Analysis of hybrids of durum wheat with Thinopyrum junceiforme using RAPD markers

 The objective of this study was to detect the presence of alien chromatin in intergeneric hybrids of durum wheat (Triticum turgidum, 2n=4x=28; AABB genomes) with the perennial grass Thinopyrum junceiforme (2n=4x=28; J₁J₁J₂J₂) using RAPD markers. The first step was to identify amplification of species-specific DNA markers in the parental grass species and durum wheat cultivars. Initially, the genomic DNA of five grass species (Thinopyrum junceiforme, Th. bessarabicum, Lophopyrum elongatum, Leymus karataviensis and Elytrigia pycnantha) and selected durum cultivars (‘Langdon’, ‘Durox’, ‘Lloyd’, ‘Monroe’, and ‘Medora’) was screened with 40 oligonucleotide primers (nano-mers). Three oligonucleotides that amplified DNA fragments specific to a grass species or to a durum cultivar were identified. Primer PR21 amplified DNA fragments specific to each of the five durum cultivars, and primers PR22 and PR23 amplified fragments specific to each of the grass species. Intergeneric hybrids between the durum cultivars ‘Langdon’, ‘Lloyd’ and ‘Durox’ and Th. junceiforme, and their backcross (BC) progeny were screened with all 40 primers. Six primers amplified parent-specific DNA fragments in the F₁ hybrids and their BC₁ progeny. Three primers, PR22, PR23 and PR41, that amplified Th. junceiforme DNA fragments in both F₁ and BC₁ were further analyzed. The presence of an amplified 1.7-kb Th. junceiforme DNA fragment in the F₁ hybrids and BC₁ progeny was confirmed using Southern analysis by hybridization with both Th. junceiforme genomic DNA and Th. junceiforme DNA amplified with primer PR41. With the exception of line BC₁F₂ no. 5, five selfed progeny of BC₁ and a BC₂ of line 3 (BC₁F₂ no. 3בLloyd’) from a cross of ‘Lloyd’×Th. junceiforme showed the presence of the 1.7-kb DNA fragment. All selfed BC₁ and BC₂ lines retained the 600-bp fragment that was confirmed after hybridization with Th. junceiforme DNA amplified with primer PR22. Other experiments using RFLP markers also showed the presence of up to seven Th. junceiforme DNA fragments in the F₁ hybrids and their BC progeny after hybridization with Th. junceiforme DNA amplified with primer PR41. These studies show the usefulness of molecular markers in detecting alien chromatin/DNA fragments in intergeneric hybrids with durum wheat. Received: 21 November 1996 / Accepted: 21 March 1997     

Expression of the narrow leaflet gene for yield and agronomic traits in soybean

Genes that affect plant form and function may be used to enhance the yield of soybean [Glycine max (L.) Merr.]. Most soybean cultivars have broad (ovate) leaflets. A single gene, ln, controls inheritance for the narrow leaflet characteristic. Narrow leaflet cultivars (ln/ln) also tend to have a higher percentage of four-seeded pods than ovate (Ln/Ln) leaflet cultivars. Heterozygous (Ln/ln) plants have a leaflet shape intermediate between narrow and ovate. Determining the agronomic effects of the narrow leaflet allele (ln) in the heterozygous (Ln/ln) condition in soybean may have applications in practical plant breeding. We studied an ovate leaflet and a narrow leaflet cultivar, crosses between them in the F(1) and F(2), and backcrosses to both cultivars. The ratio of leaflet width to leaflet length accurately distinguished among narrow, ovate, and intermediate leaflet plants in the F(2) and backcross generations. In the F(2) generation, differences occurred among plants with different leaflet morphology. Narrow leaflet plants produced more seeds per pod and lower seed weight than ovate leaflet plants. Narrow and ovate leaflet plants produced comparable numbers of pods per plant and plant yield. Compared to ovate leaflet plants, intermediate leaflet plants produced similar numbers of seeds per pod and seed weight. Intermediate leaflet plants produced significantly more pods per plant and plant yield than plants with either ovate or narrow leaflets. The heterozygous condition at the locus for leaflet morphology resulted in heterosis for plant yield and may be of benefit in association with commercialization and development of hybrid soybean.     

