Inheritance of kernel row number, a multicategorical threshold trait of maize ears

Information about the inheritance of threshold traits is scarce, especially in plants. We examined the genetic control of kernel row number in maize (Zea mays). Knowledge of this inheritance is especially important because it is a primary component of grain yield. This trait has a discontinuous distribution. Characters like these are conceptualized as threshold traits. Crosses were made between the inbred line Geneze 3 (G3) with many kernel rows and the inbreds Argentino IV (A4) and Dente de Cravo (DC), with fewer kernel rows. The F(1) and F(2) generations and the backcrosses BC(11) and BC(21) were obtained for the combinations G3 x A4 and G3 x DC. These populations were evaluated under field conditions, and the kernel row number was determined by direct counting of approximately 14, 140 and 75 ears for the F(1), F(2) and backcrosses, respectively. Genetic control was determined through estimates of generation means and variance analysis and was also performed by Wright's method for threshold traits. It was found that genetic control is predominantly due to additive alleles. The component a, was greater than zero, additive variance was positive and the variance of dominance did not differ from zero. In the F(2) generation, the range of the kernel row number was 10 to 28 in G3 x A4, while in G3 x DC it was 12 to 26. Inheritance of the number of kernel rows, estimated by the two methods, gave similar results. This correspondence is due to adjusting of the data to the normal distribution.     

Extensive diversity and inter-genepool introgression in a world-wide collection of indeterminate snap bean accessions

Common bean can be grown as a grain crop (dry beans) or as a fresh vegetable (snap beans/green beans), both items being important in nutritional terms for providing essential minerals and vitamins to the diet. Snap beans are thought to be derived predominantly from dry beans of the Andean genepool and to be of a recent European origin; however, the existence of Mesoamerican genepool characteristics especially in traditional indeterminate growth habit snap beans indicates a wider origin. The objective of this study was to evaluate genetic diversity within a set of 120 indeterminate (pole type) snap beans and 7 control genotypes representing each genepool using amplified fragment length polymorphism (AFLP) and simple sequence repeat or microsatellite (SSR) markers. The genotypes were predominantly from Asia, Europe and the United States but included some varieties from Latin America and Africa. AFLP polymorphism ranged from 53.2 to 67.7% while SSR polymorphism averaged 95.3% for the 32 fluorescent and 11 non-fluorescent markers evaluated and total expected heterozygosity was higher for SSR markers (0.521) than for AFLP markers (0.209). Both marker systems grouped the genotypes into two genepools with Andean and Mesoamerican controls, respectively, with the Mesoamerican group being predominant in terms of the number of genotypes assigned to this genepool. Phaseolin alleles were not tightly associated with genepool assignment indicating that introgression of this locus had occurred between the genepools, especially with phaseolin “S” in the Andean group (23.5%) and phaseolins “T” and “C” in the Mesoamerican group (12.2 and 8.2%, respectively). The implications of these results on the origin of pole type snap beans and on breeding strategies for this horticultural crop are discussed.     

Hybrid Weakness in Phaseolus vulgaris L. II. Disruption of Root-Shoot Integration

We have been examining the importance of the root system on shoot growth and development using a developmentally disabled hybrid of the common bean Phaseolus vulgaris L. Parental cultivars (P. Vulgaris cv. Redkloud of Mesoamerican origin, and P. vulgaris cv. Batt of Andean origin) grow normally, but crosses produce F1 hybrids exhibiting hybrid weakness associated with reduced root and shoot growth. In this study, applications of benzylaminopurine (BAP) to roots of F1 hybrids increased the number of root tips and leaves. Reciprocal grafting was used to study the effects of the root system on shoots. Grafting of roots of the Mesoamerican cultivar onto shoots of F1 hybrids increased the cytokinin concentrations in leaves of F1 hybrids and removed the characteristics associated with hybrid weakness. To determine whether factors in the xylem sap enhanced leaf growth, leaf discs were incubated on sap collected from Mesoamerican and Andean cultivars. Sap from Mesoamerican plants enhanced the growth of leaf discs excised from F1 hybrids more than sap collected from Andean cultivars. Estimates of the transport of zeatin riboside (ZR)–type cytokinins from roots of F1 hybrids indicated that transport out of hybrid roots was reduced compared with those transported out of Mesoamerican or Andean roots. Results suggest that ZR-type cytokinins are involved in hormonal integration between roots and shoots of P. vulgaris and that one of the barriers to hybridization between Andean and Mesoamerican landraces is related to hormone transport. Received October 15, 1998; accepted May 12, 1999     

