Inheritance of groat-oil content and high-oil selection in oats (Avena sativa L.)
Post on 06-Jul-2016
Euphytica 34 ( 1985) 25 I~-263
INHERITANCE OF GROAT-OIL CONTENT AND HIGH-OIL SELECTION IN OATS
(A VENA SATIVA L.)
A. M. TH RO and K. J. FREY
Department of Agronomy, Iowa State University, Ames. Iowa 50011. USA
Rrwived 1 MLIJ, 1984
Avena sativa, oats. groat-oil content, high-oil selection. lipids, gene action, transgressive segregation. recur- rent selection. SUMMARY
The potential for breeding for high groat-oil content in oats was investigated by (a) conducting generation means analyses on data from three matings among adapted Avenu sutiva L. cultivars, (b) practicing one cycle of phenotypic recurrent selection in a segregating population derived from eight species backcrosses (Avencr sativn x (A. sativa x A. sterilis)) among 24 parents. and (c) identifying transgressive segregates from interspecific (A. satiny x A. sterilis) matings,
Additive gene action was the most important component in explaining the variation among generation means for groat-oil content. Dominance and epistatic interactions involving dominance were not significant in any mating. Significant residual genetic variation occurred in one mating, even after additive, dominance. and three digenic interactions were fitted. The importance of additive genes action implies that desired allelic combinations for high groat-oil content can be obtained in pure-line cultivars.
One cycle of phenotypic recurrent selection using single plants as the selection units resulted in a genetic gain of 1.7 to 2.1% in groat-oil content. Individual plants selected for initiating the second cycle had from 9.5 to 12.6% groat oil.
Over all 12 interspecific matings, the Fz progeny means were similar to the midparent values. Only two were significantly deviant. Transgressive segregates for high and low groat-oil content from these matings provided evidence that A. sterilis possesses alleles for high and low groat-oil content that are different from those in the gene pool of cultivated oats.
The energy content of oat grain is lower than that of other cereals (HUTCHINSON & MARTIN, 1955; BROWN & CRADDOCK, 1972). An increase in groat (caryopsis)-oil con- tent, however, could improve the energy content of oats because lipid digestion gives 2.25 times greater energy equivalent than does protein or carbohydrate (PRICE & PAR- SONS, 1974). STOTHERS (1977) found that high-oil (9%) oats approached barley in feeding value for hogs. One way to increase the energy value of oats, therefore, is
Journal Paper Nb. J-l 1340 of the Iowa Agric. and Home ECon. Exp. Sm., Ames, Iowa 5001 I. Project 2447. This study was supported in parts by grants from the Iowa Committee for Agricultural Development and the International Harvester Company. Present address: Agron. Dep.. Louisiana State University. Baton Rouge. LA 70803, USA.
A.M. THRO AND K. J. FREY
to develop oat cultivars with high groat-oil content(BRowN et al., 1966; FORSBERG ET AL., 1974; FREY & HAMMOND, 1975). FREY & HAMMOND (1975) calculated that if oats had 17% groat oil combined with present levels of grain yield and protein content they might compete as an oilseed crop for producing high quality culinary oil (KALBA- SI-ASHTARI & HAMMOND, 1977). HAMMOND (1983) calculated that extraction of oil from oats with 10% groat oil would add 2 4 net per kilogram.
A wide range in groat-oil content is typical of hexaploid oats. BROWN et al. (1966) observed a range of 3.9 to 9.0% oil in 169 USA cultivars grown in Illinois, and SAHAS- RABIJDHE (1979) found 4.2 to 11.3% oil in USA and Canadian cultivars grown in Ontar- io. Most strains in recent USA Uniform Early and Midseason Oat Performance Nur- series have from 5 to 8% groat oil]. Groat-oil contents among A. sterilis L. collections vary from 2.0 to 11.6% (BROWN & CRADDOCK, 1972; FREY ; HAMMOND, 1975; REZAI, 1977). These values seem relatively low when compared with oilseed crops, but oats have the highest seed-oil content of any cereal (WEBER, 1973; PRICE & PARSONS, 1975).