Fine mapping of <Emphasis Type="Italic">Sta1</Emphasis>, a quantitative trait locus determining stele transversal area,on rice chromosome 9

The stele (root vascular cylinder) in plants plays an important role in the transport of water and nutrients from the root to the shoot. A quantitative trait locus (QTL) on rice chromosome 9 that controls stele transversal area (STA) was previously detected in an F₃ mapping population derived from a cross between the lowland cultivar ‘IR64’, with a small STA, and the upland cultivar ‘Kinandang Patong’, with a large STA. To identify the gene(s) underlying this QTL, we undertook fine mapping of the locus. We screened eight plants from BC₂F₃ lines in which recombination occurred near the QTL. Progeny testing of BC₂F₄ plants was used to determine the genotype classes for the QTL in each BC₂F₃ line. Accordingly, the STA QTL Sta1 (Stele Transversal Area 1) was mapped between the InDel markers ID07_12 and ID07_14. A candidate genomic region for Sta1 was defined more precisely between markers RM566 and RM24334, which delimit a 359-kb interval in the reference cultivar ‘Nipponbare’. A line homozygous for the ‘Kinandang Patong’ allele of Sta1 had an STA approximately 28.4% larger than that of ‘IR64’. However, Sta1 did not influence maximum or total root length, suggesting that this QTL specifically controls STA.     

Fine mapping the soybean aphid resistance gene Rag1 in soybean

The soybean aphid (Aphis glycines Matsumura) is an important soybean [Glycine max (L.) Merr.] pest in North America. The dominant aphid resistance gene Rag1 was previously mapped from the cultivar ‘Dowling’ to a 12 cM marker interval on soybean chromosome 7 (formerly linkage group M). The development of additional genetic markers mapping closer to Rag1 was needed to accurately position the gene to improve the effectiveness of marker-assisted selection (MAS) and to eventually clone it. The objectives of this study were to identify single nucleotide polymorphisms (SNPs) near Rag1 and to position these SNPs relative to Rag1. To generate a fine map of the Rag1 interval, 824 BC₄F₂ and 1,000 BC₄F₃ plants segregating for the gene were screened with markers flanking Rag1. Plants with recombination events close to the gene were tested with SNPs identified in previous studies along with new SNPs identified from the preliminary Williams 82 draft soybean genome shotgun sequence using direct re-sequencing and gene-scanning melt-curve analysis. Progeny of these recombinant plants were evaluated for aphid resistance. These efforts resulted in the mapping of Rag1 between the two SNP markers 46169.7 and 21A, which corresponds to a physical distance on the Williams 82 8× draft assembly (Glyma1.01) of 115 kilobase pair (kb). Several candidate genes for Rag1 are present within the 115-kb interval. The markers identified in this study that are closely linked to Rag1 will be a useful resource in MAS for this important aphid resistance gene.     

Soybean aphid resistance genes in the soybean cultivars Dowling and Jackson map to linkage group M

The soybean aphid [Aphis glycines Matsumura] is an important pest of soybean [Glycine max (L.) Merr.] in North America. Single dominant genes in the cultivars ‘Dowling’ and ‘Jackson’ control resistance to the soybean aphid. The gene in Dowling was named Rag1, and the genetic relationship between Rag1 and the gene in Jackson is not known. The objectives of this study were to map the locations of Rag1 and the Jackson gene onto the soybean genetic map. Segregation of aphid resistance and simple sequence repeat (SSR) markers in F _2:3 populations developed from crosses between Dowling and the two susceptible soybean cultivars ‘Loda’ and ‘Williams 82’, and between Jackson and Loda, were analyzed. Both Rag1 and the Jackson gene segregated 1:2:1 in the F _2:3 populations and mapped to soybean linkage group M between the markers Satt435 and Satt463. Rag1 mapped 4.2 cM from Satt435 and 7.9 cM from Satt463. The Jackson gene mapped 2.1 cM from Satt435 and 8.2 cM from Satt463. Further tests to determine genetic allelism between Rag1 and the Jackson gene are in progress. The SSR markers flanking these resistance genes are being used in marker-assisted selection for aphid resistance in soybean breeding programs. Trade and manufacturers’ names are necessary to report factually on available data; however, the USDA neither guarantees nor warrants the standard of the product, and the use of the name by USDA implies no approval of the product to the exclusion of others that may also be suitable.     

