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1.
Verticillium albo‐atrum is responsible for considerable yield losses in many economically important crops, among them alfalfa (Medicago sativa). Using Medicago truncatula as a model for studying resistance and susceptibility to V. albo‐atrum, previous work has identified genetic variability and major resistance quantitative trait loci (QTLs) to Verticillium. In order to study the genetic control of resistance to a non‐legume isolate of this pathogen, a population of recombinant inbred lines (RILs) from a cross between resistant line F83005.5 and susceptible line A17 was inoculated with a potato isolate of V. albo‐atrum, LPP0323. High genetic variability and transgressive segregation for resistance to LPP0323 were observed among RILs. Heritabilites were found to be 0·63 for area under the disease progress curve (AUDPC) and 0·93 for maximum symptom score (MSS). A set of four QTLs associated with resistance towards LPP0323 was detected for the parameters MSS and AUDPC. The phenotypic variance explained by each QTL (R2) was moderate, ranging from 4 to 21%. Additive gene effects showed that favourable alleles for resistance all came from the resistant parent. The four QTLs are distinct from those described for an alfalfa V. albo‐atrum isolate, confirming the existence of several resistance mechanisms in this species. None of the QTLs co‐localized with regions involved in resistance against other pathogens in M. truncatula.  相似文献   

2.
Black stem, caused by Phoma macdonaldii , is one of the most important diseases of sunflower in the world. Quantitative trait loci (QTLs) implicated in partial resistance to two single pycnidiospore isolates of P. macdonaldii (MP8 and MP10) were investigated using 99 recombinant inbred lines (RILs) from the cross between sunflower parental lines PAC2 and RHA266. The experimental design was a randomized complete block with three replications. High genetic variability and transgressive segregation were observed among RILs for partial resistance to P. macdonaldii isolates. QTL-mapping was performed using a recently developed high-density SSR/AFLP sunflower linkage map. A total of 10 QTLs were detected for black stem resistance. The phenotypic variance explained by each QTL (R2) was moderate, ranging from 6 to 20%. Four QTLs were common between two isolates on linkage group 5 and 15 whereas the others were specific for each isolate. Regarding isolate-specific and isolate-nonspecific QTLs detected for partial resistance, it is evident that both genetic effects control partial resistance to the disease isolates. This confirms the need to consider different isolates in the black stem resistance breeding programmes. The four SSR markers HA3700, SSU25, ORS1097 and ORS523_1 encompassing the QTLs for partial resistance to black stem isolates could be good candidates for marker assisted selection.  相似文献   

3.
Baseline sensitivity to flumorph, a carboxylic acid amide (CAA) fungicide used to control some oomycetes, was examined using 83 Phytophthora capsici isolates, resulting in a unimodal distribution of effective concentration for 50% inhibition of mycelial growth ranging from 0·716 to 1·363, with a mean of 1·033 ± 0·129 μg mL?1. To assess the potential risk of developing flumorph resistance, 13 flumorph‐resistant mutants of P. capsici were obtained using ultraviolet irradiation. Most of these mutants and their progeny had high levels of fitness, including mycelial growth, sporulation and virulence. The resistance to flumorph changed slightly, either increasing or decreasing, after 10 transfers on agar media. Cross‐resistance was found between flumorph and other CAA fungicides (dimethomorph and iprovalicarb), but not between flumorph and non‐CAA fungicides (cymoxanil, metalaxyl, azoxystrobin and cyazofamid). To investigate the genetics of the flumorph resistance, 619 progeny were obtained by self‐crossing and sexual hybridization. Segregation of sensitivity to fungicide was measured as a ratio of sensitive (S) to resistant (R) isolates. Segregation of the progeny, from self‐crossed isolate PCAS1 (flumorph resistant), was 1:15 in the first generation; and 0:1 or 1:15 in the second generation. In sexual hybridization, segregation of progeny was 0:1 and 1:7 for R × R hybridization; and 1:3 for R × S hybridization. Therefore, the resistance of P. capsici against flumorph was controlled by two dominant genes.  相似文献   

