Browsing by Subject "Zea mays"

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Differences in mucilage properties and stomatal sensitivity of locally adapted Zea mays in relation with precipitation seasonality and vapour pressure deficit regime of their native environment
(2023) Berauer, Bernd J.; Akale, Asegidew; Schweiger, Andreas H.; Knott, Mathilde; Diehl, Dörte; Wolf, Marc‐Philip; Sawers, Ruairidh J. H.; Ahmed, Mutez A.
With ongoing climate change and the increase in extreme weather events, especially droughts, the challenge of maintaining food security is becoming ever greater. Locally adapted landraces of crops represent a valuable source of adaptation to stressful environments. In the light of future droughts—both by altered soil water supply and increasing atmospheric water demand (vapor pressure deficit [VPD])—plants need to improve their water efficiency. To do so, plants can enhance their access to soil water by improving rhizosphere hydraulic conductivity via the exudation of mucilage. Furthermore, plants can reduce transpirational water loss via stomatal regulation. Although the role of mucilage and stomata regulation on plant water management have been extensively studied, little is known about a possible coordination between root mucilage properties and stomatal sensitivity as well as abiotic drivers shaping the development of drought resistant trait suits within landraces. Mucilage properties and stomatal sensitivity of eight Mexican landraces of Zea mays in contrast with one inbred line were first quantified under controlled conditions and second related to water demand and supply at their respective site of origin. Mucilage physical properties—namely, viscosity, contact angle, and surface tension—differed between the investigated maize varieties. We found strong influences of precipitation seasonality, thus plant water availability, on mucilage production (R2 = .88, p < .01) and mucilage viscosity (R2 = .93, p < .01). Further, stomatal sensitivity to increased atmospheric water demand was related to mucilage viscosity and contact angle, both of which are crucial in determining mucilage's water repellent, thus maladaptive, behavior upon soil drying. The identification of landraces with pre‐adapted suitable trait sets with regard to drought resistance is of utmost importance, for example, trait combinations such as exhibited in one of the here investigated landraces. Our results suggest a strong environmental selective force of seasonality in plant water availability on mucilage properties as well as regulatory stomatal effects to avoid mucilage's maladaptive potential upon drying and likely delay critical levels of hydraulic dysfunction. By this, landraces from highly seasonal climates may exhibit beneficial mucilage and stomatal traits to prolong plant functioning under edaphic drought. These findings may help breeders to efficiently screen for local landraces with pre‐adaptations to drought to ultimately increase crop yield resistance under future climatic variability.
Dissecting the genetic basis of root- and rhizosphere-related phosphorususe efficiency in European elite maize (Zea mays L.) lines and landraces
(2021) Li, Xuelian; Ludewig, Uwe
In agriculture, farmers massively apply P fertilizer to maintain high yield. Due to the long-term high fertilization rates and long-term organic residue accumulation, the total P pool per hectare has increased between 1900 and 2020. Since modern varieties have often been selected in high-nutrient input conditions for high yields, concerns are being raised that the beneficial traits for P uptake under a limited P supply will gradually decline in elite varieties. Regarding to maize (Zea mays L.), thousands of varieties have been bred since it was domesticated as a food product. It is an open question whether traits and genes related to P deficiency in European maize have changed since the Green Revolution, the start of hybrid breeding and high-intensity fertilization. This is the core research question of this dissertation. Here I present the analysis of roots in response to P deficiency using a diverse panel of European