Bacillus amyloliquefaciens FZB42 is a plant growth-promoting rhizobacteria that stimulates plant growth, and enhances resistance to pathogens and tolerance of salt stress. Instead, the mechanistic basis of drought tolerance in Arabidopsis thaliana induced by FZB42 remains unexplored. Here, we constructed an exopolysaccharide-deficient mutant epsC and determined the role of epsC in FZB42-induced drought tolerance in A. thaliana. Results showed that FZB42 significantly enhanced growth and drought tolerance of Arabidopsis by increasing the survival rate, fresh and dry shoot weights, primary root length, root dry weight, lateral root number, and total lateral root length. Coordinated changes were also observed in cellular defense responses, including elevated concentrations of proline and activities of superoxide dismutase and peroxidase, decreased concentrations of malondialdehyde, and accumulation of hydrogen peroxide in plants treated with FZB42. The relative expression levels of drought defense-related marker genes, such as RD29A, RD17, ERD1, and LEA14, were also increased in the leaves of FZB42-treated plants. In addition, FZB42 induced the drought tolerance in Arabidopsis by the action of both ethylene and jasmonate, but not abscisic acid. However, plants inoculated with mutant strain epsC were less able to resist drought stress with respect to each of these parameters, indicating that epsC are required for the full benefit of FZB42 inoculation to be gained. Moreover, the mutant strain was less capable of supporting the formation of a biofilm and of colonizing the A. thaliana root. Therefore, epsC is an important factor that allows FZB42 to colonize the roots and induce systemic drought tolerance in Arabidopsis.

Lanzhou lily (Lilium davidii var. unicolor Cotton) is an important bulb edible crop which mostly distributes in middle area of Gansu Province in China (2). Recently, plants of Lanzhou lily developed symptoms of severe wilting. In early autumn of 2012 to 2013, a survey of Lanzhou lily disease was carried out in Yuanjiawan, Caoyuan, Xiguoyuan, and Hutan villages of Lanzhou City and Xuding and Guanshan villages of Linxia Prefecture. Disease symptoms included stem and root rot, vessels showed a brown to dark brown discoloration, plus a progressive yellowing and wilting of leaves from the base. Small pieces of symptomatic leaves, stems, and roots were surface disinfected with 75% ethanol for 30 s, 3% sodium hypochlorite for 5 min, and then washed three times in sterile distilled water. The tissues were placed on Martin Agar at 25°C for 7 days. Three isolates were consistently isolated from diseased tissues and all isolates with morphology similar to Fusarium spp. Isolates were transferred to potato dextrose agar (PDA) and carnation leaf agar (CLA) and incubated at 25°C in darkness. These isolates grew rapidly on PDA and formed abundant dense aerial mycelium, initially white, that became deep pink with age and formed red pigments in the medium. On CLA, macroconidia with 3 to 5 septa were abundant, relatively slender, and curved to lunate. Microconidia were abundant, oval and 0 to 1 septa. Chlamydospores were globose with a smooth outer wall in chains. The rDNA internal transcribed spacer (ITS) region comprising ITS1, ITS2, and 5.8S rDNA was amplified using primers ITS-1 and ITS-4 (3) and sequenced. On the basis of a comparison of 563 bp, all the three isolates had the identical sequence (GenBank Accession No. KF728675). BLASTn analysis of the sequence showed 100% match with the ITS sequences of those F. tricinctum sequences in GenBank (Accession Nos. FJ233196, AY188923, and JF776663). Pathogenicity test was performed by transplanting 2-month-old tissue culture seedlings to plastic pots in a sterile mixture of vermiculite and torf substrate at 1:3 (v/v). Seedlings were inoculated with 6 ml of the conidial suspension (104 conidia/ml) on the roots of plant in each pot, three plants per pot, and three replicates for each treatment. Seedlings treated with sterile water served as controls. The seedlings were placed in a plant growth chamber maintained at 22 ± 3°C, relative humidity >70%, 16 h light per day, and irrigated with sterile water. After 4 weeks, inoculated plants exhibited wilting foliage that with symptoms similar to those observed in the field, while the control plants remained healthy. F. tricinctum was re-isolated from all inoculated plants. The disease has been reported previously in ornamental lily in China (1). However, to the best of our knowledge, this is the first report of F. tricinctum causing wilt on edible Lanzhou lily in China and the disease must be taken into consideration of current disease management. This work supported by NSFC No. 31370447 and Hundred Talents Program of CAS “Molecular mechanism of biological control on plant diseases.” References: (1) Y. Y. Li et al. Plant Dis. 97:993, 2013. (2) R. Y. Wang et al. Virol. J. 7:34, 2010. (3) T. J. White et al. Page 315 in: PCR Protocols: A Guide to Methods and Applications. Academic Press, San Diego, CA, 1990.