Fine-mapping of <Emphasis Type="Italic">qRfg2</Emphasis>, a QTL for resistance to <Emphasis Type="Italic">Gibberella</Emphasis> stalk rot in maize

Stalk rot is one of the most devastating diseases in maize worldwide. In our previous study, two QTLs, a major qRfg1 and a minor qRfg2, were identified in the resistant inbred line ‘1145’ to confer resistance to Gibberella stalk rot. In the present study, we report on fine-mapping of the minor qRfg2 that is located on chromosome 1 and account for ~8.9% of the total phenotypic variation. A total of 22 markers were developed in the qRfg2 region to resolve recombinants. The progeny-test mapping strategy was developed to accurately determine the phenotypes of all recombinants for fine-mapping of the qRfg2 locus. This fine-mapping process was performed from BC₄F₁ to BC₈F₁ generations to narrow down the qRfg2 locus into ~300 kb, flanked by the markers SSRZ319 and CAPSZ459. A predicted gene in the mapped region, coding for an auxin-regulated protein, is believed to be a candidate for qRfg2. The qRfg2 locus could steadily increase the resistance percentage by ~12% across different backcross generations, suggesting its usefulness in enhancing maize resistance against Gibberella stalk rot.     

Fine mapping of quantitative trait loci Hd-1, Hd-2 and Hd-3, controlling heading date of rice, as single Mendelian factors

 Fine mapping was carried out on three putative QTLs (tentatively designated as Hd-1 to Hd-3) of five such QTLs controlling heading date in rice that had been earlier identified using an F₂ population derived from a cross between a japonica variety, ‘Nipponbare’, and an indica variety, ‘Kasalath’, using progeny backcrossed with ‘Nipponbare’ as the recurrent parent. One BC₃F₂ and two BC₃F₁ plants, in which the target QTL regions were heterozygous and most other chromosomal regions were homozygous for the ‘Nipponbare’ allele, were selected as the experimental material. Self-pollinated progeny (BC₃F₂ and BC₃F₃) of the BC₃F₁ or BC₃F₂ showed continuous variation in days to heading. By means of progeny testing based on BC₃F₃ or BC₃F₄ lines, we determined the genotypes of each BC₃F₂ or BC₃F₃ individual at target QTLs. Their segregation patterns fitted Mendelian inheritance ratios. When the results obtained by RFLP analysis and progeny tests were combined, Hd-1, Hd-2 and Hd-3 were mapped precisely on chromosomes 6, 7 and 6, respectively, of a rice RFLP linkage map. The results demonstrated that QTLs can be treated as Mendelian factors. Moreover, these precise locations were in good agreement with the regions estimated by QTL analysis of the initial F₂ population, demonstrating the high reliability of QTL mapping using a high-density linkage map. Received: 5 November 1997 / Accepted: 10 February 1998     

Accumulation of additive effects generates a strong photoperiod sensitivity in the extremely late-heading rice cultivar ‘Nona Bokra’

Many rice cultivars that originated from lower-latitude regions exhibit a strong photoperiod sensitivity (PS) and show extremely late heading under long-day conditions. Under natural day-length conditions during the cropping season in Japan, the indica rice cultivar ‘Nona Bokra’ from India showed extremely late heading (202 days to heading) compared to the japonica cultivar ‘Koshihikari’ (105 days), from Japan. To elucidate the genetic factors associated with such extremely late heading, we performed quantitative trait locus (QTL) analyses of heading date using an F₂ population and seven advanced backcross progeny (one BC₁F₂ and six BC₂F₂) derived from a cross between ‘Nona Bokra’ and ‘Koshihikari’. The analyses revealed 12 QTLs on seven chromosomes. The ‘Nona Bokra’ alleles of all QTLs contributed to an increase in heading date. Digenic interactions were rarely observed between QTLs. Based on the genetic parameters of the QTLs, such as additive effects and percentage of phenotypic variance explained, these 12 QTLs are likely generate a large proportion of the phenotypic variation observed in the heading dates between ‘Nona Bokra’ and ‘Koshihikari’. Comparison of chromosomal locations between heading date QTLs detected in this study and QTLs previously identified in ‘Nipponbare’ × ‘Kasalath’ populations revealed that eight of the heading date QTLs were recognized nearby the Hd1, Hd2, Hd3a, Hd4, Hd5, Hd6, Hd9, and Hd13. These results suggest that the strong PS in ‘Nona Bokra’ was generated mainly by the accumulation of additive effects of particular alleles at previously identified QTLs.     

