Days After Silking Research Articles

Effect of Defoliation on Growth and Yield of Maize

The experiment was conducted to evaluate the effect of defoliation on grain and fodder yield of maize at the research field and laboratory of Crop Physiology and Ecology Department, Hajee Mohammad Danesh Science and Technology University, Dinajpur during the period of December 2018 to June 2019. The trial was carried out in a randomized completely block design with three replications. The experimental treatments were: T1– Control (without leaf removal), T2–Defoliating all leaves except ear and adjacent two leaves above the ear at 7 days after silking (DAS), T3–Defoliating all leaves except ear and adjacent two leaves above the ear at 14DAS, T4–Defoliating all leaves below the ear at 7 DAS, T5–Defoliating all leaves below the ear at 14 DAS, T6– Detopping except two leaves above the ear at 7 DAS and T7–Detopping except two leaves above the ear at 14 DAS. Light intensity was increased (66.9 to 81.05%) when only lower leaves (T5) or both upper and lower leaves (T2) were removed, but when only the upper leaves (T6) were removed it was not increased. SPAD value was increased (13.58 to 24.5%) but number of leaves and leaf area plant-1 were reduced (60.5 to 63.09% and 64.4%) due to defoliation. Substantial amount of green fodder was obtained (0.776 Kg m-2) due to defoliation of maize. Grain yield of maize was reduced (5.56 to 21.83%) due to different defoliation treatments but the yield reduction was not significant when only lower (T4) or upper (T7) leaves were removed.
 Bangladesh Agron. J. 2022, 25(2): 31-41

QTL analysis of the developmental changes in cell wall components and forage digestibility in maize (Zea mays L.)

Cell wall architecture plays a key role in stalk strength and forage digestibility. Lignin, cellulose, and hemicellulose are the three main components of plant cell walls, and they can impact stalk quality by affecting the structure and strength of the cell wall. To explore cell wall development during secondary cell wall lignification in maize stalks, conventional and conditional genetic mapping were used to identify the dynamic quantitative trait loci (QTLs) of the cell wall components and digestibility traits during five growth stages after silking. Acid detergent lignin (ADL), cellulose (CEL), acid detergent fiber (ADF), neutral detergent fiber (NDF), and in vitro dry matter digestibility (IVDMD) were evaluated in a maize recombinant inbred line (RIL) population. ADL, CEL, ADF, and NDF gradually increased from 10 to 40 days after silking (DAS), and then they decreased. IVDMD initially decreased until 40 DAS, and then it increased slightly. Seventy-two QTLs were identified for the five traits, and each accounted for 3.48–24.04% of the phenotypic variation. Six QTL hotspots were found, and they were localized in the 1.08, 2.04, 2.07, 7.03, 8.05, and 9.03 bins of the maize genome. Within the interval of the pleiotropic QTL identified in bin 1.08 of the maize genome, six genes associated with cell wall component biosynthesis were identified as potential candidate genes for stalk strength as well as cell wall-related traits. In addition, 26 conditional QTLs were detected in the five stages for all of the investigated traits. Twenty-two of the 26 conditional QTLs were found at 30 DAS conditioned using the values of 20 DAS, and at 50 DAS conditioned using the values of 40 DAS. These results indicated that cell wall-related traits are regulated by many genes, which are specifically expressed at different stages after silking. Simultaneous improvements in both forage digestibility and lodging resistance could be achieved by pyramiding multiple beneficial QTL alleles identified in this study.

The central role of ear nitrogen uptake in maize endosperm cell and kernel weight determination during the lag period

