the Symposium on Wheats for More Tropical Environments - cimmyt

66In <strong>the</strong> central and peninsular parts of<strong>the</strong> country. wheat is cultivated underrainfed conditions. In most of India.although <strong>the</strong> monsoon rains end byabout <strong>the</strong> middle of September. wheatcannot be sown until <strong>the</strong> end of Octoberor <strong>the</strong> beginning of November, whentemperatures make seeding possible.During <strong>the</strong> intervening period. <strong>the</strong>re issevere loss in soil moisture. A numberof cultural practices are recommendedto conserve moisture but. in manyfields. moisture levels in <strong>the</strong> upperlayers become so depleted thatachieving good plant stands becomesalmost impossible.None of <strong>the</strong> improved varieties iscapable of being sown earlier thannormal. as such sowing leads to severehigh temperature symptoms. In recentyears. attempts have been made toidentify genotypes which show aminimum of adverse effects from hightemperatures when wheat is seededearly. Some of <strong>the</strong>se are Hindi 62. Raj1771. Raj 1777. HIlOll. HIl012 andVL616. These varieties possess somesort of temperature insensitivity and donot show reduced tillering or decreasedvegetative phase. and <strong>the</strong>y give goodplant establishment and growth. Thesematerials are being used as sources fordeveloping superior strains for earlySOWing. In fact. VL616 has recentlybeen recommended for early sowing in<strong>the</strong> hills; however. high temperaturesare not a serious constraint <strong>the</strong>re. Themain purpose of its release is to escapefrost damage to floral parts. which isacute if ears emerge dUring <strong>the</strong> verycold temperatures of December toFebruary. Most of <strong>the</strong> improvedvarieties show early ear emergencewhen planted prior to <strong>the</strong> end ofOctober. even in <strong>the</strong> hills. In <strong>the</strong>development of VL616. one of <strong>the</strong> genesgoverning vernalization response hasbeen exploited to regulate entry into <strong>the</strong>reproductive phase when severe coldhas passed.High temperatures during grain fillingpose ano<strong>the</strong>r constraint to wheatproduction. although crop duration inmost parts of <strong>the</strong> country is so adjustedthat it matures before extremelyunfavorable temperatures are reached.However. a sudden rise in temperatureprior to normal maturity is a widelyprevalent phenomenon in almost allparts of <strong>the</strong> country. Such erratic rises- 30 Co)o-----------_.....~'=:::::::--... ------- .........-............::..- .. __ Annigeri ............ ....-...... ..._--- .._-------------' .../........ ......~ ...... p ...."...._..................-atna....-..- .._ ..- ..-.- A bal..-.."-..--............ m a .-..--....-. -.. ..-- --..- ..- ..- BhowaIiOct Nov Dec Jan Feb Mar AprFigure 2. Average temperatures during <strong>the</strong> wheat crop season in variousregions of India