DNA hybridization analyses of a Gossypium allotetmploid and two closely related diploid species.

The DNAs of two diploid species of Gossypium, G. herbaceum var. africanum (A1 genome) and G. raimondii (D5 genome), and the allotetraploid species, G. hirsutum (Ah and Dh genomes), were characterized by kinetic analyses of single copy and repetitive sequences. Estimated haploid genome sizes of A1 and D5 were 1.04 pg and 0.68 pg, respectively, in approximate agreement with cytological observations that A genome chromosomes are about twice the size of D genome chromosomes. This differences in genome size was accounted for entirely by differences in the major repetitive fraction (0.56 pg versus 0.20 pg), as single copy fractions of the two genomes were essentially identical (0.41 pg for A1 and 0.43 pg for D5). Kinetic analyses and thermal denaturation measurements of single copy duplexes from reciprocal intergenomic hybridizations showed considerable sequence similarity between A1 and D5 genomes (77% duplex formation with an average thermal depression of 6 °C). Moreover, little sequence divergence was detectable between diploid single copy sequences and their corresponding genomes in the allotetraploid, consistent with previous chromosome pairing observations in interspecific F1 hybrids.

Centromere Orientation of Quadrivalents of Heterozygous Translocations and an Autoploid of GOSSYPIUM HIRSUTUM L.

Cytological observations of quadrivalents of heterozygous translocations in Gossypium hirsutum L. demonstrate that, in addition to alternate-1 and alternate-2 orientations, a third alternate orientation (alternate-3), which occurs as a three-dimensional, V-type configuration, can be identified.-Two additional types of disjunctions, the centromere orientations of which are rotational modifications of either adjacent or alternate configurations, were also observed in quadrivalents of a translocation heterozygote. These two types are rare, and both appear in the form of the Roman numeral X . The X and the alternate-3 types also occur in quadrivalents of an autoploid of G. hirsutum.-The two X types, along with adjacent-1, adjacent-2, alternate-1 and alternate-2 orientations, represent the six possible types of planar 2 x 2 random orientation of the four centromeres of a quadrivalent. Including the three-dimensional alternate-3 type, there are seven types of orientation.

Cytogenetics of Disomics, Monotelo- and Monoisodisomics and ml st Mutants of Chromosome 4 of Cotton.

The linkage relationships and arm locations of the ml(1) and st(1) mutants of cotton were determined with the use of monotelodisomics, a monoisodisomic and disomics. The ml(1) st(1) mutants are more than 50 cM apart on chromosome 4. The ml(1) locus is in the short arm and 16 cM from the centromere, and st(1) is in the long arm and 48 or more cM from the centromere. Recombination in the monoisodisomic was twice the expected value and higher, but not significantly, than in its monotelodisomic counterpart. It was concluded that the increase indicates a greater frequency of proximal exchange in the monoisodisomic than in the monotelodisomic.

The Effects of B, K10, and AR Chromosomes on the Resistance of Maize to Viral Infection.

Studies were conducted to determine if accessory (B) chromosomes, the abnormal tenth (K10) chromosome or the aberrant ratio (AR) phenomenon of maize (Zea mays L.) affect the resistance of the plants to viral infection. Genetically similar stocks of maize with and without these elements were compared to determine what effect they would have on the plants response to Brome Mosaic Virus (BMV), Maize Dwarf Mosaic Virus (MDMV), Wheat Streak Mosaic Virus (WSMV) and Barley Stripe Mosaic Virus (BSMV).-The test results with BSMV were not found to be conclusive. With BMV and MDMV, neither the B orK10 chromosomes were found to alter infections; however, these chromosomes were found to affect the resistance of the plants to WSMV infection. The B chromosomes were found to delay the onset of leaf necrosis by 15%, while the K10 chromosome was found to increase the susceptibility to necrosis by 100%. The AR phenomenon was not found to alter the resistance of maize to BMV infection. However, it was found to increase the susceptibility of maize to MDMV infection by 36% and to decrease the susceptibility of maize to WSMV infection by 92%.

Analysis of repetitive DNA in three species of Gossypium.

The rate of reassociation of denatured DNA was determined for two selected diploid species, Gossypium thurberi (D genome) and G. arboreum (A genome), and one allotetraploid species, G. hirsutum (AD genome). The relative genome size and DNA content of the chromosomes of the diploids were A greater than D. Renaturation curves indicated that the differences in genome sizes were due primarily to the repetitive DNA content.