Although kernel weight (KW) has proven to be an increasingly important driver behind grain yield (GY) variability in modern maize hybrids, nitrogen’s (N) role in the determination of individual sink capacity (i.e., potential KW) during the lag phase of reproductive development remains unclear. The research objective was to study the relationships between endosperm cell number (ECN) during the lag phase (an indicator of potential KW) and final KW within the context of changing plant N dynamics in field-grown maize during the lag phase. Field experiments tested 3–4 N rates at different plant densities or N timing applications over a 3-year period (2017–2019). Kernels were removed from ears collected at 9, 10, 13, and/or 17 days after silking (DAS) and treated for ECN determination via tissue dissection, staining, enzymatic digestion, and digital microscopy. Plant growth rate, plant N uptake rate, ear growth rate, and ear N allocation rate during the lag phase were studied, as well as plant growth rate during the critical period and its relationship with kernel number per plant. Low N treatments consistently reduced ECN, thereby limiting KW during this early post-silking stage. Following data normalization, the majority of final KW variation was consistently explained by ECN across all experiments and relative DAS sampling times. Nitrogen rate effects on potential KW were not associated with plant growth rate per kernel during the critical period bracketing silking. ECN was highly correlated with ear N allocation rate during the lag phase, but not with plant N uptake rate during that period. Overall, these results show that higher N availability, independently of N timing and plant density, increased final KW by enhancing the sink capacity of individual kernels (at a wide range of kernel numbers per plant) via gains in ECN during lag-period development.

Carbon accumulation in kernels of low‐nitrogen maize is not limited by carbon availability but by an imbalance of carbon and nitrogen assimilates

AbstractBackground: Carbon (C) and nitrogen (N) assimilate availability and their ratios are crucial for maize grain production and N‐use efficiency.Aim: Our aim was to give a mechanistic understanding of yield formation regulated by assimilate C:N balance during both early ear development and rapid grain filling.Methods: Maize was grown under field conditions with 0, 200, and 300 kg N ha−1 (referred to as N0, N200, and N300, respectively). Ear growth, grain yield, and dynamics of total C and N accumulation in ear leaves, cobs, and developing kernels (apical and basal proportions separated from the longitudinally middle of ear) were investigated, as well as the non‐structural carbohydrates and free amino acids.Results: Compared to N‐sufficient plants, low‐N plants contained 16% to 70% less N and 8% to 50% less C in the developing kernels, causing 43% to 52% yield losses, which indicated that low‐N kernels received less amino acid per unit sugar from the maternal plants. This was supported by lower concentrations of the main N transport molecules (glutamine and asparagine) in ear leaves at silking and 21 days after silking (DAS) coupled with the larger amounts of C accumulated as starch under N deficient compared to adequate N supply. Nitrogen treatment did not influence the concentrations of total free amino acids and soluble protein in the cob, neither at silking nor 21 DAS, but it did influence cob free amino acid composition. Compared to the adequate N supply, low‐N plants contained 75% and 57% less glutamine and asparagine in apical kernels at silking, as well as 36% and 31% less in basal kernels. Free amino acid concentrations in both cob and kernels were less responsive to N treatments at 21 DAS than at silking, especially in the basal ear halves.Conclusion: Maize grain production under low‐N environment can be more attributed to the balance in assimilate composition, particularly the amino acid profile, than the C‐assimilate availability for ear growth and development.

Husk Leaf Senescence Characteristics of Spring Maize (Zea mays L.) Cultivated in Two Row Directions and Three Plant Spacings in Northeast China

Row direction and plant spacing influence crop senescence. An experiment was conducted to analyze the effect of row direction and plant spacing on the husk leaf senescence. Physiological indicators related to husk leaf senescence at days after silking (DAS) 12, 22, and 40 were investigated under two row directions (east to west and south to north, abbreviated as EW and SN, respectively) and three plant patterns (single rows spaced at 65 cm, 40 cm twin rows spaced at 90 cm between the paired rows of narrow–wide rows, and 40 cm twin rows spaced at 160 cm between the paired rows of narrow–wide rows, abbreviated as SR, WN1, and WN2, respectively). Row direction affects the chlorophyll content and dehydration rate according to our results. Superoxide dismutase activity at DAS 22, catalase (CAT) activity at DS, and abscisic acid (ABA) concentrations at DAS 12, 22, and 40 were significantly affected by plant spacing. The CAT activities of WN1 and WN2 were significantly higher than those of SR, and WN2 had a lower ABA concentration than WN1 and SR. Our results suggest that row direction from SN and plant spacing from WN1 and WN2 were the suitable conditions for delaying the senescence of husk leaves of maize in the experimental site.

