Primary Tillers Research Articles

Studies on Heading Characteristics of Primary and Secondary Tillers in Rice(Oryza sativa L.). I. Influence of leaf cutting on heading characteristics of primary and secondary tillers.

同じ個体の主稈と分げつおよび分げつ相互間に幼穂発育及び出穂日の差が生ずるメカニズムを明らかにしようと試みた. イネ3品種, 農林1号, 日本晴, 農林8号を供試し, 水田土壌を詰めたa/2000ワグネルポットに直播土耕法によって野外で栽培を行った. 葉齢指数約70- 90の時期に伸長した葉を展開完了時に剪除し, 止葉の葉鞘から穂の先端が5 mm以上抽出したものを出穂と認め, その日付を止葉に記入した. 成熟期に抜き取り, 分げつ節位別に出穂日を記録整理した. 分げつの葉を展開完了時に剪除するとその分げつの出穂が遅れたが, それぞれの止葉葉位はほとんど変わらなかった. 出穂に対する分げつ葉剪除の影響はその分げつに著しく見られ, 葉を剪除しない分げつへの影響は少なかった. 剪葉による分げつの出穂遅延は早生品種で著しかった. 二次分げつと一次分げつの出穂日の関係は一次分げつと主稈の関係に類似しているが, 二次分げつ相互間の出穂日の異なることが分かった. 主稈とその二次分げつの出穂日の差は, 晩生品種より早生品種の方が大きかった. 剪葉処理により一, 二次分げつともに出穂が遅れたが, 二次分げつは一次分げつよりも更に遅れ, この傾向は早生品種で著しかった. また, 二次分げつの場合も剪葉処理の影響は剪葉処理を受けなかった分げつでは少なかった. 二次分げつの止葉葉位は一次分げつより増加する傾向を示したが, 剪葉処理の影響は認められなかった. 葉齢指数90の時期の分げつ別の幼穂長が長いほどそれの出穂日が早く,剪一次, 二次分げつの出穂の早晩は幼穂分化の早晩に基づいたものであると推察された.

Nitrate and ammonium nutrition in ryegrass: Changes in growth and chemical composition under hydroponic conditions

Abstract Nitrogen (N) is one of the most critical elements affecting grass seed yield. In soil and cropping conditions of Western Oregon, ammonium‐N may play an important role in the growth and development of ryegrass grown for seed. Our objectives were to determine the physiological and biochemical effects of ammonium and nitrate nutrition on ryegrass vegetative growth and subsequent expression of floral tillers, and changes in plant reduced‐N and carbohydrate composition. Plants were grown in hydroponics (active pH‐controlled) and fed nitrate and ammonium alone or in combination at 10 mM total N. The experiment was terminated at anthesis, which occurred at 68 days after planting (DAP). Changes in plant tiller number, height, dry weight, reduced‐N, and water‐soluble carbohydrates (WSC) were recorded. Vegetative growth rate of plants receiving lower ratios of nitrate/ammonium was up to twice those receiving total nitrate or 75/25 nitrate/ammonium. Total primary tiller number at 68 DAP (anthesis) was 30% g...

Morphological Studies on the Regularity of Shoots Development in Rice Plants. IV. Structural regularity in the growth types of tillers and their mother shoots.

It has already shown that the main shoots of two different growth types coexist even in a precisely cultured plot. These types are : (i) N type with n leaves, (ii) N-1 type with n-1 leaves ; these types may be identified by the pattern of the length of leaves and elongated internodes, that successively develop on the main stem. In this paper, I present a comparative analysis of the growth types of tillers and their mother shoots. 1) When the number of leaves on tiller (including propyll, expressed as NLT) is equal to that of leaves in the nodes above the mother node which subtend the tiller in question (expressed as NLM), the growth type of the tiller is identical to the mother shoot. There are generally two patterns in this case : both tiller and its mother shoot represent N-1 type or N-2 type. 2) When NLT is one less than NLM, the mother shoot represents N-1 type and the tiller represents N-2 type. However ; the lower primary tillers represent N-1 type on the main shoot of N type. 3) On the main shoot of N type, the upper primary tillers represent N-2 type. 4) It is considered that the growth types, as in case 1), are fundamental ones. The growth patterns in case 1), namely mother shoot replica-tiller growth pattern shall be designated as replicative tiller-growth.

Analysis on the Bending Response of Rice Tillers to the Upright Position.

