Exotic Parent Research Articles

Construction of an intraspecific integrated linkage map of pepper using molecular markers and doubled-haploid progenies

An integrated molecular linkage map of pepper (Capsicum annuum L.), including mainly RFLP and RAPD markers, has been constructed by alignment of three intraspecific linkage maps generated by segregating doubled-haploid progenies. A total of 85 markers covered approximately 820 cM in 14 linkage groups. Four linkage groups were assigned to 4 chromosomes. Two new genes of agronomic interest were located: L controlling hypersensitive resistance to TMV and up controlling the erect habit of the fruits. The C gene controlling the fruit pungency was more precisely located. This map is estimated to represent from 36 to 59% of the total pepper genome. An examination of segregation data has revealed several genomic regions with aberrant segregation ratios often favouring the agronomic big-fruited parents, particularly in crosses involving the exotic parent CM334, suggesting that these genome regions are subjected to selection during the process of doubled-haploid production. The suitability of doubled-haploid progenies for mapping projects and the differences observed between this intraspecific integrated map with earlier published interspecific pepper maps are discussed.

Comparison of trait associations in adapted � exotic matings of sorghum developed by two introgression methods

The association among six traits in the F2 lines derived from adapted × exotic backcrosses of sorghum developed via two introgression methods was studied using principal component analysis. The first principal component defined a hybrid index in matings of the wild accession ('12-26') but not in matings of the cultivated sorghum genotypes ('Segeolane' and 'SC408'), no matter which adapted parent was used. This component accounted for 27-42% of the total variation in each mating. The 'recombination spindle' was wide in all matings of CK60 and KP9B, which indicated that the relationships among traits were not strong enough to restrict recombination among the parental characters. The index scores of both CK60 and KP9B matings showed clear differentiation of the backcross generations only when the exotic parent was the undomesticated wild accession ('12-26'). None of the distributions of the first principal component scores in any backcross population was bimodal. The frequency of recombinant genotypes derived from a mating was determined by the level of domestication and adaptation of the exotic parent and the genetic background of the adapted parent. Backcrossing to a population (KP9B) was found to be superior to backcrossing to an inbred line (CK60) to produce lines with an improved adapted phenotype.

Genetic Analysis of Pericarp Thickness in Progenies of Eight Corn Hybrids

Pericarp thickness in maize (Zea mays L.) was analyzed by generation mean analysis for backcross and F2 populations from eight hybrids, derived from two thin-pericarped sweet corn inbreds—AA8 and 677a (55 and 51 μm)—crossed with four field corn inbreds—B37, B68, H55, and Hi26 (range 82-132 μm). Average heterosis was −12.5% and segregating progeny distributions were skewed toward those of thin-pericarped parents. Narrow-sense heritability was high, averaging 55.2%, and the number of effective factors was low, ranging from 1.4 to 5.9 and averaging 3.3. Epistatic effects were as large as additive or dominance effects in many crosses, urging caution in applying models that exclude gene interactions to determine variance components and heritabilities. The mode of action in reducing pericarp thickness appeared to differ among the two thin parents, with AA8 affecting the differential thickening of germinal vs. abgerminal walls, and 677a reducing the number of pericarp cell layers. All genetic parameters suggested that genetic progress in backcross conversions to thin pericarp in sweet corn breeding would be rapid irrespective of the pericarp thickness of exotic parents.

Manipulation of Larval Diapause of the European Corn Borer (Lepidoptera: Pyralidae) as a Potential Mechanism of Integrated Pest Management

Survival of reciprocal populations of European corn borer, Ostrinia nubilalis (Hübner), equaled or was intermediate to natural populations and an introduced low-diapause population (exotic), which survived less well. When peak natural second-generation hatch (31 July–3 August) north of 39°00′ N lat. was approximated, most of seven natural populations approached 100% diapause. However, only 0.25–22.95% of the exotic population diapaused. Diapause by progenies of reciprocal crosses was greatly influenced by this exotic parent. At the most northern locations, Ankeny, Iowa, and St. Paul, Minn., influence of the parental male was particularly evident. When peak natural third-generation hatch (13–16 August) south of 39°00′ N lat. was approximated, five reciprocal populations diapaused similarly to their corresponding natural populations (≈85%). Late-season hatch allowed larval diapause of the exotic population to increase to 46%. Under these late-season conditions, influence of the parental male was evident only at the most southern locations, Portageville, Mo., and Tifton, Ga. This apparent contradition of parental male influence between midsummer and late-summer hatch is because heterogeneity for diapause remains in a low-diapause population. Introductions of a low-diapausing population north of 39°00′ N lat. during late July apparently encourage resultant progeny from reciprocal crosses to avoid larval diapause and to perish in late autumn.

