Identification and characterization of seedling and adult plant resistance to Puccinia hordei in Chinese barley germplasm

Leaf rust of barley, caused by Puccinia hordei, occurs in all barley‐growing regions of Australia causing significant yield losses under epidemic conditions. The development and use of resistant cultivars are the most economical and environmentally sustainable method to control leaf rust which in turn relies on ongoing efforts to identify and characterize new sources of resistance. The aim of this study was to postulate known genes and/or identify new sources of resistance to P. hordei. Fifty‐two genotypes were assessed at the seedling and adult plant growth stages. On the basis of multipathotype tests, 39 genotypes lacked detectable seedling resistance, and nine were postulated to carry the genes Rph2, Rph4, Rph12 and Rph19 singly. Four genotypes carried uncharacterized seedling resistance; however, the gene(s) present in each were ineffective to at least one of the pathotypes used. Field tests at the adult plant growth stage revealed the presence of adult plant resistance (APR) in 12 genotypes. Tests of allelism and marker analysis indicated that resistance genes present in these genotypes were independent of the APR gene Rph20.     

Comparison of resistance of triticale,wheat and spelt to septoria nodorum blotch at the seedling and adult plant stages

Summary On average, the cereal species studied were susceptible to septoria nodorum blotch (SNB), except for spring triticale on leaf and head and winter titicale on leaf, that appeared to be significantly more resistant, than the other ones.In all three species the SNB response of the adult plants was to a limited extent only predicted by the reaction on first leaf seedlings. In most cases it was impossible to predict the response to SNB of adult plants on the basis of seedling reaction. Correlations between the adult plant stage and the seedling stage, or detached seedling leaves, appears not to be sufficient for use in practical breeding work. A reversal of reaction to SNB was even found between the above growth stages in studied spring and winter wheat varieties.     

Inhibition of rice (Oryza sativa L.) seedling elongation by a Pseudomonas fuscovaginae toxin

Summary The effects of a Pseudomonas fuscovaginae toxin, on germination, root formation and seedling elongation, after soaking rice grains in the toxin prior to sowing, was investigated. The toxin enhanced germination, but had no apparent effect on the number of roots of the seedlings. It induced a drastic inhibition of seedlings elongation correlated to varieties susceptibility to the disease in the rice field. After denaturation of the bioactive compounds of the extract, all the previously observed effects were lost. Using the toxin and the present test, could be a reliable tool for screening genotype susceptibility to P. fuscovaginae disease.     

Reaction of triticale,wheat and rye accessions to graminaceous Fusarium spp. infection at the seedling and adult plant growth stages

Summary Pathogenicity of 20 isolates of 12 Fusarium species recovered from triticale seed against seedlings of 14 varieties of winter cereals (triticale, wheat, and rye) was tested. The most pathogenic inoculum was a mixture of isolates (a composite isolate) of all the species. The following species were individually the most pathogenic: F. avenaceum, F. culmorum, F. sambucinum var. coeruleum, and F. graminearum. Winter triticale was more resistant to seedling blight than rye but more susceptible than wheat.Also reactions of 31 winter and 12 spring varieties of cereals to head inoculation with a composite isolate of 4 Fusarium spp. (F. avenaceum, F. culmorum, F. graminearum, and F. sambucinum var. coeruleum) was studied. In comparison to other cereals of similar type winter and spring wheat appeared to be the most susceptible while winter rye reaction was comparable to winter triticale. Spring and winter triticale varieties responded to head infection intermediately.There was no significant correlation between seedling and head reactions to infection with Fusarium spp. for winter rye and triticale. For winter wheat a negative trend was found. The above findings imply that screening of cereals at the seedling stage can not be used to predict the resistance to head blight. Nevertheless, resistance at the stage is highly desirable to prevent excessive damage of the crops due to the seedling blight incited by Fusarium spp..     

Expression of resistance to downy mildew at cotyledon and adult plant stages in Brassica oleracea L.

