Agriculture Reference
In-Depth Information
both reduced photosynthesis per unit leaf area, though the earlier the deficit
was imposed the longer was the negative effect in this respect. Only the deficit
imposed at
days after full bloom led to reduction in leaf area.
Effects of irrigation on fruit growth and final size are very dependent on crop
load. Goode
et al.
(
b) found that irrigation from July to mid-September
only led to increased fruit size when crops were in excess of
tha
−
.The
tha
−
then declined at higher cropping levels.
response peaked at about
Naor
et al.
(
) found the effect of increasing the number of fruits on fruit size
was more severe at lower irrigation rates or, expressed differently, the effect of
increasing irrigation on fruit size was greater the higher the number of fruits
per tree. It seems probable that irrigation influences fruit size through its effect
on leaf area, and hence assimilate production and carbon resources, as well as
possibly in more direct ways.
Scion cultivars differ greatly in intrinsic fruit size. This is also modified by the
rootstock used and, to a lesser extent, by the pollenizer cultivar.
Apple cultivars give fruits ranging from those the size of a cherry or plum,
produced by different
Malus
species including crab apples, to fruits weighing
over
g when grown in such a way as to meet local market demand (Fukuda,
).
Fruit size is under polygenic control (Brown,
). There has been rigorous
selection for size over many years and, since there is a tendency for progeny
to be smaller than the parents, it has been important to include large-fruited
cultivars in breeding programmes (Brown,
). Triploids, e.g. 'Jonagold',
usually have larger fruits than their diploid parents.
Pear fruits may be only
cm in diameter in some clones of
Pyrus betulifolia
and
P. calleryana
, while in some clones of
P. communis
and
P. pyrifolia
they may
exceed
). As with apples, fruit
size in
P. communis
cultivars appears to be under polygenic control. There are
some large-fruited triploid cultivars.
Smith (
cm in diameter (Layne and Quamme,
) found that cultivar differences in apple size were due to
both differences in the amount of cell division (i.e. cell number) and cell size.
The characteristic cultivar size was determined primarily by the amount of cell
multiplication occurring after pollination. 'Bramley's Seedling', a triploid, was
anomalous in that its large fruit size was related to both more numerous and
larger cells, and a greater volume of tissue, at the pre-pollination flower stage.
The average size of individual cells was related to the length of the growing
season of the cultivar but there is no general relationship between the length
of the growing season of a cultivar and its average fruit size.
Genotype also controls the pattern of growth within the fruit. The ratio of
fruit length to diameter varies between cultivars and also between strains of
'Red Delicious' (Greenhalgh and Godley,
,
).
