An examination of the pedigrees for 158 USA and Canadian soybean [Glycine max (L.) Merr.] cultivars of hybrid origin indicated that the North American soybean gene pool could be traced to only 50 plant introductions. Evaluations were made of the relative genetic contributions of those introductions to the cultivars released in the northern and southern gene pools of North America over four time periods, i.e.
Estimates of genetic similarity or distance between populations or strains of plants are useful in planning crosses for hybrid or pureline cultivar development. We compared coefficients of parentage (r) and similarity indices (s, sz, and sM, based on 20, 13, and 7 genetic loci, respectively) for combinations of 115 soybean [Glycine max (L.) Merr.] cultivars and ancestral introductions. Correlations between r and s were higher than those between r and sz or sM, primarily because s includes information from more loci. The correlation between r and s was higher for the group of soybean cultivars released in the 1970s than for earlier cultivar groups, primarily because of the greater importance of identity by descent relative to identity in phenotype in determining s. The most useful estimate of genetic relationship is a composite index that includes both r and s.
Pedigree and acreage data were utilized to determine trends in genetic diversity of soft red winter (SRW) and hard red winter (HRW) wheats. Four uniformity estimates were computed: (a) T1, the mean relationship among all cultivars grown in a given year; (b) 72, the mean relationship among primary cultivars; (c) 73, the mean relationship of primary cultivars weighted by acreage; and (d) T4, the mean relationship of primary cultivars grown in different years, weighted by acreage. In the SRW region, there has been a slow but steady increase in relationship among cultivars Qrj and T2).There was a dramatic increase in field uniformity (T3) during the 1970s, but T3 had sharply decreased by 1984 to its lowest point ever (0.22). All uniformity estimates decreased sharply for HRW wheats from 1919 to 1949 and have decreased gradually since. Uniformity is higher in HRW than in SRW wheats, primarily because of the persistence of a core of HRW germ plasm from cultivar 'Turkey,' but the difference is diminishing. Both classes appear to be entering a new era of increasing diversity.In 1972, the National Academy of Sciences reported that, for the major field crops of the United States, a small number of cultivars covered a large proportion of the acreage in production (1). Ten years later, there had been a noticeable increase in cultivar diversity in the cotton (Gossypium hirsutum L.) and soybean [Glycine max (L.) Merrill] crops, but the situation had not changed for wheat (Triticum aestivum L.) (2).In the wheat-growing regions of the United States, genetic uniformity exists at three levels. First, large tracts of land, especially in the Great Plains, are sown with a single species of wheat. Second, a small number of cultivars, representing a very small sample ofwheat germ plasm in general, accounts for a large proportion of the wheat acreage. Third, most cultivars used in production are related to other cultivars through common parents (3, 4). Extensive genetic uniformity can result in crop losses if there is uniform susceptibility to new pest or pathogen genotypes or to a severe stress. To avoid this problem and to sustain genetic gain, breeders periodically introduce new germ plasm into their populations.Increases in genetic variability have been tempered by the tendency to concentrate on selections from matings between highly adapted cultivars that carry the many specific gene complexes necessary in a successful cultivar. Furthermore, superior cultivars are often grown on large proportions of the wheat acreage. Successful breeding, therefore, can inadvertently reduce genetic diversity in the field.One approach to evaluating genetic diversity is through examination of the frequencies in commercial cultivars of known genes with individually identifiable effects, such as electrophoretic (5) or disease-resistance loci. Such data could be gleaned from cultivar-acreage surveys conducted over time. This uniformity, though critical, fails to consider the total genomic diversity between cultivars that might contain high leve...
Genetic relationships for all 903 pairwise combinations of 43 hard red winter wheat cultivars were evaluated using two indices: coefficient of parentage (r), computed from pedigree analysis, and a similarity coefficient (s), based on gliadin polyacrylamide gel electrophoresis (PAGE) patterns. Each index may vary from 0 for two unrelated cultivars to 1 for two identical cultivars. Mean r and s over all cultivars were 0.24 and 0.55, respectively. Cluster analyses based on the r and s matrices revealed dissimilar patterns of relationship in the hard red winter wheat gene pool. When cultivars were separated into two clusters based on the r matrix, mean r within and between clusters was 0.29 and 0.17, respectively. Separation of cultivars into two clusters based on s gave a mean s within and between clusters of 0.60 and 0.49, respectively. The rank correlation coefficient between r and s for all pairs of cultivars was 0.27 (significant at 0.01). Genetic drift and selection probably reduced the correlation between r and s. There was no relationship between ancestor‐cultivar r and s values because of the heterogeneous nature of the ancestors. Efficiency of breeding programs could be improved by computing r values and emphasizing crosses between diverse parents.
