Determining to what degree seed weight differences are due to competition among seeds for insufficient source is critical for the rational design of breeding and management strategies aimed at ...maximizing crop yields. While the crop physiology literature cites many examples of source and/or sink yield limitations during seed filling, interpretation of these data has usually been qualitative in nature, biasing our view of the source–sink yield limitations during this period. In the present review, we applied a quantitative approach for determining the magnitude of seed dry weight changes in response to manipulations in assimilate availability during seed filling for previously published articles in wheat (
Triticum aestivum), maize (
Zea mays L.) and soybean (
Glycine max L.). This quantitative approach demonstrates that yield is usually more sink than source limited during seed filling in the three crops, though: (i) interspecific variation exists in the magnitude of limitation, and (ii) intraspecific variability is larger in soybean than in cereals. Seeds of wheat appeared to grow mostly at saturated assimilate availability, so yield is mainly sink limited in all growing conditions×cultivar combinations explored in the analysis. Soybeans seem to experience a large degree of co-limitation by the source and the sink, as seeds greatly respond to source–sink modifications. Maize displayed a consistent trend to dramatic reductions in seed dry weight when assimilates produced during seed filling are reduced, but a virtual lack of responsiveness to improvements in potential availability of assimilates per growing seed. This results in a sink-limited crop in most growing conditions, but a source-limited crop if resource availability is strongly reduced during seed filling.
The fraction of intercepted photosynthetically active radiation (fPARi) is typically described with a non-linear function of leaf area index (LAI) and k, the light extinction coefficient. The ...parameter k is used to make statistical inference, as an input into crop models, and for phenotyping. It may be estimated using a variety of statistical techniques that differ in assumptions, which ultimately influences the numerical value k and associated uncertainty estimates. A systematic search of peer-reviewed publications for maize (Zea Mays L.) revealed: (i) incompleteness in reported estimation techniques; and (ii) that most studies relied on dated techniques with unrealistic assumptions, such as log-transformed linear models (LogTLM) or normally distributed data. These findings suggest that knowledge of the variety and trade-offs among statistical estimation techniques is lacking, which hinders the use of modern approaches such as Bayesian estimation (BE) and techniques with appropriate assumptions, e.g. assuming beta-distributed data. The parameter k was estimated for seven maize genotypes with five different methods: least squares estimation (LSE), LogTLM, maximum likelihood estimation (MLE) assuming normal distribution, MLE assuming beta distribution, and BE assuming beta distribution. Methods were compared according to the appropriateness for statistical inference, point estimates' properties, and predictive performance. LogTLM produced the worst predictions for fPARi, whereas both LSE and MLE with normal distribution yielded unrealistic predictions (i.e. fPARi < 0 or > 1) and the greatest coefficients for k. Models with beta-distributed fPARi (either MLE or Bayesian) were recommended to obtain point estimates. Each estimation technique has underlying assumptions which may yield different estimates of k and change inference, like the magnitude and rankings among genotypes. Thus, for reproducibility, researchers must fully report the statistical model, assumptions, and estimation technique. LogTLMs are most frequently implemented, but should be avoided to estimate k. Modeling fPARi with a beta distribution was an absent practice in the literature but is recommended, applying either MLE or BE. This workflow and technique comparison can be applied to other plant canopy models, such as the vertical distribution of nitrogen, carbohydrates, photosynthesis, etc. Users should select the method balancing benefits and tradeoffs matching the purpose of the study.
► We examined heat stress effects on grain yield and its physiological determinants. ► Hybrids of contrasting genetic background were tested (temperate and tropical). ► Negative effects of heat were ...largest on radiation use efficiency and harvest index. ► Variation in harvest index was associated with changes in apparent reserves use. ► Tropical genetic background conferred an enhanced capacity for enduring heat effects.
