High Plant Density Research Articles

Effect of sodium dodecyl sulfate (SDS) on microbial community structure and function in lake–terrestrial ecotones: A simulation experiment

Even a low concentration of sodium dodecyl sulfate (SDS), a widely used bactericidal surfactant, can significantly change the species, quantity and genetic functions of microorganism communities in natural waters. Lake–terrestrial ecotones are areas where microorganisms are highly active, and they are also the lake areas most vulnerable to SDS pollution. Because microorganisms are very sensitive to environmental changes, their activities vary greatly among lakes and laboratories, so it is difficult to simulate their real dynamics using small-scale experiments. To study the interaction between SDS and microorganisms in a lake–terrestrial ecotone, a large artificial simulation device was used to analyse microbial community structure, phospholipid fatty acid (PLFA) content, gene function and ability to degrade SDS in a lake–terrestrial ecotone contaminated with SDS. The results showed that (1) the period from 2 to 4 days after the beginning of the experiment was the key stage for the biodegradation of SDS. The biodegradation cycle of SDS in the natural environment is shorter than that in small-scale experimental setups, and more than 90% of SDS was removed within 4 days in the simulation device. (2) Low-level SDS pollution (≤ 6 mg/L) has different effects on different types of lacustrine microorganisms. The presence of SDS can lead to a significant decrease in microbial diversity and biomass in lake–terrestrial ecotones with a high density of aquatic plants, but the opposite is true in ecosystems with degraded aquatic plant communities. (3) After SDS pollution occurred, pollution-resistant bacteria such as Chitinophaga and Flavobacterium became dominant. The relative abundance of carbon cycle functional genes increased rapidly in microorganisms, while the relative abundance of nitrogen cycle functional genes decreased. These changes were not readily reverse even after 20 days, although the communities recovered to a certain extent.

Transcriptome and metabolome profiling reveal the effects of hormones on current-year shoot growth in Chinese ‘Cuiguan’ pear grafted onto vigorous rootstock ‘Duli’ and dwarf rootstock ‘Quince A’

BackgroundDwarf rootstocks have important practical significance for high-density planting in pear orchards. The shoots of ‘Cuiguan’ grafted onto the dwarf rootstock were shorter than those grafted onto the vigorous rootstock. However, the mechanism of shorter shoot formation is not clear.ResultsIn this study, the current-year shoot transcriptomes and phytohormone contents of ‘CG‒QA’ (‘Cuiguan’ was grafted onto ‘Quince A’, and ‘Hardy’ was used as interstock) and ‘CG‒DL’ (‘Cuiguan’ was grafted onto ‘Duli’, and ‘Hardy’ was used as interstock) were compared. The transcriptome results showed that a total of 452 differentially expressed genes (DEGs) were identified, including 248 downregulated genes and 204 upregulated genes; the plant hormone signal transduction and zeatin biosynthesis pathways were significantly enriched in the top 20 KEGG enrichment terms. Abscisic acid (ABA) was the most abundant hormone in ‘CG‒QA’ and ‘CG‒DL’; auxin and cytokinin (CTK) were the most diverse hormones; additionally, the contents of ABA, auxin, and CTK in ‘CG‒DL’ were higher than those in ‘CG‒QA’, while the fresh shoot of ‘CG‒QA’ accumulated more gibberellin (GA) and salicylic acid (SA). Metabolome and transcriptome co-analysis identified three key hormone-related DEGs, of which two (Aldehyde dehydrogenase gene ALDH3F1 and YUCCA2) were upregulated and one (Cytokinin oxidase/dehydrogenase gene CKX3) was downregulated.ConclusionsBased on the results of transcriptomic and metabolomic analysis, we found that auxin and CTK mainly regulated the shoot differences of ‘CG–QA’ and ‘CG–DL’, and other hormones such as ABA, GA, and SA synergistically regulated this process. Three hormone-related genes ALDH3F1, YUCCA2, and CKX3 were the key genes contributing to the difference in shoot growth between ‘CG–QA’ and ‘CG–DL’ pear. This research provides new insight into the molecular mechanism underlying shoot shortening after grafted onto dwarf rootstocks.

