Since the dawn of time, humans have consciously and unconsciously improved the plants they grow for food and the animals they raise. The concept is simple: breed from plants and animals which have desirable characteristics, and produce an offspring which combines the best qualities of its parents. Selecting plants with larger seeds, stronger stems and a healthier appearance has come naturally to farmers since they first domesticated food crops. Equally, animals have been bred for qualities which the farmer requires: wool length and quality in sheep, muscle growth or udder size in cows, and strength or speed in horses.
The Austrian monk Gregor Mendel is recognized as the pioneer of genetic science. He demonstrated, through pollinating different types of peas with each other, that genetic characteristics are inherited and that new varieties can be produced that share the traits of both parents. For a more detailed description of Mendelian genetics, see: http://en.wikipedia.org/wiki/Gregor_Mendel  and http://en.wikipedia.org/wiki/Mendelian_inheritance 
Hybridization is the process in agriculture of breeding new, hardy and disease-resistant crops. It involves crossing two genetically different individuals to result in a third individual with a different and often preferred set of characteristics. A full explanation can be found here: http://lifeofplant.blogspot.com/2011/03/hybridization.html 
Farm Radio Weekly has covered variety choice several times. Two stories in this vein come from Kenya, including last issue’s (#240) article about upland rice: (http://weekly.farmradio.org/2013/03/24/kenya-upland-rice-gives-hope-to-small-scale-maize-farmers-by-sawa-pius-for-farm-radio-weekly-in-kenya/ ) and this one about new wheat varieties: http://www.barzaradio.com/content/kenya-farmers-optimistic-about-new-wheat-varieties-irin-0 
A Notes to broadcasters on new varieties of cassava which can be found here: http://weekly.farmradio.org/2013/02/04/notes-to-broadcasters-on-new-cassava-varieties-2/ 
A script from July 2001 suggests one way of introducing, on radio, the subject of selective breeding for favourable characteristics: http://www.farmradio.org/radio-resource-packs/package-60-local-knowledge-for-local-radio/indigenous-knowledge-and-livestock-raising/ 
This story may inspire you to produce a program on the advantages and disadvantages of growing new varieties. Here are some general questions to get your research started. You could interview farmers, seed merchants, researchers or NGO staff.
-Under what circumstances are new varieties beneficial?
-What benefits have farmers seen with new varieties?
-Why do farmers choose newly bred varieties?
-What are the main drawbacks – for example, do farmers need to buy seed each year?
-Are any farmers returning to traditional varieties instead of seeking seeds of new varieties?