GmTLP8-RNAi lines. 3,3-diaminobenzidine and nitro blue tetrazolium staining and physiological indexes also showed that overexpression of GmTLP8 enhanced the tolerance of soybean to drought and salt stresses; in addition, downstream stress-responsive genes were upregulated in response to drought and salt stresses. This study provides new insights into the function of GmTLPs in response to abiotic stresses.