As the world’s largest producer of kiwifruit, China faces significant yield and quality losses due to the widespread occurrence of kiwifruit root rot. To explore alternative biological control strategies for kiwifruit root rot, this study isolated 11 fungal isolates from diseased kiwifruit roots and identified Fusarium solani as the primary pathogen. Additionally, a biocontrol strain, Bacillus subtilis C3, was isolated from the rhizosphere of healthy kiwifruit and shown to significantly inhibit pathogen growth. The B. subtilis C3 strain effectively controls root rot via multiple mechanisms, including direct antagonism, secretion of antimicrobial proteins, promotion of seedling growth, and induction of plant defense enzymes. In pot and field trials, C3 treatment increased root fresh weight by 84.1%, enhanced root SOD and APX activities by 45.7 and 38.2%, respectively, and reduced disease severity. Moreover, C3 improved rhizosphere soil microbial diversity of the Rhizosphere, with the Shannon index increasing from 3.0 to 3.4. Unlike previous studies focusing solely on pathogen suppression, this work highlights the dual role of B. subtilis C3 in controlling root rot and restoring rhizosphere ecological function, offering a green and sustainable biocontrol strategy for kiwifruit production.

The soil environment, crop growth and fruit quality of melons are negatively affected by long-term continuous cropping. It is important to study the mechanism of continuous cropping obstacles and their biological control.

[This corrects the article DOI: 10.3389/fmicb.2021.756329.].

旨在通过盆栽试验,探究生防菌K3不同施用量和施用时期对甜瓜根结线虫的抑制效果.结果表明:(1)接种根结线虫后,K3菌剂在施用量为4 g/kg和8 g/kg时均能够促进甜瓜幼苗的生长,甜瓜幼苗株高、根长、叶片数、最大叶面积、地上鲜质量随K3菌剂施用量的增加而提高,且施用量为8 g/kg时生长最好.同时施用K3菌剂后,甜瓜叶片PAL和PPO酶活性显著提高.在幼苗期(一叶一心期)和伸蔓期(四叶一心期)施用K3菌剂,均能促进甜瓜的生长.(2)施用K3菌剂,能显著抑制根结线虫的发生.施用量为4 g/kg和8 g/kg时,甜瓜线虫根结指数下降为对照的50％和33％.在幼苗期和伸蔓期施用K3菌剂8 g/kg,对根结线虫的相对防效达到100％.因此发生根结线虫的甜瓜土壤中,在定苗后至伸蔓期的任何时间,土壤施用K3菌剂,均可防治甜瓜根结线虫.

Context Root rot is common for kiwifruit (Actinidia chinensis var. diliciosa) plants. It is not easily controlled by chemical methods, and biological agents are an alternative. Aims This study investigated the effects of biological agents on the activity and diversity of soil microorganisms, soil enzyme activity and physicochemical indices during the growth period of kiwifruit plants. Methods There were four treatments: (1) root-rot plants applied with traditional fertiliser (RP); (2) root-rot plants applied with biological agents CY (CY); (3) root-rot plants applied with biological agents CL (CL); and (4) healthy plants with traditional fertiliser (HP). Most samples were taken during the growth period of kiwifruit plants, while activities of defensive-related enzymes and quality of kiwifruits were tested in the fructescence period. Key results CY and CL treatments significantly improved microbial activity, changed microbial structure, increased the diversity, richness and uniformity of microbial species, and altered the relative utilisation ratio of six carbon sources. Soil nutrients of kiwifruit plants with root rot improved with CY and CL compared to RP. Health of kiwifruit plants with CY and CL also improved compared to RP. Activities of defensive-related enzymes in CY and CL treatments were significantly higher than in RP treatment (P < 0.05). Fruit quality indices were also higher than RP. Conclusions CY and CL changed the microbial communities in soil, and improved soil nutrients and plant health. Implications By altering the soil microbial structure, biological agents used to control root rot in kiwifruit plants improved tree health and fruit quality, and provide an alternative to chemical control of root rot.

