Molecular Mapping of the rps1.a Recessive Gene for Resistance to Stripe Rust in BBA 2890 Barley

ABSTRACT Stripe rust, caused by Puccinia striiformis f. sp. hordei, is one of the most important diseases of barley in the south-central and western United States. Growing resistant cultivars is the best approach for controlling the disease. The barley genotype BBA 2890 has all-stage resistance against all races of P. striiformis f. sp. hordei (PSH) identified thus far in the United States. The resistance in BBA 2890 is controlled by a single recessive gene, rps1.a. The objectives of this study were to identify resistance gene analog polymorphism (RGAP) markers for the all-stage resistance gene rps1.a, to map the gene on a barley chromosome using chromosome-specific simple sequence repeat (SSR) markers, and to determine the presence or absence of the flanking RGAP markers for the gene in 24 barley genotypes. Seedlings of the parents and 200 F(8) recombinant inbred lines (RILs) were tested for resistance to pathogen races PSH-14, PSH-48, and PSH-54 in the greenhouse in 2005. Genomic DNA was extracted from the parents and 150 F(8) RILs. The RGAP technique was used to identify molecular markers for the rps1.a gene. Twelve primer pairs generating repeatable polymorphic bands were selected for genotyping the 150 F(8) RILs. A genetic linkage group was constructed for the resistance gene with 13 RGAP markers and four chromosome-specific SSR markers. The four SSR markers mapped the gene on the long arm of barley chromosome 3H. The closest RGAP marker for the resistant allele was within a genetic distance of 2.1 centimorgans (cM). The closest marker for the susceptible allele was 6.8 cM away from the locus. The two closest RGAP markers for the resistant allele detected polymorphisms in 67 and 71% of the 24 barley genotypes when used individually, and detected polymorphism in 88% of the genotypes when used in combination. This information should be useful in incorporating the resistance gene into barley cultivars and in pyramiding the gene with other resistance genes for superior stripe rust resistance.     

The Race-Specific Resistance Gene to Powdery Mildew, MlRE, Has a Residual Effect on Adult Plant Resistance of Winter Wheat Line RE714

ABSTRACT Race-specific resistance genes to powdery mildew have been extensively used in wheat breeding programs, but the complete resistance they provide breaks down when confronted by pathogen isolates with matching virulence. However, when overcome, some race-specific genes have a residual action leading to a reduction of the symptoms. Our objective was to determine if the resistance genes MlRE and Pm4b have a residual effect on adult plant resistance (APR) and on vernalized seedling plant resistance (VPR) in the line RE714. Individuals from two populations (double haploid [DH] and F(3) families) were genotyped for the race-specific genes MlRE and Pm4b and assessed for their resistance under field conditions at the adult plant stage (in 1996 and 1997 for the DH lines and in 1997 for the F(3) families). Vernalized seedlings of the DH population were tested with four powdery mildew isolates. Only the MlRE gene had a significant effect (dominant type) on APR. Neither MlRE nor Pm4b had a significant effect on VPR. The dominant residual effect of the defeated race-specific gene MlRE was a component of APR in the line RE714.     

Association of Mmd1, a Major Gene for Resistance to Melampsora medusae f. sp. deltoidae, with Quantitative Traits in Poplar Rust

ABSTRACT A single gene, Mmd1, which conditions resistance and a necrotic flecking response to a monouredinial isolate of Melampsora medusae f. sp. deltoidae and is presumed to possess the corresponding avirulence gene, was previously shown to segregate 3:1 (resistant to susceptible) in an interspecific hybrid poplar F(2) progeny. Some inoculated clones of the resistant phenotypic class of this progeny were completely resistant and bore no uredinia, but most bore some sporulating uredinia with accompanying necrotic flecking. The dominant allele at the Mmd1 locus in these incompletely resistant clones was significantly associated with reduced uredinial density and diameter and longer latent period in a growth-room assay and with reduced disease incidence and infection efficiency and longer latent period in a leaf-disk assay. However, high clone-mean heritabilities within the susceptible phenotypic class indicated that genes other than Mmd1 also contribute to control of quantitative traits. Leaf age had a significant effect on uredinial density and latent period but not on uredinial diameter in the growth-room assay. All quantitative traits were intercorrelated to varying extents. A principal components analysis (PCA) demonstrated that uncorrelated components associated with uredinial diameter and uredinial density explained two-thirds of the total variation. Since uredinial diameter (PC1) and necrotic flecking are the visual components of an infection-type rating scale, genetic analyses of poplar rust should be based on infection type. Mmd1 is a major gene for resistance associated with a significant effect on all quantitative traits measured. Gene complexes in domesticated, agricultural rust pathosystems known to provide durable resistance consist of similar "pivotal" major genes and inferred ancillary genes or quantitative trait loci.     