The genotype is the major source of variation for groat-oil content in oats, and genotypic and environmental effects on this trait are additive (HUTCHINSON & MARTIN, 1955; STUKE, 1960; BAKER & MCKENZIE, 1972). BAKER & MCKENZIE (1972) reported that progeny mean heritability ranged from 68 to 93%. Single plant heritabilities were reported by STUKE (1960) to be from 83 to 98%, and BROWN et al. (1974) obtained values of 59 to 79%. BAKER & MCKENZIE (1972) and BROWN et al. (1974) found additive gene action for groat-oil content and that general combining ability (gca) effects were larger than those for specific combining ability and gca effects were correlated with parent groat-oil content.
Groat-oil content is determined largely by the genotype of the maternal plant, and this control is due to nuclear and not plasmagenes (BROWN & ARYEETEY, 1973; BROWN et al. 1974). Thus the oil content of the groats from a plant estimates the capacity of the maternal genotype for oil production.
This paper reports on (a) the gene action involved in the inheritance of groat oil of oats, (b) the effectiveness of phenotypic recurrent selection for high groat-oil content in segregating populations, and (c) transgressive segregates from interspecific oat mat- ings. This information is pertinent to choosing an optimum breeding procedure for increasing oat oil yield.
MATERIALS AND METHODS
Generation means analysis. Three intraspecific matings of A. sativa were used to study gene action for total groat-oil content (Table 1). L x H and H x L matings were genetically equivalent because groat oil content does not exhibit cytoplasmic inheri- tance. Nine generations were produced for each mating: P,, P,, F,, F,, F,, BC,F,, BC2FI, BC,F,, and BC2F2 (BC, and BC2 refer to backcrosses made to P, and P2, respec- tively). The designated generation refers to the plants on which the groats used for analysis were produced. These materials were grown in the field in 1980 in a rando- mized complete block experiment with 25 entries (the seven progeny generations in
H. W. RINES & R. P. HALSTEAD. Unpublished data.
252 Euphyiica 34 (I 985)
Table I. Designations of levels (i.e., H = high and 1. = low) of groat-oil content in parents of three oat matings.
Mating Groat-oil level designation
M I: Garland x Pettis LxH M2: Jaycee x Richland HxL M3: Garland x Richland LXL
each mating, plus the four cultivars used as parents) and eight replicates. Four repli- cates were sown at the Agronomy Field Research Center, Ames, and four at the North- ern Iowa Experimental Farm, Kanawha, Iowa. A plot was a hill sown with 15 seeds. and hills were spaced 30 cm apart in perpendicular directions. Experimental areas were fertilized with 28-45-45 kg/ha of N, PzO,, and KzO, respectively, and hoed as necessary to keep the experiments weed-free. Plants were sprayed with a fungicide (Dithane) at weekly intervals from anthesis to maturity to prevent foliar diseases. When the plants were mature, they were harvested, dried, and threshed.
Chemical analysis were performed on a sample of oat seeds, dehulled to provide a 3.5 to 5 g lot of groats, from each plot. The nuclear magnetic resonance method (NMR) described by CONWAY & EARLE (1963) was used to analyze for oil content of the groats. For statistical analyses, for each mating a data set was constructed that contained values for seven progeny generations and the parents, and each mating was analyzed separately.
The generation-means analysis (HAYMAN, 1958) was used to estimate the contribu- tions of several genetic effects to the variation among generation means. GAMBLES notation (1962) for the genetic parameters was used, i.e. m equals the mean of the Fz, a and d are pooled additive and pooled dominance effects, respectively, over all loci, and aa, ad, and dd represent the pooled additive x additive, additive x dom- inance, and dominance x dominance digenic interaction effects, respectively. The in- verse of the variance of a generation mean was used as the weighting factor for that generation, and a weighted analysis of variance was performed on the data to obtain a weighted sum of squares for generations. Next, genetic parameters, beginning with m, were fitted sequentially. A model was judged adequate to describe the variation among generation means when the mean square for lack of fit was no longer significant when tested against the mean square for generations x environment interaction from the overall analysis of variance. Genetic effects were estimated for each trait in each mating via weighted least squares analysis, and standard errors of the estimates were calculated by using the method of DARnAH (1970).