A reexamination of the diploidlike meiotic behavior of polyploid cotton.

Chromosome associations at pachytene, diakinesis, and metaphase I were analyzed in haploids of the allotetraploid G.hirsutwn, in the F1 hybrid between G.arboreum (A2) and G. raimondii (D5), and in the doubled hybrid 2(A2D2) in an effort to define more clearly the mechanism responsible for the diploidlike behavior of the natural allotetraploids. The mean number of bivalents per cell at pachytene, diakinesis, and MI were respectively 10.00, 7.40, and 0.80 for the haploids and 11.00, 9.50, and 5.82 for the A2D5 hybrid. The two pachytene means were not significantly different, but the two diakinesis means and the two MI means were significantly different.At early pachytene members of paired chromosomes were not equal in length, but at late pachytene both members were equal in length in most bivalents. It was particularly evident in the unpaired regions that one partner was much thicker or more deeply stained than its counterpart. Since A chromosomes are twice the size, have twice the amount of DNA, and contain greater amounts of repetitive DNA than D chromosomes, it was concluded that the bivalents consisted of A and D homoeologs. In order for the paired homoeologs to attain equality in length at late pachytene, it is presumed that the A chromosomes either started contracting before the D chromosomes or contracted at a faster rate. During the stages following late pachytene, the D chromosomes contracted at a faster rate than the A chromosomes resulting finally in a two-fold difference in the size of the A and D chromosomes at MI. It is assumed that this differential rate of contraction would limit intimate pairing attraction and chiasma formation between homoeologous chromosomes.We concluded that a gene control system analogous to that wheat and oats does not determine the diploidlike meiotic behavior of the natural allotetraploids of Gossypium. This is based on the high frequency of homoelogous pairs at pachytene in the haploids, on the strict homologous pairing in the synthetic 2(A2D5) hybrid, and on the roles repetitive DNA is assumed to have in regulating synapsis and chiasma formation and in structurally differentiating the A and D homoeologs.It was proposed that differences in genome chromosome size may determine whether a gene or non-gene control mechanism is required for regulating homologous pairing in allotetraploids.

Alternate-1 and alternate-2 disjunctions in heterozygous reciprocal translocations.

Alternate-1 and alternate-2 orientation of chromosomes, as well as the two types of adjacent orientation, were observed cytologically in the ring configurations of three reciprocal translocation heterozygotes of Gossypium hirsutum L. The observations indicate that the two types of alternate orientation should be characteristic of ring-forming translocations.

Studies on the 70S Ribosomal Content of a Plastid Mutant in Gossypium hirsutum.

Analysis of a mutation in cotton (Gossypium hirsutum), which is maternally inherited, revealed that the completely white sectors of leaves were deficient in the 70S class ribosomes, whereas the yellow sectors exhibited the same level of the latter as in the green leaves.

Seed esterases, leucine aminopeptidases and catalases of species of the genus Gossypium.

Polyacrylamide and starch gel electrophoresis were used to analyze the isozyme makeup of three enzyme systems (esterases, leucine aminopeptidases and catalases) from the dormant seeds of twenty-nine species within the genus Gossypium.Isozyme variation was observed for all three enzymes between the species of the different genome groups. The within species polymorphism noted for the esterases was not observed for the leucine aminopeptidase and catalase patterns. In general, only minor qualitative banding pattern differences distinguished the A and B genome species, whereas, band variations were greatest between the more distantly related species in the C, D and E genomes. Gossypium longicalyx (F genome) showed an overall banding pattern unique to itself. The species of the genomes (C, D, E and F) removed from the postulated area of genetic origin (Southern Africa) also exhibited greater isozyme variability than that of the wild species of the A and B genomes, both located in Southern Africa.Synthetic mixtures of seed extracts from parent species of recently formed synthetic allopolyploids produced additive isozyme patterns for esterase, leucine aminopeptidase and catalase that were closely comparable to the zymograms produced by their hybrids. In contrast all three enzyme systems showed significant qualitative isozyme variations between the three natural allotetraploids, G. tomentosum, G. barbadense and G. hirsutum when compared to the zymograms of the synthetic mixtures of their alleged parental forms.