Tiller Mortality Research Articles

Growth and carbon allocation of Agropyron desertorum following autumn defoliation.

Growth and carbon allocation of a cool season tussock grass, Agropyron desertorum, following defoliation of newly initiated tillers in the autumn of 1988 and 1989 were investigated. Tiller density and mortality, reproductive shoot density, root density, biomass, individual tiller weight, carbon allocation, and soil water depletion were used to evaluate the response of A. desertorum to autumn grazing. Tiller recruitment was lower in the autumn-defoliated treatment in both years compared with the control because of the cessation of tiller development following autumn defoliation. Autumn defoliation also significantly reduced the movement of 13C to the roots in 1988 but not in 1989. Soils were cooler and drier in 1989. Other plant growth measurements and soil water depletion rates were not different between treatments. Autumn defoliation in 1988 did not influence tiller recruitment in the following autumn. Two consecutive years of autumn defoliation did not affect tiller overwinter mortality or peak standing crop in 1990.

Flood tolerance of rice grown under intermediate deepwater conditions (15–50 cm) as affected by phosphorus fertilization

SUMMARYThe effect of phosphorus fertilizer on the performance of an improved semi-dwarf (100 cm), long duration (170 days), photosensitive rice variety CR 1016, grown under conditions of intermediate deepwater (15–50 cm) and simulated flash flooding (80 cm), was investigated at Cuttack, India in 1985, 1987 and 1988. Growth and yield of rice subjected to overhead flash flooding (complete submergence) at the vegetative stage for 10 days was decreased significantly compared with partial submergence in water of intermediate depth. The adverse effect of complete submergence was due to greater tiller mortality and lower number and/or weight of panicles at maturity. Rice plants fertilized with P tolerated flooding better and produced significantly higher grain yields than when no P was applied. There was no significant effect of P application on the crop grown under natural unsubmerged conditions, except when it was raised in the same plots as the previous year and may therefore have benefited from residual effects. Therefore, application of 8.7–17.5 kg P/ha along with 60 kg N and 16.7 kg K/ha at sowing was essential to overcome the deleterious effects of submergence on rice grown under waterlogged conditions.

Performance of oligoculm spring wheats grown in a semiarid environment

Oligoculm and low-tillering spring wheat (Triticum aestivum L.) genotypes were compared to free-tillering cultivars in each of 3 yr. On average, oligoculms yielded 20–40 and 4–27% less than the free- and low-tillering genotype groups, respectively. Averaged over years, oligoculms produced 44% fewer tillers and headed 3 d earlier than the free-tillering genotypes. These two groups did not differ consistently in tiller mortality across years. Key words: Triticum aestivum L., restricted tillering, grain yield, wheat (spring)

Preanthesis Tiller Mortality in Spring Wheat

A primary determinant of yield in wheat (Triticum aestivum L.) is the number of spike‐bearing tillers per unit area. Many tillers that emerge do not survive to produce spikes. This study was conducted to determine the point in development when tillers begin to senesce and to examine how premature senescence is affected by water deficits and plant population. Cultivars Edwall and Waverly were planted in a 2‐yr field study at two plant densities (168 and 84 kg ha−1 in 15‐ and 30‐cm rows, respectively) and with both irrigated and nonirrigated treatments. The Haun stage of leaf development was monitored weekly on five plants per plot. Tiller mortality was monitored from tiller emergence until maturity. For tillers destined to die prematurely, a reduced rate of leaf emergence and development was evident immediately after tiller emergence. The majority of tillers senesceduring main stem extension, while almost no tillers were lost during grain filling. The maximum Haun stage reached by senescing tillers was normally ≤3 for all tillers excepthe coleoptile (TO) tiller. For this tiller, the maximum Haun stage was ≤4. Premature tiller senescence occurred in both irrigated and nonirrigated plots and was greatest at the higher plant density. Water deficits increased the number of tillers that died but did not affect the stage at which senescence occurred. Tillers that emerged late during plant development were most likely to senesce prematurely.

