栽培稻与普通野生稻BC2F2群体产量相关性状的QTL分析

以广陆矮4号(Oryza sativa ssp. indica)为母本及轮回亲本,普通野生稻（Oryza rufipogon）为父本,分单株连续回交2次,构建BC2F2群体。首先用241对具有双亲多态性的SSR标记对BC2F1单株进行代换片段分析,在此基础上,根据BC2F1的表型选产量较优的单株自交获得BC2F2群体,用代换片段上具有双亲杂合型基因型的24对SSR标记进行QTL定位。在所选的BC2F1单株上,共检测到分布于7条染色体上的20个野生稻的代换片段,平均每条染色体上有2.86个;代换片段长度最小为0.55 cM,最大为33.00 cM,平均长度为12.36 cM,总覆盖长度为247.20 cM,覆盖率为16.21%。利用BC2F2群体对14个产量相关性状进行QTL定位,共检测到控制8个性状的20个QTL。对性状表型值起增效作用的有11个,占总检出数的55%。控制产量相关性状的QTL存在簇状分布现象,这与表型相关分析结果相符合。     

Heritability of,and genotypic correlations between,aflatoxin traits and physiological traits for drought tolerance under end of season drought in peanut (Arachis hypogaea L.)

More rapid progress in breeding peanut for reduced aflatoxin contamination should be achievable with a better understanding of the inheritance of, aflatoxin trait and physiological traits that are associated with reduced contamination. The objectives of this study were to estimate the heritability of aflatoxin traits and genotypic (r_G) and phenotypic (r_P) correlations between drought resistance traits and aflatoxin traits in peanut. One hundred-forty peanut lines in the F_4:6 and F_4:7 generations were generated from four crosses, and tested under well-watered and terminal drought conditions. Field experiments were conducted under the dry seasons 2006/2007 and 2007/2008. Data were recorded for biomass (BIO), pod yield (PY), drought tolerance traits [harvest index (HI), drought tolerance index (DTI) of BIO and PY, specific leaf area (SLA), and SPAD chlorophyll meter reading (SCMR)], and aflatoxin traits [seed infection and aflatoxin contamination]. Heritabilities of A. flavus infection and aflatoxin contamination in this study were low to moderate. The heritabilities for seed infection and aflatoxin contamination ranged from 0.48 to 0.58 and 0.24 to 0.68, respectively. Significant correlations between aflatoxin traits and DTI (PY), DTI (BIO), HI, biomass and pod yield under terminal drought conditions were found (r_P = −0.25** to 0.32**, r_G = −0.57** to 0.53**). Strong correlations between SLA and SCMR with A. flavus infection and aflatoxin contamination were also found. Positive correlations between SLA at 80, 90, and 100 DAP and aflatoxin traits were significant (r_P = 0.13** to 0.46**, r_G = 0.26** to 0.81**). SCMR was negatively correlated with aflatoxin traits (r_P = −0.10** to −0.40**, r_G = −0.11** to −0.66**). These results indicated that physiological-based selection approaches using SLA and SCMR might be effective for improving aflatoxin resistance in peanut.     

Molecular Mapping of Sterility QTLs qSS-3, qSS-6a and qSS-7 as Single Mendelian Factors via NIL strategy

Hybrid sterility between Oryza glaberrima and O. sativa seriously hampers the introgression of favorable genes from each other. In order to further understand this issue, identification and isolation of hybrid sterility QTLs as single Mendelian factors are an effective strategy. A genetic map was constructed using a BC₁F₁ population derived from a cross between an O. sativa japonica cultivar and an O. glaberrima accession. Four main-effect QTLs for pollen sterility were detected in the BC₁F₁. Five BC₈F₁ advanced backcross populations were developed via successive backcrosses based on phenotype and molecular selections. The BC₈F₁ populations showed bimodal distribution for pollen fertility and could be classified into semi-sterile and fertile types, fitting single Mendilian factor inheritance ratios. Three QTLs detected in the BC₁F₁ corresponding to qSS-3, qSS-6a and qSS-7 were mapped on chromosomes 6, 3 and 7, respectively, as single Mendilian factors.     

