The phenotypic expression of QTLs for partial resistance to barley leaf rust during plant development

Laboratory of Photosynthesis and Environmental Molecular Physiology, Institute of Botany, Chinese Academy of Sciences, Xiangshan Nanxincun 20, Beijing, 100093, China.
Theoretical and Applied Genetics (Impact Factor: 3.79). 09/2010; 121(5):857-64. DOI: 10.1007/s00122-010-1355-0
Source: PubMed

ABSTRACT Partial resistance is generally considered to be a durable form of resistance. In barley, Rphq2, Rphq3 and Rphq4 have been identified as consistent quantitative trait loci (QTLs) for partial resistance to the barley leaf rust pathogen Puccinia hordei. These QTLs have been incorporated separately into the susceptible L94 and the partially resistant Vada barley genetic backgrounds to obtain two sets of near isogenic lines (NILs). Previous studies have shown that these QTLs are not effective at conferring disease resistance in all stages of plant development. In the present study, the two sets of QTL-NILs and the two recurrent parents, L94 and Vada, were evaluated for resistance to P. hordei isolate 1.2.1 simultaneously under greenhouse conditions from the first leaf to the flag leaf stage. Effect of the QTLs on resistance was measured by development rate of the pathogen, expressed as latency period (LP). The data show that Rphq2 prolongs LP at the seedling stage (the first and second leaf stages) but has almost no effect on disease resistance in adult plants. Rphq4 showed no effect on LP until the third leaf stage, whereas Rphq3 is consistently effective at prolonging LP from the first leaf to the flag leaf. The changes in the effectiveness of Rphq2 and Rphq4 happen at the barley tillering stage (the third to fourth leaf stages). These results indicate that multiple disease evaluations of a single plant by repeated inoculations of the fourth leaf to the flag leaf should be conducted to precisely estimate the effect of Rphq4. The present study confirms and describes in detail the plant development-dependent effectiveness of partial resistance genes and, consequently, will enable a more precise evaluation of partial resistance regulation during barley development.