This research compared the expression of resistance to downy mildew at cotyledon and adult plant stages in seven Brassica oleracea genotypes against two P. parasitica isolates of different virulence. Seven day old seedlings were dual inoculated under controlled environment by depositing two 10 μl droplets of a spore suspension of a different isolate on each cotyledon and the interaction phenotype (IP) evaluated 7 days later using a 0–5 scale of increasing susceptibility. The seedlings were transplanted to 16 cm pots and grown in the greenhouse for 110 days (15 to 28 leaves). Adult plants were tested using a single leaf inoculation method that allowed the same plant to be simultaneously inoculated with the two P. parasitica isolates. Leaves were scored 10 days after inoculation using a 0–5 scale of increasing susceptibility. The inoculation of the same plant with the two isolates produced different combinations of cotyledon (CT) and adult-plant (AP) interaction-phenotype according to the genotype. CrGC 3.1 was susceptible at CT and AP stages, ‘Algarvia’ resistant at CT and AP stages, and broccoli ‘A’ susceptible at CT and resistant at AP stage against the two isolates. ‘Murciana’ and broccoli ‘B’ were differential at CT and AP stages. Savoy and Shetland cabbages were differential at CT stage and resistant to both isolates as adult plants. Cotyledon resistance could not be used to predict adult-plant resistance since the two types of resistance were very poorly correlated. Resistance can be race specific either at cotyledon or at adult-plant stage. This revised version was published online in July 2006 with corrections to the Cover Date.     

Evaluation of seedling and adult plant resistance to leaf rust in European wheat cultivars

Summary A set of 105 European wheat cultivars, comprising 68 cultivars with known seedling resistance genes and 37 cultivars that had not been tested previously, was tested for resistance to selected Australian pathotypes of P. triticina in seedling greenhouse tests and adult plant field tests. Only 4% of the cultivars were susceptible at all growth stages. Twelve cultivars lacked detectable seedling resistance to leaf rust, and among the remaining cultivars, 10 designated genes were present either singly or in combination. Lr13 was the most frequently detected gene, present in 67 cultivars, followed by the rye-derived gene Lr26, present in 19 cultivars. Other genes present were Lr1, Lr3a, Lr3ka, Lr10, Lr14a, Lr17b, Lr20 and Lr37. There was evidence for unidentified seedling resistance in addition to known resistance genes in 11 cultivars. Field tests with known pathotypes of P. triticina demonstrated that 57% of the cultivars carried adult plant resistance (APR) to P. triticina. The genetic identity of the APR is largely unknown. Genetic studies on selected cultivars with unidentified seedling resistances as well as all of those identified to carry APR are required to determine the number and inheritance of the genes involved, to determine their relationships with previously designated rust resistance genes, and to assess their potential value in breeding for resistance to leaf rust.     

Evaluation of seedling and adult plant resistance to stem rust in European wheat cultivars

A total of 105 European wheat cultivars were assessed for seedling and adult plant resistance (APR) to stem rust using an array of Australian isolates of Puccinia graminis f. sp. tritici. Twenty-seven cultivars were susceptible at both seedling and adult plant growth stages. Twelve catalogued seedling stem rust resistance genes (Sr7b, Sr8a, Sr8b, Sr9b, Sr9g, Sr11, Sr15, Sr17, Sr29, Sr31, Sr36 and Sr38) were detected in the remaining cultivars, and 13 cultivars carried additional seedling resistance genes that could not be postulated with the isolates used. Low levels of APR to stem rust were found in the cultivars Artaban, Forno, Mec, Mercia, Pandas and Vlada. Although the genetic identity of this APR was not determined, it was clear that the only designated stem rust APR gene Sr2 was not present in any of the cultivars tested based on the absence of the linked traits seedling chlorosis and pseudo black chaff. One of these cultivars, Forno, is believed to carry the leaf rust APR gene Lr34, previously reported to be associated with improved resistance to stem rust. A detailed genetic characterisation of the APRs in these cultivars will be needed to understand their modes of inheritance and relationships with catalogued stem rust resistance genes. Such knowledge may help in developing cultivars with effective gene combinations that confer higher levels of protection.     

Inheritance of plant elongation ability at seedling stage in rice

Summary In a comparison of methods to study inheritance of plant elongation ability, 15-, 20-, 25-, 30-, and 35-day-old F₂ populations of a cross between Baisbish (floating variety) and IR42 (nonelongating semidwarf modern variety) of rice, (Oryza sativa L.) were subjected to 65 cm water depth for 7 days. Frequency distribution of plant height before and after submergence was obtained. Bimodal curves in 15-, 20- and 25-day-old populations gave good fits to 9:7 elongating: nonelongating plants, suggesting that elongation was due to two dominant complementary genes. Segregation in the 30-day-old population was not clear-cut. A seedling age of 20 days was subsequently chosen for further studies.Two F₂'s involving floating rice and a nonelongating semidwarf; four F₂'s involving floating rice and an elongating semidwarf; and two F₂'s involving elongating and nonelongating semidwarf parents were studied with 20-day-old seedlings in the same way. Floating rice combinations with nonelongating semidwarf parents as well as with elongating semidwarf parents segregated into 9:7 elongating: nonelongating ratio. It is possible that because elongating and nonelongating dwarf parents did not differ much in elongation ability at seedling age, their combination with floating rice parents provided similar segregation. The F₂ distributions for height in elongating and nonelongating dwarf cross combinations were continuous with one peak.Genetic constitution of parents proposed are Sd1 Sd1 El El for floating parents, sd1 sd1 El El for semidwarf elongating, and sd1 sd1 el el for dwarf nonelongating.     