Physiological characterization of introgression lines derived from an indica rice cultivar, IR64, adapted to drought and water-saving irrigation

Water scarcity threatens sustainable rice production in many irrigated areas around the world. To cope with the scarcity, aerobic rice culture has been proposed as a promising water-saving technology. The objective was to elucidate the physiological attributes behind the performance of rice introgression lines in water-saving culture. We evaluated yield potential and physiological adaptation traits to water deficit of BC₃-derived lines with the genetic background of an elite indica cultivar, IR64, in the field and in pot experiments. One line, YTH183, had 26% higher yield than IR64 under non-stress conditions (895 vs. 712 g m⁻² on average). This was attributed to enlarged sink capacity due to large grain size, which contributed to more efficient use of assimilates and hence a higher harvest index. YTH183 also showed better dehydration avoidance under intermittent soil drying, due to the adaptive response of deep rooting to water deficiency. The grain yield of YTH183 exceeded that of IR64 by 92-102% under moderate water deficit caused by limited irrigation in aerobic rice culture (143 vs. 72 g m⁻²). Two introgressed segments on chromosomes 5 and 6 might, at least in part, confer the higher yield potential and greater dehydration avoidance in YTH183 simultaneously. Advanced backcross breeding combined with molecular genetics and physiological characterization of introgressed segments would be effective for developing new rice cultivars with high yield potential and drought adaptation traits.     

Perennial O. sativa × O. rufipogon interspecific hybrids: I. Photosynthetic characteristics and their inheritance

A survey of 24 wild Oryza accessions identified Oryza australiensis and Oryza rufipogon as potential sources of enhanced photosynthetic rate for introgression into cultivated rice. Photosynthetic capacity per unit leaf area (CER) was associated with leaf N content but not with leaf chlorophyll concentration, flag leaf area, or specific leaf area. Eight fertile, perennial F₁ hybrids between O. sativa and O. rufipogon were grown in non-flooded soil, and CER was measured at flowering under saturating light. Two F₁ hybrids had greater CER than the average of 26.1 μmol m² s⁻¹. The F₂ progeny from these hybrids were screened for CER in the field, and segregants with even greater rates of photosynthesis were selected. The basis of high photosynthetic rate in the F₂ populations was not leaf thickness or leaf chlorophyll content. One F₂ line had exceptionally high CER and stomatal conductance. Broad-sense heritability on an individual plant basis for CER in two F₂ populations was 0.44 and 0.37. A highly significant offspring-parent regression of 0.89 for CER was observed in a replicated field evaluation (four blocks, five plants per plot) of 20 vegetatively propagated F₂ selections and their F₃ seedling progeny. Broad-sense heritability for CER on a plot-mean basis was estimated as 0.74 for both selected F_2:3 families and for the selected F₂ clones. Genetic resources in the genus Oryza may represent a source of alleles to increase leaf photosynthetic rate in the cultivated species, which we have demonstrated to be a heritable, though environmentally variable, trait in an O. sativa/O. rufipogon population.     

Development of elite breeding lines conferring Bph18 gene-derived resistance to brown planthopper (BPH) by marker-assisted selection and genome-wide background analysis in japonica rice (Oryza sativa L.)

