Evaluation of the Spanish maize landrace core collection for drought tolerance

Constructing a Core Collection for Maize ( Zea mays L.) Landrace from Wuling Mountain Region in China

Maize (Zea mays L.) landraces in the northern Guinea savanna and Sudan savanna in West and Central Africa appear to have some drought-adaptive traits. This study was initiated to assess the level of improvement in yield potential and other agronomic traits achieved under drought stress (DS) and in multiple locations (ML) after introgression of alleles from maize landraces into an elite maize variety (AK9443-DMRSR) via backcrossing. Six backcross (BC) populations together with recurrent parent (AK9443-DMRSR), a commercial hybrid (Oba Super-II), and an improved variety (TZLCOMP4C1) were evaluated under controlled DS and full irrigation (FI) during the dry seasons of 1999 and 2000, as well as in seven ML trials. No significant differences were observed among genotypes for grain yield and most of the traits measured under DS and FI. Significant differences were recorded among genotypes for grain yield and other agronomic traits measured in ML and across 11 environments. Drought stress reduced grain yields of the BC1F2 populations by 64% and recurrent parent by 71%. In ML trials, at least half of the populations were better than recurrent parent. The top three BC1F2 populations produced more grains than the recurrent parent (258–360 kg/ha) and Oba Super-II (555–657 kg/ha) with introgression of only 25% genome of the landraces. We concluded that backcross procedure was able to transfer a quantitative trait of grain yield of an elite recurrent parent into maize landraces. Additional backcross generations are needed for improved performance of the BC1F2 populations in drought-prone environments.

Drought is the main limiting factor for maize production, and climate change can aggravate this water scarcity. One way to mitigate this problem is to plant drought tolerance maize genotypes. In landrace maize grown under rainfed conditions there are drought-adapted genotypes, which can be used in breeding programs for drought tolerance. The objective of this study was to evaluate the effect of an early water deficit on the seedling growth of 41 maize landraces from Nuevo León, Mexico, plus seven varieties, by means of drought tolerance indices based on biomass accumulation during both stress and post-stress recovery period, for identifying tolerant and susceptible genotypes. This study was performed at 2016 in Texcoco, Mexico (19°27’N, 98°54’W, 2241 masl). In the greenhouse, 96 treatments were compared (48 genotypes × two soil water regimes: without and with drought) under randomized complete blocks experimental design. After the drought stress period, normal irrigation was resumed for 15 days for recovery. In maize landraces there is genetic diversity in drought tolerance. Landraces GalTrini and SITexas outstanded as the most water deficit tolerant, whereas landraces Berrones, Rodeo, Sabanilla, Carmen, AraTrini and the inbred line L65 were the most drought susceptible. The total biomass measured before water stress was not related to drought adaptability. This study demonstrates that the post stress recovery is more important in drought stress adaptability than the drought resistance, regarding root biomass, shoot biomass and total biomass. Thus, to include the post stress recovery in drought tolerance studies can produce a more precise genotypic classification for drought stress resistance and adaptability.

Because of their local adaptation and economic factors that limit the adoption of commercial hybrids, farmer-saved maize landraces are still grown over a considerable area concentrated in southwest China. To evaluate the potential of using maize landraces, the germplasm characteristics of 96 landraces from southwest China were evaluated at phenotypic, cellular, and molecular levels. The existence of high phenotypic variation and elite germplasm tolerant to low-N, low-P, as well as drought stress was observed. Of the total landraces, 81.25, 7.29, 5.21, and 2.08% were found with 0, 1, 2, 3, and 4 B chromosomes. Using 42 microsatellite (simple sequence repeat) loci, 246 alleles were detected among the landraces. The number of alleles per SSR locus varied from 2 to 10, averaging 5.67 allele per locus, which revealed a high level of genetic diversity of maize landraces in southwest China. Cluster analysis showed that 96 landraces could distinctly be clustered into four groups, which tended to associate with their geographic origins. We propose that the genetic diversity center of maize landraces in southwest China might be in Sichuan. A sharp genetic deviation from Hardy-Weinberg equilibrium was observed from heterozygosity deficiency and a considerable genetic variation was revealed within, rather than among, the landraces. Based on their germplasm characteristics, the innovation and utilization of maize landraces in southwestern China for theoretical and applied research could be achieved by constructing heterosis groups, developing inbred lines with high combining ability, and maintaining the landraces with elite germplasm and B chromosomes using bulked pollen.

