Iowa State University Capstones, Theses and Retrospective Theses and Dissertations Dissertations 1983 Introgression of wild germplasm into cultivated sorghum Thomas Stanton Cox Iowa State University Follow this and additional works at: https://lib.dr.iastate.edu/rtd Part of the Agricultural Science Commons, Agriculture Commons, and the Agronomy and Crop Sciences Commons Recommended Citation Cox, Thomas Stanton, "Introgression of wild germplasm into cultivated sorghum " (1983). Retrospective Theses and Dissertations. 7705. https://lib.dr.iastate.edu/rtd/7705 This Dissertation is brought to you for free and open access by the Iowa State University Capstones, Theses and Dissertations at Iowa State University Digital Repository. It has been accepted for inclusion in Retrospective Theses and Dissertations by an authorized administrator of Iowa State University Digital Repository. For more information, please contact [email protected]. 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Universi^ Micionlms International 300 N.Zeeb Road Ann Arbor, Ml 48106 8323274 Cox, Thomas Stanton INTROGRESSION OF WILD GERMPLASM INTO CULTIVATED SORGHUM Iowa State University PH.D. 1983 University Microfilms I ntornâtionâ! SOO N. zeeb Road, Ann Arbor, Ml48106 Introgression of wild germplasm into cultivated sorghum by Thomas Stanton Cox A Dissertation Submitted to the Graduate Faculty in Partial Fulfillment of the Requirements for the Degree of DOCTOR OF PHILOSOPHY Department: Agronomy Major: Plant Breeding and Cytogenetics Approved: Signature was redacted for privacy. In Charge of Major Work Signature was redacted for privacy. )r the Major Department Signature was redacted for privacy. For tl Iowa State University Ames, Iowa 1983 ii TABLE OF CONTENTS Page GENERAL INTRODUCTION 1 SECTION I. EXPECTATIONS OF MEANS AND GENETIC VARIANCES IN BACKCROSS POPULATIONS 15 ABSTRACT 16 INTRODUCTION 17 RESULTS 20 DISCUSSION 31 REFERENCES CITED 34 SECTION II. GENETIC VARIATION FOR GRAIN YIELD AND RELATED TRAITS IN SORGHUM INTROGRESSION POPULATIONS 35 ABSTRACT 36 INTRODUCTION 37 EXPERIMENTAL PROCEDURES 39 RESULTS 49 DISCUSSION 61 REFERENCES CITED 69 SECTION III. POTENTIAL OF WILD GERMPLASM FOR INCREASING YIELD OF GRAIN SORGHUM 70 ABSTRACT 71 INTRODUCTION 72 EXPERIMENTAL PROCEDURES 73 RESULTS 87 DISCUSSION 103 REFERENCES CITED 106 i i i Page SECTION IV. TRAIT ASSOCIATION IN SORGHUM INTROGRESSION POPULATIONS 107 ABSTRACT 108 INTRODUCTION 109 EXPERIMENTAL PROCEDURES 112 RESULTS 124 DISCUSSION 134 REFERENCES CITED 135 GENERAL CONCLUSIONS AND DISCUSSION 136 ADDITIONAL REFERENCES CITED 139 ACKNOWLEDGMENTS 143 APPENDIX A 145 APPENDIX B. DERIVATION OF Vg(F^)^. 168 APPENDIX C. DERIVATION OF Vg(F2/F^)^. 169 1 GENERAL INTRODUCTION Whereas introgression of genes from one race or species into an­ other has been a factor in the evolution of plants in nature, both natural and artificial introgression have played a part in the develop­ ment of many agricultural species. Stebbins (1970) outlined the sequence of events in natural intro­ gression: (1) hybridization, (2) backcrossing, and (3) stabilization of backcross types by selection. In nature, a direct hybrid between two very diverse parents is usually unadapted to the habitat of either parent and is at a selective disadvantage. Backcrossing, by producing progeny adapted to the habitat of one parent but containing small amounts of germplasm of the other, can permit an enduring transfer of genes. Likewise in plant breeding, crosses between cultivated strains and wild or weedy relatives usually produce very few or no agronomically acceptable progeny. MacKey (1963) suggested in the case of wide crosses that the breeder backcross one or more times to the adapted parent. The number of backcrosses is determined by the relative importance of (1) mean performance and (2) genetic variability. For example, if a base population for recurrent selection is being established, fewer back- crosses will be made than if a single disease-resistance allele is be­ ing added to a cultivar. In this study, the results of introgressing germplasm from wild diploid sorghum (Sorghum bicolor L. Moench) races into grain sorghum cultivars are examined. The wild, weedy, and cultivated sorghum races intercross readily; introgression of wild germplasm into cultivars has 2 occurred continuously in Africa since the domestication of the crop (Doggett, 1965; DeWet et al., 1970). It is possible, however, that some agronomically useful genes or gene complexes present in the wild races were not retained during the development of modern grain sorghum cultivars. The objectives of this study are: (1) To determine the theoretical and actual degree of genetic variation produced by introgressing germplasm of three wild sorghum races into cultivated sorghum strains; (2) To evaluate the potential of introgression for grain yield improvement in sorghum and find the relationship, if any, between the proportion of wild germplasm in a population and the occurrence of high-yielding progeny; and (3) To determine the degree and pattern of association among traits in the introgression populations and whether there are tightly coherent complexes of "wild" traits. Review of Literature Natural introgression in crop species Gene flow between crops and sympatric wild relatives occurs natu­ rally, often facilitated by weedy intermediate forms (Harlan, 1965). African sorghum represents a crop-weed-wild complex in which introgression has played an important role (DeWet and Huckabay, 1967; Doggett and Majisu, 1967). For example, race arundinaceum is a wild grass of the west and central African tropical forests and hybridizes with cultivated race guinea, producing troublesome weeds. Introgression 3 of genes from arundinaceum into the early cultivated types may have pro­ duced the guinea phenotype and permitted extension of grain sorghum cultivation into the forests (DeWet et al., 1976). In addition, race virgatum crosses with durra sorghums in north­ east Africa. Race verticilliflorum is widespread and crosses with culti­ vated types over the entire African savanna. Race aethiopicum crosses with cultivated races caudatum and durra in the dry savanna of West Africa (DeWet et al., 1976). Doggett and Majisu (1967) showed 105 progeny rows derived from a natural wild x cultivated hybrid to local Ugandan women, who selected 57 heads to which they gave names of varieties currently in cultivation in the area. This suggests the possibility of natural introgression, since a few hybrid progeny surviving to the Fg (or a backcross genera­ tion) might not be rogued out of a field, though containing, and pass­ ing on to their progeny, wild genes. Doggett and Majisu (1967) considered African sorghum to be a case of disruptive selection. Despite considerable gene flow between wild and cultivated races, it was found that the contrasting influences of artificial and natural selection maintained a wide phenotypic divergence between the two populations. According to Manglesdorf (1961), teosinte (Zea mays ssp. mexicana, L. Schrad.) grows extensively in and around maize (Z. mays, ssp. mays) fields in Mexico and Guatemala. Farmers remove teosinte and hybrid plants (which make up 50% of the stand in some cases), but only after pollen has been shed. Introgression from Tripsacum into maize is also evident in areas 4 of South America where, despite the absence of teosinte. the local maize has tripsacoid characters. Stalker et al. (1977) demonstrated that Tripsacum germplasm can be introgressed into maize by repeated backcrossing. However, DeWet et al. (1968) pointed out that experimental introgression cannot prove that natural introgression