• C. A. Krug

      Articles written in Journal of Genetics

    • Cytological observations inCoffea. III

      C. A. Krug

      More Details Abstract Fulltext PDF

      1. In form of a table a résumé is given on chromosome numbers in representatives of the genusCoffea; the basic number of 11 is now definitely established for this genus; seven species arediploids, sixteen varieties ofC. arabica aretetraploids andC. arabica var.Bullata Cramer is eitherhexa- oroctoploid.

      2. The main morphological characters of these two polyploids are described briefly.

      3. Meiosis, gametic sterility and seed setting in these polyploids are discussed; meiotic behaviour is abnormal and normal seed set is very scanty in both forms.

      4. Chromosome counts at meiosis and the results of selfing and crossing theoctoploids indicate that their functional gametes have either 22 or 44 chromosomes.

      5. Octoploid plants often arise by somatic chromosome doubling and a few instances of vegetative reversions of octoploids to the tetraploid condition were observed (somatic chromosome reduction).

      6. Chromosome counts at meiosis of hexaploids and in root-tips of their progeny showed that the functional gametes of these polyploids have usually 33 chromosomes.

      7. The influence of disharmonious chromosome combinations at fertilization on perisperm formation is pointed out.

      8. Onetriploid plant was obtained by crossingC. canephora (2n = 22) × normalC. arabica (2n = 44); in metaphases of somatic divisions in root tips some of the longer chromosomes ofC. canephora are recognizable.

    • The genetics ofCoffea - Part I. The inheritance of a dwarf type-nana

      C. A. Krug

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      1. A general outline is given of the work on the genetics ofCoffea being carried out by the Genetics Department of the Instituto Agronomico, São Paulo, Brazil.

      2. The occurrence of a dwarf type of coffee is described, found in progenies ofC. arabica L. var.Murta Cramer among other seedlings of the parent type and also of theBourbon variety; the dwarfs have extremely short internodes and very small leaves; they are completely sterile, as they do not flower.

      3. Selfing a number ofMurta plants and crossing these toC. arabica L. var.Bourbon, it is concluded, that this dwarf type is caused by the action of one pair of recessive genes—nana, theMurta plants being always heterozygousNana, and theBourbon variety having both dominant genesNaNa.

      4. Individuals of theMurta and the dwarf types vary considerably in height of the plants and leaf characters; it is supposed that modifying genes are responsible for this variation.

      5. CrossingMurta plants withC. arabica L. var.typica Cramer, theF1 individuals are all large leafed, indicating the presence, in the latter variety, of one or more pairs of genes, inhibiting the action of the dwarf gene.

      6.C. arabica typica andBourbon plants are genetically different.

      7. To obtain pureBourbon seedlings it is not necessary to plantMurta seeds as the former is homozygous forNaNa.

      8. The genesNa andna are relatively unstable, mutating frequently to the allelomorphic condition.

    • Cytological observations inCoffea. IV

      C. A. Krug A. J. T. Mendes

      More Details Abstract Fulltext PDF

      1. A short description is given of the main morphological characters of two interspecific triploid hybrids (C. arabica × C. canephora); their growth habit is normal and leaf and flower characters are intermediate in shape and size when compared with their parents.

      2. The meiotic behaviour of the chromosomes at microsporogenesis is given in detail; the expected abnormalities were observed at the distribution of the chromosomes at first and second divisions, resulting in the formation of sterile pollen grains which are extremely variable in size.

      3. The megasporogenesis in this triploid is believed to show the same abnormalities as observed in microsporogenesis.

      4. The sterility of some interspecific hybrids grown in Java, as suggested in previous articles, is therefore confirmed and cleared up.

      5. The intimate pairing of some chromosomes at early prophase up to metaphase suggests the possible autotetraploid origin ofCoffea arabica.

      6. The occasional association of a third chromosome at prophase and metaphase to groups of two suggests that some of thecanephora chromosomes may have regions analogous to ones of somearabica elements; nothing can be stated, however, regarding a possible genetical relationship betweenC. arabica andC. canephora.

      7. Two progeny plants of a triploid, obtained from open pollinated flowers, revealed to have 2n = 44; it is suggested that they derived from cross pollination, 22 chromosome pollen from normalarabica plants in the neighbourhood having fertilized two occasional 22 chromosome egg cells of the triploid.

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