Selection for high groat-oil content. Selection was initiated among and within the pro- genies of eight three-way matings (species backcrosses). Initially, eight interspecific single-cross matings were made by crossing each one of eight A. sterilis accessions with a different one of eight A. sativa cultivars (Table 2). All 16 parents used in the interspecific matings had high groat-oil content. Parents of both species were chosen from geographically separate regions so as to include as much genetic diversity as possible. A. sativa parents mated with the interspecific single-cross matings to produce
A.M. THRO AND K. J. FREY
Table 2. Geographic origin and groat-oil content for parents of eight three-way matings (Avena sativq~ x (A. sativq x A. sterilis)) of oats.
Parent Geographic origin
Avena sativa I. High-oil group CI 6857 Florida, USA Lodi Wisconsin, USA MO-0-5499 Missouri, USA wright Wisconsin, USA MO-0-205 Missouri, USA Orbit New York, USA CI 3445 India Dal Wisconsin, USA
A. sterilis PI 28273 1 Israel PI 296247 Israel PI 309193 Israel PI 309430 Israel PI 324806 Algeria PI411540 Algeria PI411971 Iraq PI 412443 Sicily
A. sativa II. Agronomic group Noble Indiana, USA Otee Wisconsin, USA Spear South Dakota, USA Lang Illinois, USA stout Indiana, USA CI 9273 Iowa, USA Pettis Missouri, USA PI 469112 Iowa, USA
Groat oil content (%I
10.7 8.2 9.2 8.6 8.9 7.2
10.0 9.1 9.3
10.2 9.4 9.7
6.8 7.3 8.8 7.0 5.9 9.3 9.0 9.3
three-way matings were eight cultivars and breeding lines (Table 2) chosen for excel- lence of grain yield, groat-oil content, test weight, and lodging resistance.
F, seeds within three-way matings were heterogeneous, so to adequately sample the variation within a three-way mating, 20-25 F, seeds of each three-way mating were sown in the greenhouse, and ca. 100 selfed seeds were harvested from each of 10 plants per mating. The 8000 F, seeds from the three-way matings (100 seeds from each of 10 F, plants from each of the eight three-way crosses) were space-sown in the field in April, 1979, at the Agronomy Field Research Center near Ames, Iowa, on a Webster loam soil (line loamy, mixed, mesic Typic Haplaquodoll). Spacing was 15 cm within rows and 0.9 m between rows. Cultural practices were the same as those described for the generation-means experiment.
When plants were mature, the surviving 4447 plants were harvested and threshed individually. Threshed seed lots from individual plants were examined for agronomic
254 Euphytica 34 (1985)
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Table 3. Parents, their geographic origin, and means of groat-oil content for parents and Fz progenies from Avenn sativa x A. sterilis matings.
Female parent (A. sativa)
Groat-oil Male parent (A. strrilis) x content (7;)
PI PI PI PI 411540 412443 411971 324819 (Algeria) (Turkey) (Iraq) (Algeria) 9.3 8.5 8.5 9.3 x.9
Dal (Wisconsin, USA) 7.7 8.8 8.5 7.6 8.7 8.4 Orbit (New York, USA) 6.1 7.9 7.4 7.9 8.3 7.9 CI 3445 (India) 9.7 9.6 8.5 9.1 10.0 9.3
X 8.0 8.8 8.1 8.2 9.0 8.5
quality, and 667 lots that had white or yellow hulls and were awnless were used for oil analyses. A 3.5 to 5.0 g sample of groats from each of the 667 F2 plants was analysed for oil content by using the NMR method (CONWAY & EARLE, 1963). Next, 72 F, lines derived from 72 F, plants that bore seed with groat-oil content of 7.5:: or greater were selected as parents for the first cycle of recurrent selection.
Remnant seeds from the 72 F, plants were sown in the greenhouse, and 36 biparental matings were made with each mating involving parent lines derived from different three-way matings. F,s from the 36 matings were sown in the greenhouse, and when mature approximately 100 F, seeds were harvested from one or more F, plants from each mating. About 2500 F, seeds were space-sown in the field in 1981 at the Agron- omy Field Research Center, Ames, utilizing cultural conditions similar to those de- scribed before. Drought was severe at Ames in 1981, and only 286 plants produced sufficient seed for groat oil analysis. Ninety lines derived from F, plants with groat-oil content of 9.5% or greater in their seeds were selected to continue this project. This 90-line sample included at least one line from each of 25 of the 36 biparental matings.
