COVER The source region of the Yellow River contributes more than one-third of total runoff for the entire basin, and is regarded as the “water tower” of the river. Discharge in this region declined significantly after 1990. Low discharge in the 1990s can be explained by a decrease of precipitation amount and intensity, and evaporation increase from warming. However, observed discharge after 2002 was persistently low, when precipitation recovered to above normal levels. This study reproduces the regional surface water budget by modeling, and discusses regional water budget response to climatic changes from the standpoint of spatial distribution of water and energy availability. The result indicates that the spatial pattern of precipitation change is an important factor in the response of runoff to precipitation. During 1990–2002, precipitation was below normal, especially in the center and southeast source region. This, together with near-normal evaporation, reduced runoff yield. After 2002, precipitation decreased in the southeast source region. Evaporation in this subregion was mainly limited by energy availability, and therefore increased. Precipitation increased in central and northwest areas. Evaporation in these subregions was mainly limited by precipitation, so the increased precipitation largely evaporated. This resulted in the persistently low runoff. This finding may provide a valuable reference for research on the relationship between water budget and climatic changes in other basins (see the article by ZHOU DeGang et al. on page 2155).

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CONTENTS CONTENTS

Volume 57 Number 17 June 2012

Progress of Projects Supported by NSFC

ARTICLE Organic Chemistry2051 Fragmentation mechanism of product ions from protonated proline-containing tripeptides in electrospray ionization mass

spectrometry YOU ZhuShuang, WEN YongJun, JIANG KeZhi & PAN YuanJiang

REVIEW Mechanical Engineering2062 Progress in experimental study of aqueous lubrication MA LiRan, ZHANG ChenHui & LIU ShuHai

LETTERS Semiconductor Technology2070 Experimental observation of spontaneous chaotic current oscillations in GaAs/Al0.45Ga0.55As superlattices at room

temperature HUANG YuYang, LI Wen, MA WenQuan, QIN Hua & ZHANG YaoHui

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Electron Physics2087 Comparative investigation of three types of ethanol sensor based on NiO-SnO2compositenanofibers SHEN RenSheng, LI XiangPing, XIA XiaoChuan, LIANG HongWei, WU GuoGuang, LIU Yang, CHENG ChuanHui & DU GuoTong

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Bioinformatics2106 Apathwayprofile-basedmethodfordrugrepositioning YE Hao, YANG LinLin, CAO ZhiWei, TANG KaiLin & LI YiXue

Plant Pathology2113 A combination of leaf rust resistance gene Lr34 and lesion mimic gene lmsignificantlyenhancesadultplantresistanceto

Puccinia triticina in wheat LI Tao, BAI GuiHua & GU ShiLiang

Ecology2120 An analysis of the spatial and temporal changes in Chinese terrestrial ecosystem service functions SHI Yao, WANG RuSong, HUANG JinLou & YANG WenRui

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CONTENTS CONTENTS

Geophysics2132 A new global zenith tropospheric delay model IGGtrop for GNSS applications LI Wei, YUAN YunBin, OU JiKun, LI Hui & LI ZiShen

Geochemistry2140 InfluenceofvariationinprecipitationontheδD values of terrestrial n-alkanes on the southern Tibetan Plateau XIE Ying, XU BaiQing, WU GuangJian & LIN ShuBiao

2148 Reconstructing the food structure of ancient coastal inhabitants from Beiqian village: Stable isotopic analysis of fossil human bone

WANG Fen, FAN Rong, KANG HaiTao, JIN GuiYun, LUAN FengShi, FANG Hui, LIN YuHai & YUAN ShiLing

Atmospheric Science2155 Response of water budget to recent climatic changes in the source region of the Yellow River ZHOU DeGang & HUANG RongHui

Materials Science2163 In vitro degradation and biocompatibility of Mg-Nd-Zn-Zr alloy WANG YongPing, HE YaoHua, ZHU ZhaoJin, JIANG Yao, ZHANG Jian, NIU JiaLin, MAO Lin & YUAN GuangYin

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2177 LLDPE/TiO2 nanocomposites produced from different crystallite sizes of TiO2 via in situ polymerization CHAICHANA Ekrachan, PATHOMSAP Somsakun, MEKASUWANDUMRONG Okorn, PANPRANOT Joongjai, SHOTIPRUK Artiwan & JONGSOMJIT Bunjerd

