Agriculture Reference
In-Depth Information
that step however, it was essential to understand what constitutes a brassica species.
Detailed research by a Korean-born scientist working in Japan in the 1930s uncov-
ered the plasticity of brassicas and the natural formation of new species through
allopolyploidy (U
1935
). As a consequence, brassicas now constitute the world's
most important fresh food and industrial processing crops second only to the cereals
in their importance in the diets of humans and domesticated animals (Dixon
2007
).
Photoperiodism and the Control of Vegetative
and Flowering Phases
Investigations beginning in the 1920s revealed that plants may react to the duration
of the light environment by reproducing or remaining vegetative (Garner and Allard
1920
,
1923
). Subsequently, plants were divided into short-day responsive, long-
day responsive or day-neutral forms (Wareing
1956
; Schwabbe
1950
,
1951
,
1952
).
Since these original discoveries, botanical science has invested huge amounts of
time and effort into understanding the manner by which variations in light quality
and quantity are perceived and translated into signals which result in the initiation
of flowering or the retention of a vegetative state. Modern molecular biology ex-
plains these processes in terms of the genetic components of plants and the manner
by which the signals are generated. In the intervening years however, huge multi-
national horticultural industries have developed which produce flower and foliage
crops worldwide using artificial control of day-length (such as chrysanthemum,
poinsettia,
Kalenchöe
, carnation and rose) (Bernier et al.
1981
). Crops are grown on
very precise schedules where flower production is predicted over the entire growing
period to within a few hours to high degrees of quality and consequently financial
value. Basic knowledge of the manner by which flowering is triggered created mul-
tibillion dollar, global industries growing cut flowers and flowering pot plants.
Rooting Media
Original studies at the John Innes Institute in the 1920s, aimed at providing a root
environment for potted experimental plants and germinating seed, which offered
standardised structure and texture combined with regulated nutrient supplies. This
aimed at limiting one of the variables which beset geneticists when studying the
effects of breeding experiments. The results produced the John Innes series of pot-
ting and seed composts (Darlington
1949
) which remain in common use, especially
in the huge hobby markets today and are increasingly used where peat composts
are not acceptable (Carlile and Waller
2013
). These composts are based on stan-
dardised mixtures of sand and loam-based compost into which precise quantities
of nutrient fertilisers and calcium carbonate (lime) were mixed. John Innes com-
posts remained as research standards into the 1950s. A new industry developed
that manufactured these composts for sale to plant propagators, nurserymen and