We studied how the tiller axes move toward the upright positon using one of the Japonica type rice Sasanishiki (Oryza sativa L.). In the first trials, each plant was grown in a pot. The tiller shoots were sampled at the 11th leaf-stage and at 10 days after the panicle heading. The curvature of each pulvinus was measured and indicated as a degree angle. Maximum angle of 28.4 degrees was found in the pulvinus positon 0 located at the base of a lowest internode among elongated internodes in the tiller stem. Then, the curvature of each pulvinus at the positon -1, +1 and -2 was 14.0, 12.7 and 10.9 degree angle, respectively. The curvature of the lower primary tillers of a main stem was greater than those of the upper tillers. The number of pulvini curvatured was also greater in the lower ones. This shows that pulvini of the lower primary tillers were successively responding to gravity more than one time and restored their shoots to the upright position. Almost the same results are obtained in the field experiment where the seedlings were transplanted at the rate one per hill and 5 per hill in both the space of 30×30 cm and 30×15 cm, respectively. In conclusion, it was found that the pulvini at and around the position 0 plays an important role to allow tiller axis to move into the upright position.

Estimation of Potential Tiller Production and Site Usage During Tall Fescue Canopy Development

Tiller appearance in tall fescue (Festuca arundinacea Schreb.) occurs in an orderly, predictable manner with the potential for a high degree of synchronization among tillers on a given plant. Estimates of potential cumulative tiller production (Tmax) are made for synchronous (Tmax 1x =2 Lx+1 -1, where Lx is the axil number of the youngest leaf on the main stem which bears an emerged tiller) and non-synchronous (Tmax 1 =2 L.NLAT -1, where L is the number of leaves on the main stem and NLAT the number of leaves above the youngest primary tiller at its appearance) conditions

Allocation of Photoassimilate by Main Shoots and Nonsurviving Tillers in Barley

Field‐grown barley (Hordeum vulgare L.) plants produce many tillers that do not survive to bear grain, especially under water‐stressed conditions. Such nonsurviving tillers have traditionally been regarded as wasteful of plant resources. To test this premise, a greenhouse study was conducted to evaluate the contribution of nonsurviving tillers to the C economy of a barley plant. The study quantified the reciprocal transfer of photoassimilate between the main shoot and nonsurviving tillers during the tillering phase of development under well‐watered and water‐deficient (stressed) conditions. Main shoots and two primary tillers (T1 and T2) were labeled by exposure to 14CO2. Radiocarbon export and retention by the labeled shoots were monitored at maturity. The radioactivity partitioning data were combined with changes in the dry mass of labeled shoots over the study period to estimate dry matter exchange between shoots. For nonstressed plants, 33% of the initially fixed radioactivity was lost prior to maturity, probably due to respiration. The percentage of radioactivity lost was higher under conditions of water stress. Nonsurviving tillers retained only 18% of their initially fixed radioactivity at maturity, regardless of watering regime. Under both well‐watered and later‐imposed water stress conditions, the calculated dry matter exchange between shoots showed that nonsurviving T1 tillers returned twice as much dry matter to the main shoot as was provided to them by the main shoot. Tiller T2 also exported more than it imported but less than T1. When water stress was imposed early, tillers allocated slightly less assimilate to the main shoot than they received. We conclude that nonsurviving tillers may contribute more dry matter to surviving shoots than has previously been recognized.

The Effect of Moisture Stress on the Yield and Yield Components of Several Wheat Cultivars and their F1Hybrids

The effect of moisture stress on yield and yield components of five winter wheats and their F1, hybrids were investigated by maintaining the material at 80 % and 50 % field capacity respectively. Yield, kernel number, and kernel mass of the secondary tillers were affected severely by moisture stress. Kernel number and kernel mass of both primary and secondary tillers were correlated to yield significantly (r > 0.75) at both moisture levels. The rankings of the characters most significantly correlated to yield remained much the same at moisture levels despite a significant cultivar X moisture level interaction.

Reproductive Morphology of Five Kentucky Bluegrass Cultivars

AbstractA problem associated with plant growth retardant applications in Kentucky bluegrass, Poa pratensis L., is the application window for effective seedhead and vegetative growth suppression. Theoretically, the optimum timing for growth retardant applications would be just prior to the peak growth period in spring and before the inflorescence becomes visible above the youngest leaf. The objective of this field study was to determine if time of primordia initiation as an indicator of inflorescence development is consistent in selected Kentucky bluegrass cultivars in successive growing seasons. Initiation of inflorescence primordia was determined by randomly sampling and dissecting primary tillers of each cultivar during the late winter‐early spring and observing under a dissecting microscope. Our research showed that dates marking a transition from vegetative toward a predominately reproductive growth habit varied significantly among Kentucky bluegrass cultivars in both years. Also, one of the six cultivars, Kenblue “low maintenance” was not in a similar reproductive condition on several observation dates occuring in the same calendar week of 1986 compared with 1987. These results, based on our 2‐yr study, show that reproductive variation exists among Kentucky bluegrass cultivars, and that some cultivars may not develop inflorescences annually within calendar date application windows for growth retardants with much predictability.