Factorial interspecific matings. A factorial set of 12 interspecific matings was made among four A. sterilis accessions and three A. sativa cultivars (Table 3). All parents were chosen for high groat-oil content. As far as possible, parents were chosen from geographically separated regions. Seeds from the exact plants used as parents and F1 seeds of the matings were space sown in a split-plot randomized block design with two replicates at the Agronomy Field Research Center, Ames, Iowa. Whole plots were matings and subplots were generations within a mating (P, or A. sativa parent, PJ or A. sterilis parent, and F,). Rows within plots were 3 m long with 0.9 m between rows, and 20 seeds were sown per row at 15-cm intervals. In each whole plot, parents were represented by one row (20 seeds) each and the F, progeny by five rows (100 seeds). Soil type and cultural practices for this experiment were as described earlier.
Panicles of A. sterilis parents and of Fz segregates that shattered were covered when panicles were completely emerged with bags made of Delnet PQ 218 high density polyethylene nonwoven fabric (Hercules, Inc., Wilmington, DE 19899). Light intensity under the bags was reduced by 9.5%. At maturity, 10 random plants were harvested from each row. Plants were threshed separately, and a 3.5 to 5 g groat sample from
Euphyrica 34 (1985) 255
A. M. THRO AND K. J. FREY
each plant was analyzed for oil content by the NMR method (CONWAY & EARLE, 1963).
Oil percentages from individual plants in a plot were averaged to give a plot mean, and plot means were used to compute analyses of variance according to the model for a split-plot design. Next, F, progeny data were analyzed as a cross-classification design to permit the computation of components of variance for effects of males, ef- fects of females, and interaction of males and females. Components for males and female equate to variance due to general combining ability ($&, and the interaction component equates to specific combining ability (oz8J (COMSTOCK & ROBINSON, 1948).
A transgressive segregate from these matings was defined as an F2 plant with groat- oil content greater than the high parent mean of less than the low parent mean by 2.086~~ or 2.086s,,, respectively, where sHP and s,, are standard deviations of the high and low parent, respectively, and 2.086 is the tabular value of t at c1 = 0.05, n = 20. Standard deviations and numbers of transgressive segregates were calculated separately for each mating.
Generation means analyses. Variation among generation means within M 1, M2, and M3 was highly significant and generation x location interaction was nonsignificant in all matings (Table 4). Additive gene action accounted for nearly all genetic variation among generations in Ml and M2 as shown in Fig. 1. Residual genetic variation in M2 was still significant after all six parameters were fitted in the model (Table 5).
Figure 2 summarizes the analysis of variance (HAYMAN, 1958) and describes the partition of total genetic variance among generations into various sources. Variation among generations was quantified by expressing the sums of squares for each succes- sive model as a percent of the total sums of squares for generations. Additive genetic
Table 4. Mean ssuares from the analyses of variance for groat-oil content of three oat matings grown at two locations.
Source of variation Degrees of freedom
Generation 8 1 (g-1) 2
Generation x location 8 (g-l)(c-1) : 3 Pooled
Replicates (location) x generation 48 1 I(r-l)(g-1) 2
0.070** 0.030** 0.003** 0.030 0.003 0.001 0.001 0.003 0.002 0.001 0.001 0.002
**Significant at the 0.01 level of probability.
256 Euphytica 34 (1985)
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0 25 50 75 100 0 25 50 75 100 0 25 50 75 loo % of germplasm from Pl % of germplasm from Pl % of germplasm from Pl
Fig. 1. Relationship between means for total groat-oil content (as I,,) and percentage of germplasm from PI (high parent) in the nine generations in each of three matings. If all gene action in a mating is additke. this relationship is expected to be a straight line. (P, = loo/,; BC,F, and BC,F, = 750,,; F,, Fz, and F3 = 50%; BC,F, and BCzFz = 2570; and P2 = 0;. The standard error of a generation mean is 0.02 in matings I and 3 and 0.01 in mating 2).
