Showing papers in "Crop Science in 2008"
TL;DR: Key lessons learned from apply- ing markers in plant breeding include the purpose of detecting QTL should be clearly defined before embarking on QTL map- ping and procedures for marker-based selection depend on the number of QTL.
Abstract: In the mid-1980s, the development of abundant molecular markers, appropriate statistical pro- cedures, and user-friendly computer software that implemented these statistical procedures permitted the detection of molecular markers associated with quantitative trait loci (QTL) for complex traits. Marker-assisted selection was then proposed as a means of exploiting mark- ers linked to QTL to develop improved cultivars. But while thousands of marker-trait associations have been reported for many traits in different plant species, far fewer examples of success- fully exploiting mapped QTL have been reported in the literature. Key lessons learned from apply- ing markers in plant breeding include the follow- ing: (i) the purpose of detecting QTL should be clearly defi ned before embarking on QTL map- ping; (ii) procedures for marker-based selection depend on the number of QTL; (iii) estimates of QTL effects for complex traits are often incon- sistent; and (iv) gain per unit cost and time rather than gain per cycle should be considered. Future applications for complex traits will likely focus on predictive methodologies for marker-based selection before phenotyping and for marker- based selection without QTL mapping. These applications will take advantage of cheaper costs of genotyping than of phenotyping.
814 citations
TL;DR: Fundamental issues remain to be resolved, particularly regarding complex traits, before marker-assisted selection realizes its full potential in public sector breeding programs, including the development of high throughput precision phenotyping systems for QTL mapping, improved understanding of genotype by environment interaction and epistasis, and development of publicly available computational tools tailored to the needs of molecular breeding programs.
Abstract: The volume of publications on the development and to a lesser extent the application of molecular markers in plant breeding has increased dramatically during the last decade. However, most of the publications result from investments from donors with a strategic science quality or biotech advocacy mandate leading to insufficient emphasis on applied value in plant breeding. Converting promising publications into practical applications requires the resolution of many logistical and genetical constraints that are rarely addressed in journal publications. This results in a high proportion of published markers failing at one or more of the translation steps from research arena to application domain. The rate of success is likely to increase due to developments in gene-based marker development, more efficient quantitative trait locus (QTL) mapping procedures, and lower cost genotyping systems. However, some fundamental issues remain to be resolved, particularly regarding complex traits, before marker-assisted selection realizes its full potential in public sector breeding programs. These include the development of high throughput precision phenotyping systems for QTL mapping, improved understanding of genotype by environment interaction and epistasis, and development of publicly available computational tools tailored to the needs of molecular breeding programs.
809 citations
TL;DR: This review addresses more than 20 issues that require clarification after controversial statements and contrasting conclusions have appeared in recent reviews of two prominent statistical models for analyzing yield-trial data.
Abstract: Recent review articles in this journal have compared the relative merits of two prominent statistical models for analyzing yield-trial data: Additive main effects and multiplicative interaction (AMMI) and genotype main effects and genotype × environment interaction (GGE). This review addresses more than 20 issues that require clarification after controversial statements and contrasting conclusions have appeared in those recent reviews. The AMMI2 mega-environment display incorporates more of the genotype main effect and captures more of the genotype × environment (GE) interaction than does GGE2, thereby displaying the which-won-where pattern more accurately for complex datasets. When the GE interaction is captured well by one principal component, the AMMI1 display of genotype nominal yields describes winning genotypes and adaptive responses more simply and clearly than the GGE2 biplot. For genotype evaluation within a single mega-environment, a simple scatterplot of mean and stability is more straightforward than the mean vs. stability view of a GGE2 biplot. Diagnosing the most predictively accurate member of a model family is vital for either AMMI or GGE, both for gaining accuracy and delineating mega-environments.
466 citations
TL;DR: The association models, genotypic data, and germplasm panel described here provide a starting point for sorghum researchers to begin association studies of traits and markers or can- didate genes of interest.
Abstract: Association mapping is a powerful strategy for identifying genes underlying quantitative traits in plants. We have assembled and characterized genetic and phenotypic diversity of a sorghum (Sorghum bicolor (L.) Moench) panel suitable for association mapping, comprised of 377 acces- sions representing all major cultivated races (tropical lines from diverse geographic and cli- matic regions), and important U.S. breeding lines and their progenitors. Accessions were pheno- typed for eight traits, and levels of population structure and familial relatedness were assessed with 47 simple sequence repeat (SSR) loci. The panel exhibited substantial morphological variation and little genotypic differentiation was observed between the converted tropical and breeding lines. The phenotypic and genotypic data were used to evaluate the performance of several association models in controlling for spurious associations. Our analysis indicated that association models that accounted for both population structure and kinship performed bet- ter than those that did not. In addition, we found that the optimal number of subpopulations used to correct for population structure was trait dependent. Although augmentation of the geno- typic data with additional SSR loci may be nec- essary, the association models, genotypic data, and germplasm panel described here provide a starting point for sorghum researchers to begin association studies of traits and markers or can- didate genes of interest.
