Root Lodging Resistance Research Articles

Knockdown of microRNA390 Enhances Maize Brace Root Growth.

Brace root architecture is a critical determinant of maize's stalk anchorage and nutrition uptake, influencing root lodging resistance, stress tolerance, and plant growth. To identify the key microRNAs (miRNAs) in control of maize brace root growth, we performed small RNA sequencing using brace root samples at emergence and growth stages. We focused on the genetic modulation of brace root development in maize through manipulation of miR390 and its downstream regulated auxin response factors (ARFs). In the present study, miR167, miR166, miR172, and miR390 were identified to be involved in maize brace root growth in inbred line B73. Utilizing short tandem target mimic (STTM) technology, we further developed maize lines with reduced miR390 expression and analyzed their root architecture compared to wild-type controls. Our findings show that STTM390 maize lines exhibit enhanced brace root length and increased whorl numbers. Gene expression analyses revealed that the suppression of miR390 leads to upregulation of its downstream regulated ARF genes, specifically ZmARF11 and ZmARF26, which may significantly alter root architecture. Additionally, loss-of-function mutants for ZmARF11 and ZmARF26 were characterized to further confirm the role of these genes in brace root growth. These results demonstrate that miR390, ZmARF11, and ZmARF26 play crucial roles in regulating maize brace root growth; the involved complicated molecular mechanisms need to be further explored. This study provides a genetic basis for breeding maize varieties with improved lodging resistance and adaptability to diverse agricultural environments.

Unmanned aerial vehicles (UAVs)-based crop lodging susceptibility and seed yield assessment during different growth stages of rapeseed (Brassica napus)

Lodging is a great challenge in rapeseed production that significantly affects seed yield and quality. Prediction of lodging susceptibility and seed yield through unmanned aerial vehicles (UAVs)-based framework offers remarkable prospects for higher applicability in agriculture. This study aims to explore the possibility of using a UAV-based framework for predicting the stem and root lodging susceptibility (represented by safety factor, SFs and SFr respectively) and seed yield at different growth stages of rapeseed. The Red-Green-Blue (RGB) and multispectral (MS) images were captured during various growth stages by UAV platforms to calculate 16 vegetation indices (VIs). Furthermore, the relationships of these VIs with lodging susceptibility and seed yield were also established using multiple linear regression (MLR) and four machine learning methods (including random forest machine (RFR), support vector machine, artificial neural network, and K-nearest neighbors). The results revealed that MS-VIs provided a good estimation of seed yield, and stem and root lodging susceptibilities. Among the 16 VIs analyzed, MS-VI SR85 emerged as the best predictor for both seed yield and lodging susceptibility, as is evident by its highest importance scores. Furthermore, when RGB-VIs were coupled with MS-VIs, the R2 values for estimating seed yield, stem lodging and root lodging resistance were enhanced by 150%, 69.6% and 106%, respectively, in comparison with RGB-VIs. Similarly, the RFR provided a more accurate machine learning method for predicting seed yield and lodging susceptibility compared to the other three models. Stem elongation stage was the optimum growth stage for the estimation of seed yield, and stem and root lodging susceptibilities due to its maximum prediction accuracy, as is suggested by the highest R2 values. It can be inferred that a UAV-based framework in combination with RFR could serve as a high-throughput technique for large-scale prediction of lodging susceptibility and seed yield, as early as at stem elongation stage and thus provides an opportunity for timely agronomic intervention.

The Potential Role of Zinc and Silicon in Improving Grain Yield and Lodging Resistance of Rice (Oryza sativa L.)