Origin of yield gains in maize hybrids

AbstractIncreasing grain yields in maize (Zea mays L.) have been widely witnessed over the lifespan of many aging farmers. This paper aims to capture and summarize the overlapping explanations for the significant increases in maize yields. Changes in management practices have resulted in higher planting densities; however, genetic alterations allowed for maize varieties to tolerate increased stress levels. Increased stress levels, such as light availability, prompted genetic changes to leaf area index, radiation use efficiency, and leaf angles. The narrowing of the anthesis–silking interval is more significant in maize planted in higher densities. Stress factors affecting maize grain yields can be managed by both management changes such as water or pesticide application, and breeding modifications, such as genetic resistance to abiotic, temperature, or moisture, and biotic, pest, disease, and insect stressors. The increase in maize grain yields over the past century can be attributed to a combination of achievements in crop breeding and alternations of management practices.

Integrated nutrient management practices in Mrig bahar crop of guava under high density plantation

Integrated nutrient management practices in Mrig bahar crop of guava under high density plantation

Effects of pan evaporation-based drip irrigation levels on performance of guava grown in Udaipur and Rewa regions of India

A field experiment was conducted for three years (2019-20, 2020-21 and 2021-22) on 4 years old guava orchard established at 3×2 m spacing with drip irrigation treatments at two locations viz. Udaipur Rajasthan and, Rewa, Madhya Pradesh. Plant growth, yield contributing parameters, fruit yield and water use efficiency was significantly affected by different pan evaporation-based drip irrigation levels (70, 80, 90 & 100% of Epan) over local control. In existing climatic conditions of Udaipur and Rewa regions, the daily irrigation water requirement of high-density planting guava tree was varied from 7.8 to 26.3 and 4.5 to 26.5 liter/plant/day, respectively. Among all the pan evaporation-based drip irrigation levels, the irrigation supplied at 80% and 90% of daily pan evaporation were found as best approach for irrigating high density plantation (HDP) guava orchard through drip irrigation in Udaipur & Rewa regions with maximum fruit yield (37.3 & 30.7tha-1), irrigation water use efficiency (0.359 & 0.263tha-1-cm) along with significant water saving (29.2 & 22.2%), respectively over local control. Results will help farmers, policy makers and irrigation managers to conserve available fresh water resources in water scares regions of Rajasthan and Madhya Pradesh.

Apple Growing in Norway—Ecologic Factors, Current Fertilization Practices and Fruit Quality: A Case Study

This paper presents some features of apple production in Norway, the northernmost apple-growing country in the world. Acceptable growing conditions prevail along the fjords in western Norway and around the lakes in eastern Norway at 60° north. These specific mesic climate conditions are associated with very long summer days (18 h daylight mid-summer) and short winter days (6 h daylight), with frost rarely occurring in the spring along the fjord areas. The present apple-growing technique in Norway is similar to that of other developed apple-growing countries, taking into account that all local growing phases involve a considerable delay in progress (1.5–2 months). Therefore, high-density planting systems based on the use of dwarf rootstocks (mainly M.9) with imported early maturing international apple cultivars are used in most orchards. The most common soil type has high organic matter content (2–18%), which persists due to the cool climate and low mineralization, and a clay content of <15%, which results from the formation of the soil from bedrock. The increase in average temperatures caused by current climatic changes leads to a complex combination of different physiological effects on apples, which can have positive or negative effects on the phenology of the trees. The main advantage of Norwegian apple production is that the quality and aroma of the fruit meet the current demands of the local market.

Apple (Malus × domestica Borkh.) production and quality in response to anti-hail nets.