Analysis of the Tillering Behavior of the Rice Plant in the Paddy Field. I. The tillering pattern under two nitrogen levels of basal dressing.

宮城県の慣行栽培法を基に, 水田で基肥窒素量の異なる2区(N 3.0区:窒素成分で3.0g m-2, N 4.5区:4.5g m-2)を設定し, 標準的な管理下での水稲品種ササニシキの生長を調べ, 茎数増加様式を解析した. 1次分げつは2号分げつ(T2:以降n号分げつをTnと略記)からT7までが出現し, 特にT3からT6までの出現率が高かった. 2次分げつはT2からT5までの1次分げつから出現し, 特にT3, T4からの2次分げつが多かった. 茎数増加はN4.5区で早く, 最高茎数も多かったが, 有効茎数は両区でほぼ同じであった. 主茎葉齢はN 4.5区の方が早く進み, 特に茎数急増期には両区間の差は0.5となった. 主茎葉齢をタイムスケールとして実測の茎数増加曲線を描くと, 茎数急増期に両区とも重なる. これは, この時期に主茎葉齢の進み方がN 4.5区で速かったために, 茎数増加もN 4.5区で速かったことを示す. 一方, 各分げつが同伸葉理論通りに出現したと仮定したときの茎数増加曲線を, 分げつ位ごとの出現率から描くと, N4.5区の方が茎数増加が速かった. このことについては, T3の相対葉齢差(主茎と分げつの葉齢の進み方の差)がN 3.0区の方が大きく, N 3.0区でT3からの2次分げつがN 4.5区より早く出現したため, 両区の主茎葉齢をタイムスケールとした実測値の茎数増加曲線が重なったと考察した. また, 「有効分げつ決定期」が, 水稲の生育を解析する上であまり意味を持たないことを示した. さらに, 稚苗移植栽培においてもT2が出現・生長したことに関して, T2の分化・発達をも含めて考察した.

Barley Tiller Response to Plant Density and Ethephon

AbstractEthephon ([2‐chloroethyl] phosphonic acid), typically increases barley (Hordeum vulgare L.) spikes per square meter by increasing the frequency of late emerging green tillers, resulting in uneven crop maturity. This study was conducted to evaluate barley tiller grain yield and malting quality response to plant density and ethephon, with special reference to late‐emerging green tillers. Field studies were conducted at Powell, WY between 1987 and 1989 on a Garland clay loam (fine, mixed, mesic Typic Haplargid). Target plant densities of 150 and 300 plants m−2 were established. Ethephon was applied at the Zadoks growth stages (ZGS) of 13, 32, or 39, and one treatment was split‐applied at ZGS 32 and 39. Early emerging primary tillers (Tl, T2, and T3) and the main shoot contributed 86% of the total grain yield at high plant density vs. 73% at low plant density. In general, increasing plant density resulted in progressively greater differences for kernel plumpness and kernels per spike on the MS, Tl, T2, and T3. Ethephon applied at ZGS 39 reduced plant height 6 to 15 cm depending on year. Lodging was reduced by ethephon application, although the lodging level was low in every year of the study. Ethephon did not affect grain yield or protein content, but it often reduced volume mass and kernel plumpness compared to the untreated control. Regardless of ethephon treatment, kernels on late emerging tillers were of lower mass, volume mass, and plumpness than kernels on early emerging tillers. Ethephon applied at ZGS 39 increased the number of late emerging green tillers by 225 spikes m−2 compared with the control. These late emerging green tillers contributed 8% to the total grain yield but produced grain of substandard malting quality.

Flag Leaf Number Determination of Secondary and Tertiary Tillers and Heading Characteristics of Rice Plants.

