How can the pest resitant plants of tobacco be developed?

Tobacco plants resistant to a nematode have been developed by the introduction of DNA that produces (in the host cells):

How can healthy potato plants be obtained from a desired potato variey which is viral infected? Explain.

Who demonstrated that extract of infected plants of tobacco could cause as Contagium vivum fluidum.

Give the names of variety that are resistant to pests development by hybridisation and selection of Okra

Give the names of variety that are resistant to pests development by hybridisation and selection of Flat bean.

Give the names of variety that are resistant to pests development by hybridisation and selection of Brassica

How did process of RNA interference help to control the nematode from infecting the roots of tobacco plants?

The plant body in higher plants is well differentiated and well developed. Roots are the organs used for the purpose of absorption. Which is the equivalent of roots in the less developed lower plants?

How can the pea plant be prevented from self pollination? How is cross pollination carried out?