Chromosome Counts, Cytology, and Reproduction in the Cactaceae'

Chromosome counts and observations of reproduction for 55 taxa of Cactaceae indicate that polyploidy is correlated with self-fertility, adventive embryony, profuse branching, and vegetative reproduction. Six genera (Blossfeldia, Cleistocactus, Frailea, Pelecyphora, Rebutia, and Strombocactus) and 35 species or varieties are reported here for the first time. Preliminary observations of pachytene and diplotene indicate that these stages may be more useful in chromosome recognition than mitotic stages. Secondary association at metaphase I and II is interpreted as a retention of homologue association at interphase I and II (interkinesis). During meiosis of certain species, Feulgen negative bodies are present. The production of an abnormal premeiotic division is suggested as a mechanism for polyploid origin. SEVERAL cytogenetic studies establish that the Cactaceae have a base number of x = 1, and polyploidy is the principle variation (Beard, 1937; Remski, 1954; Pinkava and McLeod, 1971). Earlier counts of n = 9 and n = 12, as summarized by Pinkava and McLeod (1971), were in error, but aneuploidy has been reported in meiotic material of Deamia testudo (Karw.) Britt. & Rose, n = 12 (Bhattacharyya, 1970). Either autopolyploidy or allopolyploidy have been reported in ten genera, including the large, well-surveyed Mammillaria and Opuntia (Katagiri, 1953; Remski, 1954). The significance of polyploidy, however, has not been related to the biology of the plants, particularly the mode of reproduction. Data from this study and from earlier works on embryology (Maheshwari and Chopra, 1955; Engleman, 1960; Tiagi, 1970), systematics (Philbrick, 1963; Fischer, 1971), and pollination ecology (Alcorn, McGregor and Olin, 1962) of the family, allow an initial comparison between reproductive mode and ploidy level. There are a number of cytological features reported in the literature on Cactaceae which were reinvestigated during the examination of meiotic material to determine ploidy level. In the first chromosome report for the family, cytomixis in a species of Mammillaria was noted and illustrated (Ishii, 1929). The only illustrated study of cactus meiosis (Beard, (1937) does not show this phenomenon nor is 1 Received for publication 29 January 1980; revision accepted 18 November 1980. This investigation represents a portion of a dissertation submitted for the Ph.D. degree, University of Oklahoma, Norman, Oklahoma. The author is grateful for the assistance and suggestions offered by Drs. N. H. Boke, J. Estes, Edwin Leuck, D. J. Pinkava and Mr. Jim Weedin in preparation of this manuscript. it reported by other authors. Beard, however, found extra-nuclear bodies in Echinocereus papillosus Linke (=E. blanckii (Poselger) F. Palmer var. blanckii) and other unspecified taxa. These bodies were also observed in Hylocereus undatus (Haw.) Britt. & Rose (Banerji and Sen, 1954). Finally from Beard's work is the interesting description of tetraploid Mammillaria compressa"pollen mother cells at interkinesis show twenty-two pairs of chromosomes." Similar pairing of chromosomes at metaphase I and II is reported by Lawrence (1931) and Darlington (1937) as secondary association. The cactus collection at the University of Oklahoma provided meiotic material for the examination of the above mentioned cytological features and for the determination of chromosome numbers in many unreported taxa. Flowering and fruiting of plants in the collection also permitted study of reproductive modes and their relation to polyploidy in the family. MATERIALS AND METHODS-South American plants obtained from commercial sources and field-collected Mexican and United States plants were grown in University of Oklahoma greenhouses for floral and meiotic material. Buds and roots were fixed in Carnoy's solution (3 ethanol: 1 glacial acetic acid, V:V) between 9:00 a.m. and 11:00 a.m. and stored for 2 days. After washing in 70% ethanol, the material was stained with alcoholic-carmine-HC 1 (Snow, 1963) or Feulgen's stain (Jensen, 1962). Squashing in 45% acetic acid and immediately photographing with a Leitz phase contrast microscope and high contrast copy film produced the best results. Material was mounted either in Hoyer's medium or air dried and