effects accounted for 95% of the variation among generation means in Ml, 80% in M2, but only 50% in M3. Even though ca. 50% of the variation among generation means in M3 was due to dominance effects, no mating showed a reduction in residual sums of squares from significance to nonsigniticance when dominance or dominance x dominance epistatis was added to the model (Table 5). Additive effects were signiti- cant in Ml with the six-parameter analysis. Dominance effects were not significant in any mating. All estimates of additive, dominance, and epistatic genetic effects were small relative to the effects of m. Next, a three parameter model containing additive and additive x additive parameters was fitted to the means for the three matings (Table 6). Additive effects were significant in all three matings with the three parameter analyses.
Because digenic interaction effects were not significant for any mating, estimates for m, a, and d in this study may be considered unbiased (HAYMAN, 1958). HAYMANS model for generation means analysis involves a number of assumptions about the genetic system under study. First, the phenotypic value must be a linear function of genotypic and environmental effects, an assumption that was satisfied by our matings (Table 4). This analysis further assumes absence of trigenic or higher order interac- tions. Significant residual variation for groat-oil content in M2 suggests that higher- order interactions and/or linkage may have been present in this mating. Effects of
Table 5. Tests of significance for six genetic components of generation means for groat-oil content in three oat matings and tests of significance of residual sums of squares for the simplest adequate model (compo- nents not required in the simplest adequate model are in parenthesis).
Mating Genetic component Rest
m a d aa ad dd
I ** ** (ns) (ns) W (ns) ns 2 ** ns 3 ** ns FZS)
ns ;lf S)
(ns) W ns
t A significant F value indicates that the complete model was not suflicient to account for the observed variation among generations. **Significant at the 0.01 level of probability.
Euphytica34 (1985) 257
A.M. THRO AND K. 1. FREY
.s c 60 t
6 d 60 s 2 z 40 i = 5 20
Fig. 2. Percentages of the total variation among generation means for groat-oil content attributable to additive (a), dominance (d), additive x additive (aa), additive x dominance (ad), and dominance x dom- inance (dd) effects in three oat matings.
higher-order interactions and linkage cannot be separated in the generation means analysis. Linkage biases estimates of all genetic effects except the pooled additive ef- fects.
Recurrent selection for high groat oil. Mean groat-oil content for the 667 F, plants from the eight threeway cross matings was 6%, and the 72 progenies chosen for high groat oil content had a mean of 8.1% and a range of 7.5 to 9.9%. The mean groat-oil content of the 286 F, plants from intermatings of the 72 selected F,-derived lines was 9.0x, and the 90 plants chosen from this population had a mean of 10.7% and a range from 9.5 to 12.6%. The 12.6% groat-oil content in one progeney was higher than that of any parent from either species used to initiate this breeding population.
It is not possible to evaluate how successful recurrent selection would be for increas- ing groat-oil content from our experiments because the plant materials from various cycles were not grown in a common environment. Some indirect comparisons can be made, however, to provide estimates of our success.
In studies conducted in the USA and Europe, the additive effect of environment on groat-oil content has ranged from 0.7 to 1.9% with a mean of 1.3% when a common set of cultivars was tested (HUTCHINSON & MARTIN, 1955; STUKE, 1961; THRO ; FREY, 1984; also RINES & HALSTEAD, unpublished data). The mean groat-oil content of all
Table 6. Tests of significance for three genetic components of generation means for groat-oil content in three oat matings and tests of significance of residual sums of squares for the simplest adequate model (components not required in the simplest adequate model are given in parenthesis).
Mating Genetic component Rest
m a aa
1 ** ** W ns 2 ** ** ns ** 3 ;* ** (ns) ns
t A significant F value indicates that the complete model was not sufficient to account for the observed variation among generations. **Significant at the 0.01 level of probability.
258 Euphytica 34 (1985)
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Table 7. Analysis of variance for groat-oil content of parents and F2 progeny from AvP~~ .surivtr x 9. sterilis matings.
