The inheritance of style length in Oxalis rosea

Abstract

In Oxalis rosea it is found that some short-styled plants are dominant to non-short (mid-or long-styled plants) whilst others are recessive. Breeding experiments show that the short style form is under the control of two gene pairs (A, a and S, s) with shorts having either of the genotypes aaSS and aaSs. In plants segregating for A, a on an SS background, shorts appear as recessive whilst in plants segregating for S, s on an aa background, shorts appear as dominant. Among non-shorts, mids (MM, Mm) are dominant to long (mm). Genes at the three loci (i) A, a, (ii) S, a and (iii) M, m show independent assortment. These results are compared with previous suggestions of recessive short in 0. rosea by von Ubisch (1926) and in 0. articulata by Fyfe (1956). INTRODUCTIONFyfe (1956) first drew attention to the existence of two different genetic systems controlling style length inheritance in different tristylic species of Oxalis. In some species, the short-style form was found to be dominant to non-short (mid-or longstyle forms) whilst in other species short was recessive to non-short. Fyfe named four Oxalis species having a dominant short (0. valdiviensis, 0. hirta, 0. tragapoda, 0. boweii) and two other species in which short was said to be recessive (0. articulata and 0. rosea). She presented her own genetical data for 0. articulata indicating that short is recessive whilst for 0. rosea she referred to the work of von Ubisch (1926). Subsequently Mulcahy (1964) reported that Fyfe had stated in a personal communication that when she sent some of her specimens of 0. articulata to von Ubisch, the latter had replied that the material was taxonomically identical to what she, von Ubisch, had identified as 0. rosea. Mulcahy says that "the actual identity of the specimens variously referred to as 0. articulata or 0. rosea was not indicated by Fyfe" and he also comments that, "since it is extremely unlikely that a single species could possess two genetic systems, it is apparent that at least one and perhaps even both of the proposed systems may be incorrect". What Mulcahy here describes as "two genetic systems" are Fyfe's twolocus model and von Ubisch's three-locus model, which we shall discuss later. The present study was undertaken in the hope of removing some of the confusion as to the mode of inheritance of the short style form in 0. rosea. MATERIALS AND METHODSSeed of 0. rosea was obtained from the Royal Botanic Gardens, Kew, England. Following seed germination, plants of the three style forms were established and maintained in pots in a glasshouse. The plants of this species are clearly distinguishable from those of 0. articulata cultivated by Fyfe.Plants of all style forms in 0. 'rosea may readily be induced to set seed either by self-pollination or by intercrossing. Crosses of both kinds were used in this study. RESULTSThe foundation plants comprised four shorts, seven mids and one long. Crosses made between these shorts and mids gave the progenies shown in table 1. Whilst some of these progenies contain approximately h...

The Breeding System of Oxalis squamata, a Tristylous South American Species

“…Even more difficult is the problem of the evolutionary origin of tristyly, although Charlesworth (1979) developed a 3-locus model for the origin and breakdown of tristyly. The model permits exploration of the effects of changes in pollinator effectiveness, rate of selfing, and inbreeding depression, and has been proven to be adequate for Oxalis rosea (Bennett et al, 1986).…”

Genetic basis of tristyly in tetraploidOxalis alpina(Oxalidaceae)

“…In contrast to O. alpina and related diploid species, considerable crossing over in O. valdiviensis is necessary to explain the segregation of long-styled progeny from shortstyled morphs with the M allele linked in repulsion (table 1 in Fyfe, 1950). Genetic control of tristyly diverges significantly in O. articulate Savgny, in which the S allele is recessive to the L allele (Fyfe, 1956;Bennett, Leach & Goodwin, 1986), and in O. tuberosa Molina, in which short-styled morphs consistently appeared in small numbers in the progeny of mid-× long-styled crosses, complicating interpretation of the genetic basis of style morph expression for this species (Trognitz & Hermann, 2001). Features of the genetic system controlling expression of tristyly in O. alpina are shared by species in Lythraceae and Pontederiaceae, in which S and M loci control expression of style morphs, the S locus is epistatic to the M locus, the loci may be linked or unlinked, and polyploidy occurs in some species (Fisher & Mather, 1943;Barrett, Morgan & Husband, 1989;Eckert & Barrett, 1993;Gettys & Wofford, 2008 Fisher (1941) developed equations to calculate the equilibrium frequencies of the mid-styled morphs with more than a single copy of the M allele in disomic, tetrasomic and hexasomic cases.…”

To What Extent Has Fisher's Research Program Been Fulfilled in Australia?

“…My colleagues have shown that three-or even four-gene models are needed for some species of Oxalis, and their elucidation is only just beginning (Bennett, Leach & Goodwins, 1986).…”