Trait Associations in Introgressed Populations of Pearl Millet

AbstractPrincipal component analysis has been used in this study to describe the associations among 17 traits measured on progenies developed from matings of two adapted pearl millet inbreds with three exotic pearl millets. The exotic parents were a primitive I and race, a weedy relative, and a wild relative. The first three components were calculated for these matings and the associations defined. Correlations between these components and grain yield and growth rate were also determined. The first principal component described a hybrid index in five of the six matings, and a number of other complexes of traits were determined by this component or the other two. Some were common to several matings. The first three components accounted for only 50–60% of the total variability; thus no strong association of trans was found that would hinder recombination of parental types to select agronomically desirable segregates with high grain yield or growth rate.

Exotic Germplasm for Improving Grain Yield and Growth Rate in Pearl Millet1

The potential of a germplasm source for improving certain productivity traits in a crop may be assessed by mating representative genotypes of the potential sources to the crop species or by measuring traits on the various genotypes per se. In this study, to evaluate the potential of three exotic strains of pearl millet [Pennisetum americanum (L.) Leekel to improve the grain yield and growth rate of cultivated pearl millet, a primitive landrace, a weedy relative, and a wild relative, were mated with two pearl millet inbred lines in a mating scheme designed to evaluate both the variability within the exotic strains and the progeny from their matings with the inbred lines. The experiment was evaluated in the rainy season of 1982 at Patancheru, India. The introgressed progeny were evaluated for grain yield and growth rate. The results of the study indicated that it was possible to select lines with transgressively increased grain yield and growth rate in all the matings. The exotic strain with the most potential to improve growth rate in pearl millet inbreds was the wild accession. The best exotic parents for improving grain yield (based upon a number of criteria) were the primitive landrace and the weedy relative.

F4 Bulk Testing in Testcrosses of 27 Exotic Peanut Cultivars1

Peanuts (Arachis hypogaea L.) are potentially a genetically vulnerable crop in the United States because of their narrow genetic base. To broaden the base, breeders must identify exotic parents for inclusion in programs of hybridization and selection. Parental, F1, and/or F2 performance could be used as indices to predict performance of inbred lines derived from crosses of adapted by exotic parents. Twenty‐seven exotics representing five South American centers of diversity, Africa, and China were testcrossed to an adapted Virginia (ssp. hypogaea var. hypogaea) breeding line. The parents had been previously sorted into five morphological groups,. Parents, F1'S, and F2's were tested in 1979. Twenty F2 families per cross were bulked in the F4 and tested in 1981. Variation among bulks for pod and seed yield and other characters was due predominantly to differences among morphological groups. Exotics of ssp. hypogaea produced higher yielding bulks than those of ssp. fastigiata. Spanish (var. vulgaris Harz.) parents produced the hightest yielding fostigiata‐derived bulks. Variation among bulks within morphological groups was significant for pod and seed size parameters and meat content, but not for yield. Performance of parents per se and F2's were the best indicators of F4 bulk performance, based on product moment and rank correlations. F1 performance, heterosis, inbreeding depression, and epistatic effects were largely unrelated to F4 performance. It was proposed that exotics' performance per se could be used as a criterion for selection of parents for yield, although inclusion of F2 yields in a multiple‐variable index was more accurate in predicting F4 bulk means. Selection should be practiced within morphological groups of parents in order to retain parents from ssp. fastigiata.

Heterosis in Testcrosses of 27 Exotic Peanut Cultivars1

A study was conducted to determine the extent of and genetic basis for heterosis in crosses between 27 exotic peanut (Arachis hypogaea L.) cultivars and an adapted virginia breeding line. Because their subspecific taxonomy was not always clear, principal components were used to cluster the exotic parents into five morphologically distinct groups roughly corresponding to the botanical divisions of the species. Heterosis (measured as the deviation of F1 performance from the midparent) was observed for pod yield, pod size parameters, seed yield and other traits. Heterosis up to 19% above the higher parent occurred for pod size and length. A significant portion (27 to 68%) of the variability in heterotic effects was attributable to difference among the parental groups with generally higher levels expressed in intersubspecificcrosses. Heterotic deviations were broken into two components reflecting the relative contributions of dominance and epistasis to nonadditive genetic variation. For pod and seed yield and pod length, dominance was the more important source while epistasis was more important for pod and seed number and meat content. The two sources made approximately equal contributions to heterosis for pod and seed size. The degree of genetic divergence between exotic parents and the adapted line was estimated by a Euclidean distance based on the vegetative and reproductive characters used in the principal component analysis. For characters exhibiting more dominance, the relationship of heterosis to divergence between parents was linear and increasing. The relationship was curvilinear for traits largely influenced by epistasis. An optimum level of divergence was detected for pod number only.

