玉米穗柄长研究进展

The vascular bundle of the shank is an important ‘flow’ organ for transforming maize biological yield to grain yield, and its microscopic phenotypic characteristics and genetic analysis are of great significance for promoting the breeding of new varieties with high yield and good quality. In this study, shank CT images were obtained using the standard process for stem micro-CT data acquisition at resolutions up to 13.5 μm. Moreover, five categories and 36 phenotypic traits of the shank including related to the cross-section, epidermis zone, periphery zone, inner zone and vascular bundle were analyzed through an automatic CT image process pipeline based on the functional zones. Next, we analyzed the phenotypic variations in vascular bundles at the base of the shank among a group of 202 inbred lines based on comprehensive phenotypic information for two environments. It was found that the number of vascular bundles in the inner zone (IZ_VB_N) and the area of the inner zone (IZ_A) varied the most among the different subgroups. Combined with genome-wide association studies (GWAS), 806 significant single nucleotide polymorphisms (SNPs) were identified, and 1245 unique candidate genes for 30 key traits were detected, including the total area of vascular bundles (VB_A), the total number of vascular bundles (VB_N), the density of the vascular bundles (VB_D), etc. These candidate genes encode proteins involved in lignin, cellulose synthesis, transcription factors, material transportation and plant development. The results presented here will improve the understanding of the phenotypic traits of maize shank and provide an important phenotypic basis for high-throughput identification of vascular bundle functional genes of maize shank and promoting the breeding of new varieties with high yield and good quality.

Ear shank length (ESL) has significant effects on grain yield and kernel dehydration rate in maize. Herein, linkage mapping and genome-wide association study were combined to reveal the genetic architecture of maize ESL. Sixteen quantitative trait loci (QTL) were identified in the segregation population, among which five were repeatedly detected across multiple environments. Meanwhile, 23 single nucleotide polymorphisms were associated with the ESL in the association panel, of which four were located in the QTL identified by linkage mapping and were designated as the population-common loci. A total of 42 genes residing in the linkage disequilibrium regions of these common variants and 12 of them were responsive to ear shank elongation. Of the 12 genes, five encode leucine-rich repeat receptor-like protein kinases, proline-rich proteins, and cyclin11, respectively, which were previously shown to regulate cell division, expansion, and elongation. Gene-based association analyses revealed that the variant located in Cyclin11 promoter affected the ESL among different lines. Cyclin11 showed the highest expression in the ear shank 15 days after silking among diverse tissues of maize, suggesting its role in modulating ESL. Our study contributes to the understanding of the genetic mechanism underlying maize ESL and genetic modification of maize dehydration rate and kernel yield.

… essential for developing high-yielding, machine-harvestable maize cultivars with optimized … Phenotypic variation and correlation analysis of ear shank length (ESL) in the maize–teosinte …

In maize, the ear shank is a short branch that connects the ear to the stalk. The length of the ear shank mainly affects the transportation of photosynthetic products to the ear, and also influences the dehydration of the grain by adjusting the tightness of the husks. However, the molecular mechanisms of maize shank elongation have rarely been described. It has been reported that the maize ear shank length is a quantitative trait, but its genetic basis is still unclear. In this study, RNA-seq was performed to explore the transcriptional dynamics and determine the key genes involved in maize shank elongation at four different developmental stages. A total of 8145 differentially expressed genes (DEGs) were identified, including 729 transcription factors (TFs). Some important genes which participate in shank elongation were detected via function annotation and temporal expression pattern analyses, including genes related to signal transduction hormones (auxin, brassinosteroids, gibberellin, etc.), xyloglucan and xyloglucan xyloglucosyl transferase, and transcription factor families. The results provide insights into the genetic architecture of maize ear shanks and developing new varieties with ideal ear shank lengths, enabling adjustments for mechanized harvesting in the future.

