Synopsis A comparison was made between heritability percentages calculated by two regression methods, the conventional, and the standard unit or correlation. Their comparative reliability was determined by comparing predicted and actual gains in hypothetical selection experiments for date of heading in oat crosses. In an F3—F4 selection experiment, the mean actual and predicted gain in days was 2.8 and 1.5 respectively when conventional heritabilities were used. With the standard unit method, the predicted and actual gains were both 0.9 standard deviation units. In an F2‐F4 comparison, both methods showed satisfactory agreement between actual and predicted gains.
Cultivars for use in low‐productivity environments (LPE) can be selected directly, in LPE, or indirectly, in medium‐ or high‐productivity environments (MPE or HPE, respectively). These contrasting strategies were compared by means of predictions and an empirical selection experiment in which random populations of oat (Avena sativa L.) lines were selected for grain yield in LPE, MPE, or HPE; selected lines were then evaluated at each productivity level. The influence of replication (across environments) of the selection unit on the relative effectiveness of direct and indirect selection for yield in LPE was also examined. At low levels of replication, the greatest predicted and realized response in LPE resulted from selection in MPE. However, when replication was increased, direct selection resulted in the greatest predicted and realized yield gains in LPE. A positive correlation between degree of replication and the relative effectiveness of direct selection in LPE is expected when: (i) heritability (h2) is greater in HPE than in LPE and (ii) when the genetic correlation (rg) between yield in HPE and in LPE is less than one. These conditions were shown to exist in the present case, and may occur often in plant breeding programs. The results indicate that separate breeding programs may result in the greatest yield gains for some low‐productivity cropping systems. Estimates of h2 in HPE and LPE, and rg between yields in HPE and LPE, can be used to predict such situations.
Oat (Avena sativa L.) β‐glucan lowers serum cholesterol in humans. Development of oat cultivars with greater groat (caryopsis) β‐glucan content would increase the nutritional and economic value of the crop. The objectives of this experiment were to evaluate the response to phenotypic selection among individual S0 plants for greater groat β‐glucan content in two genetically broad‐based populations; to compare selected experimental lines to standard check cultivars; and to estimate genetic variances and heritabilities and to test for nonadditive genetic variance for β‐glucan content. We measured groat β‐glucan contents of check cultivars and parental lines and random S0:1 lines from initial and selected generations of each population grown in field experiments in 1996 and 1997 at two Iowa locations. Mean β‐glucan content increased from 53.9 to 59.9 g kg−1 in one population, and from 63.5 to 66.0 g kg−1 in the other, following selection. Genetic variance of β‐glucan content decreased by 9 to 22% following selection, but heritability for β‐glucan content did not change significantly. Heritability estimates ranged from 0.80 to 0.85 on a line mean basis. Additive variance was the only substantial component of genetic variance. Some experimental lines had significantly greater β‐glucan content than the best check cultivars and lines. Phenotypic selection for greater groat β‐glucan content will be effective for developing cultivars with elevated β‐glucan contents.
In breeding crop varieties for stress environments, it must be decided whether to select directly, in the presence of stress, or indirectly, in a nonstress environment . The relative effectiveness of these two strategies depends upon the genetic correlation (r G) between yield in stress and nonstress environments and upon heritability in each . These parameters were estimated for grain yield of 116 random oat lines grown in nonstress, P-deficient, N-deficient, and late-planted environments . Estimates of r G between yield in nonstress and yield in P-deficient, N-deficient, and late-planted environments were 0 .52 ± 0.24, 1 .08 ± 0.16, and 0 .06 ± 0.24, respectively . No consistent relationship between heritability and environment mean yield was observed . Direct selection in the presence of stress was predicted to be superior for yield in low-P and late-planted environments, but indirect selection in high-N environments was predicted to be as effective as direct selection in producing yield gain in low-N environments . These results confirm that neither high-yield environments nor environments in which the heritability of yield is maximized are necessarily optimum when the goal is to maximize yield gain in stress environments .