Brown planthopper (BPH) is a serious threat to rice production. In this study, we have used the novel resistance gene Bph18 derived from Oryza australiensis and incorporated it into an elite japonica cultivar, Junambyeo, which is highly susceptible to BPH. The Bph18 gene was introduced by marker-assisted backcross (MAB) breeding into Junambyeo. The backcrossed progenies were evaluated for desirable agronomic and grain quality traits and the selection of improved breeding lines while simultaneously evaluating BPH resistance by bioassays in the greenhouse and foreground selection. Of the 26 advanced backcross breeding lines (ABL), four lines showed agronomic traits similar to those of the recurrent parent, with strong resistance to BPH. Molecular genotyping of the four ABL revealed the conversion of genotypes closely resembling the genotype of Junambyeo. The percentage of donor chromosome segments in ABL decreased from 12.3% in the BC₂ to 9.4%, 8.4% and 5.3% in BC₃, BC₄ and BC₅ generations, respectively. ABL retained small sizes of the donor chromosome segments on chromosomes 1, 2, 10, 11 and 12 but the genomes of ABL2, ABL3 and ABL4 were homosequential to the recurrent parent on chromosomes 3, 4, 5, 6, 7 and 9 without donor chromosome segment introgression. The ABL1 and ABL2 retained only some small segments of the donor genome on chromosomes 9 and 8, respectively. Fine structure analysis of the Bph18 flanking region between RM511 and RM1584 markers on chromosome 12 showed a progressive elimination of donor-derived chromosome segments from BC₂ to BC₅ generations. The percentage of O. australiensis derived chromosome segment substitution in the recurrent parent background decreased from 28% of the donor parent to 6.7%, 3.9%, 3.4% and 3.4% in BC₂, BC₃, BC₄ and BC₅ generations, respectively. However, it was revealed that the O. australiensis-derived chromosome segment (1320 kb) in ABL containing the Bph18 gene was consistently maintained irrespective of advances in backcross generations. BPH resistant elite breeding lines with agronomic and grain quality traits similar to those of the recurrent parent were successfully developed by foreground and background analysis in japonica background without linkage drag.     

Perennial hybrids of Oryza sativa × Oryza rufipogon: Part II. Carbon exchange and assimilate partitioning

Oryza species differ in their degree of perenniality, which has implications for patterns of carbon distribution in the plant. Interspecific F₁ hybrids of Oryza sativa × Oryza rufipogon were compared with their parental lines to assess whether they differed in assimilate storage and distribution at flowering and after maturity of the first cohort of panicles. The F₁ hybrids varied widely in plant type, but on average they had small plant size and low main tiller weights at anthesis, similar to O. rufipogon, and had intermediate tiller numbers and final single plant weights similar to cultivated rice. O. rufipogon had higher concentrations of starch in stems at anthesis, while interspecific hybrids exhibited comparatively low leaf, stem + sheath, and root sugar concentrations. Near anthesis, substantial ¹⁴C label remained in the source (flag) leaf in O. sativa and F₁ hybrids, while in O. rufipogon more label was exported to sink tissues. The hybrids partitioned more ¹⁴C label to panicles than did cultivated rice and less to leaf sheaths than either parent. Hybrids that had previously been identified as having above-average carbon exchange rates (CER) did not differ consistently from the low-CER hybrids in carbohydrate dynamics. The cultivated species itself maintains some perennial features, and changes in these traits might increase productivity.     

Genetic analysis for resistance to bean fly (Ophiomyia phaseoli) and seed yield among common bean genotypes in a semi-arid environment

Bean fly (Ophiomyia spp.) is a major field pest limiting common bean production in eastern Africa. The genetic enhancement of beans for resistance to insect pests is essential for minimizing yield losses arising from crop damage. The objectives of this study were to (1) assess combining ability for bean fly resistance and seed yield accumulation in common bean and (2) estimate genetic parameters associated with resistance for formulating further breeding strategy. Four parents with known reaction to bean fly were crossed with four locally adapted genotypes in an 8 × 8 half diallel mating design. Parents and F₂ progenies were grown in an alpha-lattice design replicated twice in an open-field and subjected to natural populations of bean fly for two cropping seasons under semi-arid conditions. Similarly, two resistant and two susceptible parents were selected and crossed to produce populations for generation means and variances components analysis. Results revealed that both general combining ability (GCA) and specific combining ability (SCA) mean squares were significant (p ≤ 0.05) for all four traits studied except SCA for stem damage during one cropping season. Among the parents, GBK 047858 was the best general combiner for all the traits studied across seasons except for stem damage during long rains (LR) 2009. Besides, genotypes GBK 047821 and Kat × 69 (a locally adapted variety) were generally good general combiners for resistance traits as well as seed yield. General predictability ratio (GPR) values ranging from 0.63 to 0.90 were obtained for plant mortality, stem damage, pupae in stem and seed yield across cropping seasons. These results established the predominance of additive gene effects (fixable variation) over the non-additive effects in controlling the traits. Low to moderate narrow sense heritability values ranging from 0.22 to 0.45 were obtained for pupae in stem. Such heritability estimates indicate that although additive gene components were critical in the inheritance of resistance for the trait, non-additive gene action were also important in addition to the environmental effects.     