Understanding the agronomic interventions that ensure higher crop yields and minimize their chances of failure is critical for meeting global nutritional demands. Rice is a staple food crop that is prone to lodging risk, particularly when higher yields are desired. The potential role of a combined application of Zinc (Zn) and Silicon (Si) in determining the grain yield and lodging resistance has been rarely investigated under field conditions. Thus, field trials were carried out to evaluate the grain yield and lodging resistance of rice at two different locations i.e., Qionghai and Wuzhishan, under three levels of Zn (0, 40, and 80 kg ha−1) and Si (0, 120, and 240 kg ha−1). The results showed that Zn application at the rates of 40 and 80 kg ha−1 increased rice yield by 9% and 5% at Qionghai, and by 5% and 6% at Wuzhishan, respectively. The improved grain yield due to Zn application could be attributed to the increased panicles m−2, splikelets m−2, and aboveground biomass. Meanwhile, Zn failed to show any remarkable impact on stem and root lodging susceptibility. Conversely, no significant influence of applying Si on grain yield was observed, while its application at the rates of 120 and 240 kg Si ha−1 enhanced the stem and root lodging resistance (denoted by their respective safety factors, for stem (SFs) and for root (SFr) by 32% and 22% at Qionghai, and by 11% and 34% at Wuzhishan, respectively, compared to zero Si application. The improved lodging resistance in terms of SFs and SFr could be ascribed to the increased stem bending strength and anchorage strength, while self-weight moment of whole plant decreased. In summary, a beneficial role of Si in lodging resistance and Zn in yield enhancement were evidenced in the present study across the two sites. It can be concluded that by combining 40 kg Zn ha−1 with 120 kg Si ha−1, both grain yield and lodging resistance could be simultaneously improved in rice crops.

Impact of straw and its derivatives on lodging resistance and yield of maize (Zea mays L.) under rainfed areas

Addressing the negative impacts of lodging on crops is a global topic, but it is not clear whether and how straw and its derivatives positively affect the lodging resistance, yield, and quality of spring maize in rainfed areas. Therefore, a field experiment with three organic amendments, straw (at 9000 kg ha−1), cattle manure (at 7140 kg ha−1), and biogas residue (at 6554.52 kg ha−1), was set up in a typical rainfed area with film mulching. The results showed that straw and its derivatives significantly improved the mechanical properties of the third internode by improving the cellulose and lignin contents and their related synthase activities, which resulted in a significant increase in the stalk lodging-resistant index by 3.65∼7.23% (P < 0.05); contributed to a deeper and longer root system that significantly improved root pulling force by 1.41∼4.75%, further enhancing the positive correlation between root in the secondary zone and root lodging resistance; and improved the 1000- kernel weight, content of crude fat and crude protein by constructing a lush above-ground population, which significantly increased the grain yield by 5.95∼13.22%. Among them, the performance of biogas residue fermented by both anaerobic and composting was better than that of other treatments, which provided an informative organic solution for synchronizing the spring maize lodging resistance and yield increase.

Row spacing, seeding depth, seeding rate, and trinexapac‐ethyl effects on oat yield and lodging

AbstractLodging can reduce the yield and quality of oats (Avena sativa L.). Root lodging, as opposed to stem lodging, is the predominant form of lodging in oats. Therefore, identifying management practices that enhance root lodging resistance should be prioritized. The objective of this study was to investigate the effect of four management practices on oat grain yield, yield components, grain quality, observed lodging, and plant traits that contribute to root lodging resistance. Row spacing and seeding depth were tested in three oat cultivars across two environments in Ontario, Canada. Seeding rate and the application of the plant growth regulator trinexapac‐ethyl (TE) at different nitrogen (N) fertilizer rates were tested in two‐to‐three oat cultivars across four environments. Lodging occurred naturally in all environments, with root lodging always occurring, sometimes in combination with stem lodging. Under high lodging pressure, shallow seeding increased lodging. Similarly, lodging increased with greater seeding rates when lodging pressure was high. Reducing row spacing had no effect on lodging but was the only management practice to consistently increase grain yield. TE reduced lodging in some environments, especially as N rates increased. Root plate spread, root plate depth, and root safety factor were minimally affected by the management practices studied and had complex interactions with genotype and environment. Among the measured crop traits, plant height had the strongest and most consistent relationship to observed lodging.

Local auxin biosynthesis regulates brace root angle and lodging resistance in maize.

