Bru1 gene and potential alternative sources of resistance to sugarcane brown rust disease

Brown rust, caused by the fungus Puccinia melanocephala, is responsible for important yield losses in sugarcane production globally and it is therefore an important objective to introduce resistance to this disease in breeding programs. A major gene, Bru1, has been shown to confer resistance to P. melanocephala strains from different parts of the world and two molecular markers, R12H16 and 9O20-F4, closely associated to this gene have been previously reported. The usefulness of these molecular diagnostic markers in order to predict a rust resistant phenotype under natural high pressure inoculums conditions was analyzed. A total of 129 sugarcane accessions were evaluated under field infection for resistance or susceptibility to brown rust and subsequently screened for presence or absence of the two Bru1 diagnostic markers. A total of 49 genotypes (38 %) were phenotyped as resistant to brown rust but only eight (16.3 %) of them were harboring the Bru1 gene. To determine overall frequency of the Bru1 in the local sugarcane germplasm collection, 190 additional genotypes were examined. Presence of Bru1, as determined by the diagnostic markers, was detected in only 7 % of the genotypes evaluated. In conclusion, Bru1 diagnostic markers enable positive selection for brown rust resistance in sugarcane and moreover allowed detecting at least one additional source(s) of resistance. Interestingly, whilst only little genetic variability of rust resistance independent of Bru1 has been reported previously, this alternative genetic resource(s) found in our local germplasm constitutes the predominant one and should be helpful in order to amplify the narrow genetic basis for brown rust resistance in sugarcane.     

Survey of the Bru1 gene for brown rust resistance in Brazilian local and basic sugarcane germplasm

Bru1 is currently the major gene conferring brown rust resistance in sugarcane, and diagnostic markers are available. A survey for the presence of this gene was conducted on 391 genotypes including Brazilian cultivars, clones and basic germplasm. The efficiency of these markers for identifying resistant cultivars and artificially inoculated basic germplasm was also evaluated. The Bru1 frequency among cultivars (73.5%) suggests this gene is the prevalent source of brown rust resistance in Brazilian sugarcane breeding programmes. Most of the cultivars known to be resistant were positive for Bru1, although other genes for resistance could be present in lines not having Bru1. Only 17.8% of the basic germplasm accessions were positive for the Bru1 gene, and a low correlation between Bru1 diagnostic markers and brown rust severity was observed for basic germplasm accessions. Overall, Bru1 diagnostic markers proved to be efficient identifying resistant cultivars and clones and have potential to be in screening brown rust resistance in Brazilian breeding programmes.     

Frequency and distribution of the brown rust resistance gene Bru1 and implications for the Louisiana sugarcane breeding programme

Brown rust, caused by the fungus Puccinia melanocephala, poses an increasing threat to sugarcane industries worldwide. Recently, markers R12H16 and 9020‐F4 were developed for a major resistance gene Bru1 that contributes to a significant proportion of brown rust resistance in multiple sugarcane industries. Marker‐assisted screening of Louisiana sugarcane germplasm showed a low frequency (4.3%, five out of 117 clones) of Bru1 among sugarcane cultivars and elite breeding clones. Likewise, among progeny of crosses involving wild/exotic germplasm, only 14 of 208 clones (6.7%) tested Bru1 positive. However, Bru1 frequency was higher (28.7%, 52 of 181 clones) in wild/exotic germplasm, which indicated that diverse genetic resources are available for Bru1 introgression. Commercial Bru1‐positive cultivar, ‘L 01‐299', was resistant to brown rust. However, Bru1‐positive cultivar, ‘L 10‐146’, was susceptible while Bru1‐negative cultivars, such as ‘L 99‐233’, showed resistance to brown rust. Bru1‐negative clones with brown rust resistance offer an opportunity to identify alternate sources of resistance, which can be pyramided with Bru1 for effective and durable resistance in sugarcane against the changing pathogen.     