321 citations
TL;DR: Objectives of this research were to quantify the effects of short episodes of HT stress during reproductive development on physiological, growth, and yield processes of grain sorghum and to identify the stage(s) most sensitive during the reproduc- tive development phase to HT stress.
Abstract: Sorghum (Sorghum bicolor L. Moench) grown in semiarid regions is often exposed to short periods of high-temperature (HT) stress dur- ing reproductive development. Objectives of this research were (i) to quantify the effects of short episodes of HT stress during reproductive development on physiological, growth, and yield processes of grain sorghum and (ii) to identify the stage(s) most sensitive during the reproduc- tive development phase to HT stress. Plants of hybrid DK-28 E were grown in growth chambers at daytime maximum/nighttime minimum opti- mum temperature (OT) of 32/22°C until 29 d after sowing. Thereafter, plants were exposed to OT or HT (40/30°C) or were reciprocally transferred at 10-d intervals (10 d before fl owering, 0, 10, 20, and 30 d after fl owering (DAF)) from OT to HT and vice versa. Transferred plants remained in the new temperature regime for 10 d before being returned to their original temperature regime. Continuous HT stress delayed panicle emergence and decreased plant height, seed set, seed numbers, seed yield, seed size, and harvest indices but did not infl uence leaf pho- tosynthesis. Exposure to short (10-d) periods of HT stress at fl owering and 10 d before fl ower- ing caused maximum decreases in seed set and seed yield, and HT stress during postfl owering stages (10, 20, and 30 DAF) decreased seed yield, with a larger reduction at early stages of seed development.
290 citations
TL;DR: It is concluded that altering grain and stem sugar genetic potential for yield traits should lead to greater feedstock improvement than altering composition traits.
Abstract: Genetic improvement of sorghum [Sorghum bicolor (L.) Moench] has traditionally focused on a single nonstructural carbohydrate, either grain starch or stem sugar. Sorghum starch and sugar may both be used as feedstocks for biofuel production. To investigate genetic tradeoffs between grain and stem sugar, a population derived from sweet sorghum cultivar Rio and grain sorghum ‘BTx623’ was evaluated for 27 traits related to grain and stem sugar yield and composition. Across three environments, a total of 129 quantitative trait loci (QTL) were identifi ed. Tradeoffs identifi ed between grain and stem sugar yield QTL colocalized with height and fl owering time QTL. Most importantly, QTL were identifi ed that increased yield and altered the composition of stem sugar and grain without pleiotropic effects. For example, a QTL on chromosome 3 that explained 25% of the genetic variance for stem sugar concentration did not colocalize with any grain QTL. These results suggest that total nonstructural carbohydrate yield could be increased by selecting for major QTL from both grain and sweet sorghum types. We conclude that altering grain and stem sugar genetic potential for yield traits should lead to greater feedstock improvement than altering composition traits.
280 citations
TL;DR: It is suggested that selection under drought stress reveals genes that correct inefficiencies inherited from the wild Phaseolus vulgaris, and are key to yield improvement of common bean.
Abstract: An estimated 60% of common bean (Phaseolus vulgaris L.) production worldwide is at risk of drought. A breeding program was developed at the International Center of Tropical Agriculture (CIAT) to create drought resistant breeding lines with varietal potential in the small red, small black, cream (mulatinho) and cream-striped (carioca) grain classes. Breeding populations were created from triple or double crosses. Field screening under terminal drought was performed at Palmira, Colombia in the dry season in F 2 , F 3:5 , and F 6:8 generations over two cycles of recurrent selection in the small red and small black classes, and one cycle in the mulatinho and carioca classes. Drought resistant lines yielded significantly more than commercial check cultivars under drought in all color classes. Some outyielded the respective checks by 15 to 25% (depending on color class and trial) in one or more of three favorable environments, or in the combined analysis across favorable environments, and were also earlier to mature. Drought resistant lines presented up to 36% greater yield d -1 in favorable environments. Some also expressed superior yields in a phosphorus-limited environment. Thus, selection for drought resistance has improved yield potential and plant efficiency across different environments. It is suggested that selection under drought stress reveals genes that correct inefficiencies inherited from the wild Phaseolus vulgaris, and are key to yield improvement of common bean.
275 citations
TL;DR: The use of cost-effective DNA markers derived from the fine mapped position of the genes for important agronomic traits and MAS strategies will provide opportunities for breeders to develop high-yielding, stress-resistant, and better-quality rice cultivars.