Cluster analysis was conducted using the coefficients of parentage (r) between all pairwise combinations of 110 recently released or historically important red winter wheat (Triticum aestivum L.) cultivars. The objectives were to determine the overall pattern of relationships and to search for genetic clusters within the soft red winter (SRW) and hard red winter (HRW) wheat gene pools. The two classes contained overlapping germplasm (r̄ between the two classes = 0.05). Thirty‐eight SRW cultivars formed six clusters based on predominant parents (‘Arthur’, ‘Benhur’, ‘Coker 68‐15’, ‘Lucas’, ‘Knox’, and ‘Blueboy’), whereas 49 HRW cultivars formed seven clusters (based on ‘Triumph’, ‘Sturdy’, ‘Scout’, ‘Blackhull’‐ ‘Tenmarq’, ‘Turkey’, ‘Parker’‐‘Centurk’, and ‘Warrior’). Principal coordinate analysis separated these 13 clusters primarily by class (HRW vs. SRW), but also by geographical origin of predominant parents within classes. These results may have application in parental selection for conventional cultivar, hybrid cultivar, and population development in winter wheat.
The genetic relationships among, and grain yields of spring oat (Avena sativa L.) cultivars released in the north central and northeastern USA between 1941 and 1980 were investigated using coefficients of parentage (r) and least squares means (LSM). These parameters were evaluated in two data sets, Early and Midseason, which were based on uniform regional nursery trials conducted between 1944 and 1980. The mean coefficient of parentage (r̄) among oat cultivars released within the same 5‐year period has oscillated between approximately 0.1 and 0.3 since the mid‐1940's in each data set with no apparent long‐term positive or negative trend. The level of r̄ during 1976–1980 was 0.22 and 0.13 in the Early and Midseason data sets, respectively. The LSM's were used to estimate genotypic value for grain yield of each cultivar tested for 3 or more years. The LSM's of cultivars released within the same 5‐year period were averaged (x̄LSM) and compared with the LSM of ‘Gopher’ (LSMG), a selection from the 19th century cultivar ‘Kherson’. Increases in x̄LSM were relatively modest from 1941 to 1975. In the 1971–1975 period, the x̄LSM's were 116 and 111% of LSMG for the Early and Midseason data sets, respectively. However, in the 1976–1980 period, a substantial increase in x̄LSM to 134% of LSMG was observed in the Early data set indicating a genetic gain during this 5‐year period which equaled that of the entire 35‐year period prior to 1976. A breakthrough in yield was also suggested in the Midseason data set because two recently released cultivars, ‘Ogle’ and ‘Porter’, had LSM's ≥130% of LSMG. The recent large increases in oat grain yield were obtained over a broad base of germplasm. Coefficients of parentage among the five cultivars having LSM's ≥130% of LSMG indicated that a minimum of three distinct sources of germplasm with high yield potential was involved.
Lodging of grain sorghum [Sorghum bicolor] a serious problem under certain environmental conditions such as water stress or heat stress. Lodging at the base of the stalk or the base of the panicle has been attributed to a complex of stalk rotting organisms, which includes Macrophomina phaseolina (Tassi) Goid and Fusarium moniliforme Sheldon. The field study reported here evaluated the use of a toothpick inoculation technique to artificially infect plants with these two organisms and determined inheritance of resistance. The experimental material consisted of the 45 F1's from a 10‐parent diallel with no reciprocals, the 10 parents, and five hybrid checks grown in 2 yr under two water regimes. The inoculated and noninoculated plants in a plot were rated for stalk disintegration on a scale of 1 (resistant) to 6 (susceptible). Hybrids differed nificantly and consistently across environments for the two inoculation treatments but not for the noninoculated. General combining ability was significant in both dryland environments for both inoculation treatments; specific combining ability was significant for F. moniliforme in both years but only in 1984 for M. phaseolina. The expression of resistance seems to depend upon the environment, especially for F. moniliforme.
This was produced from a copy of a document sent to us for microfilming. While the most advanced technological means to photograph and reproduce this document have been used, the quality is heavily dependent upon the quality of the material submitted. The following explanation of techniques is provided to help you understand markings or notations which may appear on this reproduction. 1.The sign or "target" for pages apparently lacking from the document photographed is "Missing Page(s)". If it was possible to obtain the missing page(s) or section, they are spliced into the film along with adjacent pages. This may have necessitated cutting through an image and duplicating adjacent pages to assure you of complete continuity. 42 Means of the H. vulgare parents, H. vulgare histori cal checks, and the H. spontaneum parents for grain yield, biomass, straw yield, height, heading date, harvest index and growth rate index 46
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