Heterosis,combining ability and genetic effect,and relationship with genetic distance based on a diallel of hybrids from five diverse <Emphasis Type="Italic">Gossypium barbadense</Emphasis> cotton genotypes

The cultivated tetraploid Gossypium barbadense L. cotton produces superior natural fibers for the textile industry in the world. However, the possibility in utilization of heterosis to further increase its lint yield has not been extensively explored. In this study, two commercial US Pima cotton cultivars and three exotic G. barbadense lines, together with all of their possible hybrids in F₁ and F₂ progeny without reciprocals, were tested for lint yield, yield components, and fiber quality traits in four environments in 2005–2007. With a few exceptions, genotype (G), environment (E), and G × E were all significant or highly significant for all the traits studied. General combining ability (GCA) variances for all the traits in both F₁ and F₂ were also significant, while specific combining ability (SCA) variances were detected only for lint yield, fiber length, and micronaire in both generations and boll weight in F₁. GCA × E was also detected for lint percent, seed index, and fiber length in both F₁ and F₂, and boll weight in F₁, but none of the traits had significant SCA × E. As a group, F₁ and F₂ out-yielded the parent group by 20–40% and 6–10%, respectively. Mid-parent heterosis (MPH) for lint yield in F₁ was generally positive, ranging from ?4.7 to 116.4% with an average of 21.2–48.7%, while lint yield MPH in F₂ ranged from ?23.3 to 69.4% with an average of 6.4–12.4%. However, useful heterosis in lint yield was only detected in the hybrid between the two US commercial cultivars Pima S-7 and DP 340. MPH for other traits was low or not detected. MPH in F₂ was lower than that in F₁ but they were generally positively correlated. The genetic distances (GD) of the parents (based on 467 polymorphic RAPD and AFLP markers) between the five parents was not consistently correlated with MPH and SCA of their hybrids and dominant effects for lint yield and other traits. However, significant and positive correlations between GD of parents and the performance of their hybrids were detected for lint yield, lint percentage, and lint index in both F₁ and F₂ in most of the tests. GD of parents was also correlated with their GCA and additive effects in lint yield, lint percent, lint index, micronaire, plant height, and elongation. The results suggest that the close correlation between GD and hybrid performance per se was mainly due to the existence of GCA and additive effects from parents.     

Pattern of genetic inheritance of morphological and agronomic traits of sorghum associated with resistance to sorghum shoot fly, <Emphasis Type="Italic">Atherigona soccata</Emphasis>

Sorghum shoot fly, Atherigona soccata is an important pest of sorghum during the seedling stage, which influences both fodder and grain yield. To understand the nature of inheritance of shoot fly resistance in sorghum, we performed generation mean analysis using two crosses IS 18551 × Swarna and M 35-1 × ICSV 700 during the 2013–2014 cropping seasons. The F₁, F₂, BC₁ and BC₂ progenies, along with the parental lines were evaluated for agronomic and morphological traits associated with resistance/susceptibility to sorghum shoot fly, A. soccata. The cross IS 18551 × Swarna exhibited significant differences between the parents for shoot fly deadhearts (%) in the postrainy season. The progenies of this cross exhibited lower shoot fly damage, suggesting that at least one of the parents should have genes for resistance to develop shoot fly-resistant hybrids. Leaf glossiness, leafsheath pigmentation and plant vigor score during the seedling stage exhibited non-allelic gene interactions with dominant gene action, whereas 100 seed weight showed both additive and dominant gene interactions. Presence of awns showed recessive nature of the awned gene. Generation mean analysis suggested that both additive and dominance gene effects were important for most of the traits evaluated in this study, but dominance had a more pronounced effect.     

Inheritance of Dry Root Rot (Rhizoctonia bataticola) Resistance in Chickpea (Cicer arietinum)

The inheritance of resistance to dry root rot of chickpea caused by Rhizoctonia bataticola was studied. Parental F₁ and F₂ populations of two resistant and two susceptible parents, along with 49 F₁ progenies of one of the resistant × susceptible crosses were rested for their reaction to dry root rot using the blotting-paper technique. All F, plants of the resistant × susceptible crosses were resistant; the F₂ generation fitted a 3 resistant: 1 susceptible ratio indicating monogenic inheritance, with resistance dominant over susceptibility. F³ family segregation data confirmed the results. No segregation occurred among the progeny of resistant × resistant and susceptible × susceptible crosses.     

