Genetic Analysis of Maize Genotypes Under Drought, Low Soil Nitrogen and Combined Stress, and Herbicide Reaction of Selected Inbred Lines

Abstract

The maize breeding programme at the West Africa Centre for Crop Improvement (WACCI) leverages genetic diversity from collected and developed parental lines to develop hybrids that would contribute to improved maize yields in Ghana. However, the performance of newly developed maize inbred lines across varying environments remains inadequately understood as there is limited information. Evaluating genetic diversity and its relationship to plant performance under varying environments is a crucial step for the identification of elite inbred lines with broad adaptability and resilience as well as the development of resilient hybrids for commercialization using these identified inbred lines. The objectives of this research included the following: i) assess the genetic diversity among selected white and yellow kernel maize inbred lines using field phenotyping and ISSR markers, ii) evaluate the response of maize inbred lines to nicosulfuron based herbicide for potential selection of herbicide-tolerant inbred lines, iii) determine the gene action conditioning tolerance to drought, low soil N, combined drought and low soil N in maize inbred lines, and iv) assess the performance and stability of the hybrids under drought, low soil N, combined stresses, and optimum environments. One hundred maize inbred lines were evaluated under two optimal conditions - one with manual weed control and the other with chemical control using a nicosulfuron-based herbicide – to identify herbicide-tolerant lines. Based on per se performance, fifty inbred lines were subsequently selected and evaluated under drought conditions to identify drought-tolerant lines. The selected fifty lines were assayed using thirty inter-simple sequence repeats (ISSR) with only ten showing amplified bands. C316-7, DHL 258 POP 2, and TZIL 25 (60E) 0.4 EMS were consistently identified as superior inbreds across environments, showcasing their resilience and potential for use in breeding programmes with the objective of stress tolerance and yield stability. Inbred lines such as C316-7, DHL 258 POP 2, and DHL 99 POP 2 exhibited herbicide tolerance while DHL 101 POP 5, EXP 124 and TZIL 25 (35G) 0.4 EMS showed superior performance with high Yield Stability Index (YSI) and low Stress Susceptibility Index (SSI), confirming their potential as sources of drought tolerance. Molecular characterization using ISSR markers revealed high polymorphism among the 50 inbred lines, with ISSR-06 recording the highest Polymorphic Information Content (PIC = 0.78), revealing substantial genetic diversity and clutering of inbred lines into four distinct clusters. Twenty-four maize inbred lines were selected and used to generate ninety-six single cross hybrids using the North Carolina Design II (NCD II). The hybrid trials were evaluated at two locations, Legon and Kwadaso, under low soil nitrogen (N), induced drought, combined drought and low soil nitrogen and optimal environments in 2023 and 2024. There was preponderance of additive gene action (GCA) for most traits across environments indicating that recurrent and pedigree selection would be effective for yield improvement and stress tolerance. However, notable non-additive gene action for yield components such as number of ears per plant and ear aspect, highlight the importance of heterosis breeding in exploiting specific parental combinations. Hybrids such as LMI 102 X LMI 140, HP020-4/1(A)/1/1 X DHL 46 POP 1, 1368 X DHL 186 POP 2 and TZIL 25 (40C) 0.4 EMS X TZIL 25 (60E) 0.4 EMS were the superior hybrids in different stress environments, while DHL 99 POP 2 x 9006 and DHL 99 POP 2 x EXP 124 demonstrated broad adaptability across multiple environments. GGE biplot analysis identified three mega-environments and revealed that LMI 102 X LMI 140 was the highest-yielding across all the environments but with moderate stability, whereas DHL 99 POP 2 x 9006 and 1368-150GY(119)S x DHL 184 POP 2 were the most stable, making them ideal for wide adaptation. Superior hybrids identified should be further tested in multiple environments. These can be recommended for location- and stress-specific conditions.