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Article

Plant Pathology June 2012 Vol.57 No.17: 21132119

doi: 10.1007/s11434-012-5001-x

A combination of leaf rust resistance gene Lr34 and lesion mimic gene lm significantly enhances adult plant resistance to Puccinia triticina in wheat

LI Tao1,2*, BAI GuiHua3* & GU ShiLiang1

1 Jiangsu Provincial Key Laboratory of Crop Genetics and Physiology; Key Laboratory of Plant Functional Genomics of Ministry of Education, Yangzhou University, Yangzhou 225009, China;

2 Department of Plant Pathology, Kansas State University, Manhattan, KS 66506, USA; 3 USDA-ARS Hard Winter Wheat Genetics Research Unit, Manhattan, KS 66506, USA

Received October 8, 2011; accepted November 28, 2011; published online March 8, 2012

Leaf rust caused by Puccinia triticina is an economically-important disease in wheat worldwide. A combination of different types of resistance genes may significantly enhance rust resistance under rust-favorable conditions. To investigate the interactions be-tween the rust resistance gene Lr34 and the lesion mimic gene lm on 1BL in Ning 7840, a segregating F8–10 population of 180

recombinant inbred lines was developed from Ning 7840/Chokwang and evaluated for both lesion mimic expression and leaf rust response at the adult plant stage in a greenhouse. A major quantitative trait locus (QTL), derived from Sumai 3, was co-localized with Lr34 on chromosome 7D and explained 41.5% of phenotypic variations for rust severity and 22.1% for leaf tip necrosis (LTN). The presence of Lr34 was confirmed by Lr34-specific markers cssfr1 and cssfr2 in Ning 7840 and Sumai 3. Unlike Lr34, lm conditioned a spontaneous lesion mimic phenotype and had a significant effect on reducing uredinial size, and a smaller effect on severity. Additive effects were observed between lm and Lr34 for severity and LTN, and an epistatic effect was observed for infection type. Single marker analysis also identified several other QTL with minor effects on severity, infection type, or LTN.

Triticum aestivum, Puccinia triticina, lesion mimic, slow rusting gene Lr34, leaf rust resistance

Citation: Li T, Bai G H, Gu S L. A combination of leaf rust resistance gene Lr34 and lesion mimic gene lm significantly enhances adult plant resistance to Puc-cinia triticina in wheat. Chin Sci Bull, 2012, 57: 21132119, doi: 10.1007/s11434-012-5001-x

Leaf rust, caused by Puccinia triticina Erikss., is an eco-nomically-important wheat disease worldwide. More than 60 leaf rust resistance genes and quantitative trait loci (QTL) have been described in wheat [1], most of which are race- specific. Race-specific resistance genes may stop the devel-opment of epidemics by limiting the initial inoculum or re-production after infection [2]. Nevertheless, the resistance provided by these genes can be temporary because virulent races of the pathogen emerge or increase to overcome race- specific resistance. In contrast, race-nonspecific genes pro-vide durable resistance to a broad spectrum of races and may function by slowing down the rate of infection devel-opment, thus slowing down the spread of disease in the field

[2]. In wheat, only a few leaf rust resistance genes function in

a race-nonspecific manner, such as Lr34 [3,4] and Lr46 [5,6], which are also called “slow rusting genes”. Many cultivars, including Jupateco 73, Forno, Sunvale, and Chi-nese Spring have been reported to carry Lr34 since it was first described in cultivar Frontana in 1966 [7]. Lr34 confers a non-hypersensitive reaction (HR) type of resistance [6] and was recently cloned as an ABC transporter [8]. This gene remains durable, and virulence towards plants carrying Lr34 has not been observed to date [8]. Lr34 increases the latent period and reduces uredinial size and receptivity [4]. Although such resistance provides durable adult plant re-sistance, the effect on reducing rust damage is still depend-ent on environmental conditions and Lr34 alone cannot

2114 Li T, et al. Chin Sci Bull June (2012) Vol.57 No.17

provide adequate protection from rust infection during a severe epidemic. A combination of Lr34 and other genes may be required to provide sufficient protection during se-vere rust epidemics.