甘蔗新品种及主栽品种对褐锈病抗性与Bru1基因分子检测

为明确近年我国各甘蔗育种单位育成的新品种及各蔗区主栽品种对甘蔗褐锈病的抗性,筛选抗褐锈病优良新品种供生产上推广应用,本研究结合全国甘蔗新品种联合区域试验,选择甘蔗褐锈病高发的云南临沧、云南普洱、云南玉溪和广西宜州蔗区,在田间自然发病下,对我国近年来选育的60个新品种和34个主栽品种进行抗性评价,并对抗褐锈病基因Bru1进行分子检测。结果表明,94个新品种及主栽品种中,66个表现高抗到中抗,占70.21%;28个表现为感病到高感,占29.79%。分子检测结果显示,共54个抗病新品种及主栽品种含有抗褐锈病基因Bru1,频率为57.45%。目前大面积种植的桂糖29号、桂糖44号、德蔗03-83、柳城03-1137、粤糖60号、桂糖46号等主栽品种高度感病,而粤甘48号、福农09-2201、桂糖08-120、柳城09-15、中蔗1号、云蔗08-1609、云瑞10-187、中糖1201等31个新品种抗病性强。建议多雨湿润褐锈病高发蔗区,应加大淘汰感病主栽品种和推广应用抗病新品种力度,以期达到品种合理布局,从根本上控制褐锈病暴发流行,为甘蔗产业高质量发展提供安全保障。     

甘蔗新品种及主栽品种对褐锈病抗性与Bru1基因分子检测

The aim of this study was to assess brown rust resistance of new sugarcane varieties bred in China and main cultivated varieties in sugarcane planting area, and screen the elite new brown rust resistant varieties for popularization and application in production. In total, 60 new varieties in the national regional test of new sugarcane varieties were tested in Kaiyuan and Lincang, and 34 main cultivated varieties were studied in Lincang, Puer, and Yuxi, Yunnan province, and Yizhou, Guangxi province, China, where the incidence of brown rust was particularly high. The resistance of these sugarcane varieties to brown rust was investigated under natural inoculation and molecular marker-assisted identification was used to detect the brown rust resistance gene Bru1. The results of field survey showed that 66 (70.21%) of the 94 new and main cultivated varieties were highly resistant to moderately resistant, and 28 (29.79%) were susceptible to highly susceptible. Molecular detection indicated that Bru1 gene was found among 54 (57.45%) of the 94 new and main cultivated varieties. Some main cultivated varieties that were currently planted across large areas such as Guitang 29, Guitang 44, Dezhe 03-83, Liucheng 03-1137, Yuetang 60, and Guitang 46 were highly susceptible to brown rust, and 31 new varieties such as Yuegan 48, Funong 09-2201, Guitang 08-120, Liucheng 09-15, Zhongzhe 1, Yunzhe 08-1609, Yunrui 10-187, and Zhongtang 1201 were resistant. Therefore, in the sugarcane planting areas with high incidence of brown rust and wet and rainy climates, more effort should be eliminated the main susceptible varieties and promoted the application of new resistant varieties. This will help to achieve a reasonable distribution of varieties, fundamentally control the outbreak of disease in sugarcane planting areas, and provide security for the high-quality development of sugarcane industry in China in the future.     

Distribution and frequency of Bru1, a major brown rust resistance gene,in the sugarcane world collection

Brown rust, caused by Puccinia melanocephala, is an important disease of sugarcane worldwide. Molecular markers for a major brown rust resistance gene, Bru1, were used to screen a total of 1,282 clones in the World Collection of Sugarcane and Related Grasses (WCSRG) to determine the distribution and frequency of the gene in Saccharum species and related genera. Bru1 was found across all species within the Saccharum complex, but the frequency varied among species. Bru1 was more prevalent in S. robustum clones (59.1%), whereas it occurred in low frequency and exhibited the highest level of variability as determined by the presence of one or both markers (18.8%) in clones of S. spontaneum. Bru1 frequency was highest in the two secondary cultivated species, S. barberi (79.3%) and S. sinense (71.8%). The frequency of Bru1 was 26.4% and 21.0% in S. officinarum and interspecific hybrid clones, respectively. Knowledge of the distribution and frequency of Bru1 in the WCSRG will complement efforts to characterize diversity in the Saccharum complex for the expected expanded use of marker‐assisted selection in the future.     