Maize (Zea mays L.) hybrids with tropical genetic background are a promising source of heat stress tolerance, but their performance in high yielding environments remains poorly understood. Our objective was to assess (i) genotypic differences in the ecophysiological determinants of grain yield; i.e., fraction of light intercepted by crop (fIPAR), radiation use efficiency for biomass production (RUE), and harvest index (HI), and (ii) the responses of mentioned traits to brief episodes of high temperature. The contribution of stored reserves to grain yield was also analyzed. Field experiments included three contrasting maize hybrids (Te: temperate; Tr: tropical; TeTr: Te×Tr) grown under two temperature regimes (control and heated) during daytime hours. We tested heating (ca. 33–40°C at ear level) along three 15-d periods (GS1: pre-silking; GS2: from silking onwards: GS3: active grain filling). Heat stress had no effect on leaf area and fIPAR, but heating during grain filling affected light capture through reduced cycle duration, especially for the Te hybrid (average of −16.5 d). Heating caused a large reduction in RUE, but this trait had a rapid recovery after heat removal and final shoot biomass was not much affected (between −3% and −33%). HI was markedly reduced by heating and its variation was associated with changes in reserves use (r2=0.61). Grain yield in heated plots was better explained (r2≥0.92) by the variation in HI than by the variation in final shoot biomass (r2≥0.59). Heat effects on grain yield were larger (i) when they occurred around flowering (−527gm−2 for GS1 and −545gm−2 for GS2) than during grain filling (−352gm−2 for GS3), and (ii) for the Te hybrid (−599gm−2) than for the TeTr (−440gm−2) and the Tr hybrids (−384gm−2). Heating around silking (GS1 and GS2) caused apparent accumulation of reserves during the effective grain-filling period. The opposite trend was detected among plots heated during active grain formation (GS3). The tropical genetic background did not penalize yield potential and conferred an enhanced capacity for enduring heat effects.
•Kernel weight related to source-sink ratio at grain filling as nitrogen supply changed.•Source-sink ratio at flowering affects kernel weight only at high nitrogen level.•Hybrids overcome inbred ...lines in their response to nitrogen availability.
Maize (Zea mays, L.) kernel weight (KW) is regulated by the source-sink relationship at the early grain-filling period, when potential kernel size is defined, and at the effective grain-filling period, when final KW is established. The relative importance of each period is expected to depend upon the occurrence or not of environmental restrictions to plant growth. The objective of this study was to analyze the effect of nitrogen (N) availability on KW determination in two different groups of genotypes (inbreds and hybrids) when it is caused by changes in the source-sink relationship at mentioned periods. Six inbred lines of different genetic background and their F1 derived hybrids were tested in the field under two contrasting soil N levels (N0: low; N1: high). Almost all evaluated traits had greater mean values (P < 0.001) at N1 than at N0 level, except the plant growth rate per kernel during the critical period for kernel set (PGRCP kernel−1). However, the magnitude of the response to increased N was considerably higher for hybrids than for inbreds. Under contrasting N availability, plant growth during grain filling (PGGF) was the main determinant of increments registered in the source-sink ratio during this stage (i.e. PGGF kernel−1), and KW was chiefly associated with this ratio (r2 ≥ 0.50, P < 0.001). By contrast, the association between KW and PGRCP kernel-1 was important only at N1, and more robust for hybrids (r2 = 0.61, P < 0.001) than for inbreds (r2 = 0.34, P < 0.001). The uncoupling between both source-sink ratios observed at N0, as a result of a decreased post-flowering growth in this treatment, was responsible for differences in KW response to the PGRCP kernel−1 detected between N levels. The KW of inbreds was almost unaffected by mentioned N effects on the analyzed source-sink ratios, a trend attributed to negative inbreeding depression effects on traits controlling seed expansion. These differential responses between genotypic groups should be considered in breeding programs targeting KW increase.
Narrowing row spacing was expected to improve peanut crop performance, but the responses varied depending upon the evaluated environment and the growth habit of the plant. To clarify apparent ...inconsistencies, two cultivars with contrasting growth habits were sown at 52 cm and 70 cm row spacings in field experiments carried out in four environments. Vegetative and reproductive traits were evaluated. The leaf area index was always higher in the 52 cm than in the 70 cm row spacing, independently of the growth habit. Similarly, the light attenuation coefficient (k) was higher under narrow than under wide rows, but the cultivar with procumbent growth habit had a larger k and increased slightly the intercepted radiation respect to the erect type. These responses of the procumbent cultivar were driven by its lateral arrangements towards neighboring rows and its longer cycle duration. Narrow rows contributed to intercept approximately 14% more radiation than wide rows. These responses determined an improved biomass production through increases in the crop growth rate during the pod set period, with subsequent increases of the radiation use efficiency of this phase. Narrow row spacing enhanced seed and pod yields independently of the growth habit, but the relative importance of each seed yield component varied between cultivars. Seed numbers were more relevant for the erect growth habit, concurrently with the marked increase in total flower numbers of this cultivar. Seed weight was more relevant for the procumbent growth habit. On one hand, the erect growth habit caused a larger relative variation in seed and pod yields across environments than the procumbent one, particularly at narrow row spacing. On the other hand, the erect growth habit showed the lowest yield under wide rows. The small differences in biomass production between growth habits but the large difference in harvest index (procumbent > erect) contributed to an enhanced and more stable seed yield of the procumbent type, particularly when grown under narrow rows and linked to the large seed size of the runner cultivar. Results suggest that farmers should consider reducing row spacing as a way to increase peanut yield in the region under analysis.