Source of variation Degrees of freedom
Replicates Matings Error a Generations
A. sativa females vs. A. sterilis males Midparent vs. F,
Matings x generations Error b
I 23 1.20*** 11 66.32*** II 6.39
2 42.40** I 39.93* I 2.47
22 10.53*** 24 1.20
*. **. ***Significant at the 0.10,0.05 and 0.01 probability levels. respectively
Table 8. Midparent and F, progeny mean values for groat-oil content in A vena satiw x A. ytcrilis matings.
Groat-oil content (~J
Dal x PI 411540 8.9 8.8 Dal x PI 412443 8.4 8.5 Dal x PI411971 7.7 7.6 Dal x PI324819 7.8 x.7**
Orbit x PI 411540 7.8 7.9 Orbit x PI412443 7.2 7.4 Orbit x PI 411971 8.1 7.9 Orbit x PI 324819 8.2 8.3
CI 3445 x PI 411540 CI 3445 x PI 412443 C13445 x PI411971 CI 3445 x PI 324810
9.6 9.6 9.0 8.5* 9.5 9. I 9.6 10.0
Mean x.5 x.5
*, ** Significantly different from the mid-parent value at the 0.05 and 0.01 levels of probability. respectively.
progenies from the three-way matings was 6/& a value 2.8% lower than the mean of all 24 parents (Table 2). This difference may include a genetic component due to linkage between alleles for low oil content and A. sativa seed type. Selection was prac- ticed for A. sativa seed type before oil determinations were made. The low progeny mean for groat-oil content also may result from nonallelic interaction.
The means of the Co (grown in 1979) and C, (grown in 198 1) populations for groat- oil content were 6.0% and 9.0%, respectively. Assuming that the seasons in which these populations were grown were random, the expected differential due to environ- mental effect would be about 1.3%, in which case, 1.7% of the 3.0% difference between population means could be assigned to genetic improvement from one cycle of recur- rent selection. In a somewhat more direct comparison, the 72 F,-derived lines selected as parents to initiate the C, population when grown in both 1979 (as F, spaced plants)
Euphytica 34 (I%S) 259
A. M. THRO AND K. J. FREY
and 1981 )as F, spaced plants) had means of 8.1% and 9.0x, respectively. This suggest that the environment caused oil content to be 0.9% higher in 1981 than in 1979. By using this estimate of environmental effect, the gain in groat-oil content from one cycle of recurrent selection would be 2.1%. Thus, recurrent selection seems to be a successful procedure for increasing the content of oil in oat groats.
Factorial interspecific matings. In the 12 factorial matings, both matings and genera- tions were significant sources of variation for groat-oil content (Table 7). Mean groat- oil content for A. sativa parents (8.0%) was significantly lower than the mean for A. sterilis parents (8.9%) and over all matings the midparent and F, progeny mean did not differ significantly. Only in Dal x PI 324819 and CI 3445 x PI 412443 did the midparent value and F2 mean differ significantly (Table 8). Analysis of the variation among F, means alone showed that A. sativa parents differed in general combining ability, whereas A. sterilis parents did not (Table 9). Specific combining ability variance was nonsignificant.
Transgressive segregates occurred in all 12 oat interspecific matings (Table 10); few matings, however, produced equal numbers of high and low transgressive segregates. Five gave predominantly or exclusively low transgressive segregates whereas four gave predominantly or exclusively high ones. Matings involving CI 3445 (A. sativa), PI 324819 and PI 411540 (A. sterilis), the parent lines with highest oil content, had the greatest number of high-oil transgressive segregates, and matings involving Orbit (A. sativa), PI 412443 and PI 411971 (A. sterilis), the parents with lowest oil, had few or no high-oil transgressive segregates. About one-half of the transgressive segregates were low.
The fact that every interspecific mating produced transgressive segregates for groat- oil content provides evidence than A. sativa and A. sterilis contain hifferent alleles for groat-oil content; thus, A. sterihs contains genes that can be used to increase groat- oil content of cultivated oats.
Pooled additive effects in the generation means analysis were the most important gen-
Table 9. Analysis of variance, expected mean squares, and components of variance of F, progeny groat-oil content in A vena sativa x A. sterilis matings.