Inheritance of resistance to ear damage caused by Sesamia nonagrioides (Lepidoptera: Noctuidae) in maize

Sesamia nonagrioides Lefebvre is a major insect pest of maize (Zea mays L.) in northwestern Spain. The inheritance of ear resistance in field corn to this pest has not been studied. This work aims to determine the importance of genetic (additive, dominance, and epistatic effects) and environmental effects in the inheritance of ear resistance to S. nonagrioides. Three field corn inbreds (CM109, EP31, and EP42) were used as parents and two crosses (CM109 x EP31 and CM109 x EP42) were made. These inbreds show different ear resistance levels to S. nonagrioides, with CM109 more resistant than EP31 and EP42. For each cross, parents (P1, P2), F1, F2, and backcrosses to each parent (BC1 and BC2) were evaluated. Correlations among ear damage traits showed that general appearance of the ear should be useful indicator of ear resistance. Ear resistance was dominant to susceptibility and was transmitted from inbreds to their hybrids. The additive-dominance model fit the generation mean analysis for both crosses and the degree of genetic control varied depending on the cross and trait. For both crosses, additive and dominance effects were significant for most ear damage traits. Epistatic gene effects were significant for husk and shank damage, and gene effects for number and length of tunnels were not significant. Because ear resistance involved additive and dominance effects for this set of inbreds, breeding procedures based on both types of gene action should be effective.     

Evaluation of genetic behavior of some Egyption Cotton genotypes for tolerance to water stress conditions

Water stress is a critical abiotic stress for plant reduction in arid and semiarid zones and, has been discovered to be detrimental to the development of seedlings as well as the growth and physiological characteristics of many crops such as cotton. The objectives of our study were to determine the combining ability and genetic components for five quantitative traits [(leaf area (LA), leaf dry weight (LDW), plant height (PH), fiber length (2.5 percent SL), and lint cotton yield/plant (LCY/P)] under water shortage stress, a half diallel cross between six cotton genotypes representing a wide range of cotton characteristics was evaluated in RCBD with four replications. The genotype mean squares were significant for all traits studied, demonstrating significant variation among genotypes for all characters under water shortage stress. LCY/P had the highest phenotypic and genotypic correlation co-efficient with PH, LDW, and LA shortage. The highest direct effect on lint cotton yield was exhibited by leaf area (3.905), and the highest indirect effects of all traits were through LA, with the exception of 2.5 percent SL, which was through LDW. The highest dissimilarity (Euclidean Distance) between parental genotypes was between G.87 and G.94, followed by G.87 and Menoufi. G.94 was also a well-adapted genotype, and the combinations G.87 x G.94 and G.87 x Menoufi may outperform their parents. The combining ability analysis revealed highly significant differences between parental GCA effects and F1 crosses SCA effects. The variation of GCA and SCA demonstrated the assurance of additive and non- additive gene action in the inheritance of all traits studied. In terms of general combining ability (GCA) effects, parental genotype G.94 demonstrated the highest significant and positive GCA effects for all traits studied, with the exception of 2.5 percent SL, where G.87 revealed the highest significant and positive GCA effects. The effects of specific combining ability (SCA) revealed that the cross (G.87 x2G.94) revealed stable, positive, and significant SCA for all of the studied traits.     

Genetic regulation on the black phenotype mutants of moth and pupa of Helicoverpa armigera (Lepidoptera: Noctuidae)

Genetic regulation on body color of a mutant strain, JBM of Helicoverpa armigera with black body color of pupae and adults, was investigated. Reciprocal crosses between JBM and JBW (a wild strain with yellow brown body color of pupae and adults) were used to determine the inheritance characteristics of body color. Analysis of the ratio of phenotype segregation from the F1 generation, F2 generation, F3 generation, BC1 (F1 x JBM) generation and F1 generation of BC1 indicated that the black body color was controlled by one recessive gene.     