Abstract: Increasing world population, shrinking cultivable rice (Oryza sativa L.) land area, water scarcity and excess, evolution of new biotypes of pests and diseases, and climate change pose serious challenges to rice breeders to increase production and productivity with multiple resistances to biotic and abiotic stresses. Recent advances in rice genomics research and completion of the rice genome sequence have made it possible to identify and map precisely a number of genes through linkage to DNA markers. Noteworthy examples of some of the genes tightly linked to markers are resistance to or tolerance of blast, bacterial blight, virus diseases, brown planthopper (Nilaparvata lugens), drought, submergence, salinity, and low temperature and improved agronomic and grain quality traits. Marker-assisted selection (MAS) can be used for monitoring the presence or absence of these genes in breeding populations and can be combined with conventional breeding approaches. Marker-assisted backcross breeding has been used to effectively integrate major genes or quantitative trait loci with large effect into widely grown varieties. Pyramiding different resistance genes using MAS provides opportunities to breeders to develop broad-spectrum resistance for diseases and insects. The use of cost-effective DNA markers derived from the fine mapped position of the genes for important agronomic traits and MAS strategies will provide opportunities for breeders to develop high-yielding, stress-resistant, and better-quality rice cultivars.
275 citations
TL;DR: High nighttime temperature increased the expression of chloroplast protein synthesis elongation factor in both cultivars suggesting possible involvement of this protein in plant response to stress.
Abstract: Climate models predict greater increases in nighttime temperature in the future. The impacts of high nighttime temperature on wheat (Triticum aestivum L.) are not well understood. Objectives of this research were to quantify the impact of high nighttime temperatures during reproductive development on phenology, physiological, vegetative, and yield traits of wheat. Two spring wheat cultivars (Pavon-76 and Seri-82) were grown at optimum temperatures (day/night, 24/14°C; 16/8 h light/dark photoperiod) from sowing to booting. Thereafter, plants were exposed to four different nighttime temperatures (14, 17, 20, 23°C) until maturity. The daytime temperature was 24°C across all treatments. There were signifi cant infl uences of high nighttime temperatures on physiological, growth, and yield traits, but no cultivar or cultivar by temperature interactions were observed. High nighttime temperatures (>14°C) decreased photosynthesis after 14 d of stress. Grain yields linearly decreased with increasing nighttime temperatures, leading to lower harvest indices at 20 and 23°C. High nighttime temperature (≥20°C) decreased spikelet fertility, grains per spike, and grain size. Compared to the control (14°C), grain fi lling duration was decreased by 3 and 7 d at night temperatures of 20 and 23°C, respectively. High nighttime temperature increased the expression of chloroplast protein synthesis elongation factor in both cultivars suggesting possible involvement of this protein in plant response to stress.
263 citations
TL;DR: There is sufficient genetic variation in the wheat gene pool to ensure the continued improvement of wheat adaptation to abiotic stress, and three sources of novel genetic variability are explored, namely synthetic wheat, landrace cultivars, and alien introgressions and their applicability to applied wheat breeding are explored.
Abstract: Wheat (Triticum spp. L.) breeders have significantly improved wheat adaptation to stress-prone environments around the world. This progress has largely been achieved using empirical selection and genetic variability within the primary wheat gene pool. As most stress tolerance traits are quantitatively inherited, expansion of the available genetic diversity for stress tolerance is necessary if rates of genetic progress are to be maintained. This review explores three sources of novel genetic variability, namely synthetic wheat, landrace cultivars, and alien introgressions and their applicability to applied wheat breeding. Synthetic hexaploid wheat, derived by crossing tetraploid wheat with Aegilops tauschii, provides new genetic variability for adaptation to drought, high temperature, salinity, waterlogging, and soil micronutrient imbalances from the secondary wheat gene pool. Synthetic-derived materials have performed well in many stressed environments globally. There is significant unexploited variation among landraces and modern wheat cultivars to improve the stress adaptation of cultivated wheat. The tertiary gene pool, with a few significant exceptions, has been more difficult to exploit due to complex inheritance, meiotic instability, and linked deleterious effects. Nevertheless, there is sufficient genetic variation in the wheat gene pool to ensure the continued improvement of wheat adaptation to abiotic stress.
251 citations
TL;DR: These tests confirm that there are at least two distinct biotypes of A. glycines in North America and will be useful sources of resistance to both isolates.
Abstract: The soybean aphid (Aphis glycines Matsumura (Hemiptera: Aphididae)) is an invasive insect pest of soybean (Glycine max (L.) Merr.) that was fi rst reported in North America in 2000. There are currently no reports of soybean aphid bio- type diversity and this information is needed before aphid resistance genes are deployed. The objective of this research was to test for aphid biotype variation. The response of two A. glycines isolates, one collected in Ohio and the other in Illinois, were compared by infesting eight soybean genotypes in nonchoice tests. The same genotypes also were tested with the Ohio isolate using a choice test. In the nonchoice test, there was a signifi cant (P < 0.0001) effect of aphid isolate, genotype, and a signifi cant aphid isolate by soybean genotype interaction for the number of aphids per plant 10 and 15 d after infestation. The responses of the eight geno- types to the Ohio isolate in the choice test were similar to their responses in nonchoice tests. PI 200538 and PI 567597C were resistant to both the Ohio and Illinois isolates and will be useful sources of resistance to both isolates. These tests confi rm that there are at least two distinct biotypes of A. glycines in North America.
