Showing papers on "Plant breeding published in 2009"

Engineering OsBAK1 gene as a molecular tool to improve rice architecture for high yield

Abstract: Generating a new variety of plant with erect-leaf is a critical strategy to improve rice grain yield, as plants with this trait can be dense-planted. The erect-leaf is a significant morphological trait partially regulated by Brassinosteroids (BRs) in rice plants. So far, only a few genes can be used for molecular breeding in rice. Here, we identified OsBAK1 as a potential gene to alter rice architecture. Based on rice genome sequences, four closely related homologs of Arabidopsis BAK1 (AtBAK1) gene were amplified. Phylogenetic analysis and suppression of a weak Arabidopsis mutant bri1-5 indicated that OsBAK1 (Os08g0174700) is the closest relative of AtBAK1. Genetic, physiological, and biochemical analyses all suggest that the function of OsBAK1 is conserved with AtBAK1. Overexpression of a truncated intracellular domain of OsBAK1, but not the extracellular domain of OsBAK1, resulted in a dwarfed phenotype, similar to the rice BR-insensitive mutant plants. The expression of OsBAK1 changed important agricultural traits of rice such as plant height, leaf erectness, grain morphologic features, and disease resistance responses. Our results suggested that a new rice variety with erect-leaf and normal reproduction can be generated simply by suppressing the expression level of OsBAK1. Therefore, OsBAK1 is a potential molecular breeding tool for improving rice grain yield by modifying rice architecture.

Genome-Wide Reduction of Genetic Diversity in Wheat Breeding

Abstract: Public concerns about crop uniformity introduced by modern plant breeding and genetic vulnerability to biotic and abiotic stresses have been one of the major forces driving long-term efforts in plant germplasm conservation for future food security However, such concerns have gained little empirical support, as recent molecular diversity analyses of improved crop gene pools did not reveal much reduction from early to recent breeding efforts We conducted a genome-wide examination of 75 Canadian hard red spring wheat (Triticum aestivum L) cultivars released from 1845 to 2004 using 370 simple sequence repeat (or SSR) markers that were widely distributed over all 21 wheat chromosomes A total of 2280 SSR alleles were detected Allelic reduction occurred in every part of the wheat genome and a majority of the reduced alleles resided in only a few early cultivars Significant allelic reduction started in the 1930s Considering 2010 SSR alleles detected in the 20 earliest cultivars, 38% of them were retained, 18% were new, and 44% were lost in the 20 most recent cultivars The net reduction of the total SSR variation in 20 recent cultivars was 17% This clear-cut evidence not only supports the contention that modern plant breeding reduces the genetic diversity of Canadian wheat, but also underlies the need for conserving wheat germplasm and introducing genetic diversity into wheat breeding

Doubled haploids in hybrid maize breeding.

Abstract: Use of doubled haploid (DH) lines produced by in vivo induction of maternal haploids are routinely used in maize (Zea mays L.) breeding. Major advantages of DH lines in hybrid breeding are (i) maximum genetic variance, (ii) complete homozygosity, (iii) short "time to market", (iv) simplified logistics, (v) reduced expenses, and (vi) optimal aptitude for marker applications. The present paper briefly reviews the experimental basis of the haploid induction technology, explains alternative DH-line-based breeding schemes, describes the features of a new software for optimizing such schemes, and presents and discusses selected optimization results. Modern inducer genotypes display induction rates of 8 to 10% on average. Various morphological and physiological markers warrant a fast and cheap identification of haploid kernels and/or seedlings. Artificial chromosome doubling procedures have successfully been adapted to large-scale commercial applications. Most likely, haploid embryogenesis is caused by defective sperm cells. After fusion with the egg cell, the chromosomes of the sperm cell degenerate and are stepwise eliminated from the primordial cells. The induction rate is under polygenic control. One cycle of DH-line development with two stages of testcross evaluation takes only four years if off-season nurseries are available. Cycle length can be shortened to three years if the first three breeding steps (recombination, haploid induction, and DH-plant production) are completed in a single year. Genome-wide marker-assisted selection can effectively be incorporated into DH-line based breeding schemes. To maintain selection response in the long run, the loss of genetic variation needs to be minimized by setting lower limits to the effective population size (N e ). Recurrent selection and line development may be combined to a single integrated breeding scheme. A new software MBP (Version 1.0) maximizes the expected annual genetic gain subject to budget and N e restrictions. Input variables include estimated variance and covariance components, type of tester, haploid induction parameters, and costs of the individual breeding activities. For calculating N e , the software considers genetic drift caused by both sampling and selection. Optimization results demonstrate that (i) schemes with only one stage of testcross evaluation provide faster breeding progress than those with two or more stages, (ii) genetic interlinking between staggered breeding programs is more efficient than a closed-population approach. Combined phenotypic and genome-wide selection holds great promise in accelerating future breeding progress.

Reverse breeding: a novel breeding approach based on engineered meiosis.