Little heterosis for yield and yield components in hybrids of six cucumber inbreds

Heterosis and inbreeding depression for fruit yield has been reported for pickling cucumber (Cucumis sativus L.). However, cucumber inbreds often perform as well as hybrids, and there is little inbreeding depression. The objectives of this study were to reexamine the amount of heterosis and inbreeding depression for fruit yield and yield components in pickling cucumber, and to determine the relationship between yield components and yield for heterosis. Two pickling cucumber inbreds (M 12, M 20) and inbreds from four open-pollinated monoecious cultivars (‘Addis’, ‘Clinton’, ‘Wisconsin SMR 18’, ‘Tiny Dill’) were hybridized to form four F₁ hybrids (‘Addis’ × M 20, ‘Addis’ × ‘Wis. SMR 18’, ‘Clinton’ × M 12, M 20 × ‘Tiny Dill’). F₁ hybrids were then self-pollinated or backcrossed to generate F₂, BC_1A, and BC_1B progeny. Thirty plants of each generation within each hybrid family were grown in plots 3.1 m long with four replications in each of two seasons. Data were collected from once-over harvest for vegetative, reproductive, yield, and fruit quality traits. Heterosis and inbreeding depression for fruit yield and yield components were not observed in three of the hybrids. Only ‘Addis’ × ‘Wis. SMR 18’ exhibited high-parent heterosis and inbreeding depression for total, marketable, and early fruit weight. For ‘Addis’ × ‘Wis. SMR 18’, heterosis for fruit yield was associated with a decreased correlation between percentage of fruit set and fruit weight, an increased negative correlation between percentage of fruit set and both the number of branches per plant and the percentage of pistillate nodes, and an increased negative correlation between the number of nodes per branch and total fruit weight. Inbreeding depression was associated with a weakening of the strong negative correlations between percentage of fruit set and the number of branches per plant, and between the number of nodes per branch and total fruit weight. Those correlations were associated with high-parent heterosis and inbreeding depression only for one cross, and do not necessarily apply to future crosses in which heterosis may be observed for yield. We did not observe the heterosis or inbreeding depression for yield in cucumber in most of the crosses as was reported by Ghaderi & Lower (1979a; 1979c). This revised version was published online in August 2006 with corrections to the Cover Date.     

Genetic mapping of gummy stem blight (Didymella bryoniae) resistance genes in Cucumis sativus-hystrix introgression lines

Gummy stem blight (GSB, Didymella bryoniae (Auersw.) Rehm) is a devastating disease occurring worldwide in cucumber (Cucumis sativus L.) production and causing considerable yield loss. No commercially available cultivars are resistant to GSB. By screening 52 introgression lines (ILs) derived from the cross of C. hystrix × C. sativus and eight cucumber cultivar/lines through a whole plant assay, three ILs (HH1-8-1-2, HH1-8-5, HH1-8-1-16) were identified as GSB resistant lines. Six common introgression regions in these three ILs were on Chromosomes 1, 4, and 6. To further map the resistance in the ILs, three mapping populations (2009F₂, 2009F₂′ and 2010F₂) from a cross between resistant IL HH1-8-1-2 and susceptible 8419 were constructed and used for QTL mapping with SSR markers. Two quantitative trait loci (QTLs) were identified; one on Chromosome 4 and the other on Chromosome 6. The interval for Chromosome 4 QTL is 12 cM spanning 3.569 Mbp, and the interval for Chromosome 6 QTL is 11 cM covering 1.299 Mbp. The mapped QTLs provide a foundation for map-based cloning of the genes and establishing an understanding of the associated mechanisms underlying GSB resistance in cucumber.     