Diversity in the rhizobia associated with Phaseolus vulgaris L. in Ecuador, and comparisons with Mexican bean rhizobia

Common beans (Phaseolus vulgaris L.) have centers of origin in both Mesoamerica and Andean South America, and have been domesticated in each region for perhaps 5000 years. A third major gene pool may exist in Ecuador and Northern Peru. The diversity of the rhizobia associated with beans has also been studied, but to date with an emphasis on the Mesoamerican center of origin. In this study we compared bean rhizobia from Mexico and Andean South America using both phenotypic and phylogenetic approaches. When differences between the rhizobia of these two regions were shown, we then examined the influence of bean cultivar on the most probable number (MPN) count and biodiversity of rhizobia recovered from different soils. Three clusters of bean rhizobia were distinguished using phenotypic analysis and principal-component analysis of Box AIR-PCR banding patterns. They corresponded principally to isolates from Mexico, and the northern and southern Andean regions, with isolates from southern Ecuador exhibiting significant genetic diversity. Rhizobia from Dalea spp., which are infective and effective on beans, may have contributed to the apparent diversity of rhizobia recovered from the Mesoamerican region, while the rhizobia of wild Phaseolus aborigineus from Argentina showed only limited similarity to the other bean rhizobia tested. Use of P. vulgaris cultivars from the Mesoamerican and Andean Phaseolus gene pools as trap hosts did not significantly affect MPN counts of bean rhizobia from the soils of each region, but did influence the diversity of the rhizobia recovered. Such differences in compatibility of host and Rhizobium could be a factor in the poor reputation for nodulation and N2 fixation in this crop.     

Experimental designs and statistical methods for mapping quantitative trait loci underlying triploid endosperm traits without maternal genetic variation

Many endosperm traits are related to grain quality in cereal crops. Endosperm traits are mainly controlled by the endosperm genome but may be affected by the maternal genome. Studies have shown that maternal genotypic variation could greatly influence the estimation of the direct effects of quantitative trait loci (QTLs) underlying endosperm traits. In this paper, we propose methods of interval mapping of endosperm QTLs using seeds of F2 or BC1 (an equal mixture of F1 x P1 and F1 x P2 with F1 as the female parent) derived from a cross between 2 pure lines (P1 x P2). The most significant advantage of our experimental designs is that the maternal effects do not contribute to the genetic variation of endosperm traits and therefore the direct effects of endosperm QTLs can be estimated without the influence of maternal effects. In addition, the experimental designs can greatly reduce environmental variation because a few F1 plants grown in a small block of field will produce sufficient F2 or BC1 seeds for endosperm QTL analysis. Simulation studies show that the methods can efficiently detect endosperm QTLs and unbiasedly estimate their positions and effects. The BC1 design is better than the F2 design.     

Inheritance and Expression of Copies of Transgenes 1Dx5 and 1Ax1 in Elite Wheat （Triticum aestivum L.） Varieties Transferred from Transgenic Wheat through Conventional Crossing

To study the inheritance and expression of multiple copies of transgenes from transgenic wheat lines, three crosses between transgenic wheat lines B72-8-11b and B102-1-2 and Chinese elite wheat varieties Chuan89-107 and Email 8 were carried out. Chuan89-107×B72-8-11b, Chuan89-107×B102-1-2 and Email 8×B72-8-11b, and F_1 plants were selfed or backcrossed to obtain different generation populations. Protein analysis in grains of F_1 and F_2 and backcross progenies of BC_1F_1, BC_1F_2, BC_1F_3, BC_2F_1, BC_2F_2 and BC_2F_3 by sodium dodecyl sulfate-polyacrylamide gel electrophoresis showed that the transgenes lDx5 and lAx1 were expressed and segregated in the target wheat according to Mendelian laws. A range of lDx5 expression levels were observed in the progenies of Chuan89-107×B72-8-11b and Emai 18×B72-8-11b, but the expression levels of lAx1 in progenies of Chuan89-107×B102-1-2 rarely changed. It suggested that the two foreign genes had different mechanisms of expression in the cross progeny, even though they were produced in the same way and the foreign lDx5 gene of 5-10 copies had the more complicated expression mechanism than the lAx1 gene of 4-5 copies.     

甘蔗野生种割手密远缘杂交后代品质性状的遗传研究

利用甘蔗品种Co419与野生种割手密云南75-1-2远缘杂交,ROC25与远缘杂交后代云野02-356进行回交,分别获得F1和BC1群体;利用R软件,分析了2个群体全部真实性后代品质性状的遗传表现.结果表明,杂交后代品质性状广义遗传力高,正态分布特性明显,品质性状间显著正相关;F1含糖量和纤维含量高于商业亲本,但甘蔗蔗糖分、蔗汁糖分、蔗汁锤度和简纯度等性状劣于商业亲本;BC1除含糖量高于双亲外,其他性状介于双亲之间,但主要性状均优于F1,后代性状恢复快.     