Quantitative trait loci mapping and meta-analysis across three generations for popping characteristics in popcorn

Popping characteristics play a determinant role in the utilization of popcorn (Zea mays L.). In this study, the RIL population with 258 recombinant inbred lines was evaluated to detect quantitative trait loci (QTLs) for three popping characteristics (PF, popping fold; PV, popping volume; PR, popping rate) under four environments. Meta-analysis was used to integrate detected QTLs across three generations (RIL, F_2:3 and BC₂F₂) derived from the same cross. All eleven QTLs were detected for three traits, on chromosomes 1, 2, 4, 6 and 10 for PF, on chromosomes 1, 4, 6, 7 and 10 for PV, and on chromosomes 1, 4, 6 and 10 for PR. Three, 1, 3, 6 and 6 QTL were detected in the same marker intervals in 4, 3, 2, 1 cases, respectively. Four QTLs at bins 1.05–1.06, 1.08–1.09 and 7.03–7.04 were commonly detected in the same or near bins in all three generations. Six and 2 QTLs showed consistency across RIL/F_2:3 or RIL/BC₂F₂ generations respectively. Nine meta-QTLs (mQTL) were detected on chromosomes 1, 4, 6, 7, 8 and 10. Except mQTL7-1, only related with PV, other mQTLs included two or three traits, reflecting pleiotropic or tightly linkaged QTLs for popping characteristics. The QTL influencing all the three popping traits at bins 1.05–1.06 were also detected in other previous researches using different populations, which could be put into use in marker assisted breeding for popping characteristics in popcorn.     

Genetic enhancement of Sorghum (Sorghum bicolor (L) Moench) for grain mould resistance: II. Breeding for grain mould resistance

Grain mould causes qualitative and quantitative loss to grain in sorghum. Grain mould resistance is a complex problem as grain mould is caused by complex of fungi and the resistance is governed by many traits. Breeding efforts during the last 3 decades to develop grain mould resistance in high yielding genotypes have not paid many dividends. We developed a strategy to breed for grain mould resistance in high yielding back ground. Twenty five crosses between elite lines and grain mould resistant genetic stocks (susceptible × resistant/moderately resistant and moderately resistant × resistant crosses) were evaluated in F₁, and derivatives performing superiorly for grain mould resistance in F₂-F₄ at physiological maturity were advanced. The early generation material F₂s (10) and F₃s (125) in 6 locations (representing rainy-season-sorghum growing 6 states of India where grain mould is one of the major biotic stresses), and later generations F₄s and F₅s in 3 locations (one location, Parbhani is a hot spot for grain moulds and 2 locations, Hyderabad and Coimbatore in epiphytotic conditions) were evaluated. Only 25 selections out of 384 derivatives in F₄ were superior over locations for grain mould resistance at physiological maturity and harvest maturity (Our simultaneous studies in RILs for grain mould resistance across years and locations have shown that the variation obtained for grain mould resistance at physiological maturity is genetically governed and the grain mould score further gets compounded at harvest maturity depending on rainfall received after physiological maturity). These superior lines were advanced and further evaluated in F₅ and F₆ for grain mould resistance and grain yield. During 2007, out of 25 F₅ derivatives, 12 were on par (scored 3.1-4.4) with resistant check, B 58586 (3.2 score) where as susceptible check, 296 B registered a score of 7.5. GMN nos. 41, 52, 59, and 63 performed on par with resistant check, B 58586 for grain mould resistance over 9 environments. Since we selected for grain mould resistance in early generations at physiological maturity in multi-locations, we could identify superior lines for grain mould resistance. Most of these lines are high yielding and on par with elite check, C43 for grain yield. These lines are distinct for DUS testing traits from grain mould resistant check, B 58586.     