Root lodging poses a major threat to maize production, resulting in reduced grain yield and quality, and increased harvest costs. Here, we combined expressional, genetic, and cytological studies to demonstrate a role of ZmYUC2 and ZmYUC4 in regulating gravitropic response of the brace root and lodging resistance in maize. We show that both ZmYUC2 and ZmYUC4 are preferentially expressed in root tips with partially overlapping expression patterns, and the protein products of ZmYUC2 and ZmYUC4 are localized in the cytoplasm and endoplasmic reticulum, respectively. The Zmyuc4 single mutant and Zmyuc2/4 double mutant exhibit enlarged brace root angle compared with the wild-type plants, with larger brace root angle being observed in the Zmyuc2/4 double mutant. Consistently, the brace root tips of the Zmyuc4 single mutant and Zmyuc2/4 double mutant accumulate less auxin and are defective in proper reallocation of auxin in response to gravi-stimuli. Furthermore, we show that the Zmyuc4 single mutant and the Zmyuc2/4 double mutant display obviously enhanced root lodging resistance. Our combined results demonstrate that ZmYUC2- and ZmYUC4-mediated local auxin biosynthesis is required for normal gravity response of the brace roots and provide effective targets for breeding root lodging resistant maize cultivars.

Effects of Plant Growth Regulators and Nitrogen Management on Root Lodging Resistance and Grain Yield under High-Density Maize Crops

Lodging is one of the main factors causing yield loss of maize under high-density planting conditions. Root lodging as an important lodging type has received little attention. Plant growth regulators (PGRs) and nitrogen fertilizer can coordinate the relationship between root lodging and yield. This two-year field experiment was conducted with two nitrogen levels of N225 (225 kg ha−1) and N300 (300 kg ha−1) at a high planting density (90,000 plants ha−1) during the maize growth season from 2019 to 2020. Plant growth regulator (Yuhuangjin, the mixture of 3% DTA-6 and 27% ethephon) was sprayed at the V8 stage. The results showed that PGRs significantly decreased plant height, improved root distribution and dry weight, enhanced photosynthetic rate and activities of photosynthetic carboxylase in ear leaves, and improved root bleeding sap and root activities after the silking stage. N225 combined with PGRs reduced the occurrence of root lodging and was conducive to photosynthate accumulation and root nutrient supply; it coordinated root regulation and morphological and physiological shoot functions, and played a crucial role in reducing root lodging and improving maize yield.

Evaluation of root lodging resistance during whole growth stage at the plant level in maize

Root lodging due to strong storm wind is a common problem in maize (Zea mays) production, leading to reduced crop yield and quality and harvest efficiency. Little information is available on quantifying effects of vertical leaf area distribution on root lodging in crops such as maize. Anti-lodging index of root was computed by the formula: ALroot = Mroot / Mwind, where AL denotes anti-lodging index, and M moment of force. Mroot, root failure moment of force equals to moment arm times max root side-pulling force measured in situ by means of the digital pole dynamometer, and Mwind, wind resultant moment of force is estimated with vertical leaf area distribution and wind speed. Two maize cultivars were examined at 5 different growth stages from V8 to physiological maturity in 2019 and 2020, in Qingdao, China. Root anti-lodging index in tested cultivars fluctuated to a small extent within any year during whole growth period excluding at V8, while there was an inter-annual shift in index means (1.23 vs 0.84). Both root failure moment and wind resultant moment increased first and then decreased with the growth stage, and their influences on root anti-lodging index varied with the year. At wind grade 6, effect sizes, as contribution to root anti-lodging index, of root moment and wind moment were respectively 0.88 and 0.98. The difference in anti-lodging index between cultivars seemed to be disappearing as wind grade goes up. Root failure moment of force positively related to single root tensile resistance, root-soil ball volume, root number and total root length, whose correlation coefficient was the maximum of 0.94. Root anti-lodging index of maize proved stable from V8 on during whole growth period, and vertical leaf area distribution played a substantial role in maize root lodging in terms of wind resultant moment. Our findings provide the insights into root lodging events in crops such as maize, and would serve an approach to assessing crop root lodging resistance in breeding and cultivation programs.