Hybrid Weakness in Phaseolus vulgaris L. I. Disruption of Development and Hormonal Allocation

A reduced concentration of cytokinins may cause the abnormal growth and development found in F1 hybrids between Andean and Mesoamerican races of Phaseolus vulgaris L. In this study, concentrations of the transportable cytokinin zeatin riboside (ZR) were measured by ELISA for ZR (cross reactivities dihydrozeatin, 14%, zeatin 7.6%) in roots, stems, and leaves of a Phaseolus Mesoamerican landrace (P. vulgaris L. cv. Redkloud), an Andean landrace (P. vulgaris L. cv. Batt), and their F1 hybrids. Concentrations of ZR in roots and leaves of F1 hybrids were significantly less than that found in roots and leaves of parental cultivars. Approximately 90% of the ZR found in F1 hybrids was found sequestered in the stems, whereas cytokinins of the parental cultivars were distributed throughout the plant (roots: Batt 37%, Redkloud, 44%; stems: Batt 35%, Redkloud 42%; leaves: Batt 28%, Redkloud 14%). These results suggest that abnormal growth and development of F1 hybrids may involve interruption of the regulation of cytokinin allocation, thereby disrupting the root-shoot feedback loop between root-sourced cytokinins and putative shoot-produced factors. Received October 15, 1998; accepted May 12, 1999     

Frequency and fidelity of alien chromosome transmission in Gossypium hexaploid bridging populations.

The Australian diploid Gossypium species possess traits of potential agronomical value, such as gossypol-free seeds and Fusarium wilt resistance. However, they belong to the tertiary germplasm pool, which is the most difficult group of species from which to introgress genes into G. barbadense L. and G. hirsutum L. Interspecific triploid hybrids can be generated but they are sterile. The sterility barrier can be overcome using synthetic polyploids as introgression bridges, but whether there is sufficient homoeologous chromosome interaction at meiosis to allow recombination is still an open question. To ascertain, genetically, observable levels of homoeologous introgression, 2 synthetic hexaploid lines (2x G. hirsutum x G. australe and 2x G. hirsutum x G. sturtianum) were crossed to G. hirsutum to generate pentaploid F1 plants that, in turn, were backcrossed to G. hirsutum to generate BC1 and BC2 multiple alien chromosome addition lines (MACALs). Gossypium australe F. Muell. and G. sturtianum Willis chromosome-specific markers were used to track the frequency and fidelity of chromosome transmission to the BC1 and BC2 MACALs. The chromosomal location of the AFLP markers was determined by their distribution among the MACALs and confirmed in parental F2 families. Roughly half the available chromosomes were transmitted to the G. hirsutum x G. australe (54%) and G. hirsutum x G. sturtianum (52%) BC1 MACALs. The BC2 MACAL families again inherited about half of the available chromosomes. There were, however, notable exceptions for specific chromosomes. Some chromosomes were preferentially eliminated, while others were preferentially transmitted. Consistent with the genomic stability of Gossypium synthetic polyploids, the de novo loss or gain of AFLP fragments was rarely observed. While restructuring of the donor G. australe and G. sturtianum chromosomes was observed, this is more likely the result of chromatin loss, and no clear cases of introgression of donor chromatin into the recipient G. hirsutum genome were observed.     

Qualitative inheritance of rind pattern and flesh color in watermelon

Watermelon [Citrullus lanatus (Thunb.) Matsum. & Nakai var. lanatus] is a diverse species, with fruits of different sizes, shapes, rind patterns, and flesh colors. This study measured the inheritance of novel rind phenotypes and verified the genetics of white, red, salmon yellow, and canary yellow flesh colors. For each of the 11 crosses, six generations (P(a)S1, P(b)S1, F1, F2, BC1P(a), and BC1P(b)) were produced to form 11 families. Three new genes were identified and designated as follows: Scr for the scarlet red flesh color of Dixielee and Red-N-Sweet, Yb for the yellow belly (ground spot) of Black Diamond Yellow Belly, and ins for the intermittent stripes of Navajo Sweet. The inheritance of the C gene for the canary yellow flesh color was verified as single dominant, and a new inbred type line was developed possessing that gene. Aberrations in the segregation of red, white, and salmon yellow flesh colors were recorded, raising questions on the inheritance of these traits. Finally, the spotted phenotype from Moon and Stars was combined with light green and gray rind patterns for the development of novel cultivars with distinctive rind patterns.     

