Agriculture Reference
In-Depth Information
measured as a biennial bearing index,
I
(Hoblyn
et al.
,
), calculated as
difference between two successive crops
of two successive crops
I
=
×
which varies between
(biennial).
Anumberofcultivarsaresostronglybiennialthattheyhavebeenmuchused
instudiesonbiennialbearing,e.g.'Laxton'sSuperb'and'Miller'sSeedling'ap-
ples. Among commercially important apple cultivars Jonkers (
(completely regular) and
) concluded
that 'Elstar', 'Idared' and 'Jonagold' showed no biennial tendency whereas
'Granny Smith', 'Starking' and 'Golden Delicious Spur' showed medium sus-
ceptibility.Ofthenumerouscultivarsclassedasstronglysusceptibleonly'Cox's
Orange Pippin' is now of any importance and there are differences of opinion
about the strength of its biennial tendency. Jonkers placed 'Golden Delicious'
in the first, regular bearing, category but with a note that opinions differed
on this. Lauri
et al.
(
), from an experimental study of the fate of individ-
ual buds, categorized 'Jonagold', 'Royal Gala' and 'Granny Smith' as having
a low 'alternation to fruit' index, 'Golden Delicious' as being intermediate
and 'Braeburn', 'Fuji' and, especially, 'Oregon Spur Delicious' as having a
high index. Bernhard (
) showed that many
spur-type cultivars have a strong alternate-bearing tendency.
) and Looney and Lane (
Rootstock effects on flowering
Apple rootstocks have a major effect on the proportion of buds that become
floral. This is very pronounced when the trees are young, influencing precocity
of cropping as discussed in Chapter
. It is also so for mature trees, Blasco
(
) reporting
,
,
and
% of all 'Cox' buds to be floral on 'M.
',
'M.
). 'Quince
C' rootstock induces flower bud formation in pear. Although those rootstocks
that check scion growth most tend to enhance fruit bud production, this is not
an invariable relationship.
', 'M.
' and 'MM.
', respectively (
=
.
at
p
=
.
Plant hormone and growth regulator effects
on flowering
Guttridge (
) first showed that applied gibberellins inhibit apple flowering,
and many subsequent studies have confirmed this. Tromp (
) found that
GA
and GA
were particularly active whereas GA
had little effect. Both
reduced flowering of spur buds of 'Cox's Orange Pippin' when applied at full
bloom and GA
had negative effects when applied
weeks later. GA
reducedfruitbudformationonshootswhenappliedinJuly.RamirezandHoad
(
or
) found GA
or GA
+
applied via cut petioles to spurs at
or
weeks
