Gxperimental studies in Quantitative Genetics I. Reasonea for the research Zasic quantitative genetics in corn ta being done at aoma institutions in the U.3., particularly at North Carolina where emphasis is civen to breeding mathodology. The experimental schemes being employed and material under investigation in the U.3. ta, of necessity, restricted with regard to genetic diversity among types adapted to different regions. ‘While the information being sought vill be of tremendous value, both in providing genetic understanding and as the basis for development of breeding techniques, it is not likely to have general applicability to the corns of Central and South dmerica. The kind of information being sought in quantitative genetics research in the U. 3. programa is also needed for the Latin American programs. The nature of the action of genes in the corn ia of prime importance in understanding the genetics of these races as well as providing 3 sound and effictent basis for utilising thea in leeal and U. 5. breeding programs. Further, it is not possible to cove these corns to the U. 5. or other sress where they are not adapted and do the required research. The programs of study must be carried out where the races have evolved if reliable and meaningful information is to be developed. owever, the program does envisage movement of the exotic types into regions of non-adaptation as attespts are made to incorporate the germ plasms into U. 3. corns. This Latter phase of the work will have more concarn with possible utilization of Latin American corns to broaden the zenetic base of more highly evolved varieties. Qne of the most important justifications for the axuaios to be outlined below is their use in providing theses topic for Latin American atudents who will be working for the 4.3. and PhD degrees in Lstin America and U. 3. ge institutions. This will provide a variety of opportunities for students to be involved vith basic cenetic research at the graduate level and should lead co tha kind of development in their thinking that will be of aost vaiuc in thedr 2uture amployment. Tha students chosen to do advanced study in the Ue Se VELL have tha oppertunity to carry gut the oxperimental work on a theaia problem at a Latin American center and have a problem that is fully acceptable at the J. 5. university. Skamplos of the kinds of questions for which information ia needed are: i, hat is the nature of ueterosis in the intere and intraeracial oresses? 2. what is the relationship between the Leterosis among sacical erosees and proposed avolutionary development of the races: 3. Is the nature of gene action simdlar in ancient and modern saces? 4. www important is additive genetic, dominance and apistasia in che actions of zenes conditioning the expression of the quantitative traits such as yield? 5. whet ts the potential improvement in ylold within races af maice and ow doas this differ .n ancient and modsorn complox races? 5. Does the senetic variability of potential usefulness increase and iow auch with interecrossing of races? je Presumably strong Linkage complexes exist and may persist for long periods in interbreeding populations of the Latin American corns. What effects do the linkaze affeeta have on mean and variance astinates of the jenetic affacts in different kinds af populations and senerationa? 3. low can the axotic and axotic « Ue. 5. corn interbreeding popula- cions le aanipulated to increase recombinations and attainment of linkage aquilfbrium? (Possibility of ineprporatiny; factors such as vasbaeds 2 for increasing recombination ratas.) S, What is the potential value of races of maize in Central and South imeriea for corn improvement throughout the world? Joma oxamples of the kinds of studies thet are visualized are outlined below. in some instancea work has already been initiated and others, studies are in ¢he planning stages. Tha program of work siven is for Mexico and involves the races of maize of that country. Jome of the same type of investizations are planned for other centers in South America with other materials and it la intended for these plans to serve as axamples of cypea ox sesearch neaded. The detaila on the procedures of 2 specific atuady will ve developed with the Latin American project leader. iI. Studies to ve conducted Ae Ueterosis in inter~ and intraeracial crossas. 1. intereracial crosses én important question in basic genetics and appiied >reeding is the nature of naterosis and mean yield performance of racial crosses. ‘{vidence from inter-crossing of U.S. open-pollinated varieties indicates heterosis in yield, measured from mideparent, may be from 10% - 20%. The yield nerformance of U. 3. variety crosses has, in some instances, approached that af commercially important double cross hybrids. Preliminary information from tha Haxican corn program indicates that race crosses may excel, by as much ag 25%, the yield of the adapted commercial lybrids. In order to curvey the caces and their crosses it is proposed to do the followin; ae ike all possible crosses among the 25 basid’ Mexican races. A ‘representative’ type will be chosen for cach race in ordar to procead with this study. A minimum of 100 slants will be ued ag female parenta in making the sacial crosses and afforta ‘411 be made to have many wore individual plants represented. nqual quantities of seed from aach of the pollinated ears vill ve bulked for testing. ue Intereregional crosses The 25 races will 4s crossed with selected broad-base antries from other areas; @e3. Southern J.5. prolific variety croos Garvia x Indian Chief), corn belt synthatics (Iowa stlff stalk synthetic) and other corn belt composites involving elite lines, Superior varieties from Columbia, 3. A. &e Svaluation of race crosses ie The 300 crosses of the 25 races, the races themselves and inter-regional race and variety crosses will be studied in replicated yield performance trials at Ligh, medium and iow altitudes in ifaxico. Some auparior hybrids, adapted to the region of the testa, will be included. It is anticipated that poor performance may result from inter-crosses of uon= adapted types. llowever, the first performance study will be attempted with all possible crosses (reciprocal crosses not distinguished) in order to provide the preliminary evaluaticn. Repeat evaluations planned for future years will be seduced to types where first year evaluation indicated