Domestication patterns in common bean (Phaseolus vulgaris L.) and the origin of the Mesoamerican and Andean cultivated races

Chloroplast DNA polymorphisms were studied by PCR sequencing and PCR-restriction fragment length polymorphism in 165 accessions of domesticated landraces of common bean from Latin America and the USA, 23 accessions of weedy beans, and 134 accessions of wild beans covering the entire geographic range of wild Phaseolus vulgaris. Fourteen chloroplast haplotypes were identified in wild beans, only five of which occur also in domesticated beans. The chloroplast data agree with those obtained from analyses based on morphology and isozymes and with other DNA polymorphisms in supporting independent domestications of common bean in Mesoamerica and the Andean region and in demonstrating a founder effect associated with domestication in each region. Andean landraces have been classified into three different racial groups, but all share the same chloroplast haplotype. This suggests that common bean was domesticated once only in South America and that the races diverged post-domestication. The haplotype found in Andean domesticated beans is confined to the southern part of the range of wild beans, so Andean beans were probably domesticated somewhere within this area. Mesoamerican landraces have been classified into four racial groups. Our limited samples of Races Jalisco and Guatemala differ from the more widespread and commercially important Races Mesoamerica and Durango in types and/or frequencies of haplotypes. All four Mesoamerican races share their haplotypes with local wild beans in parts of their ranges. Independent domestications of at least some of the races in Mesoamerica and/or conversion of some locally adapted wild beans to cultigens by hybridization with introduced domesticated beans, followed by introgression of the domestication syndrome seem the most plausible explanations of the chloroplast and other molecular data.     

Mitochondrial restriction fragment length polymorphisms in wild Phaseolus vulgaris L.: insights on the domestication of the common bean

Summary Previous examination of intraspecific mitochondrial DNA (mtDNA) diversity in common bean, Phaseolus vulgaris, showed that five restriction fragment length polymorphisms (RFLPs) distinguish the mitochondrial genomes of the two major gene pools of cultivated beans, the Mesoamerican and the Andean. In the study presented here, mtDNA was used to compare the amount of diversity in cultivated beans to that in collections of wild beans to gain an understanding of how and when the mitochondrial genomes of the gene pools became distinct. The mtDNA of six wild bean accessions from Central and South America were digested with nine restriction endonucleases and analyzed by Southern hybridization. A total of twenty RFLPs were detected demonstrating a significantly higher amount of mtDNA variability in wild beans than in cultivated ones. All of the wild beans had the same mtDNA pattern for four out of the five inter-gene pool RFLPs, indicating that the polymorphism arose soon after domestication: two in the gene pool of the cultivated Mesoamerican beans and two in the gene pool of the cultivated Andean beans. The fifth RFLP must have occurred before domestication since the locus was also polymorphic in the wild beans. Wild beans from the south Andes were distinct and less variable than wild accessions of the north Andes and Mesoamerica. The distribution of mtDNA RFLPs among the wild beans supports the concept of two distinct domestication events for P. vulgaris.     

Development of a Mesoamerican intra-genepool genetic map for quantitative trait loci detection in a drought tolerant?×?susceptible common bean (Phaseolus vulgaris L.) cross

Drought is a major constraint to common bean (Phaseolus vulgaris L.) production, especially in developing countries where irrigation for the crop is infrequent. The Mesoamerican genepool is the most widely grown subdivision of common beans that include small red, small cream and black seeded varieties. The objective of this study was to develop a reliable genetic map for a Mesoamerican × Mesoamerican drought tolerant × susceptible cross and to use this map to analyze the inheritance of yield traits under drought and fully irrigated conditions over 3 years of experiments. The source of drought tolerance used in the cross was the cream-seeded advanced line BAT477 crossed with the small red variety DOR364 and the population was made up of recombinant inbred lines in the F5 generation. Quantitative trait loci were detected by composite interval mapping for the traits of overall seed yield, yield per day, 100 seed weight, days to flowering and days to maturity for each field environment consisting of two treatments (irrigated and rainfed) and lattice design experiments with three repetitions for a total of six environments. The genetic map based on amplified fragment length polymorphism and random amplified polymorphic DNA markers was anchored with 60 simple sequence repeat (SSR) markers and had a total map length of 1,087.5 cM across 11 linkage groups covering the whole common bean genome with saturation of one marker every 5.9 cM. Gaps for the genetic map existed on linkage groups b03, b09 and b11 but overall there were only nine gaps larger than 15 cM. All traits were inherited quantitatively, with the greatest number for seed weight followed by yield per day, yield per se, days to flowering and days to maturity. The relevance of these results for breeding common beans is discussed in particular in the light of crop improvement for drought tolerance in the Mesoamerican genepool.     

