222 Glossary
Perlite: A light weight white-coloured soil additive from volcanic materials.
Pest: Any species, strain or biotype of plant, animal or pathogenic agent injurious to
plants or plant products.
Pest management: The control of a pest or group of pests by a broad range of
techniques from biological control to pesticides. The goal is to keep damage
below economic levels without completely eliminating the pest.
Petals: Structures collectively making the corolla, which protect the inner
reproductive structures and often attract insects by either their colour or
their nectar and thus facilitate pollination.
pH: The scale used to denote the acidity or alkalinity (lime content) of a soil. A pH
of 7 is neutral, less than 7 is acidic, more than 7 is basic and 6.5 supports
most plant life.
Phenotype: The visual appearance of a plant regardless of genetics.
Physiological maturity: The stage of development when a plant or plant part will
continue ontogeny even if detached.
Pistil: The female reproductive organ consists of stigma, style and ovary.
Pistillate: An imperfect flower with a pistil, or seed organ, but having no functional
stamens.
Plant growth: A permanent increase in volume, dry weight or both.
Plant pathogen: A microorganism that causes a plant disease.
Plant propagation: Increase in numbers or perpetuation of a species by reproduction.
Planting ratio: The recommended ratio in which the male and female plants are to
be planted to make a crossing block in hybrid seed production.
Pollen: The male cells or microspores produced by the stamens.
Pollen parent: Parent that furnishes the pollen that fertilises the ovule of the other
parent in the production of seed.
Pollination: The transfer of pollen from the stamen to the pistil, which results in
formation of a seed.
Pollinator: Line or population used as a male parent or pollen donor.
Polycarpic: Flowering and fruiting takes place many times.
Polygamous: Bearing unisexual and bisexual flowers on the same plant.
Polyploid: Plant having other than the diploid (2n) number of chromosomes.
Precocity: Tendency of a given species/cultivar to mature early.
Producer: A person who grows or distributes certified seed in accordance with the
procedures and standards of the certification agency.
Protogynous: Having the stigma receptive to pollen before the pollen is released
from the anthers of the same flower.
Pure seed: Seed of all botanical varieties of each species under analysis.
Purity: The relative stability and uniformity of a breeding line.
Recessive gene: A gene not expressed in the heterozygous state when a dominant
gene is present at the same locus on the other homologous chromosome
or a gene masked by the effect of another specifically by a dominant
allele.
Recurrent: A plant more or less blooming in two or more sessions or months.
Registered: A cultivar catalogued with an International Registrar (IRA).
Relative humidity: The measurement of the amount of moisture in the atmosphere.