谷子品种对粟锈病的抗性鉴定研究

１９９１～１９９５年共对４０１０份谷子品种进行抗粟锈病鉴定，筛选出５９份抗和中抗粟锈病的品种，占鉴定，总数的１．４７％。在５９份中抗以上的谷子品种中，兼抗粟瘟病，粟白发病两种病害的有１份，兼抗粟瘟病的有１０份，兼抗白发病的有４份，兼抗粟黑穗病的有１份，研究表明来自我国长江以南一些省和国外引入的品种中抗类型以上的品种较多，分别占各自鉴定数的２０％和５．９％。     

Evaluation of Wheat Leaf Rust Resistance Genes in 10 Wheat Genotypes

Journal of Plant Diseases and Protection - Wheat leaf rust (Puccinia triticina) is one of the most important plant diseases in the world, and growing resistant cultivars is the most economical,...     

Genetic Variation for Virulence and Resistance in the Wheat-Mycosphaerella graminicola Pathosystem III. Comparative Seedling and Adult Plant Experiments

ABSTRACT Fourteen Dutch Mycosphaerella graminicola isolates were studied for their virulence to 22 wheat cultivars in the seedling stage in an experiment set up as a completely randomized block design with three repetitions. Isolate x cultivar interactions were highly significant. Cluster analyses were applied to select three isolates with significantly different virulence characteristics for both disease parameters. These were retested in the seedling stage and used to inoculate two field experiments that were planted according to a split plot design in 1992 and 1995. Overhead inoculations were conducted after flowering to avoid the effects of plant height; hence, these experiments were intended as monocyclic tests for virulence differences between the isolates. Significant isolate x cultivar interactions were detected in each experiment, demonstrating specificity in the wheat-M. graminicola pathosystem in the adult plant stage under field conditions. The reproducibility of the adult plant data was high. Genetic differences among the isolates were additionally demonstrated by randomly amplified polymorphic DNA (RAPD) patterns, which also showed that no significant contamination of the inoculated plots with the natural M. graminicola population had occurred. Rank correlations between seedling and adult plant data were significant for M. graminicola isolates IPO323 and IPO290, but not for isolate IPO001. Hence, evaluation of resistance and virulence may require seedling, as well as adult plant, tests.     

43个中国小麦品种(系)抗叶锈性研究

 选用12个墨西哥叶锈菌生理小种对43个中国小麦品种(系)所携带的抗叶锈病基因进行了推导,在25个品种(系)中推导出6个抗叶锈基因Lr1,Lr10,Lr13,Lr14a,Lr16和Lr26,9个品种(系)对本试验所使有的12个叶锈菌生理小种都表现感病反应,另有9个品种(系)携带未知的抗叶锈基因。在墨西哥2个地点进行的田间成株期抗叶锈性试验表明,12个品种(系)表现慢叶锈性,在将来的抗病育种中有一定的应用价值。     

不同小麦品种对条锈病的抗性比较

利用抗病品种防治小麦条锈病是一项十分经济有效的措施,为了寻找既抗病又丰产的小麦品种,2007年度我们在九集镇马家洲村一组开展了不同小麦品种抗条锈病效果比较试验,取得了一定效果,现报告如下:1材料与方法1.1试验处理A:郑麦9023;B:鄂麦18;C:西农88;D:绵农6号;E:豫麦49;F:扬辐麦2号。共6个处理,3次重复,小区面积200m2,随机区组排列。1.2试验地情况试验地肥力中等,沙壤土,上茬作物为水稻。试验区域沿河、平坦,属条锈病早发区、常发区和重发区。1.3施肥情况每667m2用碳铵50kg、过磷酸钙40kg、氯化钾7.5kg作底肥,分蘖期每667m2追尿素2.5kg,…     

Amy1, the alpha-Amylase Gene of Aspergillus flavus: Involvement in Aflatoxin Biosynthesis in Maize Kernels

ABSTRACT Aspergillus flavus is the causal agent of an ear and kernel rot in maize. In this study, we characterized an alpha-amylase-deficient mutant and assessed its ability to infect and produce aflatoxin in wounded maize kernels. The alpha-amylase gene Amy1 was isolated from A. flavus, and its DNA sequence was determined to be nearly identical to Amy3 of A. oryzae. When Amy1 was disrupted in an aflatoxigenic strain of A. flavus, the mutant failed to produce extracellular alpha-amylase and grew 45% the rate of the wild-type strain on starch medium. The mutant produced aflatoxin in medium containing glucose but not in a medium containing starch. The alpha-amylase-deficient mutant produced aflatoxin in maize kernels with wounded embryos and occasionally produced aflatoxin only in embryos of kernels with wounded endosperm. The mutant strain failed to produce aflatoxin when inoculated onto degermed kernels. In contrast, the wild-type strain produced aflatoxin in both the endosperm and embryo. These results suggest that alpha-amylase facilitates aflatoxin production and growth of A. flavus from a wound in the endosperm to the embryo. A 14-kDa trypsin inhibitor associated with resistance to A. flavus and aflatoxin in maize also inhibited the alpha-amylase from A. flavus, indicating that it is a bifunctional inhibitor. The inhibitor may have a role in resistance, limiting the growth of the fungus in the endosperm tissue by inhibiting the degradation of starch.     