Post-silking Phosphorus Recycling and Carbon Partitioning in Maize Under Low to High Phosphorus Inputs and Their Effects on Grain Yield.

Phosphorus (P) recycling and carbon partitioning are crucial determinants of P-use efficiency and grain yield in maize (Zea mays), while a full understanding of how differences in P availability/plant P status affect these two processes underlying yield formation remains elusive. Field experiments were conducted for 3 years to investigate the maize growth, P remobilization, and carbohydrate accumulation in leaves and developing ears of plants receiving low to high P inputs. In plots that 75 kg P2O5 ha-1 and above was applied (corresponding to 7.5 mg kg-1 and higher Olsen-P concentration in 0–20 cm soil layer), no additional response occurred in leaf area, ear growth, and grain yield. Despite the higher P uptake with P fertilization above this threshold, the lack of additional plant growth and yield resulted in decreased P-use efficiency. Regardless of P application rates, P remobilization to the ear during the first half of the grain filling phase preferentially came from the stem (50–76%) rather than from leaves (30–44%), and with a greater proportion in the inorganic P (Pi) form over organic P fractions. Leaf photosynthesis was maintained under P-limiting conditions due to the greater P investment in organic P pools than Pi. More and larger starch granules were found in the bundle sheath cells at silking or 21 days after silking (DAS) than under P-sufficient conditions. The amount of total carbohydrate production and export was lower in the P-deficient plants than the high-P plants, corresponding to decreased leaf size and lifespan. Nonetheless, similar or significantly greater starch levels were observed in both cob and kernels at silking and 21 DAS, implying there was an adequate carbohydrate supply to the developing ears under the diminished kernel sink of the P starvation. In addition, there was a strong correlation between the accumulation rates of carbon and remobilized P in the developing kernels, as well as between carbon and total P. Overall, the results indicated that diminished sink size and lower capacity of carbon deposition may limit yield formation in P-deficient maize, which in turn imposes a feedback regulation on reducing carbon and P remobilization from source leaves. An integrated framework considering post-silking P recycling and carbon partitioning in maize and their effects on grain yield has been proposed.

PLOUGH PAN IMPACTS MAIZE GRAIN YIELD, CARBON ASSIMILATION, AND NITROGEN UPTAKE IN THE CORN BELT OF NORTHEAST CHINA

This study aims to investigate the responses of carbon assimilation, grain yield, leaf stay-green rate, nitrogen uptake and distribution to soil compaction in the hard plow pan caused by repeated use of tractor-driven cultivator in Northeast China. The typical hybrid maize variety “Zhengdan 958” was exposed to two treatments of simulated plow pan (SP) and simulated subsoiling (SS, control) in pot experiments from 2012 to 2014. Compared with SS, SP significantly reduced net photosynthetic rate (Pn) during growth stage, leading to a decrease in dry matter accumulation (DMA) and grain yield (GY) in three consecutive experimental years. Leaf stay-green degrees (LSD), which showed a fast descending trend from 20 days after silking (DAS), significantly decreased in the later filling stage under SP treatment. The translocation efficiency of the stored N (TEN) in stalk and leaf to the grain during pre-silking was enhanced, whereas leaf and grain N concentration (LNC/GNC), together with N accumulation amounts at maturity were significantly reduced under SP treatment. Also, plough pan reduced the N distribution to the organs of stalk, leaf and grain. In conclusion, subsoiling is a possible way to delay leaf senescence and achieve higher DMA and GY, and increased grain N in the corn belt of Northeast China.

Global transcriptome analysis of the maize (Zea mays L.) inbred line 08LF during leaf senescence initiated by pollination-prevention.

