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A high-resolution chromosome arm-specific mapping population was used in an attempt to locate/detect gene(s)/QTL for different root traits on the short arm of rye chromosome 1 (1RS) in bread wheat. This population consisted of induced homoeologous recombinants of 1RS with 1BS, each originating from a different crossover event and distinct from all other recombinants in the proportions of rye and wheat chromatin present. It provides a simple and powerful approach to detect even small QTL effects using fewer progeny. A promising empirical Bayes method was applied to estimate additive and epistatic effects for all possible marker pairs simultaneously in a single model. This method has an advantage for QTL analysis in minimizing the error variance and detecting interaction effects between loci with no main effect. A total of 15 QTL effects, 6 additive and 9 epistatic, were detected for different traits of root length and root weight in 1RS wheat. Epistatic interactions were further partitioned into inter-genomic (wheat and rye alleles) and intra-genomic (rye-rye or wheat-wheat alleles) interactions affecting various root traits. Four common regions were identified involving all the QTL for root traits. Two regions carried QTL for almost all the root traits and were responsible for all the epistatic interactions. Evidence for inter-genomic interactions is provided. Comparison of mean values supported the QTL detection.

The spontaneous translocation of the short arm of chromosome 1 of rye (1RS) in bread wheat is associated with higher root biomass and grain yield. Recent studies have confirmed the presence of QTL for different root morphological traits on the 1RS arm in bread wheat. This study was conducted to address two questions in wheat root genetics. First, does the presence of the 1RS arm in bread wheat affect its root anatomy? Second, how does root morphology and anatomy of bread wheat respond to different dosages of 1RS? Near-isogenic plants with a different number (0 to 4 dosages) of 1RS translocations were studied for root morphology and anatomy. The F(1) hybrid, with single doses of the 1RS and 1AS arms, showed heterosis for root and shoot biomass. In other genotypes, with 0, 2, or 4 doses of 1RS, root biomass was incremental with the increase in the dosage of 1RS in bread wheat. This study also provided evidence of the presence of gene(s) influencing root xylem vessel number, size, and distribution in bread wheat. It was found that root vasculature follows a specific developmental pattern along the length of the tap root and 1RS dosage tends to affect the transitions differentially in different positions. This study indicated that the inherent differences in root morphology and anatomy of different 1RS lines may be advantageous compared to normal bread wheat to survive under stress conditions.

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.

Background and aimsMost plant scientists, in contrast to animal scientists, study only half the organism, namely above-ground stems, leaves, flowers and fruits, and neglect below-ground roots. Yet all acknowledge roots are important for anchorage, water and nutrient uptake, and presumably components of yield. This paper investigates the relationship between domestication, and the root systems of landraces, and the parents of early, mid- and late green-revolution bread wheat cultivars. It compares the root system of bread wheat and 'Veery'-type wheat containing the 1RS translocation from rye.MethodsWheat germplasm was grown in large pots in sand culture in replicated experiments. This allowed roots to be washed free to study root characters.Key resultsThe three bread wheat parents of early green-revolution wheats have root biomass less than two-thirds the mean of some landrace wheats. Crossing early green-revolution wheat to an F(2) of 'Norin 10' and 'Brevor', further reduced root biomass in mid-generation semi-dwarf and dwarf wheats. Later-generation semi-dwarf wheats show genetic variation for root biomass, but some exhibit further reduction in root size. This is so for some California and UK wheats. The wheat-rye translocation in 'Kavkaz' for the short arm of chromosome 1 (1RS) increased root biomass and branching in cultivars that contained it.ConclusionsRoot size of modern cultivars is small compared with that of landraces. Their root system may be too small for optimum uptake of water and nutrients and maximum grain yield. Optimum root size for grain yield has not been investigated in wheat or most crop plants. Use of 1RS and similar alien translocations may increase root biomass and grain yield significantly in irrigated and rain-fed conditions. Root characters may be integrated into components of yield analysis in wheat. Plant breeders may need to select directly for root characters.