Lodging resistance in maize: A function of root–shoot interactions

The differences in root and stem structure between lodging resistant (LR) and susceptible (LS) genotypes have yet to be fully understood in maize (Zea mays L.). To clarify these differences, lodging rates and yield of LS genotype XunDan20 (XD20) and LR genotype FuMin985 (FM985) across five locations in China from 2014 to 2018 were investigated. Simultaneously, field experiments including genotypes XD20 and FM985 and two plant densities of 75,000 (D75000) and 105,000 plant ha−1 (D105000) were specifically performed at two locations in North China Plain in 2018. Stem and root lodging rates of XD20 were significantly higher than that of FM985 mainly because FM985 had a larger root system and a stronger basal stem. Compared to XD20, FM985 had significantly larger values in root crown width, root angle, length (+37.1 %), volume (+25.5 %), and length density (+29.9 %) in 0−10 cm soil. Although FM985 had longer and thinner basal stem internodes, the larger sclerenchyma and more compact distribution of epidermal cells in the rind resulted in greater rind penetration strength in FM985 than in XD20. Results from 13C and 15N isotope labelling revealed that the high stem strength and root anchorage strength of FM985 were related to the large assimilate allocations to roots and basal internodes. With increased plant density, XD20 had larger reductions in stem morphological parameters, leading to a smaller stem lodging resistance; FM985 showed larger reductions in root traits but still had a high root lodging resistance at high plant density due to the large root system. LR maize allocates more photosynthetic assimilates to roots and stems and maintains a higher capacity of nutrient absorption, reflecting a function of root–shoot interactions during formation and maintenance of lodging resistance.

Wide–Narrow Row Planting Pattern Increases Root Lodging Resistance by Adjusting Root Architecture and Root Physiological Activity in Maize (Zea mays L.) in Northeast China

Root lodging (RL) in maize can reduce yield and grain quality. A wide–narrow row planting pattern can increase maize yield in the growing regions of northeastern China, but whether it can improve RL resistance is not clear. Therefore, in this study, the root architecture distribution, root physiological activity, and root lodging rate under planting pattern 1 (uniform ridge of 65 cm, east–west ridge direction) and pattern 2 (wide–narrow rows, 40 double narrow rows and 90 wide rows, north–south ridge direction) were studied. The results showed that the RL rate under pattern 2 was significantly lower than that under pattern 1. The number and diameter of nodal roots on the upper node, the root failure moment, and the root bleeding sap intensity at the 3 weeks after VT under pattern 2 were significantly higher than those under pattern 1. Root length density in the 0–40 cm soil layer tended to be inter-row distributed. Therefore, the RL resistance of maize under pattern 2 was increased through an adjustment in the root architecture distribution and root physiological activity in northeastern China.

Identifying quantitative trait loci for lodging‐associated traits in the wheat doubled‐haploid population Avalon × Cadenza

AbstractLodging affects grain quality and grain yield in wheat (Triticum aestivum L.) and is difficult to breed for because its sporadic incidence and laborious protocols to measure lodging traits. Thus, developing molecular markers for these traits can increase selection efficiency in breeding programs. The aim of this article is to identify quantitative trait loci (QTL) associated with stem/anchorage strength and leverage traits (lodging traits) in a doubled‐haploid population of UK bread wheat Avalon × Cadenza. Field experiments were conducted in the UK during 2012–2013 near High Mowthorpe and during 2013–2014 at Sutton Bonington. Phenotypic and genetic analysis indicated significant genetic variation for all traits. Stem strength (diameter, wall width, and material strength) and leverage (plant height) traits were highly heritable (0.64–0.95), whereas anchorage strength traits (root plate spread and structural rooting depth) and ear number per plant (leverage trait) were less heritable (0.21–0.33). This study identified 18 QTL for lodging traits and grain yield in chromosomes 1D, 2B, 2D, 3A, 3B, 4A, 4D, 5B, and 6B. Two QTL for stem strength on chromosome 1D and 3B explaining 49.6% of the total phenotypic variation (PVE) are estimated to reduce stem lodging risk and shortening the plant height by 12 cm. One QTL for root plate spread on chromosome 5B explaining 22.4% of the PVE could increase root lodging resistance.

The stage sensitivity of short‐term heat stress to lodging‐resistant traits and yield determination in canola (Brassica napus L.)