Abstract: Reverse breeding (RB) is a novel plant breeding technique designed to directly produce parental lines for any heterozygous plant, one of the most sought after goals in plant breeding. RB generates perfectly complementing homozygous parental lines through engineered meiosis. The method is based on reducing genetic recombination in the selected heterozygote by eliminating meiotic crossing over. Male or female spores obtained from such plants contain combinations of non-recombinant parental chromosomes which can be cultured in vitro to generate homozygous doubled haploid plants (DHs). From these DHs, complementary parents can be selected and used to reconstitute the heterozygote in perpetuity. Since the fixation of unknown heterozygous genotypes is impossible in traditional plant breeding, RB could fundamentally change future plant breeding. In this review, we discuss various other applications of RB, including breeding per chromosome.

Functional marker-assisted selection for bacterial leaf blight resistance genes in rice (Oryza sativa L.)

Abstract: With 1 figure and 3 tables Abstract Evolving high yielding rice genotypes with durable resistance to bacterial leaf blight (BLB) is pertinent considering the extensive damage caused by the disease in most of the rice growing regions. Two high yielding BLB susceptible indica rice cultivars, ‘ADT43’ and ‘ASD16’ popular among farmers and consumers across South India have been introgressed with three BLB resistance genes xa5, xa13 and Xa21 from isoline IRBB60 using functional markers. The F2 populations of 500 plants from ADT43 × IRBB60 and 806 plants from ASD16 × IRBB60 crosses were screened for the presence of all the three resistance genes. Thirty genotypes with three genes in homozygous and 55 genotypes with two genes in homozygous and one gene in heterozygous condition were identified. These pyramided genotypes with two or three resistance genes exhibited high levels of resistance against two predominant Xanthomonas oryzae isolates of South India. Among the 30 pyramided genotypes (xa5 + xa13 + Xa21), 12 were found to be significantly high yielding with desirable agronomic characteristics and the selection efficiency of the present markers was hundred percent.

Achievements and limitations of contemporary common bean breeding using conventional and molecular approaches

Abstract: Common bean (Phaseolus vulgaris L.) improvement programs have been successful using conventional breeding methods to accomplish a wide array of important objectives. Specific achievements include the extension of range of adaptation of the crop, the development of cultivars with enhanced levels of disease and pest resistance and breeding lines that possess greater tolerance to drought. The most effective breeding method depends on the expression and inheritance of the trait to be selected and the target environment. Many bean improvement programs use molecular markers to facilitate cultivar development. In fact, several recent germplasm releases have used molecular markers to introgress and or pyramid major genes and QTL for disease resistance. Related species (P. coccineus and P. acultifolius) via interspecific hybridizations remain an important albeit long-term source for resistance to economically important diseases. Slow progress has been made in the improvement of traits such as adaptation to low soil fertility and tolerance to high levels of soluble Al in the soil using conventional breeding methods. The inability to directly measure root traits and the importance of genotype × environment interaction complicate the selection of these traits. In addition, symbiotic relationships with Rhizobium and mycorrhiza need to be taken into consideration when selecting for enhanced biological N fixation and greater or more efficient acquisition of soil P. Genomic examination of complex traits such as these should help bean breeders devise more effective selection strategies. As integration of genomics in plant breeding advances, the challenge will be to develop molecular tools that also benefit breeding programs in developing countries. Transgenic breeding methods for bean improvement are not well defined, nor efficient, as beans are recalcitrant to regeneration from cell cultures. Moreover, if issues related to consumer acceptance of GMOs cannot be resolved, traits such as herbicide tolerance in transgenic bean cultivars which would help farmers reduce production costs and decrease soil erosion will remain unrealized.

Quantitative analysis and QTL mapping for agronomic and fiber traits in an RI population of upland cotton

Abstract: Genetic mapping is an essential tool for cotton (Gossypium hirsutum L.) molecular breeding and application of DNA markers for cotton improvement. In this present study, we evaluated an RI population including 188 RI lines developed from 94 F2-derived families and their two parental lines, ‘HS 46’ and ‘MARCABUCAG8US-1-88’, at Mississippi State, MS, for two years. Fourteen agronomic and fiber traits were measured. One hundred forty one (141) polymorphic SSR markers were screened for this population and 125 markers were used to construct a linkage map. Twenty six linkage groups were constructed, covering 125 SSR loci and 965 cM of overall map distance. Twenty four linkage groups (115 SSR loci) were assigned to specific chromosomes. Quantitative genetic analysis showed that the genotypic effects accounted for more than 20% of the phenotypic variation for all traits except fiber perimeter (18%). Fifty six QTLs (LOD > 3.0) associated with 14 agronomic and fiber traits were located on 17 chromosomes. One QTL associated with fiber elongation was located on linkage group LGU01. Nine chromosomes in sub-A genome harbored 27 QTLs with 10 associated with agronomic traits and 17 with fiber traits. Eight chromosomes in D sub-genome harbored 29 QTLs with 13 associated with agronomic traits and 16 with fiber traits. Chromosomes 3, 5, 12, 13, 14, 16, 20, and 26 harbor important QTLs for both yield and fiber quality compared to other chromosomes. Since this RI population was developed from an intraspecific cross within upland cotton, these QTLs should be useful for marker assisted selection for improving breeding efficiency in cotton line development.