Bulb rot disease has become one of the main diseases that seriously affects the yield and quality of Fritillaria taipaiensis P.Y.Li (F. taipaiensis). In this study, F. taipaiensis was used as the research object to explore the effect and mechanism of Bacillus subtilis C3 in preventing and curing bulb rot. Through isolation and verification of the pathogenic fungi, we determined for the first time that the pathogenic fungus that causes bulb rot in F. taipaiensis is Fusarium oxysporum. The results of the study showed that B. subtilis C3 inhibits the growth of pathogenic fungi, and the inhibition rate is as high as 60%. In the inhibition mechanism, strain C3 inhibits the conidiogenesis of pathogenic fungi and destroys the cell structure of its hyphae, causing protoplast exudation, chromatin concentration, DNA fragmentation, and ultimately cell death. Among the secondary metabolites of C3, antimicrobial proteins and main active components (paeonol, ethyl palmitate, and oxalic acid) inhibited the growth of F. oxysporum. The molecular weight of the antibacterial protein with the highest inhibition rate was approximately 50 kD. The results of a field experiment on the Taibai Mountain F. taipaiensis planting base showed that after the application of strain C3, the incidence of bulb rot in Fritillaria was reduced by 18.44%, and the ratio of bacteria to fungi in the soil increased to 8.21, which verified the control effect of C3 on Fritillaria bulb rot disease. This study provides a theoretical basis for the use of B. subtilis C3 to prevent and control bulb rot in Fritillaria.

Background and aims Phosphorus-solubilizing bacteria can colonize the surface of plant roots under natural conditions and may enter plant tissues to form endophytic symbiosis. They can convert unavailable phosphorus in the soil into available phosphorus, which can be utilized by plants. The aims of this study were to investigate the chemotaxis of Bacillus cereus YL6 and its migration and colonization sites in Chinese cabbage and to provide some technical support for the subsequent investigation of the physiological regulation mechanism of phosphate-dissolving bacteria in plants. Methods This study demonstrated that the green fluorescent protein marker did not affect the physiological and biochemical properties of YL6. Through the chemotaxis test and pot experiment, the colonization and growth promoting mechanism of YL6 in Chinese cabbage was explored. Results YL6 showed a strong positive chemotactic response to cabbage roots. The addition of organic acids to the soil promotes the colonization of YL6 in Chinese cabbage roots. Colonization of YL6 in Chinese cabbage is a dynamic process that moves from the root surface to root tissues and then up to stems and leaves. Fluorescence microscopy showed that YL6 mainly colonized cortical cells and vascular bundles of various plant tissues and was also observed in mesophyll cells. The proliferative effect of YL6 resulted from the interaction of effective phosphorus, and exuded auxin and gibberellin in the rhizosheath. Conclusion This study enhanced our understanding of the interaction mechanisms between phosphate-dissolving bacteria YL6 and Chinese cabbage. YL6 has the potential for future development into bio-fertilizer for agricultural production.

Background: Melon ( Cucumis melo L.) is one of the most important fruit crops grown in China. However, the yield and quality of melon have significantly declined under continuous cropping. Phenolic acids are believed to be associated with the continuous monocropping obstacle (CMO) and can influence plant microbe interactions. Coumaric acid (CA) is one of the major phenolic acids found in melon root exudates. The objectives of this study were to estimate the elimination of CA by the soil bacterium K3 as well as its effects on mitigating melon CMO. CA degradation was investigated by monitoring the CA retained in the growth medium using high performance liquid chromatography (HPLC). The effects of CA and K3 on rhizosphere soil microbial communities were investigated by the spread plate method and Illumina MiSeq sequencing. Furthermore, the effects of CA and K3 on melon seedling growth were measured under potted conditions. The changes in soil enzymes and fruit quality under K3 amendment were examined in a greenhouse experiment. Result: The results suggest that the addition of CA had the same result as the CMO, such as deterioration of the microbial community and slower growth of melon plants. HPLC and microbial analysis showed that K3 had a pronounced ability to decompose CA and could improve the soil microbial community environment. Soil inoculation with K3 agent could significantly improve the fruit quality of melon. Conclusion: Our results show that the effects of K3 in the soil are reflected by changes in populations and diversity of soil microbes and suggest that deterioration of microbial communities in soil might be associated with the growth constraint of melon in continuous monoculture systems.

