Abstract

The potential yield of crops is diminished by biotic and abiotic stress, therefore constant crop improvement is indispensable for sufficient and secure yields in crops both for now and in the future. The various methods used in crop breeding to improve crops can be categorized into four; selection of plants based on observed natural variations existing among native plants, or landraces or accessions, selection of plants with desirable traits after hybridization or controlled mating from different parents, selection of specific recombinants after monitoring the inheritance of within-genome variation, and the creation and introduction of novel variation into genomes through genetic engineering. Summarily, the core of plant breeding is the selection of better types among variants based on defined goals; like yield and quality of edible parts; ease of cultivation, harvest, and processing; tolerance to environmental stresses; and resistance against pests and diseases (Breseghello and Coelho, 2013). Selection is one of the scientific methods of crop improvement. In fact, cultivated crops emerged from several cycles of both natural and artificial selection (Chahal and Gosal, 2002; Goussard, 2004; Uguru, 2005). Sometimes, selection of plants based on observed variants is the only readily available strategy for improvement of plants, especially for extreme inbreeders; autogamous crops with flowers that are cleistogamous in nature, as other breeding methods are either not feasible or practicable. However, this breeding method is not fascinating as it does not create variability but only act on the natural existing variation. Furthermore, the efficiency of this breeding method depends on the amount of observable genetic variation existing in a population like, individual differences in viability, adaptability, resistance to diseases and pests, large fruit size and other selective values of the breeder; which usually is to select line(s) with good agronomic characters than others. Worse still, some of these traits are environment specific, making this crop improvement method unreliable.