Leaf-level water use efficiency determined by carbon isotope discrimination in rice seedlings: genetic variation associated with population structure and QTL mapping

Abstract: Increasing the water use efficiency (WUE) of our major crop species is an important target of agricultural research. Rice is a major water consumer in agriculture and it is also an attractive genetic model. We evaluated leaf-level WUE in young rice seedlings using carbon isotope discrimination (∆13C) as an indicator of the trait. A survey of ∆13C was undertaken in 116 diverse germplasm accessions representing O. sativa, O. glaberrima and four wild Oryza species. O. sativa cultivars were classified into sub-populations based on SSR markers, and significant differences in ∆13C were observed among the five genetically defined groups. While individual accessions explained a greater proportion of the variation than did sub-population, indica rice varieties had the lowest ∆13C values overall, indicating superior WUE, while temperate japonica had the highest ∆13C. O sativa accessions had a similar or greater range of ∆13C values than wild Oryza species, while domesticated O. glaberrima had a narrower range. Correlation analysis identified leaf morphological and physiological traits that were significantly associated with ∆13C, including longer leaves, more drooping leaves, higher tillering ability, and lower leaf nitrogen content. These trait associations were investigated by quantitative trait locus (QTL) mapping using backcross inbred lines derived from a cross between Nipponbare (temperate japonica) and Kasalath (aus). Seven QTL for ∆13C were identified using composite interval analysis, located in five chromosomal regions. The QTL with the largest additive effect came from Kasalath and co-localized with QTL for leaf length, tiller number and nitrogen content.

Cold tolerance in rice varieties at different growth stages

Abstract: Low temperature is a common production constraint in rice cultivation in temperate zones and high-elevation environments, with the potential to affect growth and development from germination to grain filling. There is a wide range of genotype-based differences in cold tolerance among rice varieties, these differences often reflecting growth conditions in the place of origin, as well as breeding history. However, improving low temperature tolerance of varieties has been difficult, due to a lack of clarity of the genetic basis to low temperature tolerance for different growth stages of the rice plant. Seeds or plants of 17 rice varieties of different origins were exposed to low temperature during germination (15°C), seedling, booting, and flowering stages (18.5°C), to assess their cold tolerance at different growth stages. Low temperature at the germination stage reduced both the percentage and speed of germination. Varieties from China (B55, Banjiemang, and Lijianghegu) and Hungary (HSC55) were more tolerant of low temperature than other varieties. Most of the varieties showed moderate levels of low temperature tolerance during the seedling stage, the exceptions being some varieties from Australia (Pelde, YRL39, and YRM64) and Africa (WAB160 and WAB38), which were susceptible to low temperature at the seedling stage. Low temperature at booting and flowering stages reduced plant growth and caused a significant decline in spikelet fertility. Some varieties from China (B55, Bangjiemang, Lijiangheigu), Japan (Jyoudeki), the USA (M103, M104), and Australia (Quest) were tolerant or moderately tolerant, while the remaining varieties were susceptible or moderately susceptible to low temperature at booting and flowering stages. Three varieties from China (B55, Lijianghegu, Banjiemang) and one from Hungary (HSC55) showed consistent tolerance to low temperature at all growth stages. These varieties are potentially important gene donors for breeding and genetic studies. The cold tolerance of the 17 rice varieties assessed at different growth stages was correlated. Screening for cold tolerance during early growth stages can therefore potentially be an effective way for assessing cold tolerance in breeding programs.

Identification of QTLs for phosphorus utilization efficiency in maize (Zea mays L.) across P levels

Abstract: It is necessary to develop maize plants that are productive when grown in phosphorus (P) deficient soils because of the high cost of P supplementation in soils. The shoot phosphorus utilization efficiency, the whole phosphorus utilization efficiency of plant and root/shoot ratio as well as the quantitative trait loci associated with these traits were determined for a F2:3 population derived from the cross of two contrasting maize (Zea mays L.) genotypes, 082 and Ye107. A total of 241 F2:3 families were evaluated in replicated trials under deficient and normal phosphorus conditions in 2007 at Southwest University. The genetic map constructed by 275 SSR and 146 AFLP markers spanned 1,681.3 cM in length with an average interval of 3.84 cM between adjacent markers. Phosphorus was determined in harvested plants separated into two portions, roots and shoots with leaves. The sum of the two portions was used as an expression for P in the whole plant. By using composite interval mapping, a total of 5–8 distinct QTLs were identified under deficient and normal phosphorus, respectively. SPUE and WPUE under deficient phosphorus were controlled by one QTL, which was in the interval bnlg1518-bnlg1526 (bins 10.04) on chromosome 10. The loci of QTLs were same for SPUE, WPUE and RSR under normal phosphorus, which were in the interval bnlg1518–bnlg1526 (bins 10.04) and P2M8/a-bnlg1839 (bins10.07) on chromosome 10. Unlike regions conferring phosphorus utilization efficiency and root shoot ratio under normal phosphorus, the region under deficient phosphorus showed that genes controlling phosphorus utilization efficiency or root shoot ratio might be different. These results may be useful to breeding programs in marker assisted selections to identify phosphorus tolerant genotypes.