AbstractWith the expected increase of abiotic stress under global climate change, significant research has been devoted to how abiotic stress will affect crop production. To date, there has been little research on the stage sensitivity of short‐term heat stress to crop lodging and yield determination in canola. This research was conducted in a controlled growth facility and aimed to examine root morphology, pod fertility, seed yield and crop lodging of two contrasting canola genotypes subjected to a short‐term heat stress (27.0/24.3°C, light/dark), imposed respectively at three growth stages, rosette vegetative stage (RVHT), early flowering stage (EFHT) and late flowering stage (LFHT), in comparison with non‐stressed control (CK) (23/17°C). The results demonstrate that heat stress imposed at RVHT and LFHT was less detrimental to seed yield and lodging resistance. However, EFHT showed significant adverse effects on both, which was further confirmed by redundancy analysis (RDA) and structural equation modelling (SEM). Compared with the CK, EFHT resulted in a yield loss of 43%, which was mainly due to poor pod fertility, less number of filled pods (−28%), decreased pollen viability (−38%) and a lower success ratio of filled pods (−29%). The taproot was found to be relatively tolerant to heat stress, but lateral roots were sensitive to heat stress at EFHT and LFHT. Root capacitance could be used as a non‐destructive method for evaluating lateral root morphology. Compared with the CK, EFHT displayed a high risk of stem lodging, as indicated by a 27% lower safety factor. This was mainly attributed to the reduced stem bending strength that was caused by the deterioration of stem mechanical properties under EFHT, as illustrated by SEM. Root lodging resistance was not altered by any stages of short‐term heat stress, as the taproot remained stable.

Field-based mechanical phenotyping of cereal crops to assess lodging resistance.

Plant mechanical failure, also known as lodging, is the cause of significant and unpredictable yield losses in cereal crops. Lodging occurs in two distinct failure modes—stalk lodging and root lodging. Despite the prevalence and detrimental impact of lodging on crop yields, there is little consensus on how to phenotype plants in the field for lodging resistance and thus breed for mechanically resilient plants. This review provides an overview of field‐based mechanical testing approaches to assess stalk and root lodging resistance. These approaches are placed in the context of future perspectives. Best practices and recommendations for acquiring field‐based mechanical phenotypes of plants are also presented.

Sprinkler irrigation increases grain yield of sunflower without enhancing the risk of root lodging in a dry semi-humid region

Sunflower (Helianthus annuus L.) is an important edible oilseed crop that is frequently exposed to drought stress due to lack and unpredictability of precipitation. Sprinkler irrigation (SI) is a promising approach for improving yield under limited availability of water, but is often associated with increased risk of root lodging. The irrigation water can soften the upper soil layer and increase the torque of the aboveground portion of the crop. This study aims to evaluate the effect of SI and nitrogen (N) application rate on grain yield, water use efficiency (WUE), and root lodging resistance of sunflower. The risk of root lodging was evaluated by a “safety factor” (SF) indicator. The results showed that soil water content (%) was 13.4 and 19.1% higher under SI in comparison with rainfed (RF) conditions in 2018 and 2019 respectively, when averaged across the whole measured period. Sprinkler irrigation exhibited 12% higher mean grain yield than RF conditions across both years (P < 0.05), although WUE was not influenced. The yield advantage under SI was supported by strong relationships of grain yield with harvest index, aboveground biomass and yield components. A positive yield response to increasing N rate from 0 to 180 kg N ha–1 was evidenced, beyond which no response was observed. Root lodging resistance in terms of SF increased with higher N application rate due to decrease in anchorage strength. Root lodging resistance between SI and RF treatments was not significantly different due to the trade-off between anchorage strength and self-weight moment, although irrigation water under SI weakened the soil shear strength and reduced the anchorage strength estimated by a theoretical model. Taken together, SI in combination with an N rate of 180 kg ha–1 could be recommended to mitigate drought stress and improve grain yield and root lodging resistance of sunflower.

Traits of plant morphology, stalk mechanical strength, and biomass accumulation in the selection of lodging-resistant maize cultivars

