Cause of varietal deterioration and maintenance of genetic purity during seed production
” To maintain genetic purity of seeds, seed should be certified by seed certifying agency and experienced technicians, which help to increase productivity of crop and reduce crop failure. “
Genetic purity define as true to type or doesn’t contaminate with other crops seed and weed seeds. The production of genetically pure seeds that contain proper moisture for long duration storage involves high technical support and it is done by seed certifying agency.
Comparatively heavy financial investment require for production of genetically pure seed and it should be certified by seed certifying agency. Quality seeds are the basic inputs of crops. It helps in increase in crop productivity by 20 – 30% and reduce seed requirements. Also, reduce chance of weeds, disease, insect /pest and cost of input reduce.
Hartman and kester (1968)and Aggrawal(1980) describe steps to maintain the genetic purity of variety during seed production
Main causes of varietal deterioration
- Developmental variation : Several consecutive generation’s developmental variations may set in different growth responses when seed crops are grown under environment with differing soil fertility, climate, photoperiod. So, variety should be grown in their areas of their natural adaptation.
- Mutation : varietal deterioration caused by minor & detectable mutation which can be control by removing the detectable mutants by rouging.
- Mechanical mixture : varietal deterioration also caused by mechanical contamination during sowing, harvesting, threshing, processing, & handling of seeds. It can control by rouging the seed field of different stage of crop.
- Natural crossing : It is an important source of varietal deterioration in cross pollinated crops. Deterioration sets due to natural crossing with undesirable types, diseased plants. It depends on breeding system of species, isolation distance, varietal mass & pollinating agent. The isolation of seed crops is the most important factor in avoiding contamination of the cross-pollinated crops. The direction of prevailing wind, the number of insects present and their activity, and mass of varieties are also important consideration in contamination by natural crossing.
- Selected influence of disease and pest : Disease affects seed size due to poor supply of carbohydrates from infected photosynthetic tissue. Soil & seed borne disease affect in commercial purpose of plants. Disease, insects/pest resistant variety grow to reduce chances of crop failure.
- The techniques of the plant breeder: serious instabilities may occur in varieties owing to cytogenetic irregularities in the form of improper assessment in the release of new varieties. Premature release of varieties, still segregating for resistance and susceptibility to disease or other factors can cause significant deterioration of varieties. This failure can be attributed to the variety testing programme.
- Minor genetic variation : It can occur even in varieties appearing phenotypically uniform and homogeneous when released. So, the care during the maintenance of nucleus and breeder’s seed of cross pollinated varieties of crop is necessary.
Following are the major ways to maintain genetic purity during seed production
- Control of seed source : seed must be certified by the seed certifying agency. There are five major class of seeds i.e. Nucleus seed, breeder seed, foundation seed, certified seed, improved seed. Among them nucleus seeds and breeder seeds are used for genetically pure seed.
- Isolation : crop field must Isolate to reduce natural crossing & mechanical mixture with undesirable weed seeds or other crops seeds in field.
- Field inspection : Qualified, trained & experienced personnel should be employed to inspect crop at different growth stages & to verify seed
- Rouging: Rouging means removing unwanted plants. Rouging of undesirable plants differ on the basis of their characters of those of seed variety is very important.
- Adaptation of crops: crop should be grown only in area where they can adopt to avoid development variation.
- GOT: Periodic testing of varieties for genetic purity.
- Approved class of seeds: Use only approved class of seed in seed multiplication and adopt generation system.
Genetic purity tests are critical tools for seed producer and plant breeder. The genetic purity of a the varietal deterioration due to several factors during production cycles cause reduction in production and quality of crop which can be maintain by isolation, rouging, field inspection etc.