Integrated genetic map and genetic analysis of a region associated with root traits on the short arm of rye chromosome 1 in bread wheat.

Abstract: A rye–wheat centric chromosome translocation 1RS.1BL has been widely used in wheat breeding programs around the world. Increased yield of translocation lines was probably a consequence of increased root biomass. In an effort to map loci-controlling root characteristics, homoeologous recombinants of 1RS with 1BS were used to generate a consensus genetic map comprised of 20 phenotypic and molecular markers, with an average spacing of 2.5 cM. Physically, all recombination events were located in the distal 40% of the arms. A total of 68 recombinants was used and recombination breakpoints were aligned and ordered over map intervals with all the markers, integrated together in a genetic map. This approach enabled dissection of genetic components of quantitative traits, such as root traits, present on 1S. To validate our hypothesis, phenotyping of 45-day-old wheat roots was performed in five lines including three recombinants representative of the entire short arm along with bread wheat parents ‘Pavon 76’ and Pavon 1RS.1BL. Individual root characteristics were ranked and the genotypic rank sums were subjected to Quade analysis to compare the overall rooting ability of the genotypes. It appears that the terminal 15% of the rye 1RS arm carries gene(s) for greater rooting ability in wheat.

Identification of novel QTLs for seedling and adult plant leaf rust resistance in a wheat doubled haploid population

Abstract: Pyramiding of genes that confer partial resistance is a method for developing wheat (Triticum aestivum L.) cultivars with durable resistance to leaf rust caused by Puccinia triticina. In this research, a doubled haploid population derived from the cross between the synthetic hexaploid wheat (SHW) (×Aegilotriticum spp.) line TA4152-60 and the North Dakota breeding line ND495 was used for identifying genes conferring partial resistance to leaf rust in both the adult plant and seedling stages. Five QTLs located on chromosome arms 3AL, 3BL, 4DL, 5BL and 6BL were associated with adult plant resistance with the latter four representing novel leaf rust resistance QTLs. Resistance effects of the 4DL QTL were contributed by ND495 and the effects of the other QTLs were contributed by the SHW line. The QTL on chromosome arm 3AL had large effects and also conferred seedling resistance to leaf rust races MJBJ, TDBG and MFPS. The other major QTL, which was on chromosome arm 3BL, conferred seedling resistance to race MFPS and was involved in a significant interaction with a locus on chromosome arm 5DS. The QTLs and the associated molecular markers identified in this research can be used to develop wheat cultivars with potentially durable leaf rust resistance.

Variation for and relationships among biomass and grain yield component traits conferring improved yield and grain weight in an elite wheat population grown in variable yield environments

Abstract: Grain yield and kernel size (grain weight) are important industry traits for wheat in the water-limited environments of the north-eastern wheatbelt of Australia. These, and underpinning morphological and physiological traits, were evaluated in a population of recombinant inbred lines from the elite CIMMYT cross Seri/Babax, segregating for the presence of the rye translocation (T1BL.1RS). The population was examined to determine the variation among lines, relationships among traits, the extent of line × environment interactions, potential efficiency of direct and indirect selection, and to identify trait combinations that are associated with higher grain yield and grain weight. Transgressive segregation was observed for all traits, and line × environment interaction effects were frequently larger than line main effects. Across six environments ranging in yield from 202 to 660 g/m2, the T1BL.1RS wheat-rye translocation had a positive effect on grain weight (+3.4%) but resulted in decreased grain number per m2 (–6.5%) and grain yield (–3.1%). Realised selection responses indicated that broad adaptation was best achieved by selection for mean performance across the range of target environments. However, specific adaptation for performance in high- or low-yielding environments was best detected by direct selection in those types of environments. A group of broadly adapted Seri/Babax lines exceeded the mean of five cultivars grown commercially in the north-eastern wheatbelt by 8% for grain yield and 17% for grain weight. These Seri/Babax lines with both high grain yield and grain weight were associated with a combination of several traits: earlier flowering, reduced tillering, a greater proportion of tillers that produce grain-bearing spikes at maturity, high water-soluble carbohydrate stem reserves at anthesis, a higher proportion of competent florets at anthesis to maximise grains per spikelet leading to a high harvest index, and possibly a greater capacity to extract soil water. These results suggest a suitable ideotype for breeding high-yielding wheat cultivars with high grain weight adapted to environments with hotter, drier conditions during the post-anthesis period.

