Effects of Soil Exogenous Nitrogen on Bamboo Shoots, Photosynthetic Characteristics, and Nitrogen Metabolism in Dendrocalamus Latiflorus Munro

BackgroundNitrogen (N) is an essential nutrient element that is involved in almost every aspect of a plant's physiological mechanism. Therefore, the current research aims to determine the optimal amount of N fertilizer to bamboo seedlings for better nutrient management practices to minimize N pollution in bamboo forests. We evaluated the physiological response of Dendrocalamus latiflorus Munro grown under five varying levels of N fertilizer; such as N0, N1, N2, N3, N4, and N5 (0, 1.5, 3.0, 4.5, 6.0, and 7.5 g·pot-1, respectively). ResultsN4 treatment had a significant effect on the number of shoots, which was greatly correlated with net photosynthetic rate (Pn) and photosynthetic pigment (Car, Chls, and Chl a/b) as well as N-related indices [leaf N, leaf ammonium N (NH4+-N), and nitrate reductase (NR)]. N supply significantly increased soil carbon and N contents, which could be conducive to the accumulation of leaf chlorophyll content, improving leaf photosynthesis mechanism, and accelerating N metabolism and conversion through an enzymatic reaction. ConclusionsOverall, the N application of 6 g·pot-1 was advantageous to improve physiological characteristics and shoot production of seedlings. As a consequence, we suggest that optimal nitrogen supply can be effective to improve soil fertility to attain high bamboo production.

Brown Culm Rot of Dendrocalamus latiflorus Munro Caused by Diaporthe guangxiensis in Sichuan Province, China

Dendrocalamus latiflorus Munro, the most widely cultivated bamboo species in southern China, has high ornamental value used in gardens, while culms are also used for buildings and as fibers and edibles (Gao et al. 2011). In June 2020, brown culm rot of bamboo was observed in Yibin city, Sichuan Province, in an area of approximately 1000 hectares. Disease incidence was approximately 60%, of which 30% of the plants had died. At the end of June, the lesions expanded but did not surround the base of the culm. From the end of June to the beginning of September, the lesions expanded upward and formed a streak, of which the color gradually deepened to purple-brown and black-brown. At the same time, the disease spots at the base of the culm also expanded horizontally. After the spots surrounded the base of the culm, the diseased bamboo died. Ten culms showing typical symptoms were collected and cut into 5×5 mm pieces at the junction of infected and healthy tissues. The tissues were sterilized for 1 to 2 min in 3% sodium hypochlorite, decontaminated in 75% alcohol for 3 to 5 min, placed on modified potato glucose agar (PDA) with streptomycin sulfate (50 μg/ml), and incubated at 26°C. Two isolates were obtained by the single-spore method (Sivan et al. 1992). The isolates both produced white round colonies similar to Diaporthe guangxiensis and two types of conidia: one was α type (5.5 to 8.2×1.0 to 2.8 µm, n=30), colourless, single-celled, undivided, and oval, containing two oil droplets; and β type (21.1 to 30.2×0.8 to 1.4 µm, n=30), colourless, single celled and hook shaped. Genomic DNA was extracted from the two isolates by using a fungal genomic DNA extraction kit (Solarbio, Beijing). The products were amplified by polymerase chain reaction (PCR) with primers for the internal transcribed spacer 1 (ITS) region (White et al. 1990), calmodulin (CAL) gene (Carbone and Kohn 1999), translation elongation factor 1-alpha (TEF) gene (Glass and Donaldson 1995) and beta-tubulin (TUB) gene (Soares et al. 2018). The amplified products were sequenced and blasted in GenBank (accession numbers MW380383, MW431318, MW431317 and MW431316 for ITS, CAL, TEF, and TUB, respectively). The ITS, CAL, TEF, and TUB sequences showed 100%, 99.33%, 100%, and 99.80% identity to D. guangxiensis JZB320094 (accession numbers MK335772.1, MK736727.1, MK523566.1, MK500168.1 in GenBank), respectively. To evaluate the pathogenicity of the isolates, five plants were each inoculated with two isolates. The cortex of potted bamboo were injured locally with sterilized needle, and the bamboo culms were inoculated with 100 μl of conidial suspension (105 cfu/ml). The surface of the inoculation wound was covered with gauze soaked with sterilized water. Five plants inoculated with sterile water were used as controls. The treated plants were maintained in a greenhouse at a temperature of 22 to 29°C and relative humidity of 70 to 80%. One month later, of all inoculated plants showed similar symptoms as those observed in the field. D. guangxiensis was re-isolated from all inoculated plants. The pathogenicity test was repeated three times with similar results. This is the first report of D. guangxiensis causing brown culm rot of D. latiflorus in China. These results will facilitate an enhanced understanding of factors affecting bamboo and the design of effective management strategies of the pathogenic species on bamboo and thus to develop corresponding control measures.

