蒙城大豆疫霉菌的鉴定及其生理小种

 在安徽省蒙城县对大豆疫霉根腐病的发生情况进行调查。应用选择性培养基对类似大豆疫霉根腐病症状的病株进行病原菌分离,在春大豆蒙城早熟青豆病株上分离到2株疫霉菌PMC1、PMC2和一些Fusarium spp.,在夏大豆上分离到的主要病原菌为Pythium spp.和Fusarium spp.,未分离到疫霉菌。根据疫霉菌分离物PMC1和PMC2形态和生理学特征以及对大豆的专化致病性,2个分离物被鉴定为大豆疫霉菌(Phytophthora sojae Kaufmann&Gerdemann)。应用国际通用鉴别寄主进行生理小种鉴定,PMC1和PMC2的毒力公式分别为1b,1d,3a,3c,5,7和1b,1d,4,5,为新的小种类型,定名为中国6号小种、中国7号小种(CNR-6和CNR-7)。这是首次报道大豆疫霉菌在我国淮北地区存在。     

苎麻疫霉对棉苗致病力的遗传与变异研究

 以分离自江苏省棉铃疫病病组织的苎麻疫霉(Phytophthora boehmeriae Sawada)野生型菌株JS-5为亲本,采用菌丝块创伤接种法测定了苎麻疫霉对棉苗致病力在游动孢子无性系和卵孢子后代的遗传。结果表明,苎麻疫霉对棉苗的致病力在单游动孢子无性系连续两代稳定遗传,而在单卵孢第1代(OG₁)则发生连续性变异。从OG₁中选致病力强、弱2个单卵孢株为亲本,分别建立单卵孢第2代(OG₂)和单游动孢子无性系,并测定其对棉苗的致病力。结果为上述2个单卵孢株的游动孢子后代对棉苗的致病力均与其各自亲本相似,而在它们的单卵孢株群体(即OG₂)中对棉苗的致病力继续发生复杂的连续性变异。上述结果表明,苎麻疫霉对棉苗的致病力可能由细胞核杂合多基因控制。     

大豆疫霉根腐病菌生理小种鉴定及毒性分析

对采自黑龙江省、吉林省的42株大豆疫霉根腐病茵进行生理小种鉴定，其中11株可被分别鉴定为1号、3号和8号生理小种。1号小种为优势小种，3号、8号小种为国内首次报道。其余31株在鉴别寄主上出现中间类型反应无法鉴定小种，但可以划分为12个毒性类型，病原茵群体具有很高的毒性多态性，其中有些菌株毒性较强。     

大豆疫霉菌单孢分离物生物学性状的遗传变异研究

 本文研究了大豆疫霉菌单游动孢子无性分离物和自交单卵孢子分离物的菌丝生长速率、菌落形态、同宗配合性状、产孢量以及对甲霜灵敏感性的遗传变异。结果表明:菌落形态、生长速率和同宗配合性状在单游动孢子后代和自交后代可稳定遗传,控制上述性状的遗传因子是纯合的;大豆疫霉菌的游动孢子产生能力和对甲霜灵的敏感性在单游动孢子后代和自交后代中均发生连续性变异,表明这两种性状可能是数量遗传性状,也可能控制这两种性状的基因为杂合基因或细胞质遗传因子。     

辽宁省辣椒疫霉菌生理小种的生物学特性及生物制剂对辣椒疫病的防效

为了明确辽宁省辣椒疫霉菌Phytophthora capsici优势小种的生物学特性及生物制剂对辣椒疫病的影响,于2013—2014年在辽宁省辣椒种植区采集样品,采用组织分离法获得33个分离物,对分离物进行单孢子囊纯化鉴定,采用单基因鉴别寄主技术鉴定生理小种,研究了不同培养条件对优势小种生长发育的影响,并测定了生物制剂对辣椒疫病的防效。结果表明,菌株Pc-2、Pc-5和Pc-6等23株菌株为3号生理小种,占分离物总数的69.7%;菌株Pc-2在9种供试培养基上均可生长,菌丝生长最适培养基为燕麦片培养基,最适pH为9,温度为28℃;番茄培养基、pH为10和光暗交替有利于其形成孢子囊;pH为7、温度为5℃以及全光照处理是游动孢子释放的最佳条件;游动孢子萌发受酸碱度和光照的影响均不明显,28℃是其萌发的最适温度;在先灌药后接种处理中肃克对辽椒12号疫病的防效为78.2%。研究表明,3号生理小种为辽宁省辣椒疫霉菌的优势小种,低温促进游动孢子的释放,肃克防效优于其它生物制剂。     