Selection for Grain Protein, Grain Yield, and Nitrogen Partitioning Efficiency in Hard Red Spring Wheat1

Progeny from three crosses of adapted hard red spring wheats (Triticum aestivum L. em Thell.) and a common exotic parent, ‘Rageni 15’, were grown in replicated field experiments for 3 years in Minnesota. Agronomic and physiologic traits were measured to evaluate Rageni 15 as a source of high grain protein and to appraise selection criteria for the combination of grain yield and grain protein percentage.The comparison of actual vs. predicted grain protein percentage, based on the linear regression of grain protein percentage on grain yield, indicated the Rageni 15 had low yield and grain protein percentage, and did not contribute higher grain protein to its progeny.Grain yield and grain protein percentage were negatively correlated (r = −0.48), and no single selection criterion proved of value in improving both traits simultaneously. Improvement of grain protein percentage with reduction of grain yield was obtained upon selection for high deviants from the linear regression of grain protein percentage on grain yield, protein content per kernel, and grain protein percentage. Selection for grain protein per se was most effective in improving this trait.Nitrogen harvest index and harvest index were correlated (r = −0.54) and both were positively correlated with grain yield. Grain protein percentage was negatively correlated with harvest index (r = −0.54), but it was not correlated with N harvest index (r 0.00). Therefore, N harvest index could prove useful as a selection criterion to improve grain yield while maintaining grain protein percentage

Genetic analysis of seed yield, oil content and their components in safflower (Carthamus tinctorius L.)

The genetic architecture of seed yield, oil content and their components was studied in a diallel cross of F1 and F2: eleven parents, representing an adequate diversity for all considered characters in safflower were used. Combining ability analysis revealed the predominance of gca variance for plant height, total capitula, seed weight, seed number and seed yield in F1 and F2 generations and for days to flowering and oil content in F1. The analysis of components of variance indicated that the non-additive factor was the major influence on total capitula and seed yield in F1s, and F2s, and on plant height, seed weight and seed number in the F2 alone. The heterogeneity of the dominance component over generations has been attributed to coupling phase linkage. All four Indian parents, namely S 144, A1, MS 49 and 6 spl, together with G 1157 and US 104 in the exotic group, were the best combiners for seed yield and/or for one of its components while the remainder of the exotic parents were characterized by high gca effects for oil content. VFstp 1 and Frio were the only parents approximating both properties of oil content and seed yield. Breeding methods, such as biparental mating followed by reciprocal recurrent selection, were suggested for the simultaneous improvement of seed yield and oil content.

Variations in enzyme phenotypes and their underlying genotypes among wild strains of the genus Neurospora.

SUMMARYTwenty-three exotic strains of four species ofNeurospora(N. crassa, N. sitophila, N. intermediaandN. tetrasperma) were grown in minimal medium and their enzyme phenotypes were compared. The exotic strains did not differ substantially with respect to the specific activities of the biosynthetic enzymes, ornithine transcarbamylase (OTC), carbamyl phosphokinase and aspartate transcarbamylase. Exotic strains ofN. crassaandN. sitophilawere crossed with laboratory mutants ofN. crassato determine whether there were significant differences among the exotic strains in the gene complexes underlying their enzyme phenotypes. Most of the exotic strains carried similar OTC structural genes and similar genetic modifiers of OTC activity: their OTC structural genes were expressed normally in the genomes of the parent strains, in the alien genomes of standard laboratory mutants and in the mixed genomes of parent × mutant hybrids. One exoticN. crassacarried a distinctive OTC structural gene that elevated OTC activity when transferred into the genome of a standard laboratory mutant. A second exoticN. crassacarried distinctive genetic modifiers of OTC activity: two mutations,c-andhi, interacted in the exotic parent to normalize OTC activity and rate of growth, buthiled to extremely high OTC activities and to a reduction in rate of growth when separated fromc-by interstrain recombination.