Global climate change, its impact on stable food production in the future and possibilities to overcome the problem are the major priorities for research. Breeding varieties with increase adaptability to changing environments, together with better tolerance/resistance to abiotic stress, pest and diseases are possible solution. Maize is one of the most important crops, with high grain yield reduction induced by drought stress. In the present study twenty-six maize landraces from drought tolerant mini-core collection were tested under optimal, drought, and a combination of drought and high density stresses in the field. Morphological traits, plant height, total number of leaves, leaf length, leaf width, anthesis-silking interval and grain yield were recorded for each entry in two replications in three experiments. Besides, drought tolerant indices were evaluated to test the ability to separate more drought tolerant accessions from those with less stress tolerance. Five stress tolerance indices, including stress tolerance index (STI), mean productivity (MP), geometric mean productivity (GMP), stress susceptibility (SSI), and stress tolerance (TOL) were calculated. Data analyses revealed that STI, MP and GMP had positive and significant correlations with grain yield under all conditions. Three-dimensional diagrams displayed assignment of landraces L25, L1, L14, L3, L26, L15 and L16 to group A, based on the stress tolerance index and achieved grain yield under optimal, drought stress, and a combination of drought and high density stress. A biplot analysis efficiently separated groups of landraces with different level of drought tolerance and grain yield. Based on all obtained results, maize landraces L25, L14, L1 and L3, as the most valuable source of drought tolerance, could be recommended for further use in breeding programs.

Maize landrace accessions constitute an invaluable gene pool of unexplored alleles that can be harnessed to mitigate the challenges of the narrowing genetic base, declined genetic gains, and reduced resilience to abiotic stress in modern varieties developed from repeated recycling of few superior breeding lines. The objective of this study was to identify extra-early maize landraces that express tolerance to drought and/or heat stress and maintain high grain yield (GY) with other desirable agronomic/morpho-physiological traits. Field experiments were carried out over two years on 66 extra-early maturing maize landraces and six drought and/or heat-tolerant populations under drought stress (DS), heat stress (HS), combined both stresses (DSHS), and non-stress (NS) conditions as a control. Wide variations were observed across the accessions for measured traits under each stress, demonstrating the existence of substantial natural variation for tolerance to the abiotic stresses in the maize accessions. Performance under DS was predictive of yield potential under DSHS, but tolerance to HS was independent of tolerance to DS and DSHS. The accessions displayed greater tolerance to HS (23% yield loss) relative to DS (49% yield loss) and DSHS (yield loss = 58%). Accessions TZm-1162, TZm-1167, TZm-1472, and TZm-1508 showed particularly good adaptation to the three stresses. These landrace accessions should be further explored to identify the genes underlying their high tolerance and they could be exploited in maize breeding as a resource for broadening the genetic base and increasing the abiotic stress resilience of elite maize varieties.

An European maize (Zea mays L.) landrace core collection (EMLCC) was formed with samples from several countries. Evaluation of the EMLCC may contribute to broad the genetic base of maize breeding programs. The objective of this study was to assess the variability of EMLCC under low nitrogen (N) in relation to high N input. Eighty-five landraces of the EMLCC, grouped in four maturity groups, and three check hybrids were evaluated for response to low (0 kg ha−1) and high (150 kg ha−1) N in Spain and Greece. Five plant size traits (plant height, ear height, leaf length, leaf width and leaf area index), two grain traits (1000-kernel weight and grain yield), and two agronomic traits [growing degree units (GDU) and lodging] were studied. Overall means of plant size and grain traits increased when genotypes were grown at 150-N relative to 0-N input. The relative increase for grain traits was smaller in landraces than in hybrids. This suggests that landraces had lower grain yield response to N supply compared to hybrids. Linear regressions of plant size traits on GDU indicated that vegetative development was primarily associated with flowering lateness. The maturity group was the main source of variation for all traits. Landrace variability within maturity groups was significant for all traits across environments, despite significant landrace × environment interactions. Estimates of genetic and genotype × environment variances, and heritabilities at both high and low N inputs were not significantly different from each other. However estimates were generally larger at high N. Genetic and phenotypic correlation coefficients between the two N levels were very high for all traits.

Yield losses of maize due to drought stress (DS) in environments with limited rains can reach 100 %. Introgression of favorable alleles from diverse landraces into adapted elite varieties will improve performance, hence reducing losses. The objective of this study was to assess the performance of BC populations under DS and multiple locations (ML) after introgression of alleles from diverse maize landraces into an elite variety. Twelve backcross (BC1F2) populations together with their recurrent parent (TZLCOMP4C1) and a commercial hybrid (Oba Super1) were evaluated under DS, well watered (WW) conditions during the dry season, and in seven ML trials in Nigeria. Significant differences were observed among genotypes for all traits except for ear aspect score under DS conditions. Grain yield and most agronomic traits measured were highly significant (p < 0.001) under WW conditions and across ML trials. In DS, eight of the 12 BC1F2 populations had similar mean grain yield compared to their recurrent parent. Four of these populations produced 3–7 % more grains than the recurrent parent. Yield improvement was accompanied by reduced barrenness, days to flowering, plant height and ear placement, and good plant and ear aspect scores. The eight BC1F2 populations should be subjected to recurrent selection under controlled DS, while four other BC1F2 populations with low grain yields could be subjected to additional backcross to increase frequency of favorable alleles for improved performance in stress environments. The resulting improved populations can be invaluable source materials for developing drought tolerant varieties and parental lines of hybrids.