辣椒疫霉产毒缺陷与抗药性突变体筛选及其遗传特性

采用MNNG诱变与自交（S1－S3）纯合的方法,从辣椒疫霉的游动孢子群体中,筛选出1株带有抗霜脲氰标记的产毒缺陷突变体、2株抗甲霜灵的产毒突变体。产毒缺陷菌体和产毒菌株均对茄门甜椒致病,但产毒缺陷菌株的致病力降低一半,证明辣椒疫霉的致病显症过程与毒素作用有关,病菌毒素是重要的致病因子。此外,突变菌株的抗药性和产毒缺陷表型在无性游动孢子后代和有性孵孢子后代群体中均可稳定遗传。在姐妹配对F2代卵孢子群体中,辣椒疫霉毒素产生和对甲霜灵的抗性为不完全显性基因所控制,而对霜脲氰的抗性为完全显性基因所控制。     

一种非离子表面活性剂对某些腐霉及疫霉无性时期的抑解作用

本试验探讨非离子表面活性剂Agral对瓜果腐霉,间型腐霉,宽雄腐霉,Pythitim traehilum和烟草疫霉无性时期的影响。结果表明,当Agral浓度达20ug/ml时,可完全抑制几种病菌孢囊或游动孢子的形成,并可使形成的游动孢子在很短时间内丧失游动性。因此,Agral在防治游动孢子传播的根病中有很大的应用潜力。     

大豆疫霉根腐病菌游动孢子的产生因素

 本文对影响大豆疫霉根腐病菌游动孢子的产生因素进行了研究。8 d的菌丝体经蒸馏水浸泡,在25℃下培养72 h可以获得高浓度的游动孢子悬浮液,菌龄越短游动孢子浓度越大,偏酸性的环境有利于游动孢子产生,温度是影响游动孢子形成的重要因素,在0、35℃下均无游动孢子产生,游动孢子产生的适宜温度范围是20~30℃,最佳温度为25℃。     

黑龙江省大豆疫霉根腐病调查与病原分离

１９９６年对黑龙江省东部和中部大豆产区２３个市、县的大豆苗期疫霉根腐病进行了调查、研究,应用ＰＢＮＩＣ疫霉选择性培养基分离大豆疫霉根腐病病原菌,从牡丹江、穆棱、林口和佳木斯豆田具疫霉根腐症状的大豆植株上分离到大豆疫霉根腐病菌,并从根腐病株上单独或与大豆疫霉菌同时分离到终极腐霉菌,研究进一步证实我国黑龙江省有大豆疫霉根腐病。调查发现,大豆疫霉根腐病和终极腐霉根腐病主要发生在土质粘重、土壤含水量高或易积水的田块。     

