Plant Propogation and Nursery Management

Clone

The term clone may be defined as a group of genetically uniform individuals, derived originally from a sexually produced individual or from mutations and maintained exclusively by asexual means from one ancestor.

• The common examples are Bartlett pear, Delicious apples, Sultana grapes and Dashehari mango.
• The goal of vegetative propagation is to reproduce progeny plants identical in genotype to a single plant. The biological process is known as cloning and the resulting population of plants is called a clone.
• The uniformity of individual plants, within a clonal population is a major advantage of clonal cultivars of fruit and nut crops.
• Clonal propagation helps in fixing genotypes, uniformity of population, facilitates propagation and reduces juvenile phase, combine more than one genotype into single plant (grafting) and control phases of development.
• If environmental conditions are favourable and the clone is managed properly, its trueness-to-type can be maintained for hundreds of years.
Genetic variations in a clone

Mutation
Mutation is a single-step genetic change or sudden heritable change within cells of a clone. In general, these changes take place spontaneously, in the plants regular but rare intervals.

• A mutation is a genetic change involving some part of the DNA molecule. Genetic mutations result from structural changes in the nuclear DNA of the chromosome in the nucleus. DNA also occurs in mitochondria and chloroplasts and defects here can produce genetic changes.
• Chromosomal changes may be due to chance rearrangement of the four bases in the DNA molecule (point mutation) rearrangement of different parts of the chromosomes (deletion, duplication, translocations and inversions), addition or subtraction of individual chromosome (aneuploidy), or the multiplication of entire set of chromosome (polyploidy).
• The rate of mutation can be increased by treatment with specific mutagenic agents e.g. X-ray, gamma rays and certain chemicals.
Bud- sports or bud mutations
When mutation occur and suddenly appear as a chance in the branch of a plant, is called bud sport or bud mutations, because they appear to have originated within a single bud.
• Detection of a new mutant within a clone may require a series of vegetative propagated generations and multiple propagations from many buds of the same plant.
• Many ‘sports’ have become commercial cultivars. Mutations may affect fruit (colour, shape, time of maturity), tree structure (spur type), time of bloom, and as a host of other traits. Sometimes these mutants have highly useful horticultural traits and have given rise to important new cultivars (‘Ruby Red’ grapefruit, red coloured sports of apple and pear.)
• On the other hand, mutations may be undesirable and give rise to misshapen fruits, low production and susceptibility to diseases.