When the number of leaves on the main culm is known, the number of leaves on secondary to quarternary tillers can be determined based on the following growth characteristics and procedures, even if the lower leaves are no longer on the stem. Growth characteristics : a) The leaves are located on stem alternately. b) Left tip outside and right tip outside sheath wrapping also appear alternately. c) The tillers which emerged from the node of left (right) tip outside of sheath wrapping have left (right) tip outside sheath wrapping at the first leaf. Procedures : 1) Mark the leaves of the main culm and record heading date of all tillers in a plant on the flag leaf. 2) Dig out the plant at maturity and separate it into its primary tiller groups. 3) Arrange odd-numbered primary tillers on the left side of the main culm and even-numbered tillers on the right side, in order of emergence, from outside to inside. 4) If the main culm has an odd-numbered flag leaf with right tip outside sheath wrapping, or an even-numbered flag leaf with left tip outside sheath wrapping, the first leaf of primary tillers appears on the front side of the primary tillers. 5) The first tertiary tiller points toward the main culm and in the same way, the first quarternary tiller points toward its parental primary tiller. Investigation findings : 1) Number of leaves on secondary and tertiary tillers of Moritawase and Norin 1 increased over the number of leaves of primary and secondary tillers, respectively. 2) Main culm of Moritawase heads first, whereas, in Norin 1, primary tillers head first. 3) Heading date of secondary tillers tend to be delayed when the number of leaves increased over that of the primary tillers.

Difference of Photosynthetic Rates among the Leaves at the Equivalent Positions on the Main Stem and Its Tillers in Rice Plants.

圃場およびポットで生育した水稲穂数型品種日本晴を用いて, 株を構成する各茎に着生する同一葉位の葉身の光合成速度の相違を主茎と分げつ茎の同伸葉の間で比較した. 展開完了直後では, 移植時に発生した5号分げつ茎を除いて, 主茎の葉身と各1次分げつ茎の主茎と同伸葉の葉身との光合成速度の間にほとんど相違は認められなかった. 葉身の老化がすすむと, 主茎の葉身の光合成速度に比べて, その葉身と同伸葉の1次分げつ茎の葉身の光合成速度は小さく, その程度は上位の分げつ茎ほど著しかった. 主茎に比べて分げつ茎の葉身の光合成速度が小さくなったことには, 拡散伝導度, クロロフィル含量およびRuBPCase 含量の低下が関係していた. これらの結果から, 展開完了後の老化に伴う光合成速度の低下程度は主茎に比べて分げつ茎の葉身で大きく, このことが圃場条件下で同一葉位の葉身の光合成速度に違いをもたらす要因の1つであることがわかった. 分げつ性の異なる品種の間で光合成速度の相違を検討した結果, 長稈穂重型の台農67号は日本晴に比べて, 老化に伴う主茎の葉身の光合成速度に対する各1次分げつ茎の主茎と同伸葉の葉身の光合成速度の低下程度は小さく, 茎間の光合成速度の相違の小さいことが明らかとなった.

Relationship between Main Stem and Primary Tillers in the Position of Lowest Elongated Internode of Deepwater Rice.

浮稲性(深水条件下における節間伸長性)は, 伸長最低節間位置(PLEI)に支配されているがこのPLEIは, 茎の発育相の第2次伸長節間形成相への転換までの遅速を意味する. 本研究は浮稲品種Habiganj Aman VIIIを用いて, 分げつ茎の第2次伸長節間形成相への転換は, 主茎と独立して起こるのか否かを明らかにするために行った. 主茎と分げつの相転換の遅速を表わす指標として, 未伸長節間数と第1次伸長節間数の和である非伸長節間数(NNEI)を設定した. 主茎の第1節から第15節までの着生節位の異なる1次分げつを対象に, 種々の時期に, 種々の程度に主茎切除処理を行なった結果, 主茎と分げつの相転換の間に, 密接な関係が認められ低節位の分げつほど, NNEIが大きな値をとる傾向を示した. 伸長茎の高節位分げつでは, NNEIは0個となった. しかし, 高節位の分げつでも, いったん休眠すると, 休眠解除までの期間が長いほどNNEIの増大が認められ, 分げつの第2次伸長節間形成相への転換は主茎の相転換によって支配されるが, 分げつのNNEIの決定には分げつ茎自体の発育ステージも関与していることが明らかにされた. ジベレリン処理でNNEIが減少することが認められた. 主茎と分げつとの関係, 主茎のPLEIの性質, 分げつのNNEIの意義について考察した.

