Assessment of Genetic Diversity for Drought, Heat and Combined Drought and Heat Stress Tolerance in Early Maturing Maize Landraces

Abstract

Climate change is expected to aggravate the effects of drought, heat and combined drought and heat stresses. An important step in developing ‘climate smart’ maize varieties is to identify germplasm with good levels of tolerance to the abiotic stresses. The primary objective of this study was to identify landraces with combined high yield potential and desirable secondary traits under drought, heat and combined drought and heat stresses. Thirty-three landraces from Burkina Faso (6), Ghana (6) and Togo (21), and three drought-tolerant populations/varieties from the Maize Improvement Program at the International Institute of Tropical Agriculture were evaluated under three conditions, namely managed drought stress, heat stress and combined drought and heat stress, with optimal growing conditions as control, for two years. The phenotypic and genetic correlations between grain yield of the different treatments were very weak, suggesting the presence of independent genetic control of yield to these stresses. However, grain yield under heat and combined drought and heat stresses were highly and positively correlated, indicating that heat-tolerant genotypes would most likely tolerate combined drought and stress. Yield reduction averaged 46% under managed drought stress, 55% under heat stress, and 66% under combined drought and heat stress, which reflected hypo-additive effect of drought and heat stress on grain yield of the maize accessions. Accession GH-3505 was highly tolerant to drought, while GH-4859 and TZm-1353 were tolerant to the three stresses. These landrace accessions can be invaluable sources of genes/alleles for breeding for adaptation of maize to climate change.

Assessing the Potential of Extra-Early Maturing Landraces for Improving Tolerance to Drought, Heat, and Both Combined Stresses in Maize

“…In agreement with previous studies [19], the wide range of variation in GY losses observed in this study indicated that indeed the applied stresses were severe and that the yield levels observed could be attributed to stress tolerance. Compared with the NS environment, HS, DS, and DSHS, on the averaged reduced GY by~23%, 49%, and 58%, respectively (Tables 1 and 2), suggesting that the effect of the combined stresses on GY of the extra-early maize accessions was higher than the individual effects but lower than their sum (hypo-additive effect).…”

“…Compared with the NS environment, HS, DS, and DSHS, on the averaged reduced GY by~23%, 49%, and 58%, respectively (Tables 1 and 2), suggesting that the effect of the combined stresses on GY of the extra-early maize accessions was higher than the individual effects but lower than their sum (hypo-additive effect). These results corroborated the findings of earlier workers who reported higher yield losses from the combined effects of DS and HS than DS and HS applied alone in cereals including maize [17,19,29,46]. The high GY loss under DSHS compared to HS and DS could be attributed to the interaction effects of HS and DS on stomatal movements [46].…”

“…Low repeatability estimates across sites for some measured traits were probably the result of inconsistent expressions as indicated by high genotype × environment variance. Similar findings were reported in maize under multiple stresses [19,29].…”

“…In particular, temperatures during flowering and early grain-filling stages substantially exceeded the optimal threshold for lowland tropical maize (34 • C during the day and 23 • C at night; Figure 2) with no incidence of rainfall, indicating that the sites selected for this study were appropriate for screening the maize accessions for tolerance to HS and DSHS. These sites were used for screening maize for high levels of tolerance to DS and/or HS in earlier studies [13,18,19].…”

“…Despite their potential, most genetic diversity studies on maize landraces have focused on the analysis of variation in genetic parameters without much consideration for traits that confer tolerance to abiotic stress conditions. Only few studies have assessed the amount and nature of variation in landrace accessions of maize under individual and combined DS and HS [19,27].…”