Introduction The ear shank, a short branch connecting the stalk and the ear, represented a key agronomic trait influenced both yield and plant architecture in maize, yet the molecular mechanism remained not fully understood. Methods In this study, BSA-seq was performed using an F2 population for two extreme bulks derived from the cross between WL134 and L135. Additionally, transcriptomic analysis and gene annotation were carried out to refine the association interval of ear shank length and identify crucial genes. Results and Discussion A total of 14 QTLs for ear shank length were detected, which included 334 non-synonymous mutants, synonymous mutants and frameshift mutant genes. Among these loci, five were known to be associated with ear shank length, while nine were newly identified. 3,460 differentially expressed genes (DEGs) were screened through RNA-seq analysis of the ear shank at the silking stage in both parents. Thirteen new candidate genes were identified through the combined analysis of BSA-seq and RNA-seq, as well as gene function annotation and gene expression analysis. Based on functional predictions, the candidate genes Zm00001eb023400, Zm00001eb023420 and Zm00001eb050490, which encoded lytic transglycosylases, significantly associated with cell wall remodeling and degradation. The candidate genes Zm00001eb282410 and Zm00001eb282430 enriched the phenylpropanoid biosynthesis pathway and played important roles in the formation of the maize ear shank. These findings provided a foundation for understanding the molecular mechanisms regulating ear shank length in maize.

Maize is one of the most important crops for human food, animal feed, and industrial raw materials. Ear shank length (ESL) and ear shank node number (ESNN) are crucial selection criteria in maize breeding, impacting grain yield and dehydration rate during mechanical harvesting. To unravel the genetic basis of ESL and ESNN in maize, an association panel consisting of 379 multi-parent doubled-haploid (DH) lines was developed for genome-wide association studies (GWAS) and genomic selection (GS). The heritabilities of ESL and ESNN were 0.68 and 0.55, respectively, which were controlled by genetic factors and genotype-environment interaction factors. Using five different models for GWAS, 11 significant single nucleotide polymorphisms (SNPs) located on chromosomes 1, 2, and 4 were identified for ESL, with the phenotypic variation explained (PVE) value of each single SNP ranging from 4.91% to 21.35%, and 11 significant SNPs located on chromosomes 1, 2, 4, and 5 were identified for ESNN, with the PVE value of each SNP ranging from 1.22% to 18.42%. Genetic regions in bins 1.06, 2.06, and 2.08 were significantly enriched in SNPs associated with ear shank-related traits. The GS prediction accuracy using all markers by the five-fold cross-validation method for ESL and ESNN was 0.39 and 0.37, respectively, which was significantly improved by using only 500-1000 significant SNPs with the lowest P-values. The optimal training population size (TPS) and marker density (MD) for ear shank-related traits were 50%-60% and 3000, respectively. Our results provide new insights into the GS of ear shank-related traits.

In maize, the shank is a unique tissue linking the stem to the ear. Shank length (SL) mainly affects the transport of photosynthetic products to the ear and the dehydration of kernels via regulated husk morphology. The limited studies on SL revealed it is a highly heritable quantitative trait controlled by significant additive and additive-dominance effects. However, the genetic basis of SL remains unclear. In this study, we analyzed three maize recombinant inbred line (RIL) populations to elucidate the molecular mechanism underlying the SL. The data indicated the SL varied among the three RIL populations and was highly heritable. Additionally, the SL was positively correlated with the husk length (HL), husk number (HN), ear length (EL), and ear weight (EW) in the BY815/K22 (BYK) and CI7/K22 (CIK) RIL populations, but was negatively correlated with the husk width (HW) in the BYK RIL population. Moreover, 10 quantitative trait loci (QTL) for SL were identified in the three RIL populations, five of which were large-effect QTL. The percentage of the total phenotypic variation explained by the QTL for SL was 13.67 %, 20.45 %, and 30.81 % in the BY815/DE3 (BYD), BYK, and CIK RIL populations, respectively. Further analyses uncovered some genetic overlap between SL and EL, SL and ear row number (ERN), SL and cob weight (CW), and SL and HN. Unlike the large-effect QTL qSL BYK-2-2, which spanned the centromere, the other four large-effect QTL were delimited to a single peak bin via bin map. Furthermore, 2, 5, 6, and 12 genes associated with SL were identified for qSL BYK-2-1, qSL CIK-2-1, qSL CIK-9-1, and qSL CIK-9-2, respectively. Five of the candidate genes for SL may contribute to the hormone metabolism and sphingolipid biosynthesis regulating cell elongation, division, differentiation, and expansion. These results may be relevant for future studies on the genetic basis of SL and for the molecular breeding of maize based on marker-assisted selection to develop new varieties with an ideal SL.