TL;DR: Fertility was highly correlated across years, suggesting a consistent and reproducible response of spikelet fertility to temperature, and the check cultivar N22 was the most heat tolerant genotype and cultivars Azucena and Moroberekan the most susceptible.
Abstract: Seed set of rice (Oryza sativa L.) is highly sensitive to short episodes of high temperature at anthesis events that are likely to be more frequent in future climates. Breeding for tolerance is therefore an essential component of adaptation to climate variability and change. Experiments were conducted in 2003 and 2004 at optimum (30 degrees C daytime) and high (35 and 38 degrees C) air temperature using parents of some prominent mapping populations (i) to determine whether there were differences in the daily flowering pattern and hence a potential heat avoidance mechanism, and (ii) to identify rice genotypes having true heat tolerance during anthesis, that is, high seed set in spikelets exposed to high temperature. Rice cultivar CG14 (O. glaberrima) reached peak anthesis earlier in the morning (1.5 h after dawn) under both control (30 degrees C) and high (38 degrees C) temperature conditions than O. sativa genotypes (>= 3 h after dawn). Exposure to high temperature (centered on the time of peak anthesis) for 6 h reduced spikelet fertility more than exposure for 2 h, and fertility was lower at 38 degrees C than at 35 degrees C. Genotypic ranking for spikelet fertility at 35 and 38 degrees C was highly correlated in both 2003 and 2004. Fertility was also highly correlated across years, suggesting a consistent and reproducible response of spikelet fertility to temperature. The check cultivar N22 was the most heat tolerant genotype (64-86% fertility at 38 degrees C) and cultivars Azucena and Moroberekan the most susceptible (<8%).
TL;DR: Proper application of SWE-based cytokinins may be an effective approach to improve summer performance of creeping bentgrass and appear to be associated with their organic, especially cytokinin, components and not the mineral fraction.
Abstract: Heat stress is the primary factor limiting summer performance of creeping bentgrass (Agrostis stolonifera L.) in many temperate to subtropical regions. Seaweed extract (SWE)-based cytokinins have been used to improve stress tolerance, but their specific effects on creeping bentgrass under supraoptimal temperatures are lacking. This study was designed to determine whether SWE-based cytokinins affect creep-ing bentgrass heat tolerance, and to compare effects of SWE-based cytokinins to those of a trans-zeatin riboside (t-ZR)-standard. Concentrations of t-ZR in two SWE sources (referred to as Oce and Aca) were determined. Treatments were applied twice to creeping bentgrass at an equivalent t-ZR concentration of 10 μM. One week after the initial treatment, heat stress was imposed (35/25°C [day/night]) for 42 d. The Oce SWE, Aca SWE, and t-ZR treatments resulted in leaf t-ZR concentrations that were 39, 32, and 28% higher, respectively, relative to the control at 14 d of heat stress. The Oce SWE, Aca SWE, and t-ZR treatments also increased superoxide dismutase activity and alleviated the decline of turfgrass quality, photochemical efficiency, and root viability. Ashed SWE provided results similar to the water control. Beneficial effects of SWE on heat tolerance appear to be associated with their organic, especially cytokinin, components and not the mineral (ashed) fraction. Proper application of SWE-based cytokinins may be an effective approach to improve summer performance of creeping bentgrass.
TL;DR: To maximize energy yields from grain and dedicated biomass sorghums, results suggest yield traits should be targeted for improvement before composition traits.
Abstract: Digestion and fermentation of lignocellulosic biomass (i.e., structural carbohydrates) are predicted to deliver higher yields of energy per hectare than sugar and starch (nonstructural carbohydrates), yet little research on genetic variation in crop feedstock biomass traits has been conducted. We investigated the genetic basis of leaf and stem biomass yield and composition in a population derived from a high-biomass sweet sorghum, ‘Rio’, and a grain sorghum inbred line, ‘BTx623’, and compared these results with those from analyses of grain and stem sugar traits that we reported previously. Thirty-one traits were evaluated and a total of 110 quantitative trait loci (QTL) were identifi ed across three locations. Many QTL for structural and nonstructural carbohydrate yields colocalized with loci for height, fl owering time, and stand density–tillering. Quantitative trait loci for composition had little colocalization across tissues and environments. Separate genetic control for leaf and stem structural carbohydrate composition was identifi ed, as well as separate genetic control of protein accumulation in leaf, stem, and grain. To maximize energy yields from grain and dedicated biomass sorghums, results suggest yield traits should be targeted for improvement before composition traits.
TL;DR: Differences between an older and a newer maize hybrid in their response to N availability throughout the life cycle at both the leaf and the whole-plant level were quantified.