Anti-hail nets are the best way to mitigate the effects of hailstorms in the orchards. Apple trees covered with nets may exhibit a variety of vegetative and reproductive responses, inclusive of changes in tree vigour, cropping, sugar contents, and fruit colour. The present study was conducted to assess the effect of timing of installation and colour of anti-hail net on cropping and fruit quality in high-density apple orchard for two consecutive seasons (2021 and 2022). White and blue colour nets of size (9m × 30m) 80 GSM (square mesh with non-sliding threaded, leno weave, and < 30% shading factor) were installed at three different time intervals (15days before estimated full bloom, at full bloom, and 15days after full bloom) on apple cultivar 'Jeromine'. The installation at different time and colour of anti-hail nets significantly exhibit variability in cropping, fruit quality, and bio-chemical metrics. The significant highest cropping (fruit yield, productivity, and yield efficiency) and fruit biochemical parameters (total soluble solids) were recorded in T3C2 (15days after full bloom + white colour anti-hail net) followed by T2C2 (installed at full bloom + white colour anti-hail net). Hence, white colour anti-hail nets installed 15days after full bloom increased fruit production and improved quality in comparison to blue colour anti-hail net in apple under high-density plantations.

EFFECT OF AGRONOMIC AMENDMENTS ON GROWTH AND YIELD OF SUNFLOWER

Proper planting geometry helps in obtaining optimum plant population and crop yield; while irrigation at right time results in improved higher crop yields and quality of the produce. Two years field experiments were conducted during (2019 and 2020) at Tandojam to examined the effect of sowing methods (Raised bed, Ridge, Drilling and Broadcasting); planting densities (Recommended, high density and ultra-high density) and nutrient management (90+60+60+0, 90+60+60+10 and 90+60+ 60+20 kg ha-1 NPK+FeSO4). The experimental design was randomized complete block design with three replicates. The best result in all parameters on average factors including drilling method, high density planting (66,666 plants ha-1), NPK+FeSO4: 90+60+60+20 kg ha-1 and their interaction resulted in economically superior overall sunflower performance in relation to its growth, seed yield and quality attributes. The drilling method was highly effective to improve seed yield apart from the lower biological yield due to greater harvest index as compared to rest of the sowing methods. Although, recommended plant spacing (55,555 plants ha-1) produced better individual plant based results, but due to lesser plant population, the overall seed yield was greater under high density planting (66,666 plants ha-1).Ultra high density plantation (83,333 plants ha-1) did not prove beneficial due to crowded plant population where harvest index became poor but biological yield increased. Higher FeSO4 improved the grain quality and no effect on foliage; hence 20 kg FeSO4 remained economically most beneficial to achieve desired seed production.

Growth and Biomass Models for Three Fast-growing Tree Species under High-density Plantation

Three fast-growing trees, viz., Populus deltoides, Eucalyptus spp. and Casuarina equisetifolia were studied, in high-density plantation at Padilla, Prayagraj, Uttar Pradesh with following treatments viz., T1: Poplar (1×1m), T2: Eucalyptus (1×1m), T3: Casuarina (1×1m), T4: Poplar (1.2×1.2 m), T5: Eucalyptus (1.2×1.2 m), T6: Casuarina (1.2×1.2 m), T7: Poplar (1.5×1.5 m), T8: Eucalyptus (1.5×1.5 m) and T9: Casuarina (1.5×1.5 m). The experiment was established in year July 2021 and data was collected in June 2022. The result indicate the maximum height was recorded in T2: Eucalyptus (1×1 m) 3.81 m followed by T5: Eucalyptus (1.2×1.2 m) 3.78 m, T8: Eucalyptus (1.5×1.5 m) 3.40 m which was at par with each other and minimum in T9: Casuarina (1.5×1.5 m) 2.42 m whereas the maximum girth was found in T4: Poplar (1.2×1.2 m) 6.91 cm followed by T2: Eucalyptus (1×1 m) 6.61 cm, T5: Eucalyptus (1.2×1.2 m) 6.16 cm, T1: Poplar (1×1 m) 5.91 cm which was at par with each other and minimum in T9: Casuarina (1.5×1.5 m) 3.22 cm after one year. Various linear function was attempted to predict biomass based on GBH (G) and Height (H). Prediction accuracy of Height, girth model was slightly better than the height and girth model. Linear model (Y=a + bH + cG), where Y denotes dependent variable (biomass) and H and G denotes independent variable (Height or Girth), performed better (than the remaining tested models) in terms of estimation precision and prediction accuracy. The AGB was maximum was found in T2: Eucalyptus (1×1m) 0.676 kg tree-1 followed by T5: Eucalyptus (1.2×1.2 m) 0.598 kg tree-1 and minimum in T9: Casuarina (1.5×1.5 m) 0.214 kg tree-1. After completion of one year Eucalyptus (1×1 m) showed best growth among all treatments.

