INTRODUCTION

Crop plants carry information acquired during their evolution and breeding that defines their performance in agricultural fields. That information is held in the genetic material of living plants and is subject to change through mutation and through recombination into new patterns, and can be lost. Proper management of this resource involves knowing the capabilities of germplasms, maintaining and improving their genetic constitution, and employing them advantageously in farming.

Terminology relating to genetic resources is in a state of flux. Here we use germplasm to denote the totality of genes and genetic combinations found in a species, or a major portion of it. A genetic population (sometimes ‘line’ or ‘strain’) describes a smaller group of individuals (plants or seed) that share common ancestry and genes, and thus common traits. This use of the term population differs from that of population ecologists, who use it to denote closely related individuals that cohabit in time and space.

GENETIC DIVERSITY IN AGRICULTURE

Species diversity

Genetic diversity in farming must be defined at several levels. At the species level, thousands of plant species have been cultivated by humans at some time or place, and several hundred are currently employed as crops, yet the great majority of crop production is derived from only a small number. Data presented in Table 4.1 account for most of the production from the arable lands and permanent crops.