Molecular mapping of pea powdery mildew resistance gene <Emphasis Type="Italic">er2</Emphasis> to pea linkage group III

Powdery mildew caused by Erysiphe pisi D.C. is one of the most serious diseases that inflict heavy losses to pea crop world-wide. Identification of resistance sources and their incorporation into susceptible cultivars remains the most effective method of controlling the disease. The present study investigated the resistance phenotype, inheritance, and genomic location of gene(s) controlling resistance to powdery mildew in pea genotype ‘JI2480’. The powdery mildew resistance in ‘JI2480’ appeared to be a spatial phenomenon showing expression only in leaf tissues. By segregation analysis of an F₂ progeny of cross ‘Lincoln/JI2480’, the leaf resistance of ‘JI2480’ was shown to be controlled by a single recessive gene, presumed to be er2. Through linkage analysis of 111 resistant F₂ progeny plants with simple sequence repeat (SSR) and random amplified polymorphic DNA (RAPD) markers adopted from the published linkage maps, the er2 gene was localized on pea linkage group III (LGIII). The assignment of er2 to LGIII, a position different from that reported for er1, has resolved the long standing controversy in the literature regarding the existence and genomic location of er2 gene. A RAPD marker OPX-17_1400, exhibiting cis phase linkage (2.6 cM) to er2 was successfully converted to a sequence characterized amplified region (SCAR) marker, ScX17_1400. The SCAR marker ScX17_1400 will ensure speedy and precise introgression of er2 into susceptible cultivars by permitting selection of er2 heterozygotes amongst BC _n F₁s without progeny tests and resistance screening.     

A major QTL for resistance to Gibberella stalk rot in maize

Fusarium graminearum Schwabe, the conidial form of Gibberella zeae, is the causal fungal pathogen responsible for Gibberella stalk rot of maize. Using a BC₁F₁ backcross mapping population derived from a cross between ‘1145’ (donor parent, completely resistant) and ‘Y331’ (recurrent parent, highly susceptible), two quantitative trait loci (QTLs), qRfg1 and qRfg2, conferring resistance to Gibberella stalk rot have been detected. The major QTL qRfg1 was further confirmed in the double haploid, F₂, BC₂F₁, and BC₃F₁ populations. Within a qRfg1 confidence interval, single/low-copy bacterial artificial chromosome sequences, anchored expressed sequence tags, and insertion/deletion polymorphisms, were exploited to develop 59 markers to saturate the qRfg1 region. A step by step narrowing-down strategy was adopted to pursue fine mapping of the qRfg1 locus. Recombinants within the qRfg1 region, screened from each backcross generation, were backcrossed to ‘Y331’ to produce the next backcross progenies. These progenies were individually genotyped and evaluated for resistance to Gibberella stalk rot. Significant (or no significant) difference in resistance reactions between homozygous and heterozygous genotypes in backcross progeny suggested presence (or absence) of qRfg1 in ‘1145’ donor fragments. The phenotypes were compared to sizes of donor fragments among recombinants to delimit the qRfg1 region. Sequential fine mapping of BC₄F₁ to BC₆F₁ generations enabled us to progressively refine the qRfg1 locus to a ~500-kb interval flanked by the markers SSR334 and SSR58. Meanwhile, resistance of qRfg1 to Gibberella stalk rot was also investigated in BC₃F₁ to BC₆F₁ generations. Once introgressed into the ‘Y331’ genome, the qRfg1 locus could steadily enhance the frequency of resistant plants by 32–43%. Hence, the qRfg1 locus was capable of improving maize resistance to Gibberella stalk rot.     