and range from 0.50 to 0.93 (Baker and McKenzie, 1972; Branson and Frey, 1989b;Brown et al., 1974; Increases in the groat (caryopsis)-oil content of oat (Avena sativa and Frey, 1991b). Genotype ϫ environment interaction L.) raise the energy value of oat grain. Nine cycles of recurrent phenotypic selection for high groat-oil content were conducted in a geneti-for groat-oil content is not a major component of its cally broad-based oat population that included germplasm from the phenotypic variance (Branson and Frey, 1989b; Gullord, wild relative A. sterilis L. Our objectives in this experiment were to 1986;Thro and Frey, 1985). Genotypic variation for determine if selection for high groat-oil content was effective and if groat-oil content has been observed among adapted culselection reduced genetic variation for oil content; to identify agrotivars (Brown and Craddock, 1972) and among wild nomically acceptable lines with high groat-oil content; and to docurelatives, including the progenitor species, A. sterilis ment the indirect effects of selection on grain yield, groat fraction, (Frey and Hammond, 1975;Martens et al., 1979). Aland oil yield. We evaluated 100 random lines from the base (C0) though the groat-oil content of wild Avena species does population and each of the nine selection cycle populations in three not exceed the levels found in domesticated oat (Rezai, (1985) reported that alleles for cycles of selection at a rate of 6.6 g kg Ϫ1 cycle Ϫ1 (equivalent to 6.7% of C0 population mean cycle Ϫ1 ) from a mean of 98.2 g kg Ϫ1 in C0 to higher oil content from A. sativa and A. sterilis are 158.5 g kg Ϫ1 in C9. The rate of gain from selection did not decrease complementary. Thus, by combining alleles for higher in later cycles. Oil yield increased at a rate equivalent to 1.9% of C0 oil content from the two species, development of oat population mean cycle Ϫ1 , while mean groat fraction did not change genotypes with higher groat-oil contents than any preand mean grain yield decreased at a rate equivalent to 3.2% of C0 viously reported in either species was facilitated (Thro population mean cycle Ϫ1 . For all traits, genetic variation did not deand Frey, 1985). environments. Mean groat-oil content increased linearly during nine 1977), Thro and Frey crease during selection cycles. Selected S 0 -derived lines from the popu-The abundance of genetic variation for oil content in lation with groat-oil contents Ͼ1 5 0gk g Ϫ1 exhibited lower yield, cultivated oat and interfertile wild hexaploid oat and greater lodging, and greater disease susceptibility compared with the the higher heritability of the trait permit relatively rapid best check cultivar.
β‐Glucan in oat (Avena sativa L.) grain is primarily responsible for the beneficial effect of oat fiber on lowering blood serum cholesterol levels in humans. Plant breeding programs designed to genetically alter the β‐glucan contents of oat germplasm would benefit from information on the inheritance of this trait. Two experiments were conducted to study the inheritance of β‐glucan. Generation means analysis of five populations derived from biparental crosses between high and low β‐glucan lines and cultivars was used to determine the genetic effects controlling β‐glucan content in these populations. Parent‐offspring regression was performed by using β‐glucan data collected from individual plants of 166 oat lines and cultivars and their selfed offspring, allowing estimation of broad‐sense heritability for β‐glucan content in a diverse sample of oat germplasm. Additive gene effects were more important, and dominant gene effects were detected in only two of five biparental populations. No evidence of epistatic gene effects was found. Broad‐sense heritability was estimated as 0.55 on an individual plant basis. This estimate is based on the covariance of inbred parents and their selfed progeny, which involves twice the additive gene action of the reference noninbred population, as well as nonadditive genetic effects. Selection based on replicated progeny families would involve a higher heritability. A positive correlation between grain yield and β‐glucan was observed in the generation means analysis. These results suggest that plant breeders should be successful in altering β‐glucan in oat through direct selection for this genetically variable trait.
We grew 27 oat cultivars at 3 levels of soil nitrogen, 4 levels of soil phosphorus, and 3 planting dates to examine the reactions of several agronomic characters to degrees of environmental stress. Each environmental factor was varied in a separate experiment. The experiments were grown in split‐plot designs in which wholeplots were levels of the environmental variables and subplots the cultivars planted in hills spaced 1 foot apart in perpendicular directions.The degree of stress imposed by a certain level of environmental factor was measured by the relative productivity of the attribute in question. For most attributes, stress was reduced with increasing increments of nitrogen and phosphorus and with earlier plantings. However, adding nitrogen increments increased the stress for 100‐seed weights, and early planting increased stress for number of spikelets per panicles and 100‐seed weights. Intraplant competitive, caused by the increased numbers of panicles produced per plot when nitrogen was applied or the oats were planted earlier, may have induced stress on spikelet and seed development.In general, genotypic variances among the oat cultivars increased as the environmental stresses were reduced. Environmental variance, however, also tended to increase so that heritabilities did not always increase with reduced environmental stress.
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