Conventional Plant Breeding Principles and Techniques

Abstract

Conventional plant breeding is the development or improvement of cultivars using conservative tools for manipulating plant genome within the natural genetic boundaries of the species. Mendel's work in genetics ushered in the scientific age of plant breeding. The number of genes that control the trait of interest is important to breeders. Qualitative traits (controlled by one or a few genes) are easier to breed than quantitative traits (controlled by numerous genes). General steps in breeding are: objectives, creation/assembly of variability, selection, evaluation and cultivar release. Breeders use methods and techniques that are based on the mode of reproduction of the species self-pollinating, cross-pollinating, or clonally propagated. The general strategy is to breed a cultivar whose genetic purity and productivity can be sustained by its natural mating system. There are six basic types of cultivars: pure line, open-pollinated, hybrid, clonal, apomictic and multilines. The common methods for breeding self-pollinated species include mass selection, pure line selection, pedigree, bulk population, single seed descent, backcrossing, multiline and composite. Methods for breeding cross-pollinated species include mass selection, recurrent selection, family selection and synthetics. Hybrid cultivar breeding exploits the phenomenon of heterosis, and is applicable to both self- and cross-pollinated species. Polyploids have complex genetics. Hybridization of parents is often accompanied by infertility of the hybrid. Mutation breeding may be resorted to when the gene of interest is non-existent in nature and may be induced. Also, sometimes, the desired trait is found in wild relatives of the species and may be introgressed into cultivated species through pre-breeding.