4.
X. Cui  J. Shao  X. Lu  Q. Meng  X. Liu 《Plant pathology》2014,63(6):1365-1373
A total of 1511 isolates of Phytophthora capsici were collected from farms with no history of exposure to the carboxylic acid amide (CAA) fungicides in 32 provinces in China during 2006 to 2013. All 1511 isolates were assayed for mating type and 403 were assayed for sensitivity to dimethomorph (DMM) and metalaxyl. The DMM EC50 values ranged from 0·126 to 0·339 μg mL?1. Both A1 and A2 mating types were detected on the same farms in four provinces and with a 1:1 ratio. Most isolates were sensitive to metalaxyl but a few exhibited intermediate resistance or resistance to metalaxyl. The segregation of DMM resistance and sensitivity among 337 progeny obtained from hybridization or self‐crossing in vitro indicated that the resistance of P. capsici to DMM is controlled by two dominant genes. Eighteen progeny that were derived from hybridization differed in DMM sensitivity and in fitness. Some progeny were as fit as parental isolates. Given the distribution of mating types and therefore the potential for sexual reproduction, the control of resistance by two dominant genes, and the fitness of hybrid progeny, the risk of P. capsici populations developing DMM resistance in China is substantial.  相似文献   

5.
Phytophthora capsici causes root, crown, and fruit rot of vegetable and tropical hosts. Cucumber, zucchini, tomato, and pepper fruits were inoculated using 6-mm-diameter agar plugs of P. capsici, incubated in clear plastic boxes at room temperature (25 ± 2°C and 100% relative humidity), and virulence was estimated by measuring the lesion diameter, pathogen growth diameter, and pathogen sporulation density three (cucumber, zucchini) or four (tomato, pepper) days later. When isolates were grouped by genetic cluster, significant differences in virulence were observed on cucumber and zucchini, with isolates belonging to genetic cluster five causing larger lesions than isolates from genetic cluster six. On tomato, no significant differences were observed for isolates grouped by genetic cluster, but isolates from vegetable crops were generally more virulent than isolates from tropical hosts. Isolates from fabaceous hosts sporulated better on cucumber fruits than isolates from solanaceous hosts. Isolates from vegetable hosts sporulated better on zucchini than isolates from tropical hosts. No significant differences in lesion diameter were noted on pepper when isolates were grouped by host family of origin or genetic cluster, but differences in pathogen sporulation were apparent by host family. Our findings suggest that isolate characteristics such as host family of origin and genetic cluster membership may be used to guide initial isolate selection for cucurbit fruit resistance screening. Final isolate selection should incorporate the phenotypic and genetic diversity of P. capsici, including isolates with differing virulence to the host organ of interest.  相似文献   

6.
Karnal bunt, a disease of wheat, durum, rye, and triticale, is subject to strict quarantine restrictions worldwide. The disease is considered a major threat to food security, due to its use as a non-tariff trade barrier by several wheat-importing countries. In this paper, we analysed seven years of phenotypic data to search for quantitative trait loci (QTLs) associated with resistance in common wheat, validated the QTLs using an independent population, and assessed the potential of genomic selection as a tool for pre-emptive breeding. The QTL study used phenotypic data collected from artificially inoculated field experiments involving two historical Karnal bunt resistance populations: WH542 × HD29 and WH542 × W485. QTL analyses detected four significant (p < 0.001) QTLs on chromosomes 1A, 3A, 4B, and 6B, which explained between 13.7% and 15.7% of the phenotypic variation. A panel of 130 cultivars was used to validate QTL effects. These were genotyped with the same DArTseq protocol, and two of the four QTLs were significantly (p < 0.001) associated with Karnal bunt resistance in the validation panel. The potential of genomic selection was investigated by comparing accuracies of a model trained with all available markers and a model based solely on validated QTL information from the biparental populations. Genomic prediction accuracy, based on the two scenarios, averaged 0.43 and 0.33, respectively, suggesting that even in situations where phenotyping is difficult due to quarantine restrictions, the prospects for pre-emptive breeding against Karnal bunt are encouraging, and resources are now available that will reduce the cost burden.  相似文献   