Mapping of QTL associated with waterlogging tolerance and drought resistance during the seedling stage in oilseed rape (Brassica napus)

Soil waterlogging and drought are major environmental stresses that suppress rapeseed (Brassica napus) growth and yield. To identify quantitative trait loci (QTL) associated with waterlogging tolerance and drought resistance at the rapeseed seedling stage, we generated a doubled haploid (DH) population consisting of 150 DH lines from a cross between two B. napus lines, namely, line No2127-17 × 275B F₄ (waterlogging-tolerant and drought-resistant) and line Huyou15 × 5900 F₄ (waterlogging-sensitive and drought-sensitive). A genetic linkage map was constructed using 183 simple sequence repeat and 157 amplified fragment length polymorphism markers for the DH population. Phenotypic data were collected under waterlogging, drought and control conditions, respectively, in two experiments. Five traits (plant height, root length, shoot dry weight, root dry weight and total dry weight) were investigated. QTL associated with the five traits, waterlogging tolerance coefficient (WTC) and drought resistance coefficient (DRC) of all the traits were identified via composite interval mapping, respectively. A total of 28 QTL were resolved for the five traits under control conditions, 26 QTL for the traits under waterlogging stresses and 31 QTL for the traits under drought conditions. Eleven QTL were detected by the WTC, and 19 QTL related to DRC were identified. The results suggest that the genetic bases of both waterlogging tolerance and drought resistance are complex. Some of the QTL for waterlogging tolerance-related traits overlapped with QTL for drought resistance-related traits, indicating that the genetic bases of waterlogging tolerance and drought resistance in the DH population were related in some degree.     

Identifying QTL for fiber quality traits with three upland cotton (Gossypium hirsutum L.) populations

Cotton fiber quality was quantitative trait, controlled by multiple genes. Identification of stable quantitative trait loci (QTL) effectively contributing to favorable fiber quality traits would provide the key basis for marker-assisted selection used in molecular breeding projects. Three upland cotton F₂ populations were established with a common parent Chinese cultivar Yumian 1 and three American commercial cultivars/lines (Acala Maxxa, CA3084 and TAM94L-25), each of which had unique fiber quality characteristic that was favorable economically. Three whole genome genetic maps were constructed with 323, 302 and 262 SSR loci for population (Yumian 1 × Acala Maxxa), (Yumian 1 × CA3084), and (Yumian 1 × TAM 94L-25) respectively, spanning 1,617.2, 1,639.9 and 1,441.4 cM. Based on these genetic maps and three generation phenotypic data of fiber quality traits (F₂, F_2:3 and F_2:4), 77 QTL were detected, including 19 for fiber length, 14 for fiber uniformity, 17 for micronaire, 10 for fiber elongation, and 17 for fiber strength. Among these QTL, 46 QTL were significant QTL and 31 were putative QTL, including that one QTL (qFL05.1) and four QTL (qFL23.1, qFM06.1, qFM06.2 and qFE25.1) were detected across three and two populations respectively; two QTL qFL10.1 (Yumian 1 × TAM 94L-25) and qFL15.1 (Yumian 1 × Acala Maxxa) were detected in three generations; qFM23.1, qFE18.1 and qFS21.2 detected in population (Yumian 1 × CA3084), qFE10.1, and qFS10.2 detected in population (Yumian 1 × TAM 94L-25), and qFS15.1 detected in population (Yumian 1 × Acala Maxxa), were all detected in two generations. Alleles underlying these stable QTL were valuable candidate gene for fine mapping, cloning, and favorable gene pyramiding projects. Our study also verified that QTL mapping of fiber quality traits using multiple populations with a common parent had higher efficiency compared to single population crossed with two parents and favorable alleles contributed to QTL effect could be conferred by parents with inferior fiber quality traits.     

Analysis of generation means and components of variance for parthenocarpy in cucumber (Cucumis sativus L.)