Potato Breeding at the Scottish Plant Breeding Station and the Scottish Crop Research Institute: 1920–2008

Abstract: Seventy-two potato cultivars have been bred at the Scottish Plant Breeding Station and the Scottish Crop Research Institute since 1920. The original genetic base contained resistance to wart disease and to viruses, but not comprehensive resistance to all strains. Introgression of resistance genes from the wild and cultivated potato species of Latin America started for late blight in 1932, for viruses in 1941 and for potato cyst nematodes in 1952. Just seven of the 219 wild tuber-bearing species recognized by Hawkes in 1990 feature in the pedigrees of our cultivars, with Solanum demissum for blight resistance in 58, S. vernei for nematode resistance in 19 and S. microdontum for Potato virus Y resistance in 15, the other four species being S. multidissectum, S. commersonii, S. maglia and S. acaule. Resistance to other fungal and bacterial diseases has been mainly due to chance rather than deliberate breeding. From 1970, selection for yield and quality included processing quality, and despite lack of commercial success, prospects remain good for cultivars resistant to sweetening during cold storage. Since 1990 prebreeding has combined desirable traits through efficient recurrent selection based on progeny testing and provided parents for the commercially funded breeding of finished cultivars. Only one cultivar is a Neotuberosum–Tuberosum hybrid, whereas 15 cultivars have the H1 gene for resistance to Globodera rostochiensis introgressed from group Andigena. Long-day Phureja cultivars are finding a market niche for their flavour attributes. Breeding strategies and methods are critically reviewed from a genetic viewpoint.

Should spring wheat breeding for organically managed systems be conducted on organically managed land

Abstract: Organic spring wheat (Triticum aestivum L.) producers in the northern Great Plains use cultivars which have been bred for conventional management systems or heritage cultivars released before the widespread use of synthetic fertilizers and pesticides. To investigate the feasibility of organic wheat breeding and to determine common genetic parameters for each system, we used a random population of 79 F6-derived recombinant inbred sister lines from a cross between the Canadian hard red spring wheat cultivar AC Barrie and the CIMMYT derived cultivar Attila. The population, including the parents, was grown on conventionally and organically managed land for 3 years. Heritability estimates differed between systems for 6 of the 14 traits measured, including spikes m−2, plant height, test weight, 1,000 kernel weight, grain protein, and days to anthesis. Direct selection in each management system (10% selection intensity) resulted in 50% or fewer lines selected in common for nine traits, including grain yield, grain protein, spikes m−2, and grain fill duration. The results of this study suggest that indirect selection (in conventionally managed trials) of spring wheat destined for organically managed production would not result in the advance of the best possible lines in a breeding program. This implies that breeding spring wheat specific to organic agriculture should be conducted on organically managed land.

Trait identification and QTL validation for reproductive stage drought resistance in rice using selective genotyping of near flowering RILs

Abstract: Drought resistance is becoming an indispensable character for rice improvement due to the dwindling global water resources. Genetic improvement for drought resistance is achieved through physiological dissection and genetic analysis of independent component traits associated with crop productivity under stress. A subset mapping population of 93 near flowering recombinant inbred lines with uniform phenology was constituted for genetic analysis of reproductive stage drought resistance. The population was phenotyped for 22 physio-morphological traits under two contrasting water regimes imposed at reproductive stage. Broad sense heritabilities of morphological traits were lower under stress than irrigated. Predominant association of plant height, panicle exsertion and harvest index with grain yield were observed under stress. The sustenance of panicle exsertion through maintaining growth during moisture stress was found as a significant trait associated with the grain yield through minimizing spikelet sterility. Selective genotyping was carried out with 23 polymorphic microsatellite markers of the established target genomic regions for drought resistance. The study validated the association of a QTL region on the long arm of chromosome 1 with plant height, panicle length, panicle exsertion, biological yield and stomatal conductance under stress. This region, flanked by markers RM246 and RM315, was known to possess the semi-dwarf gene, sd-1. Role of another major interval lying between RM256 and RM149 on chromosome 8 in defining the drought resistance could be established through identification of QTLs associated with leaf rolling, panicle exsertion, plant height, panicle length, senescence and biological yield under moisture stress condition. Few other QTLs were also identified.

Prospects of developing hybrid rice with super high yield.

Abstract: Approaches to develop hybrid rice (Oryza sativa L.) with super high yield involve the improvement of plant type, the exploitation of intersubspecific heterosis, the pyramiding of heterosis genes in different rice ecotypes, and the utilization of favorable genes from distant relatives. Three main plant types have been suggested in the literature for improving hybrid rice yield: (i) heavy panicle type, (ii) super high yielding plant type, and (iii) super high yielding ideotype. Recently, intersubspecific heterosis has been partially exploited with three strategies: (i) developing parental lines of indica-japonica intermediate type with favorable genes from both parents, (ii) introgressing intersubspecific gene with the help of wide compatibility and thermosensitive genic male sterility (TGMS) genes, and (iii) breeding pro-indica japonica lines. It is also possible to pyramid different heterosis genes from various rice ecotypes through molecular marker aided reciprocal recurrent selection. The identification of yield enhancing genes from wild rice, the construction of autoregulated senescence delaying gene, and the cloning of key enzymes related to C4 pathway have been accomplished using molecular biotechnology. By introducing these genes into the parents of the hybrid rice, the heterosis of the hybrid rice can be dramatically improved.

Impact of plant breeding on the genetic diversity of cultivated strawberry as revealed by expressed sequence tag-derived simple sequence repeat markers.

