Principles of Plant Genetics and Breeding

76 CHAPTER 5
Kingdom
Division
Class
Order
Family
Genus
Species
Binomial
nomenclature
Figure 5.1 Taxonomic hierarchy of plants. Plant breeders
routinely cross plants without problem within a species.
Crosses between species are problematic, and often
impossible between genera and beyond.
The binomial nomenclature was developed by
Carolus Linnaeus and entails assigning two names
based on the genus and species, the two bottom taxa
in taxonomic hierarchy (Figure 5.1). It is important
for the reader to understand that plant breeding by
conventional tools alone is possible primarily at the
species level. Crosses are possible within species and
occasionally between species (but are often problematic).
However, plant breeding incorporating molecular
tools allows gene transfer from any taxonomic level to
another. It is important to emphasize that such a transfer
is not routine and has its challenges.
The kingdom Plantae comprises vascular plants
(plants that contain conducting vessels – xylem and
phloem) and non-vascular plants (Table 5.2). Vascular
plants may be seeded or seedless. Furthermore, seeded
plants may be gymnosperms (have naked seed) or
angiosperms (have seed borne in a fruit). Flowering
plants may have seed with one cotyledon, called monocots
(includes grasses such as wheat, barley, and rice),
or seed with two cotyledons, called dicots (includes
legumes such as soybean, pea, and peanut) (Table 5.3).
The strategies for breeding flowering species are different
from those for non-flowering species. Flowering
species (sexually reproducing) can be genetically manipulated
through the sexual process by crossing, whereas
non-flowering species (asexually reproducing) cannot.
Furthermore, even within flowering plants, the method
Table 5.2 Divisions in the kingdom Plantae.
Division Common name
Bryophytes Hepaticophyta Liverworts
(non-vascular Anthocerotophyta Hornworts
plants) Bryophyta Mosses
Vascular plants
Seedless Psilotophyta Whisk ferns
Lycophyta Club mosses
Sphenophyta Horsetails
Pterophyta Ferns
Seeded Pinophyta Gynosperms
Subdivision: Cycadicae Cycads
Subdividion: Pinicae
Class: Ginkgoatae Ginko
Class: Pinatae Conifers
Subdivision: Gneticae Gnetum
Magnoliophyta Flowering plants
Class: Liliopsida Monocots
Class: Magnoliopsida Dicots
for breeding differs according to the mode of pollination
– self-pollination or cross-pollination.
Rules of classification of plants
The science of plant taxonomy is coordinated by the
International Board of Plant Nomenclature, which
makes the rules. The Latin language is used in naming
plants. Sometimes, the names given reflect specific plant
attributes or uses of the plant. For example, some
specific epithets indicate color, e.g. alba (white), variegata
(variegated), rubrum (red), and aureum (golden);
others are vulgaris (common), esculentus (edible),
sativus (cultivated), tuberosum (tuber bearing), or
officinalis (medicinal). The ending of a name is often
characteristic of the taxon. Class names often end in
-opsida (e.g. Magnoliopsida), orders in -ales (e.g.
Rosales), and families in -aceae (e.g. Rosaceae). There
are certain specific ways of writing the binomial name
that are strictly adhered to in scientific communication.
These rules are as follows:
1 It must be underlined or written in italics (being
non-English).
2 The genus name must start with an upper case letter;
the species name always starts with a lower case letter.
The term “species” is both singular and plural, and
may be shortened to sp. or spp.