Lesion mimic (LM) spontaneously occurs in plants and resembles HR-like phenotypes in the absence of pathogen infection [9]. Because plants with LM usually demonstrate enhanced resistance to a broad spectrum of pathogen races in a race-nonspecific manner, it is thought that LM is in-volved in plant defense signaling pathways [9–11]. In rice, LM mutants ebr3 [10,12], spl [13] and blm [14] provide race-nonspecific resistance to rice blast. In Arabidopsis, LM mutants lsd1 and acd showed enhanced resistance to the bacterial pathogen Pseudomonas syringae and oomycete Peronospora parasitica [15–17]. In wheat, both natural-ly-occurring [18] and chemical- or transgenic-induced LM have been reported [19–22]. These mutants express HR-like phenotypes in pathogen-free environments and exhibit en-hanced resistance to biotrophic pathogens, including P. trit-icina.

Previous experiments indicated that wheat line Ning 7840 exhibits LM symptoms on the leaf blade after heading that resemble the typical wheat response to early leaf rust infection. A recessive gene, lm, on chromosome 1BL con-trolled LM expression, and lines with LM demonstrated a significantly lower infection response compared with a line without LM [18]. In the current study, investigations of re-sistance components in the recombinant inbred line (RIL) population from Ning 7840/Chokwang indicated that Ning 7840 also carries Lr34. The main objectives in this study were to elucidate the effects of HR-like lm and non-HR Lr34 on adult plant response to leaf rust and to reveal addi-tional chromosomal loci involved in rust resistance.

1 Materials and methods

1.1 Plant materials and leaf rust evaluation

A population of 180 F8–10 RIL was developed from the cross Ning 7840/Chokwang by single seed descent. Ning 7840 is a Chinese wheat breeding line that has adult plant leaf rust resistance, exhibits leaf tip necrosis (LTN), and expresses the LM trait after heading. The Korean wheat cultivar Chokwang does not demonstrate LM or LTN. The two par-ents and the resulting RIL were vernalized at 4°C in a growth chamber for 7 weeks and then transplanted into 10 cm × 10 cm plastic pots in a greenhouse at 17±2°C (night) and 22±5°C (day) with supplemental light for 12 h. Experiments were arranged in a randomized complete block design with two replicates (pots) of five plants per replicate. The ex-periment was performed twice in the greenhouses at Kansas State University, Manhattan, KS, USA, in spring 2008 and 2009. LM was recorded as either presence or absence of LM symptoms on the flag leaf.

Flowering plants were inoculated with P. triticina (iso-

late PRTUS55), which is virulent to both Ning7840 and Chokwang at the seedling stage, to evaluate adult plant leaf rust response in the RIL population. Ning 7840 showed high resistance to PRTUS55 and Chokwang showed moderate resistance at the adult stage. The inoculated plants were incubated in a mist chamber at 15°C with 100% relative humidity for 12 h and then moved to a greenhouse at 17±2°C (night) and 22±5°C (day) with 12 h of supplemental light during the daytime. Rust symptoms were scored 14 d after inoculation for severity (percentage of infected flag leaf area) as described by Peterson et al. [23]. Infection type (IT) was scored following the protocol by Roelfs et al. [24], and the two modifiers “+” and “” from McIntosh et al. [25] was also introduced to describe IT. The scale for IT was: 0, necrotic flecks; 1, small uredinia surrounded by necrotic tissue; 2, small to medium uredinia surrounded by chlorotic or necrotic tissue; 3, medium uredinia with or without chlo-rosis; 4, large uredinia without chlorosis; X, random distri-bution of variable sized uredinia on a single leaf; Y, varia-ble sized uredinia with larger pustules at the leaf tip; Z, var-iable sized uredinia with larger pustules at the leaf base; +, pustules larger than average; and , pustules smaller than average. Since X, Y, Z, + and are modifiers of IT and qualitative, IT ratings were converted to numerical scales for statistical and QTL analyses following the “maximum rule”; only the highest IT score was recorded for a single leaf. For example, if an IT score of a flag leaf was 3+4, then 4 was recorded. Similarly, the modifiers X, Y, and Z were also digitalized. For the RIL carrying Lr34 that displayed Z patterns with a larger pustule size at the leaf base than at the leaf tip, only the IT at the base was scored; + or was nu-merically transformed to +/ 0.25. For example, an IT 3+ was converted to 3.25 and 3 was converted to 2.75. Con-sequently, all of the qualitative modifiers were converted to corresponding numerical values.

