Silicon induces ROS scavengers, hormone signalling, antifungal metabolites, and silicon deposition against brown stripe disease in sugarcane.

Bipolaris setariae is known to cause brown stripe disease in sugarcane, resulting in significant yield losses. Silicon (Si) has the potential to enhance plant growth and biotic resistance. In this study, the impact of Si on brown stripe disease was investigated across susceptible and resistant sugarcane varieties, utilizing four Si concentrations (0, 15, 30, and 45 g per barrel of Na2SiO3·5H2O). Si significantly reduced the incidence of brown stripe disease (7.41-59.23%) and alleviated damage to sugarcane growth parameters, photosynthetic parameters, and photosynthetic pigments. Submicroscopic observations revealed that Si induced the accumulation of silicified cells in leaves, reduced spore accumulation, decreased stomatal size, and protected organelles from B. setariae damage. In addition, Si increased the activity of antioxidant enzymes (superoxide dismutase, peroxidase, and catalase), reduced reactive oxygen species production (malondialdehyde and hydrogen peroxide) and modulated the expression of genes associated with hormone signalling (PR1, TGA, AOS, AOC, LOX, PYL8, and SnRK2), leading to the accumulation of abscisic acid and jasmonic acid and inhibiting SA synthesis. Si also activated the activity of metabolism-related enzymes (polyphenol oxidase and phenylalanine ammonia lyase) and the gene expression of PAL-dependent genes (PAL, C4H, and 4CL), regulating the accumulation of metabolites, such as chlorogenic acid and lignin. The antifungal test showed that chlorogenic acid (15ug µL-1) had a significant inhibitory effect on the growth of B. setariae. This study is the first to demonstrate the inhibitory effect of Si on B. setariae in sugarcane, highlighting Si as a promising and environmentally friendly strategy for managing brown stripe disease.

Ultrasonic treatment alleviated cadmium stress in sugarcane via improving antioxidant activity and physiological and biochemical status.

Cadmium (Cd) is a toxic element that endangers crop growth and affects food safety and human health. Therefore, the study of Cd mitigation technology is important. Ultrasonic treatment can improve crop growth and enhance their ability to resist various abiotic stresses. In this study, the effect of ultrasonic treatment on alleviating sugarcane Cd stress was studied in a barrel experiment using sugarcane varieties 'ROC22' and 'LC05-136' as test materials. Sugarcane buds without ultrasonic treatment and with ultrasonic treatment (20-40 kHz mixed frequency ultrasound for 2 min, dry treatment) were planted in soil with Cd contents of 0, 50, 100, 250, and 500 mg·kg-1. Compared with non-ultrasonic treatment, Ultrasonic treatment significantly increased the activities of antioxidant enzymes in sugarcane, significantly increased the content of osmoregulation substances, significantly reduced the content of superoxide anion (the highest decreases reached 11.55%) and malondialdehyde (the highest decreases reached 20.59%), and significantly increased the expression level of metallothionein (MT)-related genes, with the expression of ScMT1 increased by 8.80-37.49% and the expression of ScMT2-1-5 increased by 1.55-69.33%. In addition, ultrasonic treatment significantly reduced the Cd contents in sugarcane roots, stems, leaves, bagasse, and juice (the highest reduction in Cd content was 49.18%). In general, ultrasonic treatment regulated the metabolism of reactive oxygen species and MT-related gene expression in sugarcane, increased the Cd tolerance of sugarcane, promoted photosynthesis in sugarcane leaves, improved root morphology, enhanced sugarcane growth, and increased cane and sugar yield.

Kynurenine 3-Monooxygenase Gene SsCI51640 Is Required for Sporisorium scitamineum Mating/Filamentation by Regulating cAMP Pathway and Improving Sporidia Environmental Adaptability.

Sugarcane smut is a serious disease caused by Sporisorium scitamineum, which causes significant losses to the sugar industry. It is critical to reveal the molecular pathogenic mechanism of S. scitamineum to explore a new control strategy for sugarcane smut. On the basis of transcriptome sequencing data of two S. scitamineum strains with different pathogenicity, we identified the gene, SsCI51640, which was predicted to encode kynurenine 3-monooxygenase. In this study, we obtained knockout mutants and complementary mutants of this gene and identified gene function. The results showed that the sporidial growth rate and acid production ability of knockout mutants were significantly higher and stronger than those of the wild-type and complementary mutants. The growth of knockout mutants under abiotic stress (osmotic stress and cell wall stress) was significantly inhibited. In addition, the sexual mating ability and pathogenicity of knockout mutants were significantly reduced, while this phenomenon could be restored by adding exogenous cyclic adenosine monophosphate (cAMP). It is thus speculated that the SsCI51640 gene may regulate sexual mating and pathogenicity of S. scitamineum by the cAMP signaling pathway. Moreover, the SsCI51640 gene enhanced the sporidial environmental adaptability, which promoted sexual mating and development of pathogenicity. This study provides a theoretical basis for the molecular pathogenesis of S. scitamineum.