Prediction of F3 row performance from F2 individual plant data in oats

Parameters estimated from a Gardner-Eberhart analysis of the F2 generation of a six-parent diallel in oats (Avena sativa L.) were used to compare methods for predicting the performance of F3 row plots. The prediction methods were: (1) individual F2 plant performance (F2I), (2) parent average plus F2 plot deviations (PF2), (3) parent average plus weighted F2 plot deviations (PF2P), (4) best linear unbiased prediction (BLUP) of parent average plus F2 plot deviations (BPF2), and (5) BLUP plus weighted F2 deviations (BF2). The F2 single-plant traits used for prediction were biological yield to predict F3 biological yield, whole plant and primary tiller grain yield for prediction of F3 grain yield, and whole plant and primary tiller harvest index (HI) to predict F3 HI. Prediction methods were evaluated by correlations between predicted and observed F3 performance. Prediction methods and traits for which correlations were greater than for F2I included: BF2 for biological yield, PF2, PF2P and BF2 for whole plant grain yield, PF2, BPF2, and BF2 for primary tiller grain yield. None had a correlation significantly greater than F2I for either measure of HI, where heritability was large. PF2 is the recommended method for traits with low heritability because of its simplicity and because it had the largest or nearly the largest correlation for each of the yield traits. F2I is the recommended method for traits with larger heritability.

Character Expression of the Semidwarfing Gene sd-1 in Rice (Oryza sativa L.). II. Appearance and development of tillers.

イネ多収品種の育成に大きく貢献してきた半矮性遺伝子sd-1の形質発現について, 日本型長稈品種農林29号, これにsd-1を導入した準同質遺伝子系統SC-TN 1およびsd-1の供与親であるインド型品種台中在来1号を用いて, 分げつの出現率および出現後の発育を比較した. 総葉数では, 3品種間に差がほとんどなかった. 分げつ出現率においては, 上位節の1次分げつおよび2次分げつで多窒素, 少窒素両条件に共通して, 台中在来1号が日本型2品種より大きかった. 日本型2品種間では, 少窒素下での上位節1次分げつ, 少窒素, 多窒素両条件を通じて2次分げつでSC-TN 1が農林29号より大きかった. このことから, 半矮性遺伝子sd-1は発育しにくい分げつの出現率を高める効果をもつと考えられた. 1次分げつの葉齢が1に達する時期の主茎葉齢は, 半矮性2品種が農林29号より若く, 台中在来1号はSC-TN 1より若い傾向がみられ, 少窒素条件下ならびに上位節分げつで特にその傾向が強かった, 出現後の葉齢増加速度は上位節の分げつにおいてSC-TN 1が農林29号よりも大きい傾向がみられたが, 品種間差異は明らかでなかった. 半矮性品種は母茎に対する相対葉齢が大きいことが認められた. このことは, 分げつの葉齢が1に達する時期の早いことによると考えられた.

Characteristics Relating Young Panicle Development and Heading of Closely Related Calrose Rice Genotypes.

Seven near-isogenic lines which were derived from rice cultivar were sown on June 8, 1985, and transplanted on June 25 at the fourth leaf stage in rice facility of the University of California, Davis. Each plant was marked by a felt pen on every even leaf of main culm to count the number of flag leaf. At leaf number index (LNI) 85 to 95, young panicle length was investigated. At heading stage, all panicles of about 50 plants per genotype were dated their heading date on their flag leaf, and at harvest each panicle was recorded its node location from which it emerged. A high correlation coefficient between LNI and logarithm of young panicle length was obtained in all genotypes, so it was considered that LNI was an excellent index to estimate young panicle developmental stage, when the total number of leaves of genotype was known already. In ES-201, panicle of main culm and tillers headed nearly the same time, whereas in the other 6 genotypes, heading date of main culm was later than that of the first headed tiller panicle. Especially main culm heading of S-201 was delayed more than 2 weeks than that of the first headed tiller panicle. Primary tiller which emerged from 6th node on main culm headed at first in the genotype excluding ES-201. As the 6 genotypes other than ES-201 showed the most advanced young panicles in their 6th node at LNI 85 to 95, above-mentioned behavior seems to bc a characteristic of these genotypes. Heading date of main culm in M- 302 and S- 201 was prolonged by low temperature compared to that of Calrose 76 and M7, respectively. This might be based on their tolerance to low temperature for the uppermost internode elongation. An early heading genotypes showed less number of flag leaf (M-101) or higher leaf emergence rate (ES-201) than that of later ones (M7 and S-201), respectively.

Translocation of nitrogen absorbed by the roots of specific tiller in rice plant.