抗稻瘿蚊种质资源的筛选与利用

稻瘿蚊是对水稻为害极为严重的害虫,稻亩受害后叶鞘愈合成葱管状(俗称标葱),不能成穗,影响产量甚至颗粒无收。据农业部全国植保总站1994年不完全统计,该虫在国内发生面积约98万hm~2,损失稻谷达10亿kg。1992年起上升为水稻主要害虫之一,现北纬28°以南已     

Genetic variation of grain sorghum germplasm for resistance to Pseudomonas andropogonis

Pseudomonas andropogonis is the causal agent of bacterial leaf stripe of sorghum (Sorghum bicolor (L.) Moench). Fifty grain sorghum accessions were evaluated for genetic variation to P. andropogonis over a 2-year period. Plants were inoculated at the 7 to 8 leaf stage of juvenile growth with an Idico filler-plug gun calibrated to deliver one ml of inoculum. Disease severity ratings were noted 2 weeks after inoculation on a 0 to 5 scale. For 1993 and 1994, disease severity ratings were significantly different (P < 0.01) among accessions and groups of resistant, intermediate, and susceptible germplasm. Significant differences (P < 0.05) were also observed between years. Resistant accessions included SC 326-6, SC 414-12E, BTX 378, B35-6, and TX 2862. Susceptible entries included TX 2767, TX 430, TAM 428, BTx 623, R 9117, and 90B2662. This revised version was published online in July 2006 with corrections to the Cover Date.     

Identification and characterization of seedling and adult plant resistance to <Emphasis Type="Italic">Puccinia hordei</Emphasis> in selected African barley germplasm

A collection of 112 African barley accessions were assessed for response to Puccinia hordei in seedling greenhouse tests using 10 pathotypes and in adult plant field tests over three successive field seasons in Australia. One of the 10 pathotypes (viz. 5457P+) used in seedling tests was also used in field tests to allow assessment of the presence of adult plant resistance (APR) in lines that were seedling susceptible to this pathotype. The seedling resistance genes Rph1, Rph2, Rph3, Rph9.am and Rph9.z were postulated in a number of accessions, singly and in various combinations, with Rph2 and Rph9.z being the most common. Twenty-six accessions carried seedling resistance that was either uncharacterized or could not be determined using the 10 P. hordei pathotypes. One accession carried high levels of APR and 11 accessions showed moderate levels of APR, all of which were susceptible to all P. hordei pathotypes at the seedling stage. All barley accessions were genotyped for the presence of marker alleles that are closely linked to the APR genes Rph20 and Rph23 (bPb-0837 and Ebmac0603, respectively). No accession was positive for bPb-0837, suggesting that Rph20 is not frequent in African germplasm. Thirteen accessions were postulated to carry Rph23 based on the presence of the marker allele Ebmac0603 found in Yerong (Rph23), and 10 out of the 11 accessions with moderate APR lacked the bPb-0837 and Ebmac0603 marker alleles, indicating that they likely carry new uncharacterized APR genes. Inheritance studies were performed using populations derived from four of the accessions that carried APR (Clho 9776, Clho 11958, Mecknes Maroc and Sinai) by crossing with the susceptible barley genotype Gus. Chi squared analysis of the phenotypic data from F₃ populations suggested that CIho9776 carried a single APR gene and CIho11958, Mecknes Maroc and Sinai each carried two genes for APR to leaf rust.     