Abstract: Unlike other important crops analyzed so far for genetic diversity and population structure, the brief history and particularities of the genetics of the cultivated strawberry (Fragaria ·ananassa Duchesne) have limited its genetic characterization. The genomic composition and the pattern of inheritance have not been fully elucidated, although a number of studies have suggested a highly diploidized genome. In this study, the similarity relationships and structure of 92 selected strawberry cultivars with widely diverse origins have been established using simple sequence repeat (SSR) markers derived from expressed sequence tags (EST-SSR markers). Genetic analysis performed by the unweighted pair group method with arithmetic mean clustering revealed a distribution according to both date of cultivar release and breeding for a specific climatic adaptation. Additionally, a model-based clustering approach identified three populations among the strawberry cultivars with an overall FST value of 0.15 to 0.16. Both analyses support a limited differentiation of modern cultivars, most probably as a consequence of the methodology of strawberry breeding. Interestingly, the collection of strawberry cultivars here analyzed showed comparable genetic differentiation to that observed in natural populations of Fragaria chiloensis (L.) Mill., one of its wild ancestors. Our results suggest that breeding has produced a small but significant reduction on the genetic diversity of F. ·ananassa. The panel of 10 EST-SSRs described in this work provided an extremely low probability of confusion (less than 10 -11 ), offering an efficient and accurate method for cultivar identification.

Identification and validation of SSR markers linked to the stem rust resistance gene Sr6 on the short arm of chromosome 2D in wheat.

Abstract: The wheat stem rust resistance gene Sr6, present in several wheat cultivars, confers a high level of resistance against a wide range of races of Puccinia graminis f. sp. tritici. Resistance conferred by Sr6 is influenced by temperature, light intensity, and genetic background of the recipient genotype. Here, we report the identification and validation of molecular markers linked to Sr6 that can be used for the detection of this gene in wheat breeding programs. A mapping population of 136 F2 plants and their F2:3 families derived from a cross between near-isogenic lines, ‘Chinese Spring’ and ISr6-Ra, were screened for stem rust reaction in the seedling stage. Bulked segregant analysis (BSA) based on seedling tests was used to screen 418 SSR markers that covered the entire genome of wheat. Four markers, Xwmc453, Xcfd43, Xcfd77, and Xgwm484, were mapped within a chromosome region that spanned 9.7 cM from Sr6. The closest markers, Xwmc453 and Xcfd43, were linked to Sr6 at a distance of 1.1 and 1.5 cM, respectively. The markers Xwmc453 and Xcfd43 amplified Sr6-specific marker alleles that were diagnostic for Sr6 in a diverse set of 46 wheat accessions and breeding lines developed and/or collected in Australia, Canada, China, Egypt, Ethiopia, Kenya, Mexico, South Africa, and USA. These markers can now be used for marker-assisted selection of Sr6 and for pyramiding it with other stem rust resistance genes.

Heterosis and heritability in crosses among Asian and Ethiopian parents of hot pepper genotypes

Abstract: Hot pepper is the most important worldwide grown and consumed spice and vegetable crop. Though hybrid breeding has been proposed for genetic improvement in the crop, but there is lack of information on heterosis in crosses among crop genotypes in Ethiopia. Twelve genotypes (nine Asian and three Ethiopian parents) of hot pepper were crossed in 2003 cropping season in a half-diallel fashion to fit Griffing’s fixed effect model analysis. An open field experiment was conducted in 2004/2005 to investigate heterosis for fourteen traits in 66 F1 hybrids grown together with their 12 selfed parents. Highly significant genotypic differences were observed for all the traits except for leaf area. Variance component due to specific combining ability (dominance) were larger than that due to general combining ability (additive) for each of the studied traits with few exceptions. Broad sense heritability (Hb2) for fruit traits were more than 60% and with wide gap from narrow sense heritability (hn2) for most of the important traits like number of fruit per plant (Hb2 = 88.3% and hn2 = 46.0%), days to maturity (Hb2 = 87.2% and hn2 = 23.1%) and dry fruit yield per plant (Hb2 = 72.6% and hn2 = 14.6%). Maximum heterosis over mid-parent and better-parent, and economic superiority of hybrid over standard check were recorded, respectively for dry fruit yield per plant (163.8, 161.8 and 92.1%), number of fruits per plant (104.4, 79.6 and 136.4%) and days to maturity (−29.8, −31.5 and −23.6%). These observations suggested a possibility of utilizing dominance genetic potentiality available in diverse genotypes of the crop by heterosis breeding for improving hot pepper to the extent of better economic return compared to the current commercial cultivar under production in the country. Low narrow sense versus very high broad sense heritability for days to maturity and dry fruit yield per plant could be a sign for achievability of earliness and high fruit yield using heterosis in hot pepper. The maximum heterobeltiosis were recorded either from F1s obtained from Ethiopian and Asian crosses or from within Asian crosses, suggesting the possibility of maximizing heterosis by considering genetically diverse parental genotypes. The manifestation of highest heterosis in hybrids from among Asian lines indicated existence of genetic diversity among Asian genotypes and the potentiality for improvement of hot pepper using genotypes from different regions of the world along with elite inbred lines from local cultivars.