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Codonopsis pilosula Franch., also known as Dangshen, is an important medicinal plant in China. It is widely cultivated for a major income of local farmers in Dingxi, Gansu Province. Its dried roots have the effects of supplementing vital energy, nourishing spleen and lung, enhancing organic immunity, helping depressurization, and improving microcirculation, etc., for humans. In June to October, 2018-2020, root rot disease was observed on C. pilosula with incidences up to 20% in the Dingxi region. We collected ten diseased and healthy plants from Dingxi (35°06′N, 104°29′E, 2206 m a.s.l.) in October 2019. The rotting root tissues were sterilized with 70% ethanol for 30 s and 3% NaOCl for 5 min and placed on potato dextrose agar (PDA) plates incubated at 25℃to isolate the pathogen (Shang et al. 2014). From the similar fungal cultures isolated after 7 days on PGA, isolate B17 was purified for morphological and molecular characterization. Its colony appeared light purple and produced long aerial hyphae. Slightly curved macroconidia (12.3 to 31.7 × 3.1 to 5.1 μm, n=40) and oval-ellipsoid and cylindrical microconidia (6.1 to 9.9 × 2.8 to 4.5 μm, n=30) were observed. The internal transcribed spacer region (ITS) and the translation elongation factor-1 alpha (TEF-1α) gene were amplified using primers ITS1/ITS4 and EF-1/EF-2 (Uwaremwe et al. 2020), respectively. The 489 bp (ITS) and 631 bp (TEF-1α) sequences were deposited in GenBank (Accession No. MN744360 and MN786974, respectively). The ITS sequence had 100% homology to isolate JJF2 (No. MN626452, ITS) (Ma et al. 2020), and the TEF-1α sequence had 100% homology to isolate Fo353 (No. KM065860) (Koyyappurath et al. 2016) of Fusarium oxysporum Schlecht. emend. Snyder & Hansen, which caused root rot of Panax ginseng and Vanilla planifolia, respectively. A phylogenetic tree was generated using the unweighted pair-group method with arithmetic average in the MycoBank database (O’Donnell et al. 2015), which clustered isolate B17 in the F. oxysporum species complex. Twenty 1-year-old plants of C. pilosula were inoculated with were inoculated by dipping the washed roots in a conidial suspension (2 ×106 conidia/ml added with 0.2% Tween 20) for 20 min before transplanted into pots (16 × 16 × 23 cm) with four plants per pot filled with sterilized peat and soil mixture (2:1 v/v) and grown in a greenhouse at 26oC with >70% humidity and 16 h light. Sterilized water added with 0.2% Tween 20 was used as a control. One week after inoculation, the leaves of pathogen-inoculated plants became yellow, and wilting occurred at the leaf tips 18 days later. Some of the inoculated plants died 45 days after inoculation, and the low part of roots had dark brown to black lesions and became rotting. The control plants did not show symptoms. The pathogenicity test was repeated three times with the same fungus isolated from the infected root tissue. To the best of our knowledge, this is the first report that F. oxysporum causes root rot on C. pilosula in China. F. oxysporum is a serious threat to C. pilosula cultivation, and the finding of this pathogen provides a clear target for root rot control.

