CHROMOSOMES AND CROSSING BEHAVIOR OF HIBISCUS CANNABINUS, H. ACETOSELLA, AND H. RADIATUS

MENZEL, MARGARET Y. (Florida State U., Tallahassee), and F. D. WILSON. Chromosomes and crossing behavior of Hibiscus cannabinus, H. acetosella, and H. radiatus. Amer. Jour. Bot. 48(8): 651-657. Illus. 1961.-Chromosomes of diploid H. cannabinus L. (kenaf) form 18 bivalents at metaphase I. In autotetraploid H. cannnabinus (2n = 72), more than 50% of the chromosomes pair as trivalents or quadrivalents. In the tetraploid species H. radiatus Cav. and H. acetosella Welw. ex Hiern (h. eetveldeanus De Wild. & Dur.) (2n = 72), only 4% of the chromosomes pair as multivalents and the rest pair as bivalents. Vigorous, highly fertile F1 hybrids between H. acetosella and H. radiatus are easily obtained, show complete chromosome pairing, and give rise to a freely segregating, vigorous, fertile F2: apparently the parental species have similar genome constitutions and are closely related. Chromosome pairing in the triploid hybrids of H. radiatus and H. acetosella with H. cannabinus, in hexaploids obtained by doubling the chromosome number of H. acetosella-cannabinus F1, and in pentaploid and tetraploid backcrosses of the hexaploids to H. cannabinus shows that the tetraploid species each contain 1 genome (A) very similar to, but not identical with, that of H. cannabinus and 1 dissimilar genome (B). Morphology, fertility, and other characteristics of the various hybrids are discussed in connection with the problem of recombining the resistance to root-knot nematodes found in the tetraploid species with the desirable fiber properties of H. cannabinus. THE SUSCEPTIBILITY of Hibiscus cannabinus L. (kenaf, gamboor, Ambari or Deccan hemp) to the root-knot nematodes, Meloidogyne incognita (Kofoid and White, 1919) Chitwood, 1949, and M. incognita acrita Chitwood, 1949, is a major obstacle to selection of varieties suitable for fiber production in Florida. Resistant strains of kenaf have not been found, although some selections have a certain amount of tolerance (Summers, Pate and Wilson, 1958). Excellent resistance is present, however, in a relative of H. cannabinus, H. acetoselka Welw. ex Hiern, which is cultivated for its ornamental red foliage and flowers (Pate et al., 1954). The red-leaved form (2n 72) crosses readily with H. cannabinus (2n 36); the F1 is nematode-resistant but almost completely sterile (2n 54). Doubling the chromosome number of the F1 with colchicine yields fertile 1 Received for publication February 24, 1961. The research on which this report is based was conducted cooperatively by the Crops Research Division and the Agricultural Engineering Research Division, Agricultural Research Service, United States Department of Agriculture, and the University of Florida Agricultural Experiment Station, Everglades Experiment Station, Belle Glade, Florida. The senior author acknowledges the courtesy of the Department of Biological Sciences, Florida State University, in making available laboratory space and other facilities for the cytological studies. Thanks are extended to E. G. Nelson for his interest and encouragement during this study. 2 Geneticists, Crops Research Division, Agricultural Research Service, United States Department of Agriculture. allopolyploids (2n ca. 108) with good nematode resistance, but the resulting plant type is not particularly desirable for fiber (Pate, Summers and Menzel, 1958). Another closely related ornamental species, H. radiatus Cav. (2n = 72), shows some resistance to nematodes, although not so much as the red-leaved Hibiscus, and produces somewhat better fiber than the latter. A study of the relationships of these 3 species was undertaken as a basis for further breeding. TAXONOMIC CONSIDERATIONS-The species of Hibiscus studied belong to Section Furcaria DC., a pantropical group of about 40 species which differ from the rest of the genus in clear-cut morphological characteristics (Hochreutiner, 1900; IJlbrich, 1921), and in the basic chromosome number, x 18 (Skovsted 1935, 1941, 1944). Although the section is quite distinct, some taxonomic confusion exists within it, particularly regarding the 2 relatives of H. cannabinus under consideration here. The ornamental, red-leaved Hibiscuts commonly cultivated in southern Florida was identified by Morton and Ledin (1952) as H. eetveldeanus De Wild. and Th. Dur. Durand and De Wildeman (1899) hased their description of H. eetveldeanus on a specimen from the Belgian Congo (Alfr. Dewevre, "env. de Monbanga," 1885) in the Herbarium of the Jardin Botanique de l'Etat, Brussels. This specimen was not available to us for study, but Dr. W. Robyns of that institution kindly supplied AMERICAN JOUR NAL OF BOTANY, Vol. 48, No. 8, 1961 [The Journal for August (48: 551-650) was issued August 9, 1961]