Genetic characterization of powdery mildew resistance in U.S. hard winter wheat

Abstract: Powdery mildew significantly affects grain yield and end-use quality of winter wheat in the southern Great Plains. Employing resistance resources in locally adapted cultivars is the most effective means to control powdery mildew. Two types of powdery mildew resistance exist in wheat cultivars, i.e., qualitative and quantitative. Qualitative resistance is controlled by major genes, is race-specific, is not durable, and is effective in seedlings and in adult plants. Quantitative resistance is controlled by minor genes, is non-race-specific, is durable, and is predominantly effective in adult plants. In this study, we found that the segregation of powdery mildew resistance in a population of recombinant inbred lines developed from a cross between the susceptible cultivar Jagger and the resistant cultivar 2174 was controlled by a major QTL on the short arm of chromosome 1A and modified by four minor QTLs on chromosomes 1B, 3B, 4A, and 6D. The major QTL was mapped to the genomic region where the Pm3 gene resides. Using specific PCR markers for seven Pm3 alleles, 2174 was found to carry the Pm3a allele. Pm3a explained 61% of the total phenotypic variation in disease reaction observed among seedlings inoculated in the greenhouse and adult plants grown in the field and subjected to natural disease pressure. The resistant Pm3a allele was present among 4 of 31 cultivars currently being produced in the southern Great Plains. The genetic effects of several minor loci varied with different developmental stages and environments. Molecular markers associated with these genetic loci would facilitate incorporating genetic resistance to powdery mildew into improved winter wheat cultivars.

Analysis of diversity and linkage disequilibrium along chromosome 3B of bread wheat (Triticum aestivum L.).

Abstract: A highly polymorphic core collection of bread wheat and a more narrow-based breeding material, gathered from pedigrees of seven modern cultivars, was analysed in order to compare genetic diversity indices and linkage disequilibrium (LD) patterns along the chromosome 3B with microsatellite (SSR) and Diversity Arrays Technology markers. Five ancestral gene pools could be identified within the core collection, indicating a strong geographical structure (Northwest Europe, Southeast Europe, CIMMYT-ICARDA group, Asia, Nepal). The breeding material showed a temporal structure, corresponding to different periods of breeding programmes [old varieties (from old landraces to 1919), semi-modern varieties (1920-1959), modern varieties (1960-2006)]. Basic statistics showed a higher genetic diversity in the core collection than in the breeding material, indicating a stronger selection pressure in this latter material. More generally, the chromosome 3B had a lower diversity than the whole B-genome. LD was weak in all studied materials. Amongst geographical groups, the CIMMYT-ICARDA pool presented the longest ranged LD in contrast to Asian accessions. In the breeding material, LD increased from old cultivars to modern varieties. Genitors of seven modern cultivars were found to be different; most marker pairs in significant LD were observed amongst genitors of Alexandre and Koreli varieties, indicating an important inbreeding effect. At low genetic distances (0-5 cM), the breeding material had higher LD than the core collection, but globally the two materials had similar values in all classes. Marker pairs in significant LD are generally observed around the centromere in both arms and at distal position on the short arm of the chromosome 3B.

Genetic variability and plant character association of grain Fe and Zn in selected core collection accessions of sorghum germplasm and breeding lines.

Abstract: Sorghum is the third most important food crop in India after rice and wheat and is the staple food in Central India. It is also the staple for large tribal populations across the country. The poor and vulnerable groups in the society depend upon sorghum for their calorie and micronutrient requirement and in the absence of access and affordability to nutrient-rich foods like vegetables, fruits and animal products, biofortification of sorghum helps in enhancing the nutritional security of this group. Research efforts at ICRISAT and elsewhere showed that there is considerable genetic variability and high heritability for grain Fe and Zn contents and it is possible to genetically enhance the grain micronutrient content (Fe and Zn) in sorghum and other major staples. of variability in the sorghum germplasm accessions and breeding lines and the character association between grain Fe and Zn contents and with other agronomic traits.The main aim of this study was to identify promising donors in the core collection of sorghum germplasm accessions and breeding lines with the objective to use those with high grain Fe and Zn contents in the genetic enhancement program to develop biofortified sorghum cultivars. Significant positive correlation was observed between grain Fe and Zn contents (r=0.75) in the study. The five accessions, IS 5427, IS 5514, IS 55, IS 3760 and IS 3283, identified from the study with high grain Fe (>50 is on a continuing basis. mg kg-1) and Zn (>37 mg kg-1) contents can be utilized to increase the diversity and micronutrient density of sorghum hybrid parents in the future

Sunflower breeding for resistance to abiotic stresses.

Abstract: Due to a specific structure of its main organs (root, stem, leaves, head), sunflower can be successfully grown on marginal soils and in semi-arid conditions and it is more resistant to abiotic stresses than other field crops. In sunflower breeding for resistance to abiotic stresses, the greatest progress has been made in selection for drought resistance. Breeders use over 30 different parameters in sunflower screening for drought resistance, with physiological ones being the predominant type. Best breeding results have been achieved using the phenomenon of stay-green, with the added bonus that this method incorporates into the cultivated sunflower not only drought resistance but resistance to Macrophomina and Phomopsis as well. The diversity of the wild Helianthus species offers great possibilities for increasing the genetic resistance of the cultivated sunflower towards abiotic stresses. In using wild sunflower species in sunflower breeding for drought resistance and resistance to salinity, best results have so far been achieved with H. argophyllus and H. paradoxus, respectively. In addition to the use of wild Helianthus species, sunflower breeding for abiotic stress resistance should also make more use of molecular breeding techniques. More progress has been made in sunflower breeding for heat resistance than in that for cold resistance. Specific breeding programs dealing with sunflower resistance to mineral deficiency and mineral toxicity have yet to be established. Sunflower breeders worldwide should commit to a greater use of wild Helianthus species in breeding for resistance to abiotic stresses.