Parthenocarpy (seedless fruit) has potential for increasing yield in cucumber (Cucumis sativus var. sativus L.). To determine the inheritance of parthenocarpy in gynoecious cucumber, P₁, P₂, F₁, F₂, BC₁P₁, and BC₁P₂ generations derived from crossing two non‐parthenocarpic gynoecious inbred lines [Gy8 (P₂; processing type) and ‘Marketmore 80’ (P₂; MM, fresh market type)] with a highly parthenocarpic inbred line [2A (P₁; processing type)] were evaluated for fruit number in a greenhouse at Arlington, Wisc. in 1999 (designated 2A × Gy8 1999) and in the open‐field at Hancock, Wisc. in 2000 (designated 2A × Gy8 2000 and 2A × MM 2000). There were significant location and location × generation interaction effects, and therefore generation means analyses were conducted separately for each location. The minimum numbers of effective factors controlling parthenocarpy were estimated to be at least one (2A × Gy8 1999), two (2A × Gy8 2000) and four (2A × MM 2000). Results suggest that selection for parthenocarpy for multiple hand harvest operations will likely be more effective than that for once‐over machine harvest operations. However, the selection efficiency will likely vary across different populations and environments.     

Aluminium tolerance in lentil (Lens culinaris Medik.) with monogenic inheritance pattern

The objectives of this study were to determine genetics of Al tolerance and whether the Al tolerance observed is governed by the same gene. The lines ‘L‐7903’ and ‘L‐4602’ have been developed through breeding programme as Al‐tolerant lines. These lines showed maximum root regrowth and minimum accumulation of Al and callose as compared to sensitive genotypes (‘BM‐4’ and ‘L‐4147’). Al tolerance in the parents, F₁, F₂ and backcross generations was estimated using the regrowth of the primary root after staining and scoring of fluorescent signals. The F₁ hybrids responded similarly to the tolerant parents, indicating dominance of Al tolerance over sensitivity. The segregation ratios obtained for Al tolerance and sensitivity in the F₂ and backcross generations were 3 : 1 and 1 : 1, respectively. Test of allelism confirmed the same gene was conferring Al tolerance in both genotypes (‘L‐7903’ and ‘L‐4602’) as the F₁ was also tolerant and no segregation of tolerant : sensitive was recorded. These results indicated that Al tolerance is a monogenic dominant trait that can be easily transferred to agronomic bases through backcross breeding technique.     

Root peroxidases and Rhizobium, Bradyrhizobium nodulation affinities of Phaseolus vulgaris L. and P. acutifolius A. Gray congruity backcross populations

Four parents [P. acutifolius var.acutifolius (A₁₉), P. a.var. latifolius `Serowi' (A<sub>9</sub>),P. a. var. latifolius(A<sub>10</sub>), and P. vulgaris `Red Cloud' kidney (V₁)] were used to create six interspecific recurrent and congruity backcross pedigrees (V₁ × A₉, A₉ × V₁, V₁ × A₁₀, A₁₀ × V₁, V₁ × A₁₉, A₁₉ × V₁) for evaluation of Rhizobium, Bradyrhizobium nodulation affinities and root peroxidase banding patterns. Most primary hybrids nodulated with all Rhizobium, Bradyrhizobium strains, while recurrent generations nodulated with strains of the recurrent parent, suggesting a number of independent loci and random assortment for strain-specific nodulation. A proximity matrix of nodulation phenotypes produced a cluster with V₁, two recurrent and two congruity backcross hybrids with V₁ as the cytoplasmic parent; a separate cluster with all primary interspecific and balanced, congruity backcross hybrids. A₉ and A₁₀were clustered the farthest away from V₁. Root peroxidase zymograms of primary hybrids were the summation of the parents and controlled by independent loci. Advanced hybrids exhibited new root peroxidases, matching those found for otherPhaseolus spp., including ancestralP. coccineus. A proximity matrix of root peroxidase phenotypes produced a cluster with only A₉ ³V₁F₁, a cluster containing only A₁₉ ³V₁ F₂, and a large cluster with all P. acutifoliusparents and hybrids with P. acutifolius as the cytoplasmic parent in balanced hybrids or the majority parent in unbalanced hybrids. Estimation of genetic distances showed primary, interspecific hybrids to be more closely related with the cytoplasmic parent. Recurrent and congruity backcross generations varied in genetic distances between each respective parent. This is the first report of congruity backcrossing creating hybrids with biochemical traits of nonparental species. This revised version was published online in August 2006 with corrections to the Cover Date.     