In maize (Zea mays), leaf senescence acts as a nutrient recycling process involved in proteins, lipids, and nucleic acids degradation and transport to the developing sink. However, the molecular mechanisms of pre-maturation associated with pollination-prevention remain unclear in maize. To explore global gene expression changes during the onset and progression of senescence in maize, the inbred line 08LF, with severe early senescence caused by pollination prevention, was selected. Phenotypic observation showed that the onset of leaf senescence of 08LF plants occurred approximately 14 days after silking (DAS) by pollination prevention. Transcriptional profiling analysis of the leaf at six developmental stages during induced senescence revealed that a total of 5,432 differentially expressed genes (DEGs) were identified, including 2314 up-regulated genes and 1925 down-regulated genes. Functional annotation showed that the up-regulated genes were mainly enriched in multi-organism process and nitrogen compound transport, whereas down-regulated genes were involved in photosynthesis. Expression patterns and pathway enrichment analyses of early-senescence related genes indicated that these DEGs are involved in complex regulatory networks, especially in the jasmonic acid pathway. In addition, transcription factors from several families were detected, particularly the CO-like, NAC, ERF, GRAS, WRKY and ZF-HD families, suggesting that these transcription factors might play important roles in driving leaf senescence in maize as a result of pollination-prevention.

Temporal dynamics of post-silking nitrogen fluxes and their effects on grain yield in maize under low to high nitrogen inputs

Post-silking nitrogen (N) fluxes from vegetative tissues to developing kernels affect both N use efficiency (NUE) and grain yield in maize, while the impacts of various N applications at and especially after silking on temporal dynamics of post-silking N uptake and remobilization are poorly understood. Field experiments were conducted with N regimes ranging from low to high N levels. Nitrogen applications above optimal rates at and after silking neither increased late-season N uptake and leaf photosynthesis, nor reduced leaf N export during grain filling compared to the optimal N input, and thus significantly reduced the NUE. In most experiments, reductions in leaf N concentrations were observed around 15 days after silking (DAS). A15N labeling study revealed that remobilization of N taken up prior to silking from vegetative tissues during the entire grain-filling phase was 58%–60%, which contributed 53%–61% of the total grain N at maturity, and more than 60% of it was remobilized during the 0–30 DAS. N remobilization initially occurred preferentially from stems relative to leaves, while significant amounts of N were remobilized from leaves during late grain filling and deposited in the stem, particularly in high N treatments. No matter whether 15N was applied before or at silking, a greater proportion of 15N taken up was allocated to leaves under N deficient than under N sufficient conditions. At maturity, 70%–76% of the N taken up after silking was allocated to grain. Under N deficiency, direct N allocation to grains originating from post-silking uptake was 45%, 56%, 70% and 96% at 0–15, 15–30, 30–46 and 46–60 DAS, respectively, while these values were relatively lower and constant in N-sufficient plants (43%–50%). Overall, results indicated a strong developmental control over post-silking N fluxes with limited differences observed between N deficient and N sufficient maize, but no impact of high N applications to N-sufficient plants at or after silking.