Effect of nitrogen fertilization levels and plant density on dry weight, yield components and bulb quality of onion plant

A field experiment was carried out during the two successive winter seasons of 2020/2021 and 2021/2022 to study the effect of mineral nitrogen levels and plant density on dry weight, yield and its components, as well as bulb quality of onions (cv. ‘Ahmar Tanawy’). This experiment included 12 treatments, which were combinations between four levels of mineral nitrogen (0, 192, 240 and 288 kg N/ha) and three plant densities (4, 5 and 6 rows/ridge equal 33.33, 41.67 and 50 plants/m2, respectively). These treatments were arranged in a split-plot design with three replications. Nitrogen levels were randomly arranged in the main plots, and plant densities were randomly distributed in the subplots. Nitrogen application at 192,244 and 288 kg N/ha led to increase dry weight/plant compared to control (zero N) and 288 kg N/ha gave the highest values of dry weight of leaves, dry weight of bulbs, and total dry weight per plant at 100 days in both seasons. The increases in total dry weight per plant were about 4.84 and 4.80 g per plant for 192 kg N/ha, 4.76 and 3.87 g per plant for 244 kg N/ha, and 6.86 and 5.74 g per plant for 288 kg N/ha over the control at 100 days in the 1st and 2nd seasons, respectively. The interaction between N at 288 kg/ha and low plant density (4 rows/ridge) gave the highest values of dry weight of leaves, bulb, and total dry weight/plant and increased yield of grade 1, exportable yield, average bulb weight, as well as nitrate and sulphur contents in bulbs, whereas the interaction between N at 244 kg/ha and high plant density (6 rows/ridge) increased grades 2, 3, and 4, marketable yield, and total yield/ha.

Sorghum Densification with Changes in Plant Spacing Arrangement: Productivity and Qualitative Characteristics of Silage Material

The aim of this study was to evaluate the agronomic performance of sorghum grown in different combinations of row spacing and plant density, as well as possible interferences on silage quality. No other study dedicated to identifying the interference of plant spatial arrangement on the cultivation of silage material has been developed in the productive context of the Amazon Biome, making it necessary to understand the behavior of the studied factors. The treatments were arranged in a split-plot scheme: the plots corresponded to three row spacings (0.45 m, 0.60 m, and 0.75 m) and subplots at four densities (105,000, 120,000, 135,000, and 150,000 plants ha−1). The agronomic and productivity characteristics of sorghum and the fermentative and bromatological characteristics of forage and silage were evaluated. The sorghum plants showed an increase in plant height and green and dry mass yield when using higher densities (p &lt; 0.05). For the culm diameter variable, an isolated effect of the factors was observed, with reduced diameter when grown closer to inter-row spacing or using higher plant densities. No effect of the factors was found (p &gt; 0.05) for morphological plant components. In silage, wider spacing promoted higher dry matter content. Regarding crude protein in the silage, higher percentages were obtained at closer spacing and higher plant density. The sorghum growing in dense conditions is indicated, given the positive performance in productivity and bromatological composition.

Intercropping in maize silage versus solo‐seeding for alfalfa establishment in Wisconsin and Idaho