1.2 Genotyping and data analysis

Parents were initially screened using a genome-wide set of simple sequence repeat (SSR) markers with 12 markers per chromosome. Additional markers in chromosomal regions where markers had been correlated with rust resistance were screened. A total of 176 markers polymorphic between parents were used to genotype all RIL. DNA extraction and PCR amplification procedures followed Yu et al. [26]. Am-plified PCR fragments were separated in an ABI 3730 DNA Analyzer (Applied Biosystems, Foster City, CA) and scored using GeneMarker 1.6 (Softgenetics Inc., State College, PA). Ambiguous data were removed following visuall in-spection. Lr34-specific markers, cssfr1 and cssfr2, which were designed based on a 3 bp polymorphism on exon 11 between Lr34 alleles, were amplified in Ning 7840 (Anhui 11/Aurora//Sumai 3) and its parents following the procedure described by Lagudah et al. [27]. Agarose gels (1%) were used to resolve PCR products.

Li T, et al. Chin Sci Bull June (2012) Vol.57 No.17 2115

Composite interval mapping (CIM) was performed with Windows QTLCartographer version 2.5 [28] using data from individual experiments and the means of two experi-ments. A LOD value of 3.0 was set as the threshold to claim the presence of a QTL. If the QTL was below the threshold in CIM, then a single marker regression model was applied to reveal associations between marker loci and severity or IT. Analysis of variance (ANOVA) was performed to eval-uate differences in rust response between lm and Lr34 alone and in combination. Statistical analysis was conducted using Matlab software (MathWorks Inc, Natick, Massachusetts, 2007).

2 Results

2.1 Phenotypic variations of parents and RIL

When inoculated with P. triticina (isolate PRTUS55), the mean percentage of infected leaf area was 15.6% for Ning 7840 (5.6% in 2008 and 25.6% in 2009) but 40.0% for Chokwang (16.4% in 2008 and 63.3% in 2009). A continu-ous distribution of severities within the RIL population, ranging from 2.0% to 82.5% (Figure 1). Transgressive seg-regation for increased resistance and susceptibility suggest-ed that both Ning 7840 and Chokwang contributed different minor genes.

Ning 7840 produced an IT of 22+, Chokwang 3+4, and the RIL had IT values ranging from 22+ to 4 with a majority with 3 in both experiments. Most RIL with LM symptoms showed low IT (22+), and an IT of 3+4 was not observed in any RIL with LM. Most RIL without LM had high IT, except for six RIL (RIL 31, 60, 76, 80, 102 and 104) that had a consistent IT of 22+ in both experiments. Average rust severity for RIL with LM was 27.2% while it was sig-nificantly (P < 0.0001) higher for non-LM RIL (42.2%). RIL having both high IT (3+4) and high severity (> 80.0%) always lacked LM.

2.2 Chromosomal loci associated with leaf rust re-sistance in the Ning 7840/Chokwang population

Ning 7840 showed LTN and a Z-pattern pustule distribution

Figure 1 Frequency distribution of average leaf rust severity for the RIL population from Ning 7840/Chokwang in 2008 and 2009 experiments.

with more and larger pustules at the leaf base and gradually decreasing pustule size toward the leaf tip in the adult plant stage. Both LTN and Z-pattern pustule distribution are the characteristics of the slow-rusting resistance gene Lr34. QTL mapping identified a major QTL responsible for both low rust severity and LTN on the short arm of chromosome 7D in the individual experiments in 2008 and 2009 as well as when using the means of the two experiments. This QTL was flanked by SSR markers Xgwm295 and Xbarc352 and its peak coincided with the marker csLV34, which is a marker closely linked with Lr34 (Figure 2). The identified QTL explained 41.5% of the phenotypic variation for rust severity and 22.1% of the phenotypic variation for LTN.

Sumai 3 and Aurora were the parents of Ning 7840 (An-hui 11/Aurora//Sumai 3) and both showed LTN of different sizes, but only Sumai 3 showed a consistent Z-pattern pus-tule distribution in both experiments. PCR amplifications of Lr34-specific markers, cssfr1 and cssfr2, generated a DNA fragment (517 bp) for cssfr1 only with Ning 7840 and Su-mai 3, while a PCR fragment (523 bp) for cssfr2 was pro-duced only with Chokwang, Anhui 11, and Aurora. cssfr1 is a positive control marker for Lr34, and produced a PCR fragment of 517 bp in wheat lines carrying Lr34, but gener-ated no products in wheat lines lacking Lr34. cssfr2 is a negative control marker for Lr34 and produced a fragment of 523 bp in wheat lines lacking Lr34 but generated no products in wheat lines carrying Lr34 [27], indicating that Lr34 in Ning 7840 was derived from Sumai 3.

