Breeding and Seed Production of Ornamental Crops

Utilization of male Sterility

Introduction:

• For the production of F₁ hybrid seeds under open field conditions by using genetic male sterility, the requirements are:

• an inbred line which is to be used as male parent.
• another inbred line which is maintained by crossing together known heterozygous (Ms ms) and male sterile (ms ms) plants i.e. femina line.

 
• Male sterility is governed by a single recessive gene and therefore the maintenance of the genetic stock is difficult as there will be continuous segregation of the fertile and sterile individuals in 1:1 proportion.
• This phenomenon is present in Tagetes, Zinnia, Delphinium, Antirrhinum, Calceolaria, Salvia and Impatiens.

Male sterile flower of Zinnia

• Seeds should always be harvested from (ms ms) plants
• The cross of ms ms x Ms ms should be repeated in every generation, as it will segregate in 1 Fertile: 1 Sterile ratio.
• For maintenance of male sterility, a ratio of male sterile line to pollinating fertile line is dependent on the size of hybrid block, but ratio of 3 male sterile: 1 male fertile has proved to be the optimum.

Male sterility for hybrid seed production in flowers:

• Ageratum: In this annual crop, both the male sterility and self incompatibility systems are prevalent and a choice can be made on the basis of economy in the seed production.
• Petunia: In petunia, cytoplasmic male sterility has been observed but the use of this type of male sterility is not so practically common because of breakdown of male sterility in the maternal parent or malformation of flowers in F₁ generation.
• Sunflower: Male sterility in sunflower has been used to produce ornamental varieties like 'Sunrich Orange' (Japan) and 'Orit' (Israel) which have no pollen grains and allergic effects like in other male fertile varieties grown for their seed.
• Marigold: Male sterility has been extensively utilized for the F₁ hybrid seed production in marigold. The notable hybrids developed in India with the use of male sterility are 'Pusa Narangi Gainda' and 'Pusa Basanti Gainda'.

Characteristics of male sterile line/ femina line

• Used as a female parent in the hybridization programme.
• Male sterility should be stable.
• It should have desirable traits.
• It should have synchronous flowering with the male parent i.e. pollinator and maintainer plant
• Its genetic constitution is homozygous recessive (msms)

Male Sterile line of marigold

Characteristics of tester parent

• Used as a male parent in the hybridization programme.
• Pure with uniform population i.e. an inbred or pureline
• It should produce abundant pollens.
• Synchronous flowering with male sterile plants
• Its genetic constitution is homozygous dominant (MSMS)

Tester line of marigold

Characteristics of maintainer line

• Used for maintenance of ms-line.
• Its genetic constitution is homozygous (Msms)
• Synchronous flowering with male sterile plants.