| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
IITA, Oyo Road, PMB 5320, Ibadan, Nigeria
* Corresponding author (A.Menkir{at}CGIAR.ORG)
Twenty maize (Zea mays L.) inbred lines with resistance to foliar diseases and adaptation to tropical midaltitudes (Reg. no. GP-379 to GP-398, PI 635122 to PI 635141) were developed at the International Institute of Tropical Agriculture (IITA), Ibadan, Nigeria. The lines are at the S8 to S9 stages of inbreeding and confer combined resistance to gray leaf spot (caused by Cercospora zeae-maydis Tehon and E.Y. Daniels), Maize streak virus (MSV), northern leaf blight [caused by Exserohilum turcicum (Pass.) K. J. Leonard & E. G. Suggs.], and common rust (caused by Puccinia sorghi Schwein); diseases prevalent in the midaltitude ecology in West and Central Africa (Everett et al., 1994a, 1994b). Lines were released for use as sources of germplasm from 1999 to 2003.
Inbred lines were derived from single crosses of midaltitude-adapted inbred lines and broad-based populations (Coca-SR, Early-W-SR, and POP 43-SR) with resistance to MSV (Kim et al., 1985; Everett et al., 1994a, 1994b, 1994c). TZMI711 was derived from a cross between a maize variety grown in Tanzania, called National-1 Variety, and an IITA MSV-resistant population (TZSR), which was formed by intercrossing four populations, including TZB, TZPB, POP 21, and POP 22. TZMI712 and TZMI713 were selected from a cross between a midaltitude inbred line (TZMI501) from IITA and an inbred line from the International Maize and Wheat Improvement Center (CIMMYT) (ZSR 923 S4 bulk). TZMI714 and TZMI715 were extracted from a cross between two midaltitude-adapted inbred lines from IITA (87014 and Z28). TZMI716 was extracted from a cross between two midaltitude-adapted inbred lines (88069 and 87366) from IITA. TZMI717 was developed from a cross between two midaltitude-adapted inbred lines (89258 and Z28) from IITA. TZMI718 was selected from a cross between two midaltitude-adapted inbred lines (89302 and Z28) from IITA. TZMI719 to TZMI724 were derived from a cross between two midaltitude-adapted inbred lines with flint grain texture (TZMI101 and TZMI501). TZMI101 was extracted from a broad-based population, TZMSR, while TZMI501 was developed from a cross between a commercial hybrid from Zimbabwe (SR52) and an IITA population (TZSR). TZMI725 was developed from a cross between two midaltitude-adapted inbred lines (87036 and 87923) from IITA. TZMI726 and TZMI727 were extracted from two populations developed at IITA, Coca SR and Early-W-SR, respectively, while TZMI728 and TZMI729 were derived from a population developed at CIMMYT (POP43-SR) and improved for resistance to MSV at IITA. TZMI730 was derived from a cross of an inbred line from IITA (TZMI407) with a line from CIMMYT (8232/TZMSR-W/ZM607). The parental lines from IITA were derived from a MSV-resistant midaltitude population, TZMSR, crosses between lowland MSV-resistant populations, and midaltitude germplasm from Eastern and Southern Africa as well as germplasm sources from CIMMYT (Kim et al., 1985; Everett et al., 1994a, 1994b, 1994c).
S1 lines extracted from each cross or population were evaluated in single rows under severe natural infection with northern leaf blight and common rust and artificial inoculation with gray leaf spot at Tenti (9°48' N, 8°48' E, altitude 1350 m) and Vom (9°40' N, 8°50' E, altitude 1300 m) in Nigeria. Inoculation with gray leaf spot was done at the four- to six-leaf stage by placing a pinch of ground infected leaf samples with gray leaf spot collected in the previous season into the leaf whorls. At each location, gray leaf spot, northern leaf blight, and common rust severity were visually rated at 3 wk after silking on a scale of 1 to 5, where 1 = no visible infection and 5 = severe infection (Shagi Maroof et al., 1993). At the S1 to S3 stages of inbreeding, rows that exhibited disease severity ratings of 3.0 or less for the three foliar diseases in the two locations were selected. Single plant selections were then made from each selected row at each location on the basis of vigorous growth (visual assessment for bigger and sturdy plants with healthy leaves), low ear placement, resistance to lodging, synchrony between pollen shed, and silking, as well as well filled ears. At the S4 stage, selected lines were evaluated in the field under artificial infestation with viruliferous leafhoppers (Cicadulina spp.) for resistance to MSV at IITA, Ibadan (7°26' N, 3°54' E, altitude 150 m).
S4 lines with combined resistance to the four diseases were crossed to two inbred testers, TZMI102 and TZMI407, that are parents of the best single-cross hybrid marketed in Plateau State of Nigeria as ‘8535-23’ to form testcrosses. The S4 testcrosses and the check hybrid, 8535-23, were evaluated in single 5-m row plots at Tenti, Vom, and Saminaka (10°28' N, 8°41' E, altitude 800 m) in Nigeria in 1997 and 1998 by means of a simple lattice design. Selected S4 lines that combined well with at least one of the inbred testers were advanced from S5 to S7 stages of inbreeding with repeated evaluation for resistance to gray leaf spot, northern leaf blight, and common rust at each stage. S7 lines with combined resistance to the four diseases were selected to form experimental hybrids, which were again tested at Tenti, Vom, and Saminaka in Nigeria between 1999 and 2003. Inbred lines that did well in hybrid combinations and with better resistance to foliar diseases than the hybrid check, 8535-23, in field trials over 2 yr were selected and released to collaborators in the national agricultural research systems and seed companies in and outside of West and Central Africa.
On the basis of combining ability effects and mean grain yields of the lines in crosses with the two inbred testers, TZMI711 to TZMI718 were assigned to the TZMI02 heterotic group while TZMI719 to TZMI724 were placed in the TZMI407 heterotic group. The remaining six lines (TZMI725 to TZMI730) were found to be heterotic to both TZMI102 and TZMI407. In breeding nurseries evaluated at Tenti and Vom for six years (1998–2003), the average gray leaf spot scores for the tropical midaltitude lines varied from 1.6 to 2.9, which were similar to or significantly better than that of the standard check line, TZMI407 (2.7). In an evaluation trial conducted at Saminaka and Vom in 2003, the lines tasseled between 74 and 83 d, silked between 77 and 86 d, and had plant height varying from 91 to 188 cm and ear height varying from 40 to 96 cm. Most of the inbred lines had flint grain texture and can be used as sources of genes for combined resistance to the four foliar diseases as well as favorable alleles to broaden and diversify the genetic base of adapted germplasm in tropical midaltitude environments. They can also be used as promising sources of exotic germplasm to temperate environments because they should possess desirable traits fixed through several generations of inbreeding and selection.
Small quantities (30 kernels) of seed are available to crop researchers upon written request to the leader of the maize breeding unit at IITA, PMB 5320, Ibadan, Nigeria. It is requested that appropriate recognition of the source be given when these germplasm lines contribute to the development of new lines, hybrids, and synthetic varieties.
ACKNOWLEDGMENTS
This research was conducted at the International Institute of Tropical Agriculture (MS no. IITA 04/09/JA) and financed by IITA. The authors express their appreciation to all staff members that participated during planting, data recording, harvesting, and management of the trial at three locations.
NOTES
Accepted for publication July 31, 2004.
REFERENCES
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
| The SCI Journals | Agronomy Journal | Vadose Zone Journal | |||
| Journal of Natural Resources and Life Sciences Education |
Soil Science Society of America Journal | ||||
| Journal of Plant Registrations | Journal of Environmental Quality |
The Plant Genome | |||