No abstract

Lily (Lilium spp.) is one of the most well-known horticultural crops, and plays an important economic role in China. In September 2011, wilted plants were observed on Lilium oriental hybrid cultivar ‘Sorbonne’ growing in Longde County, Ningxia Hui Autonomous Region, China. Disease symptoms included wilting, stem and root rot, brown spots of bulbs and then bulbs rotting and spalling from the basal disc, plus a progressive yellowing and defoliation of the leaves from the base. Diseased plants were sampled from fields. Small pieces of symptomatic bulbs, stems, and roots from 10 different plants were surface disinfected with 75% ethanol for 30 s, 3% sodium hypochlorite for 5 min, and then washed three times in sterilize distilled water. The tissues were placed onto Martin Agar (2) at 25°C for 7 days. Nine isolates with morphology similar to Fusarium were obtained from the diseased tissues. Isolates were transferred to potato dextrose agar (PDA) and carnation leaf agar (CLA) and incubated at 25°C. Seven were identified as Fusarium oxysporum and one was F. solani, which have been reported as pathogens of lily in China (1). The other isolate, when grown on PDA, rapidly produced dense, white aerial mycelium that became pink with age and formed red pigments in the medium. On CLA, macroconidia with three to five septate were abundant, relatively slender, and curved to lunate. Microconidia were abundant, oval or pyriform, and one to two celled. Chlamydospores were in chains with smooth exine. The rDNA internal transcribed spacer (ITS) region and a portion of the translation elongation factor 1-alpha (EF-1α) gene of the fungus were amplified, with universal primers ITS1/ITS4 and EF1/EF2 primers respectively (3) and sequenced. In addition, the β-tubulin gene (β-tub) of the fungus was amplified with modified primers Btu-F-F01 (5′-CAGACMGGTCAGTGCGTAA-3′) and Btu-F-R01 (5′-TCTTGGGGTCGAACATCTG-3′) (4). BLASTn analysis showed that the ITS sequences of the isolate (GenBank Accession No. JX989827) had 98.9% similarity with those of F. tricinctum (EF611092, JF776665, and HM776425) and the EF-1α sequences of the isolate (JX989828) had 98.1% similarity with those of F. tricinctum (EU744837 and JX397850). The β-tub sequences of the isolate (JX989829) had 99.0% similarity with those of F. tricinctum (EU490236 and AB587077). The isolate was tested for pathogenicity. Two-month-old ‘Sorbonne’ seedlings were inoculated by placing 5 ml of conidial suspension (about 106 conidia per ml) over the roots of plants in each pot. Control plants were treated with sterile water in the same way. Plants were placed in a greenhouse at 22 to 25°C with a 15-h photoperiod. There were eight plants per pot and three replicates for each treatment. After 3 weeks, 87.5% of the inoculated plants exhibited browning of the root tips, root rot, and yellowing of the leaves, while control plants were symptomless. The pathogen was reisolated from the infected roots and identified as F. tricinctum, thus fulfilling Koch's postulates. To our knowledge, this is the first report of Fusarium wilt of lily caused by F. tricinctum. This information will provide guidance for the control of lily wilt disease and add information useful for the production of lilies. References: (1) C. Li and J. J. Li. Acta Phytopathol. Sin. (in Chinese) 26:192, 1995. (2) J. P. Martin. Soil Sci. 38:215, 1950. (3) K. O'Donnell et al. Proc. Nat. Acad. Sci. U. S. A. 95:2044, 1998. (4) M. Watanabe et al. BMC Evol. Biol. 11:322. 2011.

Two viruses that frequently occur in many Lilium species are Lily mottle virus (LMoV) and Cucumber mosaic virus (CMV), which usually co‐infect lilies causing severe disease symptoms. Recent reports have revealed that the viral coat protein (CP) affects chloroplast ultrastructure and symptom development. This study used western blot analysis to confirm that in leaves infected by mixed virus infections of LMoV and CMV, CPs of both viruses were accumulated in lily chloroplasts. Immunogold labelling further demonstrated that both the LMoV CP and CMV CP were localized in the stroma and the thylakoid membranes of the chloroplasts. In addition, it was found that CPs of both viruses were rapidly transported into isolated, intact chloroplasts (in vitro), and their transport efficiencies were positively related to CP concentrations. The lowest transmembrane concentration of CMV CP decreased from 38 μg mL−1 recorded in the single CMV CP import system to 10 μg mL−1 in the mixed import system of LMoV CP and CMV CP. CPs of both viruses exhibited species selection in their transmembrane transport into chloroplasts. This is the first report that the CPs from two viruses (LMoV and CMV) are simultaneously present in lily chloroplasts. Accumulation of high levels of LMoV CP and CMV CP inside the chloroplast appears to contribute to a synergistic interaction inducing the development of mosaic symptoms.

The roots of Codonopsis pilosula, a crucial ingredient in Chinese medicine, are prone to soft rot disease soon after transplanting seedlings in the second year. This almost always causes severe losses in yield at harvest, with severe economic consequences for farmers of this perennial vine. However, the pathogens involved remain understudied, although some gram‐negative bacteria of the Enterobacteriaceae family are well‐known pathogens of soft rot in many other plants. Here, the isolate B5‐2‐1‐30 was suspected of being a key pathogen of C. pilosula in China according to counts of bacteria from diseased, healthy and adjacent tissues of roots. Results of morphological and phylogenetic analyses, including microscopic observations, in addition to a multilocus sequence analysis (MLSA) of the concatenated partial 16S rDNA, rpoB, atpD and gyrB genes, revealed that this isolate belongs to Lelliottia nimipressuralis. In vitro and in vivo pathogenicity tests showed that L. nimipressuralis B5‐2‐1‐30 could cause root soft rot in seedlings of C. pilosula, with symptoms similar to those observed in the field. Further experiments suggested the typical symptoms of softened rotting roots and wilting shoots arose from phloem necrosis and vessel plugging, as inferred by observed anatomical characteristics of roots, providing clues for elucidating the infection mechanism of phytopathogens in L. nimipressuralis.