Mild peroxyformic acid fractionation of Miscanthus × giganteus bark. Behaviour and structural characterization of lignin

Miscanthus × giganteus bark was subjected to mild fractionation with peroxyformic acid by a two stage process. A factorial experimental design was used to study and quantify the effect of the variables (formic acid concentration (80-90%), hydrogen peroxide concentration (0.2-0.4%), temperature of the first stage (60-80 °C), and treatment time of the second stage (60-120 min)) on the main parameters of fractionation: pulp yield, remaining lignin and total polysaccharides in pulp. The dependence of lignin precipitation rate on hydrogen peroxide concentration in liquor was also studied. Hydrogen peroxide concentrations inferior to 0.5% seems to be suitable to recover high percentages of lignin. The isolated lignin was analysed by 2D-HSQC, ¹³C- and ³¹P NMR spectroscopy, FTIR spectroscopy, size-exclusion chromatography and chemical analysis. The most important chemical modifications taken place in the lignin during the fractionation were identified: β-O-4′ cleavage and hydrolysis of LC-bond structures. The C9-formula was also determined: C₉H_6.81O_2.90(OCH₃)_0.68(COOH)_0.07(OH^Ph)_0.38(OH^Al)_0.33.     

Analysis on genetic contribution of agronomic traits to total sugar in flue-cured tobacco (Nicotiana tabacum L.)

To uncover the genetic contributions of agronomic traits to content of total sugar (TS) and find indicator traits for indirect selection on TS in the flue-cured tobacco (Nicotiana tobacum L.), multivariable conditional analysis was conducted based on a genetic model containing additive–dominance and their interactions with environments. Fourteen cultivars (or breeding lines) and derived 41 F₁ crosses were grown at four locations in Yunnan province, China. Significant phenotypic contribution to TS was detected for six agronomic traits, plant height (PH), girth of stem (GS), internode length (INL), number of leaves (NL), length of middle leaves (LML) and width of middle leaves (WML). There was large contribution of additive effects due to each of the five agronomic traits (PH, GS, INL, LML and WML). The contribution ratio of dominance effect was high due to PH. By serving as high contributor of additive effects to TS and having high ratios of additive variance to phenotypic variance, INL and PH could be used as indicative agronomic traits for selecting breeding lines with suitable TS. Among the six agronomic traits, PH had the highest contribution to dominance effects of TS for most F₁ crosses, and could be used for selecting the crosses with suitable TS.     

Analysis of QTL for resistance to head smut (Sporisorium reiliana) in maize

Head smut of maize, caused by the fungus Sporisorium reiliana, is an important disease in the temperate maize-growing areas worldwide. In this study, we mapped and characterized quantitative trait loci (QTL) conferring resistance to S. reiliana using a F_2:3 population of 184 families derived from a cross between Mo17 (resistant parent) and Huangzao4 (susceptible). The population was evaluated for resistance in replicated field trials with artificial inoculation of S. reiliana chlamydospores in Gongzhuling of Jilin Province and Harbin of Heilongjiang Province of China, two hot spots of head smut incidence, in 2003 and 2004. Genotypic and G × E variances for disease incidence were highly significant in the population. Heritability estimates for percentage disease incidence in the 2-location and 2-year evaluation ranged from 0.62 to 0.70. Composite interval mapping on a linkage map (1956.1 cM distance; 9.34 cM average interval) constructed with 84 SSR and 135 AFLP markers, identified five QTL, one each on chromosomes 1, 3 and 8 and two on chromosome 2, accounting for 5.0–43.7% of the phenotypic variance across four environments. One major QTL on chromosome 2 explaining up to 43.7% of the phenotypic variance can potentially be used in molecular marker-assisted selection for head smut resistance in maize.     