Complementary Transcriptome and Proteome Analyses Provide Insight into the Floral Transition in Bamboo (Dendrocalamus latiflorus Munro)

Most woody bamboos bloom only once after long vegetative growth phases and die immediately afterwards. It is difficult, however, to determine the timing of the floral transition, as little information is available on the molecular mechanism of plant maturity in bamboos. To uncover the bamboo floral transition mechanism, its morpho-physiological characteristics, transcriptomes and large-scale quantitative proteomes were investigated in leaves which were collected at different stages during floral transition in a woody bamboo, Dendrocalamus latiflorus. We identified many flowering time-associated genes and the continued increase and decrease genes were screened as flowering biomarker genes (e.g., the MADS14 and bHLH13 genes). These different genes were assigned to specific metabolic pathways by the Kyoto Encyclopedia of Genes and Genomes (KEGG). And the photoperiod pathways depending on the circadian rhythm may play an essential role in the bamboo floral transition. In addition, a total of 721 differently expressed proteins of leaves from the vegetative-to-reproductive stages were identified. Fifty-five genes were specifically differentially expressed at both the transcriptomic and proteomic levels, including genes related to photosynthesis and nucleotide sugar, which may be involved in the floral transition. This work provides insights into bamboo flowers and the management of forest breeding.

Profiling of aroma compounds released from cooking Dendrocalamus latiflorus shoots

Volatile aroma compounds in Dendrocalamus latiflorus shoots were extracted using solid-phase microextraction (SPME) and then heated at various temperatures and for various durations. Gas chromatography-mass spectrometry (GC-MS) analyses showed that frozen D. latiflorus shoots at ambient temperature contain 18 volatile aroma compounds, with limonene and 2-pentyl furan being the major components. Limonene has the fragrance of lemon and citrus fruits, while 2-pentyl furan gives off the scent of flowers and fruits. Additionally, heating temperature had a significant influence on the volatile aroma compounds. Some, including limonene, 2-pentyl furan and n-hexanal, showed marked decrement in content and vaporized almost completely at 100 C, while others, including n-heneicosane and 4-hydroxybenzaldehyde, showed pronounced increase in relative contents. Furthermore, there was a positive relationship between n-heneicosane content and heating duration but a negative relationship between 4-hydroxybenzaldehyde content and heating duration, revealing substantial effects of heating duration on the volatile aroma compounds of D. latiflorus shoots.

Qualitative profile of volatile compounds by SPME in Dendrocalamus latiflorus, Phyllostachys pubescens, and Phyllostachys makinoi culms used as eating utensils

Volatile compounds are released when bamboo culms are used as eating utensils. Volatile compounds of Dendrocalamus latiflorus, Phyllostachys pubescens, and P. makinoi culms were extracted using solid-phase microextraction (SPME). The bamboo culms were steamed or baked at different temperatures (100 °C and 230 °C) and durations (5 min, 30 min, and 60 min). Gas chromatography-mass spectrometry (GC-MS) analyses showed that, regardless of heating method and duration, P. makinoi culms comprised the most species of volatile compounds, with sesquiterpenes being the major compounds. Steaming and baking D. latiflorus culms at 100 °C for 30 min yielded more volatile compounds than baking at 230 °C. Benzenoids were the chief compounds in heated D. latiflorus and P. pubescens culms, with phenylacetaldehyde being the dominant constituent. Phenylacetaldehyde has fragrances of herb, flower, and oil. Moreover, the major volatile compound cyclosativene, which gives a terpene-like aroma, was obtained when P. makinoi culms were heated for different durations. After baking at 230 °C for 30 min, the major volatile compound released from P. makinoi culm was α-muurolene (41.19%), which produces a woody aroma. After continuous baking for 60 min, DT 1, a kind of diterpene compound, increased remarkably in relative content, while the content of α-muurolene decreased notably.