7.
Blast disease, caused by the Magnaporthe oryzae Triticum pathotype (MoT), is a major concern for wheat production in tropical and subtropical regions. The most destructive symptoms occur in wheat spikes. Infected spikes become bleached due to partial or total sterility, producing small and wrinkled grains. High disease pressure of the disease results in significant yield losses. This study aimed to identify wheat quantitative trait loci (QTLs) conferring resistance to blast disease at the heading stage. A doubled-haploid population was developed from the cross between BRS 209 (susceptible) and CBFusarium ENT014 (resistant, carrying the 2NS translocation). A linkage map was constructed containing 5,381 molecular markers and the inclusive composite interval mapping method was employed for QTL detection. Four QTLs were mapped in response to two MoT isolates. The major QTL identified on the 2AS chromosome explained an average of 84.0% of the phenotypic variation for spike bleaching at 9 days postinoculation and reinforces the potency of the 2NS translocation. Recombination between the distal region of chromosome 2AS and the 2NS marker was found. These results could explain why some lines carrying the VENTRIUP/LN2 marker have a variable reaction to the disease. QTLs on 5B and 7B chromosomes were also identified. Two mechanisms of resistance were hypothesized: the hypersensitive response and resistance to colonization of host tissues. The KASP markers thus developed and simple sequence repeats (SSRs) allocated in QTL regions can be used in the future for the development of wheat blast-resistant cultivars.  相似文献   

8.
Bacterial wilt of forage grasses, caused by the pathogen Xanthomonas translucens pv. graminis (Xtg), is a major disease of forage grasses such as Italian ryegrass (Lolium multiflorum). The plant genotype‐bacterial isolate interaction was analysed to elucidate the existence of race‐specific responses and to assist the identification of plant disease resistance genes. In a greenhouse experiment, 62 selected plant genotypes were artificially inoculated with six different bacterial isolates. Significant differences in resistance were observed among L. multiflorum genotypes (P < 0·001) and in virulence (intensity of disease symptoms) among Xtg isolates (P < 0·001) using the area under the disease progress curve (AUDPC). No significant genotype‐isolate interaction (P > 0·05) could be observed using linear regression modelling. However, additive main effects and multiplicative interaction effects (ammi ) analysis revealed five genotypes which did not cluster close to the origin of the biplot, indicating specific interactions between these genotypes and some bacterial isolates. Simple sequence repeat (SSR) markers were used to identify marker‐resistance associations using the same plant genotypes and bacterial isolates. The SSR marker NFA027 located on linkage group (LG) 5 was significantly associated with bacterial wilt resistance across all six bacterial isolates and explained up to 37·4% of the total variance of AUDPC values. Neither the inoculation experiment nor the SSR analyses revealed major host genotype‐pathogen isolate interactions, thus suggesting that Xtg resistance, observed so far, is effective across a broad range of different bacterial isolates and plant genotypes.  相似文献   

9.
抗氟吡菌胺辣椒疫霉菌株的诱导及其生物学特性的研究   总被引：2，自引：0，他引：2  
 采用菌丝生长速率法, 测定了采自泰安、平谷、杭州和昆明4个地区的42株辣椒疫霉病菌对氟吡菌胺的敏感性, 结果表明, 其EC50值在0.618 ~0.927 μg·mL-1之间, 平均EC50 =(0.743±0.067 7) μg·mL-1。 42个菌株对氟吡菌胺的敏感性分布呈单峰曲线, 未出现抗性的病原菌亚群体, 可将其单峰曲线作为辣椒疫霉对氟吡菌胺的敏感性基线。采用药剂驯化和紫外照射对辣椒疫霉敏感菌株TA进行诱变处理, 获得了2株辣椒疫霉抗氟吡菌胺菌株;利用菌落直径法测定抗氟吡菌胺菌株的遗传稳定性、菌丝生长速率及对其它杀菌剂的交互抗性;通过活体叶盘法测定抗氟吡菌胺菌株和敏感菌株的致病力及产孢子囊能力, 分析抗性和敏感菌株之间生物学特性差异。结果表明, 敏感菌株TA经过氟吡菌胺 48代连续汰选, 其抗性达58.0倍, 获得中抗菌株TA-R;紫外照射获得了抗性达260.6倍的高抗菌株TA-UV, 且其抗性均能稳定遗传;TA-R和TA-UV对甲霜灵、霜脲氰表现出正交互抗性, 对烯酰吗啉、百菌清、代森锰锌和丙森锌无交互抗性;抗氟吡菌胺菌株TA-R、TA-UV与敏感菌株在活体叶盘上的致病力、离体产孢能力均差异不显著(P＜0.05), 但其菌丝生长速率、菌丝干重均低于敏感菌株。  相似文献   

