Soil types, water and heat stress affect seed qualities of three maize varieties grown under variable conditions

Abstract

Food security in Sub-Saharan Africa is threatened by the increasing incidence of extreme weather events like heat waves and drought. These stressors reduce the yield of maize (Zea mays L.), which is the most important staple food and the highest single source of calories in Sub-Saharan Africa. Therefore, improving maize yield under a stress environment will contribute towards promoting food security in the region. The aim of this research was to study the response of maize plants grown with different soil amendments to heat stress and combined water and heat stresses, as well as the effects of the stress on maize seed qualities and progeny. Two repeated greenhouse and a repeated field trials were performed. The first greenhouse experiment was a 2 × 3 × 3 × 2 factorial in a completely randomized design with four replications. The factors were: environment, heat-stress (HS) and non-heat-stress (NHS); maize variety: WE3128, WE5323, and ZM1523; soil amendment: poultry manure (PM), mineral fertilizer (MF), and complementary (50:50) application of poultry manure/mineral fertilizer; and soil type: sandy clay loam (SCL) and loamy sand (LS). The following growth, phenological and yield attributes were measured: plant height (PH), leaf area (LA), leaf chlorophyll content (LCC), number of leaves (NoL), plant stem diameter (SD), number of days to tassel appearances (DT), number of days silk appearances (DS), tassel silk interval (TSI), stover dry weight in grams (SDWt), dry biomass yield (DBY), harvest index (HI), cob number per plant (NoC) cob length (CL), cob width (CW), cob weight (CWt), grain weight (GWt), shelling percentage (SP), number of grains (GN) and 100-seed weight (SWt). The seeds were analysed for macro and micro mineral concentrations using inductively coupled plasma mass spectrometry. The second greenhouse experiment involved a 3 × 3 × 2 × 3 factorial in a completely randomized design with four replications. Three water stress levels; non-water stress (NS), moderate water stress (MS), and terminal water stress (TS), three soil amendments (PM, MF and MPM), two soil types (SCL and LS), and three drought–tolerant maize varieties were combined to create 54 treatment interactions with four replications. The 54 treatment interactions were grown in a HS environment. The same data were collected in the two greenhouse experiments. Data from ninteen morphological attributes from the two experiments were analysed using Pearson's correlation coefficient, principal component analysis, and path coefficient analysis to assess these attributes’ contributions to GWt under NHS, HS, and combined heat and moderate water stress (HWS) conditions. To determine if the parental growth conditions influenced progeny performance, seeds from the first greenhouse experiments were evaluated in the field for two summer planting seasons. A randomised complete block design experiment with three replications was used to grow the

progenies. The progenies were examined for nineteen morphological and yield-related attributes. The first greenhouse experiment results showed better growth and yield from SCL soil over LS soil. WE5323 and ZM1523 amended with PM produced the highest yields in the NHS and HS environments, respectively. Heat stress exerted a depressive effect on maize growth and yield attributes. HS reduced the LCC, LA, PH, SD, DBY, HI, CWt, GWt, GN, and SDWt by 35, 36, 35, 41, 59, 78, 64, 73, 69, and 23%, respectively. GN, GWt, and CWt were the most informative yield attributes. The second greenhouse experiment results demonstrated a depressive effect of water stress on the maize LA, LCC, SD, DBY, and HI due to the increasing severity of water stress, with the HI dipping by 30.3 and 92.9% in MS and TS plants, respectively. TS reduced CWt, GWt, GN, and SWt by 96, 97, 97, and 63%, respectively. The GGEbiplot explained 96.6% of the yield variation in the treatment interactions. While GN had the most discriminatory power among the maize attributes studied, CWt was the most representative attribute. The maize varieties were ranked WE5323 ≥ ZM1523 > WE3128 in terms of average performance and stability. The NS treatments together with three MS treatments performed better than the population mean following the ranking of the treatment interactions. Under HS and MS conditions, the PM amendment performed well for varieties WE5323 and ZM1523, while the MF amendment performed best for variety WE3128. Compared to the inorganic amendment, the organic amendment had a greater ameliorative capacity for grain yield under combined heat and water stress conditions. Under NHS, HS, and HWS, the correlation results revealed that eight traits consistently produced a significant and positive relationship with GWt. The principal component analysis explained 59.37% of the variation under NHS, 55.12% for HS, and 57.14% under HWS. The path coefficient analyses revealed that in the NHS, HS, and HWS conditions, five traits consistently had a positive direct effect on the GWt. Given the magnitude of the positive direct effects, increasing DBY, HI, and GN in the NHS; increasing GN, HI, and CW in the HS; and increasing HI, DS, LCC, and GN in the HWS will improve GWt. Under various abiotic stress conditions, maize phenotypic expression varied. Except for the main effect of maize variety on grain yield, the results showed significant main and interaction effects of the three factors on grain yield, grain macro, and trace minerals (Mo, Mn, Fe, Zn). The highest grain Zn was obtained with the MF amendment, while the highest grain Fe and yield were obtained from the MPM amendment. When compared to the NHS environment, the HS environment reduced grain yield while increasing grain Fe and Zn

concentrations. WE5323 had the highest concentrations of macro minerals, followed by ZM1523 and WE3128. The correlation result revealed that a proportional relationship between Fe/Zn and grain yield tends to decrease the grain Fe/Zn concentrations. The first and second principal component axes explained 69.51% of the variation in the progenies’ yield attributes. The most informative attributes were GWt and CWt. The GWt and CWt of the progenies were unaffected by the parental heat stress conditions or maize variety, but the progenies' CWt and GN were significantly influenced by the parental soil amendment. Clusters II and III contained the best-performing treatment interactions for each maize variety. WE3128 and ZM1523 had their highest yields from PM amendments in the NHS environment, while WE5323 produced its highest yield from the MPM amendment in the HS environment. The findings from this study revealed that soil type, water and heat stress affected maize seed qualities when grown under varied conditions.