三个冬小麦杂交组合中七个农艺性状的遗传分析

本文通过对冬小麦的三个杂交组合:“万年2号×丰产3号”(杂交1)、“农林110×安徽11”(杂交3)与“(丰产3号×选209”(杂交3)六个世代(家系)遗传参数的估算初步分析了七个农艺性状遗传中的群体均数、狭义遗传力与基因效应等。F₁显著偏离中亲值以杂交3最为突出,表明非加性基因对这些性状的作用相当大。狭义遗传力依     

Genetic Analysis of Resistance to Phytophthora Root Rot in Tomato (Lycopersicon esculentum Mill.)

The resistant accession, LA1312, and the susceptible cultivar ‘Peto 343′, were crossed to develop F₁, F₂ and BC₁ populations for genetic analysis of resistance in tomatoes to Phytophthora parasitica Dastur, the causal agent of Phytophthora root rot. There was no maternal effect on resistance. Generation means analysis indicated that tolerance to Phytophthora root rot was under genetic control with both simple (additive and dominance) and digenic interaction (additive × additive and additive × dominance) effects contributing to the total genetic variation among generation means. Weighted least square regression analysis indicated that the majority (ca. 96 %) of the genetic variation could be explained by simple additive effects alone. Narrow sense heritability was estimated as 0.22. Based on effective factor formulae, at least five effective factors controlled the resistance. Implications for breeding procedures are discussed.     

Genetic analysis of photosynthesis‐related traits in faba bean (Vicia faba) for crop improvement

Increasing productivity through improvement of photosynthesis in faba bean breeding programmes requires understanding of the genetic control of photosynthesis‐related traits. Hence, we investigated the gene action of leaf area, gas exchange traits, canopy temperature, chlorophyll content, chlorophyll fluorescence parameters and biomass. We chose inbred lines derived from cultivars 'Aurora' (Sweden) and 'Mélodie' (France) along with an Andean accession, ILB 938, crossed them (Aurora/2 × Mélodie/2, ILB 938/2 × Aurora/2 and Mélodie/2 × ILB 938/2), and prepared the six standard generations for quantitative analysis (P₁, P₂, F₁, F₂, B₁, and B₂). Gene action was complex for each trait, involving additive and dominance gene actions and interactions. Additive gene action was important for SPAD, photosynthetic rate, stomatal conductance and F_v/F_m. Dominance effect was important for biomass production. It is suggested that breeders selecting for productivity can maximize genetic gain by selecting early generations for canopy temperature, SPAD and F_v/F_m, then later generations for biomass. The information on genetics of various contributing traits of photosynthesis will assist plant breeders in choosing an appropriate breeding strategy for enhancing productivity in faba bean.     

Resistance in Cucumis sativus L. to Tetranychus urticae Koch. 7. The inheritance of resistance and bitterness and the relation between these characters

Summary The inheritance of resistance to the twospotted spider mite and of bitterness in cucumber has been studied in three sets of P₁, P₂, F₁, F₂, B₁₁ and B₁₂ of crosses between three bitter, resistant lines and one non-bitter, susceptible line. Resistance to the twospotted spider mite as measured by acceptance and oviposition appeared to be determined by several to many genes, which are inherited mainly in an additive fashion. Bitterness is basically governed by the gene Bi, which, contrary to earlier reports, is inherited in an intermediary way, while the expression of Bi is influenced by additively inherited intensifier genes. Whereas Bi and the bitterness intensifier genes are not related to the resistance factors acceptance and oviposition, they are related to resistance or tolerance as measured by the damage index. This relation is explained by linkage rather than by identity of the genes concerned. Changes in the test methods and breeding consequences are discussed.     