AbstractPhosphate-solubilizing bacteria (PSB) have been isolated and used in agricultural production. However, comprehensive research on PSB colonizing the rhizosphere of different plants and promoting plant growth is lacking. This study was conducted to study the growth-promoting effects and colonizing capacity of the PSB strain YL6. The YL6 strain not only increased the biomass of pot-planted soybean and wheat but also increased the yield and growth of Chinese cabbage under field conditions. The promotion of growth in these crops by strain YL6 was related to its capacities to dissolve inorganic and organic phosphorus and to produce a certain amount of indole-3-acetic (IAA) and gibberellin (GA). After YL6 was applied to soybean, wheat and Chinese cabbage, the rhizosphere soil available phosphorus (available P) content increased by 120.16%, 62.47% and 7.21%, respectively, and the plant total phosphorus increased by 198.60%, 6.20% and 78.89%, respectively, compared with those of plants without the addition of YL6. To determine whether the phosphate solubilizing bacteria colonized these plants, YL6 labeled with green fluorescent protein (YL6-GFP) was inoculated into plant rhizospheres. YL6-GFP first colonized the root surface and hairs and then penetrated into intercellular spaces and vessels. Collectively, these results demonstrate that YL6 promoted the growth of three different crops and colonized them in a similar way and therefore provide a solid foundation for probing into mechanisms by which phosphate-solubilizing bacteria affect plant growth.

原花青素是目前发现效果最好的自由基清除剂之一,珊瑚树叶中原花青含量丰富,提取其中的原花青素具有重要经济价值.在单因素试验的基础上,采用响应面试验研究乙醇体积分数、料液比、超声波时间对珊瑚树叶片中原花青素提取率的影响,通过建立超声波辅助提取珊瑚树叶原花青素的多元回归模型,优化原花青素的提取工艺参数.结果表明最佳工艺参数为:乙醇浓度85％,料液比1:40(g/mL),超声时间37 min,在此条件下提取率为16.92％.与模型理论预测值相近,说明该模型回归性良好,试验的拟合程度高,可以用于珊瑚树叶原花青素提取率的预测,为珊瑚树叶中天然原花青素的开发利用提供科学数据.

The continuous cropping obstacles caused by the increase of kiwifruit planting period resulted in imbalance of soil microbial community structure, and decrease of soil enzyme activity and physicochemical indicators, which substantially reduced both the quality and yield of kiwifruit. Under the field conditions, the traditional fertilization of fruit farmers was used as a control (CK) to study the effects of two different microbial fertilizers, JF and KF, which had been verified the growth promotion of kiwifruit aseptic seedlings test, on soil microbial community structure, soil enzyme activities, soil physicochemical characters during different growth periods of kiwifruit (germination period, florescence period, fruit enlargement period, fruit ripening period and next year germination period), as well as fruit quality. The results showed that both fertilizers significantly increased the ratio of bacteria with fungi and the ratio of actinomycetes with fungi in the kiwifruit orchard soil, indicating that they could improve and balance the soil microbial community structure. The enzymes activity in kiwifruit orchard soil with the addition of both fertilizers were significantly higher than that in CK, and among which sucrose, urease, phosphatase and polyphenol oxidase were increased by 17.9%-83.5%, 7.9%-83.0%, 7.3%-45.4% and 8.1%-140.3%, respectively. JF and KF increased soil fertility (the concentrations of available nitrogen, phosphorus, potassium, total nitrogen, total phosphorus, total potassium, and organic matter content significantly increased) and decreased soil pH (a decrease of 0.29 to 0.34). After application of microbial ferti-lizer, the content of vitamin C, soluble sugar, soluble protein and other contents of kiwifruit increased, and the titratable acid content decreased. Therefore, the application of both fertilizers could balance soil microbial community structure, enhance soil fertility, and improve the fruit quality of kiwifruit. Our results provide robust theoretical basis for the application of microbial fertilizers in the old-aged kiwifruit orchards.