AbstractAlfalfa (Medicago sativa L.) intercropping with maize (Zea mays L.) silage is being developed in the northern United States to improve the profitability and environmental sustainability of forage production. This study, conducted under rainfed conditions in Wisconsin and semiarid irrigated conditions in Idaho, compared the establishment of alfalfa and dry matter yield of four intercropping systems to three conventional systems. The former systems included alfalfa interseeded at planting or the vegetative emergence (VE) stage of maize and grown with or without prohexadione growth retardant. The latter systems included alfalfa seeded in spring, summer‐seeded after barley (Hordeum vulgare L.), or late summer‐seeded after maize silage. Spring seeded and interseeded alfalfa in Wisconsin also received foliar fungicide and insecticide during establishment. During alfalfa establishment, yield of intercropped maize silage was 1.8‐ to 4.4‐fold greater than spring‐seeded alfalfa. Compared to spring‐seeded alfalfa, interseeded alfalfa had similar or somewhat lower stand density but similar first cut yield the following year, provided that intercropped maize was harvested near September 1 to allow ample alfalfa fall regrowth. Shifting interseeding from maize planting to the VE stage decreased early‐season alfalfa growth, but improved maize silage yield, with minor effects on alfalfa fall growth, stand density, and first cut yield. Prohexadione application had little impact on establishment or yield of interseeded alfalfa. While having high plant density, alfalfa seeded after barley or especially maize had less fall growth and low first cut yield. Overall, alfalfa establishment and yield of intercropping systems compared favorably with conventional systems.

Hedgerow Olive Orchards versus Traditional Olive Orchards: Impact on Selected Soil Chemical Properties

Olive orchards cover over 10 million hectares worldwide, with production techniques undergoing significant changes in the past three decades. The traditional rainfed approach, involving minimal inputs, has given way to irrigated super-intensive systems with higher planting density, increased productivity, a greater use of fertilizers and phytopharmaceuticals, and total mechanization. Its impact on soil chemical properties remains a topic of great debate, and no definitive consensus has been reached. Our main objective was to examine the different effects of traditional olive orchards and super-intensive orchards on soil chemistry over a decade. We collected and analyzed 1500 soil samples from an irrigation perimeter in southern Portugal in 2003 and 2013. Our findings indicate that, compared to traditional olive orchards, super-intensive ones show, in a decade, a significant decrease in soil organic matter (less 22.8%—p &lt; 0.001), namely due to the increase in mineralization caused by an increase in soil moisture content as a result of irrigation practice, and an increase in sodization (more 33.8% of Ext Na—p &lt; 0.001) highlighting the importance of monitoring this factor for soil fertility. In comparison to other irrigated crops in the region, super-intensive olive orchards promote a significant soil acidification (from 7.12 to 6.58), whereas the pH values of the other crops increase significantly (3.3%, 13.5%, and 3.0% more in corn, tomato, and cereals, respectively). Mainly because of the decrease in organic matter levels with soil acidification and soil sodization, we can underline that hedgerow olive orchards can affect soil characteristics negatively when compared with traditional ones, and it is necessary to adopt urgent measures to counter this fact, namely sustainable agriculture practices.

Arabidopsis response to copper is mediated by density and root exudates: Evidence that plant density and toxic soils can shape plant communities.

Plants grown at high densities show increased tolerance to heavy metals for reasons that are not clear. A potential explanation is the release of citrate by plant roots, which binds metals and prevents uptake. Thus, pooled exudates at high plant densities might increase tolerance. We tested this exclusion facilitation hypothesis using mutants of Arabidopsis thaliana defective in citrate exudation. Wild type Arabidopsis and two allelic mutants for the Ferric Reductase Defective 3 (FRD3) gene were grown at four densities and watered with copper sulfate at four concentrations. Plants were harvested before bolting and dried. Shoot biomass was measured, and shoot material and soil were digested in nitric acid. Copper contents were determined by atomic absorption. In the highest-copper treatment, density-dependent reduction in toxicity was observed in the wild type but not in FRD3 mutants. For both mutants, copper concentrations per gram biomass were up to seven times higher than for wild type plants, depending on density and copper treatment. In all genotypes, total copper accumulation was greater at higher plant densities. Plant size variation increased with density and copper treatment because of heterogeneous distribution of copper throughout the soil. These results support the hypothesis that citrate exudation is responsible for density-dependent reductions in toxicity of metals. Density-dependent copper uptake and growth in contaminated soils underscores the importance of density in ecotoxicological testing. In soils with a heterogeneous distribution of contaminants, competition for nontoxic soil regions may drive size hierarchies and determine competitive outcomes.