Genetic analysis of field resistance to tan spot in spring wheat

Tan spot, caused by Pyrenophora tritici-repentis (Died.) Drechs., is an important constraint to wheat (Triticum aestivum L.) yield in many countries. Since the inheritance of field resistance to tan spot is poorly understood, this study was conducted to determine the genetic control of resistance in the field. Resistance was measured as disease severity caused by P. tritici-repentis race 1 in four crosses involving five wheat parents: parent 1 (P₁) = catbird; parent 2 (P₂) = Milan/Shanghai-7; parent 3 (P₃) = Alondra/Coc//Ures; parent 4 (P₄) = Bcb//Dundee/Gul/3/Gul); parent 5 (P₅) = ND/VG9144//Kal/BB/3/Yaco/4/Chil. P₁, P₂ and P₃ were resistant and P₄ was moderately resistant, whereas P₅ was susceptible to tan spot. The F₂-derived F₃ families and the parents were field evaluated at El Batán, Mexico, in 1996. When all the plants within a F₃ family expressed low levels of disease severity similar to that of the resistant parent it was classified resistant (R), otherwise the progeny was classified as susceptible (S). The progeny of the three crosses of the susceptible parent with the resistant and moderately resistant parents P₂, P₃, and P₄ segregated as 3R:13S whereas the progeny in the cross with P₁ showed a segregation ratio of 1R:15S. This suggests that each resistant parent possessed two genes conditioning resistance to tan spot severity caused by P. tritici-repentis race 1. Information on the inheritance of resistance measured as disease severity on adult plants under field conditions is of practical importance for wheat breeding programs seeking improvement in tan spot resistance.     

QTL mapping rolling,stomatal conductance and dimension traits of excised leaves in the Bala × Azucena recombinant inbred population of rice

The identification of markers linked to genes contributing to drought resistance promises opportunities to breed high yielding rice varieties for drought prone areas. Several studies using different mapping populations have previously identified quantitative trait loci (QTLs) for traits theoretically related to drought resistance. A mapping population of 176 F₆ recombinant inbred lines (RILs) derived from two upland rice varieties with contrasting aboveground drought avoidance traits (Bala and Azucena) with a linkage map of 157 markers was used to map QTLs for aboveground leaf morphological and physiological traits related to drought avoidance. Plants were grown for 6 weeks under controlled environmental conditions with three replications. Leaves were excised and placed on a balance. The rate of leaf rolling and water loss was recorded, after which leaf area, dry weight and specific leaf area were characterized. A simple method of estimating time to stomatal closure was employed. A total of 13 QTLs were detected for leaf morphological traits, three for initial transpiration and four for the proportion of water loss required to reach a specific advanced state of leaf rolling. No QTLs were detected for time of stomatal closure or speed of leaf rolling, nor for either water loss or transpiration at stomatal closure despite clear parental differences and moderate heritabilities in most of these traits. The co-location of QTLs for traits measured here and for drought avoidance previously reported from field experiments on chromosome 1, 3 and 5 link the genetics of drought resistance to leaf dimensions and physiology. However, a physiological explanation for a QTL for drought avoidance on chromosome 7 remains elusive.     

Genomic regions associated with the degree of red coloration in pericarp of rice (Oryza sativa L.)

The degree of red coloration (DRC) in pericarp of rice depends on the content of flavonoid compounds which have beneficial health effects for humans. In this study, 182 backcross-recombinant inbred lines (BILs) derived from Koshihikari (white pericarp)/Kasalath (red pericarp)//Koshihikari were used to detect the genomic regions associated with DRC through the QTL mapping approach. As a result, a total of four genomic regions were found to associate with DRC on chromosomes 1, 7, 9 and 11, respectively. Interestingly, the two genomic regions having the largest effects corresponded to previously characterized Rc and Rd genes on chromosome 7 and 1, respectively. In addition, two novel genomic regions having minor effects on DRC and located on chromosomes 9 and 11, respectively, are reported here for the first time. These results and the identification of tightly linked molecular markers that flank the genomic regions provide an opportunity for marker-aided improvement of red coloration in pericarp of rice.     

Optimization of formic/acetic acid delignification of Miscanthus × giganteus for enzymatic hydrolysis using response surface methodology

A Box-Behnken experimental design and response surface methodology were employed to optimize the pretreatment parameters of a formic/acetic acid delignification treatment of Miscanthus × giganteus for enzymatic hydrolysis. The effects of three independent variables, namely cooking time (1, 2 and 3 h), formic acid/acetic acid/water ratio (20/60/20, 30/50/20 and 40/40/20) and temperature (80, 90 and 107 °C) on pulp yield, residual Klason lignin content, concentration of degradation products (furfural and hydroxymethylfurfural) in the black liquor, and enzymatic digestibility of the pulps were investigated. The major parameter influencing was the temperature for pulp yield, delignification degree, furfural production and enzymatic digestibility. According to the response surface analysis the optimum conditions predicted for a maximum enzymatic digestibility of the glucan (75.3%) would be obtained using a cooking time of 3 h, at 107 °C and with a formic acid/acetic acid/water ratio of 40/40/20%. Glucan digestibility was highly dependent on the delignification degree.     