Weed suppression and antioxidant activity of Astragalus sinicus L. decomposition leachates.

Astragalus sinicus L. (milk vetch), a versatile plant that has a soil-enriching effect as green manure, is widely planted in the temperate zone of China. In previous experiments, milk vetch incorporated into the soil as green manure showed potential for goosegrass control. However, "what exactly happens at the chemical level?" and "what are the compounds that are potentially responsible for the phytotoxic effects observed during those previous assays?" In a recent study, in vitro phytotoxicity bioassays and chemical analyses of milk vetch decomposition leachates were carried out to explore the relationship between the temporal phytotoxic effects and the dynamics of chemical composition. For that, milk vetch decomposition leachates with a decay time of 12 h, 9 days, 12 days, 15 days, and 18 days were analyzed for organic compounds by liquid chromatography. The main results were as follows: (1) three compounds with goosegrass suppression potential produced during the decomposed process, i.e., 4-ethylphenol, N-acrylimorpholine, and allyl isothiocyanate. 2-Hydroxyethyl acrylate was present in the 12-h decomposition leachates but was at its highest concentration of 127.1 µg ml-1 at 15 days. (2) The cultures were configured according to the four concentrations of goosegrass-resistant active substances measured in the 15-day decomposition leachate and, as with the 15-day decomposition leachate, the mixture cultures inhibited 100% of goosegrass germination at the high concentrations (≥ 30%), which suggests that these substances have goosegrass suppression potential. (3) The high total phenolic content (302.8-532.3 mg L-1), the total flavonoid content (8.4-72.1 mg L-1), and the reducing activity of the decomposition leachates for different decay times may explain why the incorporation of milk vetch into the soil did not lead to peroxidation of goosegrass in the previous study. (4) Finally, the changes in acid fraction and total content (1.9-4.2 mg ml-1) for different decay times explain the variations in pH of the decomposition leachates, which, when discussed in conjunction with previous studies, may lead to changes in soil nutrient effectiveness and consequently affect crop growth. This study can provide a reference for green weed control research.

First report of ring spot disease on sugarcane caused by Curvularia ischaemi in China.

Sugarcane (Saccharum spp. hybrids) is an economically important crop widely cultivated in the south of China, such as Guangxi, Yunnan, and Guangdong for use as the main raw material of the sugar and alcohol industry (Li and Yang et al. 2015). In July 2021, the sugarcane cultivar GT94-119 planted in Guangzhou (113° 22' E, 23° 09' N), Guangdong province, China showed red to brown ring lesions on the older leaves (Fig.1A). Multiple disease spots gradually merged, eventually leading to leaf wilting and necrosis was observed. Symptoms were present on 11% and 18% of plants in the two observation areas, respectively; however, since symptoms were primarily noted on older leaves, the yield effect was limited. Symptomatic leaf pieces (0.5 × 0.5 cm) were collected and surface-sterilized for 10s in 75% ethanol, followed by 10% NaClO for 30s, washed 3 times with distilled sterile water, blotted dry with sterile tissue, and plated on potato dextrose agar (PDA). The dishes were placed in an incubator at 28 ℃ for 72 h, and the resulting mycelia were transferred to new PDA to obtain pure cultures. The fungal colonies were brownish green, with concentric rings and radial edges (Fig.1B). The hyphae were transparent, separated, and apical hypertrophy (Fig.1C). Conidia were produced within 14 days, ranging in size from 20.0 to 25.5 × 2.5 to 4.5 µm (n=50), upright or curved spindle shaped, clustered or isolated at the end of the conidia stem, with a diaphragm (Fig.1D and E). Eleven isolates purified on PDA were obtained. Morphological identification showed that six of the 11 isolates were similar in morphology and preliminarily identified as Curvularia ischaemi (Mckenzie et al., 1981). One of the above six isolates, named GZ01, was selected for molecular identification. Following the CTAB method for extracting total DNA, the internal transcribed spacer (ITS) region and glyceraldehyde-3-phosphate dehydrogenase (GAPDH) region were amplified and sequenced by using ITS4/ITS5 primer (White et al. 1990) and GDF/GDR primer (Damm et al. 2012), respectively. The amplified sequence was compared to nucleotide sequence reported in GenBank using BLAST search, with 98.49% similarity to Curvularia ischaemi strain CBS 630.82 (GenBank MH861533.1) and 99.81% similarity to the GAPDH sequence of Curvularia ischaemi (GenBank LT715790.1). The phylogenetic tree based on sequence data for the two genes mentioned above and other reference sequences indicated that our isolate (GZ01) was closely identified as Curvularia ischaemi (Fig.2). To obtain a spore suspension of GZ01 for pathogenicity test, spores were cultured (28℃) in PDA for 14 days, washed with sterilized distilled water, and filtered with cheese cloth. The pathogenicity test was carried out in a greenhouse at 28℃ using a spore suspension (1×104 mL-1) and distilled water as inoculation sources. Healthy seedlings of the susceptible sugarcane cultivar LC05-136 were inoculated at the 5 to 6 leaf stage. The spore suspension was evenly sprayed on nine seedlings until the leaves were fully wet, additional nine seedlings were evenly sprayed with the same volume of sterile water to serve as the control. At 14 days after inoculation, all inoculated plants with suspension showed the same symptoms as observed in the greenhouse (Fig.1F), while all plants inoculated with sterile water showed no symptoms. Curvularia ischaemi was again isolated from the infected leaves with symptoms. The results confirm Koch's postulates. Curvularia ischaemi has been previously reported to cause disease on Batiki blusgrass (Ischaemum indicum) (Mckenzie et al. 1981). To our knowledge, this is the first report of C. ischaemi causing ring spot disease on sugarcane in China. For different ecological types of sugarcane areas, whether this disease will occur in the early stage of sugarcane growth and have an impact on sugarcane yield is worth further investigation.