… Phenotypic analysis was also used to identify important traits suitable for studying the phenotypes of maize ear… formation and development of ear-internode vascular bundles in maize, …

… The basic internal anatomical condition is described for the … ear and tassel of golden bantam sweet corn. In the transition region from shank to ear, a distinct segregation of vascular …

The question of row number eventually arises in any complete study of the ear of corn. It is likely to become involved especially when the origin of the ear is considered. Several years ago the late Dr. R. A. Emerson was growing certain strains of corn in a study of row inheritance. He obtained several ears with four rows from some of the crosses and these were made available to the writer for anatomical study. The immediate ancestry of the plants which produced these ears is not known.

… outward-moving small vascular bundles in the shank. Reeves found … The vascular anatomy of the four-rowed ear of corn. Ann. … The vascular anatomy of the eight-rowed ear and tassel of …

… Many strains of maize have ear-shanks with various degrees … If a detailed study of the vascular anatomy of such material … the occurrence of two vascular systems in the maize cob nor the …

… The peculiarities of vascular anatomy of the normal ear and of anomalous ears such as that shown in fig. 20 leave much to be desired as evidence of fusion, unless these peculiarities …

… In a study of vascular development of the maize tassel in the … both morphological and anatomical evidence to describe the … ear inflorescence, the shank, husk leaves, and ear of maize. …

… the elaborate vascular system of an eightrowed ear following … to the number ofleaves in the ear shank, the leafy stocks of … The vascular anatomy of the four-rowed ear of corn. Ann. Mo. …

… QTL mapping and GWAS. Additionally, they were verified to be significantly associated with maize … six tissues (roots, stems, leaves, ear shanks, husks, and ears) at 15 days after silking (…

… The size of the shank of the corn ear impacts on the ear picking force essentially. The shank has two main dimensions: diameter and length, so these parameters were measured on 20 …

… The third type of damage, the weakening of stalks and ear shanks, may be much more … ear dropping and the mechanical picking of field corn, and the effect of planting and harvesting …

… machine harvest losses differed between narrow and wide cornheads and the extent of visible machine harvest … later in the harvest season when stalk or ear shank strength might be …

… machine by the gathering chains. To improve working efficiency and quality of corn headers processing of stalk parts under the corn ear … stalk is the shank that holds the maize ear thus it …

Drought is a major abiotic stress reducing maize yield worldwide especially before and during silking. The mechanism underlying drought tolerance in maize has not been elucidated especially from the perspective of different organs. Hence, we conducted field trials under pre-silking drought using two maize genotypes, FM985 (drought tolerant) and ZD958 (drought sensitive). The two genotypes did not differ in plant height, grain number, and yield under control. However, grain number per ear and yield of FM985 were 38.1% and 35.1% higher and plant height was 17.6% shorter than ZD958 under drought. More 13 C-photosynthates were transported to the ear in FM985 than in ZD958, which increased floret fertility and grain number. The number of differentially expressed genes were greatly higher in stem than in other organs. Stem-ear interactions are key determinants of drought tolerance, in which genes expression related to ABA, lignin and flavonoid biosynthesis, and carbon metabolism in the stem were induced by drought, which inhibited stem elongation and promoted assimilates allocation to the ear in FM985. In comparison with ZD958, the activities of trehalose-6-phosphate phosphatase and sucrose non-fermentation-associated kinase 1 were higher in the stem and lower in the kernel of FM958, which facilitated kernel formation. These results reveal that, beyond ear response, stem elongation is involved in the whole process of drought tolerance before silking. ABA together with T6P, lignin and flavonoid suppresses stem elongation and allocates assimilate into ear, providing a novel and systematic regulatory pathway for drought tolerance in maize.

