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Reducing evolution period of wheat
Sardar Riaz A. Khan
Wheat is the major staple food crop of Pakistan and occupies nearly 38 per cent of the total cultivated area of the country. Evolution of high yielding wheat varieties by the wheat breeders has brought a green revolution in the country which has now changed from a chronic importer of wheat to an exporter during the last couple of years thus saving its annual import ranging between 2-4 million tons causing heavy drain on our national exchequer.
However, a newly developed high yielding variety of wheat becomes obsolete after a few to several years depending upon its inherited characters .Consequently development of new varieties of wheat is a continuos process for replacing the depleted older varieties for sustainable wheat production in the country.
But at the time of establishment of Pakistan in 1947, 8-10 years were taken for making a cross between two parents and eventual release of a new wheat variety. For instance when a high yielding parent is crossed with a high disease resistant parent to obtain a high yielding and disease resistant variety, the first generation hybrid contains three types of plants possessing only high yielding character inherited from one parent ,only disease resistant character inherited from the second parent and those possessing both the combined characters of high yielding and disease resistant inherited from both the parents.
The seed of plants possessing only high yield or disease resistant characters are rejected. But the seed of those plants possessing the combined characters of high yield and disease resistance are selected for taking the second generation. The second generation again gives these three types of plants with increased number of plants possessing the combined characteristics of high yield and disease resistance. These are again selected for growing third generation.
Thus it takes 4-6 years to develop a 100 per cent pure wheat stain having both the high yielding and disease resistance characteristics. Such wheat strains are then further tested at government research farms and the farmers' fields under different ecological conditions. A strain giving consistently best performance throughout the test period in a given ecological zone is selected as a new variety for the farmers of that zone .Thus , it used to take 8-10 years to develop a new wheat variety.
Again ,the normal planting season of wheat in the canal colonies of Pakistan varies from the middle of October to the third week of November .Thereafter, late sowing may continue through early January .Earing generally starts from the middle of February and the spikes ripen in April or early May. Consequently, the wheat breeders could raise only one generation during this growing period till early sixties .
Fortunately, the Hill Agricultural Research Station was established in Kaghan hills at an elevation of 6000ft in 1964. It was essentially a facility where an off- season summer wheat crop could be grown, thus allowing a quicker advance of breeding material, increase of seed of promising lines and screening against diseases .
This station enabled the wheat scientist of various provincial wheat research institutes to cut short the varietal evolution period by 3-4 years . It resulted in rapid release of high yielding varieties of wheat. This single factor was one of the major reasons for boosting the national average wheat yield of 1025kg per hectare in 1975-76 to 2491kg per hectare in 1999-2000 .
However, there is a good potential of taking three generations of a wheat genotype in one year under the conditions obtaining in Pakistan , thus further reducing the period for the evolution of a new high yielding wheat variety. For instance, the sowing of first generation of a wheat genotype could be initiated on September 15, at Faisalabad in the Punjab plains .
This September planting forced them to ear in November or early December which is the normal planting time in the plains of Pakistan .The green spikes of each genotype could be harvested when the kernels develop to about one-half of their fully developed grain size. The immature green seeds in the green spikes be sun-dried for about 2-3 weeks or dried at 30-40C0 in temperature controlled cabinet for seven days and be replanted in December or early January during the same growing season in the plains .
The seed of this second generation plants raised from immature seed could be harvested in May .The loss in the grain weight and size of prematurely harvested kernels of the first generation was virtually retrieved in the progeny seed inspite of its late sowing . The seed of this second generation thus obtained could be then planted in May-June in Kaghan hills to get the third generation crop in the end of early September . There is no difference in the crop grown from fully mature seed and that taken from the immature seed .
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Pakissan.com;
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