Host resistances to Aphanomyces trifolii root rot of subterranean clover: first opportunity to successfully manage this severe pasture disease

Subterranean clover (Trifolium subterraneum) is an important pasture legume in Australia (29 million ha) and elsewhere. However, severe pasture decline occurs in association with several root pathogens, including Aphanomyces trifolii, that has been misidentified for decades as A. euteiches until recently confirmed as A. trifolii. A series of controlled environment experiments was undertaken to identify host resistance to A. trifolii in subterranean clover and to compare virulence and phylogeny of isolates. In experiment 1, Dalkeith, Bacchus Marsh, Riverina and Yarloop were the most resistant of 38 cultivars with a percentage disease index (PDI) ≤10 for both tap and lateral roots. Experiment 2 confirmed resistance of Yarloop, but a change in some relative varietal resistances suggested physiological specialization among A. trifolii isolates. Experiment 3 confirmed extensive variation in virulence and physiological specialization across 23 isolates of A. trifolii, with three distinct clades, two of which were distinct from isolates collected previously. Experiment 4 identified host resistance(s) effective against a mixture of 20 A. trifolii isolates, but the most resistant cultivars (Antas, Uniwager, Leura) still showed significant disease. This is the first study to show physiological specialization in A. trifolii and to identify host resistance. This study defines A. trifolii as a significant but largely unknown contributor to severe root disease of subterranean clover in southern Australia. Finally, development and calibration of a new soil commercial DNA test not only enables field quantification of the disease, but development of appropriate breeding, selection and farm management strategies to reduce its impact.     

抗生素对桉树内生细菌群落及青枯病抗性的影响

 为了探明桉树内生细菌群落变化与桉树对青枯病抗性间的关系,试验用加入抗生素的培养基继代培养尾叶桉组培苗,采用PCR-DGGE技术检测了经抗生素处理后桉苗内生细菌的变化,并测定其对青枯病的抗性。结果显示,浓度为60 mg·L^-1的氯霉素和150 mg·L^-1的氨苄青霉素显著降低了桉树组培苗根部内生细菌的数量,但对茎、叶中内生细菌的数量没有影响。DGGE图谱显示,氨苄青霉素处理的桉苗与对照苗的条带基本一致,氯霉素处理后与对照条带有明显的区别,表明氨苄青霉素只影响了桉苗内生细菌的数量,氯霉素使桉苗内生细菌的优势菌发生了变化。对DGGE条带克隆测序和Blast比对发现,A、B、C条带的序列(KU363009、KU363010和KU363011)与GenBank中不可培养细菌的序列(KJ655389.1、KF006350.1和FJ832152.1)相似性分别为100%、99%和99%;D条带序列(KU363012)与不可培养的色球藻属(Chroococcidiopsis sp.)序列(LN878320.1)相似性达到98%。氨苄青霉素和氯霉素处理后,桉苗青枯病的初发病时间与对照相比延后1~2 d,氨苄青霉素处理的桉苗发病率显著低于对照。氯霉素处理的前6 d发病率显著低于对照,之后发病率急剧上升与对照无显著差异。上述结果表明,氨苄青霉素和氯霉素可以减少桉苗根中内生细菌的数量,并推迟桉树青枯病的发病时间。     

猕猴桃溃疡病菌在中国的适生性分析

通过分析猕猴桃溃疡病菌在中国的适生性,为科学制定有效的检疫监管措施,防范其入侵和扩散,确保猕猴桃产业健康发展提供理论依据。本研究根据前人研究结果,采用模糊数学综合评判的原理和方法,定量分析猕猴桃细菌性溃疡病菌(Pseudomonas syringae pv.actinidiae)在我国各个地区的适生性。猕猴桃溃疡病菌在我国最适宜的省份主要分布在四川、云南、贵州、福建、安徽、湖南、湖北、河南、江西、陕西、浙江、重庆、西藏。鉴于该病具有发生发展迅速,危害性强,防治难度大等特点,应当加强猕猴桃种苗等繁殖材料的检疫,加强对果园的管理和病害监测,积极采取有效的防治措施并加强抗病育种方面的研究。     