玉米大斑病菌有性杂交F1代菌株的生理小种鉴定和AFLP分析

玉米大斑病菌是异宗配合真菌，有性杂交有可能增强病菌的致病力，或形成新的致病小种，因此对该病菌有性杂交后代进行致病性测定和遗传多态性分析对控制该病菌的危害具有重要意义。对亲本菌株132、135和它们杂交产生的70个单子囊孢子F1代菌株进行了生理小种鉴定和AFLP（扩增性片段长度多态性）分析。生理小种鉴定结果表明，F1代菌株中与亲本菌株132（23N号小种）属于同一小种类型的占41．4％，与亲本菌株135（23号小种）相同的占20．0％，另外还出现了0、1、2、3、13、123、12N、13N和123N号小种，所占比例分别为2．9％、1．4％、2．9％、2．9％、4．3％、8．6％、1．4％、4．3％和10．0％，说明有性杂交可使后代菌株的致病性发生比较广泛的变异。AFLP分析表明，F1代菌株之间分子遗传相似系数在0．87～0．99之间，其中84．3％的F1代菌株与亲本菌株的遗传相似系数在0．878以上，但与亲本菌株132同源性较强的F1代菌株数目大约是与亲本菌株135的5倍，说明不同菌株具有不同的遗传传递能力。比较生理小种鉴定和AFLP分析结果，发现生理小种分化和AFLP分子遗传多态性间有一定的相关性，但不能完全对应，不存在遗传谱系就等于小种的简单对应关系。     

Variability in Virulence Among Asexual Progenies of Phytophthora infestans

ABSTRACT One hundred two single zoospore isolates of Phytophthora infestans, derived asexually from four parental isolates of US-8 genotype and one isolate of US-1 genotype, were characterized for their virulence phenotypes to determine changes in virulence during asexual reproduction. Potato differentials, each containing a major gene for resistance to P. infestans (R1 to R11), were used to characterize the virulence patterns. Isolates were also characterized for mating type, glucose-6-phosphate isomerase (Gpi) banding pattern, and DNA fingerprints using probe RG57 to determine any genotypic changes in the single zoospore isolates. A subset of these single zoospore isolates was tested for response to mefenoxam to determine any shifts in sensitivity. Results showed that single zoospore isolates derived from parent PI-1 (US-8, 11 isolates) were identical to their parental virulence. Isolates derived from parent PI-191 (US-8, 29 isolates) showed some differences in virulence, mainly toward R8 and R9. Isolates derived from parent PI-126 (US-8, 14 isolates) demonstrated a higher level of virulence diversity. Isolates derived from parents PI-52 (US-1, 28 isolates) and PI-105 (US-8, 20 isolates) showed the highest level of virulence variability among the single zoospore isolates. Mating type, Gpi banding pattern, and DNA fingerprints for the single zoospore isolates were, in most cases, identical to the parental isolates. Single zoospore isolates showed different levels of sensitivity to mefenoxam. Virulence and other genetic changes during asexual reproduction are likely to play a major role in changing the race structure of P. infestans populations. This continuous change in the race structure is a serious problem and now poses a new challenge for utilization of race-specific resistance to manage late blight of potato.     

Genetic and molecular analyses in crosses of race 2 and race 7 of albugo Candida

ABSTRACT The inheritance of avirulence and polymorphic molecular markers in Albugo candida, the cause of white rust of crucifers, was studied in crosses of race 2 (Ac2), using isolates MiAc2-B1 or MiAc2-B5 (metalaxyl-insensitive and virulent to Brassica juncea cv. Burgonde) with race 7 (Ac7), using isolate MsAc7-A1 (metalaxyl-sensitive and virulent to B. rapa cv. Torch). Hybrids were obtained via co-inoculation onto a common susceptible host. Putative F(1) progeny were selfed to produce F(2) progeny. The parents and F(1) progeny were examined for virulence on the differential cultivars B. juncea cv. Burgonde and B. rapa cv. Torch. Segregation of avirulence or virulence of F(2) populations was analyzed on cv. Torch. Putative F(1) hybrids were confirmed by random amplified polymorphic DNA markers specific for each parent. Avirulence or virulence of F (2) progeny to B. rapa cv. Torch suggested 3:1 in each of three populations, supporting the hypothesis of a single dominant avirulence gene. Amplified fragment length polymorphism markers also segregated in regular Mendelian fashion among F(2) progeny derived from two F(1) hybrids (Cr2-5 and Cr2-7) of Cross-2. This first putative avirulence gene in A. candida was designated AvrAc1. These results suggest that a single dominant gene controls avirulence in race Ac2 to B. rapa cv. Torch and provides further evidence for the gene-for-gene relationship in the Albugo-Brassica pathosystem.     

