Strategies for Enhancement in Food Production Test - 15

Late blight caused by the oomycete, Phytophthora infestans is the most destructive disease in potato cultivation worldwide. New, more virulent P. infestans strains have evolved which overcome the genetic resistance that has been introgressed by conventional breeding from wild potato species into commercial varieties. R genes (for single-gene resistance) and genes for quantitative resistance to late blight are present in the germplasm of wild and cultivated potato. The species Solanum demissum proved to be an important source of resistance, and by conventional plant breeding (crossing and back-crossing) in the 1940s and 1950s this resistance was bred into commercial potato cultivars. Four major resistant genes (termed R genes) were discovered and were introduced successively into commercial cultivars. Thus, the correct answer is option A.

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. Herbicides interfere with photolysis of water, inhibits O2 evolution and also inhibits translocation of organic solutes. Thus, option D is correct.

A biofertilizer is a suspension of the living organism which remains in close association with the soil and increases the fertility of the soil. It is applied to plant surfaces, or soil colonizes the rhizosphere or the interior of the plant and promotes growth by increasing the supply or availability of primary nutrients to the host plant. Blue-green algae is a free living  nitrogen fixing bacteria. So, BGA has been recommended as a biofertilizer. VAM plays a great role in inducing plant growth. VAM are symbiotic entophytic soil fungi, which colonize the roots of approximately 80% plants. VAM also is used as biofertilizer. 

So, the correct answer is option C.

Bacillus thuringiensis (Bt) is a bacteria that can infect and kill insects and thus, it is used as an insecticide. Alfalfa webworms killed by Bacillus thuringiensis. The insecticidal activity of Bt was first discovered in 1911. However, it was not commercially available until the 1950s. In recent years, there has been tremendous renewed interest in Bt.

Meristematic tissue is present at the tips of shoot so it is easy to regenerate it.

Anabaena-Azollae is a small filamentous phototrophic cyanobacteria generally seen as a multicellular organism with two distinct, interdependent cell types. It is a small, circular, photoautotrophic vegetative cell that performs oxygenic photosynthesis and is typically blue green in color. Since it is a phototrophic cyanobacteria, it derives energy for N2 fixation by performing photosynthesis. Thus, option A is correct.

A pyrethroid is an organic compound similar to the natural pyrethrins produced by the flowers of pyrethrums (Chrysanthemum cinerariaefolium and C. coccineum). Pyrethroids now constitute the majority of commercial household insecticides. In the concentrations used in such products, they may also have insect repellent properties and are generally harmless to human beings in low doses but can harm sensitive individuals. Pyrethroids are axonic excitoxins, the toxic effects of which are mediated through preventing the closure of the voltage-gated sodium channels in the axonal membranes. The sodium channel is a membrane protein with a hydrophilic interior. This interior is a tiny hole which is shaped precisely to strip away the partially charged water molecules from a sodium ion and create a favorable way for sodium ions to pass through the membrane, enter the axon, and propagate an action potential. When the toxin keeps the  channels in their open state, the nerves cannot repolarize, leaving the axonal membrane permanently depolarized, thereby paralyzing the organism. So, pyrethroids are largest group of insecticides of plant origin. Thus, option C is correct.