甘蔗抗黄锈病G1标记的分子检测及候选抗病基因WAK的分析

甘蔗黄锈病是屈恩柄锈菌(Puccinia kuehnii Butler)引起的一种世界性真菌病害,导致产量减少和糖分降低,给甘蔗产业造成严重损失。本研究采用抗黄锈病分子标记G1,检测我国和世界上重要的甘蔗栽培品种、野生种和近缘属的抗黄锈病基因,并对扩增的代表性特异条带进行克隆测序、功能注释和聚类分析,推测其抗性基因的起源和进化。G1检测结果表明,国内124份甘蔗栽培品种检测到G1标记的有83份,占66.9%;国外46份甘蔗栽培品种检测到G1标记的有31份,占67.4%。34份甘蔗野生种和近缘属中检测到G1标记的有17份,占50%,其中割手密种含有该基因比例最高,为100%。功能注释揭示,G1标记的候选基因编码一种细胞壁连接的类受体激酶,并在甘蔗栽培品种的单倍体蛋白组数据库中鉴定到3个相似度较高的蛋白,这些蛋白都有细胞壁受体激酶结构的胞外域、跨膜域和激酶活性的胞内域。聚类结果则清晰展示了抗病候选基因的起源及进化关系,具体可分为3组,第1组来源于割手密种和大茎野生种;第2组来源于大茎野生种、热带种和河八王属;第3组来源于割手密种、大茎野生种、中国种和栽培品种。研究结果为抗黄锈病甘蔗品种的选育提供重要的抗源支撑,并为抗性分子机制的解析奠定基础。     

The contribution of Hordeum chilense to partial resistance of tritordeum to wheat brown rust

Summary Hexaploid and octoploid tritordeum and their Triticum spp. parents were studied in the seedling stage to compare their components of partial resistance to Puccinia recondita f.sp. tritici. The components studied were infection frequency, latency period and size of uredia. The non-host Hordeum chilense parent does not confer any increase of partial resistance to wheat brown rust to its amphiploids with wheat.     

A genome‐wide association study for partial resistance to southern corn rust in tropical maize

Southern corn rust (SCR) is a fungal disease found on corn in several countries worldwide. In Brazil, the disease can result in productivity losses of 65%, especially in areas with a history of the disease. In this study, the genetic architecture and identification of genomic regions associated with SCR resistance was investigated by performing a genome‐wide association study. Genotyping‐by‐sequencing was performed to carry out the association between single nucleotide polymorphism (SNP) markers and phenotypic data from two environments on a panel of 164 maize inbred lines. Eight SNPs were identified as significant for SCR resistance. These SNPs were colocalized with QTL regions, some of which underlie candidate resistance genes with functions that play an important role in the stress response during pathogen recognition. These candidate genes, involved in plant defense pathways, could be associated with partial resistance to SCR and provide a partial comprehensive insight into the genetic architecture of this trait. After validation of the SNPs, they will be useful for marker–assisted selection and for a better understanding of maize resistance to SCR.     

Induction of mutations for rust resistance in wheat

About 25,000 M₂ and M₃ seedlings of the bread wheat variety C. 591 were tested for resistance to 3 races of stem rust. A mutant with resistance to race 40 of stem rust was found in a family derived from treatment with 16,000r of X-rays. No other mutant was found. Albina seedlings were found to be totally free of rust infection. From the present study it seems that mutations for rust resistance can be induced in bread wheat by ionizing radiations but the frequency of such mutations appears to be very low.     

Postulation of leaf (brown) rust resistance genes in 70 wheat cultivars grown in the United Kingdom

Multi-pathotype tests on 70 U.K. wheat cultivars permitted postulation of eight known seedling genes for resistance to Puccinia recondita f. sp.tritici either singly or in combinations. The most commonly detected gene was Lr13 (present in approximately 57% of cultivars), followed by Lr26 (22%), Lr37 (20%), Lr10 (17%), Lr17b (LrH) (10%), Lr1 (7%), Lr3a (6%) and Lr20(4%). This information permitted assessments of adult plant resistance (APR) in some cultivars, in field nurseries inoculated with pathotypes of P. recondita f. sp. tritici of known pathogenicities for characterized seedling resistance genes. APR was identified in eleven cultivars, including Avalon and Maris Ranger, which lacked detectable seedling resistance genes. The results provided a better understanding of specific resistances in the cultivars tested than was available from previous reports. This revised version was published online in July 2006 with corrections to the Cover Date.     