The recurrent California drought necessitates investigation of the relationship between water application, crop yields, and management practices. The majority of cultivars in many crops are genetically dwarfed which allows the application of larger amounts of water and fertilizer in return for higher yields and ease of harvesting. This project used bread wheat as a model system to investigate the water use and water-use efficiency of taIl and dwarf cultivars. Four near-isogenic lines, rhtrht (tall), RhtlRhtl (semidwarf), Rht2Rht2 (semidwarf), and Rht3Rht3 (dwarf), in 'Maringa' bread wheat background and four of their near-isogenic Fl hybrids derived from crossing the original lines were used to determine the effects of dwarfing genes on plant height, water use, grain yield, total dry matter, and wateruse efficiency in well-watered and droughted pot experiments in the glasshouse. The nearisogenic lines and their six F 1 hybrids were also grown in well-watered and droughted field conditions. The glasshouse season lasted 158 days, whereas the field season took 149 days between planting and harvesting. Carbon isotope discrimination was determined as a measure of transpiration efficiency. The near-isogenic lines used similar amounts of water in well-watered (12 kg per 158 days) and droughted (9 kg per 158 days) pot experiments. The Rht3Rht3 dwarf line actually used 3% less water than the tall line in a well-watered situation, and 5% less water than tall line in a droughted situation, but these differences were not significant in this experiment. Plant height ranged from 60 to 124 em and from 53 to 121 ern in well-watered and droughted pot experiments, and it varied from 50 to 94 cm and from 49 to 90 cm in well-watered and droughted field experiments, respectively. Total dry matter, grain yield, transpiration efficiency (total dry matter/water used), and water-use efficiency (grain yield/water used) declined with plant height in well-watered glasshouse conditions. No significant relationships were found between plant height and these traits in droughted glasshouse conditions. Carbon isotope discrimination was negatively correlated with transpiration efficiency, but significantly so only in well-watered pot experiments. Plant height was negatively associated with carbon isotope discrimination in both well-watered and droughted pot and field experiments. Grain yield and aboveground dry matter also declined with plant height in field conditions. In most cases, the dwarfing genes reduced shoot dry matter more than grain yield, therefore, harvest index of the semidwarf and dwarf lines was higher than that of the tall standard line. The dwarfism caused by Rhtl, Rht2, and Rht3 genes had, in general, depressing effects on transpiration efficiency, water-use efficiency, total dry matter, and grain yield. An optimum range for plant height was determined (90- 100 ern) using these near-isogenic lines, below which shoot dry matter, grain yield, and water-use efficiency were significantly reduced.

To assess genetic and environmental variation for outcrossing in common bean (Phaseolus vulgaris L.), a bulk of nine purple-hypocotyled (dominant), black-seeded, common bean lines (pollen parents) and six green-hypocotyled (recessive), white-seeded, common bean lines (seed parents) representing Mexican germplasm were used to estimate outcrossing rate. The experiment was conducted at Irvine and Riverside, CA, in mid-May and mid-July of 1989 and 1991. Outcrossing estimates were based on the proportion of purple-hypocotyled progeny from green-hypocotyled parents. Approximately 1400 single-plant families were progeny tested in which 120 278 seedlings were scored for the presence of anthocyanin in the hypocotyl. Of these, 113 246 were classified as selfed progeny and 7031 as hybrid progeny, giving rise to a weighted mean outcrossing rate of 6.9%. Entire progenies from each maternal line were grown and scored, and the minimum and maximum rates of outcrossing observed ranged between 0.0 and 78.0%. Mean outcrossing rate for the six white-seeded lines ranged from 4.41 to 10. 16%. However, differences in outcrossing rate among these lines were not significant, nor were differences between dates of planting, locations, or years. The combined analysis of variance showed significant location x planting date x line interaction and year x location X line interaction, indicating that environmental factors had a strong effect on rate of outcrossing in the lines examined., Knowledge about the breeding system of a crop is important to design effective breeding schemes to improve that crop. Common bean was listed as a predominantly self pollinating species by [...]