Effects of Harvest Timing and Storage Conditions on Ear Quality of Waxy Corn

본 연구에서는 찰옥수수 재배 시 문제가 되는 수확 후 품질 변화를 명확히 구명하고자 찰옥수수 수확시기 및 저장조건에 따른 이삭 특성의 변화를 검토하여 최적의 수확시기와 저장방법을 제시하고자 수행하였다. 1. 암이삭은 출사 후 15일에서 25일 사이에 급격히 발달하였으며 알곡 무게도 암이삭의 발달과 같은 경향이었다. 출사 후 10일에 암이삭과 알곡의 무게는 각각 78.3 g, 1.13 g이었으며, 출사 후 25일에 224.9 g과 3.61 g으로 크게 증가하였다. 반면 출사 후 30일부터 크게 줄어들어 각각 10.6%와 6.1% 감소하였다. 2. 수확시기별 전분함량은 출사 후 25일에 73%를 나타냈고, 생육초기에 비해 약 10%의 증가를 보였다. 수확시기를 결정짓는 중요한 요인 중에 경도와 당도 만을 고려하였을 경우에는 출사 후 25일이 수확적기로 판단되었다. 3. 저장기간별 알곡 경도는 수확 직후 <TEX>$726g\;cm^{-2}$</TEX>에서 저장 28일에 <TEX>$1894g\;cm^{-2}$</TEX>로 증가하였다. 총당함량은 모든 저장 온도에서 감소하였으며, 감소폭은 온도에 따라 달랐으나 <TEX>$3^{\circ}C$</TEX> 및 <TEX>$10^{\circ}C$</TEX>보다 <TEX>$0^{\circ}C$</TEX> 저장에서 작았다. The consumption of waxy corn is steadily increasing in Korea. Waxy corn is harvested before it reaches full maturity and consumed immediately or follwing cold storage. Glutinous and sweet kernels are preferred due to their high palatability. The kernel properties can change rapidly following harvest, and, therefore, optimal conditions to maintain the kernel quality of corn should be identified. In addition, the timing of harvest of waxy corn ear should be also determined for optimal marketable corn production. From 10 days after silking (DAS) to25 DAS. fresh ear weight and single kernel weight rapidly increased from 78.3 g and 1.13 g, respectively, to 224.9 and 3.61 g, respectively. However, by 30 DAS both fresh and single kernel weight decreased by 10.6% and 6.1%, respectively. Kernel hardness significantly increased up to 25 DAS, and a further slight increase in kernel hardness was observed at 30 DAS. Total sugar content in kernel decreased from 12.5% at 10 DAS to 3.5% at 35 DAS, which was the result of the conversion of sugars to starch during ear development. Crude protein content in kernel did not vary significantly in comparison to kernel hardness. During storage of ear, kernel hardness increased from <TEX>$726g\;cm^{-2}$</TEX> at harvest to <TEX>$1894g\;cm^{-2}$</TEX> following 28 days of storage at a low temperature (<TEX>$0^{\circ}C$</TEX>). Kernel hardness increased 2.5 fold from 15 DAS to 30 DAS. Soluble protein level in kernel increased until 10 DAS, following which a slight decrease was observed. The soluble protein content decreased from 1.85% at 5 DAS to 1.45% at 35 DAS. Total sugar content in kernel decreased regardless of storage temperature; however, the rate of reduction was lower at <TEX>$0^{\circ}C$</TEX> than that observed following storage at <TEX>$4^{\circ}C$</TEX> and <TEX>$10^{\circ}C$</TEX>. The rate of reduction in kernel moisture content was also lower at <TEX>$0^{\circ}C$</TEX> than that observed at <TEX>$4^{\circ}C$</TEX> and <TEX>$10^{\circ}C$</TEX>.

Optimum leaf removal increases canopy apparent photosynthesis, 13C-photosynthate distribution and grain yield of maize crops grown at high density

Excising the upper leaves strata of maize crops cultivated at high stand densities could possibly optimize canopy architecture to achieve enhanced canopy apparent photosynthesis, a more favorable distribution of 13C-photosynthates to grain, and ultimately higher grain yields. To test this hypothesis, we conducted a leaf removal experiment in 2012 and 2013 growing seasons in Shandong, a province in the North China Plain. Jinhai5, a corn cultivar planted widely across China, was grown at a density of 105,000plantsha−1 until 3 days after silking (DAS), when plants were subjected to the removal of the uppermost and next leaves (S2), the four uppermost leaves (S4) or the six uppermost leaves (S6), with no leaf removal as control (S0). In the S2 treatment we found a longer duration of canopy apparent photosynthesis (CAP) and green leaf area index (LAI), higher total dry matter weight at physiological maturity as well as greater harvest index (HI) compared to the control, whereas those in the excessive leaf removal treatments (S4 and S6) declined substantially. In addition, modification of the number of leaves above the ear leaf led to different patterns of allocation of 13C-photosynthates. Excising two leaves promoted the distribution of 13C-photosynthates to grains, while that allocation decreased in the S4 and S6 treatments, which can be interpreted as a result of increased retention of 13C-photosynthates in the stem and ear bracts. Plants in S2 treatment displayed a yield advantage under high plant density due to higher kernel weight and more harvested ears. Relative to control, plants in the S2 treatment had 15% and 12% higher grain yields in 2012 and 2013, respectively. However, the removal of four or six leaves at the very early grain filling period, when kernel sink capacity is being established, caused a marked reduction in yields due to decreased both kernel number per plant and kernel weight, despite a relatively higher biomass availability per kernel. In conclusion, excising two leaves (the uppermost and next leaves) of maize crops cultivated at high plant density delayed leaf senescence, enhanced canopy photosynthesis and dry matter accumulation, leading to a higher post-silking source–sink ratio with its positive impact on kernel weight and higher grain yield.

