Breeding and Seed Production of Ornamental Crops (2+1)

Hibiscus Breeding

Introduction
The genus Hibiscus L. belongs to the family Malvaceae. There are 300 species widely distributed in tropical and sub-tropical parts of the world. Out of these only four ornamental species of Hibiscus, namely, H. rosa-sinensis L., H. schizopetalus Hook., H. mutabilis L. and H. syriacus L. are grown almost all over the tropics and sub-tropics. Among these ornamental species, H. rosa-sinensis L. (Shoe Flower) is the most important and beautiful of them all. A large number of types are found freely growing in India and majority of these types are hardy-and tolerant to drought conditions compared to the Hawaiian varieties.
Most of the improvement work through breeding in Hibiscus rosa-sinensis L. has been taken up in sub-tropical areas such as Mauritius, Hawaii, Fiji, India, California and Florida. In India, work on improvement of ornamental Hibiscus was mainly taken up at the Indian institute of Horticultural Research, Hessaraghatta; Lalbagh Botanic Garden, Bangalore; Tamil Nadu Agricultural University, Coimbatore and Kerala Agricultural University, Trichur, besides some leading nurserymen. An attempt has been made here to review the breeding work done in India in this crop.
Species and Cultivars
Species
Some of the important ornamental Hibiscus species grown in India and other parts of the world have been described by various workers. A brief description of each species is as follows:
H. rosa-sinensis L.: A native of Asia, probably China, but now conspicuous in all warm countries. A large evergreen shrub called the Shoe flower or Chinese rose. Corolla 10-15 cm across, column conspicuously exserted. The leaves are brightly green ovals, pointed at the apex and coarsely toothed except round the base. There are many new colours including white, yellow, pink, orange, terracotta, cerise etc.
H. schizopetalus Hook.: This is also called Coral hibiscus and was imported from Africa. A large, glabrous distinct shrub with many slender drooping branches. 11 bears red or orange-red flowers drooping and with deeply fringed and recurved petals. The staminal tube is quite long measuring up to 15 cm. Leaves ovate-elliptic, 5-7 cm long, acute or acuminate, dentate, calyx tubular, staminal column long and exerted.
H. mutabilis L.: This is native of China. It is known as the Changeable Rose or Persian Rose. Leaves large, heart-shaped, almost as broad as they are long and hairy. The edge is serrate. The flowers are single or double, 7-10 cm across, pure white in the morning and gradually turn pale pink to deep pink.
H. syriacus L.: It is a native of East Asia and is known as Rose of Sharon It is also known as Tree Hollyhock or Althea shrub. A glabrous erect growing shrub. Leaves rather small, traingular-ovate, 5-7 cm long. Thriving best in hills and Produces lovely white, blue or mauve flowers either single or double.
Cultivars
There are several hybrids of the Hibiscus rosa-sinensis type with single and double flowers in varying shades. Their brief characteristic features are as follows:
Single flower cultivars
'Agnes' : Large flowers with cyclamen-pink and deep pink centre.
'Australian Single' : Very large flowers and deep rose with maroon centre.
'Glowing Sunset' : Deep glowing salmon orange
'Lipstick' : Bright red with dark centre.
'My Beauty' : Very large pink with a prominent maroon centre.
'Netaji' : White flowers with crimson centre.
'Viceroy' : Small deep rose-red flowers.
'Waimeae' : Snow white with slightly fragrant flowers.
Double flower cultivars
'Alipore Beauty' : Grows like a tree, bearing deep rosy cerise medium-size flowers. Highly floriferous.
'Aurora' : Very large flowers with flesh pink colour.
'Chitra' : Marigold Orange flower.
'Daffodil' : Large size with true Daffodil yellow.
'Dream' : Large mauve flowers.
'Golden Gleam' : Very huge attractive shade of buttercup yellow.
'Juno' : Large flowers with cerise colour.
'Mahatma' : Big double flowers, cadmium orange with red centre.
Breeding
Many of the Hibiscus rosa-sinensis cultivars were proved to be completely sterile. Only a limited number combined desirable characters with a reasonable degree of fertility, could be used as parents for the breeding programme. The improvement of ornamental Hibiscus through breeding in India is mainly done in tropical areas of southern states like Karnataka, Tamil Nadu and Kerala where the environmental conditions like temperature and humidity are congenial for seed setting in some of the species and cultivars. The major objectives included were plant with good growth habit, floriferous nature, desirable flower colour, size, shape and good keeping quality.
Hybridization
Hybridization is one of the most important methods of breeding in Hibiscus. Before taking up hybridization, basic information on pollen morphology, production, fertility, germination, pollination techniques are prerequisites. These have been discussed below:
Pollen Morphology
Individual pollen grains of H. rosa-sinensis L. and two other species like H. mutabilis and H. schizopetalus are pantoporate, spheroidal and spinose. Pollen diameter varied and ranged from 25.91µ in Acc. 29 to 198.58µ in Acc. 25. It was also noticed that though there was variation in colour and size, the pollen grains of different types and species had similar shape.
Pollen Production
In Hibiscus, the varieties were found to differ significantly in pollen production. The number of pollen grains per anther was found to vary from 159 to 359. Variation in the pollen output per anther among different types and species of Hibiscus are varied from 87 in Acc. 16 to 500 in H. mutabilis. The pollen production per flower depended on the number of anthers per flower.
Pollen Fertility
Pollen fertility of Hibiscus was estimated by acetocarmine staining technique. Pollen grains which stained well, looked plumpy and well-shaped were considered as fertile and those unstained, small or shrivelled as sterile. Different types and species showed-significant variation in pollen- fertility and it ranged from 4.6 Per cent in Acc. 7 to 97.4 per cent in H. mutabilis.
