The aim of this work was to study the changes in the BVOCs emission rates and physiological mechanistic response of Pinus massoniana saplings in response to drought stress. Drought stress significantly reduced the emission rates of total BVOCs, monoterpenes, and sesquiterpenes, but had no significant effect on the emission rate of isoprene, which slightly increased under drought stress. A significant negative relationship was observed between the emission rates of total BVOCs, monoterpenes, and sesquiterpenes and the content of chlorophylls, starch, and NSCs, and a positive relationship was observed between the isoprene emission rate and the content of chlorophylls, starch, and NSCs, indicating different control mechanism over the emission of the different components of BVOCs. Under drought stress, the emission trade-off between isoprene and other BVOCs components may be driven by the content of chlorophylls, starch, and NSCs. Considering the inconsistent responses of the different components of BVOCs to drought stress for different plant species, close attention should be paid to the effect of drought stress and global change on plant BVOCs emissions in the future.

Sweet viburnum [Viburnum odoratissimum Ker-Gawl. var. awabuki (K. Koch) Zabel ex Rumpl.] belonging to the family Adoxaceae, is a medical and landscape plant, native to Korea (Jeju Island), Taiwan, and Japan (Edita 1988). In June and September 2019, leaf spots were observed on approximately 65% to 80% of sweet viburnum plants in a hedgerow located in Fenghe Xincheng District (28°41'52.9"N 115°52'14.3"E) in Nanchang, China. Initial symptoms of disease appeared as dark brown spots surrounded by red halos (Figure 1 A), which expanded irregularly. Finally, the center of the lesions desiccated and became light-brown, surrounded by a deep-red halos (Figure 1 B). Ten leaf samples with typical symptoms were collected and washed with tap water for about 15 min. The tissue between the healthy and necrotic area (ca. 4 mm × 4 mm) was cut with a sterile scalpel and surface sterilized with 70% alcohol for 45 s, 2% NaClO for 2 min, washed in sterile deionized water three times, dried on sterilized filter paper, then placed in Petri dishes and incubated at 25℃ in the dark. After 3 to 5 days, the hyphal tips from the edges of growing colonies were transferred to fresh PDA dishes. Eventually, 54 fungal isolates were obtained and, of these, 39 isolates were identical in their morphological characteristics. Morphological analysis was performed according with Ellis (1971). The isolate S18, chosen as representative, formed a gray to grayish brown colony with concentric circleson PDA, and a diameter of 8.5 to 9 cm after 7 days incubation at 25℃ (Figure 1 G). Conidia were hyaline, straight or slightly curved, needle shaped, truncate at the base, and acuminate at the tip, with 2 to 6 pseudosepta, 18.90 to 38.38 µm (avg. = 27.51 µm) × 1.64 to 4.50 µm (avg. = 2.60 µm) (n = 36) (Figure 1 H). The genes of fungal isolates (i.e., ITS, tub2 and ACT) were amplified with ITS4/ITS5 for ITS (White, Bruns et al. 1990), Bt2a/Bt2b for tub2 (Glass and Donaldson 1995) and ACT783R/ACT512F for ACT (Carbone and Kohn 1999) and sequenced. The sequences were deposited in GenBank (MW165772 for ITS, MW175900 for ACT and MW168659 for tub2), which showing greater than 99.1% similarity to multiple C. cassiicola accessions, respectively. Pathogenicity tests were performed on healthy leaves in field by inoculating surface-sterilized mature leaves with puncture wound (Figure C) and non-wounded young leaves with 20 µL of a conidial suspension (105 conidia ml-1) (Figure F and G) at 26℃. After 4 to 7 days, all inoculated leaves reproduced similar symptoms as observed initially in the field (Figure 1 C, E and F). To fulfill Koch’s postulates, the fungus was isolated on PDA from the margins of leaf spots on inoculated leaves and confirmed as C. cassiicola by morphological characters and ITS gene sequencing. Previously, C. cassiicola was reported as an endophyte on Viburnum spp. and Viburnum odoratissimum (Alfieri et al. 1994). More recently, C. cassiicola has been reported as a pathogen of many plant species in China, such as kiwifruit (Cui, Gong et al. 2015), American sweetgum (Mao, Zheng et al. 2021), castor bean (Tang, Liu et al. 2020), and holly mangrove (Xie, He et al. 2020). To our knowledge, this is the first report of leaf spot disease on sweet viburnum caused by C. cassiicola in China and the precise identification of the causal agent will be useful for its management.

