Increase In Number Of Kernels Research Articles

Canopy development, leaf traits and yield in high-altitude Andean maize under contrasting plant densities in Argentina

Summary In highlands, the increase in altitude results in a drastic decrease in temperature (T) that delays phenological development of maize, decreasing light interception during the cycle. This could be partially overcome by increasing plant density, but information is scarce for designing specific management options. The objective of this work was to describe changes in canopy development, photosynthetic performance, biomass and yield of maize grown at contrasting plant densities (5.7 plants m−2, locally used, and 8.7 plants m−2, 50% higher). Three experiments were carried out in two high-altitude environments within the Argentinean Andean region, Hornillos (HOR, 2380 masl, 2019–20 and 2020–21) and El Rosal (ERO, 3350 masl, 2019–20), and complementary data were obtained from samplings in 8 farmer’s fields (from 2400 to 3400 masl, 2022–23). In the experiments, mean T during the first 150 days of the cycle was 33% lower at ERO, which implied 39 extra days but 25% shorter thermal time to achieve silking. The higher plant density significantly increased leaf area index and light interception at ERO, whereas at HOR, this was only evident during the second season. At the leaf level, plants grown at ERO had thicker leaves with higher chlorophyll (+36%) and nitrogen (40%) content. Photosynthetic electron transport rate at full irradiance was +20% higher at ERO but significantly varied throughout the day with lowest values in the morning, which was not observed at HOR and was not related to light intensity or stomatal conductance. At HOR, the increase in plant density did not improve light interception, nor yield in 2019–20 (with average yields of 6356 kg ha−1) but it did improve both in 2020–21 when generally lower yields were attained (4821 kg ha−1). Across farmer’s fields, increasing densities consistently reduced yield per plant (r2 = 0.57***) but improved yield per area basis, which was maximised at 10 pl m−2 as a result of a steady increase in kernel number m−2 (up to 15 pl m−2). Thus, in these high-altitude environments, increasing plant density beyond recommended (6 pl m−2) is a promising approach for improving yield, with major penalties of supra-optimum densities being related to kernel weight. Further work is needed to explore the effect of different factors limiting kernel growth, over plant density responses.

Root plasticity and interspecific complementarity improve yields and water use efficiency of maize/soybean intercropping in a water-limited condition

Intercropping maize and soybean is renowned for improving crop production and resource use efficiencies. Interspecific competition and complementarity with respect to root plasticity is essential knowledge for understanding the mechanisms of overyielding and optimizing intercropping species selection. We conducted a three-year field experiment (2017–2019) to quantify land and water productivities in relation to above- and below-ground interspecific interactions, root growth and distribution under different nitrogen rates in maize/soybean intercropping. The land productivity in terms of land equivalent ratio (LER) in maize/soybean intercropping was 1.10 across all years and N rates. The yield increase in intercropped maize was mainly gained from an 45% increase in kernel numbers, while the yield loss of intercropped soybean was caused mainly by an 35% decrease in the pod numbers compared to sole cropping. The system level water use efficiency, defined as water equivalent ratio (WER) was also 1.10. Compared with sole stands, intercropped maize consumed more water during the vegetative stage, but intercropped soybean took up more during the reproductive stage. That indicated a temporal complementarity of water use in the intercrop, which benefited maize kernel formation and partially offset the negative shading effect of soybean grain filling. Soybean showed a marked increase in root length density (RLD). Compared to the produced aboveground biomass (DM) in the intercrop, the intercropped soybean invested more assimilates into root than shoot, as defined as root plasticity, the RLD/DM ratio of soybean in the intercrop was 76% more than sole system. However, the intercrop did not change root plasticity of maize. The overlap of maize and soybean roots, i.e. interspecific interaction interface, occurred mainly within the position between two border rows and at first soybean row. Under interspecific competition, soybean in the intercropping created both temporal and spatial differentiation for water uptake, which might be a key reason for enhancing intercropping land and water productivities. Our results contribute to understanding the mechanism of interspecific interaction for maximizing land and water productivities in rain-fed intercropping. • Maize/soybean intercrop enhanced land and water productivities in rainfed conditions. • The yield increase of intercropped maize was due to an 45% increase in kernel number. • The yield loss of intercropped soybean was caused by an 35% decrease in pod number. • Shaded soybean in intercrop produced more roots than aboveground biomass. • Interspecific complementarity enhanced crops water use efficiencies in intercrop.

