Chap 2. Biology of Propagation 1.General Terminology a. Genotype: the genetic make-up of an organism b. Phenotype: the external appearance of an organism (usually the outcome of interaction between a genotype and environment) c. Ploidy: Variation in the genomic number (x) of chromosomes x = genomic number of chromosomes n = gametic number of chromosomes 2n = “wholeness” n = “halfness”

Variation in Euploidy (for Organisms with x=12) Ploidy No. Chromosomes Somatic Gametic Diploid2x=24 2n=24 n=12 Tetraploid4x=48 2n=48 n=24 Hexaploid6x=72 2n=72 n=36 Octoploid8x=96 2n=96 n= Haploid1x=12 2n=12 n= 6 (?) Triploid3x=36 2n=36 n=18 (?) Pentaploid5x=60 2n=60 n=30 (?) Seedless watermelons are triploids

Reproductive Biology Cell Division –Somatic cell division (Mitosis) –Reproductive cell division (Meiosis) Flowering and Anthesis –Megagametogenesis (EMC to Egg Cells) –Microgametogenesis (PMC to Pollen Grains) Pollination and Fertilization –Pollen germination on stigma –Pollen tube growth through style tissue –Double fertilization

Mitosis - Somatic Cell Division - Ends up with same number of chromosomes in divided cells - Divided cells are genetically identical to maternal cells 2N ► 2N + 2N

Meiosis Reproductive cell division Undergoes 2 separate divisions Forms gametes Divided cells have a half of the chromosome numbers Ends up with genetic re- assortment by chromosomal translocation (cross-over) 2N --- ► --- ► N + N + N + N

An Example of Meiosis

Fertility in Polyploid (Euploidy) Plants PloidySomaticGameticFertility Monoploid2n=1xn = ?Very low Diploid2n=2xn = xHigh Triploid2n=3xn = ?Very low Tetraploid2n=4xn = 2xVariable Pentaploid2n=5xn = ?Variable Hexaploid2n=6xn = 3xVariable Heptaploid2n=7xn = ?Variable Octoploid2n=8xn = 4xVariable Nonaploid2n=9xn = ?Variable Decaploid2n=10xn = 5xVariable

Induction of Polyploidy Use Colchicine

Polyploidization Use of Cholchicine to induce polyploids Colchicine interferes with spindle fiber function during metaphase of meiosis

Production of Seedless Watermelon

Example of Ploidy Variation Chromosome Number SpeciesPloidy Somatic (2n) Gametic (n) Genomic (x) Spinach2x1266 Corn2x2010 Potato4x Strawberry8x56287

Polyploidy Terminology (continued) Euploidy Variation between chromosome sets Aneuploidy Variation within a chromosome set Autoploidy Multiplication of the complete set of genomes of a species Alloploidy Polyploid containing genetically different sets of chromosomes derived from 2 or more species

Aneuploidy Variation within a chromosome set Aneuploidy Somatic chromosome number Examples Trisomic 2n + 1 (extra) Monosomic 2n - 1 (deficient) _ Double-trisomic 2n (2 extra) of one chromosome 2n + 2 (2 extra) A diploid plant (2n=2x=14) would contain the following chromosome numbers depending on aneuploidy conditions:

Pollen Tetrad and Microgametophyte - One tube nucleus - Two sperm nuclei

Megagametophyte 1 egg nucleus 2 polar nuclei 3 antipodal nuclei 2 synergids

Pollination and Fertilization, Angiosperms

Double Fertilization A process of fertilization in which one male gamete (sperm nucleus, n) unites the egg nucleus (n) to form embryo (zygote, 2n) and the other sperm nucleus (n) unites polar nuclei (2n) to form endosperm (3n)

1.General Terminology (continued) a. Homozygous- Having like alleles at corresponding loci on homologous chromosomes b. Heterozygous- Having unlike alleles at one or more corresponding loci on homologous c. Meiosis- Reproductive cell division (Reduction Division) - Chromosome number is reduced to one half - Results in formation of gametes (pollen, egg cells) - Allows genetic recombination d. Mitosis- Somatic cell division - Chromosome number same in daughter cells - Results in somatic tissues genetically identical - Allows clonal duplication

Fruit Flesh Color and Skin Texture Inheritance - Peach

Inheritance of Flower Color and Color Pattern Salpiglossis sinuata RR or RrRed flower color rrYellow flower color DD or DdSolid color pattern ddDilute color pattern

Gene Symbols RR DD or R_R_ (red, solid) RR dd or R_ dd (red, dilute) rr DD or rrD_ (yellow, solid) rr dd (yellow, dilute)

P1P1 P2P2 x Dilute Red (RRdd) Solid yellow (rrDD) Solid Red (RrDd) F1F1 Solid red (R-D-) 9 Dilute red (R-dd) 3 Solid yellow (rrD-) 3 Dilute yellow (rrdd) 1 F2F2

2. Nomenclature Based on ICBN (International Code of Botanical Nomenclature) a. Botanical Classification Family-Genus-Species-Variety-Form-Individual -Subspecies - Clines- continuous variation - Ecotypes- discontinuous variation b. Cultivated Plants Genus, species, cultivar Cultivar = Cultivated variety (cv.) Cultigen = Cultivated variety that has been naturalized Examples:Syringa vulgaris cv. Mont Blanc Syringa vulgaris ‘Mont Blanc’

3. Kinds of Cultivars a. Line- Self pollinated seed-propagated cultivar (homozygous) - Inbred lines - Synthetic lines (composite lines) b. Hybrids (sexual) F-1 hybrid- first generation progeny from a cross between 2 inbred lines (single cross) c. F-2 Cultivars (sexual) Cultivars made up of self-pollination of an F-1

3. Kinds of Cultivars (continued) d. Open Pollinated Cultivar (sexual) - Cultivar made up of seeds formed by open pollination - Can be mixtures of hybrids, selfs) - Inbred lines - Synthetic lines (composite lines) e. Clonal Cultivars (asexual) Clone - Plant propagated by asexual means Asexual propagation- cuttings, tubers, bulbs, grafts, rhizomes, cormels, stolon f. Apomictic Seeds (asexual) Seed formed from maternal (ovule) tissues

4. Requirements for New Cultivar a. Distinctive- Morphologically and physiologically different characteristics b. Uniform- Homogeneity ( Variation should be minimal) Homogeneous (but, can be heterozygous as in F1) Homozygous (no segregation) c. Stable- A reasonable degree of reliability Reproducible performance d. Commercial - Must have agronomic or horticultural value