the Symposium on Wheats for More Tropical Environments - cimmyt

-188Distribution and Importance ofRoot Rot Diseases of Wheat, Barley andTriticale in South and Sou<strong>the</strong>ast AsiaE.E. Saari. Wheat Program. CIMMYT. MezlcoAbstractWheat and barley are cultivated under a wide range ofenvironments in SouthAsia. and <strong>the</strong> climates varyfrom temperate to tropical. In Sou<strong>the</strong>ast Asia.wheat. barley and triticale are experimental crops. There are a number ofrotations involved. as cropping intensities are generally greater than one crop inboth South and Sou<strong>the</strong>ast Asia. The influence ofenvtronment and croppingsystem has a pronounced effect on soil-borne cUseases. with a number ofcommon pre-emergence and post-emergence diseases reported; afew uniquesoil-borne diseases arefound in <strong>the</strong> more tropical environments. Most of <strong>the</strong>research on soil-borne diseases has been descriptive; <strong>the</strong>re is relatively littleiriformation on ei<strong>the</strong>r losses or control.Wheat and barley are traditional cropsin <strong>the</strong> South Asian countries ofPakistan. India and Nepal. The climaticconditions in <strong>the</strong>se countries varywidely. depending upon latitude andaltitude. The majority of <strong>the</strong> acreage.however. is cultivated on <strong>the</strong> plains ofnor<strong>the</strong>rn India and Pakistan. and on<strong>the</strong> plains of Nepal bordering on India.There is a small area cultivated in <strong>the</strong>mountainous areas of all threecountries. and some acreage in centraland sou<strong>the</strong>rn India which can beclassified as subtropical to tropical.The cultivation of wheat has beenexpanding into new areas in <strong>the</strong> past15 years (9). The most notable increasein acreage has been in Bangladesh.sou<strong>the</strong>rn and eastern India and. morerecently. Burma. There has been anincreasing awareness and interest in<strong>the</strong> possibUities of wheat cultivation in<strong>the</strong> countries of Sou<strong>the</strong>ast Asia as well.Wheat as a possible crop in <strong>the</strong>senontraditional areas has developedmainly as a result of <strong>the</strong> closing gap in<strong>the</strong> production of <strong>the</strong> basic food crop.rice. The growing level of wheatconsumption and imports. with itsimplications for foreign exchange. isalso contributing to <strong>the</strong> question ofwheat cultivation. There is interest in<strong>the</strong> possible cultivation of wheat forcrop diversification and intensificationduring <strong>the</strong> dry season in <strong>the</strong>se areas.The climate ofSouth and Sou<strong>the</strong>astAsia is typified by a monsoon season.The duration of <strong>the</strong> rainy season varies.depending upon several factors. but it ischaracterized by high rainfall. humidityand warm temperatures. Rice is <strong>the</strong>main crop in <strong>the</strong> lowlands or whereverwater can be contained for a floodedpaddy. In well-drained soils. numerousupland crops are available. Themonsoon season is generally followedby a drier. cooler season. The dryperiod is defined as those months withless than 100 mm of precipitation. Theaverage temperatures are <strong>the</strong> coolestduring this period of <strong>the</strong> year. andrelative humidity is lower. In <strong>the</strong>nor<strong>the</strong>rn hemisphere. December andJanuary are generally <strong>the</strong> coolest anddriest months.Historically. few crops have beencultivated during this period. unlessirrigation is available. In areas withlimited irrigation. vegetable crops oro<strong>the</strong>r high cash-value crops aregenerally grown. Where irrigation is