Minor genetic variations

Minor genetic variations may exist even in the Varieties appearing phenotypically uniform and homogeneous at the time of their release. During the later production cycle, some of this variation may be lost because of selective elimination by the environment. To overcome these yields trials are suggested.

a) Selective influence of diseases: The selective influence of diseases in varietal deterioration is also of considerable importance. New crop varieties often become susceptible to new races of diseases caused by obligate parasites and are out of seed programs. Similarly, the vegetatively propagated stocks deteriorate fast if infected by viral, fungal, and bacterial diseases. During seed production, it is, therefore, very important to produce disease-free seeds/stocks.

b) Techniques of plant breeders: In certain instances, serious instabilities may occur in varieties due to cytogenetic irregularities not properly assessed in the new varieties before their release. Other factors, such as a breakdown in male sterility, certain environmental conditions, and other heritable variations may considerably lower the genetic purity.

c) Maintenance of Genetic Purity During Seed Production:

• The various steps suggested, to maintain varietal purity, are as follows.

i) Use of approved seed only in seed multiplication.

ii) Inspection and approval of fields before planting.

iii) Field inspection and approval of growing crops at critical stages for verification of genetic purity, detection of mixtures, and weeds, and freedom from noxious weeds and seed-borne diseases etc.

iv) Sampling and sealing of cleaned lots

v) Growing of samples of potentially approved stocks for comparison with authentic stocks.