Xinkai Zhu

Foliar application of 24-epibrassinolide alleviates high-temperature-induced inhibition of photosynthesis in seedlings of two melon cultivars

Brassinosteroids (BRs), an important class of plant steroidal hormones, play a significant role in the amelioration of various biotic and abiotic stresses. 24-epibrassinolide (EBR), an active brassinosteroid, was applied exogenously in different concentrations to characterize a role of BRs in tolerance of melon (Cucumis melo L.) to high temperature (HT) stress and to investigate photosynthetic performance of HT-stressed, Honglvzaocui (HT-tolerant) and Baiyuxiang (HTsensitive), melon variety. Under HT, Honglvzaocui showed higher biomass accumulation and a lower index of heat injury compared with the Baiyuxiang. The exogenous application of 1.0 mg L−1 EBR, the most effective concentration, alleviated dramatically the growth suppression caused by HT in both ecotypes. Similarly, EBR pretreatment of HTstressed plants attenuated the decrease in relative chlorophyll content, net photosynthetic rate, stomatal conductance, stomatal limitation, and water-use efficiency (WUE), as well as the maximal quantum yield of PSII photochemistry (Fv/Fm), the efficiency of excitation capture of open PSII center, the effective quantum yield of PSII photochemistry (ΦPSII), photochemical quenching coefficient, and the photon activity distribution coefficients of PSI (α). EBR pretreatment further inhibited the increase in intracellular CO2 concentration, leaf transpiration rate, minimal fluorescence of dark-adapted state, nonphotochemical quenching, thermal dissipation, and photon activity distribution coefficients of PSII. Results obtained here demonstrated that EBR could alleviate the detrimental effects of HT on the plant growth by improving photosynthesis in leaves, mainly reflected as up-regulation of photosynthetic pigment contents and photochemical activity associated with PSI.

Responses of Phosphorus Use Efficiency, Grain Yield, and Quality to Phosphorus Application Amount of Weak-Gluten Wheat

Phosphorus (P) is one of the most widely occurring nutrients for development and growth of wheat. In this study, the effects of P application amount on grain yield, protein content, and phosphorus use efficiency (PUE) were studied by agronomic management of P fertilizer on spring weak-gluten wheat (Triticum aestivum L.) grown under field conditions for 2 yr. The experiments were performed at five levels of P2O5 application amount, including 0, 72, 108, 144, and 180 kg ha−1. As a result, with increase in P fertilizer, grain yield, and P agricultural efficiency (AEP) increased in a quadratic equitation, but partial factor productivity of P (PFPP) decreased in a logarithmic eq. When 108 kg ha−1 P2O5 was applied, the grain yield reached the highest level, but the protein content in gain was lower than 11.5%, a threshold for the protein content to evaluate weak-gluten wheat suitable for production of cake and biscuit. Yangmai 13 and Ningmai 9 could tolerate to higher P level of soils than Yangmai 9 that had more loss in grain yield when P fertilizer was over-applied. AEP had a concomitant relationship with grain yield and was a better descriptor for P use efficiency in the wheat. A high P use efficiency resulted in leaf area index (LAI), increased chlorophyll content and photosynthetic rate, and stable acid phophatase (APase) activity to accumulate more dry matter after anthesis, which explained that the optimum P fertilizer increased grain yield and improved grain quality of weak-gluten wheat.

Effect of nitrogen levels and nitrogen ratios on lodging resistance and yield potential of winter wheat (Triticum aestivum L.).

Lodging is one of the constraints that limit wheat yields and quality due to the unexpected bending or breaking stems on wheat (Triticum aestivum L.) production worldwide. In addition to choosing lodging resistance varieties, husbandry practices also have a significant effect on lodging. Nitrogen management is one of the most common and efficient methods. A field experiment with Yangmai 20 as research material (a widely-used variety) was conducted to study the effects of different nitrogen levels and ratios on culm morphological, anatomical characters and chemical components and to explore the nitrogen application techniques for lodging tolerance and high yield. Results showed that some index of basal internodes, such as stem wall thickness, filling degree, lignin content, cellulose content, water-soluble carbohydrate (WSC) and WSC/N ratio, were positively and significantly correlated with culm lodging-resistant index (CLRI). As the increase of nitrogen level and basal nitrogen ratio, the basal internodes became slender and fragile with the thick stem wall, while filling degree, chemical components and the strength of the stem decreased gradually, which significantly increased the lodging risk. The response of grain yield to nitrogen doses was quadratic and grain yield reached the highest at the nitrogen ratio of 50%:10%:20%:20% (the ratio of nitrogen amount applied before sowing, at tillering stage, jointing stage and booting stage respectively, abbreviated as 5:1:2:2). These results suggested that for Yangmai 20, the planting density of 180×104ha-1, nitrogen level of 225 kg ha-1, and the ratio of 5: 1: 2: 2 effectively increased lodging resistance and grain yield. This combination of planting density and nitrogen level and ratio could effectively relieve the contradiction between high-yielding and anti-lodging.