This study aimed to assess the drought and heat stress tolerance of nine Tunisian maize populations and their potential stress tolerance mechanisms. Over two years, nine Tunisian maize populations were evaluated under five environments with varying stress levels and one optimal growth condition in Tunisia. This work formed part of a larger study that includes a total of 223 Mediterranean maize landraces. The nine Tunisian populations were specifically chosen to assess the behavior of landraces adapted to the drought and heat stress conditions prevalent in the southern Mediterranean. In all the locations, the trials followed an augmented design with five blocks and a total of five checks over the two-year study period replicated in each block.The study demonstrated that combined drought and heat stress severely reduced maize yield, with Tunisian landraces experiencing losses of 76% to 95% relative to optimal conditions. Factorial regression analyses were performed to provide a biological interpretation of the contribution of environmental and genotypic variables, as well as their interactions, to grain yield variability. The most representative genotypic covariates were plant height (PH) followed by the number of ears (NE), thousand-grain weight (1000GW), and aerial biomass, respectively, explaining 26%, 12%, 9%, and 8% of the total variability. The significant environmental covariates were cumulative hydric deficit (DHC) and the average anthesis silking interval (ASI_ENV) in each environment, representing 48% of the total environmental variation. The interaction between thousand-grain weight and cumulative hydric deficit had the highest contribution (9%) of interaction for grain yield. The factorial regression indicated that under stress conditions, maize plants appeared to adapt to maintain yield by increasing thousand-grain weight while reducing aerial biomass, number of ears, and grain number. This response likely reflects an enhanced capacity for efficient resource reallocation, supporting the plant's resilience under combined drought and heat stress conditions. The landraces BK, KAR, and MT2 consistently outperformed in most traits under stress conditions, showing significant tolerance and adaptability for across multiple stress levels with better yields and flowering synchronization. The selected best-performing populations could serve as valuable sources of drought and heat stress tolerance sources for future breeding programs.

This study aimed to assess the drought and heat stress tolerance of nine Tunisian maize populations and their potential stress tolerance mechanisms. Over two years, nine Tunisian maize populations were evaluated under five environments with varying stress levels and one optimal growth condition in Tunisia. This work formed part of a larger study that includes a total of 223 Mediterranean maize landraces. The nine Tunisian populations were specifically chosen to assess the behavior of landraces adapted to the drought and heat stress conditions prevalent in the southern Mediterranean. In all the locations, the trials followed an augmented design with five blocks and a total of five checks over the two-year study period replicated in each block.The study demonstrated that combined drought and heat stress severely reduced maize yield, with Tunisian landraces experiencing losses of 76% to 95% relative to optimal conditions. Factorial regression analyses were performed to provide a biological interpretation of the contribution of environmental and genotypic variables, as well as their interactions, to grain yield variability. The most representative genotypic covariates were plant height (PH) followed by the number of ears (NE), thousand-grain weight (1000GW), and aerial biomass, respectively, explaining 26%, 12%, 9%, and 8% of the total variability. The significant environmental covariates were cumulative hydric deficit (DHC) and the average anthesis silking interval (ASI_ENV) in each environment, representing 48% of the total environmental variation. The interaction between thousand-grain weight and cumulative hydric deficit had the highest contribution (9%) of interaction for grain yield. The factorial regression indicated that under stress conditions, maize plants appeared to adapt to maintain yield by increasing thousand-grain weight while reducing aerial biomass, number of ears, and grain number. This response likely reflects an enhanced capacity for efficient resource reallocation, supporting the plant’s resilience under combined drought and heat stress conditions. The landraces BK, KAR, and MT2 consistently outperformed in most traits under stress conditions, showing significant tolerance and adaptability for across multiple stress levels with better yields and flowering synchronization. The selected best-performing populations could serve as valuable sources of drought and heat stress tolerance sources for future breeding programs.

Drought resistance breeding provides a hopeful way to improve yield and quality of wheat in arid and semiarid regions. Constructing core collection is an efficient way to evaluate and utilize drought-resistant germplasm resources in wheat. In the present research, 1,683 wheat varieties were divided into five germplasm groups (high resistant, HR; resistant, R; moderate resistant, MR; susceptible, S; and high susceptible, HS). The least distance stepwise sampling (LDSS) method was adopted to select core accessions. Six commonly used genetic distances (Euclidean distance, Euclid; Standardized Euclidean distance, Seuclid; Mahalanobis distance, Mahal; Manhattan distance, Manhat; Cosine distance, Cosine; and Correlation distance, Correlation) were used to assess genetic distances among accessions. Unweighted pair-group average (UPGMA) method was used to perform hierarchical cluster analysis. Coincidence rate of range (CR) and variable rate of coefficient of variation (VR) were adopted to evaluate the representativeness of the core collection. A method for selecting the ideal constructing strategy was suggested in the present research. A wheat core collection for the drought resistance breeding programs was constructed by the strategy selected in the present research. The principal component analysis showed that the genetic diversity was well preserved in that core collection.