[This corrects the article DOI: 10.1371/journal.pone.0200181.].

Phosphate-solubilizing bacteria (PSB) can promote the dissolution of insoluble phosphorus (P) in soil, enhancing the availability of soluble P. Thus, their application can reduce the consumption of fertilizer and aid in sustainable agricultural development. From the rhizosphere of Chinese cabbage plants grown in Yangling, we isolated a strain of PSB (YL6) with a strong ability to dissolve P and showed that this strain promoted the growth of these plants under field conditions. However, systematic research on the colonization of bacteria in the plant rhizosphere remains deficient. Thus, to further study the effects of PSB on plant growth, in this study, green fluorescent protein (GFP) was used to study the colonization of YL6 on Chinese cabbage roots. GFP expression had little effect on the ability of YL6 to grow and solubilize P. In addition, the GFP-expressing strain stably colonized the Chinese cabbage rhizosphere (the number of colonizing bacteria in the rhizosphere soil was 4.9 lg CFU/g). Using fluorescence microscopy, we observed a high abundance of YL6-GFP bacteria at the Chinese cabbage root cap and meristematic zone, as well as in the root hairs and hypocotyl epidermal cells. High quantities of GFP-expressing bacteria were recovered from Chinese cabbage plants during different planting periods for further observation, indicating that YL6-GFP had the ability to endogenously colonize the plants. This study has laid a solid and significant foundation for further research on how PSB affects the physiological processes in Chinese cabbage to promote plant growth.

采用盆栽试验方法,研究解磷细菌肥对普通白菜生长、品质及土壤理化性质的影响.结果表明:施用解磷细菌肥后土壤细菌数量极显著升高,解磷细菌数量随解磷细菌肥施用量的增加而极显著增加,每盆施用45 g解磷细菌肥处理的土壤解磷细菌可达2.05×106 cfu·g-1;同时土壤pH值下降.随着解磷细菌肥施用量的增加,普通白菜地上部磷积累量极显著增加,分别比其相应对照增加121.06％、226.43％和302.09％;地上部鲜质量呈显著增高趋势,分别比其相应对照增加40.19％、52.71％和33.56％;根冠比显著降低,其中每盆施用45 g解磷细菌肥处理的根冠比最低,为0.013.每盆施用45 g解磷细菌肥处理的普通白菜叶片VC、可溶性糖、可溶性蛋白含量及游离氨基酸含量分别比其相应对照增加29.97％、39.94％、30.86％、17.36％,但硝态氮含量降低21.83％.综上,以麸皮为主要载体制作的解磷细菌肥可以极显著提高普通白菜对土壤难溶性磷素的利用,并能显著提高普通白菜的产量和品质.

在金银花生长季节,从西北农林科技大学北校区药用植物园采集金银花根系及根际土壤,采用形态学方法观察研究了VAM真菌侵染其根系的过程,并对其孢子进行了初步的形态学分类.结果表明:(1)VAM真菌侵染金银花根系时,先形成附着胞,然后入侵到皮层细胞,在根内形成线性菌丝、圈状菌丝;菌丝末端产生泡囊;在较粗的菌丝上产生丛枝状菌丝,而且VAM胞内菌丝主干可以穿越相邻的2个皮层细胞,在皮层中连续形成丛枝;VAM菌丝形成丛枝时,首先是胞内菌丝上膨大产生乳状突起,而后在乳状突起上产生较粗的丛枝柄,最后在这些丛枝柄上产生极细的丛枝状菌丝形成成熟的丛枝结构.(2) VAM真菌菌丝在金银花皮层细胞中,有伸展状态、菌丝圈及丛枝状态,所以金银花与VAM真菌形成的菌根是混合型菌根.(3)金银花根际土壤中至少存在3种类型的VAM真菌孢子,因此认为金银花至少可与3种VAM真菌共生.(4)金银花种植地土壤有效磷含量(6.6 mg/kg)显著高于对照空地土壤有效磷含量(3.5 mg/kg);金银花生长旺盛季(4月下旬到5月中旬)VAM真菌对其根系的侵染率高达81％.

