Registration of 16 Striga Resistant Early Maturing Tropical Maize Inbred Lines

Sixteen tropically adapted early maturing maize (Zea mays L.) inbred lines TZEI 1 to TZEI 16 (Reg. no. GP-457 to GP472, PI 641061 to PI 641076), with moderate levels of resistance to the parasitic weed, Striga hermonthica (Del.) Benth. (Table 1), were developed by the International Institute of Tropical Agriculture (IITA), Ibadan. Striga is a major threat to increased maize production and productivity in the savanna ecologies of West and Central Africa (WCA) and can cause grain yield losses ranging from 10 to 100% (Lagoke et al., 1991). The lines, which are at the S6 to S7 stages were first released in 2001 as sources of genes for resistance or tolerance to Striga or tolerance to drought. The lines were also released for direct use as parents for the development of synthetic varieties. The inbred lines have good levels of resistance toMaize streak virus (MSV), Puccinia polysora Underw., and Bipolaris maydis (Nisikado & Miyake) Shoemaker. Seven of the 16 Striga tolerant early maturing maize inbred lines have moderate levels of drought tolerance. The inbred lines were developed from four diverse germplasm sources with resistance to Striga andMSV, and tolerance to drought; namely, TZE-W Pop DT STR C0, TZE-Y Pop DT STR C0, TZE Comp 5-Y C6, and TZE-W Pop3 1368 STR C0. Selected S0 plants from each population were advanced to S6 through inbreeding with selection under artificial Striga infestation and induced drought stress. At the S4 stage of inbreeding, 450 to 500 lines derived from each population were evaluated for general combining ability in testcrosses and for performance per se in replicated trials at Ferkessedougou (98309N, 58109W), and Sinematialli (98379 N, 38049 W) both in Côte d’Ivoire which are hereafter referred to as Ferke and Sine, respectively. The mean precipitation during the crop growing season was 720 mm at Ferke and 683 mm at Sine. Each source population which is broad base and adapted to the growing environments in West and Central Africa (WCA) served as the tester for general combining ability (GCA) for the lines derived from it. According to Hallauer and Miranda (1988), in selection for GCA, a broad base heterogeneous population is used as tester. It can be parental population or any broad genetic base (synthetic or open-pollinated variety), unrelated population. Apart from that, it is common practice in maize breeding to use the parental population as tester when proven broad based testers are not available as in the case of WCA. The testcrosses as well as the lines per se were evaluated for resistance or tolerance to Striga, tolerance to drought, and other desirable agronomic characters. Based on the line per se and testcross performance in the evaluation trials, 90 to 100 S4 lines were selected from each source population and advanced to S6 using pedigree selection under artificial Striga infestation and induced moisture stress. Striga seeds used for the artificial infestations were collected from sorghum [Sorghum bicolor (L.) Moench] fields near each testing site. Selection was based on an index of characters including Striga damage rating, Striga emergence count, ear number, grain yield under artificial Striga infestation, and grain yield and ear rot ratings under noninfested conditions. Two evaluation trials composed of 140 advanced early maturing inbred lines (S6 to S7) developed from the four source populations, and including the 16 being proposed for registration, were conducted at Ferke during the dry season and the rainy season of 2001. In the two trials, the 140 lines plus four inbred checks were evaluated for vigor, high stable grain yield, and desirable agronomic traits, using 12 by 12 simple lattice design with two replications in each season. In 2004, the performance of 100 advanced inbred lines from the source populations were confirmed using a 10 by 10 lattice in a third trial conducted at Mokwa (98189N, 58049E) and Abuja (98169N, 78209E). In the first and third trials, the performance of the lines was compared under artificial Striga infestation and Striga-free treatments. In the Striga infested treatment, the one-row plots were artificially infested with 5000 germinable Striga seeds per planting hole (Kling et al., 2000). Except for Striga seed infestation, all management practices for both Striga-infested and noninfested plots were the same. In the second trial, the 140 inbred lines were evaluated in single-row plots under induced moisture-stress and wellwatered conditions. There was one row per plot. The maize inbreds were irrigated using an overhead sprinkler irrigation system, which applied 12 mm of water per week. Under drought stress, the inbreds were irrigated up to 2 wk before flowering and thereafter, irrigation water was withdrawn until 2 wk after flowering. The irrigation was then continued until physiological maturity. Under well-watered condition, the inbreds were irrigated throughout the growing period. Grain yield, days to 50% anthesis and silking, anthesis–silking interval (ASI), grain moisture at harvest, and plant and ear heights were recorded for each plot. Results of the evaluations under Striga-infested and noninfested conditions showed that the 16 inbred lines proposed for registration had high grain yield as well as good levels of Striga resistance or tolerance (Table 1). The lines shed pollen between 51 and 61 d, silked between 54 and 63 d, and had plant height varying from 89 to 138 cm and ear height varying from 43 to 70 cm. Results of the evaluations under induced moisture stress showed that only seven of the 16 inbred lines proposed for registration produced grain. Small quantities of seed (50 kernels) of the inbred lines could be made available to crop researchers on request to the WECAMAN Coordinator, at the Maize Breeding Unit, IITA, PMB 5320, Ibadan, Nigeria. In the USA, small quantities of seed may be obtained from the National Plant Germplasm System (NPGS).We request that appropriate recognition of the source be given when the inbred lines contribute to an improved cultivar or germplasm.