Characterization and Distribution of Two Races of Phialophora gregata in the North-Central United States

ABSTRACT Genetic variation and variation in aggressiveness in Phialophora gregata f. sp. sojae, the cause of brown stem rot of soybean, was characterized in a sample of 209 isolates from the north-central region. The isolates were collected from soybean plants without regard to symptoms from randomly selected soybean fields. Seven genotypes (A1, A2, A4, A5, A6, M1, and M2) were distinguished based on DNA fingerprinting with microsatellite probes (CAT)(5) and (CAC)(5), with only minor genetic variation within the A or M genotypes. Only the A1, A2, and M1 genotypes were represented by more than one isolate. The A genotypes dominated in the eastern Iowa, Illinois, and Ohio samples, whereas the M genotypes were dominant in samples from western Iowa, Minnesota, and Missouri. In growth chamber experiments, isolates segregated into two pathogenicity groups based on their aggressiveness toward soybean cvs. Kenwood and BSR101, which are relatively susceptible and resistant, respectively, to brown stem rot. In both root dip inoculation and inoculation by injecting spores into the stem near the ground line (stab inoculations), isolates of the A genotypes caused greater foliar symptoms and more vascular discoloration than isolates of the M genotypes on both cultivars of soybean. All isolates caused foliar symptoms in both cultivars and in three additional cultivars of soybean with resistance to brown stem rot. Greater differences between the A and M genotypes were seen in foliar symptoms than in the linear extent of xylem discoloration, and greater differences were seen in Kenwood than in BSR101. Inoculation of these genotypes into five cultivars of soybean with different resistance genes to brown stem rot showed a genotype x cultivar interaction. A similar distinction was found in an earlier study of the adzuki bean pathogen, P. gregata f. sp. adzukicola, and consistent with the nomenclature of that pathogen, the soybean pathogens are named the aggressive race (race A) and the mild race (race M) of P. gregata f. sp. sojae.     

Studies on the inheritance of resistance to metalaxyl in Phytophthora infestans

Single-oospore progeny from matings between field isolates of Phytophthora infestans either highly resistant or sensitive to metalaxyl were analysed for fungicide sensitivity in vitro, mating type and, in some cases, allozyme variation at the locus for glucosephosphate isomerase ( GPI-1. ) In each cross the majority of first-generation (F₁) progeny showed intermediate sensitivity to metalaxyl. Frequency distributions were skewed towards sensitivity and a few progeny were either wholly sensitive or resistant phenotypes. Allozyme analysis of F₁ progeny from a cross between parents of Dutch and Mexican origin showed that c. 10% were selfs of both parents and of parental phenotype for metalaxyl sensitivity. The selfs of the A2 but not the Al parent segregated for mating type. Two backcross generations to the metalaxyl-resistant Dutch parent gave unexpected phenotypic frequency distributions and aberrant ratios for genotypes at the GPI-I locus.
Progeny of another backcross between an F₁ isolate of intermediate sensitivity and its sensitive Egyptian parent gave a 1:1 ratio for sensitive: intermediate phenotypes. F₂ progeny from a related sibmating between intermediate phenotypes segregated in a ratio close to 1:2:1 for sensitive: intermediate: resistant phenotypes. Segregation was also observed among sexual progeny of an intermediate self-fertile isolate from the backcross generation but not among progeny of a resistant self-fertile phenotype. Mating type segregated in both cases.
These data are consistent with resistance to metalaxyl in P. infestans being governed by a single nuclear locus exhibiting incomplete dominance. This hypothesis is discussed in relation to the incidence of resistance to metalaxyl in natural populations of P. infestans.     