… , as well as internal signals including hormones, to mediate axillary bud … In older elongated ear shanks, TRU1 expression is … Plant hormones are potential candidate substances that may …

Waterlogging (W-B) is a major abiotic stress during the growth cycle of maize production in Huang-huai-hai plain of China, threatening food security. A wide range of studies suggests that the application of 6-benzyladenine (6-BA) can mitigate the W-B effects on crops. However, the mechanisms underlying this process remain unclear. In this study, the application of 6-BA that effectively increased the yield of summer maize was confirmed to be related to the hormone and sugar metabolism. At the florets differentiation stage, application of 6-BA increased the content of trans-zeatin (TZ, + 59.3%) and salicylic acid (SA, + 285.5%) of ears to induce the activity of invertase, thus establishing sink strength. During the phase of sexual organ formation, the TZ content of ear leaves, spike nodes, and ears was increased by 24.2, 64.2, and 46.1%, respectively, in W-B treatment, compared with that of W. Accordingly, the sugar metabolism of summer maize was also improved. Therefore, the structure of the spike node was improved, promoting the translocation of carbon assimilations toward the ears and the development of ears and filaments. Thus the number of fertilized florets, grain number, and yield were increased by the application of 6-BA.

… genetic and hormonal cues as well as extrinsic signals, such … of ear branches, which were significantly longer (P < 0.001) because of elongation of ear shank internodes beneath the ear …

… Auxin is a plant hormone that plays key roles in both shoot … O, la1-ref mutants have reduced ear shank length and silk … In our experiments, we observed that mesocotyl elongation in la1-…

Many domesticated crop plants have been bred for increased apical dominance, displaying greatly reduced axillary branching compared to their wild ancestors. In maize, this was achieved through selection for a gain-of-function allele of the TCP transcription factor teosinte branched1 (tb1). The mechanism for how a dominant Tb1 allele increased apical dominance, is unknown. Through ChIP seq, RNA seq, hormone and sugar measurements on 1 mm axillary bud tissue, we identify the genetic pathways putatively regulated by TB1. These include pathways regulating phytohormones such as gibberellins, abscisic acid and jasmonic acid, but surprisingly, not auxin. In addition, metabolites involved in sugar sensing such as trehalose 6-phosphate were increased. This suggests that TB1 induces bud suppression through the production of inhibitory phytohormones and by reducing sugar levels and energy balance. Interestingly, TB1 also putatively targets several other domestication loci, including teosinte glume architecture1, prol1.1/grassy tillers1, as well as itself. This places tb1 on top of the domestication hierarchy, demonstrating its critical importance during the domestication of maize from teosinte. The TB1 transcription factor was selected for the increased apical dominance of maize compared to its ancestor teosinte. A metabolic and genomic analysis of domesticated axillary buds suggest that TB1 achieved this by regulating phytohormone signaling, sugar metabolism and other domestication genes.

Strigolactones (SLs) control lateral branching in diverse species by regulating transcription factors orthologous to Teosinte branched1 (Tb1). In maize (Zea mays), however, selection for a strong central stalk during domestication is attributed primarily to the Tb1 locus, leaving the architectural roles of SLs unclear. To determine how this signaling network is altered in maize, we first examined effects of a knockout mutation in an essential SL biosynthetic gene that encodes CAROTENOID CLEAVAGE DIOXYGENASE8 (CCD8), then tested interactions between SL signaling and Tb1. Comparative genome analysis revealed that maize depends on a single CCD8 gene (ZmCCD8), unlike other panicoid grasses that have multiple CCD8 paralogs. Function of ZmCCD8 was confirmed by transgenic complementation of Arabidopsis (Arabidopsis thaliana) max4 (ccd8) and by phenotypic rescue of the maize mutant (zmccd8::Ds) using a synthetic SL (GR24). Analysis of the zmccd8 mutant revealed a modest increase in branching that contrasted with prominent pleiotropic changes that include (1) marked reduction in stem diameter, (2) reduced elongation of internodes (independent of carbon supply), and (3) a pronounced delay in development of the centrally important, nodal system of adventitious roots. Analysis of the tb1 zmccd8 double mutant revealed that Tb1 functions in an SL-independent subnetwork that is not required for the other diverse roles of SL in development. Our findings indicate that in maize, uncoupling of the Tb1 subnetwork from SL signaling has profoundly altered the balance between conserved roles of SLs in branching and diverse aspects of plant architecture.