The symmetry of venation patterning in leaves is highly conserved within a plant species. Auxins are involved in this process and also in xylem vasculature development. Studying transgenic ...Arabidopsis plants ectopically expressing the sunflower transcription factor HaHB4, it was observed that there was a significant lateral-vein asymmetry in leaves and in xylem formation compared to wild type plants. To unravel the molecular mechanisms behind this phenotype, genes differentially expressed in these plants and related to auxin influx were investigated.
Candidate genes responsible for the observed phenotypes were selected using a co-expression analysis. Single and multiple mutants in auxin influx carriers were characterized by morphological, physiological and molecular techniques. The analysis was further complemented by restoring the wild type (WT) phenotype by mutant complementation studies and using transgenic soybean plants ectopically expressing HaHB4 .
LAX2 , down-regulated in HaHB4 transgenic plants, was bioinformatically chosen as a candidate gene. The quadruple mutant aux1 lax1 lax2 lax3 and the single mutants, except lax1, presented an enhanced asymmetry in venation patterning. Additionally, the xylem vasculature of the lax2 mutant and the HaHB4 -expressing plants differed from the WT vasculature, including increased xylem length and number of xylem cell rows. Complementation of the lax2 mutant with the LAX2 gene restored both lateral-vein symmetry and xylem/stem area ratio in the stem, showing that auxin homeostasis is required to achieve normal vascular development. Interestingly, soybean plants ectopically expressing HaHB4 also showed an increased asymmetry in the venation patterning, accompanied by the repression of several GmLAX genes.
Auxin influx carriers have a significant role in leaf venation pattering in leaves and, in particular, LAX2 is required for normal xylem development, probablt controlling auxin homeostasis.
The light attenuation process within a plant canopy defines energy capture and vertical distribution of light and nitrogen (N). The vertical light distribution can be quantitatively described with ...the extinction coefficient (k), which associates the fraction of intercepted photosynthetically active radiation (fPARi) with the leaf area index (LAI). Lower values of k correspond to upright leaves and homogeneous vertical light distribution, increasing radiation use efficiency (RUE). Yield gains in maize (Zea mays L.) were accompanied by increases in optimum plant density and leaf erectness. Thus, the yield-driven breeding programs and management changes, such as reduced row spacing, selected a more erect leaf habit under different maize production systems (e.g., China and the USA). In this study, data from Argentina revealed that k decreased at a rate of 1.1% year-1 since 1989, regardless of plant density and in agreement with Chinese reports (1.0% year-1 since 1981). A reliable assessment of changes in k over time is critical for predicting (i) modifications in resource use efficiency (e.g. radiation, water, and N), improving estimations derived from crop simulation models; (ii) differences in productivity caused by management practices; and (iii) limitations to further exploit this trait with breeding.
Most studies assessing the genetic progress in soybean have traditionally focused on retrospectives approaches, where commercial genotypes released over an extended period are tested in a limited ...number of environments. In this context, multi-environment trials (METs) from a soybean breeding program constitute an interesting approach to complement previous studies.
This study aims to quantify the rate of genetic progress in soybean genotypes developed by the private seed company Grupo Don Mario in Argentina and Brazil. Our objective was to estimate breeding effects on yield and yield stability across maturity groups (MGs) and to analyze how these effects have been affected across yield environments.
We studied 124 soybean genotypes from MGs IV to VIII in 2015 METs. Genotypes were released from 2005 onwards in Argentina and from 2010 onwards in Brazil. To assess breeding effects, genotype seed yield best linear unbiased predictor (BLUP), yield stability, and the genotype BLUP in low, medium, and high yielding environments were regressed to the year of release.