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    • "In the substitution mapping study of individual introgression segments 8.2, 2.2 and 4.2, similar plant stage dependence and complex inheritance, based on interactions between sub-QTls or possibly CnVs, was observed (den Boer et al. 2013). Plant stage-dependent effectiveness of partial resistance genes has also been reported in other plant pathosystems like in barley-rust and barley-powdery mildew (Aghnoum et al. 2009; Wang et al. 2010). "
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    ABSTRACT: Key message: In a stacking study of eight resistance QTLs in lettuce against downy mildew, only three out of ten double combinations showed an increased resistance effect under field conditions. Complete race nonspecific resistance to lettuce downy mildew, as observed for the nonhost wild lettuce species Lactuca saligna, is desired in lettuce cultivation. Genetic dissection of L. saligna's complete resistance has revealed several quantitative loci (QTL) for resistance with field infection reductions of 30-50 %. To test the effect of stacking these QTL, we analyzed interactions between homozygous L. saligna CGN05271 chromosome segments introgressed into the genetic background of L. sativa cv. Olof. Eight different backcross inbred lines (BILs) with single introgressions of 30-70 cM and selected predominately for quantitative resistance in field situations were intercrossed. Ten developed homozygous lines with stacked introgression segments (double combinations) were evaluated for resistance in the field. Seven double combinations showed a similar infection as the individual most resistant parental BIL, revealing epistatic interactions with 'less-than-additive' effects. Three double combinations showed an increased resistance level compared to their parental BILs and their interactions were additive, 'less-than-additive' epistatic and 'more-than-additive' epistatic, respectively. The additive interaction reduced field infection by 73 %. The double combination with a 'more-than-additive' epistatic effect, derived from a combination between a susceptible and a resistant BIL with 0 and 30 % infection reduction, respectively, showed an average field infection reduction of 52 %. For the latter line, an attempt to genetically dissect its underlying epistatic loci by substitution mapping did not result in smaller mapping intervals as none of the 22 substitution lines reached a similar high resistance level. Implications for breeding and the inheritance of L. saligna's complete resistance are discussed.
    Theoretical and Applied Genetics 06/2014; 127(8). DOI:10.1007/s00122-014-2342-7 · 3.79 Impact Factor
    • "Multiple studies were conducted to map QTls, and alleles were associated with leaf rust resistance in different genomic regions (e.g., Qi et al. 1998, 1999, 2000; Kicherer et al. 2000; van Berloo et al. 2001; Backes et al. 2003; Kopahnke et al. 2004; von Korff et al. 2005; Kraakman et al. 2006; Marcel et al. 2007a, b; Schmalenbach et al. 2008; Cakir et al. 2011; Castro et al. 2012; González et al. 2012). The detection of lr resistance QTls in seedlings is usually plant stage dependent (Wang et al. 2010; Castro et al. 2012). An advanced QTl approach, the 'Meta-QTl' approach, was applied by Schweizer and Stein (2011). "
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    ABSTRACT: Key message: We suggest multi-parental nested association mapping as a valuable innovation in barley genetics, which increases the power to map quantitative trait loci and assists in extending genetic diversity of the elite barley gene pool. Plant genetic resources are a key asset to further improve crop species. The nested association mapping (NAM) approach was introduced to identify favorable genes in multi-parental populations. Here, we report toward the development of the first explorative barley NAM population and demonstrate its usefulness in a study on mapping quantitative trait loci (QTLs) for leaf rust resistance. The NAM population HEB-5 was developed from crossing and backcrossing five exotic barley donors with the elite barley cultivar 'Barke,' resulting in 295 NAM lines in generation BC1S1. HEB-5 was genetically characterized with 1,536 barley SNPs. Across HEB-5 and within the NAM families, no deviation from the expected genotype and allele frequencies was detected. Genetic similarity between 'Barke' and the NAM families ranged from 78.6 to 83.1 %, confirming the backcrossing step during population development. To explore its usefulness, a screen for leaf rust (Puccinia hordei) seedling resistance was conducted. Resistance QTLs were mapped to six barley chromosomes, applying a mixed model genome-wide association study. In total, four leaf rust QTLs were detected across HEB-5 and four QTLs within family HEB-F23. Favorable exotic QTL alleles reduced leaf rust symptoms on two chromosomes by 33.3 and 36.2 %, respectively. The located QTLs may represent new resistance loci or correspond to new alleles of known resistance genes. We conclude that the exploratory population HEB-5 can be applied to mapping and utilizing exotic QTL alleles of agronomic importance. The NAM concept will foster the evaluation of the genetic diversity, which is present in our primary barley gene pool.
    Theoretical and Applied Genetics 05/2014; 127(7). DOI:10.1007/s00122-014-2315-x · 3.79 Impact Factor
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    • "The detection of plant stage dependent sub-QTLs within the three BIL introgression segments corresponds with the result of the set of 29 BILs within the whole lettuce genome, in which the majority of the 15 resistant BILs showed plant stage dependent resistance (Zhang et al. 2009a). Developmental plant stage dependent quantitative resistance has been found in multiple studies, in multiple plant species (Castro et al. 2002; Eenink and Jong 1982; Mallard et al. 2005; Monteiro et al. 2005; Prioul et al. 2004; Qi et al. 1998; Wang et al. 2010). "
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    ABSTRACT: Key message: Three regions with quantitative resistance to downy mildew of non-host and wild lettuce species, Lactuca saligna , disintegrate into seventeen sub-QTLs with plant-stage-dependent effects, reducing or even promoting the infection. Previous studies on the genetic dissection of the complete resistance of wild lettuce, Lactuca saligna, to downy mildew revealed 15 introgression regions that conferred plant stage dependent quantitative resistances (QTLs). Three backcross inbred lines (BILs), carrying an individual 30-50 cM long introgression segment from L. saligna in a cultivated lettuce, L. sativa, background, reduced infection by 60-70 % at young plant stage and by 30-50 % at adult plant stage in field situations. We studied these three quantitative resistances in order to narrow down their mapping interval and determine their number of loci, either single or multiple. We performed recombinant screenings and developed near isogenic lines (NILs) with smaller overlapping L. saligna introgressions (substitution mapping). In segregating introgression line populations, recombination was suppressed up to 17-fold compared to the original L. saligna × L. sativa F 2 population. Recombination suppression depended on the chromosome region and was stronger suppressed at the smallest introgression lengths. Disease evaluation of the NILs revealed that the resistance of all three BILs was not explained by a single locus but by multiple sub-QTLs. The 17 L. saligna-derived sub-QTLs had a smaller and plant stage dependent resistance effect, some segments reducing; others even promoting downy mildew infection. Implications for lettuce breeding are outlined.
    Theoretical and Applied Genetics 09/2013; 126(12). DOI:10.1007/s00122-013-2188-4 · 3.79 Impact Factor
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