Breeding of acid soil tolerant maize genotypes for Angola
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Breeding efforts to develop high yielding and stable maize cultivars tolerant to soil acidity is still lacking in Angola, where the main maize production environments are characterized by acid soils. Furthermore, Angola is faced with two distinct human populations, with one favouring white kernel maize while the other prefers yellow maize, making it key to develop separate breeding programmes for these two distinct groups of people. The aim of this study was to select CIMMYT inbred lines (white and yellow kernel) adapted to the mid-altitude climatic conditions (for example from CIMMYT-Zimbabwe) and those developed for acid soil tolerance (for example from CIMMYT-Colombia), that can potentially be used in breeding programmes for acid soil tolerance in Angola. The specific objectives were to: i) assess the combining ability for grain yield performance and grain yield stability of corresponding hybrids of CIMMYT-Zimbabwe yellow elite inbred lines with CIMMYT-Colombia acid tolerance yellow donor lines under acid and non-acid soil conditions; ii) assess the combining ability for grain yield performance and grain yield stability of corresponding hybrids of the CIMMYT-Zimbabwe white elite inbred lines with CIMMYT-Colombia acid tolerance white donor lines; and, iii) to assess the per se grain yield performance of CIMMYT-Zimbabwe elite white and yellow lines and CIMMYT-Colombia acid tolerant donor lines. To achieve this, ten yellow kernel and eight white kernel elite inbred lines adapted to the mid-altitude climatic conditions, as well as four yellow and eight white kernel acid tolerance donors, were sourced from the CIMMYT-Zimbabwe and CIMMYT-Colombia breeding programmes, respectively. Two separate line x tester crossing nurseries for the white and the yellow kernel lines were established at the CIMMYT-Muzarabani station during the 2014 winter season, and these yielded 47 and 36 crosses with sufficient seed, respectively. The white and yellow kernel crosses (F1s) were separately evaluated alongside eight and six check hybrids, respectively, during the 2014-2016 cropping seasons across nine acid and non-acid sites in Angola and Zimbabwe. Inbred line trials for the white kernel lines as well as the yellow kernel lines were also separately established during the same period. Multi-environmental trial data identified the most promising CIMMYT-Colombia acid tolerance donor lines as CW2, CY3 and CY1, while the most promising among the CIMMYT-Zimbabwe elite lines were ZW6, ZW8, and ZY3. These lines showed the highest positive general combining ability effects for grain yield (GY) and were involved as parents in most of the hybrids identified as the highest yielders under both acid and non-acid soil conditions. The best specific combiners that also showed yield stability, were ZW3 x CW4 and ZY10 x CY3, for the white and yellow kernel line cross hybrids, respectively. The majority of the identified high yielding crosses were also stable for yield across environments. Additionally, inbred line trial data revealed some of the CIMMYT-Zimbabwe lines (such as ZW5 and ZY3) and CIMMYT-Colombia lines (such as CW3 and CY1) as ideal for single-cross hybrid production, because of their high per se GY performance. Overall, the CIMMYT-Colombia acid tolerance donor lines and the elite lines from the CIMMYT-Zimbabwe breeding programme can potentially be used to develop maize inbred lines and hybrids adapted to the acid and non-acid soil conditions in Angola and elsewhere.