Assessment of cold tolerance at early developmental stages and allelic variation at candidate genes in South American rice germplasm

Rice is susceptible to cold during early developmental stages. Most tolerant cultivars have been developed for other conditions than those occurring in South America’s rice growing areas, or their grain type is not suitable for the local markets. If locally adapted varieties were available, growers could anticipate sowing date, making flowering time coincide with the moment of maximum solar radiation and increasing yields. In this work, 116 rice inbred lines and varieties of diverse origin within the South American gene pool were tested for seedling survival and germination percentage under low temperature in controlled conditions. As a result, lines used as controls responded as expected, whereas lines with similar behavior to controls, intermediate between susceptible and tolerant controls and more extreme than controls were detected at both seedling and germination stages. Allelic variation at candidate genes OsGSTZ1, OsGSTZ2 and OsCDPK13 was analyzed in a subset of ten contrasting lines. Ten out of thirty-four polymorphisms detected in all three genes were associated with cold tolerance in these lines. A functional marker, designed from an aminoacid-changing SNP found in gene OsGSTZ2, was tested in the 116 lines. As a result, a tight association was observed between cold tolerance and marker score. In conclusion, wide variability for cold tolerance at early developmental stages has been detected in rice advanced breeding materials that are adapted to local growing conditions. Also, a functional marker tightly associated with the trait is available for performing marker assisted selection.     

Sources of seedling and adult plant resistance to Puccinia striiformis f.sp. tritici in European wheats

One-hundred-and-forty-one wheat cultivars were tested at the seedling stage using up to 16 yellow rust isolates of diverse origin. Sixty-five resistance spectra were observed, including 20 spectra defined by differential cultivars with specific genes for resistance to Puccinia striiformis f.sp. tritici . Yr1 , Yr2 , Yr3 , Yr4 , Yr6 , Yr9 , Yr15 , Yr17 , Yr25 , Yr32 , and several additional sources of resistance were recognized. The resistance spectra were often conferred by Yr -genes and resistance factors with an unresolved genetic basis. All cultivars carried resistance and 27 had resistance for which no fully compatible isolate was detected. Yr15 was detected in four cultivars, a resistance from wild Emmer not previously reported in commercial wheat. There was no indication of Yr5 , Yr7 , Yr8 , Yr10 and Yr24 in any cultivar. Most cultivars were also investigated in field nurseries using up to nine isolates of Danish origin. Fifty-six cultivars displayed high or very high levels of resistance to any isolate in the field, and 18 of these showed full compatibility at the seedling stage to at least one isolate, i.e. revealing components of adult plant resistance.     

Inheritance of seedling and adult plant resistance to leaf rust of selected Australian spring and English winter wheat varieties

Genetic studies were conducted to gain an understanding of the inheritance of adult plant resistance (APR) to leaf rust in six common wheat varieties. The Australian varieties ‘Cranbrook’ and ‘Harrier’ each carry two genes for APR to leaf rust. These genes are genetically independent of the seedling resistance genes Lr23 and Lrl7b, carried by the respective varieties. Adult plant resistance in ‘Suneca’ was conferred by at least two genes, in addition to the seedling genes Lr1 and Lrli. It is likely that the APRs in ‘Cranbrook’, ‘Harrier’ and ‘Suneca’ are conferred by uncharacterized gene(s). Tests of allelism confirmed that seedling resistances in the varieties ‘Avocet R’, ‘Hereward’, ‘Moulin’ and ‘Pastiche’ are conferred by Lrli. Adult plant resistance in the variety ‘Hereward’ was inherited monogenically, whereas varieties ‘Moulin’ and ‘Pastiche’ each carried two dominant genes. On the basis of rust specificity and pedigree analysis, it would seem likely that the APR genes in ‘Hereward’, ‘Moulin’ and ‘Pastiche’ are also currently uncharacterized.     

Genetic analysis of salt tolerance at seedling and reproductive stages in rice (Oryza sativa)

Salinity is a major abiotic stress that limits rice production across rice areas as high‐yielding modern rice varieties are generally sensitive to salt stress. The study was conducted to deduce heritability and combining ability estimates of rice for various morphological and physiological traits using a 7 × 7 full‐diallel‐cross analysis at seedling and reproductive stages. The salinity stress treatment was 12 dS m^?1 at the seedling stage and 8 dS m^?1 at the reproductive stage. Diallel analysis revealed high for salinity tolerance scores and shoot height, moderate for shoot dry weight and root dry weight and low for Na⁺ and K⁺ concentrations and K⁺/Na⁺ ratio. The low‐to‐moderate narrow‐sense heritability for number of panicles, number of fertile spikelets, grain weight, spikelet fertility and K⁺/Na⁺ ratio suggests a large breeding population and delayed selection for tolerance until later generations. Significant maternal effects indicate that selection of the female parent is very important for desired trait development. The results of this study confirmed that salinity tolerance at the seedling and reproductive stages is regulated by a different set of genes that could be pyramided using different donors to enhance the level of tolerance.     