Diurnal dynamics of maize leaf photosynthesis and carbohydrate concentrations in response to differential N availability

Diurnal changes of the carbohydrates in maize leaves reflect transitions in photosynthesis, carbohydrate metabolism and translocation rates, and can provide insights into the control of carbohydrate export from source leaves. Relationships of diurnal courses of leaf photosynthetic rates (A), nonstructural carbohydrates (NSC), and ear dry matter accumulation were investigated in field grown maize under different nitrogen (N) regimes. Nitrogen applications increased plant N uptake and grain yield as well as leaf area, chlorophyll content and soluble protein concentration. No differences in A among N treatments were observed during periods of low light intensities early and late in the day. The largest difference of A among N treatments appeared at 12:00PM at silking, and shifted to 15:00PM at 15 and 30 days after silking (DAS). In general, leaf glucose levels tended to be lower in N fertilized than unfertilized plants. At silking, the diurnal pattern of glucose was similar to that of A, reaching a peak between 9:00AM and 12:00PM. Clear diurnal pattern of leaf sucrose and starch concentrations were found at each sampling date, albeit less pronounced as development progressed from silking, to 15 and 30 DAS. Sucrose concentrations were lower in unfertilized than in N fertilized plants for most of the 24-h cycle at all three developmental stages. At silking and 15 DAS, starch concentrations were significantly greater in unfertilized compared to N fertilized plants. Ear leaf NSC dynamics observed here suggest that factors (i.e. source–sink dynamics) other than carbon assimilation limit maize yield under low N conditions.

Ovary Growth and Maize Kernel Set

Synchronous pollination improves maize (Zea mays L.) kernel set, but the physiological reasons behind this response are yet unclear. We registered ovary fresh weight evolution at three floret positions along the ear (base, middle and tip) of plants subjected to natural (NP) or synchronous (SP) pollination during two growing seasons. Synchronous pollination of ears bagged before silking was performed five days after silking (DAS). Ovary weight increased exponentially at all floret positions (P ≤ 0.01), but a lag in this trait was detected among those at the base and middle of SP ears. At each sampling date, florets along the ear differed (P < 0.01) in ovary weight, but differences were larger for NP than for SP plants. At pollination of each floret position, however, the range in ovary weight was smaller in NP ears (ca. 4 to 5 mg ovary−1) than in SP ears (4 to 9 mg ovary−1). Contrarily, just pollinated ovaries at the tip of the ear of NP plants (i.e. on ca. 4–5 DAS) experienced the high growth rate of those already pollinated at the base (ca. 0.7 mg d−1 for the former and ca. 3.7 mg d−1 for the latter). The range in ovary growth rate along the ear was drastically reduced under synchronous pollination on 5 DAS (ca. 0.55 mg d−1 for the base and ca. 0.47 mg d−1 for the tip). The larger the tip-to-base ratio in ovary growth rate, the larger the number of kernels set per plant (r2= 0.94; P = 0.03).

Influence ofAzospirilluminoculation and nitrogen supply on grain yield, and carbon‐ and nitrogen‐assimilating enzymes in maize

Abstract Nitrogen (N) supply increased yield, leaf % N at 10 days after silking (DAS) and at harvesting, the contents of ribulose‐1,5‐bisphosphate carboxylase (RUBISCO) and soluble protein, and the activities of phosphoenolpyruvate carboxylase (PEPC), and ferredoxin‐glutamate synthase (Fd‐GOGAT), but not of glutamine synthetase (GS) for six tropical maize (Zea mays L) cultivars. Compared to plants fertilized with 10 kg N/ha, plants inoculated with a mixture of Azospirillum sp. (strains Sp 82, Sp 242, and Sp Eng‐501) had increased grain % protein, and leaf % N at 10 DAS and at harvest, but not grain yield. Compared to plants fertilized with either 60 or 180 kg N/ha, Azospirillum‐inoculated plants yielded significantly less, and except for GS activity, which was not influenced by N supply, had lower values for leaf % N at 10 DAS and at harvest, for contents of soluble protein and RUBISCO, and for the activities of PEPC and Fd‐GOGAT. Yield was positively correlated to leaf % N both at 10 DAS and at harvest, ...