解磷菌(phosphate solubilizing bacteria,PSB)可以通过提高土壤有效磷含量而增加作物产量,目前已有许多解磷菌被分离并应用于农业生产中,但关于解磷菌在植物根际中的定殖情况仍缺乏系统性的研究.WY4为本实验室前期从小白菜(Brassica chinensis)根际分离得到的一株高效解磷菌,本研究利用绿色荧光蛋白(green fluorescent protein,GFP)标记技术研究了WY4在小白菜根际及土壤中的定殖规律.与原菌株相比,GFP标记对菌株WY4-GFP生长及解磷活性具有较小影响,同时在促进小白菜生长上WY4-GFP与WY4无显著性差异;WY4-GFP具有持久的定殖能力(接种21d的自然土及30 d的小白菜根际土中,WY4-GFP的定殖数量分别为105和104 CFU/g左右),同时随时间的增加WY4-GFP在土壤中定殖数量逐渐减少;WY4-GFP在小白菜根冠及分生区大量定殖,在伸长区及侧根根毛处数量较少,同时表皮细胞间隙上也有较多的标记菌株.研究结果表明,WY4-GFP在小白菜根际及土壤中具有良好的定殖能力,这为后期深入研究解磷菌与植物间的关系提供了重要参考.

The reaserch was to explore the effects of Bacillus Subtilis and Phosphobacteria ,which supplied to the rooting zone of Kiwi fruit ,on soil physical ,chemical and microbial population in the rhizosphere soil and the fruit quality by orthogonal experiment of two factors and two levels in the field .The physical ,chemical and microbial population of soil ,leaves and fruits were measured respectively .Results showed that the trees dealt with both of Bacillus Subtilis and Phosphobacteria to the rooting zone had the best signification .The soil available P ,ammonium N contents and phos-phatase activity was 1 .93 ,1 .34 and 2 .15 times the amount of the unprocessed .The firmness ,soluble sugar and Vitamin C content was 1 .21 ,1 .06 ,1 .18 times the amount of the unprocessed .The unprocessed titratable acid was 88% of the trees dealt with both of Bacillus Subtilis and Phosphobacteria .The data being analyzed ,fruit quality had a signification positive correlation with organic matter ,available P contents and phosphatase activity .It is considerable to use both of Bacillus Subtilis and Phosphobacteria to improve the soil characteristic and the fruit quality .

将本科生科研训练和植物生理实验教学改革进行融合并轨,针对植物生理学实验教学中存在的问题,对实验教学内容和方法进行改革和探索,将实验教学与科研训练有机结合,充分调动学生的学习主动性和积极性,培养学生综合科研能力和团队协作精神,这是提高大学生实践能力与创新能力的有效途径.

Pot experiments were conducted with pakchoi as test crops to study the effect of application ammonium and nitrate on the phosphate-solubilizing activity of phosphate solubilizing bacteria fermentation broth, growth and quality of pakchoi. Ob-tained results showed that application of single form of nitrogen fertilizer, the effect of fermentation broth (T3) was better than that of the bacteria suspension (T2) and the supernatant (T1). When combined application of fermentation broth and nitrate nitrogen, the efftct was better than that with ammonium nitrogen, which was reflected in the increase of soil available phosphor-us content, more crop yields and better nutritional quality. The better pakchoi nutritional quality included higher contents of Vc, solubilizing sugar, solubilizing protein, cellulose, phosphoruse and less nitrate content. Therefore, phosphate solubiliz-ing bacteria fermentation broth could be used instead of phosphatic fertilizer in pakchoi production, what’s more, nitrate was better nitrogen source for PSB strain W1. So it would have a great increase of pakchoi yield and nutritional quality when combi-ning application with nitrate nitrogen.