The following pages are designed to give an overview of elements within VeGIN that are related to crop genetic improvement. It is hoped that the information will act as a primer for individuals to seek further information.
Crops are susceptible to pests and disease, and with greater volumes being produced the requirement for water and fertilizer increases. Our modern crops have been selectively bred for many centuries and so are not very diverse, genetically. To accommodate increasing environmental pressure, our current crops will need to be adapted to give higher yields to feed a growing population.
In crop genetic improvement we aim to address this by using Diversity Collections to identify new genes and gene combinations that can be introduced into crops, in a natural way using conventional breeding techniques (without using Genetic Modification), but using the most modern tools for selection and analysis.
Traditional plant breeding used selection based on the appearance (Phenotype) of the crop, where the best plants would be kept and used for subsequent crosses, but nowadays plants can be selected based on their DNA profile (Genotype). To do this we use Genetic Markers which indicate small differences in the DNA sequence between individuals (polymorphisms). This can speed up the breeding process considerably and can be more accurate for characteristics that show wide variation depending upon their growth environment.
The phenotype or performance of a plant can be predicted based on its genotype; however, in general the genotype cannot be predicted from the phenotype.
Genetic marker data derived from Breeding Populations, for example a population of broccoli plants, can be used in conjunction with sophisticated computer software to make a Genetic Map of the broccoli Genome. These genetic maps allow the genotype data of individuals in a population to be sorted into groups, and are used with phenotype measurements to link regions of DNA that influence a particular characteristic (trait), such as disease resistance, or post harvest yellowing; this forms the general concept of quantitative trait (QTL) mapping. Genetic markers linked to the region of DNA that influences the characteristic can then be used to screen offspring from the population (sometimes in combination with phenotypic selection) allowing the selection of only the lines that contain the beneficial region of DNA (Marker assisted selection or MAS for short). The pre-selected lines are then assessed in replicated trials to evaluate their agronomic value. This approach is particularly advantageous when the collection of phenotype data is more expensive compared to the collection of genotype data. Caution must be taken when estimating the effects associated with the presence of particular marker genotypes, plus one also must consider if the selected genotypes will still produce the desired effect (phenotype) in different genetic backgrounds and in different growth environments.
Domestication and historical crop improvement have reduced the Genetic Diversity of our modern crops. This genetic diversity can be measured in the DNA at genetic markers. These DNA markers can identify 'exotic' variation in the same regions of DNA within plants from the diversity collections. This 'exotic' DNA variation is that variation that was not captured during the domestication of the ancestors of our modern crop varieties.
Variation may be in the genes, in which case we can measure it by Transcriptome Sequencing. Once relevant genes have been identified, with useful diversity available, this can be used for crop improvement by breeding modern crop varieties with plants identified in the diversity collection.