Seed yield genetic progress was evident for all MGs and ranged from 20.5 to 46.1 kg ha−1 yr−1 in Argentina and from 23.2 to 53.6 kg ha−1 yr−1 in Brazil. Moreover, no changes were observed for yield stability during recent years. When dissecting the genetic progress by targeted environment yield, the rate in Argentina was 41.4, 23.6, and 16.6 kg ha−1 yr−1 in the high, medium, and low yielding environment, with relative rates of 0.9%, 0.6% and 0.6% yr−1, respectively. In Brazil, the rate was 43.0, 40.5, and 17.8 kg ha−1 yr−1 in the high, medium, and low yielding environment, with relative rates of 0.9%, 1.0% and 0.5% yr−1, respectively. Absolute and relative rates increased from low to high environmental quality. However, the rate varied across MGs and environmental yield.
Our study revealed that, while genetic progress was evident for MG IV to VII in Argentina and for MG V to VIII in Brazil, most genotypes did not change their response to improvements in environmental quality during the early 21st century. Moreover, the rate of progress depended on the interaction between MGs and environmental yield.
This study complements retrospective estimates of soybean genetic progress by evaluating a broader range of environments and MGs. Future research should focus on exploring the physiological and/or environmental factors behind the different rate of progress across MGs and yield environments.
•Soybean genetic progress was estimated using multi-environment trials from a breeding program.•During the early 21st century, soybean yields increased without changes in yield stability.•Absolute and relative genetic progress rates increased from low to high environmental quality.•Genetic progress rate varied with environmental yield and maturity groups.
Eco‐physiology of maize crops under combined stresses Cagnola, Juan I.; D'Andrea, Karina E.; Rotili, Diego H. ...
The Plant journal : for cell and molecular biology,
March 2024, 2024-Mar, 2024-03-00, 20240301, Letnik:
117, Številka:
6
Journal Article
Recenzirano
SUMMARY
The yield of maize (Zea mays L.) crops depends on their ability to intercept sunlight throughout the growing cycle, transform this energy into biomass and allocate it to the kernels. Abiotic ...stresses affect these eco‐physiological determinants, reducing crop grain yield below the potential of each environment. Here we analyse the impact of combined abiotic stresses, such as water restriction and nitrogen deficiency or water restriction and elevated temperatures. Crop yield depends on the product of kernel yield per plant and the number of plants per unit soil area, but increasing plant population density imposes a crowding stress that reduces yield per plant, even within the range that maximises crop yield per unit soil area. Therefore, we also analyse the impact of abiotic stresses under different plant densities. We show that the magnitude of the detrimental effects of two combined stresses on field‐grown plants can be lower, similar or higher than the sum of the individual stresses. These patterns depend on the timing and intensity of each one of the combined stresses and on the effects of one of the stresses on the status of the resource whose limitation causes the other. The analysis of the eco‐physiological determinants of crop yield is useful to guide and prioritise the rapidly progressing studies aimed at understanding the molecular mechanisms underlying plant responses to combined stresses.
Significance Statements
Drought, nitrogen deficiency, warming temperatures and neighbour crowding reduce the grain yield of plants. Here we analyse how these stresses impact on maize crops in the field when combined.
•The sunflower transcription factor HaHB11 expressed in maize delayed leaf senescence.•HaHB11 improved maize biomass and yield in greenhouse and field trials.•Such beneficial traits counterbalanced ...the negative effects of inbreeding.•Several traits triggered by HaHB11 were conserved between Arabidopsis and maize.
HaHB11 is a sunflower transcription factor from the homeodomain-leucine zipper I family. Transgenic Arabidopsis plants expressing HaHB11 had larger rosettes and improved seed yield. In this work maize plants from hybrid HiII were transformed with 35S:HaHB11, ZmUBI:HaHB11 and ProHaHB11:HaHB11 and then backcrossed to B73 to obtain a more homozygous inbred phenotype. Transgene expression levels were stable at least during three generations. Greenhouse-grown HaHB11 transgenic lines had larger leaf area and delayed senescence than controls, together with increased total biomass (up to 25%) and seed yield (up to 28%). Field trials conducted with T2 and T4 generations indicated that enhanced leaf area (up to 18%), stem diameter (up to 28%) and total biomass (up to 40%) as well as delayed leaf senescence were maintained among transgenic individuals when upscaling from pots in the greenhouse to communal plants in the field. The T4 field-grown transgenic generation had increased light interception and radiation use efficiency as well as seed yield (43–47% for events driven by the 35S promoter). Results suggest that HaHB11 is a promising tool for crop improvement because differential traits observed in the Arabidopsis model plant were preserved in a crop like maize independently of growth conditions and backcross level.
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