1. GENETIC ENHANCEMENT OF PLANTS. INTRODUCTION

The genetic improvement of plants consists in creating new varieties from existing varieties (genetic diversity) . This gene transfer is done by directed crosses and selection of the best plants from these crosses (this requires knowledge of reproduction methods ). Other means of creating successful varieties exist including mutagenesis, protoplast fusion, transgenesis and somatic variations.
Genetic improvement of plants is the process by which humans modify a given plant species by expelling the previously existing genetic diversity. By tapping into diversity, humans recombine genes by several methods including directed crosses. He then practices a selection (sorting) and a multiplication of the plant material carrying the agronomic traits desired. The listing of the improved varieties precedes the marketing of the final products.

Historical references of genetic improvement of plants:
– 1676 . Discovery of the role of sex organs in plants by Millington-Grew.
– 1880 . Visualization of chromosomes by Strasburger-Boveri, and evidence of their involvement in cell division.
– 1900 . Enforcement of Mendel’s Laws on Heredity. His work on the crossing of two pea varieties defines the basic rules of genetics. This is the birth of plant breeding.
– 1902. Discovery of the totipotency of plant cells by Haberland. A plant tissue is able to regenerate a plant.
– 1908 . Discovery of the interest of hybrids by Shull on corn. The crossing of two lines makes it possible to obtain a hybrid that exploits heterosis.
– 1911 . Genetic linkage concept by Morgan. It demonstrates that genes are linearly placed on chromosomes and that, when located on the same chromosome, they are transmitted to the offspring as a single unit. They are said to be linked
– 1930 generation of variety by mutagenic treatments (X-rays)
– 1935 . First partial genetic map of maize by Emerson.
– 1950 . First techniques of in vitro culture . This is the vegetative propagation technique developed by Morel and Martin on the potato.
– 1953 . Description of the double helix structure of DNA by Watson and Crick.
– 1960 . Discovery of the genetic code by Crick, Nirenberg, Mathaeri and Ochoa, beginning of the green revolution
– 1961.Illustration of the principles of analysis of the loci involved in the variation of quantitative characters, by Thoday
– 1964 . First cultures of male sex cells in Datura innoxia , by Guha and Maheshwari. They pave the way for the production of haploid plants.
– 1965 . Discovery of restriction enzymes by Aber, Smith and Nathans. These proteins cut DNA at particular sites.
– 1975 . Description of the method of Southern, the name of its inventor. The principle of the technique relies on hybridization of the DNA with a labeled DNA probe.
– 1977. Discovery of gene transfer by Agrobacteria, pathogenic soil bacteria of many plant species, by Schell. He showed that the virulence of these bacteria is due to a transfer of genes from the bacterium to the plant cells.
– 1978 . First protoplast melting by Melchers. They allow to partially cross the barrier between species.
– 1983 . Development of the PCR by Karry Mullis and first transgenic tobacco obtained at the same time by a Belgian team and an American team
– 1985 First variety of wheat resulting from the technique of haplodiploïdation
– 2000: Sequencing of the genome on a brassicaceae ( Arabidopsis thaliana )
– 2002 : Sequencing of the genome of the rice

Domestication of plants and beginning of agriculture
Since the beginning of agriculture, the farmers keep, at each generation, the seeds of the most beautiful plants, in order to replant them the following year.

Keeping the best seeds gradually leads to an improvement of the cultivated species. The domestication of wild varieties is accompanied by a selection of useful traits such as:
– Size of consumable parts (seeds, tubers)
– Flavor
– Resistance to stress
– Other traits

The evolution of current techniques and knowledge has allowed plant breeders to increase their efficiency, save time on vegetative cycles and to have tools of measurement and analysis in the field and in the laboratory (biology, biochemistry, statistics , biotechnologies) to confirm their choice.

2. GENETIC IMPROVEMENT OF PLANTS. EXAMPLES OF ACHIEVEMENTS

Rapeseed ( Brassica napus ), called canola in Canada, is a crucifer grown primarily for its seeds, which contain about 50% of a good quality nutritional oil (high in unsaturated fatty acids). After extraction of oil, the rest of the seed (cake), rich in protein (40% of the dry matter) is used in animal feed. There are also fast growing forage varieties used for green feeding, grazing or silage. Rapeseed oil also has industrial applications such as the manufacture of fuel (esterification with methanol).

The glucosinolate called sulfur glycosides or ‘ thioglycosides ‘ are organic compounds responsible for the bitter taste or pungent many common foods such as mustard, radishes, watercress, cauliflower. In rapeseed, glucosinolate degradation products were responsible for significant physiological inappetence and physiological disorders in cattle

Rapeseed has a double genome since it comes from the natural crossing of a cabbage and a shuttle .

3. VARIETAL CREATION. PRE-REQUIRED FOR THE BIRTH OF NEW VARIETIES

The creation of variability (and at the same time creation of new varieties) can be achieved by:
– Intra-specific or interspecific directed crosses for the improvement of current species or the creation of new species or possibly by in vitro culture of immature embryos. Several studies refer to trials of interspecific crosses .
– Mutagenesis by physical agents (X-rays, gamma) or chemical (MSE) on seeds, meristems, pollen.
– Frequent somatic changes in in vitro culture practicesfrom fragments of differentiated organs, isolated cells or protoplasts.
– Fusion of protoplasts (isolated cells without pectocellulosic wall).
– Transgenesis concerning gene transfer by genetic engineering.
The modification of a genotype can be done on a qualitative scale by changing the nature of the genes that control the desired traits (color, resistance to diseases, ..) and by acting on their assembly. It can be practiced on a quantitative scale by modifying the dosage of genetic information by increasing or decreasing the number of chromosomes of a species.