Exogenous abscisic acid (ABA) improves the filling process of maize grains at different ear positions by promoting starch accumulation and regulating hormone levels under high planting density

BackgroundHigher planting densities typically cause a decline in grain weight, limiting the potential for high maize yield. Additionally, variations in grain filling occur at different positions within the maize ear. Abscisic acid (ABA) is important for grain filling and regulates grain weight. However, the effects of exogenous ABA on the filling process of maize grains at different ear positions under high planting density are poorly understood. In this study, two summer maize hybrids (DengHai605 (DH605) and ZhengDan958 (ZD958)) commonly grown in China were used to examine the effects of ABA application during the flowering stage on grain filling properties, starch accumulation, starch biosynthesis associated enzyme activities, and hormone levels of maize grain (including inferior grain (IG) and superior grain (SG)) under high planting density.ResultsOur results showed that exogenous ABA significantly increased maize yield, primarily owing to a higher grain weight resulting from an accelerated grain filling rate relative to the control. There was no significant difference in yield between DH605 and ZD958 in the control and ABA treatments. Moreover, applying ABA promoted starch accumulation by raising the activities of sucrose synthase, ADP-glucose pyrophosphorylase, granule-bound starch synthases, soluble starch synthase, and starch branching enzyme in grains. It also increased the levels of zeatin riboside, indole-3-acetic acid, and ABA and decreased the level of gibberellin in grains, resulting in more efficient grain filling. Notably, IG exhibited a less efficient filling process compared to SG, probably due to lower starch biosynthesis associated enzyme activities and an imbalance in hormone contents. Nevertheless, IG displayed greater sensitivity to exogenous ABA than SG, suggesting that appropriate cultural measures to improve IG filling may be a viable strategy to further increase maize yield.ConclusionsAccording to our results, spraying exogenous ABA could effectively improve grain filling properties, accelerate starch accumulation by increasing relevant enzyme activities, and regulate hormone levels in grains, resulting in higher grain weight and yield of maize under high planting density. Our findings offer more evidence for using exogenous hormones to improve maize yield under high planting density.

Energy Evaluations of Several Weed Control Techniques that Undermine Cotton (Gossypium hirsutum L.) Planted in High Density

The current study was carried out at the Dr. Panjabrao Deshmukh Krishi Vidyapeeth. Akola, Cotton Research Center in Maharashtra, India, for the kharif season to assess the effectiveness of various weed management strategies in high density planting system (HDPS) cotton and also to assess the energy studies of different weed control methods used with HDPS cotton for two consecutive years (2015–16 and 2016–17). The results showed that among the other treatments, application of Pendimethalin 38.7 CS PE @ 1.25 kg a.i./ ha fbhoeing at 30 DAS and one hand weeding at 45 DAS significantly improved the energy output (84627 and 123742Mj ha-1), energy balance (73492 and 120656Mj ha-1), energy balance per unit input (6.6 and 10.8Mj ha-1) and energy output per unit input ratio (7.60 and 11), with weedy check (control), however, lower values were seen. As a result, cotton production with various weed control techniques under high density planting technique significantly improved energy output, energy balance per unit input, and energy output per unit input ratio realized that, efficient enough in terms of energy consumption as appropriate energy management (avoid excess energy input consumption) favors to maximize energy output, energy balance with higher cotton production in rainfed areas under high density planting system.

Phylogenetic and functional analysis of tiller angle control homeologs in allotetraploid cotton.

