International Journal of Horticulture, 2017, Vol.7, No.22, 180-204
201
9 Breeding Approaches for Disease Resistance
(1) Hybridization combined with pure line breeding
(2) Mutational approach
(3) Back cross breeding
9.1 Development of disease resistance in ornamental crops
Rose:
Black spot is a serious disease of roses that causes severe losses to commercial and home gardens. The
breeding lines 'Spotless Gold' (Floribunda, F
3
selection: Goldlocks ×
Rosa rugosa
), 'Spotless Yellow' (Floribunda,
F
3
selection: Goldlocks ×
Rosa rugosa
) have been used as resistant parents in breeding programmes. Some
resistant varieties have been developed through complex hybridization like 'A Makenzie', 'Charles Albert',
'Champlan', 'William Buffin' etc. resistant to black spot and mildew. Researchers at North Carolina State
University in USA observed that roses combat Botrytis or petal blight if injected with a celery gene, called
Mannitol dehydrogenase. Varieties developed at IARI, New Delhi which were found to be moderately tolerant to
powdery mildew and black spot is 'Pusa Ajay' (Pink Parfait x Queen Elizabeth), 'Pusa Mohit' (Suchitra ×
Christian Dior) is found tolerant to black spot and 'Pusa Gaurav' (Pink Parfait x Arjun) is tolerant to dieback and
black spot.
Gladiolus:
The major problem in commercial cultivation of gladiolus is a wilt disease by
Fusarium oxysporium f.
Sp. Gladioli
. The varieties Debonair, Golden Goddess, Jo Wagenaar, Katrian Local and Ratna’s Butterfly are
resistant to
Fusarium
wilt disease. Certain hybrids like SGH-13C (Pfitzer’s Sensation x Golden Goddess), SGH-6
(Jo Wagenaar x Pfitzer’s Sensation) and SGH-20 (Dedonair x Pfitzer’s Sensation) are tolerant to wilt disease. The
resistant hybrid 82-11-90 (Beauty Spot x Psittacinus hybrid) and two tolerant hybrids 82-7-59 (Watermelon Pink
x Lady John) and 82-18-16 (Watermelon x Mansock) have good vegetative characterstics. Variety 'Dhiraj'
developed at IIHR, Bangalore is resistant to
Fusarium
wilt.
Carnation:
Fusarium
wilt, bacterial wilt, stems rot and
Alternaria
leaf spot are major setbacks of carnation. A
line 91BO4-2 (cross between spray type cultivar Super Gold x
Dianthus capitatus
) is highly resistant to bacterial
wilt. Cultivars Arbel and Scarlette had novel resistance against
Fusarium
wilt. Guba evolved four cultivars
Watham Pink, Regal Pink, Spicy rose and Mrs EF Guba which were resistant to
Fusarium
wilt, rust and blight.
Chrysanthemum:
Chrysanthemum is damaged by
Phoma chrysanthemella
and
Septoria chrysanthemella
.
Varieties developed at PAU, Ludhiana which possess multiple resistance against these microorganisms are Baggi
and Ratlam Selection.
10 Biotechnological Advances for Improvement of Ornamental Plants
Apart from the various methods used in the improvement of ornamental plants discussed earlier, there is an
enormous large scope for improvement of floricultural crops using biotechnological tools like micropropagation,
in vitro
mutagenesis, somaclonal variation, embryo recovery, haploid culture, protoplast fusion, genetic
transformation and DNA finger printing.
Micropropagation:
It is the major aspect of biotechnology for large scale propagation of floriculture crops via
in
vitro
cloning.
In vitro
generated plants are uniform, true to type with increased vigour. An
in vitro
system is
generally started from a bud, an apex or meristem and is multiplied by stimulation of axillary branching or by
nodal culture. Axillary shoot proliferation is widely used in ornamentals. Besides, explants such as bulbs scales,
base plate of corms, bulbs and inflorescence are generally used in Liliaceae, Iridiaceae and Amaryllidaceae
families. Leaf and root segments, flower buds, flower stalks, petioles are also used as explants.
Some of the important flower crops propagated through
in vitro
techniques are given below along with explant
source:
