Glossary Plant Breeding

Promoter. A regulator region of a short distance from the 5’ end of a gene that acts as the
binding site for RNA polymerase (for the initiation of transcription).
Propagule. The means of propagation and/ or dissemination. It may be unicellular or
multicellular agent (seed, for example).
Proper Plot Technique. A technique to minimize experimental error as much as
possible. Some common plot techniques are proper choice of plot size and shape,
block size and shape, number of replication, and the like.
Prophage. A phage “chromosome” inserted as a part of the linear structure of the DNA
chromosome of a bacterium.
Prophase. The early stage of nuclear division during which chromatins condense and
chromosomes become visible.
Proplastid. An immature plastid.
Protandry. A mating system that involves maturation of anthers before pistils (pollen
shed first as in maize, carrots, etc.).
Protein-for-Protein Hypothesis (Van der Plank 1976, ’78). A hypothesis pertaining to
host-parasite interaction. The products of genes of both host and pathogen recognize
and interact with each other that lead either to incompatibility (resistance) or
compatibility (diseased condition). According to Van der Plank, the protein-forprotein
hypothesis is applied to diseases to which the gene-for-gene hypothesis has
been applied. The two hypotheses differ somewhat in emphasis; the latter centres
around genes for resistance, whereas the former is concerned primarily, albeit not
exclusively, with compatible host - pathogen combinations. Strobel (1975) objected
the explanation made by Van der Plank. According to him, it is the protein from the
susceptible allele that recognizes and binds the toxin produced by the pathogen, and
thus the explanation of Van der Plank (1978) that pathogen protein copolymerizes
with that of host protein giving rise to compatibility reaction, cannot be true.
According to Samborski (1978), it also does not account for the fact observed by Flor
(1956) that interaction of recessive alleles of host and dominant alleles of pathogen in
flax rust could lead to compatibility. Therefore, according to him, compatibility arises
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