In addition to Lr34 and lm, other genes with minor ef-fects were involved in resistance to PRTUS55. Single marker analysis identified four additional markers associated with rust severity (Table 1). These additional markers were located on four chromosomes. Xsts3B-189 on 3BS and Xgwm3 on 3DS were positively associated with severity, and Ning 7840 contributed the favorable alleles. Markers Xgwm469 on 6DS and Xgwm361.2 on 7BS displayed nega-tive associations with severity, suggesting Chokwang con-tributed alleles for rust resistance at these two loci.

Six additional markers were associated with IT. They were assigned to five chromosomes: 3AS, 3BS, 3DS, 6AS and 7BS (Table 1). Markers Xbarc323 on 3DS, Xsts3B-189 on 3BS, Xbarc3 on 6AS, and Xgwm43 on 7BS were posi-tively associated with IT, suggesting that Ning 7840 con-tributed alleles associated with resistance. Markers Xbarc321 on 3AS and Xgwm361.2 on 7BS were negatively associated with IT, suggesting that Chokwang carried alleles associat-ed with resistance at these loci.

In addition to Lr34, three other loci were identified in Ning 7840 associated with LTN (Table 1). Xwmc710 on 4BS was negatively associated with the length of LTN (P <

0.01), suggesting that the Ning7840 allele at this locus ex-tended LTN. The other two markers, Xgwm539 on 2DL and Xgwm 361.2 on 7BS, were positively correlated to the length of LTN, suggesting Ning7840 alleles at these two loci reduced the length of LTN.

2116 Li T, et al. Chin Sci Bull June (2012) Vol.57 No.17

Figure 2 LOD curves for the Lr34 locus showing the QTL effect and location on chromosome 7D using percentages of infected flag leaf area (PIA) from 2008 (PIA08), 2009 (PIA09), the means over the two experiments (PIAm), and LTN data from 2009.

Table 1 Additional marker loci associated with severity, infection type (IT) and leaf tip necrosis (LTN) in the RIL population from Ning 7840/ Chokwang in 2008 and 2009 greenhouse experiments, as indicated by linear regression analysis using Matlab software at = 0.01

Trait Marker Effect VEa) P value Chromosome

Severity Xsts3B-189 4.408 0.029 <0.001 3BS

Xgwm469 4.13 0.029 <0.01 6DS

Xgwm361.2 4.08 0.028 <0.01 7BS

Xgwm3 3.983 0.027 <0.01 3DS

IT Xbarc323 0.102 0.05 <0.0001 3DS

Xbarc321 0.155 0.047 <0.0001 3AS

Xsts3B-189 0.139 0.039 <0.001 3BS

Xgwm361.2 0.224 0.038 <0.0001 7BS

Xbarc3 0.086 0.036 <0.0001 6AS

Xgwm43 0.19 0.03 <0.01 7BS

LTN Xwmc710 0.729 0.056 <0.0001 4BS

Xgwm539 0.705 0.05 <0.001 2DL

Xgwm361.2 0.603 0.039 <0.01 7BS

a) Proportion of phenotypic variances explained by the marker.

2.3 Relationship between lm and Lr34 in terms of rust response

The LM phenotype had a marked effect on rust infection type and severity (P < 0.0001) and a marginally significant effect on LTN (P = 0.012) (Table 2). The presence of Lr34 significantly reduced both severity and LTN (P < 0.0001), but not IT. The interaction between lm and Lr34 was mar-

ginally significant for IT (P < 0.05), but not for severity and LTN. Since lm and Lr34 have much larger effects, to ana-lyze the interactions between lm and Lr34, the RIL were classified into four groups: lm+Lr34+, lm+Lr34, lm-Lr34+, and lm-Lr34. Variations in rust severity were significant among the four groups (Table 3). The two groups with Lr34 had significantly lower severities than the groups without Lr34. The group with both resistance alleles showed the lowest severity (14.5%), and the group without any of the resistance alleles showed the highest severity (54.4%). The group having Lr34 alone had significantly lower rust sever-ity than the group having lm alone, suggesting that Lr34 had a larger effect on the reduction of rust severity than lm, alt-hough both lm and Lr34 played a role in reducing disease severity.

