Registration of 16 Extra‐Early Maturing Striga Resistant Tropical Maize Inbred Lines

Sixteen extra-early maturing maize (Zea mays L.) inbred lines TZEEI 1 to TZEEI 16 (Reg. no. GP-473 to GP-485, PI 641251 to PI 641266) with moderate levels of resistance to the parasitic witchweed, Striga hermonthica (Del.) Benth were developed at the International Institute of Tropical Agriculture (IITA), Ibadan, Nigeria (Table 1). Extra-early maize is particularly suitable for cultivation in areas with short growing periods, such as the northern fringes of theGuinea savanna and the Sudan savanna of West and Central Africa (WCA). These zones are characterized by terminal drought and infestation by S. hermonthica, which are major constraints to increased maize production and productivity. Losses caused by the parasitic weed in farmers’ fields can be up to 100% (Lagoke et al., 1991). The inbred lines also have good levels of resistance to Maize streak virus (MSV), tropical lowland rust (incited by Puccinia polysora Underw.) and blight [caused by Bipolaris maydis (Nisikado & Miyake) Shoemaker]. The lines, which are at the S6 or S7 stages of inbreeding, have white or yellow endosperm, silk in about 56 d after planting and grow to a height of about 1 m. In 2001, they were released to national maize programs inWCAas source germplasm for broadening the genetic base of tropical extra-early populations and as parents for the development of Striga resistant synthetic varieties for the savanna ecologies. The 16 extra-early inbred lines were derived from several broad-based Striga and MSV resistant populations, TZEE-W Pop STR C0, and crosses (TZEE-W SR BC5 3 1368 STR, TZEE-W Pop STR3 LD and TZEF-Y SR BC1 3 9450 STR). S1 lines extracted from each population were evaluated at Ferkessedougou (9839 N, 58109 W, mean annual rainfall of 1400 mm) and Sinematialli (98379 N, 38049 W, mean annual rainfall of 1200 mm), in Côte d’Ivoire during the rainy season of 1997. At Ferkessedougou, the lines were evaluated under artificial Striga infestation (about 5000 germinable Striga seeds per maize hill [Kling et al., 2000]) and outstanding S1 lines selected from each population were taken through six cycles of pedigree inbreeding and selection under artificial Striga infestation. At the S4 stage, 250 to 300 lines derived from each population were crossed to the corresponding base population as the tester. The S4 lines per se and the testcrosses were evaluated at Sinematialli under Striga-free conditions and at Ferkessedougou under artificial infestation with S. hermonthica seeds collected from sorghum [Sorghum bicolor (L.) Moench] fields near each testing site. About 5000 germinable Striga seeds per maize hill were used for the artificial infestation. The yield performance of the lines per se, their combining abilities for grain yield, Striga damage rating, Striga emergence count, and ear number and other desirable agronomic characters across the two locations were used as criteria for selecting 90 to 100 S4 lines, which were advanced to S6.