A STUDY OF TRIPLOID AND 3 X -1 ANEUPLOID PLANTS IN THE GENUS GOSSYPIUM'

Cytological comparisonis were made of triploid and 3x 1 plants of Gossypium hirsutum (haplo 17 and 18) X G. aridum, G. armourianum, G. harknessii, and G. raimondii. Tests and observations led to these conclusions: (1) Chromosome conj ugation varied significantly from plant to plant and date to date within plants. (2) The D genome chromosomes of G. hirsutum are closer in homology to G. raimondii than to the other species tested. (3) The chromosomes of G. aridum have closer homology to the A genome of G. hirsuztum than do the chromosomes of the other D species tested. (4) The D genome of G. hirsutum has a small tranislocation as compared to the genomes of the foutr D species stuidied. MORE THAN 30 species are currently recognized in the genus Gossypium, which includes the commercial species of cotton. The four cultivated species inelude two allotetraploids (n = 26), (G. hirsutum L. auid G. barbadense L., and two diploids (n= 13), G. heerbaceum L. and G. arboreurn L. The wild species, which are xerophytic shrubs, have no commercial value. These include one allotetraploid (n = 26), but the rest are diploid (n = 13). The wild diploid species have been placed in five geniome groups (B, C, D, E, and F). These five groups were established on the basis of geographic distribution and chromosome pairing relationships in hybrids (Beasley, 1940; Phillips anld Strickland, 1966). Two distinct groups of chromDsomes occur in the tetraploid species: those of the A genome, similar to the large chromosomes of G. herbaceum and G. arbore 1rn and those of the D genome, similar to the small chromosomes of the American wild species. The wild diploid species provide a source of getnes for the improvement of the commercial cottons. The amount of germplasm that can be transferred into a eultivate-d tetraploid species from a diploid is partially dependent, upon the degree of homology of the chromosomes of the diploid anld the recurrent parenit. The primary aim of the study reported herein was to determine the relationships of the chromosomes of G. hirsutum and(I four diploid species of Gossypium that carry various D genomes. These relationships were to be elucidated by comparing meiotic activity in the 3x and 3x 1 cytotypes to reveal the effect of a specific chromosome from the various diploid species. I Received for publication 20 May 1970. NMost of the data were collected for a dissertation, which was submitted to the Graduate College, Texas AM Brown and Meizel, 1952a,b; Cannon, 1903; Denham, 1924; Enidrizzi, 1957; Endrizzi and Brown, 1964; Kammacher, 1960; Skovsted, 1937; Webber, 1935, 1939) have made cytological examinations of the triploid hybrids between G. hirsutum and the Americaii diploid species. Monosomic planits of G. hirsutum are collected, identified, and maintained at Beasley Laboratory, Texas A& M University. Crosses between the monosomics anld diploid species produce 3x and 3x 1 progeny. Comparisons of the chromosome conjuvation in the two cytotypes provides a inew method for compiling information on gene compositioIn and chromDsome relationships. MATERIALS AND METHODs-The plants used in the study reported hereiin were progenies from crosses between monosomic plants of G. hirsutum, (AD)1, and the following four American diploid species: G. armourianurnt Kearney, D2-1; G. harknessii Brandagee, D2-2; G. aridum (Rose and Stanidley) Skovsted, D4; and G. raimondii Ulbrich, D5. The monosomic plants used in this experiment lacked either chromosome D-17 (haplo 17) or chromosome D-18 (haplo 18). Monosomic plants were used as female parents. These monosomics had been backcrossed two to six times to a highly inbred line, called Texas Marker-I (TM-1). Only one plant of each diploid, except Da, was crossed to the monosomics, which insured a measure of uniformity. The hybrids were grown in ten-inch pots in the greenhouse. Cytological data were obtained from collections of flower buds picked from 31 hybrid plants on four separate dates in 1960, 31 dates in 1967, and five dates in 1969. The buds were killed and fixed