• There is no correlation in current maize cultivar’s resistance to stalk or root lodging. • Stalk breakage is primarily affected by dry weight per unit length during grain filling. • Vertical root pulling resistance is primarily affected by the ratio of root depth to width. • High ratios of shoot fresh weight to vertical root pulling resistance increase maize root lodging risk. Lodging resistance is a major desired trait in modern maize breeding. Identifying parameters to evaluate lodging resistance could help crop breeders develop maize cultivars with improved lodging resistance. Thirty-four summer maize cultivars currently planted in China were grown in 2017 and 2018 in order to identify relationships between stalk and root lodging resistance and to analyze the main reasons for differences in lodging resistance between maize cultivars. Twenty-five lodging resistance indicators, including aspects of morphology, dry matter, moisture content, and the mechanical strength of the stalk and root, were investigated at silking and 35 d after silking. The experiments showed that the ratio of shoot fresh weight to vertical root pulling resistance (VRPR) was a better indicator of root lodging potential than VRPR alone. Stalk breaking force was not associated with VRPR and was significantly positively correlated with shoot fresh weight/VRPR. Classification of the 34 cultivars revealed that resistance to stalk and root lodging were not correlated. Correlation and regression analyses revealed that approximately 63 % of the breaking force was explained by the average dry weight per unit length (DWUL) of the basal three internodes, ear height, and fresh weight of the basal three internodes at silking. At 35 d after silking, approximately 88 % of the difference in breaking force was explained by the plant height, ear ratio, crush strength (CS) of the fourth internode, average DWUL and fresh weight per unit volume (FWUV) of the basal three internodes. The main indicator affecting VRPR was the ratio of root depth to width at 35 d after silking. Therefore, an important strategy for increasing maize lodging resistance is to breed cultivars with high internode DWUL, low ear position, and deep roots.

Enhancing root lodging resistance of maize with twin plants in wide-narrow rows: a case study

ABSTRACT Root lodging is known to reduce the yield and quality of maize, which will be more serious driven by the changes in agriculture such as the higher planting density and the more extreme precipitation events. Here we describe a new cultivation method to reduce the root lodging of maize. We designed two planting layouts: twin plants (TP) and single plant (SP) in a hole with the same density. The vertical root-pulling resistance, angle and rate of natural root lodging, root and shoot morphology related to root lodging and maize yield were compared between two planting layouts. TP planting significantly increased the vertical root-pulling resistance and angle of natural root lodging. This can be partly attributed to the gripping force between the staggered crown roots of the two adjacent plants. Moreover, the TP planting could increase root-lodging resistance by increasing the root angle (acute angle between the stem direction and root) and stem diameter. Additionally, TP planting did not reduce the maize yield and biomass. Consequently, our study demonstrated that the twin plants in a hole are effective to decrease the root lodging of maize in southwest of China. This technique is simple, inexpensive, safe, stable, and has broader potential for increasing maize yield and quality.

On‐farm Performance and Farmers’ Perceptions of DroughtTEGO‐Climate‐Smart Maize Hybrids in Kenya

Maize (Zea mays L.) productivity in the sub‐Saharan Africa is constrained by biotic and abiotic stresses that reduce yield. In the region, one of the most serious abiotic factor is frequent intermittent droughts, which has been attributed to climate change. The purpose of this paper was to use on‐farm demonstration studies and farmer field days to demonstrate new drought mitigation technology and provide information on how small farmers can reduce yield losses. A total of 4814 demonstration plots of 39 DroughtTEGO maize hybrids and 19 commercial check hybrids were established in 17 counties across the low‐to‐mid‐altitude maize‐growing agroecologies of Kenya between 2015 and 2017. A total of 246 field‐day workshops were conducted. Combined analyses across years and locations showed that top five DroughtTEGO hybrids increased maize yields 33 to 54% (5.5–6.3 Mg ha−1) relative to conventional hybrids. The highest yield advantage of DroughtTEGO hybrids over commercial checks was observed in the drier lower eastern region in Kenya. Farmers particularly women, preferred the DroughtTEGO hybrids because of the stay‐green character, whiteness of flour (milling quality), root lodging resistance, drought‐tolerance and shelling percentage. Results from this study suggested that smallholder farmers can reduce the impact of drought by seeding drought‐tolerant maize hybrids.Core Ideas High yields and farmer‐preferred traits determine adoption of new varieties. Conducting on‐farm demonstrations can overcome adoption barriers. Planting of drought‐tolerant hybrids mitigates drought stress for smallholder‐farmers.