maize genotypes via several experiments. In Chapter I, we focus on whether maize seedlings of the flint and dent heterotic pools vary in the P acquisition and utilization since the onset of hybrid breeding using 34 genotypes in mini-rhizotrons. These genotypes included 16 flint lines that were released over more than five decades ago, 7 doubled haploid lines from the flint landraces (DH_LR), 8 dent lines, and 3 hybrids. Seedling P use efficiency (PUE) and related traits were measured and compared at two P levels in a calcareous soil. In Chapter II, we compared the root exudated organic acids and mycorrhizal fungi colonization degree among 24 genotypes which have been evaluated in Chapter I. These genotypes included 16 flint lines, 6 DH_LR and 2 old dent lines. Seedling colonization with arbuscular mycorrhizal fungi (AMF) and organic acid anion release were measured. P-uptake-related root traits were compared under P-sufficient and P-deficient conditions. In Chapter III, using nearly isogenic maize lines, the B73 wild type and the rth3 root hairless mutant, we quantified the effect of root hairs and AMF infection in a calcareous soil under P deficiency. Wild-type root hairs extended the rhizosphere for acid phosphatase activity by 0.5 mm compared with the rth3 hairless mutant. Total root length of the wild type was longer than that of rth3 under P deficiency. Higher AMF colonization and mycorrhiza-induced phosphate transporter gene expression were identified in the mutant under P deficiency, but plant growth and P acquisition were similar between mutant and the wild type. The mycorrhizal dependency of maize was 33 % higher than the root hair dependency. Root hairs and AMF inoculation are two alternative ways to increase Pi acquisition under P deficiency, but these two strategies compete with each other. In Chapter IV again two nearly isogenic maize lines, the B73 wild type and the rth2 root hairless mutant, were used to address the importance of root hairs during drought and under P deficiency. The results indicate that drought and P deficiency synergistically impair maize growth; while P concentrations were little affected by the loss of root hairs, the P content was massively reduced at combined stress, showing that P deficiency is much more severe under drought. In Chapter V, we first compared the root traits response to low P and high P of six preselected genotypes in European flint in Chapter I. We then generated RNA libraries from the roots of these lines under both low P and high P. Using an expressed genes matrix, we conducted a Weighted Genomic Coexpression Network Analysis (WGCNA), and detected general low P-induced modules and modules that were higher in founder flints. The P deficiency-responsive metabolic processes common to all six genotypes included: (1) acceleration of carbon supply for organic acid synthesis through glycolysis and TCA cycle; (2) alteration of lipid metabolism; (3) changes of activity of transmembrane transporters; (4) carotenoid metabolism. Additionally, the founder flint line EP1, F2 and doubled haploid landrace SM1 have their specific strategies and mechanism to cope with low P. Our findings well support other studies with transcriptome, proteome and metabolome experiments in maize and other species, and point to molecular events involved in the efficient alleviation of P stress in efficient maize accessions. Altogether, this study presents informative analyses in how maize genotypes with distinct breeding history adapt to P deficiency in regard of root, rhizosphere traits and root transcription. It showed correlation between phenotypic traits and gene transcription, which is much more complex than previously reported. It also opened a novel insight into molecular regulation on Pi utilization, resulting in promotion of vegetative biomass in P deficiency. These findings will also provide precious knowledge for plant breeders and agronomists who work on P research in maize and other cereal crops.
Dissection of the genetic architecture of stalk mechanical strength and in vivo haploid induction in maize
(2016) Hu, Haixiao; Melchinger, Albrecht E.
