the Symposium on Wheats for More Tropical Environments - cimmyt

70The stripe rust races 66EO. 6E16.66E16 and 38E16 have been found tobe <strong>the</strong> most important while. for leafrust. races 57 and 77 have been mostaggressive and frequent. S.A. Rizvi hasreported that LR19, LR24, LR25, LR28and LR29 genes have shown resistanceagainst a number of virulent isolates ofleaf rust. For controlling leaf rustattack, fungicides such as Indar,Daconil and Balytan have proveneffective.Wheat varieties Chat"S", Bulbul, Chris,Super X, WLl145, WLl146, WL1257and WL1562 have shown resistanceagainst smut inoculum. The fungicidesBaytan, Topsin-M, Vitavax-200 andBenlate have given good control of loosesmut, as has <strong>the</strong> solar energy methodwhich involves soaking wheat seed inwater for four hours and drying it in <strong>the</strong>sun. Diseases such as flag smut,powdery mildew, helminthosporiumleaf spots and foot and root rots, whichearlier were not of much significance,are now becoming important.Insect pestsFortunately, wheat is not attacked byany serious pests; however, infestationwith armyworm, cutworm, stem borer,cornstalk borer and green aphids hasoccurred in localized areas.DroughtAbout 21 % of total wheat area in <strong>the</strong>country is rainfed. The screening ofplant materials and <strong>the</strong> testing of newvarieties for drought tolerance arecarried out in rainfed areas or undersimulated moisture stress. Some of <strong>the</strong>varieties (Blue Silver, Lyp 73 and Pak81), which were developed for irrigatedareas, have also proved very successfulunder rainfed conditions; <strong>the</strong>refore, <strong>the</strong>testing of new varieties under bothirrigated and rainfed conditions isencouraged. The new variety Barani 83is now awaiting release.SaliDlty/sodicityAt present, 2.4 million ha of land inPakistan have been rendered salinesodicand, with <strong>the</strong> continuous use oflow-quality water. this menace isincreasing every year. Wheat yield hasbeen found to be reduced by 19%under moderately saline-sodie soils.Lack of nutrientsYield constraint experiments inirrigated and rainfed areas have shownthat <strong>the</strong> proper application of fertilizeris of utmost importance. Yieldreductions ranging from 51 to 73%have been observed without properfertilizer use. This clearly demonstratesthat wheat yields can be substantiallyincreased if fertilizer use is properlyregulated in <strong>the</strong> country.Planting dateMore than 50% of <strong>the</strong> wheat in Pakistanis planted late, I.e., during <strong>the</strong> month ofDecember. Planting date experimentshave shown that yield is progressivelyreduced with delays in planting. Yieldwas found to be reduced by 28.8 and57.8%, respectively, when sowing wasdelayed from November to Decemberand from November to January.WeedsChenopodium spp., Phalaris minor andConvolvulous spp. have been found tobe <strong>the</strong> major weeds. Wheat yields werefound to be increased by 167.7, 140.7and 136.3%, respectively, over <strong>the</strong>weedy control when weeds werecontrolled by <strong>the</strong> herbicides DicuranMA, Tribunil and Graminon.Durum Wheat ImprovementSystematic durum wheat improvementwork was begun in <strong>the</strong> mid-1970s, andtwo promising durum lines, V79717and V79736, have shown superiority inyield and disease tolerance as comparedto <strong>the</strong> bread wheat checks; <strong>the</strong>y are in<strong>the</strong> final stages of release.