Inbreeding is the mating of relatively close blood relatives. In plant breeding, this is done by self-pollination (self-fertilisation) and crossing of close relatives in order to obtain inbred lines that are as genetically homozygous (pure) as possible. In animal breeding, inbreeding occurs through sibling mating and back mating. The measure of inbreeding is the inbreeding coefficient. Inbreeding depression stands for the loss of genetic fitness and performance due to the continuous crossbreeding of individuals of the same lineage. The effect can occur when crossing new grape varieties if positive characteristics of a variety are to be strengthened and therefore ancestors are continuously crossed.
However, inbreeding effects also occur when the berry seeds produced by 98% self-fertilisation during vine flowering are sown and grow into a seedling. In the course of evolution, many thousands of new varieties have emerged naturally, from which humans have then selected the best (for example, the highest-yielding, most resistant and most flavoursome). However, this is not usually the case in viticulture today because propagation is not generative (sexual), but vegetative through the division of a plant.
Advantages and disadvantages
Inbreeding leads to more and more alleles becoming homozygous or homozygous, i.e. equally present in both diploid chromosome sets. According to Mendelian rules, inbreeding also causes recessive genes of the genotype to appear in the phenotype. The consequence of inbreeding is therefore an increase in the probability of the homozygous occurrence of extremes in both directions, i.e. both possible pathological and particularly efficient gene combinations.
It is not uncommon for genetically pure-bred organisms to exhibit lower vitality and resistance to disease, as the genetic information in both sets of chromosomes is the same and therefore fewer different genes are present (inbreeding depression). On the other hand, breeding consists of utilising the positive side of inbreeding by combining targeted inbreeding with selection of the most suitable and best types.
Hermaphroditic flowering
In nature, many plants protect themselves against the negative effects of inbreeding by means of a molecular mechanism. A highly diverse gene destroys the pollen (pollen) that has the same genotype as the mother plant. This means that if the pollen comes from the plant itself or from a close relative, the plant cannot be successfully pollinated. In viticulture, however, self-fertilising hermaphrodite flowers are used because the aim is yield and not the production of offspring. Their flower buds contain both male and female organs.
Heterosis effect
Fitness is the adaptation to the environment (in plants, e.g. resistance to pests, diseases, frost or drought). If closely related plants are repeatedly crossed with each other, the same genetic information is passed on. As a result, only certain alleles (gene segments) are passed on. The gene pool of the corresponding population or species is thus constantly reduced. Among other things, this causes a decrease in vigour, lower yields, later budding and susceptibility to various vine diseases (see also vine enemies). Modern plant breeding is strongly focussed on heterozygous (heterozygous) individuals. Mixed offspring (hybrids) of two homozygous parents are more resistant and produce higher yields, which is known as the heterosis effect.
Further information
For more information on this topic, see also flowering, chromosome, DNA, crossing, new breeding, grape variety determination and breeding, as well as lists of relevant keywords under the keywords vineyard and grapevine.
Source: WIKIPEDIA Inbreeding