Different Resistance Mechanisms of Medicago truncatula Ecotypes Against the Rust Fungus Uromyces striatus

ABSTRACT A pathosystem consisting of the model plant Medicago truncatula and the rust fungus Uromyces striatus was characterized. From a collection of 113 mostly European accessions of M. truncatula, the vast majority were found to be susceptible to U. striatus, whereas 5 accessions showed strong resistance reactions. Stomatal surface characteristics, even if partly occluded, did not interfere with the ability of U. striatus germ tubes to infect. After penetration, the resistant ecotypes reacted with various degrees of cell death during different stages of haustorial establishment. Whereas four ecotypes showed a typical hypersensitive reaction by developing necrotic lesions, one ecotype (F11.008) exhibited a prehaustorial type of defense without hypersensitive response. This ecotype may be used as a source of nonhost-type of resistance against U. striatus.     

Genetics of Stem Rust Resistance in Wheat Cvs. Pasqua and AC Taber

ABSTRACT Canadian wheat cvs. Pasqua and AC Taber were examined genetically to determine the number and identity of stem rust resistance genes in both. The two cultivars were crossed with stem rust susceptible line RL6071, and sets of random F(6) lines were developed from each cross. The F(6) lines, parents, and tester lines with single stem rust resistance genes were grown in a field rust nursery, inoculated with a mixture of stem and leaf rust races, and evaluated for rust resistance. The same wheat lines were tested by inoculation with specific stem rust races in seedling tests to postulate which Sr genes were segregating in the F6 lines. Segregation of F(6) lines indicated that Pasqua had three genes that conditioned field resistance to stem rust and had seedling genes Sr5, Sr6, Sr7a, Sr9b, and Sr12. Leaf rust resistance gene Lr34, which is in Pasqua, was associated with adult-plant stem rust resistance in the segregating F(6) lines. Adult-plant gene Sr2 was postulated to condition field resistance in AC Taber, and seedling genes Sr9b, Sr11, and Sr12 also were postulated to be in AC Taber.     

Prehaustorial Resistance against Alfalfa Rust (Uromyces striatus) in Medicago truncatula

The legume species Medicago truncatula is gaining interests as a plant for structural and functional genomics that can be used to identify agronomically important genes in crop legumes. Resistance to the alfalfa rust (Uromyces striatus) was studied in a germplasm collection of M. truncatula. Accessions varied in resistance, as expressed by disease severity, but none showed macroscopically visible necrosis. Histological investigations, in selected lines covering the whole range of resistance reactions, revealed little difference in spore germination and none in orientation of germtubes on the leaf surface. However, appressorium formation on the stoma was significantly reduced in some accessions. Differences in resistance among accessions were more evident once the stoma were penetrated by the infection structures. Resistance was mainly due to a restriction of haustorium formation with varying levels of early abortion of the colonies, a reduction in the number of haustoria per colony, and hampered colony growth. In addition, necrosis of the host cells associated with infection hyphae was detectable in some accessions from the beginning of colony development. This information will be useful for eventual mapping and cloning analyses of resistance genes in M. truncatula that will in turn be useful for understanding other legume/rust interactions.     

持久抗条锈小麦品种抗病性特点分析

利用我国１５个小麦条锈菌主要流行小种和致病类型，测定了国内外７个持久抗条锈小麦品种的抗病性。结果表明，尽管不同持久抗病品种苗期抗病谱有很大差异，但成株期对许多供试菌系均表现有效抗性。抗病温度敏感性试验显示，随着培养温度由低温、常温向高温提高，持久抗性品种抗性逐渐增强，表现为反应型和严重度降低。抗病基因分析表明，持久抗病品种不仅含有温敏型微效抗病基因，而且含有成株抗病基因，它们共同对品种持久抗条锈性起作用     

Frequency of the Ht1 Gene in Populations of Sweet Corn Selected for Resistance to Exserohilum turcicum Race 1