Genetic variation exists for season-long water-use efficiency (WUE) among bread wheat (Triticum aestivum L.) cultivars. To facilitate the study of such varation, we define WUE and its components so that the contribution of each component trait to variation in WUE can be evaluated. Seven diverse bread wheat cultivars were grown in replicated glasshouse pot experiments under well-watered conditions. Significant genotypic variation was observed for WUE (ratio of grain yield to water used), evapotranspiration efficiency (ETE, ratio of total dry matter to water used), and harvest index (HI, ratio of grain yield to total dry matter). Old tall cultivars, on average, had relatively higher ETE (3.95 vs. 2.67 g [kg.sup.- 1]), but much lower HI (0.35 vs. 0.53) than modern semidwarf and dwarf cultivars. Cultivars with similar WUE showed different patterns of component traits. Evapotranspiration efficiency, and HI accounted for 59%, and 41%, respectively, of the genotypic variation in WUE. A path coefficient analysis revealed that ETE had a higher direct effect on WUE than did HI. However, their positive direct effects were counterbalanced by negative indirect effects via each other, because ETE and HI were negatively correlated. Carbon isotope discrimination showed a negative correlation with WUE (-0.62) and ETE (-0.84), but a positive correlation with HI (0.43). Days from planting to maturity, plant height, root dry matter, and shoot dry matter each had a positive correlation coefficient with ETE, but a negative correlation with HI.

Successful breeding of guayule (Parthenium argentatum Gray) for increased rubber yield requires knowledge about the traits that influence rubber production directly and indirectly. This study was undertaken to examine the interrelationships of several agronomic traits through path-coefficient analyses, to determine broad-sense heritability, and to estimate genetic advance under selection. Plant height, width, dry weight, rubber content, resin content, rubber yield, and resin yield from guayule selections planted at two locations (Riverside, CA, and Maricopa, AZ) were used for analyses. The guayule selections exhibited significant differences for all traits at both locations, except for plant dry weight and plant width at Maricopa. Broad-sense heritability estimates ranged from a low of 75.1% (for rubber content) to a high of 96.5% (for resin content) at Riverside, and from 6% (for plant width) to 93.1% (for resin content) at Maricopa. Expected genetic advance ranged between 18% (for plant width) and 76% (for resin yield) at Riverside, and between 0.72% (for plant width) and 41% (for resin content) at Maricopa. Rubber yield, the most critical trait for economic commercialization of guayule, showed expected genetic advance of 58% at Riverside and 37% at Maricopa. Path-coefficient analyses indicated plant height to be less important than plant width as a component of dry weight at Riverside. Dry weight and percent rubber content had positive direct effects on rubber yield and accounted for 99% of its variation at Riverside and 85% at Maricopa.

A high-resolution chromosome arm-specific mapping population was used in an attempt to locate/detect gene(s)/QTL for different root traits on the short arm of rye chromosome 1 (1RS) in bread wheat. This population consisted of induced homoeologous recombinants of 1RS with 1BS, each originating from a different crossover event and distinct from all other recombinants in the proportions of rye and wheat chromatin present. It provides a simple and powerful approach to detect even small QTL effects using fewer progeny. A promising empirical Bayes method was applied to estimate additive and epistatic effects for all possible marker pairs simultaneously in a single model. This method has an advantage for QTL analysis in minimizing the error variance and detecting interaction effects between loci with no main effect. A total of 15 QTL effects, 6 additive and 9 epistatic, were detected for different traits of root length and root weight in 1RS wheat. Epistatic interactions were further partitioned into inter-genomic (wheat and rye alleles) and intra-genomic (rye-rye or wheat-wheat alleles) interactions affecting various root traits. Four common regions were identified involving all the QTL for root traits. Two regions carried QTL for almost all the root traits and were responsible for all the epistatic interactions. Evidence for inter-genomic interactions is provided. Comparison of mean values supported the QTL detection.

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.