CYTOGENETICS AND PHYLOGENY OF HAPLOPAPPUS SECTION ISOPAPPUS (COMPOSITAE)
1966; NRC Research Press; Volume: 8; Issue: 1 Linguagem: Inglês
10.1139/g66-003
ISSN0008-4093
Autores Tópico(s)Plant Diversity and Evolution
ResumoIntroduction The section Isopappzls of Haplopappzls consists of three species: H. divaricatza (Nutt.) Gray ( ~ z = 4), H. rigidifolizis Smith (12 = 5), and H. validz~s (Rydb.) Cory. The latter is composed of three subspecies: validz~s (72 = 5), torreyi Smith (17 = 6), and gm~riticzls Smith (12 = 7), malting a total of five taxa in the section. T h e species in the section are genetically isolated by strong sterility barriers acting primarily in the F, hybrids (chromoson~al sterility). The three subspecies of H . validzls are less strongly isolated and probably exchange genes to a limited extent (Smith, 1965). The inorphology and taxonomy of the taxa of this section, as well as some preliminary genetic data, have been presented elsewhere (Sinith, 1965). The purpose of this paper is to suggest the phylogenetic relationships of the different taxa as determined from cytogenetic analyses of F, hybrids and certain correlative data. Materials and Methods Live plants, seeds, and cytological material were collected throughout the range of the taxa. Parental, F1, F,, and BC, plants were grown in the greenhouse. A4eiotic chromosome counts were made by the propiocarmine squash technique after fixation of heads for 2 1 hours to 2'weeks in a modified Carnoy's solution (95 , ethanol, cl~loroforin, propionic acid; 2: 1: 1 ). Allitotic chromosomes for the preparation of idiograms were measured with an ocular micronleter at 970X from root tip squashes prepared as follows: (a) 1 hour pretreatnleilt in 0.1% colchicine, (b) 2-3 minutes fixation in 100% propionic acid, (c) 3-5 minutes hydrolysis in 15% HCI, (d) 30-60 seconds wash in 33% propionic acid, and (e) stain and squash in aceto-orcein. Chromoson~es from a minimum of 10 cells were measured for the preparation of each idiogram. Reciprocal pollinations were made between all pairs of taxa in the section according to the technique previously used in the genus (Jackson, 1962), except that individual heads were pollinated only once. All taxa in the section are self-incompatible. One specimen of each successful F, hybrid combination is in the University of Icansas Herbarium. Pollcn fertili&, as judged by stainability, was detcrrnined for all parental taxa and the F,, F2, and BC, progeny. A minimum of 300 pollen grains were sampled from each individual. Pollen diameter was measured with an ocular nlicrometer at 130X. Parental Taxa Thc distributions (Fig. 1) of all of the taxa approach one another or overlap in Texas, especially in the area near Austin. Ho~vever, in Texas they generally grow in rather small, isolated colonies such that they are mostly discrete, even though their geographic ranges overlap. Chromosome counts of the parental taxa showed essentially no variation in their norinal chromosome complcinents (Smith, 1965). However, snlall super-
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