Transgenic Breeding: Perspectives and Prospects

Abstract: Transgenic technology serves to introduce gene sequences for expression of a desired trait. Pro-duction of transgenic plants is reported in many crops, but commercialization is limited to a few selected crops, such as cotton ( Gossypium hir-sutum L.), corn ( Zea mays L.), soybean [ Glycine max (L.) Merr.], and canola ( Brassica napus L. and B. rapa L.). This paper presents the sequen-tial processes of transgenic event design, event selection, and “cleaning up” genetic background for forward breeding programs. Expression of the foreign gene cannot be viewed in isolation and is more complex than has been assumed because of the interaction of transgene with native genes. Variations among clones and within the progeny are observed, and hence all the clones are taken into account for evaluation. Plant breeding must be involved to move trans-genes from transformable but agronomically unacceptable genotypes into elite breeding lines with two backcrosses. Production of transgenic plants in large numbers is diffi cult and laborious and requires large investments. It is worthwhile investing in parallel efforts to incorporate the transgene into improved plant material to satisfy commercial interests.National Research Centre for Sorghum (NRCS), Rajendranagar, Hyderabad 500 030, A.P., India. Received 3 Oct. 2008. *Correspond-ing author (visarada@nrcsorghum.res.in).

Molecular Improvement of Tropical Maize for Drought Stress Tolerance in Sub-Saharan Africa

Abstract: The C4 grass Zea mays (maize or corn) is the third most important food crop globally after wheat and rice in terms of production and the second most widespread genetically modified (GM) crop, after soybean. Its demand is predicted to increase by 45% by the year 2020. In sub-Saharan Africa, tropical maize has traditionally been the main staple of the diet, 95% of the maize grown is consumed directly as human food and as an important source of income for the resource-poor rural population. However, its growth, development and production are greatly affected by environmental stresses such as drought and salinization. In this respect, food security in tropical sub-Saharan Africa is increasingly dependent on continuous improvement of tropical maize through conventional breeding involving improved germplasm, greater input of fertilizers, irrigation, and production of two or more crops per year on the same piece of land. Integration of advances in biotechnology, genomic research, and molecular marker applications with conventional plant breeding practices opens tremendous avenues for genetic modifications and fundamental research in tropical maize. The ability to transfer genes into this agronomically important crop might enable improvement of the species with respect to enhanced characteristics, such as enriched nutritional quality, high yield, resistance to herbicides, diseases, viruses, and insects, and tolerance to drought, salt, and flooding. These improvements in tropical maize will ultimately enhance global food production and human health. Molecular approaches to modulate drought stress tolerance are discussed for sub-Saharan Africa, but widely applicable to other tropical genotypes in Central and Latin America. This review highlights abiotic constraints that affect growth, development and production of tropical maize and subsequently focuses on the mechanisms that regulate drought stress tolerance in maize. Biotechnological approaches to manage abiotic stress tolerance in maize will be discussed. The current status of tropical maize transformation using Agrobacterium as a vehicle for DNA transfer is emphasized. This review also addresses the present status of genetically modified organisms (GMOs) regulation in sub-Saharan Africa.

Changes in genetic diversity of U.S. flue-cured tobacco germplasm over seven decades of cultivar development.

Abstract: Plant breeding methodologies have been applied to fl ue-cured tobacco (Nicotiana tabacum L.) for approximately seven decades. As has been observed in several other crops, stringent quality requirements have resulted in use of conservative breeding strategies in the development of new cultivars. The impact of breeding practices on genetic diversity within U.S. fl ue-cured tobacco germplasm has not been investigated. In this study, we genotyped 117 tobacco cultivars from eight sequential time periods with 71 microsatellite primer pairs. A total of 294 alleles were scored. Only a fraction (48%) of alleles present in the initial germplasm pool was represented in cultivars released during the 1990s and 2000s. Only 13 and 18 alleles were detected in the 1990s and 2000s, respectively, which were undetected in the initial gene pool. The overall trend was one of gradual reduction in allelic counts at microsatellite loci, indicating a reduction in diversity over time at the gene level. Average genetic similarity was highest among cultivars of the 1990s and 2000s, refl ecting a reduction in genetic diversity at the population level. This observed narrowing of the U.S. fl ue-cured tobacco germplasm base in combination with low rates of genetic gain for yield in the last 20 years may point to a need for diversifi cation of parental materials used in future breeding crosses. Reported genetic relationships among the group of genotyped cultivars may be valuable for future strategic germplasm choices.

Method for improved plant breeding

Abstract: The invention relates generally to an improved plant breeding system. More particularly, this invention relates to a method for automated, high throughput analysis of plant phenotype and plant genotype in a breeding program.