Genomic selection for durable stem rust resistance in wheat

Inheritance of stem rust (caused by Puccinia graminis f. sp. tritici) resistance in wheat can be either qualitative or quantitative. While quantitative disease resistance is believed to be more durable, it is more difficult to evaluate if it is expressed only in mature plants, i.e. adult plant resistance (APR). Marker-assisted selection (MAS) methods for APR would be useful; however, the multigenic nature of APR impedes the use of MAS efforts that aim to pyramid only a few target genes. A promising alternative is genomic selection (GS), which utilizes genome-wide marker coverage to predict genotypic values for quantitative traits. In turn, GS can reduce the selection cycle length of a breeding program for traits like APR that could take several seasons to generate reliable phenotypes. In this paper, we describe the GS process for use in crop improvement, both specifically for APR and in general. We also propose a GS–based wheat breeding scheme for quantitative resistance to stem rust that, when compared to current breeding schemes, can reduce cycle time by up to twofold and facilitates pyramiding of major genes with APR genes. Thus, GS could be an important tool for achieving the Borlaug Global Rust Initiative’s (BGRI) goal of developing durable stem rust resistance in wheat.     

Transgressive segregation for resistance to yellow rust in wheat

Summary Crosses were made between wheat varieties Joss Cambier, Nord Desprez and Maris Bilbo, all classified as susceptible to yellow rust in field tests, and between Cappelle Desprez and Maris Huntsman, both classified as moderately and durably resistant. Selection for resistance to yellow rust among the progeny was carried out using races of Puccinia striiformis able to overcome all the known race-specific components of resistance in both parents of each cross. Lines with greater resistance than in both parents were obtained from each cross, those with greatest resistance being obtained from the cross between the moderately resistant parents. Three lines selected for resistance from the cross of Joss Cambier with Nord Desprez and one from the cross of Cappelle Desprez with Maris Huntsman, together with the parents, were tested in the field with 12 races of P. striiformis. Nord Desprez possessed a previously undetected race-specific component. The selected lines also displayed race-specific resistance, some of which was clearly related to race-specificity of the parents, and a component of resistance, greater than in both parents, that was effective against all 12 races. The possible origin and potential durability of this transgressive level of resistance is discussed. It is suggested that such transgressive resistance is more likely to be durable if it is derived from parents that have shown durable resistance.     

Molecular insights into brown rust resistance and potential epidemic based on the <Emphasis Type="Italic">Bru</Emphasis>1 gene in sugarcane varieties and new elite clones

In most sugarcane cultivation areas, sugarcane brown rust (SBR), caused by Puccinia melanocephala, is an economically important fungal disease that leads to severe yield loss in susceptible cultivars. Bru1, which is the major dominant SBR resistance gene, has been widely used in the prediction of brown rust resistance in sugarcane. In this study, three panels of sugarcane germplasms, the major varieties approved over the past 10 years and new elite clones in the current national regional trial, together with one panel of Saccharum spontaneum, were employed in estimating the possibility of SBR epidemic and to assess the efficiency of 9O20-F4-HaeIII in eliminating false positives. Among the current top five varieties used as sucrose feedstock, accounting for more than 68.9% of the total cultivated area, all were highly resistant to SBR, although only three harboring Bru1. Two major varieties Yuetang60 and Guitang46 without harboring Bru1 were highly susceptible to SBR, together with highly susceptible Funong41, which need prudent promotion. Approximately 60.5% of the 38 new elite clones were Bru1 positive. Considering the susceptibility of Liucheng03-1137, which exhibits a strong promotion momentum, together with Funong41, Guitang46, Yuetang60, and Yunzhe06-47, four were favored by the enterprise due to their superior sucrose content and good stalk yield, despite their high susceptibility to SBR, and additional Yuetang93-159, one current top five varieties with declining resistance, which results in a potential risk for brown rust epidemic. Furthermore, low frequency of the wild germplasm of S. spontaneum from five different countries was Bru1 positive. In addition, a perfect molecular diagnostic result was observed in all modern sugarcane clones using two dominant markers, and HaeIII can prevent the occurrence of false positive results when the 9O20-F4 PCR products of S. spontaneum are digested by RsaI. The prevalent chewing cane Badila without Bru1 is highly resistant to SBR. Our results provide valuable information for the extension of sugarcane varieties and a batch of novel SBR resistance sources with superior comprehensive characters for crossbreeding, and for SBR-resistant gene pyramiding by crossing or through mining and using of new SBR-resistant genes.     