Compensating effect of fulvic acid and super-absorbent polymer on leaf gas exchange and water use efficiency of maize under moderate water deficit conditions

A field-based pot experiment with maize plants was conducted to examine the effect of combined fulvic acid (FA) and super-absorbent polymer (SAP) on leaf gas exchange, water use efficiency, and grain yield under soil water deficit. SAP (45 kg hm−2) was applied to the topsoil at sowing. Plants were well-watered (80% field capacity), but subjected to water deficit (50% field capacity) from tassel stage to grain-fill. FA solution (2 g L−1) was sprayed onto plant leaves at 2 and 9 days after imposing water deficit. Under water deficit, SAP and FA application did not affect evapotranspiration, but increased leaf abscisic acid and decreased leaf transpiration rate with a little change in photosynthesis, thus improving instantaneous water use efficiency. Applying SAP and FA under water deficit also increased grain yield by 19% and grain water use efficiency by 24%, largely attributed to an increase in kernel number. In contrast, under well-watered condition the two chemicals increased stomatal conductance, leaf transpiration, photosynthesis and chlorophyll content, but did not change kernel number and were relatively less effective in respect to water use efficiency compared to water-stressed condition. This study showed that application of foliar FA and soil SAP had little effect on evapotranspiration but maintained high photosynthesis and kernel number, and improved water use efficiency under soil water deficit.

A single point mutation in Ms44 results in dominant male sterility and improves nitrogen use efficiency in maize

SummaryApplication of nitrogen fertilizer in the past 50 years has resulted in significant increases in crop yields. However, loss of nitrogen from crop fields has been associated with negative impacts on the environment. Developing maize hybrids with improved nitrogen use efficiency is a cost‐effective strategy for increasing yield sustainably. We report that a dominant male‐sterile mutant Ms44 encodes a lipid transfer protein which is expressed specifically in the tapetum. A single amino acid change from alanine to threonine at the signal peptide cleavage site of the Ms44 protein abolished protein processing and impeded the secretion of protein from tapetal cells into the locule, resulting in dominant male sterility. While the total nitrogen (N) content in plants was not changed, Ms44 male‐sterile plants reduced tassel growth and improved ear growth by partitioning more nitrogen to the ear, resulting in a 9.6% increase in kernel number. Hybrids carrying the Ms44 allele demonstrated a 4%–8.5% yield advantage when N is limiting, 1.7% yield advantage under drought and 0.9% yield advantage under optimal growth conditions relative to the yield of wild type. Furthermore, we have developed an Ms44 maintainer line for fertility restoration, male‐sterile inbred seed increase and hybrid seed production. This study reveals that protein secretion from the tapetum into the locule is critical for pollen development and demonstrates that a reduction in competition between tassel and ear by male sterility improves grain yield under low‐nitrogen conditions in maize.

Genetic improvement in density and nitrogen stress tolerance traits over 38 years of commercial maize hybrid release

Research attention to improving source and sink strength in maize production is requisite for enhancing yield. Improvement in source strength has been achieved with higher post-silking dry matter accumulation, whereas historical improvement in sink strength has been mostly attributed to increasing kernel number (KN) per unit area, in part because KN is known to be more vulnerable to abiotic stresses compared to kernel weight (KW). However, KW can also vary widely as it is dependent on both genotype and dry matter accumulation during the post-silking period. In order to illustrate the consequences of breeding efforts over a 4-decade period for enhancing source and sink strength at varying nitrogen rates and plant densities, a 2-year and 2-location study was conducted in 2013 and 2014. Eight commercial hybrids from DeKalb released from 1967 to 2005 were compared at 2 nitrogen rates (55 and 220kgNha−1) and 3 plant densities (54,000 (D1), 79,000 (D2) and 104,000 (D3) plants ha−1). Breeding progress increased grain yield per hectare (GY) by an average of 66kgha−1year−1, and grain yield per plant (GYP) by 0.91g plant−1year−1 across all treatments and environments. This yield increase with hybrid improvement was attributed more to an increase in KW (1.29mgkernel−1year−1 across all treatments and both locations), than to any increase in KN. The overall source-sink ratio (SSR − ratio of post-silking dry matter accumulation to kernel number per plant) also increased by an average of 1.25mgkernel−1year−1 across all treatment and locations. The hybrid improvement in SSR was more pronounced at the high N rate or low plant density. Post-silking dry matter accumulation (PostDM) increased by an average of 54kgha−1year−1 across all treatments and locations. KW was highly correlated with ear growth rate (EGR) during grain fill. New hybrids had much higher KW gain per unit of EGR. Newer hybrids also had a longer active grain filling period, but the correlation of post-silking dry matter accumulation to the duration of active grain filling period was weak. This study showed that the breeding progress for yield gain in these DeKalb hybrids was achieved by (i) longer duration of the grain filling period plus longer leaf stay green that accompanied a higher PostDM of newer hybrids, (ii) enhanced source to sink strength during grain filling by a higher SSR in newer hybrids, (iii) improved efficiency for transferring source from cob and husk to grain by increasing KW gain per unit of EGR, and (iv) enhanced stress tolerance in newer hybrids to maintain grain yield even under high density.