Stalk lodging causes yield losses in maize cultivation ranging from 5 to 20% annually worldwide and stalk mechanical strength is widely accepted as an indirect indicator for its measurement. QTL mapping can reveal the genetic basis of stalk strength and provide information about markers suitable for marker-assisted selection (MAS). Constantly increasing market demands urge maize geneticists and breeders not only to enhance the field performance of new hybrids, but also to improve the breeding process. During the last decade, advances in the double haploid (DH) technology based on in vivo haploid induction (HI) shifted the breeding paradigm and greatly accelerated the breeding process in maize. Further spread of DH technology urgently demands a simple but efficient way for developing new inducers, which could be achieved by introducing the mandatory QTL/gene(s) of HI to advanced breeding lines. Therefore, the main goal of my thesis was to dissect the genetic architecture of stalk strength and detect the mandatory genomic region(s) of HI using genome-wide molecular markers. Several methods have been developed and applied in the literature to evaluate stalk mechanical strength, among which the rind penetrometer resistance (RPR) is a simple, rapid and non-destructive measurement during data collection, whereas stalk bending strength (SBS) is more closely associated with stalk lodging in the field. According to common knowledge in the mechanics of materials, SBS is reflected by the maximum load exerted to breaking (Fmax), the breaking moment (Mmax) and the critical stress (σmax). Thus, to have a complete understanding of the genetic architecture of stalk strength in maize, RPR and SBS (measured by Fmax, Mmax and σmax) were used to characterize stalk strength in our study. Utilizing a segregating population with 216 recombinant inbred lines, our analysis showed that stalk strength traits, RPR and SBS, have high heritability, ranging from 0.75 to 0.91. Nine QTL and one epistatic interaction between QTL were detected for RPR. Two, three and two QTL were detected for Fmax, Mmax and σmax, respectively. All QTL showed minor effects and only one QTL on chromosome 10 had overlapping support intervals between RPR and SBS. Co-locations of QTL and high positive correlations between stalk strength traits and other stalk traits suggested presence of pleiotropism and a complex genetic architecture of stalk strength. Owing to lack of major QTL, MAS solely based on molecular markers was found to be less effective than classical phenotypic selection for stalk strength. However, for SBS we observed considerably higher proportions of genetic variance explained by a genomic selection approach than obtained in QTL mapping with cross validation. Therefore, genomic selection might be a promising tool to improve the efficiency of breeding for stalk strength. All QTL mapping studies conducted hitherto for unraveling the genetic architecture of HI rate detected a major QTL, termed qhir1, in bin 1.04. Dong et al. (2013) further narrowed down this QTL to a 243 kb region. Considering the complex genetic architecture of HI and genetic background noise possibly affecting fine mapping of qhir1, we attempted to validate these results with an alternative approach before embarking on map-based gene isolation. Utilizing 51 maize haploid inducers and 1,482 non-inducers collected worldwide, we were able to investigate the genetic diversity between inducers and non-inducers and detect genomic regions mandatory for HI. The genetic diversity analyses indicated that the inducer group was clearly separated from other germplasm groups and had high familial relatedness. Analyzing our data by a case-control association approach failed because the segregation of HI was heavily confounded with population structure. Moreover, selective sweep approaches commonly used in the literature that are designed for capturing selective sweeps in a long-term evolutionary context failed due to high familial relatedness among inducers. To solve this problem, we developed a novel genome scan approach to detect fixed segments among inducers. With this approach, we detected a segment, termed qhir12, 4.0 Mb in length, within the support interval of the qhir1. This segment was the longest genomic segment detected by our novel approach and was entirely absent in all non-inducers analyzed. However, qhir12 has no overlap with the fine mapping region of Dong et al. (2013), termed qhir11. This indicates that the genomic region harboring the mandatory gene of HI should be confirmed by further experiments to corroborate its existence and identify its location in the maize genome.
Effects of stand density and N fertilization on the performance of maize (Zea mays L.) intercropped with climbing beans (Phaseolus vulgaris L.)
(2022) Villwock, Daniel; Kurz, Sabine; Hartung, Jens; Müller-Lindenlauf, Maria
Maize is Germany’s most important fodder and energy crop. However, pure maize cultivation has ecological disadvantages. Moreover, its yield is low in crude protein, an important feed quality parameter. Maize–bean intercropping can potentially address both issues. A bean variety specially developed for intercropping was first introduced in 2016. Using this variety, a network of institutions conducted 13 field trials from 2017 to 2020 on four sites in Germany. We sought to determine the effects of stand density and nitrogen (N) fertilization on dry matter yield, crude protein yield, and soil mineral N content (Nmin) at harvest of intercropped vs. pure maize. The three intercropping bean densities we tested (7.5, 5.5, and 4 plants/m2) produced non-significantly different yields of dry matter or crude protein, given a maize density of 7.5–8 plants/m2. Intercropping was inferior to pure maize in dry matter yield, but non-significantly different in crude protein yield. Under neither cropping strategy were significant losses in dry matter or crude protein yield recorded with reduced compared to full N fertilization. At full fertilization, however, both pure maize systems and the 8/4 maize–bean intercrop system left significantly higher Nmin at harvest than the other variants of the corresponding system or N fertilization level and thus an increased risk of nitrate leaching. We encourage further optimization of yield performance in maize–bean intercropping, e.g., through breeding or promotion of biological N fixation via rhizobia inoculation. Furthermore, we recommend reducing N fertilization levels in maize cultivation.