河北省甘薯镰孢菌腐烂与溃疡病的病原鉴定

为明确河北省甘薯镰孢菌腐烂与溃疡病的症状特点和病原种类,在不同种植区采集储藏期和育秧期病样,描述其症状特征;对病原菌进行分离纯化,采用柯赫氏法则回接验证,依据病原菌的形态特征和基因序列确定病原菌种类。结果表明,在储藏期甘薯发病可导致薯块表面腐烂的占总病薯的59.09%,端部腐烂的占40.91%;薯块带有褐色轮纹病斑的占61.36%,病斑没有轮纹或者轮纹不明显的占38.64%;发病初期薯块内部病斑浅、黑褐色的占27.27%,发病后期薯块内部形成空腔、布满白色菌丝的占72.73%;病斑带有苦味的占59.09%,病斑没有苦味或苦味不明显的占40.91%;在育秧田发病导致薯秧溃疡,表现为主茎基部呈点片发生黑色或者褐色病斑,部分有开裂。分离的病原菌能够同时侵染薯块和薯秧;病原菌单瓶梗产孢,大型分生孢子稍弯,两端钝圆,多数3~7个分隔,顶细胞钝圆,基细胞足跟较明显。其rDNA-ITS、EF-1α、β-tubulin基因序列与茄镰孢菌Fusarium solani的同源性分别为97%、99%和98%。初步确定甘薯镰孢菌腐烂与溃疡病的病原菌为茄镰孢菌F.solani。     

黄芪根腐病生防放线菌筛选鉴定及其优化培养

为获得对黄芪根腐病具有强抗菌活性的生防菌株,采用平板对峙法、抑制菌丝生长速率法对分离于河西走廊盐碱土中的172株放线菌进行拮抗菌的筛选,获得优菌株DA4-4-1,根据其形态、培养特征、生理生化特性和16S rDNA基因序列进行系统发育学分析鉴定,并根据单因素试验与正交试验对培养基条件进行优化。结果表明,菌株DA4-4-1对黄芪根腐病的2种主要致病菌尖孢镰刀菌Fusarium oxysporum和茄腐镰刀菌F.solani均有较好的抑制作用,抑菌圈直径最大分别为20.16 mm和19.33 mm,抑菌率最大分别为34.62%和32.44%。结合16S rDNA基因序列的系统发育分析,将菌株DA4-4-1鉴定为链霉菌属蓝紫链霉菌Streptomyces tuirus。培养基最佳碳源为麦芽糖,氮源为(NH_4)_2SO_4,其优化条件为麦芽糖15 g/L、(NH_4)_2SO_4 0.5 g/L、NaCl 10 g/L、pH 7,在此条件下菌株DA4-4-1的抑菌率可达到86.72%。表明菌株DA4-4-1是1株具有较强抗菌活性的放线菌,具有良好的生物防治和开发应用潜力。     

烟草青枯病菌在烟草根际的定殖及最适发病条件

为明确烟草青枯病菌在根际的定殖情况和最适发病条件,采用绿色荧光蛋白(gfp)标记病原菌,监测其在根际的定殖位置及数量动态变化,并运用荧光定量PCR法测定病原菌在根际和土体土壤的数量,通过响应曲面法探索病原菌致病的临界浓度、发病最适温湿度以及对烟株青枯病发病的影响。结果表明,从贵州省烟田土壤中分离到烟草青枯病病原菌茄科劳尔氏菌Ralstonia solanacearum,gfp-标记的茄科尔劳尔氏菌主要定殖于根尖和根毛区,少数菌落定殖于初生根的延长区,定殖部分表现为非连续性;第10、15、20天根际土壤的茄科劳尔氏菌数量均显著高于土体土壤数量,分别是土体土壤中的1.15、1.33、1.42倍;当土壤中每克土病原菌数量为106.82 CFU、温度为30.55℃、相对湿度为81.42%以上时,烟草青枯病的病情指数最高为91.13,烟株易发生青枯病。表明茄科尔劳尔氏菌在根际土壤中比土体土壤更易定殖,烟草青枯病发病条件主要取决于病原菌浓度、温度以及相对湿度3项指标。     

地块破碎度对软硬变化检测法识别冬小麦分布精度的影响

软硬变化检测作物识别(soft and hard change detection,SHCD)是一种新型的作物识别方法。该研究针对不同耕地地块破碎程度的农业景观地区进行SHCD冬小麦识别,分析地块破碎程度对SHCD冬小麦识别精度的影响。试验结果表明,在种植地块破碎试验区,SHCD的RMSE对分辨率不敏感,均小于0.15,bias也比较小,R2随着检测窗口的增加,相关性逐步升高,达到98%以上。在种植地块规整试验地区,亦能够得到相同试验结论。SHCD方法综合了硬变化(hard change detection,HCD)和软变化(soft change detection,SCD)各自的优势,能够达到稳定且较高的识别精度,不受影像分辨率的影响;有效地解决了SCD在硬变化区(纯净像元)受到光谱不稳定性和HCD在软变化区(混合像元)识别为"0-1"排他性结果的不足,保证了冬小麦的识别精度,为大范围进行冬小麦识别以及其他作物的变化检测识别提供前期的试验基础。     