sutficiently hish performance to varrant further testing. Tha resulta will provide information on (a) genetic diversity among the races as reflected in natorosls (bh) indications as to which races should =e chesen for mere intensive Dasie ,enetic atudies (c) possible races for base populations to be utilized in breeding programs 2. Intraeracial crosses Many collections (varieties) of various races are oresentiy available and being maintained. ‘hile it is planned in other areas of research of the Inter-American Maize Program to develop composite interbreeding pools of zerm plasm, evaluation atudies are necessary on certain collections of varieties within the races. it is propesed to atudy variety crosses within some af tha races to provide information on tha zenetic diversity among such varieties. The studies will ve the baais for decisions on (a) Necessity for zsaintaining separate :erm plasm pocls with the race (b) The validity of present racial classifications (Implications to be derived from inter- and intraeracial er03303) {c) Preliminary, information on racial origin. Varietias that are apparent alutures of two or amore caces compared to true intra-ractal collection will Se of interest in this regard. Materials to be studied in the imoediate future are (a) All possible crosses among 12 varieties within Tuxpeno,. This study will include the varieties, variety crosses and certain adapted hybrids {b) All possible crosses among 10 varioties of Jalvadoreno valuation trials will include varictics, varicty erosses, and race composite crossed with a series of othar races {c) Variety « tester evaluation A series of studies would utilize elite varieties such as Yer. 131, Azteca, and AES301 which would 5e uséd as common testers of sroups of varieties with certain races. 3. Neture and uagitude of cenetic variability The relative anounts of various kinds of gemetic variances in the yagie -aeed of aaice is of importence in Pundemettal semrtics and breeding “ercnedalogy. Tt is proposed that extensive genetic variability investiga- tions be conduttad on 2 linited mmber of races in the Inter-jmerican Maize Precram. In general, these studies vould not be initiated until prelimine ary investigations of the races and racial crosses have been conducted. Aluo, — the develoment of subteble composites of collections within the races vould — alreniy been done. ‘While the orelininary work and ideal ecmaxposites are agt vet available in the Mexican program, it is uroposed to proceed with sane intensive senetic variability studies. It is likely that ourficient informa- siog is alresdy svellable to aneble the choice of suitable stocks. 1. Design I studles Tt is oroposed to follow the scheme ocreaently being used at Torth Carolina for the conduct of these studies. Biparental srougs sr yaire cul Gubllesib families will be produced Im aach population for evaluation tn yield trials. d4ixzty-four nele groups, four females per =ale, will de utdliusd with two to four realieations of each entry. Studies will, in 30 fay 33 oooaible, be canducted at two or more locations and in different years. Zomilaticns to be used in the initiel phase of the vork in Mexico are: (1) Tuxpenc (2) Chaloqueno (3) Contes (4) Nabetel (3) ‘Texceno x Mal-tel - Thess vopulations represent the range of races of maise trom the ancient indicenocus to the sodern ineiplent and complex forms. The infor- ction witnin each wwomilation will indiesate: {1} \mewrts of ubiitive senetic variance engbling tcrediction of nosalble VO MEINBG SS URYIER IML GLO G Le IC pee a. qith ihe race ond eembrcibute heavily te the dominance variance In either true tgdnance ob the senda leval or eifects of Linkave samy reflect in these asti- ares. “nistatic variance uay also be Daportant wai contribute to the variance 38% Late « (3) 2ffecta of previous selection on races within Mexico and comearicons i galeetion consequences with exotic ani 0. 5. ponulotions Comparison of estiustes between races is trportant to vrovide aor tion oi (i) Uature of sanetic veriances as a consequence of racial evolution. 42) Potemtial breeding value af di?feremt igdiuis of races in terme of cogsible selection progracs snd gern plaem to be utilized. (2) Dffecte of ractel abciag and lybridication on ~emebic vertabilicy. (4) Uecessity for utilising different breeding senemes with dicterent inimdla af races. G. Sxreedling Methololesy 1. ‘ttaae selection It is likely tiust aasa selection vill be effective in the inprovenent of yield in weny of the exotic races of Latin America. The imitial ani continued progress will depend upon tha availability of addi- tive jenetic varisnce within the populations. Mass selection should be init. datel and contimied for several cycles to provide an evaluetion of rate and wliioete progresa in vield ieprovenent with ouch naterial. The studies would be conducted with part af all of the follorins: a) ‘Tkecpens 9b) Chalqueno 2) Conteo 4) Heletel e) Tuxpeno «x Hal-tel These jogulations are chesen in order that informstion ja. vived in (B) and (C) will have cress interpretations of iaportance to genetic understanding as vell as peectical breeding value. In regard to the latter, srequency of Pavorable genes will be accumulated and result in matertal of increasing value for breeding stocks. LO 3. Tnter-racial Gene Action “yo or more races would be chosen to be used in series of studies Ghat “ALL utilize inter- oni intra-racial entries at different generationg. The vaces to he used will be selected on the baals of the inter-racial cross stuckr and the choiee should be made of races Indicating different kinds of gene action operating in the race crosses. Some studies to be conducted are: (1) Inbreeding depression with different levels of water sygosity narents (races), Py Foy first and second back crosses, * 1 seifed, ond P, selfed generationa would be utilised. (2) Btfects of interemating on zene comlexes. The material to be utilized would be sarents (yaces = 4% B)y F, =A x3, F, = AB, and various advanced generations thst have been produced by alb mating e.g. ABss AB, 5+ Also, it may be desir- able to inelude the two kinds ov backcross entries, ABB and AAB. These weld also be advanced to the oth end 10th cemerations with remdom mating. This study would provide information on: (1) Optivnaa mixing time in racial crosses linkage affects. (2) Possible effects of epistasis. (3) Rate of dissipation of heterosis.