Domestication potential of Marula (Sclerocarya birrea subsp. caffra) in South Africa and Namibia: 3. Multiple trait selection

An understanding of the inter-relationships between the traits characterising tree-to-tree variation in fruits and kernels is fundamental to the development of selected cultivars based on multiple trait selection. Using data from previously characterised marula (Sclerocarya birrea) trees in Bushbuckridge, South Africa and North Central Region of Namibia, this study examines the relationships between the different traits (fruit pulp, flesh/juice mass, and nut shell and kernel mass) as a means to determine the opportunities to develop cultivars. Strong and highly significant relationships were found between fruit mass and pulp mass in trees from South Africa and Namibia, indicating that size is a good predictor of fruit pulp production. However, fruit size is not a good predictor of nut or kernel production, as there were weak relationships between fruit and nut and/or kernel mass, which varied between sites and landuses. Generally, the relationships between fruit mass and kernel mass were weaker than between fruit mass and nut mass. Relationships between kernel mass and shell mass were generally weak. The lack of strong relationships between fruit and kernel mass does, however, imply that there are opportunities to identify trees with either big fruits/small nuts for pulp production, or trees with large kernels in relatively small fruits for kernel oil production. However, within fruits from the same tree, nuts could contain 0–4 kernels, indicating that even in trees with an inherent propensity for large kernels, improved pollination may be required to maximise kernel mass through an increase in kernel number. Finally, the relationships between percentage kernel oil content and the measured morphological traits were also very weak. The conclusions of these results are that there is merit in identifying different combinations of traits for the selection of trees producing either pulp or kernels. Consequently, fruit and kernel ‘ideotypes’ are presented as guides to the selection of elite trees for cultivar development. These results have important implications for the domestication of the species as a producer of fruits or kernels for food/beverages or cosmetic oils.

A simulation analysis that predicts the influence of physiological traits on the potential yield of wheat

Physiological traits such as increased kernel number, early flowering, and an increased rate and duration of kernel filling, are thought to increase the potential yield of wheat in certain environments. A crop simulation model ( apsim– nwheat) was used to evaluate the role of these traits in improving potential yield under a range of environmental conditions. apsim– nwheat calculates the potential yield for a specific environment limited only by temperature, solar radiation, water and nitrogen supply. The model predicted crop production, soil water and N dynamics for low and high-yielding environments in Australia, The Netherlands and China. Applying the model to the various traits showed that a 20% increase in kernel number, early anthesis and a 20% increase in kernel filling rate had no or only minor effects on increasing potential yield in high- and extremely high-yielding environments. In these environments, when a maximum specific kernel size was imposed, a yield increase resulted mainly from a 20% extension in the duration of kernel filling, suggesting that the crop is usually source limited. In a low-yielding environment, each trait, except early flowering showed a small positive effect on average on increasing potential yield. Early flowering reduced the potential yield on a low water-holding capacity soil. The effect of the various traits on potential yield was also very variable in a low-yielding environment, varying with both seasonal rainfall and soil type, and all traits, except the increased rate of kernel filling, reduced potential yields in some seasons. The effect of the various traits on yield in the low-yielding environment depended on biomass accumulation at anthesis and water availability during kernel filling. When all the traits were simulated together, the relative increase in potential yield was of similar magnitude in both low- and high-yielding environments. The analysis suggested that an increase in the potential yield from 9 to 22% can be expected from selection for the above physiological traits, but selection in the appropriate environment is important.