Inheritance of seed color in Capsicum

The mode of seed color inheritance in Capsicum was studied via an interspecific hybridization between C. pubescens Ruiz and Pav. (black seed color) and C. eximium Hunz. (yellow seed color). Black seed color was dominant over yellow seed color. The F(2) segregation pattern showed continuous variation. The generation means analysis indicated the presence of a significant effect of additive [d], dominance [h], and additive x additive [i] interaction for seed color inheritance. The estimate for a minimum number of effective factors (genes) involved in seed color inheritance was approximately 3.     

Development, characterization, and comparative analysis of polymorphism at common bean SSR loci isolated from genic and genomic sources.

Microsatellites or SSRs (single sequence repeats) have been used to construct and integrate genetic maps in crop species, including Phaseolus vulgaris. In the present study, 3 cDNA libraries generated by the Bean EST project (http://lgm.esalq.usp.br/BEST/), comprising a unigene collection of 3126 sequences and a genomic microsatellite-enriched library, were analyzed for the presence of SSRs. A total of 219 expressed sequence tags (ESTs) were found to carry 240 SSRs (named EST-SSR), whereas 714 genomic sequences contained 471 SSRs (named genomic-SSR). A subset of 80 SSRs, 40 EST-SSRs, and 40 genomic-SSRs were evaluated for molecular polymorphism in 23 genotypes of cultivated beans from the Mesoamerican and Andean genetic pools, including Brazilian cultivars and 2 related species. Of the common bean genotypes, 31 EST-SSR loci were polymorphic, yielding 2-12 alleles as compared with 26 polymorphic genomic-SSRs, accounting for 2-7 alleles. Cluster analysis from data using both genic and genomic-SSR revealed a clear separation between Andean and Mesoamerican beans. The usefulness of these loci for distinguishing bean genotypes and genetic mapping is discussed.     

Mapping QTL for climbing ability and component traits in common bean (<Emphasis Type="Italic">Phaseolus vulgaris</Emphasis> L.)

Common bean (Phaseolus vulgaris L.) varies in growth habit from aggressive climbing types to bush beans. Growth habit is determined by a combination of factors including determinate versus indeterminate growth, total plant height, degree of branching and internode length. Together these factors make up climbing ability. The objective of this research was to determine the quantitative trait loci (QTL) controlling climbing ability in a F_5:8 recombinant inbred line population derived from an inter-gene pool cross of an aggressive indeterminate climbing bean with type IV growth habit (G2333) by an indeterminate bush bean of type IIb growth habit (G19839). The population was planted in four randomized complete block design experiments across environments that varied in altitude (from 1,000 to 1,750 masl) and soil fertility (low versus high phosphorus). QTL were identified for plant height, internode length and number of branches per plant on a genetic map covering all common bean linkage groups with a total length of 1,175 cM. In addition a scale was developed to evaluate overall climbing ability and was also used to identify QTL. A total of 7 QTL were found for plant height, 9 for climbing ability, 6 for internode length and 1 for branch number. The largest number and most significant QTL were found on the lower half of linkage group B04 suggesting a major pleiotropic locus for growth habit traits at this location of the genome that is distinct from previously characterized genes which control plant morphology of the crop.     

分子标记辅助选择改良蜀恢527对白叶枯病的抗性

以含抗性基因Xa2 1和Xa4的抗白叶枯病近等基因系IRBB6 0为供体亲本 ,以不抗白叶枯病强恢复系蜀恢5 2 7为轮回受体亲本 ,连续回交 3代 ,自交 1代 ,在分离世代用分别与Xa2 1和Xa4紧密连锁的标记pTA2 48和MP12对目标基因Xa2 1和Xa4进行辅助选择 ,直至BC3F2 。在BC3F2 中选出株型、粒型、播抽期等农艺性状与蜀恢 5 2 7相似且pTA2 48和MP12的扩增带型纯合的 10个单株 ,用 10 0个RAPD和 12 0对SSR引物进行背景选择 ,决选出 5个单株 ,作为改良的蜀恢 5 2 7。抗性分析表明 ,这些改良的蜀恢 5 2 7株系对我国菌系CⅠ CⅦ和来自菲律宾的P1 和P6 均表现抗性 ,说明抗性基因已成功导入蜀恢 5 2 7中并表达。同时对pTA2 48和MP12在亲本间的多态性和选择的准确性也进行了分析 ,结果显示这两个标记在亲本间的多态性明显 ,共显性 ;选择的准确率分别在 97%和 83%以上 ,可以用其进行标记辅助选择。