Enhance root-bleeding sap flow and root lodging resistance of maize under a combination of nitrogen strategies and farming practices

A cultivation technique in combination of nutrient strategies has not been implemented on root growth, root-bleeding sap, lodging resistance and production of corn. Therefore, we conducted field trials implementing different cultivation techniques (ridge-furrow system with film covered (RF), ridge-furrow system with soil crust (SC), and flat soil planting system with no ridge and no cover (TF); with four nitrogen levels: 300 kg N ha−1 (3); 200 kg N ha−1 (2); 100 kg N ha−1 (1) and 0 kg N ha−1 (0), during 2015–2016. The aim of this work was to improve soil water storage, yield components, and production through regulating root growth and lodging resistance. The results showed that the RF system under different nutrient levels had significantly improved soil water storage, yield components which led to promote the development of roots in deep soil (0–50 cm) than that of SC and TF planting. The RF2 treatment significantly increased the root volume density (RVD), root weight density (RWD), and root diameter at various growth stages and attained the maximum value at 125 DAP (except root diameter) than that of TF2 treatment. The root surface area density (RSD) and root length density (RLD) were significantly increased in the upper 10–60 cm soil layer under the RF and SC cultivation patterns during silking and maturity stages than that of TF planting under different N levels. However, among the different treatments, there was non-significant variation in RSD and RLD at below 70 cm soil profile. The RF2 and SC2 considerably increased the root dry weight, and the root bleeding sap during entire growth stages of maize crop than that of TF2 planting. The RF system with different N levels delayed roots senescence in the later growth stage, and the production was significantly increased compared with SC and TF planting. Compared with SC2 and TF2 treatment, the RF2 treatment significantly increased the grain yield 5.7 t ha−1 (104%) and reduces root (79%) and stem (95%) lodging rate; therefore, RF2 cultivation method might be an appropriate water saving approach in semi-arid regions.

Yield gains and associated changes in an early yellow bi-parental maize population following genomic selection for Striga resistance and drought tolerance

BackgroundMaize yield potential is rarely maximized in sub-Saharan Africa (SSA) due to the devastating effects of drought stress and Striga hermonthica parasitism. This study was conducted to determine the gains in grain yield and associated changes in an early-maturing yellow bi-parental maize population (TZEI 17 x TZEI 11) F3 following genomic selection (GS) for improved grain yield, Striga resistance and drought tolerance. Fifty S1 lines were extracted from each of cycles C0, C1, C2 and C3 of the population and crossed to a tester TZEI 23 to generate 200 testcrosses. The testcrosses were evaluated under drought, artificial Striga-infested and optimal (free from Striga infestation and without limitation of water and nitrogen) environments in Nigeria, 2014-2017.ResultsGains in grain yield of 498 kg ha− 1 cycle− 1 (16.9% cycle− 1) and 522 kg ha− 1 cycle− 1 (12.6% cycle− 1) were obtained under Striga-infested and optimal environments, respectively. The yield gain under Striga-infested environments was associated with increased plant and ear heights as well as improvement in root lodging resistance, husk cover, ear aspect and Striga tolerance. Under optimal environments, yield gain was accompanied by increase in plant and ear heights along with improvement of husk cover and ear rot resistance. In contrast, genomic selection did not improve grain yield under drought but resulted in delayed flowering, poor pollen-silk synchrony during flowering and increased ear height. Genetic variances and heritabilities for most measured traits were not significant for the selection cycles under the research environments. Ear aspect was a major contributor to grain yield under all research environments and could serve as an indirect selection criterion for simultaneous improvement of grain yield under drought, Striga and optimal environments.ConclusionThis study demonstrated that genomic selection was effective for yield improvement in the bi-parental maize population under Striga-infested environments and resulted in concomitant yield gains under optimal environments. However, due to low genetic variability of most traits in the population, progress from further genomic selection could only be guaranteed if new sources of genes for Striga resistance and drought tolerance are introgressed into the population.

The genetic architecture of nodal root number in maize.

The maize nodal root system plays a crucial role in the development of the aboveground plant and determines the yield via the uptake of water and nutrients in the field. However, the genetic architecture of the maize nodal root system is not well understood, and it has become the 'dark matter' of maize genetics. Here, a large teosinte-maize population was analyzed, and high-resolution mapping revealed that 62 out of 133 quantitative trait loci (QTLs), accounting for approximately half of the total genetic variation in nodal root number, were derived from QTLs for flowering time, which was further validated through a transgenic analysis and a genome-wide association study. However, only 16% of the total genetic variation in nodal root number was derived from QTLs for plant height. These results gave a hint that flowering time played a key role in shaping nodal root number via indirect selection during maize domestication. Our results also supported that more aerial nodal roots and fewer crown roots might be favored in temperate maize, and this root architecture might efficiently improve root-lodging resistance and the ability to take up deep water and nitrogen under dense planting.