A significant difference existed between the groups with lm compared with those without the allele (P < 0.0001) (Ta-ble 3). RIL in the group with lm had a smaller uredinial size than those in the group without lm, indicating that lm, rather than Lr34, played a significant role in reducing IT in Ning 7840.

The differences in the mean length of flag leaf tip necro-sis were significant among the four groups (P < 0.001) (Ta-ble 3). The group with both genes displayed the longest LTN, whereas the group without either exhibited the short-est LTN. On average, the presence of lm alone increased LTN by 1.2 cm, and the presence of Lr34 increased it by 2.1 cm. Lr34 and lm appeared to have an additive effect on LTN and intergenic interaction was not significant (Table 2, P = 0.512).

Li T, et al. Chin Sci Bull June (2012) Vol.57 No.17 2117

Table 2 ANOVA analysis of the effects of lm and Lr34 on severity, infection type (IT), and leaf tip necrosis (LTN) of RIL from Ning 7840/Chokwang in 2008 and 2009 greenhouse experiments

Severity IT LTN

DFa) SS F P MS F P MS F P

lm 1 9974.542 28.402 2.989×107 12.539 102.893 2.498×1019 48.636 6.433 0.012

Lr34 1 28707.217 81.742 2.778×1016 0.115 0.947 0.332 284.028 37.568 5.638×109

lm×Lr34 1 434.812 1.238 0.267 0.560 4.596 0.033 3.264 0.432 0.512

Error 176 351.194 0.122 7.560

a) DF, degree of freedom; SS, sums of squares; MS, mean square; F, F statistics; P, probability.

Table 3 Pair-wise comparisons of gene effects on rust severity, infection type (IT), leaf tip necrosis (LTN), and Z-pattern rust distribution on flag leaves among four lm and Lr34 gene combinations in a RIL population from Ning 7840/Chokwang in 2008 and 2009 greenhouse experiments

Groupa) No. of RIL

Severityb) ITb) LTNb) Z pat-ternc)

lm+Lr34+ 44 14.47±3.57 a 2.7±0.07 a 7.7±0.46 c +

lm+Lr34 35 43.19±4.01 c 2.6±0.07 a 5.3±0.52 a

lm-Lr34+ 55 31.96±3.20 b 3.1±0.06 b 6.2±0.41 b +

lm-Lr34 46 54.43±3.49 d 3.3±0.06 b 4.1±0.45 a

a) Gene combination in RIL. lm+, RIL with LM phenotype; lm, RIL without LM phenotype; Lr34+, RIL carrying Lr34; and Lr34, RIL without Lr34. b) Mean ± standard error; a, b, c, and d indicate significant differ-ences between groups at LSD0.05. c) More and larger pustules occurred at the leaf base and gradually decreased in size toward the leaf tip in adult plants; wheat lines carrying Lr34 displayed a typical Z-pattern. +, presence of Z pattern; and , absence of Z-pattern.

3 Discussion

Ning 7840 carries the non-HR resistance gene Lr34 and an HR-like resistance gene lm, and both conferred partial re-sistance to leaf rust in adult plants. Lr34 is widely recog-nized as reducing severity or receptivity as measured by the percentage of infected leaf area and accounts for 20%–50% of the phenotypic variation in various reports [4,29–33]. In this study, the effect of the rust resistance QTL at the Lr34 locus was consistent with previous reports [4,34]. In con-trast, lm increased rust resistance by reducing IT, a compo-nent different from that of Lr34. Thus, these two genes showed a complementary effect on overall rust resistance.

The Z-pattern pustule distribution on infected wheat leaves is a typical response of Lr34 and is characterized by more and larger pustules at the leaf base than at the leaf tip [4,34] (Figure S1(a)). Therefore, Lr34 should reduce IT, at least at the leaf tip. The insignificant association between Lr34 and IT in this study was due to the “maximum rule” used in the IT scoring system where IT is scored only at the leaf base, not at the tip. On average, RIL with both genes had a slightly higher IT than RIL with lm alone and a slightly lower IT at the leaf base than RIL carrying Lr34 alone (Table 3). Therefore, the expression of lm appeared to be negatively affected by expression of Lr34. This was also

supported by the observation that LM symptoms appearing in the earlier stages of infection were reduced when LM was expressed in the presence of Lr34. This result could be due to the differences in the chronological expression patterns of the HR-like lm and the non-HR Lr34. The effect of Lr34 was more pronounced at the grain filling stage than at other stages, and resistance at the flag leaf was most effective [4,8]. LM spots initially appeared around the heading stage [18]. Thus, the appearance of LM occurred earlier than the peak expression of Lr34 (i.e., at the grain filling stage) and the later expression of non-HR Lr34 might negatively affect lm expression, resulting in slightly higher IT for RIL with both genes than for RIL with lm alone (Table 2).