Genetic mapping of seedling and adult plant stem rust resistance in two European winter wheat cultivars

A recombinant inbred line (RIL) population derived from the cross Arina/Forno was field tested for 2 years against Puccinia graminis f. sp. tritici under artificially created epidemic conditions. Both parents showed intermediate adult plant stem rust responses and the RIL population showed continuous variation for this trait. Composite interval mapping identified genomic regions controlling low stem rust response on chromosomes 5B and 7D consistently across all experiments. These genomic regions were named QSr.Sun-5BL and QSr.Sun-7DS and explained on an average 12% and 26% of the phenotypic variation in adult plant stem rust response, respectively. QSr.Sun-5BL mapped close to Xglk0354 and was contributed by Arina. The Lr34-linked markers csLV34 and swm10 were closely associated with QSr.Sun-7DS suggesting the involvement of Lr34 in controlling adult plant stem rust response of cultivar Forno. Additional minor and inconsistent QTLs explaining variation in adult plant stem rust response were identified on chromosome arms 1AS and 7BL. The QTL located on chromosome 7BL corresponded to the stem rust resistance gene Sr17 carried by cultivar Forno. A seedling stem rust resistance gene carried by Arina, SrAn1, was ineffective under field conditions and was mapped on the long arm of chromosome 2A. Genotypes carrying combinations of QSr.Sun-5BL and QSr.Sun-7DS based on positive alleles of the respective closest marker loci Xglk0354 and XcsLV34 or Xswm10 exhibited a lower response than either parent indicating an additive effect of these genes. Transfer of these genes into cultivars carrying Sr2 would provide a more effective and durable resistance against the stem rust pathogen. Markers csLV34 and/or swm10 could be used in marker assisted selection of QSr.Sun-7DS in breeding programs.     

绿豆种质资源苗期耐盐性鉴定及耐盐种质筛选

土壤盐渍化已成为影响中国农业生产的重要问题,筛选耐盐绿豆种质资源对于盐渍化土地利用具有重要意义。本研究对346份国内外绿豆种质苗期用150 mmol L–1 NaCl进行胁迫处理,测定了株高、地上部鲜重、根鲜重、地上部干重、根干重、根长、根体积等12个指标,采用主成分分析和隶属函数分析、耐盐性综合评价分析及聚类分析对各样本的耐盐性进行了综合评价和归类,并采用逐步回归分析建立了耐盐性预测回归方程。结果表明,处理组与对照组各性状评价指标存在极显著差异,且12个指标的耐盐系数间均存在着不同程度的相关性。结合盐害症状等级划分与耐盐性综合评价结果,筛选到苗期高耐盐(1级)绿豆26份,耐盐(3级)绿豆65份,对盐分敏感(7级)绿豆74份,对盐分极敏感(9级)绿豆18份。其中来自江西的C04125、菲律宾的C06310等10份耐盐能力最强,可作为绿豆耐盐育种的优异种质资源。地上部鲜重、根鲜重、根干重、根长、根体积和根分枝数可以作为绿豆苗期耐盐性评价指标。     

水稻资源全生育期耐盐性鉴定筛选

对来自国内外不同地区的550份水稻资源进行全生育期耐盐性鉴定。设置淡水、0.3%和0.5%盐溶液浇灌3个处理,插秧10d后,通过浇灌不同体积的淡水与海水调至设计浓度对水稻进行不同浓度的盐胁迫处理。分别调查了淡水及0.3%盐处理下水稻株高、有效分蘖数、主穗长度、主穗结实率、单株产量、抽穗期6项农艺性状和0.5%盐处理下的水稻耐盐表型。与淡水浇灌相比,全生育期在0.3%盐溶液处理下,550份水稻(100%)株高显著降低;124份(22.55%)水稻有效分蘖数(90份增加, 34份减少)、414份(75.27%)水稻主穗长度(405份变短、9份增长)、145份(26.36%)水稻主穗结实率(84份减少, 61份增加)、375份(68.18%)水稻单株产量(343份减少, 32份增加)存在(极)显著差异;水稻资源的抽穗期无显著差异。主成分分析表明,主穗结实率、有效分蘖数及单株产量3项性状累计贡献77.25%的变异。根据产量耐盐系数筛选了121份耐盐水稻资源(产量耐盐系数≥0.8),在0.5%盐胁迫持续处理42 d后,筛选了78份耐盐水稻资源(耐盐表型为3级),其中25份水稻资源全生育期在0.3%盐处理下单株产量耐盐系数≥0.8,在0.5%盐胁迫持续处理42 d后的耐盐表型为3级。筛选的耐盐水稻资源为培育耐盐新品种及深入研究耐盐机制提供材料。