Squalene Monooxygenase Gene SsCI80130 Regulates Sporisorium scitamineum Mating/Filamentation and Pathogenicity.

Sugarcane is an important sugar crop and energy crop worldwide. Sugarcane smut caused by Sporisorium scitamineum is a serious fungal disease that occurs worldwide, seriously affecting the yield and quality of sugarcane. It is essential to reveal the molecular pathogenesis of S. scitamineum to explore a new control strategy of sugarcane smut. Based on transcriptome sequencing data of two S. scitamineum strains Ss16 and Ss47, each with a different pathogenicity, our laboratory screened out the SsCI80130 gene predicted to encode squalene monooxygenase. In this study, we obtained the knockout mutants (ΔSs80130+ and ΔSs80130-) and complementary mutants (COM80130+ and COM80130-) of this gene by the polyethylene glycol-mediated (PEG-mediated) protoplast transformation technology, and then performed a functional analysis of the gene. The results showed that the deletion of the SsCI80130 gene resulted in the increased content of squalene (substrate for squalene monooxygenase) and decreased content of ergosterol (the final product of the ergosterol synthesis pathway) in S. scitamineum. Meanwhile, the sporidial growth rate of the knockout mutants was significantly slower than that of the wild type and complementary mutants; under cell-wall stress or oxidative stress, the growth of the knockout mutants was significantly inhibited. In addition, the sexual mating ability and pathogenicity of knockout mutants were significantly weakened, while the sexual mating ability could be restored by adding exogenous small-molecular signal substance cAMP (cyclic adenosine monophosphate) or tryptophol. It is speculated that the SsCI80130 gene was involved in the ergosterol biosynthesis in S. scitamineum and played an important role in the sporidial growth, stress response to different abiotic stresses (including cell wall stress and oxidative stress), sexual mating/filamentation and pathogenicity. Moreover, the SsCI80130 gene may affect the sexual mating and pathogenicity of S. scitamineum by regulating the ergosterol synthesis and the synthesis of the small-molecular signal substance cAMP or tryptophol required for sexual mating. This study reveals for the first time that the gene encoding squalene monooxygenase is involved in regulating the sexual mating and pathogenicity of S. scitamineum, providing a basis for the molecular pathogenic mechanism of S. scitamineum.

Morphological, agronomical, physiological and molecular characterization of a high sugar mutant of sugarcane in comparison to mother variety.

Sugarcane is a significant crop plant with the capability of accumulating higher amount of sucrose. In the present study, a high sucrose content sugarcane mutant clone, GXB9, has been studied in comparison to the low sucrose mother clone B9 on morphological, agronomical and physiological level in order to scrutinize the variation because of mutation in GXB9 in field under normal environmental condition. The results showed that GXB9 has less germination, tillering rate, stalk height, leaf length, leaf width, leaf area, number of internodes, internode length and internode diameter than B9. Qualitative traits of leaf and stalk displayed significant variation between GXB9 and B9. Endogenous hormones quantity was also showed variation between the two clones. The relative SPAD reading and chlorophyll a, b concentrations also showed variation between GXB9 and B9. The photosynthetic parameter analysis indicated that the GXB9 has significantly higher net photosynthetic rate (Pn), stomatal conductance (gs) and transpiration rate (Tr) than B9. The qRT-PCR analysis of genes encoding enzymes like SPS, SuSy, CWIN, and CeS showed upregulation in GXB9 and downregulation in B9. However, these genes were significantly differentially expressed between the immature and maturing internodes of GXB9. The cane quality trait analysis showed that GXB9 had higher juice rate, juice gravity purity, brix, juice sucrose content and cane sucrose content than B9. The yield and component investigation results indicated that GXB9 had lower single stalk weight, however higher number of millable stalks per hectare than B9, and GXB9 had lower theoretical cane yield than B9. SSR marker analysis showed genetic variation between GXB9 and B9. This study has shown significant variation in the traits of GXB9 in comparison to B9 which advocates that GXB9 is a high sugar mutant clone of B9 and an elite source for future breeding.