Abstract: Nitrogen use efficiency is higher in newer than in older maize (Zea mays L) hybrids, but the physiological mechanisms underlying differences in N-use efficiency are unknown The objective of this study was to quantify differences between an older and a newer maize hybrid in their response to N availability throughout the life cycle at both the leaf and the whole-plant level An older and a newer maize hybrid were grown in a field hydroponic system located near Guelph, ON, in 2005 at a high and a low N level Leaf carbon exchange rate (CER), chlorophyll index, and the thylakoid electron transport rate (ETR) were measured weekly from 2 wk presilking to 8 wk postsilking Plant-component dry matter and N content were determined from 1 wk presilking to maturity At the leaf level, leaf CER declined during the grain-filling period, and the decline was greater under low than high N availability The decline in leaf CER during the grain-filling period was less in the newer than in the older hybrid under both high and low N availability, and differences in leaf CER were associated most strongly with a reduction in leaf CER per unit absorbed photosynthetic photon flux density At the whole-plant level, reduction in grain yield in low vs high N was greater in the older than in the newer hybrid The hybrid x N interaction for grain yield was attributable predominantly to a greater decline in the proportion of dry matter allocated to the grain in the older hybrid
TL;DR: The clustering of genotypes based on the AFLP markers shows that the genetic diversity of J. curcas in Guizhou was notably different from the other samples, and this collection has not been characterized using molecular techniques associated with germplasm management and utilization.
Abstract: Globally, Jatropha curcas L. (Euphorbiaceae) holds much promise for producing biodiesel; it is cultivated in many tropical countries. In the South China Botanical Garden, a germplasm collection of J. curcas has been assembled on the basis of geographic location. However, this collection has not been characterized using molecular techniques associated with germplasm management and utilization. In this study, the genetic relationships of 58 J. curcas accessions were assessed based on simple sequence repeat (SSR) and amplifi ed fragment length polymorphism (AFLP) analyses. Seventeen microsatellite markers were developed using the FIASCO (Fast Isolation by AFLP of Sequences Containing repeats) protocol; only one SSR primer was polymorphic with two alleles. The seven AFLP primer combinations amplifi ed 70 polymorphic loci in total, 14.3% of which were polymorphic. The clustering of genotypes based on the AFLP markers shows that the genetic diversity of J. curcas in Guizhou was notably different from the other samples.
TL;DR: The study determined that integration of crops with livestock had generally positive effects on crop yield and soil organic matter despite the potential for livestock to compact soil during winter grazing.
Abstract: Integrated crop-livestock systems directly link crop and livestock production together to generate positive economic and environmental outcomes. Some methods used in integrated systems, like winter grazing on cropland, could negatively affect soil properties and crop productivity. We compared soil compaction, corn (Zea mays L.) yield, and soil nutrient pools between an integrated crop-livestock system and continuous corn system to address this issue. The study was conducted near Pana, IL, between 2002 and 2006. Soil compaction was evaluated indirectly by measuring soil penetration resistance (PR) and surface CO 2 effluxes. Total soil C, N, and microbial biomass C, were measured from 2002 to 2005. Soil PR and CO 2 effluxes showed inconsistent trends related to soil compaction and cattle presence. Corn yield from 2004 to 2006 was higher (P = 0.01) in the integrated system (11.6 Mg ha -1 ) compared with continuous corn (10.6 Mg ha -1 ). Total soil C concentration increased significantly from 2002 to 2005 within components of the integrated system but remained unchanged in continuous corn. Microbial biomass C was also higher in the integrated system but only in 2005. The study determined that integration of crops with livestock had generally positive effects on crop yield and soil organic matter despite the potential for livestock to compact soil during winter grazing.
TL;DR: The robustness of the csLV34 marker in postulating the likely occurrence of Lr34/Yr18 across a wide range of wheat germplasm and its utility in wheat breeding was confi rmed.
Abstract: The Lr34/Yr18 adult plant resistance gene contributes signifi cantly to durable leaf rust (caused by Puccinia triticina Eriks.) resistance. Simple and robust molecular markers that enable early detection of Lr34/Yr18 are a major advancement in wheat (Triticum aestivum L.) breeding. An insertion/deletion size variant located at the csLV34 locus on chromosome 7D within an intron sequence of a sulfate transporter-like gene tightly linked to the Lr34/Yr18 dual rust resistance gene was used to examine a global collection of wheat cultivars, landraces, and D genome–containing diploid and polyploid species of wheat relatives. Two predominant allelic size variants, csLV34a and b, found among the wheat cultivars showed disparate variation in different wheat growing zones. A strong association was observed between the presence of Lr34/Yr18 and the csLV34b allele and wheat lines known to have Lr34/Yr18 that had the csLV34a allele were rare. All landraces with the exception of those from China were predominantly of the csLV34a type. Only one size variant, csLV34a, was detected among the diploid and polyploid D genome–containing species, indicating that csLV34b arose subsequent to hexaploid bread wheat synthesis. The lineage of the csLV34b allele associated with Lr34/Yr18 in modern wheat cultivars from North and South America, CIMMYT, Australia, and Russia was tracked back to the cultivars Mentana and Ardito developed in Italy by Nazareno Strampelli in the early 1900s. The robustness of the csLV34 marker in postulating the likely occurrence of Lr34/Yr18 across a wide range of wheat germplasm and its utility in wheat breeding was confi rmed.