Current climate change models predict an increased frequency and intensity of drought for much of the developing world within the next 30 years. These events will negatively affect maize yields, potentially leading to economic and social instability in many smallholder farming communities. Knowledge about the genetic resources available for traits related to drought tolerance has great importance in developing breeding program strategies. The aim of this research was to study a maize landrace introgression panel to identify chromosomal regions associated with a drought tolerance index. For that, we performed Genome-Wide Association Study (GWAS) on 1326 landrace progenies developed by the CIMMYT Genetic Resources Program, originating from 20 landraces populations collected in arid regions. Phenotypic data were obtained from early testcross trials conducted in three sites and two contrasting irrigation environments, full irrigation (well-watered) and reduced irrigation (drought). The populations were genotyped using the DArTSeq® platform, and a final set of 5,695 SNPs markers was used. The genotypic values were estimated using spatial adjustment in a two-stage analysis. First, we performed the individual analysis for each site/irrigation treatment combination. The best linear unbiased estimates (BLUEs) were used to calculate the Harmonic Mean of Relative Performance (HMRP) as a drought tolerance index for each testcross. The second stage was a joint analysis, which was performed using the HMRP to obtain the best linear unbiased predictions (BLUPs) of the index for each genotype. Then, GWAS was performed to determine the marker-index associations and the marker-Grain Yield (GY) associations for the two irrigation treatments. We detected two significant markers associated with the drought-tolerance index, four associated with GY in drought condition, and other four associated with GY in irrigated conditions each. Although each of these markers explained less than 0.1% of the phenotypic variation for the index and GY, we found two genes likely related to the plant response to drought stress. For these markers, alleles from landraces provide a slightly higher yield under drought conditions. Our results indicate that the positive diversity delivered by landraces are still present on the backcrosses and this is a potential breeding strategy for improving maize for drought tolerance and for trait introgression bringing new superior allelic diversity from landraces to breeding populations.

Background: Drought is the critical abiotic stress constraining the productivity of maize and lack of germplasm possessing drought tolerance results in low maize productivity in Kashmir. Because only 15% of the land in Kashmir Valley is irrigated and 85% of the land is rainfed, maize landrace evaluation for drought desirable traits becomes important. Methods: To identify elite genotypes for drought tolerance, seventy maize landraces designated as K-L 1 to K-L 70 from Kashmir were evaluated for morpho-physiological traits: shoot height, shoot biomass, root depth, root biomass allocation, shoot to total biomass, root to total biomass, relative water content, canopy temperature, cell membrane stability and chlorophyll content. Result: A significant decrease in root and shoot traits, relative water content, cell membrane stability, chlorophyll content and a significant increase in canopy temperature was recorded under drought conditions. The evaluation led to identifying landraces exhibiting desirable traits for drought tolerance that would prove useful for further crop improvement.

Yield performance of the European Union Maize Landrace Core Collection under multiple corn borer infestations

Maize (Zea mays L.) landraces are an important source of genes for improving commercial germplasm. Today, drought tolerance and grain quality are major challenges in maize cultivation due to climatic changes and population growth. The Maize Research Institute genebank has a drought tolerant collection, which includes 13 landraces (from the former Yugoslavia) and 12 introduced populations (from different countries). These accessions were analyzed for protein, oil, starch and tryptophan contents, in order to identify drought tolerant accessions with high grain quality. Also, simple sequence repeat (SSR) analysis with specific primers for opaque2 recessive allele (o2) was carried out. All analyzed accessions showed high levels of protein. Oil content ranged from 3.75 % to 5.40 % and starch content from 67.5 % to 71.30 %. Average protein content was not different (p < 0.01) between landraces and introduced populations. Starch and oil contents were higher in introduced populations at 0.84 % and 0.39 %, respectively (p < 0.01). Twenty-three accessions had high levels of tryptophan content. A high percentage of kernel type 1 and 2 indicated the presence of endosperm hardness modifier genes. Recessive o2 allele was found in most of the accessions. Absence of o2 in some high tryptophan accessions indicated action of another mutation. In two high tryptophan accessions an unknown band was detected. Absence of negative correlations between proteins, tryptophan and oil makes certain accessions suitable for use in the simultaneous improvement of target genotypes for these traits. Identified drought tolerant, high quality accessions can be used in breeding programs aimed at nutritional improvement of maize grown under drought conditions.