the Symposium on Wheats for More Tropical Environments - cimmyt

84maturity in most parts of India. In fact,wheat growth duration in various partsof <strong>the</strong> country is determined bytemperature limits.Agronomists and physiologists havefound that, for <strong>the</strong> planting of wheat,average temperatures should be around20 to 22°C. They have also found thatgrain development is adversely effectedif <strong>the</strong> average temperature exceeds25°C. These temperature limitsrepresent <strong>the</strong> limits of crop growthduration. The spring wheats, which arecommonly grown in India, seem to becapable of adjusting <strong>the</strong>ir growthduration to <strong>the</strong>se temperature variations.It is interesting to note that appropriatetemperatures for sowing are reached atmore or less <strong>the</strong> same time throughoutIndia, and <strong>the</strong> recommended dates forplanting are also similar for all partsexcept <strong>the</strong> hills, where <strong>the</strong>y are earlier.Days to flowering offive widely adaptedwheat genotypes in some of <strong>the</strong>representative parts of <strong>the</strong> country aregiven in Table 3, shOWing how <strong>the</strong>number of days is inversely related totemperature.It is obvious from this table that cropduration is reduced to less than half in<strong>the</strong> extremely hot temperatures ascompared to <strong>the</strong> cooler climate of <strong>the</strong>hills. O<strong>the</strong>r unfavorable effects of hightemperature include:• Reduced crop stand;• Rapid entry into <strong>the</strong> reproductivephase, leading to very earlyflowering;• . Reduced tillering due to inadequatevegetative growth;• Reduction in grain size (physiologistshave estimated that <strong>the</strong>re is a 10 to15% reduction for every 5 to 6degree rise in temperature above24°C);• Dessication of <strong>the</strong> leaves;• Changes in disease and pestprevalence patterns, and• ~Low yield.Table 2. Wheat area, production and yield in important wheat-growingstates, India, 1981-82Area Production YieldState (Iakh ha)!.! Uakh tons) (kg/ha)Assam 1.02 1.16 1130Bihar 17.44 25.69 1473Gujarat 7.04 14.07 2000Haryana 15.62 36.82 2357Himachal Pradesh 3.54 4.30 1216Jammu and Kashmir 1.98 2.04 1032Karnataka 3.42 2.30 674Madhya Pradesh 32.93 32.74 994Maharashtra 11.28 9.88 876Punjab 29.17 85.53 2932Rajaithan 17.73 29.42 1660Uttar Pradesh 78.49 128.83 1641West Bengal 2.13 3.0.2 1417Total India 223.08 378.33 1696!of 1 lakh = 100,000