Heterotic patterns and combining ability of CIMMYT early maize (Zea mays L.) lines under moisture and nitrogen stress and optimal conditions

[摘要] English: Since the initiation of a product oriented breeding programme aimed at improving maize for drought prone mid altitudes of southern Africa, CIMMYT developed several inbred lines and single cross hybrids using pedigree selection methods, with emphasis on earliness, drought and low nitrogen stress tolerance. This resulted in increased volumes of seed inventories. Sixteen inbred lines and 71 single cross hybrids were crossed to three (single cross) testers, CML312/CML442 and CML505/CML509 (heterotic group A) and CML395/CML444 (heterotic group B) and evaluated as two separate experiments for general and specific combining ability in contrasting environments (optimal, managed drought and nitrogen stressed). The objective was to asses the relative importance of general combining ability (GCA) and specific combining ability (SCA) in identifying promising early maturing maize lines, single crosses and testers that could tolerate drought and nitrogen stress conditions, thus simulating prevailing conditions in most resource poor farmers' fields in the mid altitude environments of southern Africa. The first experiment consisted of 48 experimental crosses and 24 additional crosses. Six trails were planted in a lattice (Alpha 0,1) with eight plots per incomplete block. The second experiment consisted of 213 experimental crosses and additional 27 double crosses and synthetics. Five trials were planted in a lattice (Alpha 0,1) with 12 plots per incomplete block. Trials were planted under optimal conditions at ART farm, Rattray Arnold and Kadoma, nitrogen stressed conditions at Harare and drought stressed conditions at Chiredzi in Zimbabwe in 2006. Data was collected on grain yield (GY), anthesis dates (AD), anthesis silking interval (ASI), plant heights (PH), ears per plant (EPP), and leaf senescence (SEN). Data was analysed first according to Lattice (alpha 0.01) design using computer software Fieldbook, for the general performances of all crosses for all traits. Line x tester analysis for general combining ability and specific combining ability was performed using SAS and AGROBASE II computer software. The first experiment identified heterotic group B line 15 as superior with a GCA value of 0.56. The line had a SCA value of 0.21 with early maturing (heterotic group A tester) CML505/CML509. The hybrid had grain yield of 7.9t/ha and 1.3t/ha across optimal and stress environments respectively and was early maturing (69 days) (silking anthesis days). In the second set of materials heterotic group A single crosses 51, 37, 55, and 7 had good general combining ability above 0.64. Heterotic group B single crosses 11, 38, 39 and 22 had good specific combing ability with CML505/CML509. The hybrid combinations ranged between 6.1-7.4 t/ha across optimal environments and 0.8-1.4 t/ha across stressed environments. These hybrids were very early (AD 64-66 days), could be evaluated in wide environments for GCA with heterotic group A lines and single crosses in order to identify an early maturing group B tester. CML505/CML509 classified the early maturing lines and single crosses into heterotic groups better than CML312/CML442.

[发布机构] University of the Free State