TL;DR: Garvin et al. as discussed by the authors developed genetic and genomic resources for Brachypodium distachyon, a new model system for grass crop research, and used it for grass field research.
Abstract: Garvin, D. F., Gu, Y. Q., Hasterok, R., Hazen, S. P., Jenkins, G., Mockler, T. C., Mur, L. A. J., Vogel, J. P. (2008). Development of genetic and genomic research resources for Brachypodium distachyon, a new model system for grass crop research. Crop Science, 48, S69-S84 journalsupplement: 1 IMPF: 01.32 RONO: 00
TL;DR: Biweekly V-node and R-stage, stem node number, internode length, and other traits were quantifi ed in an irrigated split-plot, four-replicate, randomized complete block experiment conducted in Lincoln, NE, in 2003–2004.
Abstract: The sensitivity of soybean [Glycine max (L) Merr] main stem node accrual to ambient temperature has been documented in greenhousegrown plants but not with fi eld-grown plants in the north-central United States Biweekly V-node and R-stage, stem node number, internode length, and other traits were quantifi ed in an irrigated split-plot, four-replicate, randomized complete block experiment conducted in Lincoln, NE, in 2003–2004 Main plots were early-, mid-, late
TL;DR: The dominant Vrn-D1 allele showed the highest frequency in the Chinese wheat cultivars, and is associated with the latest heading time,Vrn-A1 the earliest, and Vn-B1 intermediate values, which is important for breeding programs in countries interested in using Chinese wheats.
Abstract: Information on the distribution of vernalization genes and their association with growth habit is crucial to understanding the adaptability of wheat (Triticum aestivum L.) cultivars to different environments. In this study, 278 Chinese wheat cultivars were characterized with molecular markers for the vernalization genes Vrn-A1, -B1, -D1, and -B3. Heading time was evaluated in a greenhouse under long days without vernalizaton. The dominant Vrn-D1 allele showed the highest frequency in the Chinese wheat cultivars (37.8%), followed by the dominant Vrn-A1, -B1, and -B3 alleles. Ninety-two winter cultivars carried recessive alleles of all four vernalization loci, whereas 172 spring genotypes contained at least one dominant Vrn allele. All cultivars released in the North China Plain Winter Wheat Zone were winter type. Winter (53.0%), spring (36.1%), and early-heading (10.9%) cultivars were grown in the Yellow and Huai River Valley Winter Zone. Most of the spring genotypes from this zone carried only the dominant Vrn-D1 allele, which was also predominant (64.1%) in the Middle and Lower Yangtze Valley Winter Zone and Southwestern Winter Wheat Zone. In three spring-sown wheat zones, all cultivars were early-heading spring types that frequently possessed the strongest dominant Vrn-A1a allele and combinations with other dominant Vrn gene(s). The Vrn-D1 allele is associated with the latest heading time, Vrn-A1 the earliest, and Vrn-B1 intermediate values. The information is important for breeding programs in countries interested in using Chinese wheats.
TL;DR: On average, increasing species richness in perennial herbaceous polycultures increased productivity and weed suppression, but well-adapted species produced high biomass yield regardless of richness.
Abstract: Species diversity can increase natural grasslands productivity but the effect of diversity in agricultural systems is not well understood. Our objective was to measure the effects of species composition, species richness, and harvest management on crop and weed biomass in perennial herbaceous polycultures. In 2003, 49 combinations of seven species (legumes, C 3 and C 4 grasses) including all monocultures and selected two to six species polycultures were sown in small plots at two Iowa, USA, locations in a replicated field design. Plots were split in half and managed with either one or three harvests in each of 2004 and 2005. Biomass increased log-linearly with species richness in all location-management environments and the response was not different between managements. Polycultures outyielded monocultures on average by 73%. The most productive species in monoculture for each management best explained the variation in biomass productivity. The biomass of plots containing this species did not increase with richness in most environments but biomass of plots without this species increased log-linearly in all cases. Weed biomass decreased exponentially with richness in all environments. On average, increasing species richness in perennial herbaceous polycultures increased productivity and weed suppression, but well-adapted species produced high biomass yield regardless of richness.
TL;DR: A comprehensive multitrait selection procedure is proposed that coherently combines independent selection, independent culling, and index selection so that all the aspects in breeding line selection are taken into consideration.
Abstract: Breeding line selection, either for potential varieties or for useful parents, must be based on multiple breeding objectives (or traits). Varieties cannot have any major defects, while parents must have outstanding levels in at least one trait. Due to undesirable associations among breeding objectives, it is difficult to accomplish both tasks (variety selection and parent selection) through a single selection strategy. Additional complication results when a program is breeding for different end-uses such that both high and low levels of a trait are desirable. The first purpose of this paper was to propose a comprehensive multitrait selection procedure that coherently combines independent selection, independent culling, and index selection so that all the aspects in breeding line selection are taken into consideration. A dataset of 150 oat (Avena sativa L.) breeding lines with values evaluated for four quality traits (groat, oil, protein, and beta-glucan concentrations) was used for illustration. A genotype by trait biplot is a useful tool for exploring multiple trait data and can aid in multitrait selection because it graphically displays the trait associations across, and the trait profiles of, the genotypes. Procedures are outlined to avoid possible misinterpretation of such a biplot when the biplot does not fully display the patterns.