苜蓿根腐病的病原分离、鉴定与杀菌剂毒力测定

为了解河北苜蓿根腐病病原种类,以便有目的地加以防治,对从河北采集的苜蓿根腐病样品进行了病原分离、鉴定以及致病性和室内毒力测定。根据形态学和核糖体内转录间隔区ITS4和ITS5、延伸因子EF-1H和EF-2T序列作为引物鉴定,分离出的71株致病菌株均为镰孢菌属(Fusarium),其中,木贼镰孢(F.equiseti)55株,尖孢镰孢(F.oxysporum)7株,层出镰孢(F.proliferatum)6株,变红镰孢(F.incarnatum)2株,茄镰孢(F.solani)1株。尖孢镰孢菌株D19-2、层出镰孢菌株S45和茄镰孢菌株Q1的致病性最强。通过含毒介质法测定,结果表明,40%腈菌唑可湿性粉剂(WP)、50%多菌灵WP、嘧环·咯菌腈(37%嘧菌环胺和25%咯菌腈)水分散粒剂(WDG)、50%福美双WP、70%甲基硫菌灵WP和10%苯醚甲环唑WDG对这3个菌株菌丝生长均有较好抑制作用,而80%代森锰锌WP、99%恶霉灵WP、40%菌核净WP的抑制作用较弱。     

产麻痹性贝毒塔玛亚历山大藻共培养菌群的物种多样性研究

产毒赤潮藻与其共生菌的互作关系是揭示麻痹性贝毒(PSP)产生机制的关键,而其共培养菌群的分离及其多样性解析是开展此研究的必要前提。塔玛亚历山大藻(Alexandrium tamarense)是典型产PSP赤潮原因甲藻,为揭示其共培养菌群的物种多样性信息,本文通过免培养海洋微生物高通量测序技术,解析了东海塔玛亚历山大藻(at3#)共培养菌群的种类、丰度及多样性信息。结果表明,其共培养菌群共有87个种与已有数据库匹配,此外尚有5%的未知种。其包含57个属,其中优势菌属5个,分别为Rhodobacteraceae、Marinobacter、Methylophaga、Nitratireductor及Phycisphaera。研究表明东海产PSP塔玛亚历山大藻(at3#)含有物种丰富的共培养菌群,且具有发掘海洋特殊生境微生物新种属的良好潜力。     

Effects of a probiotic (Bacillus subtilis FY99‐01) on the bacterial community structure and composition of shrimp (Litopenaeus vannamei,Boone) culture water assessed by denaturing gradient gel electrophoresis and high‐throughput sequencing

In China, many commercial probiotics are added as water additives into shrimp culture ponds with no sediment. In these ponds, probiotics should have great effects on the bacterial community of culture water at different culture stages. However, the specific effects have not been clarified yet. In this study, the effects of applying the probiotic Bacillus subtilis FY99‐01 on the bacterial community of shrimp (Litopenaeus vannamei) culture water at different culture stages were determined by denaturing gradient gel electrophoresis and high‐throughput sequencing. The water quality parameters, shrimp production, survival rate and feed conversion ratio (FCR) were also analysed. The results showed that application of probiotics improved the water quality by reducing the levels of pH, nitrite and soluble reactive phosphorus, whereas there was no significant effect on shrimp production, survival rate and FCR. Application of probiotics brought no obvious effect on bacterial α diversity while had effect on bacterial β diversity. In addition, probiotics brought different effects on the bacterial community structure at different culture stages, and the effects are stronger in the early and middle phase than in the late phase. Sequencing results demonstrated that probiotics could increase the abundance of Flavobacteria, whereas decrease the abundance of α‐Proteobacteria in the late phase of culture. Besides, principle component analysis results indicated that using probiotics also could increase the abundance of beneficial microalgae (Bacillariophyta and Chlorophyta) and decrease the abundance of Vibrionaceae.