Mapping quantitative trait loci associated with regeneration ability of seed callus in rice, Oryza sativa L.

 Quantitative trait loci (QTL) controlling the regeneration ability of rice seed callus were detected using 245 RFLP markers and 98 BC₁F₅ lines derived from two varieties, ‘Nipponbare’ and ‘Kasalath’. Regeneration ability was evaluated by two indices: average number of regenerated shoots per callus (NRS) and regeneration rate (RR). The BC₁F₅ lines showed continuous segregation for both indices. Five putative QTL for NRS (tentatively named qRg1, qRg2, qRg4a, qRg4b and qRg4c) located on chromosomes 1, 2 and 4 were detected. Digenic interaction among these detected QTL was not significant (P<0.01). Among the five QTL detected, four ‘Kasalath’ alleles and one ‘Nipponbare’ allele increased NRS. According to an estimate based on the nearest marker loci, the five QTL accounted for 38.5% of the total phenotypic variation of the BC₁F₅ lines. For RR, four putative QTL were detected on chromosomes 2 and 4, and all of these were in the same chromosomal regions as the NRS QTL. The four RR QTL accounted for 32.6% of the total phenotypic variation. Received: 7 November 1996 / Accepted: 25 April 1997     

Identification and fine-mapping of a major QTL conferring resistance against head smut in maize

Head smut is one of the most devastating diseases in maize, causing severe yield loss worldwide. Here we report identification and fine-mapping of a major quantitative trait locus (QTL) conferring resistance to head smut. Two inbred lines ‘Ji1037’ (donor parent, highly resistant) and ‘Huangzao4’ (recurrent parent, highly susceptible) were crossed and then backcrossed to ‘Huangzao4’ to generate BC populations. Four putative resistance QTLs were detected in the BC₁ population, in which the major one, designated as qHSR1, was mapped on bin 2.09. The anchored ESTs, IDPs, RGAs, BAC and BAC-end sequences in bin 2.09 were exploited to develop markers to saturate the qHSR1 region. The recombinants in the qHSR1 region were obtained by screening the BC₂ population and then backcrossed again to ‘Huangzao4’ to produce 59 BC_2:3 families or selfed to generate nine BC₂F₂ families. Individuals from each BC_2:3 or BC₂F₂ family were evaluated for their resistances to head smut and genotypes at qHSR1. Analysis of genotypes between the resistant and susceptible groups within the same family allows deduction of phenotype of its parental BC₂ recombinant. Based on the 68 BC₂ recombinants, the major resistance QTL, qHSR1, was delimited into an interval of ~2 Mb, flanked by the newly developed markers SSR148152 and STS661. A large-scale survey of BC_2:3 and BC₂F₂ progeny indicated that qHSR1 could exert its genetic effect by reducing the disease incidence by ~25%. Yongsheng Chen, Qing Chao and Guoqing Tan contributed equally to this work.     

High-resolution mapping of <Emphasis Type="Italic">Rsn1</Emphasis>, a locus controlling sensitivity of rice to a necrosis-inducing phytotoxin from <Emphasis Type="Italic">Rhizoctonia solani</Emphasis> AG1-IA

Rhizoctonia solani is a necrotrophic fungal pathogen that causes disease on many crop-plant species. Anastomosis group 1-IA is the causal agent of sheath blight of rice (Oryza sativa L.), one of the most important rice diseases worldwide. R. solani AG1-IA produces a necrosis-inducing phytotoxin and rice cultivar’s sensitivity to the toxin correlates with disease susceptibility. Unlike genetic analyses of sheath blight resistance where resistance loci have been reported as quantitative trait loci, phytotoxin sensitivity is inherited as a Mendelian trait that permits high-resolution mapping of the sensitivity genes. An F₂ mapping population derived from parent cultivars ‘Cypress’ (toxin sensitive) and ‘Jasmine 85’ (toxin insensitive) was used to map Rsn1, the necrosis-inducing locus. Initial mapping based on 176 F₂ progeny and 69 simple sequence repeat (SSR) markers located Rsn1 on the long arm of chromosome 7, with tight linkage to SSR marker RM418. A high-resolution genetic map of the region was subsequently developed using a total of 1,043 F₂ progeny, and Rsn1 was mapped to a 0.7 cM interval flanked by markers NM590 and RM418. Analysis of the corresponding 29 Kb genomic sequences from reference cultivars ‘Nipponbare’ and ‘93-11’ revealed the presence of four putative genes within the interval. Two are expressed cytokinin-O-glucosyltransferases, which fit an apoptotic pathway model of toxin activity, and are individually being investigated further as potential candidates for Rsn1.     