TL;DR: Heterosis for biomass yield in switchgrass may need the competitive conditions of swards to be fully expressed, and results do provide ample justification for additional research to develop switchgrass population and specific hybrids.
Abstract: Improving the biomass yield of switchgrass (Panicum virgatum L.) will improve its utility as a dedicated energy crop by increasing both its net and total energy yield per hectare. In a previous space-transplanted study, midparent heterosis for biomass yield was reported for population and specific F 1 hybrids of the lowland-tetraploid cultivar Kanlow and the upland-tetraploid cultivar Summer. These two cultivars were proposed to be two different heterotic groups. The objective of this study was to determine the extent of heterosis for biomass yield in reciprocal Kanlow (K) and Summer (S) F 1 population hybrids grown in simulated swards and to determine the effect of advance in generation on biomass yield. Parent populations and their F 1 , F 2 , and F 3 population hybrids were grown in transplanted sward plots located near Mead, NE, for a three-year period. Plant density in the simulated swards was equivalent to acceptable stands in seeded plots. Plots were not harvested the establishment year to enable them to become fully established. Biomass yields were determined for the following two years. There was significant high-parent heterosis of 30 to 38% (P < 0.01) for biomass yield for both the K x S F 1 and S x K F 1 hybrid populations. Heterosis for biomass yield declined with advance in generation. Heterosis for biomass yield in switchgrass may need the competitive conditions of swards to be fully expressed. Additional trials of specific hybrids established from seed are needed to further verify these conclusions. These results do provide ample justification for additional research to develop switchgrass population and specific hybrids.
TL;DR: These conditions are more frequently achieved for half-sib mating systems due to the greater partitioning of additive genetic variance within families, but AWF selection can also be heavily favored in a full-siber mating system under conditions that are a bit more restrictive.
Abstract: Genetic gains in forage yield lag far behind the gains made in grain yield of cereal crops, partly because of the use of ineffi cient selection methods that make little use of additive genetic variance within half-sib or full-sib families. The objectives of this study were (i) to compute expected genetic gains for among-and-withinfamily (AWF) selection methods, (ii) to compare these selection methods to standard family and progeny-test selection methods, and (iii) to defi ne the conditions under which AWF selection methods may be superior to progeny-test selection. Among-and-within-family selection is equal to or better than family selection under all circumstances provided the within-family selection criterion (X or Y) is heritable and has a positive genetic correlation with the desired trait (Y). Among-and-within-family selection is favored over progeny-test selection by (i) high heritability on an individual-plant basis (relative to heritability on a family-mean basis), (ii) withinfamily selection intensity ≥ among-family selection intensity, and (iii) possibly a shorter cycle time (for some species and some breeding programs). These conditions are more frequently achieved for half-sib mating systems due to the greater partitioning of additive genetic variance within families, but AWF selection can also be heavily favored in a full-sib mating system under conditions that are a bit more restrictive.
TL;DR: The objectives of this study were to document differences in agronomic and physiological performance for two cotton genotypes when grown under an ambient temperature control and a warm temperature regime.
Abstract: An optimal temperature range exists for cotton (Gossypium hirsutum L.). When Mississippi Delta cotton experiences temperatures above the upper threshold, as can occur during the summer, it is not entirely clear what growth parameters are affected by the heat. The objectives of this study were to document differences in agronomic and physiological performance for two cotton genotypes (SureGrow 125 and SureGrow 125BR) when grown under an ambient temperature control and a warm temperature regime (about 1˚C warmer). Field studies were conducted from 2003 through 2005. White bloom counts, nodes above white bloom (NAWB) data, dry matter partitioning data, lint yield, yield components, and fi ber quality data were collected. Genotypes responded similarly to the temperature regimes. Warmer temperatures resulted in lower NAWB data, indicating a slightly advanced crop maturity. In two out of three years, the lint yield from the warm regime was 10% lower than that of the control. This reduction was primarily caused by a 6% smaller boll mass, with 7% fewer seed produced per boll in the warm regime. Fiber produced in the warm temperature regime was consistently 3% stronger than fi ber in the control treatment. When temperatures become too hot, ovule fertilization may be compromised, leading to fewer seeds produced per boll, smaller boll masses, and ultimately, lint yield reductions. USDA-ARS, Crop Genetics and Production Research Unit, P.O. Box 345, Stoneville, MS 38776. Trade names are necessary to report factually on available data; however, the USDA neither guarantees nor warrants the standard of the product or service, and the use of the name by USDA implies no approval of the product or service to the exclusion of others that may also be suitable. Received 8 May 2007. *Corresponding author (bill.pettigrew@ars.usda.gov).