Grain Yield, Starch Content and Activities of Key Enzymes of Waxy and Non-waxy Wheat (Triticum aestivum L.)

Waxy wheat has unique end-use properties; however, its production is limited due mainly to its low grain yield compared with non-waxy wheat. In order to increase its grain yield, it is critical to understand the eco-physiological differences in grain filling between the waxy and non-waxy wheat. In this study, two waxy wheat and two non-waxy wheat cultivars were used to investigate the differences in starch-associated enzymes processes, sucrose and starch dynamics, yield components, and the final grain yield. The results indicated that the mean total grain starch and amylose content, the average 1000-kernel weight and grain yield of the waxy wheat were lower than those of the non-waxy wheat at maturity. The amylose content was significantly and positively correlated with the activity of GBSS (r = 0.80, p < 0.01). Significant positive correlation also exists among activities of AGPase, SSS, GBSS, and SBE, except for GBSS-SBE. In summary, our study has revealed that the reduced conversion of sucrose to starch in the late grain filling stage is the main cause for the low kernel weight and total starch accumulation of the waxy wheat. The reduced conversion also appears to be a factor contributing to the lower grain yield of the waxy wheat.

Evaluation of Seed Emergence Uniformity of Mechanically Sown Wheat with UAV RGB Imagery

The uniformity of wheat seed emergence is an important characteristic used to evaluate cultivars, cultivation mode and field management. Currently, researchers typically investigated the uniformity of seed emergence by manual measurement, a time-consuming and laborious process. This study employed field RGB images from unmanned aerial vehicles (UAVs) to obtain information related to the uniformity of wheat seed emergence and missing seedlings. The calculation of the length of areas with missing seedlings in both drill and broadcast sowing can be achieved by using an area localization algorithm, which facilitated the comprehensive evaluation of uniformity of seed emergence. Through a comparison between UAV images and the results of manual surveys used to gather data on the uniformity of seed emergence, the root-mean-square error (RMSE) was 0.44 for broadcast sowing and 0.64 for drill sowing. The RMSEs of the numbers of missing seedling regions for broadcast and drill sowing were 1.39 and 3.99, respectively. The RMSEs of the lengths of the missing seedling regions were 12.39 cm for drill sowing and 0.20 cm2 for broadcast sowing. The UAV image-based method provided a new and greatly improved method for efficiently measuring the uniformity of wheat seed emergence. The proposed method could provide a guideline for the intelligent evaluation of the uniformity of wheat seed emergence.

MORPHOLOGICAL AND PHYSIOLOGICAL RESPONSES OF WINTER WHEAT SEEDLINGS TO NITROGEN AND PHOSPHORUS DEFICIENCY

Nitrogen (N) and phosphorus (P) deficiencies are major yield limiting factors in many parts of the world. A greenhouse experiment was conducted to study the effects of both N and P deficiency on morphological and physiological responses of wheat cultivars with and without purple coleoptiles in three types of soils. Before the 3-leaf stage, cultivar ‘Jagger’ with greenish coleoptile showed typical green color in leaves even if grown in soils known to be deficient in N and P. After 3-leaf stage, however, ‘Jagger’ grown in the same soils exhibited purple on leaves, which was considered a typical symptom of P deficiency. Before 3-leaf stage, cultivar ‘2174’ with purplish coleoptile showed purple on the tips of leaves even if grown in a soil not deficient in P, indicating that the leaf purple color is genetically controlled. Pre-plant P but not N fertilizer application could alleviate the purple severity of young seedlings (before 3 leaf stage). Top-dressing N fertilizer could alleviate the purple severity, but top-dressing P fertilizer could enable the severe purple leaves to return green at older seedlings (5–6 leaf stage), indicating that N and P had different effects on the morphological phenotype. There was a correlation between the purple severity and leaf chlorophyll readings, and N and P accumulation. The various responses of the cultivars to N and P deficiency resulted in significant differences in tiller occurrence and shoot and root dry matter production. Purple coloration is not only a visible symptom due to P deficiency but also a phenotype that can be used to diagnose N deficiency in wheat seedlings.