10.
The goal of this research was to identify quantitative trait loci (QTLs) for potato tuber resistance to the soil- and seedborne bacterium Dickeya solani and for tuber starch content, to study the relationship between these traits. A resistant diploid hybrid of potato, DG 00-270, was crossed with a susceptible hybrid, DG 08-305, to generate the F1 mapping population. Tubers that were wound-inoculated with bacteria were evaluated for disease severity, expressed as the mean weight of rotted tubers, and disease incidence, measured as the proportion of rotten tubers. Diversity array technology (DArTseq) was used for genetic map construction and QTL analysis. The most prominent QTLs for disease severity and incidence were identified in overlapping regions on potato chromosome IV and explained 22.4% and 22.9% of the phenotypic variance, respectively. The second QTL for disease severity was mapped to chromosome II and explained 16.5% of the variance. QTLs for starch content were detected on chromosomes III, V, VI, VII, VIII, IX, XI, and XII in regions different from the QTLs for soft rot resistance. Two strong and reproducible QTLs for resistance to D. solani on potato chromosomes IV and II might be useful for further study of candidate genes and marker development in potato breeding programmes. The relationship between tuber resistance to bacteria and the starch content in potato tubers was not confirmed by QTL mapping, which makes the selection of genotypes highly resistant to soft rot with a desirable starch content feasible.  相似文献   

11.
Laboratory studies were conducted to evaluate the risk of developing field resistance to zoxamide, a new Oomycete fungicide which acts on microtubules. Zoxamide, metalaxyl and dimethomorph were compared with respect to the ease with which fungicide‐resistant mutants could be isolated and their level of resistance. Attempts to generate mutants of Phytophthora capsici and P infestans with resistance to zoxamide by mycelial adaptation on fungicide‐amended medium were unsuccessful. Similarly, changes in sensitivity to zoxamide were small (resistance factors ≤2.2) in mutants of P capsici isolated by chemical mutagenesis of zoospore cysts. In parallel experiments with metalaxyl, highly resistant mutants were obtained using both adaptation (P capsici or P infestans) and chemical mutagenesis (P capsici). For dimethomorph, chemical mutagenesis (P capsici) yielded moderately resistant mutants (maximum resistance factor = 20.9), and adaptation (P capsici or P infestans) did not induce resistance. It is proposed that failure to isolate mutants resistant to zoxamide results from the diploid nature of Oomycete fungi and the likelihood that target‐site mutations would produce a recessive phenotype. Our studies suggest that the risk of a highly resistant pathogen population developing rapidly in the field is much lower for zoxamide than for metalaxyl. However, as with any site‐specific fungicide, appropriate precautions against resistance development should be taken. © 2001 Society of Chemical Industry  相似文献   

12.
Clubroot, caused by Plasmodiophora brassicae, is a worldwide disease affecting Brassica. Until now, the detection of genetic factors (QTLs) implicated in clubroot resistance has been based on estimates of disease index. However, as the amount of resting spores released in soil after club disintegration influences clubroot epidemics and resistance‐breaking dynamics, its genetic control may deserve specific attention. In a previous report, it was shown that nitrogen fertilization modulated quantitative partial resistance toward clubroot symptom development in rapeseed. The present work aimed to identify genetic factors involved in the control of resting spore production and to assess their regulation by nitrogen supply. A flow cytometer method was adapted for rapidly estimating resting spore content in a large series of samples. Linkage analysis was conducted to detect QTLs implicated in resting spore production in a Brassica napus doubled haploid progeny from the cross Darmor‐bzh × Yudal. DH lines inoculated with the P. brassicae isolate eH were grown under low‐ and high‐nitrogen supply. Under low‐nitrogen conditions, resting spore production was reduced compared to high‐nitrogen conditions, regardless of genotypes. Genetic architecture controlling resting spore production and clubroot symptom development was similar. Under high‐nitrogen conditions, resting spore production was controlled by one major QTL (C09a) and a few small‐effect QTLs. By contrast, two major QTLs (C02 and C09a) controlled resting spore production under low‐nitrogen conditions. This work highlighted a large see‐saw effect between the relative contribution of the C09a QTL (high effect under high‐nitrogen conditions) and the C02 QTL (high effect under low‐nitrogen conditions), with possible implications in resistance breeding.  相似文献   