Foliar humic acid and salicylic acid application stimulates physiological responses and antioxidant systems to improve maize yield under water limitations
(2023) Altaf, Adnan; Nawaz, Fahim; Majeed, Sadia; Ahsan, Muhammad; Ahmad, Khawaja Shafique; Akhtar, Gulzar; Shehzad, Muhammad Asif; Javeed, Hafiz Muhammad Rashad; Farman, Muhammad
Background: Humic acid (HA) is an organic acid that is naturally present in soil organic matter and improves nutrient availability and the mechanisms involved in plant growth and development. Likewise, salicylic acid (SA) is an important plant hormone involved in the regulation of plant growth and development. A pot experiment was carried out to determine the effects of individual or combined HA and SA application on growth and yield of maize (Zea mays L.) under drought stress conditions. Two maize hybrids, namely, 30T60 (drought tolerant) and 75S75 (drought sensitive), were grown in semi-controlled conditions and foliar applied with SA (1 mM), HA (100 mg L1 ) and their combination (HA + SA). The plants were exposed to drought stress at the tasseling stage (R1, 60 days after sowing) for 2 weeks, while control plants were given normal irrigation. Results: The results showed that HA and SA applications significantly enhanced the gas exchange characteristics (photosynthetic rate, transpiration rate, and stomatal conduc- tance), and antioxidant activity (catalase, guaiacol peroxidase, and superoxide dismutase) of water stressed maize plants. Foliar SA spray significantly increased the photosynthetic efficiency and activity of enzymatic antioxidants closely followed by HA + SA applica- tion that ultimately improved the yield and net benefit cost ratio of maize under water deficit conditions. Conclusion: Our findings suggest that foliar spraying of SA at the initiation of the repro- ductive stage is a cost-effective strategy to obtain a high maize yield under limited water conditions.
Inheritance of Barley yellow dwarf virus resistance in maize
(2015) Horn, Frederike; Stich, Benjamin
Barley yellow dwarf (BYD) is one of the economically most important virus diseases in cereals. Due to increasing winter temperatures it is expected that BYD will become an increasing problem in maize cultivation. In earlier studies, it was reported that BYD has a negative impact on plant performance of maize. BYD virus (BYDV) is transmitted by aphids and the best control of the virus is the development of resistant maize cultivars. Therefore, the first objectives of my thesis research were to (i) determine phenotypic and genotypic variation in five segregating populations and in a broad germplasm set of maize with respect to BYDV tolerance and resistance as well as to (ii) quantify the influence of BYDV infection on the plant traits plant height, ear height, and flowering time. I observed a negative impact of BYDV infection on maize plant traits which shows that the development of resistant maize cultivars is of high importance for maize cultivation. Furthermore, in the connected biparental populations as well as in the association mapping population, I observed a high genotypic variance with regard to BYDV resistance which is the requirement for successful breeding and the identification of genome regions which contribute to BYDV resistance. The evaluation of BYDV resistance by the inoculation with BYDV and by double antibody sandwich enzyme-linked immunosorbent assay (DASELISA) is dificult to be included in the breeding process. Therefore, molecular markers are of high importance for the improvement of BYDV resistance by breeding. Therefore, the objective of this study was the (iii) identification of genome regions which are involved in the BYDV resistance by a genome wide association study (GWAS). For the BYDV resistance traits, significantly (α=0.01) associated SNPs were identified in the GWAS on chromosome 10 and 4. The SNPs identified for virus extinction on chromosome 10 explained in a simultaneous fit 25% of the phenotypic variance and were located in gene regions which were in other plants described to be involved in resistance mechanisms. This suggests that BYDV resistance is inherited oligogenically and that genes involved in general resistance mechanisms are also involved in BYDV resistance in maize. GWAS has the advantage that a large number of alleles per locus can be surveyed simultaneously, and because historical recombinations can be used, the mapping resolution is higher compared to classical linkage mapping. Nevertheless, genes contributing to phenotypic variation which show