Abstract The maize doubled haploid (DH) technology plays an important role in accelerating breeding genetic gain. One major challenge in fully leveraging the potential of DH technology to accelerate genetic gain is obtaining a consistent seed return from haploid (DH0) plants after chromosome doubling. Here we demonstrated that DH0 seed production can be increased by increasing the number of mature axillary female inflorescences (ears) at anthesis. To determine the maximum capacity of a maize plant to develop ears, we first characterized the developmental progression of every axillary meristem. We found that all axillary meristems developed to a similar developmental stage before the reproductive transition of the shoot apical meristem (SAM). Upon reproductive transition of the SAM, all axillary meristems are released for reproductive development into ears in a developmental gradient reflective on their positions along the main stem. However, under most circumstances only the top one or two ears can generate silks at anthesis. We found that applying the GA inhibitor paclobutrazol (PAC) during the early reproductive transition of axillary meristems increased the number of silking ears at anthesis, leading to increased success of self‐pollination and seed production. These results provide a blueprint to improve DH efficiency and demonstrate the potential of breeding innovation through understanding crops’ developmental processes.

… maize inbred lines. Results showed that the W27 (heat-sensitive line) suffered severe damage to the peduncle and silk, accompanied by reduced ear … , and cell wall invertase activities …

Summary The peduncle vascular system of maize is critical for the transport of photosynthetic products, nutrients, and water from the roots and leaves to the ear. Accordingly, it positively affects the grain yield. However, the genetic basis of peduncle vascular bundle (PVB)‐related traits in maize remains unknown. Thus, 15 PVB‐related traits of 386 maize inbred lines were investigated at three locations (Yongcheng, 17YC; Kaifeng, 20KF; and Yuanyang, 20YY). The repeatability for the 15 traits ranged from 35.53% to 92.13%. A genome‐wide association study was performed and 69 non‐redundant quantitative trait loci (QTL) were detected, including 9, 41, and 27 QTL identified at 17YC, 20KF, and 20YY, respectively. These QTL jointly explained 4.72% (SLL) to 37.30% (NSVB) of the phenotypic variation. Eight QTL were associated with the same trait at two locations. Furthermore, four pleiotropic QTL were identified. Moreover, one QTL (qPVB44), associated with NSVB_20KF, was co‐localized with a previously reported locus related to kernel width, implying qPVB44 may affect the kernel width by modulating the number of small vascular bundles. Examinations of the 69 QTL identified 348 candidate genes that were classified in five groups. Additionally, 26 known VB‐related homologous genes (e.g. VLN2, KNOX1, and UGT72B3) were detected in 20 of the 69 QTL. A comparison of the NSVB between a Zmvln2 EMS mutant and its wild type elucidated the function of the candidate gene ZmVLN2. These results are important for clarifying the genetic basis of PVB‐related traits and may be useful for breeding new high‐yielding maize cultivars.

… peduncle is so short that it is also usually overlooked, but sufficiently real so that pairs of grains firmly attached to it can be removed from the mature ear. … Later the formation of cell walls …