QTL analysis reveals context-dependent loci for seed glucosinolate trait in the oilseed <Emphasis Type="Italic">Brassica juncea</Emphasis>: importance of recurrent selection backcross scheme for the identification of ‘true’ QTL

Seed glucosinolate content in Brassica juncea is a complex quantitative trait. A recurrent selection backcross (RSB) method with a doubled haploid (DH) generation interspersing backcross generations was used for the introgression of low glucosinolate alleles from an east European gene pool B. juncea line, Heera into an Indian gene pool variety, Varuna. Phenotypic comparisons among the DH populations derived from early to advanced backcrosses revealed a shift in the mean values for various glucosinolates with the advancement of backcrossing, indicating a change in the selective values of the alleles with change in the genetic background due to the existence of epistasis and context dependencies. QTL mapping for various seed glucosinolates from early (F₁DH) and advanced generation (BC₄DH) populations confirmed the presence of epistasis and context dependency. The common QTL detected in both F₁DH and BC₄DH changed their R ² values from the former to the later generation. Some of the QTL detected in the F₁DH became irrelevant in the BC₄DH population. Further, new QTL were detected in the BC₄DH population for various glucosinolates. A validation study on a population of low glucosinolate DH lines derived from all the backcross generations of the RSB breeding programme revealed that the QTL detected in BC₄DH were the ‘true’ QTL. Using glucosinolate as an example, the study provides strong evidence for the importance of the RSB method for the identification of the ‘true’ QTL which would be significant for marker assisted introgression of a complex quantitative trait whose expression is influenced by epistatic interactions. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. Authors N. Ramchiary, N. C. Bisht, V. Gupta, A. Mukhopadhyay and N. Arumugam have contributed equally to this work.     

Mapping of resistance to spot blotch disease caused by Bipolaris sorokiniana in spring wheat

Spot blotch caused by Bipolaris sorokiniana is a destructive disease of wheat in warm and humid wheat growing regions of the world. The development of disease resistant cultivars is considered as the most effective control strategy for spot blotch. An intervarietal mapping population in the form of recombinant inbred lines (RILs) was developed from a cross ‘Yangmai 6’ (a Chinese source of resistance) × ‘Sonalika’ (a spot blotch susceptible cultivar). The 139 single seed descent (SSD) derived F₆, F₇, F₈ lines of ‘Yangmai 6’ × ‘Sonalika’ were evaluated for resistance to spot blotch in three blocks in each of the 3 years. Joint and/or single year analysis by composite interval mapping (CIM) and likelihood of odd ratio (LOD) >2.2, identified four quantitative trait loci (QTL) on the chromosomes 2AL, 2BS, 5BL and 6DL. These QTLs were designated as QSb.bhu-2A, QSb.bhu-2B, QSb.bhu-5B and QSb.bhu-6D, respectively. A total of 63.10% of phenotypic variation was explained by these QTLs based on the mean over years. Two QTLs on chromosomes 2B and 5B with major effects were consistent over 3 years. All QTL alleles for resistance were derived from the resistant parent ‘Yangmai 6’.     

Genomic Location of a Gene Conditioning a Miniature Phenotype in Soybean [<Emphasis Type="Italic">Glycine max</Emphasis> (L.) Merr.]

