NOTE TO USERS This reproduction is the best copy available. ® UMI Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. / MECIAIIMS OF SELF- AID CROSS-IHCOMPATIBILIT? IN SWEET CLOVER, MELILOTO'S OFFICINALIS LAM. Paul Conrad Sandal A D issertation Submitted to the Graduate Faculty In P artial Fulfillm ent of The Requirements for the Degree of DOCTOR OF PHILOSOHfr Major Subject* Crop Breeding Approved* SSF'ofr,Ma|or S^i^meSb Iowa State College 1961 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. UMI Number: DP13456 INFORMATION TO USERS The quality of this reproduction is dependent upon the quality of the copy submitted. 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Further reproduction prohibited without permission. ii TABLE OF CONTENDS IimiDSDQTEOX....................................................................... ......................................... 1 Jtsn&r OF LITERATURE ....................... 3 M orphological Regions Where Incom patibility Occurs . . . . . . 4 Heteromorphic Incom patibility .................... . . . . . . . . . . . . 6 Homomorphic I ncompat i b i l i t y ....................... 9 Simple personate type s te rility . . . . . . . . . . . . . 9 M odifications of the personate type of incom patibility • . 10 Polyploidy and incom patibility . . . . . . . . . 13 Member of a lle les ............................ 14 M utations of the s te rility gene 15 Physiology of in c o m p a tib ility .............................................................. 17 Incom patibility in M elllotus o fficin alis lam. ............................ . 18 MATERIALS AH© METHODS ............................ 33 EXPERIMENTAL RESULTS .......................................... 37 Self-oom patIbility Study of a Madrid Population . . . . . . . . 27 Self-com patibility Study of Selected Sj Fam ilies ............................. 30 Data from progenies grown in 1949-50 .................................. 30 Bata from progenies grown in 1950-51 ................................................ 37 SoIf-com patibility of Sg Progenies, 1950-51 . . . . . . . . . . 48 Family 129 . . . . . . . . . . . . . . . . . .................... . . 48 Family 1 4 2 ................................ 49 Family S3 . . . . . . . . . . . . . . . . . . . . . . . . 52 Family 2 2 ....................... 52 Self-com patibility of Intra-fam ily Crosses, 1950-51 . . . . . . 57 C orrelation Between Parent-Progeny Self-com patibility . . . . . 60 C ross-com patibility Studies . . . . . . . . . . . . . . . . . . 61 Fam ily 129 ............................ 63 Family 2 2 ............................ 79 Family 62 88 MSCBSSIOI . . . ............................ 93 m m& m and conclusions ......................................................102 T ? ?<.■?$ Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. i i i himmmm cxw®......................... 106 ACRMOWLEDGMEOT . ....................... I ll Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. I INTRODUCTION A working knowledge of the mechanisms of self- and cross- incom patibilities in crop plants becomes important when a breeding program is undertaken. In many breeding plans, selfing of selected plants is required to determine the extent of segregation. In annual and biennial plants inbreeding is necessary to m aintain germ plasm of selected and tested plants which may ultim ately be used in controlled crosses or synthetic strains* Various incom patibility systems have been found in forage plants in the comparatively short time th at greater emphasis has been placed on th eir improvement by breeding* The personate type of s te rility has been established in red clover and white clover. A s e lf-fe rtility gene also has been found in these crops so that inbred lines can be estab­ lished. Self-incom patibility also is very common in orchard grass, bromegrass and perennial rye grass populations. These cases illu stra te the common occurrence of self-Incom patibility in economic forage plants th at have been studied genetically. Undoubtedly many d istin ct genetic mechanisms are responsible for the incom patibilities found in crop plants. The occurrence of natural self-incom patibility In plants has been a major factor contributing to random crossing among plants to increase v a ria b ility and m aintain heterosygosity. Natural crossing undoubtedly has played an important part in the evolutionary development of flowering plants. H eterosygosity also tends to mask the expression of deleterious reoessives and thus raaintainsplant vigor generally accepted as a Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. z consequence of heterosygosity* The genetic control of the se If-incom patibility observed in M elilotus o fficin alis has not been studied as extensively as th is phenomenon in red ©lover and white ©lover* Research reported to date indicates th at the personate type of incom patibility and/or a complex associate type involving many facto rs, is the mechanism which controls self-com patibility in sweetclover* The purpose of th is study was to estim ate the extent of self-inoom patibility in th is crop and to secure additional evidence concerning the mechanisms involved in its expression* Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. vamm op u ism tore Many species of flowering plants exhibit the phenomenon of self- incom patibility, In many oases cross-pollination is ineffective w ithin certain groups of plants. Sarly reports indicate th is phenomenon as se lf- and c ro ss-ste rility hut more recent interpretations indicate that se lf- and cross-incom patibility are only relative terns because in many oases some seed is produced following self- and cross-incom patible matings* Self-incom patibility is an important breeding mechanism in natural populations as I t encourages cross-pollination, A survey by Bast and Park (23) in 1917 showed th at about one hundred cases of s e lf-s te rility were known in over th irty -fiv e fam ilies. These workers were of the opinion th at KSlreuter should probably be credited fo r the discovery of s e lf-s te rility in plants when he reported in 1764 th at ferbaacum phoenlceum set no seed when selfed over a two-year period, but set seed readily upon crossing. This report was considerably earlier than the se lf-s te rility phenomenon reported by Darwin in 1872. Bast and Park (23) were convinced a t th is time that self- and c ro ss-ste rility in plants was heritable and both were controlled by the same genetic mech­ anism. By 1940, Bast (21) estim ated that self-incom patibility was to be found in more than three thousand species, distributed among twenty fam ilies* In a study of eight hundred species, s e lf-s te rility was quite eoimon but the distribution was not at random. I t was much more frequent in herbaceous than In woody plants. In eighteen orders of woody plants, two showed s e lf-s te rility whereas among tw enty-five orders of herbaceous plants, s e lf-s te rility has been found in fourteen. One reason for th is Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 4 unequal frequency of known s e lf-ste rility may be th at the economically important herbaceous plants haw© been mors thoroughly studied. The greater incidence of s e lf-s te rility in the herbaceous plants is expected if they have been derived from the woody forms a® the geological and anatom ical evidence indicates. S e lf-ste rility must be a relatively recent innovation in the reproductive process in view of its biological .and genetic complexity. S e lf-ste rility insures cross-pollination and is an im portant factor in producing v ariab ility and perpettiatea hetero­ sygosity, both genetic and stru ctu ral, in loci adjacent to s e lf-s te rility alleles* This heterozygosity and variation, as a resu lt of se lf-s te rility , has undoubtedly played an important part in the evolutionary development of the flowering plants, Sast (21). Harland and A ttack (33) expressed the opinion that the heterozygosity enforced by self-incom patibility was of value in m aintaining heterosis in plant populations. Extensive reviews on the subject of incom patibilities in flowering plants have been reported by Stout (66), Sears (62) and Lewis (52). The careful interpretations of these workers help a reader comprehend the general principles of incom patibilities in plants* M orphological legions Where Incom patibility Occurs By cytological studies Sears (62) classified three morphological regions of the flower where the self-incom patibility phenomenon can occur* (l) the stigm atic surface, where pollen grains fa il to germ inate, (2) the ovule, where incompatible ovules abort and (3) in the sty le, where pollen tub© growth is inhibited* Sears (62) reported Erassica oleraoeae var. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.