Wheat normally needs between 110-130 days between sowing and harvesting, depending upon climate, seed types and soil conditions. Knowledge of stages is also important to identify periods of high risk from the climate. For example pollen formation from the mother cell and the stage between an thesis and maturity are susceptible to high temperature and this adverse effect is made worsen by water stress (23, 24). Several systems exist to identify crop stages with the Freekes and Zadoks scales being the most widely used.
Harvesting of the crop began in Sindh and South Punjab in late March and expected to continue till mid June in North Punjab. Harvesting of wheat and other Rabi crop in rain-fed area will begin after May 15. At harvesting time, what stalks begin to bend over from the weight of their kernels, and the entire plant has become golden in color. After wheat is harvested form the field, machinery separates the stalks and chaff away from the kernels. The stalks and chaff often are used in applications ranging from mulch to animal bedding.
The germination of seeds is affected by temperature, water availability, oxygen, light, and substrate, maturity of seed and physiological age of the seed. Various plants require different variable for successful seed germination. This also linked with individual seed variety and ecological conditions of plant natural habitat. The minimum water content required to wheat germination is 35% to 45% by weight. Air is composed of 20% oxygen, 0.03% Carbon di oxide and 80% Nitrogen and seeds of most plant species germinate well in and environment providing this mixture of gases. The optimum temperature for germination is 12 to 250C .Specific seed often have a temperature range within which it will germinate. Winter wheat requires exposure to cold temperature to enable flowering. This process is termed vernalization. This is the acquisition of a plant ability to flower in the spring by exposure to the prolonged cold of winter.
Factors affecting seed quality of pre and post-harvest seed
Precipitation prior to harvest can result in to pre-harvest germination. It is also result in to attack of fungi Cladosporium and Alternaria. Immature seed harvesting having lot of moisture develop microflora grown in the seed lot. If mechanical damage occurs during cleaning, dressing with chemicals, seed treatment, bagging, transportation of seed result in to lost the seed quality. 12% is the ideal moisture for harvesting of wheat. The correct chemical and doses are used when seeds are treated with fungicides and insecticides. Other wise seed may show symptoms of phytotoxicity.