13.
Ma HX  Bai GH  Zhang X  Lu WZ 《Phytopathology》2006,96(5):534-541
ABSTRACT Chinese Spring Sumai 3 chromosome 7A disomic substitution line (CS-SM3-7ADS) is highly resistant to Fusarium head blight (FHB), and an F(7) population of recombinant inbred lines derived from the cross CS-SM3-7ADS x Annong 8455 was evaluated for resistance to FHB to investigate main effects, epistasis, and environmental interactions of quantitative trait loci (QTLs) for FHB resistance. A molecular linkage map consists of 501 simple sequence repeat and amplified fragment length polymorphism markers. A total of 10 QTLs were identified with significant main effects on the FHB resistance using MapQTL and QTLMapper software. Among them, CS-SM3-7ADS carries FHB-resistance alleles at five QTLs on chromosomes 2D, 3B, 4D, and 6A. One QTL on 3BS had the largest effect and explained 30.2% of the phenotypic variance. Susceptible QTLs were detected on chromosomes 1A, 1D, 4A, and 4B. A QTL for enhanced FHB resistance was not detected on chromosome 7A of CS-SM3-7ADS; therefore, the increased FHB resistance in CS-SM3-7ADS was not due to any major FHB-resistance QTL on 7A of Sumai 3, but more likely was due to removal of susceptible alleles of QTLs on 7A of Chinese Spring. QTLMapper detected nine pairs of additive-additive interactions at 17 loci that explained 26% phenotypic variance. QTL-environment interactions explained 49% of phenotypic variation, indicating that the environments significantly affected the expression of the QTLs, especially these epistasis QTLs. Adding FHB-enhancing QTLs or removal of susceptible QTLs both may significantly enhance the degree of wheat resistance to FHB in a wheat cultivar.  相似文献   

14.
四倍体马铃薯SSR遗传图谱的构建及晚疫病抗性QTL初步定位   总被引：1，自引：0，他引：1  
利用四倍体马铃薯栽培种‘大西洋'和‘陇薯6号'杂交得到的190个F_1株系为作图群体,构建了四倍体马铃薯的分子遗传图谱,采用区间作图法对马铃薯晚疫病抗性进行了QTL初步定位。结果显示:通过对190个F_1株系进行检测,共发现有7个与晚疫病抗性相关的QTL位点,分别分布在第5、6、7、10和11连锁群上;各位点的LOD值在2.70~10.32之间,其中主效QTL位点3个(LOD≥3.5),可解释17.37%~65.68%的表型变异。获得紧密连锁的特异标记(S183-210、S148-460)为进一步进行QTL精确定位提供了参考。  相似文献   

15.
Two Potato virus Y (PVY) isolates collected in Brazil, PVY‐AGA and PVY‐MON, were identified as recombinants between two parent genomes, PVYNTN and PVY‐NE‐11, with a novel type of genomic pattern. The new recombinants had an ordinary PVYNTN genome structure for approximately 6·7‐kb from the 5′‐end of the genome whereas the 3′‐terminal 3·0‐kb segment had two fragments of NE‐11‐like sequence separated by another small PVYNTN‐like fragment. PVY strains are defined based on the hypersensitive resistance (HR) response in potato indicators. Both PVY‐AGA and PVY‐MON isolates did not induce the HR in potato cultivars carrying Ny, Nc, or (putative) Nz genes and thus were able to overcome all known resistance genes to PVY. Only one of the two isolates, PVY‐AGA, induced a vein necrosis reaction in tobacco. The biological responses of the potato indicators and tobacco defined PVY‐MON as an isolate of the PVYE strain. To distinguish PVY‐AGA and PVY‐MON from other PVYNTN isolates, an RT‐PCR test was developed utilizing new specific primers from the capsid protein gene area and producing a characteristic 955‐bp band. Serological profiling of these PVY isolates with three monoclonal antibodies revealed an unusual reactivity, where one of the two commercial PVYN‐specific monoclonal antibodies did not recognize PVY‐AGA. The ability of these new PVY recombinants to overcome resistance genes in potato producing mild or no symptoms, combined with the lack of serological reactivity towards at least one PVYN‐specific antibody may present a significant threat posed by these isolates to seed potato production areas.  相似文献   