Interactions amongst Mycorrhiza,Azotobacter chroococcum and Root Characteristics of Wheat Varieties

A field experiment was conducted in a randomized block design with three replications over 2 years to evaluate the effect of wheat cultivar and dual inoculation of Azotobacter chroococcum (Azc) and arbuscular mycorrhiza fungi (AMF, Glomus fasciculatum) on root characters and AMF infection in three crosses of wheat. The experimental material comprised four wheat parents, WH‐147, WH‐157, WH‐542 and PBW‐175, and three F₁ crosses, WH‐147 ×WH‐157, WH‐147 × WH‐542 and WH‐147 × PBW‐175. Comparison of treatment averages, i.e. control (mineral nutrients 60 kg N + 30 kg P₂O₅ + 12.5 kg ZnSO₄ ha^?1, as in other two treatments), AMF and AMF + Azc, revealed that inoculation of Azc led to an increase in AMF infection in roots. Maximum root biomass was obtained in F₁ hybrids WH‐147 × WH‐157 in the AMF treatment and in WH‐147 × PBW‐175 receiving AMF + Azc. Total root length and AMF infection of roots was maximum in WH‐147 × PBW‐175 for all the treatments during both years. A positive association between AMF infection in roots and Azotobacter survival in the rhizosphere was apparent. Similarly, maximum A. chroococcum counts were observed 80 and 120 days after sowing in the AMF + Azc treatment in cross WH147 × PBW175.     

Genetic analysis of plant height using two immortalized populations of “CRI12 × J8891” in Gossypium hirsutum L.

Plant height is an important plant architecture trait that determines the canopy structure, photosynthetic capacity and lodging resistance of upland cotton populations. To understand the genetic basis of plant height for marker-assisted breeding, quantitative trait loci (QTL) analysis was conducted based on the genetic map of recombinant inbred lines (RILs) derived from the cross “CRI12 × J8891” (Gossypium hirsutum L.). Three methods, including composite interval mapping, multiple interval mapping and multi-marker joint analysis, were used to detect QTL across multiple environments in the RILs and in the immortalized F₂ population developed through intermating between RILs. A total of 19 QTL with genetic main effects and/or genetic × environment interaction effects were identified on 15 chromosomes or linkage groups, each explaining 5.8–14.3 % of the phenotypic variation. Five digenic epistatic QTL pairs, mainly involving additive × additive and/or dominance × dominance, were detected in different environments. Seven out of eight interacting loci were main-effect QTL, suggesting that these loci act as major genes as well as modifying genes in the expression of plant height. The results demonstrate that additive effects, dominance and epistasis are all important for the genetic constitution of plant height, with additive effects playing a more important role in reducing plant height. QTL showing stability across environments that were repeatedly detected by different methods can be used in marker-assisted breeding.     

Involvement of higher order interactions addressing complex polygenetically controlled inheritance of downy mildew [Sclerospora graminicola (Sacc.) Schrot] resistance in pearl millet [Pennisetum glaucum (L.) R.Br.]

Inheritance of downy mildew [Sclerospora graminicola (Sacc.) Schrot]resistance was studied using generation mean analysis in pearl millet [Pennisetum glaucum (L.) R.Br.]. Eleven basic generations, namely, P₁, P₂, F₁, F₂, B₁, B₂, B₁F₂, B₂F₂, L₁, L₂ and L₃ of three crosses involving six diverse lines for downy mildew incidence were evaluated under artificial epiphytotic conditions over two environments. The downy mildew incidence was best fitting for digenic, trigenic and tetragenic ratios when fitted into classical Mendelian ratios demonstrating involvement of two or more genes. Digenic and trigenic interaction models were adequate in the case of crosses I and III respectively, to account for the total variability in generation means. Unlike severity, comparative estimates of gene effects over two environments were mostly consistent in all crosses for prevalence. Most of the epistatic and major gene effects were found significant in all crosses for both the disease traits. Non-allelic interactions particularly at three-gene loci viz., w (additive × additive × additive) and y (additive × dominance × dominance) in cross II and all trigenic interactions in cross III were predominant. Duplicate dominance (cross I) and complementary epistasis (crosses II and III) were observed for both the traits revealing inconsistency of gene effects over crosses. The gd₁ (interaction of additive gene effect with e₁) and gh₁(interaction of dominant gene effect with e₁) were significant in crosses I and II, indicating interaction of additive and dominance gene effects with environments. Thus a breeding method that can mop up the resistant genes to form superior gene constellations interacting in a favorable manner against pathotype I would be more suitable to accelerate the pace of resistance improvement. This revised version was published online in August 2006 with corrections to the Cover Date.     