The internodes of forage maize (Zea mays L.) stems were studied at anthesis for variation in anatomy and chemical composition in relation to digestibility. The study was carried out with a short (Vitaro) and a tall (Volens) cultivar differing in whole-plant digestibility, both of which were grown in the field in the growing seasons of 1999 and 2000. Internode diameter increased from the top to the base of the stem and Vitaro had shorter and thicker internodes than Volens. The cell walls of the sclerenchyma tissue in the rind were thicker and the numbers of sclerenchyma layers around vascular bundles in the rind higher in lower than in upper internodes. The neutral detergent fibre content (NDF%) of the internodes increased from the top to the base of the stems of both cultivars, but was very high for the peduncle. NDF% was lower for Vitaro than for Volens in all internodes. The sugar content of the dry matter was highest for Internode 12, i.e., the internode near the position of the ear, and was very low for the peduncle. Vitaro always had a higher sugar content than Volens. When subjected to fermentation tests with rumen fluid in an automated gas production system, gas production values after 3, 20 or 72 h of incubation were higher for internodes from the top than for internodes from the base of the stem, and were lower for the peduncle than for Internode 14. The values were consistently higher for Vitaro than for Volens internodes; in general, this difference was most apparent for Internode 10. The differences in gas production amongst internodes and between cultivars were in line with differences expressed by in vitro digestibility measurements. Fermentation results of cross sections suggest that the cell walls in lower internodes disappeared faster and to a greater extent than the cell walls in upper internodes, except for Volens in 1999, and with the exception of the peduncle. The rate of cell wall disappearance was higher for Volens than for Vitaro, but ultimately similar amounts of cell wall material disappeared.

… maize (Zea mays), it is often attributed to a carbon limitation via the disruption of sucrose cleavage by cell wall … of husks, peduncle, ear, and silks were measured immediately, ears were …

… The DK670 hybrid showed less injured cell membranes in … /m2 increased the membrane injury significantly with respect … the peduncles vascular bundles of the ear in both maize hybrids …

… eg thickness, wax layer, cell wall phenolic acids and flavonoid pigments… ear peduncles was also observed, showing an endophyte-like behaviour of the fungus in association with maize …

The kernel setting of maize varies greatly because of the timing and intensity of water deficits. This variation can limit leaf productivity (source), the translocation of assimilated sugars (flow), and yield formation (sink). To explain the decline in kernel setting of maize under water deficits from the perspective of source-flow-sink, a 3-year experiment was conducted under a rain shelter. Five water regimes were studied. One regime included well-irrigated (CK) treatment. Four regimes involved water deficits: irrigation was withheld during the 6- to 8-leaf stage (V6−8), the 9- to 12-leaf stage (V9−12), the 13-leaf stage to tasseling stage (V13−T), and the silking stage to blister stage (R1−2). Water deficit effects on kernel setting began when the water deficit occurred at V9 and became more significant with time. Kernel weight was reduced by 12 and 11% when there were water deficits during V9−12 and V13−T, respectively. This was the result of reduced leaf area (limited source) and an altered vascular bundle in the ear peduncles (limited assimilate flow). The reduced vascular bundle number, rather than the ear peduncle cross-sectional area, significantly affected the final kernel weight when exposed to a water deficit prior to the silking stage. The water deficits prior to and close to the flowering stage significantly reduced ear kernel number; that is, 14 and 19% less during V13−T and R1−2, respectively, compared with the kernel number during the CK treatment. This reflects a smaller sink under water deficit conditions. Additionally, ovary size was reduced the most in the V13−T water deficit compared with other treatments. After rewatering, the water deficit before or during flowering stage continued to have residual effects on grain-filling in the late growth period. The grain-filling rate decreased under the V9−12 water deficit; the grain-filling duration shortened under the R1−2 water deficit; and both negative effects occurred under the V13−T water deficit. This study clearly indicated that (1) the water deficit during the vegetative organ rapid growth period both limited leaf source development and assimilate flow and slowed down kernel development, and (2) the water deficit just before and during flowering reduced kernel sink. Deficits at both times could retard grain-filling and reduce maize yield. The results of the present study might guide irrigation practices in irrigated maize or inform the management of sowing time in rainfed maize, to desynchronize the water deficit and the plant’s reactions to such deficits at different stages.