In order to determine the tiller-to-tiller translocation of nitrogen in rice plants, changes in the percentage content and percentage distribution of absorbed 15 in each tiller and the main stem were investigated by the 15 treatment of the roots of fourth tiller (the fourth tiller in primary tiller was expressed as T4) that emerged from the fourth node of the main stem. The quantity of translocated 15 in tillers after absorption by the roots of T4 was arranged in genealogical order by the site of its distribution as follows: daughter tillers of T4 (T41, T44; secondary tillers) > T4 itself > > mother stem (main stem) > younger sister tillers (T5, T7; primary tillers) that emerged from the upper nodes of the T4 emerging node > elder daughter tillers that emerged from elder sister tiller (niece tiller; T31, T34) > elder sister tiller (T3) that emerged from the lower node of the T4 emerging node. It was made clear that the nitrogen-distribution from T4 to T3 that emerged from lower node of the T4 emerging node and to secondary tillers on T3 was extremely low. It was therefore, presumed that a remarkably small quantity of nitrogen was translocated from tillers that emerged from the upper nodes to tillers that emerged from the lower nodes of the stem in rice plant.

Difference in grain productivity of tillers among main stem nodes in rice plant. I. Effects of the number and position of tillering nodes on grain productivity.

ポットに1株1本立で直播した水稲主稈の第2節から第11節の範囲で特定の節位に分げつを1節あるいは2, 3, 5節組み合わせて残存させ, それ以外の節から出現する1次分げつを毎日除去して生育させ, 主稈の節位別分げつの子実生産力に及ぼす1次分げつ出現節数および節位の影響について検討した。1) 1次分げつ残存節数が少なく, 残存節位が上位の区ほど主稈葉数が多くなり, 主稈穂重は優った。2) 1次分げつの出現日および出現率は第6節までは分げつ残存節数および残存節位の影響を受けなかったが, それ以上の節位では下位節に出現節数の多い区ほど出現日が遅れ, 出現率も低下する傾向がみられた。また, 下位節の1次分げつほど出現から出穂まで日数あるいは止葉葉数は多くなったが, 穂重との間に明瞭な関係は認められなかった。3) 主稈の節位別分げつ穂重 (子実生産力) は, 一般に穂数の差により下位節ほど優るが, ある特定節位の分げつの子実生産力については1次分げつの出現数の多少, および他の1次分げつの出現節位によって著しく変化するものと考えられた。すなわち, 主稈第n節分げつの子実生産力は他節からの分げつ出現数が少なく, さらに分げつ出現節数が同一の場合には, 第n節位より上位に他節の分げつが位置するほどその子実生産力は大となった。4) 主稈の中, 上位節にのみ1～2節とごく少数の1次分げつが出現すると, 高次分げつの割合が高くなり株当り穂数は対照 (無処理) 区に比べて減少した。しかし, 平均1穂重は主稈および各次位別分げつとも対照区を上回り, 株当り穂重の低下はわら重に比べて小さくなり, その結果穂重/わら重比は向上した。

Modification of seedling growth of triticale and barley by seed-applied chlormequat

Seeds of triticale and barley were soaked in a range of dilutions of chlormequat. Germination was monitored and the growth of seedlings assessed for up to five weeks. Some concentrations of chlormequat produced seedlings with significantly more leaves on the main stem, more primary tillers, a greater leaf lamina area and a higher shoot dry weight. It is argued that these modifications could lead to an increased yield potential.

Canopy Light and Tiller Mortality in Spring Barley

Mortality of tillers in barley (Hordeum vulgare L.) is an important developmental event affecting spike number and yield potential of the crop. It has traditionally been thought that increased shading of young tillers by the developing canopy initiates the premature senescence of tillers. A series of field experiments were conducted in 1982, 1983, and 1984 at St. Paul, MN on a Waukegan silt loam soil (fine‐silty over sandy or sandy skeletal, mixed, Typic Hapludoll) to test this hypothesis. Degree of shading within the crop canopy was measured in relation to the position of tiller leaves during the vegetative phase of development for three genotypes. The decline in rate of leaf appearance on nonsurviving primary tillers, monitored as an early indicator of tiller senescence, was noted within 3 to 4 wk after crop emergence and before appreciable shading of tillers occurred. This indicates that tiller mortality was not initiated by lack of light. However, after main stem elongation began, tillers soon became heavily shaded suggesting the possibility that shading plays an auxiliary role in the senescence of barley tillers. We discuss the possibility that changes in light quality early in the growing season may be important for initiating the senescence of tillers.