Plants can adapt their growth to optimize light capture in competitive environments, with branch angle being a crucial factor influencing plant phenotype and physiology. Decreased branch angles in cereal crops have been shown to enhance productivity in high-density plantings. The Tiller Angle Control (TAC1) gene, known for regulating tiller inclination in rice and corn, has been found to control branch angle in eudicots. Manipulating TAC1 in field crops like cotton offers the potential for improving crop productivity. Using a homolog-based methodology, we examined the distribution of TAC1-related genes in cotton compared to other angiosperms. Furthermore, tissue-specific qPCR analysis unveiled distinct expression patterns of TAC1 genes in various cotton tissues. To silence highly expressed specific TAC1 homeologs in the stem, we applied CRISPR-Cas9 gene editing and Agrobacterium-mediated transformation, followed by genotyping and subsequent phenotypic validation of the mutants. Gene duplication events of TAC1 specific to the Gossypium lineage were identified, with 3 copies in diploid progenitors and 6 copies in allotetraploid cottons. Sequence analysis of the TAC1 homeologs in Gossypium hirsutum revealed divergence from other angiosperms with 1-2 copies, suggesting possible neo- or sub-functionalization for the duplicated copies. These TAC1 homeologs exhibited distinct gene expression patterns in various tissues over developmental time, with elevated expression of A11G109300 and D11G112200, specifically in flowers and stems, respectively. CRISPR-mediated loss of these TAC1 homeologous genes resulted in a reduction in branch angle and altered petiole angles, and a 5 to 10-fold reduction in TAC1 expression in the mutants, confirming their role in controlling branch and petiole angles. This research provides a promising strategy for genetically engineering branch and petiole angles in commercial cotton varieties, potentially leading to increased productivity.

Molecular mechanisms underlying coordinated responses of plants to shade and environmental stresses.

Shade avoidance syndrome (SAS) is triggered by a low ratio of red (R) to far-red (FR) light (R/FR ratio), which is caused by neighbor detection and/or canopy shade. In order to compete for the limited light, plants elongate hypocotyls and petioles by deactivating phytochrome B (phyB), a major R light photoreceptor, thus releasing its inhibition of the growth-promoting transcription factors PHYTOCHROME-INTERACTING FACTORs. Under natural conditions, plants must cope with abiotic stresses such as drought, soil salinity, and extreme temperatures, and biotic stresses such as pathogens and pests. Plants have evolved sophisticated mechanisms to simultaneously deal with multiple environmental stresses. In this review, we will summarize recent major advances in our understanding of how plants coordinately respond to shade and environmental stresses, and will also discuss the important questions for future research. A deep understanding of how plants synergistically respond to shade together with abiotic and biotic stresses will facilitate the design and breeding of new crop varieties with enhanced tolerance to high-density planting and environmental stresses.

Breeding maize of ideal plant architecture for high-density planting tolerance through modulating shade avoidance response and beyond.

Maize is a major staple crop widely used as food, animal feed, and raw materials in industrial production. High-density planting is a major factor contributing to the continuous increase of maize yield. However, high planting density usually triggers a shade avoidance response and causes increased plant height and ear height, resulting in lodging and yield loss. Reduced plant height and ear height, more erect leaf angle, reduced tassel branch number, earlier flowering, and strong root system architecture are five key morphological traits required for maize adaption to high-density planting. In this review, we summarize recent advances in deciphering the genetic and molecular mechanisms of maize involved in response to high-density planting. We also discuss some strategies for breeding advanced maize cultivars with superior performance under high-density planting conditions.

Genetic regulation of self-organizing azimuthal canopy orientations and their impacts on light interception in maize.

The efficiency of solar radiation interception contributes to the photosynthetic efficiency of crop plants. Light interception is a function of canopy architecture, including plant density; leaf number, length, width, and angle; and azimuthal canopy orientation. We report on the ability of some maize (Zea mays) genotypes to alter the orientations of their leaves during development in coordination with adjacent plants. Although the upper canopies of these genotypes retain the typical alternate-distichous phyllotaxy of maize, their leaves grow parallel to those of adjacent plants. A genome-wide association study (GWAS) on this parallel canopy trait identified candidate genes, many of which are associated with shade avoidance syndrome, including phytochromeC2. GWAS conducted on the fraction of photosynthetically active radiation (PAR) intercepted by canopies also identified multiple candidate genes, including liguleless1 (lg1), previously defined by its role in ligule development. Under high plant densities, mutants of shade avoidance syndrome and liguleless genes (lg1, lg2, and Lg3) exhibit altered canopy patterns, viz, the numbers of interrow leaves are greatly reduced as compared to those of nonmutant controls, resulting in dramatically decreased PAR interception. In at least the case of lg2, this phenotype is not a consequence of abnormal ligule development. Instead, liguleless gene functions are required for normal light responses, including azimuth canopy re-orientation.