Plant development and reproduction

Gene modification to produce plants more suitable for high-density orchards can be performed both on cultivars and rootstocks (Table 3.1). Plants with an extensive root system and/or with reduced water consumption or changes in canopy architecture, dwarf and semi-dwarf canopy, with short and numerous shoots, could increase orchard density and improve plant performance. At present, reduction of plant size is achieved by using mainly dwarfing rootstocks and, in a few cases, by using spur varieties, selected by clonal selection or among seedling population. Both dwarfing rootstocks and spur varieties are available for only a few species and graft compatibility often presents a problem. Biotechnology techniques may contribute to the creation of dwarfing rootstocks and dwarf varieties either by somaclonal variation (better if in combination with gamma irradiation treatments) or by genetic engineering to modify hormone activity or light receptors. in vitro cultures treated with ionising radiation frequently produce shoots modified in their growth which maintain this characteristic also in the field. More interesting, however, is a transformation approach with some already available genes. Both phytohormone, or phytohormone- like and phytochrome genes seem to be good candidates in modifying plant architecture, particularly in response to different light conditions. Phytohormones are recognised as modulators of growth and differentiation in plants, since their levels can influence the growth rate such as branching, apical dominance, flowering, sex determination, regrowth and rest period. Since their synthesis is linked to light quality, modifying genes for hormone synthesis or for light receptors (phytocromes), some interesting modifications should be expected.
  Table 3.1 Genetic modification of fruit crops for plant development and reproduction
Fruit crop
Technique
Alien gene(s)
System/Plasmid or selective agents
Origin of plant material
Modification in planta
Authors

Apple
(Malus X domestica)

M26 rootstock
T
RiT-DNA
A.rh.
Microcutting
Increased rooting ability and altered morphology
Lambert and Tepfer 1992
Apple (Malus X domestica) cv Granny Smith
T
Ipt
A.t.
Leaf segment
Bushy phenotype
Trifonova et al. 1994
Apple (Malus X domestica) (M26) rootstock
T
rolA
A.t.
Leaf
Altered morphology
Holefors et al. 1998
Apple (Malus X domestica) (M26) rootstock
T
rolB
A.t.
Leaf
Rooting capacity
Welander et al. 1998;
Zhu et al. 2001
Banana (Musa spp AAA group)
S.V
Meristem
Dwarfism, abnormal leaves colour of pseudostem; ploidy change
Hawang 1986; Hawang and Ko 1987; Reuveni et al. 1985; Stover 1987; Stover and Buddenhagen 1986
Banana (Musa spp AAB group)
S.V
Meristem
Flower and leaf abnormalities
Ramcharan et al. 1985; Vuylsteke et al. 1988
Blackberry (Rubus laciniatus)
S.V
Shoot tips
Thornyness, dwarf phenotypea
Swartz et al. 1983
Blackberry (Rubus fruticosus)
S.V.
Tissue culture
Buds
Thornless
Hall et al. 1986
Citrange troyer (C. sinensis X Poncirus trifoliata) and Orange (C. sinensis) cv Tarocco
T
rolABC
A.t.
Internodes
Altered morphology
Gentile et al. 1999
Clementine (Citrus clementine)
S.V
Nucellus
Thornlessness
Navarro et al. 1985
Colt rootstock (P. avium X P. pseudocerasus)
T
RiT-DNA
A.rh.
Roots
Hairy root phenotype
Gutierrez-Pesce et al. 1998; Rugini and
Gutierrez-Pesce 1999
Colt rootstock (P. avium X P. pseudocerasus)
T
PhyA
A.t.
Stem
light perception light perception
Negri et al. 1998; Muleo and Iacona 1998 and Iacona 1998
Grape (Vitis vinifera) cv Koshusanjaku
T
RiT-DNA
A.rh.
Leaf embryogenic calli
Ri phenotype Increase root mass
Nakano et al. 1994
Grape (Vitis vinifera) cv Parodok Magaracha
S.V.
Gamma irradiation
Tetraploids
Kuksova et al. 1997
Kiwi fruit (Actinidia deliciosa) male (cv GTH) and female (cv Hayward)
T
rolABC
A.t.
Leaf discs
Altered morphology (Hairy root phenotype)
Rugini et al. 1991;
Rugini et al. 2000b
Kiwi fruit (Actinidia deliciosa) female (cv Hayward)
T
rolB
A.t
Leaf discs
Normal phenotype
Rugini and Mariotti 1992
Kiwi fruit (A. deliciosa), cvs: Hayward, Abbot, Matsua and Bruno
T
RiT-DNA
A.rh.IFO14555,
A5, ArM123,
A13
Petiole
(Adventitious buds)
Yamakawa and Chen
1996
Kiwi fruit (Actinidia deliciosa)
T
RiT-DNA
A.rh. NIAES
1724
Hypocotils
Hairy root phenotype
Yazawa et al. 1995
Kiwi fruit (Actinidia deliciosa)
T
OSH1
A.t.
Leaf
Dwarf
Kusaba et al. 1995
Kiwi fruit (A. kolomikta)
T
rolC
A.t.
Leaf
Altered morphology
Firsov and Dolgov 1997
Mexican lime
(C. aurantifolia)
T
RiT-DNA
A.rh.
Internode
Perez and Ochoa 1998
Perez and Ochoa 1998
Papaya (Carica
papaya L.)
T
Ri-TDNA
A.rh.
Hairy root phenotype
Hairy root phenotype
Rugini et al. 1994
Papaya (Carica
papaya L.)
T
rol genes
A.rh.
Petiole leaf
Hairy root phenotype
Cabrera-Ponce et al. 1996
Peach (Prunus persica)
T
Ipt
A.t.
Zygotic embryos
Compact habit
Hammerschlag and
Smigocki 1998
Pear (Pyrus communis)
S.V
Protoplasts
Leaf morphology,
rootability
Ochatt 1987
Persimmon (Diospiros kaki)
T
RiT-DNA
A.rh.
Stem of micropropagated
shoots
Altered morphology
Tao et al. 1994
 
Plum rootstock (MRS2/5)
 
T
 
RiT-DNA
 
A. rh
 
Transgenic roots
 
Altered morphology
 
Rugini and
Gutierrez-Pesce 1999
Red raspberry (Rubusideaus)
T
Hpt, SAMase
A.t.
Leaf and petiole
Altered morphology
Mathews et al. 1995
  (Rubus laciniatus and Robus ursinus loganobaccus)   S.V.       Meristem callus   Thornlessness   McPheeters and Skirvih 1983; Hall et al. 1986
  Strawberry (Fragaria X Ananassa) cv Calypso   T   rolC   A.t.   A.t.   Compact habit   Mazzara et al. 1998
  Strawberry (Fragaria X ananassa)   T   rolABC   A.t.   Leaf stipule   Compact habit   Lolletti 1999
  Trifoliate Orange (P. trifoliata)   T   RiT-DNA   A.rh. 1724   Epicotyl   Altered morphology (reduced geotropism)   Kaneyoshi and Kobayashi 1999
  Trifoliate Orange (P. trifoliata)   T   rolC   A.t.   Epicotyl   Altered morphology   Kaneyoshi and Kobayashi 1999