a low allele frequency can remain undetected. Due to a balanced allele frequency in segregating populations, linkage mapping has the advantage of higher QTL detection power compared to GWAS. Therefore, the objective of this study was to (iv) validate the genome regions with a linkage analysis in connected biparental crosses. The genome region on chromosome 10 which was identified in the GWAS to be linked to BYDV resistance could be validated in the linkage mapping study with connected populations as well as in the single populations. Furthermore, the QTL on chromosome 10 colocalized with the QTL identified in controlled greenhouse conditions. In earlier studies, QTL for other virus resistances were identified on chromosome 10. This suggests that these genes are involved in multiple virus resistances. The identified genome regions explain 45% of the phenotypic variance and are, therefore, promising for the use in MAS. The broad genotypic variation with regard to BYDV resistance, observed in my thesis research, provided a good basis for the successful identification of molecular markers which are associated with BYDV resistance in maize. The markers identified in my study by GWAS were validated by a linkage mapping approach and are promising for the use in marker assisted selection on BYDV resistance in maize breeding.
Resistance of Maize (Zea mays L.) Against the European Corn Borer (Ostrinia nubilalis Hb.) and its Association with Mycotoxins Produced by Fusarium spp.
(2004) Magg, Thomas; Melchinger, Albrecht E.
The European corn borer (ECB, Ostrinia nubilalis Hübner) is a major pest of maize (Zea mays L.) in Europe and continues to spread to northern maize growing regions. The ECB severely affects commercial maize production by decreasing yield stability. In addition, damaged plants often show an increased susceptibility to secondary infections caused by Fusarium spp.. Information about the potential of Bt hybrids (event 176, MON810) to reduce yield losses and mycotoxin contamination under Central European growing conditions is still lacking. However, such monogenic resistances with a strong negative effect on the ECB will break down rapidly. Improving the natural host plant resistance of maize could provide an economical and ecological tool for an integrated pest management system. The overall goal of this study was to evaluate alternative breeding strategies for improving resistance of maize against ECB damage and Fusarium spp.. The objectives were to (1) initiate a selection experiment in the early maturing European flint pool and evaluate a breeding program for ECB resistance in the European dent pool, (2) compare the efficiency of host plant resistance vs. Bt resistance in maize, (3) determine Fusarium-caused mycotoxin contamination of maize genotypes with improved host plant resistance to ECB, and (4) study the association between important agronomic traits, ECB resistance traits, and mycotoxin concentration in early European maize germplasm. The goal of the Hohenheim ECB breeding program, initiated in 1992, was to select lines with improved per se and testcross performance for multiple agronomic traits and ECB resistance. In the standard breeding scheme, line development started from a segregating S1 population. Genotypes were evaluated for their line per se ECB resistance in generations S1, S3, and S5. Lines from the S2, S4, and S5 generations were testcrossed and evaluated for their agronomic performance. Selection was based on ECB resistance and TC performance for grain yield and maturity. In order to compare transgenic Bt maize hybrids carrying event 176 or MON810 with their isogenic counterparts and commercial hybrids or experimental hybrids, field trials in multiple environments were conducted in 1998 to 2000. Furthermore, a laboratory bioassay with neonate ECB larvae was performed to assess mortality and subsequently the level of Bt antibiosis present in the used hybrids of 1998. Resistance traits such as damage rating of stalks, number of damaged plants, and number of larvae per plant were assessed exclusively in manually ECB infested plots. Grain yield, grain dry matter content and plant height were determined in the insecticide protected and the ECB infested main plots. In addition, grain samples from each subplot were drawn at random and analyzed separately for Fusarium mycotoxins such as type B trichothecenes (DON, NIV), Zearalenon (ZEN), Fumonisins (FUM), and Moniliformin (MON). The inbred lines displayed a significant genotypic variance for all ECB resistance traits