Pollen Germination
Pollen germination studies in vivo showed that the pollen grains of only six ('Rose', 'Sunset', 'Juno', 'Australian Single', 'Splendens' and H. schizopetalus) out of ten varieties germinated on the stigma. Among the above six varieties pollen tubes elongated only in four 'Rose', 'Sunset', 'Jluno' and H. schizopetalus.
Pollination and Fruit Set
The pollination technique followed during hybridization' is quite simple. After selecting the desired female parents, flower buds are emasculated with a fine forceps one day prior to the opening and these buds can be tied in the middle with a thread so as to make it convenient for bagging. On the following day, pollen from- desired male parent which have been bagged properly are brought along with the staminal column and slowly smeared on the sticky stigmatic surface of the female parent. After crossing, the crossed flowers are bagged with a butter paper bag to protect from further cross-pollination by insects. The pollinated flowers are labelled indicating the parents involved and the date of crossing. After a week of crossing, the bags can be removed and the young capsules may be allowed to develop under natural conditions. Generally, the successful crosses will show swelling of the capsule and do not fall easily. Generally, the capsules take for seed maturity after hybridization 40 to 71 days under Bangalore conditions.
Promising Hybrids and Seedlings
The intraspecific hybridization of H. rosa-sinensis was undertaken mainly at the Indian institute of Horticultural Research, Hessaraghatta, Lalbagh, Bangalore and Tamil Nadu Agnoultural University, Coimbatore resulted in raising of large number of F₁ progeny. The promising seedlings from the segregating population were tested thoroughly for various attributes before release.
Varieties developed at IIHR, Hessaraghatta: Out of the nearly 1200 intravarietal hybrids and opan-pollinated seedlings of H. rosa-sinensis, 25 new varieties with attractive flowers were released between 1972 to 1979. These are mentioned below along with their flower colour. 'Aikta' (Post Office Red), 'Anuradha' (Golden Buff), 'Arunodaya' (Nasturtium Orange), 'Ashirwad' (Yellow), 'Basant' (SulphurYellow), 'Benazeer' (Bright Yellow), 'Bharat Sundari' (Deep Neyron Rose), 'Chitralekha' (China Rose with white variegated petal), 'Dilruba' (Mark Golden Buff), 'Geetanjali' (Turkey Red), 'Jogan' (Azalea Pink), 'Nartaki' (Marigold Orange), 'Nazneen' (Tangerine Orange), 'Neelofer' (Magenta Rose), 'Pakeezah' (Carmine Red), 'Phulkari' (Delft Rose with yellow border), 'Priya' (Rose Bengali), 'Queen of Hessaraghatta' (Orange), 'Ratna' (light yellow with orange stripe), 'Red Gold' (Dutch Vermilion), 'Red Saturn' (Signal Red), 'Shanti' (Primrose Yellow), 'Smt. Indira Gandhi' (Indian Yellow), 'Smt. Kamala Nehru' (Rose Bengal) and 'Tribal Queen' Cardinal Reds. Some of the very popular ones are briefly described below:
'Arunodaya': This seedling was produced from the cross 'IIHR-H 2' and 'Rachaiah'. A vigorous shrub with many lateral branches, highly floriferous. Flowers are single, 16-18 cm across. Petals are incurved along the margin. Corolla Nasturtium Orange (25 B) and the basal part of the corolla is Rose Bengal (57 B) which spreads upto 3 cm.
'Ashirwad': This is a cross between 'H.S. 21' and 'Hombe Gowda'. A vigorous plant with prominent lenticells all over the surface of branches, floriferous. Flowers are single, 18-21 cm across. Corolla Cadmium Orange (23 B) and slightly Mandarin Red (40 C) towards one side of the border. Petals with slightly- ruffled margin. The basal part of the corolla Currant Red (46 A) with Neyron Rose (55 A) border which spreads upto 3.5 cm.
'Basant': This hybrid seedling is across between 'IIHR-1' and 'Rachaiah'. A moderately vigorous shrub with erect lateral branches. Leaves are slightly pubescent. Flowers are single, 17-20 cm across. Petals are slightly incurved along the margin. Corolla Sulphur Yellow (6 A) without any conspicuous centre. This is one of the best yellow coloured varieties in hibiscus.
'Nazneen': This seedling was produced from the cross 'H.S. 203' and 'Rashtrapati'. A moderately vigorous shrub with slightly pubescent leaves, floriferous. Flowers are single, Nightly cup-shaped, 18-22 cm across. Corolla is Tangeririe Orange (24 B). Petals are recurved along the margin and with silky texture. Basal part of the corolla is red -with light mauve border which spreads up to 3 cm.
'Dr. B.P. Pal': This is also a seedling of 'Lahiana'. Flowers single, measures 22 cm across. The base of the corolla is whitish pink and turns to rose pink later on. The petals are Mandarin Red with prominent veins. The general colour effect of the flower is rich deep gold washed with vermilion.
'Mother': This is a hybrid seedling between 'Honi Honi' and 'Cornet'. Leaves cordate, ovate, acute and undulate. Flower 15-17 cm across. The base Clothe corolla is Capsicum Red and the margin of the petal is Saffron Red.
Mutation Breeding
Three somatic mutants have been isolated, one in cv. 'Cruenthus' and two others in 'Alipore Beauty'. Both the varieties were exposed in pots, under semi-acute exposures. In cv. 'Cruenthus', a mutation with change of flower form from double to single type has been established. In cv. 'Alipore Beauty' two somatic mutants one with deep red flower colour as against light red carmine colour and the other with deep red flower colour coupled with semi-double form with an average of 2-15 petals have been isolated. Single flower mutant of cv. 'Alipore Beauty' through induction of gamma rays and it has been named as 'Anjali'.