Agriculture Reference
In-Depth Information
though not of vertebrates or higher plants. Endochitinase and chitobiosidase
inhibit spore germination and germ tube elongation of
Venturia inaequalis
, the
apple scab pathogen. The cDNA of endochitinase has been cloned into vec-
tors and the construct used to transform 'Royal Gala' apple using
Agrobacterium
tumefaciens
. Some but not all of the transgenic 'Royal Gala' lines produced show
increased scab resistance in greenhouse tests (Wong
et al.
,
).
Gene transfer for resistance to fire blight
Genes encoding proteins that lyse bacterial cells are found in the giant silk
moth,
Hyalophora cecropia
. These are cecropin B and attacin E. Two
-amino
acid peptides, SB-
, are synthetic analogues of cecropin B. Hen
egg white lysozyme is also potentially effective. The relevant genes have been
transferred to 'M.
and Shiva-
' rootstock and 'Royal Gala' apple scion using an
Agrobac-
terium tumefaciens
mediated leaf piece transformation system. Transformed
shoots with the gene encoding attacin E have significantly increased resis-
tance to fire blight caused by
Erwinia amylovora
(Norelli
et al.
,
). Transgenic
clones of the pear cv. 'Passe Crassane' containing the attacin E gene show
enhanced fire blight resistance (Reynoird
et al.
,
a,b). One transgenic line
with the SB-
cecropin transgene was significantly more resistant to fire blight
than untransformed 'Royal Gala' (Norelli and Aldwinkle,
). The bacte-
riophage T
lysozyme has been found to give increased fire blight resistance
to transgenic 'Galaxy' apples.
Fire blight resistance in apple may be positively associated with sorbitol con-
centration, and transgenic apple trees with elevated levels of sorbitol synthesis
have been produced. A key enzyme in the synthesis of sorbitol (S
PDH) has
been cloned from apple (Norelli and Aldwinkle,
).
Gene transfer for resistance to insects
A gene encoding a cowpea trypsin inhibitor (
Cp
T
) that is anti-metabolic to a
wide range of Lepidopteran and Coleopteran insects has been transferred to
apple ( James
et al.
,
). The
Cryl
A(c) gene from
Bacillus thuringiensis
, which
codesforendotoxinswithinsecticidaleffects,hasalsobeentransferredtoapple.
Use of transformed plants
No commercial cultivars have yet been developed using transformation. There
is currently popular concern about the use of genetically modified food plants.
Utilization of clones of major, well-accepted, commercial cultivars that have
been genetically modified to overcome specific problems or incorporate novel
benefits will therefore depend on consumer acceptance of the technology as
well as on the comparative advantages of its products.