ABSTRACT The possibility that the Ht1 gene or genes tightly linked to Ht1 convey general resistance to races of Exserohilum turcicum that are virulent against Ht1 (i.e., residual resistance) could be useful in sweet corn where the Ht1 gene is present in many commercial hybrids and breeding populations. The objective of this study was to determine if the frequency of the Ht1 gene changed in populations of sweet corn selected for general resistance to E. turcicum race 1, thus conveying residual resistance. Four populations were developed with theoretical initial frequencies of the Ht1 gene of 0, 0.25, 0.25, and 0.5. The populations were advanced by recurrent mass selection with parental control through four or five cycles of selection following inoculation with an Ht-virulent race of E. turcicum (i.e., race 1). Plants from each cycle of each population were evaluated for severity of northern corn leaf blight (NCLB) and chlorotic lesion reactions following inoculation in field and greenhouse trials with either race 0 or 1 of E. turcicum. Recurrent mass selection for general resistance to E. turcicum race 1 reduced the severity of NCLB in all four populations of sweet corn, although the change in the most susceptible population was minimal. Percent gain per cycle was 14.5, 12.3, 14, and 3.7% for populations I, II, III, and IV, respectively. The Ht1 gene did not convey levels of general resistance to E. turcicum race 1 that were substantial enough to be selected for in this population improvement program. There was no apparent selection advantage for resistance to E. turcicum race 1 in the populations that contained the Ht1 gene. The frequency of the Ht1 gene did not differ among cycles of selection within any of the populations in response to improved levels of general resistance to NCLB. The lack of change in frequency of Ht1 in these populations and the similarity in gain per cycle among populations with and without Ht1 lead us to conclude that the Ht1 gene itself did not have a residual effect on resistance.     

Gene Action and Linkage of Avirulence Genes to DNA Markers in the Rust Fungus Puccinia graminis

ABSTRACT Two strains of the wheat stem rust fungus, Puccinia graminis f. sp. tritici, were crossed on barberry, and a single F(1) progeny strain was selfed. The parents, F(1), and 81 F(2) progeny were examined for virulence phenotypes on wheat differential cultivars carrying stem rust resistance (Sr) genes. For eight Sr differentials, phenotypic ratios are suggestive of single dominant avirulence genes AvrT6, AvrT8a, AvrT9a, AvrT10, AvrT21, AvrT28, AvrT30, and AvrTU. Avirulence on the Sr; (Sr 'fleck') differential showed phenotypic ratios of approximately 15:1, indicating epistatic interaction of two genes dominant for avirulence. Avirulence on Sr9d favored a 3:13 over a 1:3 ratio, possibly indicating two segregating genes-one dominant for avirulence and one dominant for avirulence inhibition. Linkage analysis of eight single dominant avirulence genes and 970 DNA markers identified DNA markers linked to each of these avirulence genes. The closest linkages between AvrT genes and DNA markers were between AvrT6 and the random amplified polymorphic DNA marker crl34-155 (6 centimorgans [cM]) AvrT8a and the amplified fragment length polymorphism marker eAC/mCT-197 (6 cM) and between AvrT9a and the amplified fragment length polymorphism marker eAC/mCT-184 (6 cM). AvrT10 and AvrTU are linked at distance of 9 cM.     

Signal Transduction in Resistance to Plant Viruses

Salicylic acid is part of a signal transduction pathway that induces resistance to viruses, bacteria and fungi. In tobacco and Arabidopsis the defensive signal transduction pathway branches downstream of salicylic acid. One branch induces PR-1 proteins and resistance to bacteria and fungi, while the other triggers induction of resistance to RNA and DNA viruses. This virus-specific branch can be activated using antimycin A and cyanide, or inhibited with salicylhydroxamic acid, suggesting a role for alternative oxidase in resistance to viruses. The virus-specific defensive pathway activates multiple resistance mechanisms. In tobacco, salicylic acid induces resistance to systemic movement of cucumber mosaic virus but has no effect on its replication or cell-to-cell movement. However, in the case of tobacco mosaic virus in tobacco, salicylic acid appears to induce interference with the synthesis of viral RNA.     

植物的抗病机理探讨

自然环境中 ,植物与各种病原物如真菌、细菌、病毒等的接触无时无处不在 ,但在大多数情况下 ,植物并不患病而是正常生长。从这种意义上说 ,植物病害的发生率是很低的 ,这是因为植物体内存在着多种抗病途径。1　固有抗病性指病原物侵染植物前 ,植物体已存在的一些抗病因素 ,包括组织解剖结构和抗菌化合物两类 [1] 。1 .1　组织解剖结构植物表皮角质层、细胞壁是病原物入侵的天然屏障。一般认为 :角质层越厚、细胞壁强度越大的植物组织抗病性越强。另外 ,水孔、气孔的多少和构造及开闭的习性也与抗病性相关。如 Mclean,F·T (1 92 1 )比较了…