Quantitative trait loci mapping and meta-analysis across three generations for popping characteristics in popcorn

Popping characteristics play a determinant role in the utilization of popcorn (Zea mays L.). In this study, the RIL population with 258 recombinant inbred lines was evaluated to detect quantitative trait loci (QTLs) for three popping characteristics (PF, popping fold; PV, popping volume; PR, popping rate) under four environments. Meta-analysis was used to integrate detected QTLs across three generations (RIL, F_2:3 and BC₂F₂) derived from the same cross. All eleven QTLs were detected for three traits, on chromosomes 1, 2, 4, 6 and 10 for PF, on chromosomes 1, 4, 6, 7 and 10 for PV, and on chromosomes 1, 4, 6 and 10 for PR. Three, 1, 3, 6 and 6 QTL were detected in the same marker intervals in 4, 3, 2, 1 cases, respectively. Four QTLs at bins 1.05–1.06, 1.08–1.09 and 7.03–7.04 were commonly detected in the same or near bins in all three generations. Six and 2 QTLs showed consistency across RIL/F_2:3 or RIL/BC₂F₂ generations respectively. Nine meta-QTLs (mQTL) were detected on chromosomes 1, 4, 6, 7, 8 and 10. Except mQTL7-1, only related with PV, other mQTLs included two or three traits, reflecting pleiotropic or tightly linkaged QTLs for popping characteristics. The QTL influencing all the three popping traits at bins 1.05–1.06 were also detected in other previous researches using different populations, which could be put into use in marker assisted breeding for popping characteristics in popcorn.     

Genetic gains in grain yield, net photosynthesis and stomatal conductance achieved in Henan Province of China between 1981 and 2008

Knowledge of the changes in agronomic and photosynthetic traits associated with genetic gains in grain yield potential is essential for an improved understanding of yield-limiting factors and for determining future breeding strategies. The objectives of this study were to identify agronomic and photosynthetic traits associated with genetic gains in grain yield of facultative wheat (Triticum aestivum L.) between 1981 and 2008 in Henan Province, the most important wheat producing area in China. During the 2006-2007 and 2007-2008 crop seasons, a yield potential trial comprising 18 leading and new cultivars released between 1981 and 2008 was conducted at two locations, using a completely randomised block design of three replicates. Results showed that average annual genetic gain in grain yield was 0.60% or 51.30 kg ha⁻¹ yr⁻¹, and the significant genetic improvement in grain yield was directly attributed to increased thousand grain weight which also contributed to the significant increase in harvest index. The genetic gains in rates of net photosynthesis at 10, 20 and 30 days after anthesis were 1.10% (R² = 0.46, P < 0.01), 0.68% (R² = 0.31, P < 0.05) and 6.77% (R² = 0.34, P < 0.05), respectively. The rates of net photosynthesis at 10 (r = 0.58, P < 0.05), 20 (r = 0.59, P < 0.05) and 30 (r = 0.65, P < 0.01) days after anthesis were closely and positively correlated with grain yield. A slight decrease in leaf temperature and an increase in stomatal conductance after anthesis were also observed. Grain yield was closely and positively associated with stomatal conductance (r = 0.69, P < 0.01) and transpiration rate (r = 0.63, P < 0.01) at 30 days after anthesis. Therefore, improvement of those traits was the likely basis of increasing grain yield in Henan Province between 1981 and 2008. The genetic improvement in yield was primarily attributed to the utilization of two elite parents Yumai 2 and Zhou 8425B. The future challenge of wheat breeding in this region is to maintain the genetic gain in grain yield and to improve grain quality, without increasing inputs for the wheat-maize double cropping system.