Agriculture Reference
In-Depth Information
Relative susceptibility of apple scion and rootstock cultivars to fire
blight following artificial inoculation
Incidence reflects frequency of infection (scale -). Severity is also on a scale
(least severe) to (most severe). Indexreflects both these factors on a scale
of to and Class reflects a broad band grouping from (most resistant) to
(most susceptible).
Table
.
Cultivar
Incidence
Severity
IndexClass
Apple cvs.
'Delicious'
'Jonagold'
'Gala'
a
'Golden Delicious'
'Elstar'
'Fuji'
'Granny Smith'
'Braeburn'
'Cox'
'Idared'
Apple rootstocks
'MM.'
'MM.'
'M.'
'M.'
'Pajam
' ('M.
')
'Pajam
' ('M.
')
'Supporter
' ('P.
')
'M.
'
'MM.
'
a
Although 'Gala' is only slightly susceptible on shoots it is highly susceptible
on flowers.
Adapted from Lespinasse and Aldwinkle (
), with permission.
(Li) cultivars less so. Quince rootstocks are moderately susceptible. New pear
rootstocks with 'Old Home' as a parent are relatively resistant. Pear cultivar
breeding for resistance is concentrating on selecting for resistance within high
quality susceptible cultivars and by selecting parents on the basis of phenotypic
values in the absence of strong evidence for major gene control (Lespinasse
and Aldwinkle,
). Transfer of resistance genes from non-pear sources is
discussed in Chapter
, on biotechnology.
Susceptibility to fire blight in the field also depends very largely on time of
floweringinrelationtoweatherconditionssuitedtoinfection.'PasseCrassane',
'Packham's Triumph' and 'Bartlett' pear all produce secondary (late) blossom
and 'Golden Delicious' and its progeny flower late on one- year-old wood. The
correlation between flower and shoot susceptibility is sometimes weak. 'Gala'
