Principles of Quality Seed Production
During seed production strict attention must be given to maintenance of genetic purity and other qualities of seed in order to exploit the full dividends sought to be obtained by introduction of new superior crop plant varities.
Deterioration of varities:
Genetic purity (trueness to type) of a variety can be deteriorating due to several factors during production cycles.
The important factor & real deterioration of varities listed by Kadam (1942) & these are
Minor genetic variations
Selective influence of diseases
The technique of plant breeder
Mechanical mixtures, natural crossing and selective influences of diseases are most important reasons for genetic deterioration.
Mechanical mixture may take place at the time of sowing, it more than one variety is sown with same drill or through different varieties grown in adjacent field.
Two varities growing alongside each other the field are often mixed at the time of harvesting and threshing operation. Threshing equipments (i.e. threshing machine) is often contaminated with seeds of other varities.
The gunny bags, seed bines are also quite responsible mechanical mixture with seeds of other varities.
To avoid mechanical mixture, it must be necessary to rogue the seed fields and care should be taken at the time of harvesting, threshing and handling.
In sexually propagated crops, natural crossing is most important source of vertical deterioration.
The deterioration in varieties due to natural crossing is of three reasons
Natural crossing with undesirable type
Natural crossing with diseases plants
Natural crossing with off- type of plants
According to Bateman (1947) genetic contamination is seed field due to natural crossing depends upon the some factors and these are
The breading system of species
As the isolation between varieties is increased the contamination decreases. Isolation of seed crop is a primary factor in the seed production of crop plants of cross pollinated by wind or insects and their activities, humidity and temp. at the time of anthesis etc.
Selective Influences of Diseases:
New crop varieties often become susceptible to new races of diseases often caused by parasite.
Some vegetative propagated stocks deteriorate fast it infected by viral, fungal and bacterial diseases. It is very important to produce diseases free-seeds /stocks.