Source of variation
Females (Avena sativa) Males (A. sterilis) Females x males
Replicates x matings
(32, = 0.14
Degrees of freedom
Expected mean squares
1 5.41** 11 1.3s**
2 4.69** o2 + 202mf + 8&f 3 1.25 cr2 + 202mf + 602f 6 0.39 02~ + 2cGmf
11 0.27 0
Of = 0.54** 02,f = 0.06
**Significant at the 0.01 level ofprobability.
260 Euphytica 34 (1985)
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Table 10. Numbers of transgressive segregates for low and high groat-oil content in Avenn .sativa x A. sterilis matings.
Dal x P1411540 Dal x PI412443 Dal x PI411971 Dal x PI 324819
Orbit x PI411540 Orbit x PI412443 Orbit x PI 411971 Orbit x PI 324819
Cl 3445 x PI 411540 Cl 3445 x PI 412443 Cl3445 x P1411971 Cl 3445 x PI 324819
3 8 I ? 1 7 3 4
0 3 0 4 0 4 I 2
4 3 0 8 2 2 I I
etic component of variation for groat-oil content, accounting for 50 to 95% of the genetic variation for this trait. Further, in interspecific matings, F, progeny means were similar to midparent values, showing that gene action for groat-oil content was additive and that the transgressive segregates from these matings resulted from the cumulative effects of new combinations of alleles. In addition, specific combining abili- ty was not a significant source of variation for groat-oil content. Because additive gene action controls groat-oil content, desired allelic combinations for this trait can be fixed in pure-line genotypes.
Because groat oil content is an unselected trait that exhibits much genetic diversity, probably alleles for high groat-oil content are randomly distributed among oat geno- types, with the results that no existing genotype is likely to contain all alleles for high groat oil. It should, therefore, be possible to obtain higher groat-oil content than pre- sently exists in cultivated oats without using alleles from A. sterilis. BAKER & MCKEN- ZIE (1972) also reached this conclusion. And higher levels of groat-oil content should be possible if high-oil alleles from A. sterifis are used in a breeding program.
Positive and independent relationships of groat-oil content with grain yield and maturity (THRO & FREY, 1984), respectively, suggest that agronomically desirable, high-yielding cultivars of oats with high groat-oil content can be developed. Further, our results indicate that any alleles for low grain yield and late maturity introduced from A. sterilis can be eliminated from the resultant populations without losing alleles for high groat-oil content.
Because groat-oil content is inherited polygenically, recurrent selection would be the plant breeding procedure of choice to improve this trait in agronomically desirable genotypes (HALLAUER, 1981). Single plants could be used as the units of selection be- cause heritability of groat-oil content based on single plants ranges from 59 to 98yo (BROWN et al., 1974; STUKE, 1960), and genotype x environment interaction for this trait is nearly nonexistent. This method of phenotypic recurrent selection was used successfully to increase oil content in maize grain (Zea map L.), a species in which
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seed-oil content is inherited polygenically with largely additive genetic control (SPRAGUE et al., 1952). In fact, selection could be based on the analysis of selfed seed form F, oat plats in the recurrent selection program to provide more rapid cycling of the breeding population. The F, genotypes being evaluated would be heterozygous, but with additive gene action, heterozygosity is no deterent to correct evaluation of alleles in whatever state they occur. Negative additive x additive interaction effects, of course, when fixed in progeny from selected hybrid plants could result in a mean lower than expected. Gain per cycle certainly would be higher by using F2 plants as the units of selection for groat-oil content, but gain per unit time might be higher by using plants from the intercross F,s.
The financial assistance of an International Harvester Corporation Dissertation Fel- lowship (A.M.T.) is gratefully recognized. Parts of the data analyses were carried out while one of us (A.M.T.) was a guest of the Institut fiir Pflanzenziichtung, Universitat Hohenhem, West Germany, by courtesy of Drs H. H. Geiger and F. W. Schnell, and with support of a short-term stipend from the German Academic Exchange Service (DAAD). Sincere thanks are extended to Drs Geiger and Schnell and the DAAD.
Appreciation is expressed to Dr D. E. Alexander and MS Evelyn Marriott, Agron. Dept, Univ. Illinois, Urbana, IL, who conducted the NMR oil analyses and also to F. Rattunde, who made the 1981 selections and assumed responsibility for the continu- ation of the recurrent selection project.
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