Tag: breeding and biotechnology

Heterosis is also called as hybrid vigour. It is the increase in such characteristics as size, growth rate, fertility and yield of a hybrid organism over those of its parents. Plant and animal breeders exploit heterosis by mating two different pure-bred lines that have certain desirable traits. Because of this, hybrids are generally found to be superior to their parents. Thus, the correct answer is option B.

 A mutation is a permanent change in the sequence of DNA. Mutations can be caused by external (exogenous) or endogenous (native) factors, or they may be caused by errors in the cellular machinery. Physical or chemical agents that induce mutations in DNA are called mutagens and are said to be mutagenic. Exogenous factors: environmental factors such as sunlight, radiation, and smoking can cause mutations. Endogenous factors: errors during DNA replication can lead to genetic changes as can toxic by-products of cellular metabolism.

Gurdev S. Khush crossed 13 varieties of rice from Oryza nivara to develop IR - 36 which was resistant to grassy stunt virus.

The first step in breeding for disease resistance is identifying and screening the available germplasm to find sources of resistance that can be incorporated into commercial varieties.

Herbicides, also commonly known as weed killers, are pesticides used to kill unwanted plants. Selective herbicides kill specific targets, while leaving the desired crop relatively unharmed. Some of these act by interfering with the growth of the weed and are often synthetic mimics of natural plant hormones. A large number of different herbicide classes inhibit photosynthesis by binding to the quinone-binding protein, D-1, to prevent photosynthetic electron transfer. Mostly they interfere with photolysis of water. Thus, option C is correct. Herbicides does not interfere with water absorption, translocation of sugar and CO$ _{2}$ absorption. Thus, other options are wrong.

The shoot tip culture used for obtaining disease free plant without genetical changes. The plant which affected by any contaminant mostly by viruses have saved by shoot tip culture, because shoot tip of any affected plant is less or free from contamination (viruses, bacteria, fungus or others). Plant shoot tip are more efficient to cultivation or differentiation in-vitro because cells of them newly generated and healthy comparison to other parts. 

Rust of wheat is caused by fungus. Diseased plants show rust coloured orange patches on the infected plant part.

Himgiri is a wheat hybrid variety, which yields 26-30 qtls/ha. It is a disease resistance variety to stripe rust or yellow rust. This is Triticum aestivum species. The variety was developed by IARI. Thus, the correct answer is option A.

Breeding for disease resistance is a comprehensive process that requires identifying a source of resistance, planning the hybridization, and rigorously testing the progeny for resistance.

Mutation breeding is associated with Staddler (4), Inbreeding depression with Shull (5), Pureline selection with Johannsen (1), and Intergeneric hybridization with Karpechenko (2).