… maize kernels and their resistance to ear rot, suggesting that a … in the transcriptomics during both periods, and its expression … the transcriptomic and proteomic analyses, five genes were …

… the performance of mechanized grain harvest. However, it remains unclear what influences grain dehydration rate. In this study, maize grain dehydrating process was investigated in a …

… loss from the grain surface. Higher … ear angle, and increased looseness of grain arrangement likely accelerated the rate of water loss from the grain surface, thereby reducing the grain …

… maize in eastern Jilin Province, we analyzed the number, thickness, dry weight, moisture and dehydration rate of husk leaves in six maize … of cob-pedicel, ear and grain at harvest. The …

Rapid dehydration of maize grain is one of the main characteristics of cultivar selection for mechanical grain harvest; however, the dominant driving forces and mechanisms of grain dehydration before physiological maturity remain disputable and obscure. This study compared the grain moisture content and dehydration rate of coated treatment (no surface evaporation) and control grains. Meanwhile, the xylem-mobile dye was infused from stem and cob, and its movement was observed in cob, ear-stalk and stem xylem. The development dynamics of husk, grain and cob were analyzed to determine the mechanism of grain dehydration. The results showed that, from grain formation to 5-10 days before physiological maturity, the main driving force of grain dehydration of the early and middle-maturity maize cultivars was filling, followed by surface evaporation. In the dye movement experiment, the movement of the stem-infused xylem-mobile dye through the pedicel xylem was observed during but not after the grain formation period. Moreover, the cob-infused xylem-mobile dye moved to the ear- stalk and the stem via the xylem. There was a significantly positive correlation between grain filling rate and dehydration rate from grain formation to physiological maturity. According to these results, we proposed that in the grain dehydration phase driven by filling, the surplus water in the grain flows back to the cob via the pedicel xylem, of which some flowed back to the plant via the cob and ear- stalk xylem. This provides a new theoretical basis for selecting and breeding maize cultivars suitable for mechanical grain harvesting.

… Maize, one of the most important crops in the food chain, is … Maize grain development requires assimilate uptake from the … ) within ear and its relationship with grain development under …

ABSTRACT A mixture of ethephon (ETH) and thidiazuron (TDZ) (called ETTD) has been proven to effectively reduce maize grain moisture content and improve yield and quality of mechanical grain harvesting, but the underlying mechanism is unclear. Field trials were conducted in 852 Farm, Heilongjiang Province, China, in 2017 and 2018, to study the effects of ETH, TDZ and ETTD sprayed on Xianyu335 at 25 days after flowering (appropriate time in the pre-experiment) on grain filling and dehydration characteristics. ETH, TDZ and ETTD significantly accelerated leaf senescence, increased grain, bract, and cob dehydration rates, and decreased grain filling duration and moisture content. TDZ and ETTD significantly increased grain filling rate and auxin (IAA), zeatin riboside (ZR), and abscisic acid (ABA) and decreased gibberellic acid (GA). ETH had no significant effect on ABA and GA, but significantly reduced IAA and ZR in the later period. The grain dehydration rate was significantly negatively correlated with grain filling duration and positively correlated with rates of grain filling and bract and cob dehydration. ETTD significantly decreased the rates of breakage, impurity, and increased mechanical grain harvesting yield. In conclusion, ETTD can be an effective measure to improve yield and quality of maize mechanical grain harvesting.

The rapid dehydration rate of maize grain is one of the main characteristics of cultivar selection of mechanical grain harvest, but the dominant driving force and mechanism of grain dehydration before physiological maturity remains disputable and obscure, respectively. This study found that, from grain formation to 5-10 days before physiological maturity of early and middle maturity maize cultivars, the main driving force of grain dehydration is filling and then converts to surface evaporation, by comparing the grain moisture content and dehydration rate between grain coated treatment and control. In the dye movement experiment, xylem-mobile dye movement into grain through pedicel xylem was observed during grain formation period, and declined and gradually not observed after grain formation. Xylem-mobile dye movement out of ear via cob, ear-pedicel and stem xylem was observed after grain formation. In addition, from grain formation to physiological maturity, there was a very significant positive correlation between grain filling rate and dehydration rate. According to these results, it is proposed here that in the grain dehydration phase driven by filling, the surplus water in grain flows back to cob via pedicel xylem, and some of it flows back to plant via cob and ear-pedicel xylem. Highlight The surplus water in grain driven by grain filling flows back to the cob and plant for recyclingvia the xylem during the development of maize grain.