16.
In Calabria (southern Italy), control of crown and root rot of capsicum caused by Phytophthora capsici has relied primarily on soil drenches of metalaxyl. However, severe outbreaks occur every year in glasshouse crops, in which the practice of using plastic mulch and furrow irrigation favours the disease. Single‐hypha isolates of P. capsici collected in Calabria in 1992/1998 were tested in vitro for their level of sensitivity to metalaxyl. Isolates of other species of Phytophthora were used as reference. Fungicide sensitivity was determined by plating mycelial plugs onto potato dextrose agar amended with metalaxyl, at final concentrations ranging from 0.1 to 1000μg mL?1 a.s. Inhibition of radial growth (%) was determined when colonies on unamended medium had covered approximately two‐thirds of the plate. The ED50 values for inhibition of mycelial growth of P. capsici isolates ranged from 1.41 to44.6μg mL?1 a.s. More than 80% of the P. capsici isolates from commercial plastic‐house crops in Calabria showed a moderate level of resistance as they were inhibited less than 60% at 5 μg mL?1 but more than 60% at 100μg mL?1  相似文献   

17.
ABSTRACT A random set of recombinant inbred (RI) lines (F2:7) derived from the cross of the inbred lines Mo17 (resistant) and B73 (susceptible) were evaluated for resistance to southern leaf blight (SLB) caused by Cochliobolus heterostrophus race O. The RI lines were genotyped at a total of 234 simple sequence repeat, restriction fragment length polymorphism, or isozyme loci. Field plots of the RI lines were inoculated artificially with an aggressive isolate of C. heterostrophus race O in each of two growing seasons in North Carolina. Lines were rated for percent SLB severity two (1996) or three (1995) times during the grain-filling period. Data also were converted to area under the disease progress curve (AUDPC) and analyzed using the composite interval mapping option of the PLABQTL program. When means of disease ratings over years were fitted to models, a total of 11 quantitative trait loci (QTLs) were found to condition resistance to SLB, depending upon which disease ratings were used in the analyses. When the AUDPC data were combined and analyzed over environments, seven QTLs, on chromosomes 1, 2, 3, 4, 7, and 10 were found to come from the resistant parent Mo17. An additional QTL for resistance on chromosome 1 came from the susceptible parent B73. The eight identified QTLs accounted for 46% of the phenotypic variation for resistance. QTL x environment interactions often were highly significant but, with one exception, were the result of differences in the magnitude of QTL effects between years and not due to changes in direction of effects. QTLs on the long arm of chromosome 1 and chromosomes 2 and 3 had the largest effects, were the most consistently detected, and accounted for most of the phenotypic variance. No significant additive x additive epistatic effects were detected. These data support earlier reports of the polygenic inheritance of resistance to SLB of maize.  相似文献   

18.
为选育抗倒伏玉米品种,挖掘甜玉米茎秆强度相关性状的数量性状基因座（quantitative trait locus,QTL）,应用复合区间作图法以甜玉米组合T49×T56的F2为作图群体,通过测定F2：3家系的茎秆穿刺强度、茎秆抗压强度和茎秆弯折性能3个性状进行相关性状的QTL定位。结果表明,遗传连锁图谱包含153个SSR标记位点,覆盖玉米基因组1 199.1 cM,平均图距7.83 cM。3个性状共检测到10个QTL,其中与茎秆穿刺强度相关的2个QTL位于第3、7染色体上,解释11.81%和22.15%的表型变异,与茎秆抗压强度相关的4个QTL位于第1、3、7染色体上,单个QTL可解释3.68%~33.26%的表型变异,与茎秆弯折性能相关的4个QTL位于第3、6、8染色体上,单个QTL可解释3.55%~18.58%的表型变异。第7染色体检测到1个同时控制茎秆穿刺强度和茎秆抗压强度2个性状的QTL,位于umc1015~umc1987标记区间,分别可解释11.81%和33.26%的表型变异,第3染色体检测到1个同时控制茎秆穿刺强度、茎秆抗压强度、茎秆弯折性能3个性状的QTL,位于umc1400~dupssr23标记区间,分别可解释22.15%、13.27%和18.58%的表型变异。3个茎秆强度性状共同检测到的主效QTL,可在育种实践中用于分子标记辅助选择和抗倒伏玉米品种的选育。  相似文献   