Ear Temperature and Pollination Timing Effects on Maize Kernel Set

Maize (Zea mays L.) kernel set can be improved through synchronous pollination within and between ears. Reductions in kernel set could be expected because of asynchronous pollination between early‐ and late‐appearing silks. We analyzed the effect of (i) selective ear heating around the time of silking, and (ii) different time gaps between early‐ and late‐pollinated silks in an attempt to modify kernel set. Tip ear heating was expected to minimize the advantage of early silking ovaries. Lateral heating and pollination gaps were expected to exaggerate this advantage. Three pollination gaps (2, 4, and 6 d) were tested for two plant populations (3 and 9 plants m−2). Ear temperature in the heated zone averaged 4.5°C above air temperature. Temperature in the nonheated side closely followed air temperature. Treatments promoted greater differences in maize kernel number (KN) per ear (73% variation) than in the number of silks exposed 5 d after silking (6% variation). Lateral ear heating reduced KN per ear in comparison with the nonheated control, but tip ear heating did not modify KN per ear. At 9 plants m−2, synchronous pollination resulted in ∼15% increase in KN per plant. Pollination gaps of 2 and 4 d reduced KN per plant drastically (up to 51%), but the reduction was smaller for the 6‐d gap. This study (i) gives evidence of the negative impact of delayed pollination timing among silks on kernel set, which was not related to reduced silk receptivity, and (ii) defines the time gap for maximum interference of early‐ on late‐pollinated ovaries, a period shorter than 4 d.

Ear and Kernel Formation in Maize Hybrids Representing Three Decades of Grain Yield Improvement in Ontario

Increased prolificacy and reduced barrenness have been identified as physiological traits in maize (Zea mays L.) hybrids that are tolerant of environmental stresses induced by high plant density. The objective of this study was to investigate ear and kernel formation under a range of plant densities in old and new hybrids. Experiments were carried out during 1987 and 1988 at two locations in Ontario with nine maize hybrids representing three decades of yield improvement in Ontario, grown at 2, 4, 8, 10, and 13 plants m−2. Dry matter was measured at 1 wk presiiking, 3 wk postsilking, and at physiological maturity and plant growth rates calculated for both periods. Grain yield, kernel weight, and kernel number were determined at physiological maturity. Kernels per plant and plant growth rate for the period from 1 wk presilking to 3 wk postsilking could be fitted to a discontinuous function of multiple rectangular hyperbolae; a single rectangular hyperbola was associated with the kernel number on each grain‐bearing ear. The first rectangular hyperbola for each hybrid had a positive x‐axis intercept, which was interpreted as the threshold plant growth rate for ear formation. The analysis showed that grain yield improvement of Ontario maize hybrids was associated with an increase in kernel number per plant and higher plant growth rates from 1 wk presilking to 3 wk postsiiking. The increase in kernels per plant was associated with an increase in ears per plant. The increased prolificacy of recent hybrids appeared to be the combined result of higher rates of plant dry matter accumulation during silking and a greater inherent tendency to exhibit prolificacy. The lower barrenness of recent hybrids at high plant densities was associated with higher plant growth rates, but was not the result of a lower threshold plant growth rate for ear formation.

Veränderte Ährenfertilität bei einhalmiger Sommergerste durch Einsatz von Bioregulatoren

Abstract Changes in fertility of ears in monoculm summer barley after application of plant growth regulators The effect of plant growth regulators (PGR) upon the structure of the ears in the monoculm summer barley Kindred Uniculm was tested during four years in pot experiments.The influence of CCC + Ancymidol and RSW on yield structure of the whole plant and the ear which was divided in three parts (basal = 1.–5. spike internode, medial = 6.–10. spike internode, apical = off 11. spike internode) was measured. The application of PGR's in EC 32 increased kernel yield every year in a range from 11–21 %. Number of kernels were strongly improved while the thousand kernels weight remained unchanged. The increase in number of kernels in the apical zone was higher (26–64 %) than in the basal zone (0–10 %). Obviously “medial dominance” was reduced as the single kernel weight was the same in untreated plants.The decrease of GA1‐content was evident after application of PGR's. A correlation between GA1‐content and plant height was found.