ENHANCING NITROGEN USE EFFICIENCY BY COMBINATIONS OF NITROGEN APPLICATION AMOUNT AND TIME IN WHEAT

Nitrogen (N) is one of the most important impact factors on development and growth of wheat. In this study the effects of nitrogen use efficiency on quantity and quality of grains were studied by agronomic management of N fertilizers on spring wheat (Triticum aestivum L.) grown under field conditions for two years. The experiments were performed at 16 combinations of N application amount and time, including four levels of N at 0, 60, 120 and 180 kg N ha−1 that were used as pre-plant fertilizers, sub-treated with four levels of the same N amount used as top-dress fertilizers. As a result, with an increase in total N fertilizers, grain yield increased in a cubic equitation, but partial factor productivity (PFPN, kg grain yield per kg N applied) decreased exponentially. With total fertilizers, N content and accumulation in vegetative tissues and grains increased linearly, but N uptake efficiency (UtEN, kg nutrient taken up per kg N applied) decreased exponentially. When N was over-applied (>360 kg N ha−1 in this study), grain yield clearly declined, due to decrease in productivity from per unit N. The high N level (240∼300 kg N ha−1), the reasonable distribution between pre-plant and top dress from the same amount N fertilizer not only increased grain yield but also enhanced N use efficiency.

Author Correction: Grain Yield, Starch Content and Activities of Key Enzymes of Waxy and Non-waxy Wheat (Triticum aestivum L.)

A correction to this article has been published and is linked from the HTML version of this paper. The error has not been fixed in the paper.

Nitrogen use efficiency is regulated by interacting proteins relevant to development in wheat

Summary Wheat (Triticum aestivum) has low nitrogen use efficiency (NUE). The genetic mechanisms controlling NUE are unknown. Positional cloning of a major quantitative trait locus for N‐related agronomic traits showed that the vernalization gene TaVRN‐A1 was tightly linked with TaNUE1, the gene shown to influence NUE in wheat. Because of an Ala180/Val180 substitution, Ta VRN‐A1a and Ta VRN‐A1b proteins interact differentially with Ta ANR1, a protein encoded by a wheat orthologue of Arabidopsis nitrate regulated 1 (ANR1). The transcripts of both TaVRN‐A1 and TaANR1 were down‐regulated by nitrogen. TaANR1 was functionally characterized in TaANR1::RNAi transgenic wheat, and in a natural mutant with a 23‐bp deletion including 10‐bp at the 5′ end of intron 5 and 13‐bp of exon 6 in gDNA sequence in its gDNA sequence, which produced transcript that lacked the full 84‐bp exon 6. Both Ta ANR1 and Ta HOX1 bound to the Ala180/Val180 position of Ta VRN‐A1. Genetically incorporating favourable alleles from TaVRN‐A1, TaANR1 and TaHOX1 increased grain yield from 9.84% to 11.58% in the field. Molecular markers for allelic variation of the genes that regulate nitrogen can be used in breeding programmes aimed at improving NUE and yield in novel wheat cultivars.

Does cyclic water stress damage wheat yield more than a single stress

The occurrence of water stress during wheat growth is more frequent due to climate change. Three experiments (cyclic drought, cyclic waterlogging, and cyclic drought plus waterlogging) were conducted to investigate the effects of mild and severe cyclic/single water stress at elongation and heading stages on winter wheat (Triticum aestivum L.) yield. The effect of either mild drought at elongation or mild waterlogging at heading on wheat yield was not significant; however, significance did occur under other single water stresses. As the stress becomes more severe, the yield loss significantly increases. Extreme drought/waterlogging treatment at elongation caused a greater yield penalty than stress at heading stage. Except the combination of mild drought and mild waterlogging treatment, cyclic water stress significantly decreased wheat yields. The decrease in wheat yield under cyclic severe drought and waterlogging was significantly higher than any other treatment, with percentage decreases of 71.52 and 73.51%, respectively. In general, a yield reduction from mild cyclic water stress did not indicate more severe damage than single treatments; in contrast, grain yield suffered more when water stress occurred again after severe drought and waterlogging. Drought during elongation significantly decreased kernel number, whereas drought at heading/waterlogging during elongation and heading decreased the spike weight, which might be the main reason for the yield penalty. Furthermore, water stress caused variation in the decrease of total biomass and/or harvest index. The present study indicates comprehensive understanding of the types, degree, and stages of water stress are essential for assessing the impact of multiple water stresses on wheat yield.