The potential for global warming and climate change has increased the focus of research on plant genes that respond to high temperatures. Previous research identified a temperature-sensitive miniature soybean mutant that was controlled by a single gene. The objectives of our research were to confirm the single-gene control and to determine the genomic location of this gene. Segregation of the combined progeny of four BC₆F₅ plants heterozygous for the miniature trait in a Tracy-M background confirmed that the trait was conditioned by a single gene (1:2:1, χ ² = 4.38, P = 0.1120). Molecular marker analysis identified three SSR markers and a SNP marker on molecular linkage group B2 (chromosome 14) associated with segregation for the miniature trait. One of these, marker Satt560, co-segregated perfectly with the miniature trait. The data from these four polymorphic markers indicated that the gene conditioning this miniature phenotype is at or near Satt560. Given this newly identified location of the gene and the recently published soybean genomic sequence, it may be feasible to isolate the gene and determine its mechanism of action in responding to temperature. Such knowledge may be of use in understanding how plants respond to increased temperature.     

QTL underlying the resistance to soybean aphid (<Emphasis Type="Italic">Aphis glycines</Emphasis> Matsumura) through isoflavone-mediated antibiosis in soybean cultivar ‘Zhongdou 27’

Soybean aphid (Aphis glycines Matsumura) results in severe yield loss of soybean in many soybean-growing countries of the world. A few loci have been previously identified to be associated with the aphid resistance in soybean. However, none of them was via isoflavone-mediated antibiosis process. The aim of the present study was to conduct genetic analysis of aphid resistance and to identify quantitative trait loci (QTL) underlying aphid resistance in a Chinese soybean cultivar with high isoflavone content. One hundred and thirty F_5:6 derived recombinant inbred lines from the ‘Zhongdou 27’ × ‘Jiunong 20’ cross were used. Two QTL were directly associated with resistance to aphid as measured by aphid damage index. qRa_1, close to Satt470 on soybean linkage group (LG) A2 (chromosome 8), was consistently detected for 3- and 4-week ratings and explained a large portion of phenotypic variations ranging from 25 to 35%. qRa_2, close to Satt144 of LG F (chromosome 13), was detected for 3- and 4-week ratings and could explain 7 and 11% of the phenotypic variation, respectively. These two QTL were highly associated with high isoflavone content and both positive alleles were derived from ‘Zhongdou 27’, a cultivar with higher isoflavone content. The results revealed that higher individual or total isoflavones contents in soybean lines could protect soybean against aphid attack. These two QTL detected jointly provide potential for marker-assisted selection to improve the resistance of soybean cultivars to aphid along with the increase of isoflavone content.     

Identification of QTLs controlling somatic embryogenesis using RI population of cultivar × weedy soybean

Quantitative trait loci (QTLs) controlling ability of somatic embryogenesis were identified in soybean. A frame map with 204-point markers was developed using an RI population consisting of 117 F₁₁ lines derived from a cross between cultivar ‘Keburi’ and a weedy soybean ‘Masshokutou Kou 502’. The parents differed greatly in their abilities of somatic embryogenesis using immature cotyledons as explants. The ability of somatic embryogenesis was evaluated in five different experiments: the F₁₁ (evaluated in 1998) and F₁₅ (2002) generations cultured on basal media supplemented with 40 mg l⁻¹ 2,4-D (2,4-D1998 and 2,4-D2002), F₁₄ (2001) generation on medium with 40 mg l⁻¹ 2,4-D and high sucrose concentration [2,4-D2001 (30 g l⁻¹ sucrose)], and the F₁₁ (1998) and F₁₂ (1999) generations on medium with 10 mg l⁻¹ NAA (NAA1998 and NAA1999). The RILs showed wide and continuous variations in each of the five experiments. In the composite interval mapping analysis, 2 QTLs were found in group 8 (D1b + W, LOD = 5.42, r ² = 37.5) in the experiment of 2,4-D1998 and in group 6 (C2, LOD = 6.03, r ² = 26.0) in the experiment of 2,4-D2001 (high concentration sucrose). In both QTLs, alleles of ‘Masshokutou Kou 502’ with high ability of somatic embryogenesis contributed to the QTLs. For the other three experiments, no QTL was detected in the criteria of LOD >3.0, suggesting the presence of minor genes.