Recombinant inbred lines from tropical x temperate single crosses
--Hyeon Gui Moon and James L. Brewbaker
A series of 1068 RILs (recombinant inbred lines) have been created by selfing 6 generations from 9 single crosses of elite maize inbreds. The single crosses involve both tropical and temperate parents. The temperate parents included B73 (Iowa), DB544 (S. Korea), Fla2BT73 (Florida) and Hi31 (Hawaii, ex Iowa inbred B68). The tropical parents included Hi34 (Hawaii, ex Antigua), Ki14 (Thailand), Narino330 (Philippines, ex. Colombia), Tx601 (Texas), Tzi4 (Nigeria, ex Guatemala x Nigeria) and Tzi17 (Nigeria). At least 20 sublines were derived from each of the 9 parents by selfing, for use in establishing expected normal distributions for QTLs (Brewbaker, Quantitative Genetics on a Spreadsheet, 1994).
All crosses were made to exploit genetic differences in disease and pest resistance (Kim, Brewbaker and Hallauer, Proc. Corn and Sorghum Res. Conf. 43:194-226, 1988). The RIL families are simply designated A through J. Set G has been subjected to extensive RFLP mapping, as noted by Ming et al. in an accompanying article.
High-priority QTLs that distinguish the parents of the 9 sets of RILs are indicated below. Dentiness and daylength susceptibility segregated in almost all sets.
(A) Hi34 x Tx601: Sphacelotheca reilana = head smut (HEAD), Spodoptera frugiperda = fall armyworm (FAW), Ostrinia stalk borers (OST), plant height (PH), ear height (EH), kernel weight (KW).
(B) B73 x Narino330: Maize Dwarf Mosaic Virus (MDMV), Maize Mosaic Virus (MMV), Downy mildew (DM), Puccinia polysora rust (POLY), Exserohilum turcicum blight (TURC), OST, maturity, PH, EH, internode length (INT), tassel branches.
(C) B73 x Tx601: MDMV, DM, Fusarium moniliforme kernel rot (FUS), FAW, EH, leaf number (LNO), INT.
(D) B73 x Tzi4: DM, Maize Streak Virus (MSV), POLY, Puccinia sorghi rust(SORG), TURC, FAW, OST, maturity, seed color, LNO, INT, Striga helmonthica = witchweed (STRIGA).
(E) DB544 x Fla2BT73: Black Streak Dwarf Virus (BSDV), Bacterial Leaf Blight (BLB), Helminthosporium (Bipolaris) maydis (MAYD), STRIGA, maturity, PH, EH, LNO, tip leaf burn, tassel branches.
(G) Hi31 x Ki14: MDMV, MMV, DM, Maize Stunt Mycoplasm (STUNT), Curvularia (CURV), POLY, Xanthomonas stewartii = Bacterial (Stewart's) wilt (WILT), MAYDIS, Ustilago maydis (SMUT), TURC, DS, pericarp thickness (PT), staygreen (SG), tassel type, KW.
(H) Hi34 x Tzi4: MMV, MSV, DM, SORG, root lodging, seed color, INT.
(I) Hi34 x Tzi17: MMV, MSV, SMUT, SORG, TURC, Stalk rot, OST, STRIGA, seed color, SHK, tassel length, KW.
(J) Tx601 x Tzi4: MMV, SMUT, SORG, TURC, OST, seed color, PH.
Evaluations conducted since 1993 suggest that the following QTLs are associated with monogenic variation among the parents (H.G. Moon, PhD thesis, U. Hawaii, 1995): common and polysora rusts, bacterial leaf blight, Stewart's bacterial wilt, maydis and turcicum blights, MMV and MSV viruses, and "Staygreen" (probable tolerance to Fusarium moniliforme). Digenic variations have been suggested for pericarp thickness and tolerance to European corn borer and to Striga (witchweed). Where desirable and possible, closely linked molecular markers of these QTLs are being identified to serve as "flags", hopefully to accelerate genetic gains in maize.
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