稻瘟病菌营养体亲和配对筛选及其亲和能力遗传

 在白米玫瑰红培养基上对江苏省的稻瘟病菌Magnaporthe grisea(Hebert) Barr.不同小种间营养体亲和菌株配对组合进行了筛选。当不同小种的菌株对峙接种,在21±1℃、黑暗中培养18 d后,部分配对组合的菌落交界处出现一条肉眼明显可见的菌丝融合带,且具有稳定的重复性。出现菌丝融合带的配对菌株在玻璃纸上对峙微培养2~3 d后,镜检观察到菌丝融合现象普遍存在;未出现明显菌丝融合带的菌株组合经对峙微培养,菌丝融合现象未见或较少。从ZA₄₉、ZG₁、ZF₁和ZD₁ 4个小种的12个菌株中筛选出3对营养体亲和性强的小种间菌株配对组合。以所选菌株为亲本建立单分生孢子无性系,测定营养体亲和能力在单孢后代的遗传。结果是,营养体亲和能力在单孢后代遗传不稳定,与另一亲本的单孢株配对产生融合带的百分率为53%~74%之间。进一步研究发现,来自同一个分生孢子不同细胞的单芽管株与配对菌株的营养体亲和能力相同;亲和能力在单芽管株的单孢株后代继续发生分离。     

Progeny derived from Thanatephorus cucumeris (Rhizoctonia solani) AG-2-2 IV isolates on sugar beet foliage show more clonal diversity in somatic compatibility grouping than those from roots and petioles

Twenty-nine isolates of Thanatephorus cucumeris (Rhizoctonia solani) AG-2-2 IV were collected from the roots, petioles, and leaves of diseased sugar beets in Hokkaido, Japan. We examined the genetic variation of the field isolates using somatic compatibility grouping of progeny (cultured isolates derived from induced basidiospores) based on analysis of hyphal anastomosis reactions (i.e., hyphal perfect fusion) and inter-simple sequence repeats (ISSRs). The number of somatic compatibility groups (SCGs) of single basidiospore isolates was strongly correlated with the host plant tissue from which the parental isolates were obtained. Parental isolates from roots and petioles tended to be genetically heterogeneous and generated plural SCGs, whereas isolates (except for two non-self-anastomosing isolates) from leaves tended to be homogeneous and generated a single SCG. Heterogeneous sibling basidiospore isolates yielded homogeneous progeny within a few generations. These findings were supported by the results of ISSR analysis, which showed that the homogeneous isolates generated progeny with the same genotype, whereas heterogeneous isolates generated progeny with different genotypes. However, like SCGs, ISSR genotypes of heterogeneous progeny tended to be homogeneous within two or three generations. Additionally, we examined clonal diversity during the basidiospore infection process over a 2-year period. A heterogeneous isolate generated a large number of progeny SCGs, thereby increasing clonal diversity. In contrast, progeny SCGs were almost all the same in a homogeneous isolate plot with a few exceptions. These results indicate that infection of T. cucumeris basidiospores play a role in the clonal diversity of AG-2-2 IV isolates, as indicated by progeny SCGs in the field.     

The inheritance of virulence of Phytophthora infestans to potato

Of 31 matings between isolates of P. infestans from several countries, six yielded enough progeny for analysis of inheritance of the virulence phenotype. Virulence was determined in vitro after inoculation of detached leaflets of nine differential lines of potato, each carrying a different gene for resistance. Parents of three matings carried an isozyme marker (glucosephosphate isomerase) which allowed the hybridity of most progeny to be confirmed. Apparently non-hybrid progeny from all three matings were probably selfs or apomicts; these were discarded. The inheritance of virulence in two sib-cross and one backcross family was determined. Patterns of inheritance in F₁ and F₂ indicated the presence of a gene-for-gene interaction in which alleles of a single locus in the pathogen conditioned virulence or avirulence on each differential. Although the hypothesis that avirulence alleles were dominant and virulence alleles were recessive was supported by many of the data, unexpected segregations were obtained. Alternative hypotheses to explain the latter included low aggressiveness in a proportion of the progeny, a second locus inhibiting avirulence in one parent, a different locus in each parent determining avirulence/virulence on one R-gene, and dominance of some alleles determining virulence. Avirulent field isolates appeared to be heterozygous ( A vravr ) rather than homozygous ( Avr Avr ) at avirulence loci. A somatic segregation from avirulence to virulence at three avirulence loci was postulated for one parental isolate. Evidence for linkage of these three loci suggested that the observed somatic segregation resulted from mitotic crossing-over.