Camphor tree (Cinnamomum camphora) is native to east Asia, which could produce pharmaceutical metabolites, such as camphor, linalool, and so on (Chen, Tang et al. 2020). In September 2020, severe anthracnose symptoms were observed on the leaves of camphor trees in Nanchang, and estimated incidences ranged from 30% to 80%, which could inhibit leaf growth and reduce their biomass. The lesions were appeared on the leaves of annual branchlets, which the irregular dead areas appeared on leaf tips or margins (Figure 1 A and B), sometimes moving onto the shoots and small twigs. For pathogen isolation, fifteen leaves with typical symptom were randomly collected in Jiangxi Agricultural University (N28°45'38", E115°50'0.006") and the fungi were isolated from the symptomatic-asymptomatic junction and cultured on potato dextrose agar (PDA) at 25℃ in darkness. A total of 40 isolates were obtained from tissue samples, in which 32 isolates were identified as belonging to Colletotrichum spp. following the published works (Damm, Cannon et al. 2012, Damm, Cannon et al. 2012, Weir, Johnston et al. 2012). Based on the morphologies of conidia, all the 32 isolates were classified into two categories. For further precise identification, the represented isolate YK1 and YK18 were selected to analyzed using morphological characters after 7 days of incubation, and multiple genes including ITS (White, Bruns et al. 1990), ACT, GAPDH, TUB (Damm, Woudenberg et al. 2009) and RPB2 (Réblová, Gams et al. 2011). Sequences were deposited in GenBank with accession numbers from MZ229311 to MZ229326. Conidia of isolate YK1 were aseptate, primarily fusiform and measured 14.07-21.21 µm × 4.99-6.79 µm (n = 51) (Figure 1 L) and acervulus were 60.24 to 113.56 µm × 44.24 to 102.63 µm (n = 6) (Figure 1 K), while that of YK18 were one-celled, cylindric with obtuse ends (Figure 1 N) and measured 13.28-16.51 µm × 4.10-5.82 µm (n = 52) and acervulus were 73.85 to 131.70 µm × 63.93 to 105.66 µm (n = 6) (Figure 1 M). Acervulus of isolate YK1 and YK18 were produced on alfalfa stems 40 days after inoculation and dark brown to black in color. For all the genes showed greater than 99% similarity to multiple C. fioriniae and C. siamense accessions, respectively. The phylogram reconstructed from the combined dataset using W-IQ-TREE (Trifinopoulos, Nguyen et al. 2016) showed that isolate YK1 and YK18 clustered with C. fioriniae and C. siamense, respectively. Pathogenicity of both species was tested in the field by ten inoculating surface-sterilized mature leaves with puncture wound (Figure 1 C and D) and ten non-wounded young leaves with 20 µL of a conidial suspension (105 conidia ml-1) (Figure F and G). Leaves treated with sterilized water under the same conditions served as controls. After 4 to 7 days, the inoculated leaves of camphor tree developed typical dark brown to black lesions, similar to symptoms observed in the field, whereas controls remained symptomless. To fill the Koch’s postulates, C. fioriniae and C. siamense were consistently re-isolated, and confirmed morphologically and molecularly. C. siamense have been found to cause anthracnose on Cinnamomum camphora in China (Xu, 2017). To our knowledge, this is the first report of anthracnose on Cinnamomum camphora with C. fioriniae in China. In addition, this is an indication to the complexes about pathogens to anthracnose on camphor tree, which can pose serious threat to the production of Cinnamomum camphora in China.