Either Lr34 or lm alone may not be sufficient to control leaf rust under diverse climatic conditions. Singh et al. [35] reported that cultivars with Lr34 alone showed approxi-mately 40% of severity, but could reach unacceptably severe levels in epidemics. Results from this study suggest that Lr34 and lm have different but complementary functions. The effect of Lr34 on severity reduction was superior to reductions in uredinial size, whereas lm functioned in the opposite manner. Seventeen of 21 lines consistently show-ing low severity (< 10.0%) across the two experiments ex-hibited LM phenotype, LTN and Z-pattern pustule distribu-tion, suggesting that a combination of race-nonspecific HR- like lm and non-HR Lr34 may significantly improve adult plant resistance to a desirable level. It is commonly known that RIL with low IT do not always have low severity and vice versa. Only lines simultaneously having low IT and low severity were resistant in nature, and they usually car-ried both Lr34 and lm (Figure S1(c)). Our results indicate that a combination of the two distinct types of resistance genes could enhance the level of adult plant resistance. However, whether the expression of lm has a negative im-pact on yield remains to be determined.

In addition to Lr34 and lm, the transgressive segregation of the RIL for severity (Figure 1) suggests that additional genes are involved in conferring resistance to PRTUS55. Single marker association analysis detected four and six additional markers that were significantly associated with severity and IT, respectively (Table 1). Xsts3B-189 on the short arm of chromosome 3B of Ning 7840, previously as-sociated with the fusarium head blight resistance gene Fhb1

2118 Li T, et al. Chin Sci Bull June (2012) Vol.57 No.17

[36], was positively associated with both severity and IT, suggesting a gene on 3BS might also contribute to rust re-sistance. The marker Xgwm361.2 on 7BS chromosome was negatively associated with both severity and IT (Table 1). Thus, the associated locus in Ning 7840 might suppress the expression of leaf rust resistance to increase both severity and IT.

Results from this study indicated that Ning 7840 provided a unique source of resistance for improving adult plant leaf rust resistance in wheat. Resistance in Ning 7840 was mainly mediated by two distinct types of resistance genes (HR-like and non-HR) that conditioned complementary components of adult plant resistance. A combination of Lr34 and lm resulted in reduced severity and smaller ure-dinial size.

We thank Robert Bowden (USDA-ARS Hard Winter Wheat Genetics Re-search Unit, Manhattan, KS 66506, USA) for providing the Puccinia triti-cina isolate used in this study. This work was partly funded by the Priority Academic Program Development of Jiangsu Higher Education Institution, the National Research Initiative of the USDA Cooperative State Research, Education and Extension Service, CAP (2006-55606-16629) and the Kan-sas Agricultural Experiment Station, Manhattan, Kansas, USA (10-325-J).

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Li T, et al. Chin Sci Bull June (2012) Vol.57 No.17 2119

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Supporting Information

Figure S1 Typical phenotypes of both lm and Lr34 alone and in combination during PRTUS55 infection. (a) Typical phenotype of Lr34 with Z pattern; (b) susceptible line with high IT and high severity; (c) the RIL carrying Lr34 and lm plus one or more genes with a highly reduced to almost immune pheno-type; (d) typical phenotype of lm.

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© The Author(s) 2012. This article is published with open access at Springerlink.com csb.scichina.com www.springer.com/scp

Article

Plant Pathology June 2012 Vol.57 No.17: 11

doi: 10.1007/s11434-012-5001-x

Figure S1 Typical phenotypes of both lm and Lr34 alone and in combination during PRTUS55 infection. (a) Typical phenotype of Lr34 with Z pattern; (b) susceptible line with high IT and high severity; (c) the RIL carrying Lr34 and lm plus one or more genes with a highly reduced to almost immune phenotype; (d) typical phenotype of lm.

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