TL;DR: The unique qualities of these improved species along with high seedling vigor, ease of establishment, and general competitiveness ensure that red and white clover will continue to be the major forage legumes of the United States and justify breeding efforts.
Abstract: The perennial clovers, red (Trifolium pratense L.) and white clover (T. repens L.), have been important legumes for livestock feeding in the United States during the past century, par- ticularly in the eastern United States. Recently, sustainable agriculture, organic farming, inte- grated crop-livestock systems, and high nitro- gen prices have stimulated interest in forage legumes. This paper describes the present status of clover improvement programs—their objectives, successes, short falls, and chal- lenges for the future. One goal of most clover breeding programs is increased persistence (longevity of individual plants) because of its association with general adaptability and yield. Persistence, which limits life of clovers to about three to four years, is largely governed by pro- grammed senescence but can be infl uenced somewhat by breeding for general adaptation to the area of use. New, more-adapted red clo- ver cultivars have been bred in Wisconsin for use in the northern states, in Kentucky for the middle states, and in Florida for the southern states. For white clover, researchers in several states in the southeast have cooperated in the development of improved cultivars. The unique qualities of these improved species along with high seedling vigor, ease of establishment, and general competitiveness ensure that red and white clover will continue to be the major forage legumes of the United States and justify contin- ued breeding efforts.
TL;DR: The objectives of this study were to examine the diversity in maize landraces, modern open pollinated varieties, and inbred lines adapted to nontemperate growing areas to find unique sources of allelic diversity that may be used in maize improvement.
Abstract: CIMMYT is the source of improved maize (Zea mays L.) breeding material for a signifi cant portion of the nontemperate maize growing world. Landraces which did not serve as sources for improved maize germplasm may contain untapped allelic variation useful for future breeding progress. Information regarding levels of diversity in different germplasm would help to identify sources for broadening improved breeding pools and in seeking genes and alleles that have not been tapped in modern maize breeding. The objectives of this study were to examine the diversity in maize landraces, modern open pollinated varieties (OPVs), and inbred lines adapted to nontemperate growing areas to fi nd unique sources of allelic diversity that may be used in maize improvement. Twenty-fi ve simple sequence repeat markers were used to characterize 497 individuals from 24 landraces of maize from Mexico, 672 individuals from 23 CIMMYT improved breeding populations, and 261 CIMMYT inbred lines. Number of alleles, gene diversity per locus, unique alleles per locus, and population structure all differ between germplasm groups. The unique alleles found in each germplasm group represent a great reservoir of untapped genetic resources for maize improvement, and implications for hybrid breeding are discussed.
TL;DR: Fenugreek genotypes tested in western Canada have demonstrated genetic variability for biomass production andNutraceutical properties indicating that there is much potential for enhancing the properties desired by agricultural and nutraceutical industries in this region.
Abstract: Fenugreek (Trigonella foenum-graecum L.) is extensively used as a spice in India and the Mediterranean region and is known to possess a number of medicinal properties. Steroidal sapogenins and mucilaginous fibers present in the seed and leaves of this legume plant contribute to anti-diabetic and hypocholesterolaemic properties attributed to the plant. In recent years selected genotypes of this species have formed a niche crop that produces high yields of bloat-free forage that can increase both beef and milk production in semiarid regions of western Canada. Fenugreek genotypes tested in western Canada have demonstrated genetic variability for biomass production and nutraceutical properties indicating that there is much potential for enhancing the properties desired by agricultural and nutraceutical industries in this region. This paper reviews the history, culture and documented medicinal, agronomic and environmental value of fenugreek as well as discusses future potential of this crop for use in semiarid regions of North America.
TL;DR: Results validate that selecting germplasm based on high root/ shoot ratio in the greenhouse is a viable method for improving the fi eld drought tolerance of turftype tall fescue.
Abstract: Freshwater resources for turfgrass irrigation are becoming limited. Hence, the development of drought tolerant turf cultivars will be of great value to turf managers. The objective of the following research was to evaluate the fi eld drought tolerance of turf-type tall fescue (Festuca arundinacea Schreb.) entries that were selected based either on high root/shoot ratio under greenhouse conditions or under severe drought stress conditions in the fi eld. Twelve tall fescue entries (two selected by root/shoot ratio, two selected by screening fi eld drought tolerance, the four parents, and four standard controls) were established under a rain-out shelter, and their green turf coverage was evaluated during drought stress (irrigation withheld) and drought recovery (irrigation reapplied) events in 2003 and 2004. In both years, entries selected for high root/shoot ratio demonstrated signifi cantly improved drought tolerance compared to their parents, whereas improved drought tolerance for fi eld-selected entries was less consistent. Turf green-up following drought conditions was correlated to the drought tolerance of each entry, in that those cultivars that were the most drought tolerant were also the fi rst to green up on rewatering. These results validate that selecting germplasm based on high root/ shoot ratio in the greenhouse is a viable method for improving the fi eld drought tolerance of turftype tall fescue.