the Symposium on Wheats for More Tropical Environments - cimmyt

127Wide Crosses and New Genesfor Wheats for <strong>the</strong> TropicsA. Mujeeb-Kazi, Wheat Wide Cross Program, CIMMYT, MezicoAbstractThe benefits breeders have derivedfrom alien species through <strong>the</strong> introgressionofalien genetic material are best exemplified by <strong>the</strong> current CIMMYT IB/IRwheat lines. Several lines have been released by various countries as varietiesbecause of <strong>the</strong>ir wide adaptation, yield stability, aluminum tolerance andresistance to Septoria tritici. O<strong>the</strong>r institutions have made significantimprovements in wheat through alien introgressions, specificallyfor resistanceto <strong>the</strong> pathogens that caUse stem rust. leaf rust, stripe rust, powdery mildewand wheat streak mosaic virus, as well as resistance to greenbug. There havebeen, however, only a limited number ofalien species involved in <strong>the</strong> abovementionedstudies, Aegilops umbellulat.a. Agropyron elongatum, Agropyronintennedium and Secale cereale; considering <strong>the</strong> extent ofalien germplasmavailable, <strong>the</strong> promise offuture success is extremely high. The larger <strong>the</strong>number ofalien genera that are combined with wheat and <strong>the</strong> larger <strong>the</strong>number of resulting hybrids that are advanced, <strong>the</strong> more diversified will be <strong>the</strong>environmental conditions under which wheat production can occur. Thispotential is <strong>the</strong> reasonfor CIMMYT's wide cross program.Conventional plant breeding hasmaintained its predominant role in cropimprovement and has been remarkablyinfluenced by <strong>the</strong> wealth of prevalentgenetic infonnation. This has provided<strong>the</strong> necessary genetic variability for useby plant breeders. and genetic advanceshave adequately demonstrated <strong>the</strong>irconsistent impact. Prevalent breedingprocedures and genetic variability haveso far pennitted routine handling foreach problematic situation that hassurfaced.Complementing research thatcontributed to <strong>the</strong> success ofconventional programs was developedwith great success in <strong>the</strong> 19th centuryin <strong>the</strong> disciplines of mutation breedingand interspecific and intergenerichybridization. The latter two. inessence. have incorporated anundirected. modified genetic system orhave exploited. to a limited extent. <strong>the</strong>unique gene pool of a few closelyrelated or more distant relatives ofcultivated crops. In both cases. newgenes have been identified thato<strong>the</strong>rwise might never have beenavailable through conventional geneticsystems.More recently. <strong>the</strong> exciting areas oftissue culture, multiple shoot fonnationtechnology. an<strong>the</strong>r culture, somaclonalvariation and <strong>the</strong> broadly designatedarea of DNA technology have emerged.It should be recognized. however. that<strong>the</strong>se new methodologies are fanciful;<strong>the</strong>y offer immense promise in <strong>the</strong>orybut. for <strong>the</strong> budgetors of time. <strong>the</strong>y canbe classified as being of high risk andextremely futuristic. They do, however,definitely warrant continued research.In <strong>the</strong> CIMMYT wheat program,agricultural demands have dictated aworking methodology that has taken usfrom a stage of research fantasy to oneof practicality and accountability. Themajority of <strong>the</strong> disease resistance andstress tolerance objectives pursued haveno demonstrable genetic association or