Discuss the importance of testing of new plant varieties in a geographically vast country like India.
Before the new plants are generated through plant breeding programs, they need to be evaluated for their yield and other agronomic traits of quality, disease resistance, etc.
The testing is done on the farmers' field for at least three growing seasons, at different locations in the country representing all the agroclimatic zones, where the crop is usually grown. The material is evaluated in comparison to the best available local crop cultivar known as a check or reference cultivar.
Define the term 'stress' for plants. Discuss briefly the two types of stress encountered by plants.
Stress for plants can be defined as any external factor that negatively influences plant growth, productivity, reproductive capacity or survival. This includes a wide range of factors which can be broadly divided into abiotic or environmental stress factors like salinity, extreme temperatures, drought, etc., and biotic or biological stress factors.
Discuss natural selection and artificial selection. What are the implications of the latter on the process of evolution?
Natural selection is a gradual, non-random process by which biological traits become either more or less common in a population as a function of differential reproduction of their bearers. It is a key mechanism to evolution.
In natural selection the environment acts as a sieve through which only certain variations can pass.
Artificial selection is a process in which animals and plants with desirable traits are considered by human breeders and favoured for reproduction. It is an artificial mechanism by which evolution can occur.
It is also called selective breeding as it promotes traits that suit human preferences. In contrast to natural selection, here the evolution is intentional or guided.
$$ \text { Discuss briefly how pure lines are created in animal husbandry. } $$
When breeding is between animals of the same breed, it is called inbreeding. If we want to evolve a pureline in any animal, inbreeding (for 4-6 generation) is necessary. It also helps in accumulation of superior genes and elimination of less desirable genes by increasing homozygosity.
What are the physical barriers of a cell in the protoplast fusion experiment? How are the barriers overcome?
Cell wall is the most important physical barrier in protoplast fusion experiments. This can be overcome by treatment with enzymes like cellulase and pectinase which have the ability to digest the cell wall and liberate the naked protoplast surrounded only by the cell membrane.