New sources of resistance for stripe rust in barley

Eight spring barley accessions from the gene bank in Gatersleben, Germany, and 10 cultivars were tested for stripe rust resistance. Tests were performed at the seedling stage in the growth chamber and as adult plants in the field. All accessions and six cultivars were scored as resistant against race 24 under all test conditions, with very few plants as exceptions, while the susceptible control cultivars ‘Karat’ and ‘Certina’, and four other cultivars were attacked in all cases. Differences between accessions and between cultivars were detected after infection with isolates from ‘Trumpf’ and ‘Bigo’ (seedling tests only). Infection structures within seedling leaves without pustules and for the first time within leaves of adult plants from the field were analysed by fluorescence microscopy. With this method additional genetic Differences in the resistance reaction could be detected which could not to be seen in the resistance test. Crosses between the accessions and the susceptible cultivar ‘Karat’ led to segregating F₂ progenies. The percentage of resistant plants varied between the accessions. This also indicates a different genetic basis of resistance in the accessions. The infection structures observed by fluorescence microscopy stopped earlier in leaves of the two accessions HOR 8979 and HOR 8991 than in leaves of other accessions in all the tests. These accessions were the only ones with more than 50% resistant plants in all F₂ tests. In general, the accessions from the gene bank can be used as new resistance sources against stripe rust.     

Identification of genomic regions for rust resistance in sorghum

The location and effects of genomic regions for rust resistance in sorghum were determined. One hundred and sixty recombinant inbreds, which derived from a cross between QL39 and QL41, were used as a segregating population for genome mapping and rust resistance evaluation. Phenotypic data were collected in replicated field trials in two years. Interval mapping and non-parametric mapping identified four regions, each in a separate linkage group, associated with rust resistance. The region with the largest effect on rust resistance is on linkage group 10; it accounted for 40% of the total phenotypic variation. This revised version was published online in July 2006 with corrections to the Cover Date.     

Components of rust resistance in lentil

Four components of resistance to Uromyces viciae-fabae, namely, latent period (LP), infection efficiency (IE), pustule size (PS) and spore production (SP) were evaluated on lentil (Lens culinaris) in glasshouse experiments. Four cultivars, Gudo, R-186, FLIP-87-66L and FLIP-89-60L, with different levels of resistance, and the susceptible check EL-142, were included in this study. The cultivars were also compared for area under the disease progress curve (AUDPC), area under the pustule density curve (APDC), apparent infection rate (r_G), disease severity (DS), pustule density (PD), LP and PS under field conditions. Gudo and R-186 had significantly smaller and fewer pustules, lower spore yield and longer latent period than EL-142. FLIP-87-66L was intermediate for infection efficiency and pustule size. In addition, significant differences were found between cultivars for AUDPC, APDC, DS and r_G. Estimates of AUDPC, APDC, DS and r_G were reduced in Gudo, R-186 and FLIP-87-66L compared with the susceptible check EL-142. FLIP-89-60L also showed low AUDPC, APDC and DS. Some of the components obtained in the field were significantly correlated with each other (r = 0.92–0.99, P 0.05) and those measured in the glasshouse. Most of the components studied in the glasshouse were significantly (P 0.05) correlated with AUDPC and DS. Data indicated the existence of incomplete [partial (PR)] resistance in the test cultivars, and the possibility of using IE, LP, SP and PS as selection criteria in the evaluation of PR to rust in lentil. Since there was an interdependence of the components, selection based on more than one component should help obtain lines with higher levels of PR. The AUDPC, DS and r_G could also be used for selecting lines with PR in the field.     

Inheritance of temperature-sensitive leaf rust resistance and adult plant stripe rust resistance in common wheat cultivar PBW343

Genetic analysis of common wheat cultivar PBW343 confirmed temperature-sensitive leaf rust resistance and adult plant stripe rust resistance. At low temperatures, PBW343 was resistant to P. triticina (Ptr) pathotype (pt.) 121R63-1, and at high temperature it was resistant to Ptr pt. 121R127. The low temperature resistance to pt. 121R63-1 was attributed to interaction between dominant and recessive genes. The dominant gene involved in low-temperature resistance to pt. 121R63-1 also conferred resistance to pt. 45R35. The high-temperature resistance to Ptr pt. 121R127 was governed by a different single partially dominant gene. Agra Local (a commonly used susceptible check) and IWP94 (a leaf rust differential used in India) are also resistant to pt. 121R127 at high temperatures. An allelism test indicated that PBW343 and IWP94 possessed a common gene for high temperature resistance to this pathotype. The adult plant stripe rust resistance against P. striiformis (Pst) was possibly conferred by one gene in addition to Yr27.