19.
The plasmodiophoromycete Polymyxa betae is an obligate root parasite that transmits Beet necrotic yellow vein virus (BNYVV), the cause of sugar beet rhizomania disease. Currently, control of this disease is achieved through the use of cultivars with monogenic (Rz1) partial resistance to the virus. To improve the level and durability of this resistance, sources of resistance to the virus vector, P. betae, were sought. Over 100 accessions of the wild sea beet (Beta vulgaris ssp. maritima) from European coastal regions were evaluated for resistance in controlled environment tests. Quantification of P. betae biomass in seedling roots was achieved using recombinant antibodies raised to a glutathione‐s‐transferase expressed by the parasite in vivo. Several putative sources of resistance were identified and selected plants from these were hybridized with a male‐sterile sugar beet breeding line possessing partial virus resistance (Rz1). Evaluation of F1 hybrid populations identified five in which P. betae resistance had been successfully transferred from accessions originating from Mediterranean, Adriatic and Baltic coasts. A resistant individual from one of these populations was backcrossed to the sugar beet parent to produce a BC1 population segregating for P. betae resistance. This population was also tested for resistance to BNYVV. Amplified fragment length polymorphism and single‐nucleotide polymorphism markers were used to map resistance quantitative trait loci (QTL) to linkage groups representing specific chromosomes. QTL for resistance to both P. betae and BNYVV were co‐localized on chromosome IV in the BC1 population, indicating resistance to rhizomania conditioned by vector resistance. This resistance QTL (Pb1) was shown in the F1 population to reduce P. betae levels through interaction with a second QTL (Pb2) found on chromosome IX, a relationship confirmed by general linear model analysis. In the BC1 population, vector‐derived resistance from wild sea beet combined additively with the Rz1 virus resistance gene from sugar beet to reduce BNYVV levels. With partial virus resistance already deployed in a number of high‐yielding sugar beet cultivars, the simple Pb1/Pb2 two‐gene system represents a valuable additional target for plant breeders.  相似文献   

20.
Mycosphaerella species that cause the ‘Sigatoka disease complex’ account for significant yield losses in banana and plantain worldwide. Disease surveys were conducted in the humid forest (HF) and derived savanna (DS) agroecological zones from 2004 to 2006 to determine the distribution of the disease and variation among Mycosphaerella species in Nigeria. Disease prevalence and severity were higher in the HF than in the DS zone, but significant (P < 0·001) differences between agroecological zones were only observed for disease severity. A total of 85 isolates of M. fijiensis and 11 isolates of M. eumusae were collected during the survey and used to characterize the pathogenic structure of Mycosphaerella spp. using a putative host differential cultivar set consisting of Calcutta‐4 (resistant), Valery (intermediate) and Agbagba (highly susceptible). Area under disease progress curve (AUDPC) was higher on all cultivars when inoculated with M. eumusae than with M. fijiensis, but significant (P < 0·05) differences between the two species were only observed on Valery. Based on the rank‐sum method, 8·3% of the isolates were classified as highly aggressive and 46·9% were classified as aggressive. About 11·5% of all the isolates were classified as least aggressive, and all of these were M. fijiensis. The majority of M. eumusae isolates (seven out of 11; 64%) were classified as aggressive. A total of nine pathotype clusters were identified using cluster analysis of AUDPC. At least one M. fijiensis isolate was present in all the nine pathotype clusters, while isolates of M. eumusae were present in six of the nine clusters. Isolates in pathotype clusters III and V were the most aggressive, while those in cluster VIII were the least aggressive. Shannon’s index (H) revealed a more diverse Mycosphaerella collection in the DS zone (H = 1·81) than in the HF (H = 1·50) zone, with M. fijiensis being more diverse than M. eumusae. These results describe the current pathotype structure of Mycosphaerella in Nigeria and provide a useful resource that will facilitate screening of newly developed Musa genotypes for resistance against two important leaf spot diseases of banana and plantain.  相似文献   

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