evaluated. However, in the further course of selection and topcross testing, most dent and flint lines, especially those displaying improved resistance to ECB larvae feeding, were discarded because of their poor agronomic performance. Negative correlations between grain yield, early maturity and the damage rating of stalks were identified. However, three dent lines (P028, P029, P030) with moderate resistance to ECB were developed. In all experiments, Bt hybrids were superior to other hybrids in the control of ECB larvae. Non-Bt hybrids displayed a significant genotypic variance for all evaluated resistance traits; grain yield reductions ranged from 8.6 to 21.8% under manual infestation of ECB. All evaluated resistance traits were highly significantly correlated with each other and showed significant negative correlations to grain yield reduction. Bt hybrids did not differ from their isogenic counterparts for most agronomic traits. Highly significant location and genotype × location interactions were identified for all mycotoxins evaluated, except MON. MON concentration doubled under manual infestation of ECB compared to insecticide protected conditions and a similar trend was found for FUM. Bt hybrids displayed significantly lower MON concentrations than non-Bt hybrids and significantly lower DON concentrations than their isogenic counterparts under ECB infestation. Highly significant correlations between ECB resistance traits and MON were found. However, a significant genotypic variance was observed for DON, 15-A-DON, FUM, and MON concentrations, suggesting variation for resistance against Fusarium spp. in current elite hybrids. By combining different sources of monogenic Bt resistance and quantitatively inherited resistances to ECB, it may be possible to develop hybrids with multiple resistance by pyramiding the underlying genes in one genotype. Therefore, further research is required to identify new sources of ECB resistance and new breeding strategies should be developed. Furthermore, there is indication that an improved resistance against Fusarium spp. possesses a greater potential for reducing mycotoxin contamination of maize kernels than a high level of ECB resistance. Since resistance to ECB and resistance to Fusarium spp. are inherited fairly independently, simultaneous improvement of both resistances seems to be necessary for improving the stability and quality of future maize hybrids.
Thermal imaging for assessment of maize water stress and yield prediction under drought conditions
(2022) Pradawet, Chukiat; Khongdee, Nuttapon; Pansak, Wanwisa; Spreer, Wolfram; Hilger, Thomas; Cadisch, Georg
Maize production in Thailand is increasingly suffering from drought periods along the cropping season. This creates the need for rapid and accurate methods to detect crop water stress to prevent yield loss. The study was, therefore, conducted to improve the efficacy of thermal imaging for assessing maize water stress and yield prediction. The experiment was carried out under controlled and field conditions in Phitsanulok, Thailand. Five treatments were applied, including (T1) fully irrigated treatment with 100% of crop water requirement (CWR) as control; (T2) early stress with 50% of CWR from 20 days after sowing (DAS) until anthesis and subsequent rewatering; (T3) sustained deficit at 50% of CWR from 20 DAS until harvest; (T4) late stress with 100% of CWR until anthesis and 50% of CWR after anthesis until harvest; (T5) late stress with 100% of CWR until anthesis and no irrigation after anthesis. Canopy temperature (FLIR), crop growth and soil moisture were measured at 5‐day‐intervals. Under controlled conditions, early water stress significantly reduced maize growth and yield. Water deficit after anthesis had no significant effect. A new combination of wet/dry sponge type reference surfaces was used for the determination of the Crop Water Stress Index (CWSI). There was a strong relationship between CWSI and stomatal conductance (R² = 0.90), with a CWSI of 0.35 being correlated to a 64%‐yield loss. Assessing CWSI at 55 DAS, that is, at tasseling, under greenhouse conditions corresponded best to the final maize yield. This linear regression model validated well in both maize lowland (R² = 0.94) and maize upland fields (R² = 0.97) under the prevailing variety, soil and climate conditions. The results demonstrate that, using improved standardized references and data acquisition protocols, thermal imaging CWSI monitoring according to critical phenological stages enables yield prediction under drought stress.