Inheritance and allelic relationship among gene(s) for blast resistance in pearl millet [Pennisetum glaucum (L.) R. Br.]

Six blast‐resistant pearl millet genotypes, ICMB 93333, ICMB 97222, ICMR 06444, ICMR 06222, ICMR 11003 and IP 21187‐P1, were crossed with two susceptible genotypes, ICMB 95444 and ICMB 89111 to generate F₁s, F₂s and backcrosses, BC₁P₁ (susceptible parent × F₁) and BC₁P₂ (resistant parent × F₁) for inheritance study. The resistant genotypes were crossed among themselves in half diallel to generate F₁s and F₂s for test of allelism. The F₁, F₂ and backcross generations, and their parents were screened in a glasshouse against Magnaporthe grisea isolates Pg 45 and Pg 53. The reaction of the F₁s, segregation pattern of F₂s and BC₁P₁ derived from crosses involving two susceptible parents and six resistant parents revealed the presence of single dominant gene governing resistance in the resistant genotypes. No segregation for blast reaction was observed in the F₂s derived from the crosses of resistant × resistant parents. The resistance reaction of these F₂s indicated that single dominant gene conferring resistance in the six genotypes is allelic, that is same gene imparts blast resistance in these genotypes to M. grisea isolates.     

Identification of QTL controlling adventitious root formation during flooding conditions in teosinte (Zea mays ssp. huehuetenangensis) seedlings

Adventitious root formation (ARF) at the soil surface is one of the most important adaptations to soil flooding or waterlogging. Quantitative trait loci (QTL) controlling ARF under flooding condition were identified in a 94 F₂ individual population by crossing maize (Zea mays L., B64) × teosinte (Z. mays ssp. huehuetenangensis). A base-map was constructed using 66 SSR and 42 AFLP markers, covering 1,378 cM throughout all ten maize chromosomes. The ARF capacity for seedlings was determined by evaluating the degree of root formation at the soil surface following flooding for 2 weeks. ARF showed continuous variation in the F₂ population. Interval mapping and composite interval mapping analyses revealed that the QTL for ARF was located on chromosome 8 (bin 8.05). Utilising a selective genotyping strategy with an additional 186 F₂ population derived from the same cross combination and 32 AFLP primer combinations, regions on chromosomes 4 (bin 4.07) and 8 (bin 8.03) were found to be associated with ARF. Z. mays ssp. huehuetenangensis contributed all of the QTL detected in this study. Results of the study suggest a potential for transferring waterlogging tolerance to maize from Z. mays ssp. huehuetenangensis.     

Identification and validation of a major QTL for salt tolerance in soybean

To identify quantitative trait loci (QTLs) conditioning salt tolerance in soybean (Glycine max (L.) Merr.), two recombinant inbred line (RIL) populations derived from crosses of FT-Abyara × C01 and Jin dou No. 6 × 0197 were used in this study. The FT-Abyara × C01 population consisted of 96 F₇ RILs, and the Jin dou No. 6 × 0197 population included 81 F₆ RILs. The salt tolerant parents FT-Abyara and Jin dou No. 6 were originally from Brazil and China, respectively. The QTL analysis identified a major salt-tolerant QTL in molecular linkage group N, which accounted for 44.0 and 47.1% of the total variation for salt tolerance, in the two populations. In the FT-Abyara × C01 population, three RILs were found to be heterozygous around the detected QTL region. By selfing the three residual heterozygous lines, three sets of near isogenic lines (NILs) for salt tolerance were developed. An evaluation of salt tolerance of the NILs revealed that all the lines with FT-Abyara chromosome segment at the QTL region showed significantly higher salt tolerance than the lines without the FT-Abyara chromosome segment. Results of the NILs validated the salt tolerance QTL detected in the RIL populations.