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

Introduction

Introduction

• F₁ hybrids are the result of crossing of two homozygous but genetically distinct parental lines. Hybrid vigour is defined as the increase in the size or vigour of a hybrid over its parents.
• Shull (1911) gave his idea and coined the term heterosis and explained hybrid vigour in connection with the optional uniformity, a heterozygosity giving rise to the strong, segregation of characters in F₂ and necessity of being reproduced by constant new crossing of two parental lines bred to homozygosity.
• Hybrid vigour is entirely due to bringing together, a large number of favorable dominant genes contributing to vigour in the first generation period. F₁ hybrids are of immense importance particularly in floricultural crops where the hunt for new flower colors or yield is unending
• F₁ hybrids in ornamental crops were known even before Shull propounded the classical theory of hybrid vigour in plant breeding for the first time. Hybrid variety 'Prima Donna' in begonia (Begonia semperflorens Link et Otto) was probably the first F₁ released in floricultural crops by Benary Seed Company in Germany in 1909.
• The breeding for F₁ hybrid seed production, however gained importance only after 1942 and onwards when Japan produced the first commercial F₁ hybrids in Petunia.
• Later, F₁ hybrids were produced in flower crops like Ageratum, Anemone, Gerbera, Primula, Petunia, Tagetes, Cyclamen, Pansy, Begonia, Geranium, Portulaca, Dianthus, balsam, stock, wall flower, ornamental sunflower (Helianthus annus), Gazania, hollyhock, Calceolaria and Zinnia by several seed companies in the U.S.A., China, Japan, the Netherlands, Denmark, Germany, the United Kingdom and Israel.
• For the production of F₁ hybrid we require purelines in self pollinated species or inbred lines in case of cross pollinated species.
• A pureline is the progeny of a single, homozygous, cross pollinated plant.
• An inbred line is the progeny of a single, homozygous self pollinated plant.

Advantages of F₁ hybrids

• All the F₁ hybrids resulting from a cross are uniform in growth and yield.
• They show a greater vigour over parents which is expressed in terms of yield and other targeted desirable traits.
• Since the genetic constitution of F₁ hybrids is constant and show homozygous, they show greater adaptability to different environmental conditions.
• Breeder has all the control of the F₁ hybrids produced by him/her as the parental lines are maintained by the breeder.
• The variety shows stability over a period of years.

Techniques for the production of F₁ hybrid seeds

• The conventional method of F_l hybrid production involves selection of inbred lines for desired characters, testing their combining ability and production of hybrid seeds, evaluation of F_l hybrid performance. However there are special techniques which can be exploited for F_l hybrid production in ornamentals e.g. use of femina lines in marigold.

Two basic requirements for hybrid seed production are:

1. Easy emasculation of the female parent
2. Effective pollen disposal from the male parent to ensure a satisfactory seed set in the female parent.

Both these factors are largely governed by the floral structures of the crop species in question.