Discuss the two main limitations of plant hybridisation programme.
The limitations of plant hybridisation programme include
(i) Availability of a limited number of identified disease resistant genes that are present in various crop varieties or wild relatives.
(ii) Compatibility of parents.
(iii) Time consuming and tedious process.
Interspecific crosses are rare in nature and intergeneric crosses almost unknown. Why?
In interspecific crosses, male and female animals of two different related species are mated. In some cases, the progeny may combine desirable features of both the parents, and may be of considerable economic value, e.g., the mule.
An interspecific hybrid's fertility varies. Many of Panthera (ligers, tigons leopons etc.) hybrid males are infertile, while the female counterparts can breed with the species she contains (female ligers can breed with a lion or a tiger to produce li-ligers or ti-tigers). These are rare in nature.
Intergeneric hybridisation is the crossing of two different animals/plants of different genus. It is almost unknown in nature. Intergeneric hybrids more or less never form complete zygotes/embryos. These are sterile/infertile.
Differentiate between pisciculture and aquaculture.
Fish farming in isolated water bodies is called pisciculture.
Similarly, when culturing of aquatic plants and animals is done in freshwater bodies, it is called aquaculture.
$$ \text { Give two important contribution of Dr. MS Swaminathan. } $$
Contributions of Dr. MS Swaminathan are as follows
(i) Introduction of short, high yielding varieties of wheat in India.
(ii) Development of short duration, high yielding varieties of rice.
The term 'desirable trait' can mean different things for different plants. Justify the statement with suitable examples.
The desirable trait can be different for different for different plants. The breeders have tried to incorporate these into crop plants. The list may be as follows
(i) Increased tolerance to environmental stress (salinity, extreme temperature, drought) e.g., hybrid maize, jowar and bajra which are resistant to water stess.
(ii) Resistance to pathogens (viruses, fungi and bacteria) e.g., moong bean (resistance to yellow mosaic virus and powdery mildew).
(iii) Increased tolerance to insect pests. e.g., a new variety of Brassica (rapeseed mustard) is resistant to aphids.
(iv) High-yielding and improved quality of crop plant. e.g., Atlas 66 used as a donor for developing wheat varieties with improved protein content.