HETEROSIS BREEDING IN HORTICULTURAL CROPS

Prabhu G 2016603111Msc(Floriculture&Landscaping)

HETEROSIS• Heterosis refers to the superiority of F1 hybrids in

one or more characters over its parents. • The term hybrid vigour is used as synonym for

heterosis. • The term heterosis was first used by Shull in 1914.

CLARIFICATION B/W ‘HETEROSIS, AND HYBRID VIGOUR.

Hybrid vigour: According to shull, the developed superiority of the hybrid is the ‘hybrid vigour.

Heterosis:

The mechanism by which superiority is develoed.

SPECIFIC FEATURES OF HETEROSIS

• Superiority over Parents: Heterosis leads to superiority in adaptation, yield, quality, disease resistance, maturity and general vigour over its parents. Generally, positive heterosis is considered as desirable. But in some cases negative heterosis is also desirable.

IMPORTANT FEATURES OF HETEROSIS

Superiority of over parents

Confined to F1

Genetic control

Reproducible

Association with specific combining ability

Effect of heterozygosity

Conceals recessive genes

Low frequency

MANIFESTATION OF HETEROSIS

Increased yield

Increased reproductive ability

Increased size and general vigour

Better quality

Earlier flowering and maturity

Greater resistance to diseases and pests

Greater adaptability

Faster growth rate

GENETIC BASIS OF HETEROSIS

The genetical basis of heterosis is still following two hypothesis:

• Dominance hypothesis of heterosis.• Over dominance hypothesis of heterosis.

DOMINANCE HYPOTHESIS OF HETEROSIS

• Holds that increased vigour and size in a hybrid is due to combination of favourable growth genes by crossing two inbred races.

OVER DOMINANCE HYPOTHESIS OF HETEROSIS

• Considered that there is a physiological stimulus to development that increases with the diversity of the uniting gametes.

TYPES OF HETEROSIS

On the basis of origin and nature have 2 types:A.Euheterosis or true heterosis. 1.mutational heterosis 2.balanced heterosisB.Pseudoheterosis:On the basis of types of estimation:Average heterosisHeterobeltiosis heterosisUseful heterosis

Mutational heterosis Leathal(mostly),recessive, adaptively unfavourable mutants are either eliminated by their non-lethal dominant and adaptively superior alleles in cross pollinated crops.Balanced heterosis well balanced gene combinations which are more adaptive to environmental conditions and useful from the agriculture point of view result in balanced heterosis.

Pseudoheterosis Also termed as an luxuriance. progeny posses superiority over parents is in vegetative growth, but not in yield and adaptation ,usually sterile or poorly fertile. this concept cannot be utilized in hybrid varieties production.

ON THE BASIS OF TYPE OF ESTIMATION

Average or relative heterosis: When heterosis is estimated over mid parent value i.e. average of two parents value.Heterobeltiosis: When heterosis is estimated over better parent it is called heterobeltiosis.Standard heterosis: When heterosis is estimated over standard commercial hybrid it is called as standard heterosis. It has practical importance in plant breeding. It is also referred as a useful or economic heterosis .

FACTORS AFFECTING HETEROSIS

There are four genetic factors which affect magnitude of heterosis in crop plants. Mode of Pollination Genetic Diversity of Parents Genetic base of Parents Adaptability of Parents

HETEROSIS IN ORNAMENTAL PLANTS

Marigold: High heterosis was observed in the crosses

Alaska x Hawaii(flower size) Alaska x Cupid orange mum (flower weight) Katrain local x Cupid orange mum (flower number).

Antirrhinum: F1 dwarf hybrids -(Antirrhinum majus x Antirrhinum glutinosum). -over dominance was observed in the inheritance of all characters.

Verbena: Free flowering and heat resistant hybrids were developed.

China aster: shell pink x Azure blue AST 20 x Azure blue AST 20 x AST 16. these 3 were developed for manifestation of heterosis - Flower size, Number of flowers per plant and stalk length.

Petunia: In single multiflora and grandiflora types, heterosis involving diallel crosses using 8 parental lines - all characters.

Hollyhock: Five F1 hybrids were developed- Pusa pink beauty, Pusa yellow beauty, Pusa pastel pink, Pusa apricot supreme, Pusa pastel pink supreme

BHENDI

Co-2: It is a F1 hybrid between A.E 180 × Pusa Sawani. The crop duration is only 90 days and yield on an average of 16.51 t/ha, Fruits are fairly long with a mean length of 20.60cm, girth of 6.8cm and each wt. 33g. Co-3: It is a high yielding F1 hybrid between Parbhani Kranti × MDU.1. It exhibits moderate resistance to YVMV. The variety has an yield potential of 16-18 t/ha which is 56% more than that of Parbhani Kranti. The fruit is dark green, medium in size and suitable for fresh market.

Tomato• Cross of EC-156 × Marglobe showed high heterosis

for number of fruits per plants that gave 83.18% more yield then better parent.

• High degree of heterosis over better parent for pericarp thickness has been observed in cross of S-14 × Pusa Ruby.

Brinjal:• The cross of Pusa Purple Long × Pusa Purple Cluster

and Erangre × Pusa Purple.• Cluster exhibited high degree of heterosis for yield

and other fruit characters.

Reference:Plant Breeding principles and method – B.D.Singh.Breeding of Horticultural Crops – Dr.N.Kumar.Breeding and Protection of Vegetable – M.K.Rana.Ornamental Crop Breeding – Dr.L.C.De &

S.K.Bhattacharjee.