Nitrogen and density influences on silk emergence, endosperm development, and grain yield in maize ( Zea mays L.)

Grain yield in maize ( Zea mays L.) can be limited by supplies of carbon and/or nitrogen through reduced kernel number, due to slow growth of silks, preventing pollination, and through reduced kernel size due to fewer and/or smaller endosperm cells. A field experiment was conducted under irrigation to evaluate effects of changes in nitrogen and carbon supplies on development of yield components in plants having similar ear size at anthesis. Attention was given to silk extrusion of distal ovaries and to endosperm growth and development. Two levels of nitrogen of fertilizer at planting (0 and 167 kg N ha −1; n and N) and two plant densities (36 600 and 73 200 plants ha −1; d and D), imposed at initiation of silking, were used to manipulate nitrogen and carbon supplies. Although nitrogen stress reduced whole-plant nitrogen concentration ([N]) and area, phenology and aboveground dry mass per plant at silking were not affected. Spikelet number and initial mass of developing kernels were also similar among treatments. Nitrogen stress led to fewer kernels due mainly to reduced emergence of distal silks through less cell division; subsequent abortion was more density dependent. Unfertilized and high-density treatments resulted in less kernel mass per ear and smaller kernel [N]. Only density affected individual-kernel mass. In treatments where distal kernel mass varied, maximum endosperm length, 25 days after silking (DAS), was correlated with kernel volume and individual-kernel dry mass. The greater endosperm cell number in high-nitrogen treatments was accompanied by a smaller cell size. In most cases, maximum cell number in endosperm of proximal kernels was apparently not achieved by 25 DAS. Constant carbon/nitrogen ratio in apparent fluxes of substrates to the ear during the exponential phase of kernel growth was observed with all treatments. Crop parameters were strongly affected by density, and compensatory growth was evident in the grain yield of the low-density treatments. Harvest indices were similar.

Physiological Maturity and Vigor in Production of ‘Florida Staysweet’ Shrunken‐2 Sweet Corn Seed

Shrunken‐2 (sh‐2) sweet corn (Zea mays L.) exhibits relatively poor germination and seedling vigor. Early harvest is sometimes advocated for avoidance of seedborne fungi. Our objectives included studying the effect of maturity on seed vigor, defining physiological maturity, and optimizing vigor testing. Six crops of ‘Florida Stay sweet’ seed were produced in 1987 and 1988 and harvested 22 to 90 days after silking (DAS). Maximum kernel dry weight was obtained 43 to 47 DAS except for very late (mid‐June) plantings, which required 48 and 66 DAS. Decline in kernel moisture content was linear. Unreated seed, harvested 72 to 75 DAS from mid‐April plantings. produced an 80% stand in the field the following year. Harvest at maximum dry weight (43 to 47 DAS) produced final stands of 20% of lower. Delaying planting of the seed crop until mid‐May resulted in a decrease of maximum attainable field emergence to 50% in 1987 but not in 1988. Delaying planting until mid‐June lowered maximum attained field emergence to 30% in 1987 and 40% in 1988. laboratory germination test maxima preceded field emergence maxima by 12 to 26 d. Black layer formation preceded low vigor resulting from immaturity. The soil cold test, accelarated aging, and mean leachate conductance (ASA 610) were more highly correlated wiht final stand (median r = 0.87, 0.85, and ‐0.88, respectively) than was rolled‐towel germination (median r = 0.71). In conclusion, early harvest (45 to 60 DAS) resulted in seed with high germination and low vigor. Leaving the crop in the field as long as 80 to 90 DAS resulted in consistent production of relatively high vigor seed, as long as the crop was not planted very late (mid‐June).