Influence of drought and flowering on growth and water relations of perennial ryegrass populations

SummarySpring‐sown (vegetative) and autumn‐sown (flowering) swards of Lolium perenne cvs Melle, Aurora and their hybrid growing in 0.9 m deep bins of soil in the glasshouse were compared, a) as drought progressed from June to August 1986, and b) after cutting, fertilising and re‐watering.During drought, vegetative plants produced more herbage, had initially higher leaf extension rates, had longer and wider leaves, maintained more tillers, had lower mortality, adjusted osmotic potential more effectively and had stomata less sensitive to stress than did flowering plants. On re‐watering, previously stressed flowering plants regrew more slowly than the irrigated controls, whereas previously stressed vegetative plants regrew more rapidly than the controls.Aurora was the most drought‐resistant population, mainly because of low tiller death rates. The hybrid tended to have the lowest leaf water potentials and conductances and grew poorly during drought. Possible underlying physiological mechanisms are discussed.

The influence of crown rust (Puccinia coronata) on tiller production and survival of perennial ryegrass (Lolium perenne) plants in simulated swards

AbstractPopulations of Aberystwyth S23 and S24 ryegrass tillers were individually labelled and harvested at intervals to follow their life histories and productivity in response to the effect of infection with crown rust at two levels of nitrogen fertilization.The number of tillers in a population was reduced as a result of infection with crown rust. Increased rates of tiller death due to the pathogen occurred throughout the population age‐range and were most pronounced in the youngest tillers. Population changes were evident following infection and continued to be apparent in the following spring. The disease caused alterations in sward age structure, leading both to a higher proportion of older tillers in the more rust‐damaged treatments and to a decrease in the weight of the herbage produced. It is concluded that rust infection of a sward may lead to changes in population structure with long‐term yield effects, in addition to the immediate direct yield reductions commonly reported. The significance of these results to the ecological and agronomic balance of grassland is discussed.

Effects of Green-stage Grazing on Rainfed Barley in Northern Syria. I. Tiller Production and Other Agronomic Characters

SUMMARYEffects of simulated and actual grazing at the tillering stage on tiller production and other agronomic characters were studied over a number of seasons at two sites in northern Syria with two local barley landraces. In general, grazing encouraged tiller production but reduced head number per unit area because of a higher tiller mortality or infertility. Seed number per head and seed weight were not affected by grazing except in one season. Grazing delayed heading and maturity and reduced plant height. Simulated and actual grazing produced similar effects on the different characters investigated.

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.

TILLERING PATTERNS OF SPRING WHEAT GENOTYPES GROWN IN A SEMIARID ENVIRONMENT

Replicated field trials were conducted for 2 yr at two locations in a semiarid short-season environment to compare the tillering patterns of three spring wheat genotypes. Neepawa (high tillering), Siete Cerros (low tillering) and M1417 (oligoculm) were evaluated at five seeding rates (40–640 seeds m−2). Genotypes, locations, years, and seeding rates had significant effects on tiller appearance rate (TAR), maximum tiller number (TMAX), days to TMAX (DTMAX), tiller senescence rate (TSR), tiller mortality (TM) and number of spikes (SN). Genotype × seeding rate and/or year × genotype interactions were detected for TAR, TMAX, TSR, TM and SN. For Siete Cerros, TAR and TSR were constant proportions of those for Neepawa over the four lowest seeding rates. In contrast, TAR and TSR for M1417 increased in proportion to those for Neepawa with increased seeding rate. Similar relationships were observed for TMAX and SN in 1984, but not in 1985. Siete Cerros had higher TM than Neepawa and M1417, especially at low seeding rates. Changes in genotype rank from one seeding rate to another were observed for TAR, TMAX, TSR, and TM, but not for SN. Changes in rank suggest that different tillering patterns may be better suited to different growing environments.Key words: Wheat (spring), tillering patterns, seeding rates

Quantitative Translocation of Photoassimilates from Nonsurviving Tillers in Barley

Many tillers produced in barley (Hordeum vulgure L.) crop communities senesce without bearing grain. To better understand the physiological and agronomic implications of this tiller mortality, partitioning of photoassimilate by nonsurviving tillers was monitored for field‐grown plants at St. Paul, MN on a Waukegan silt loam soil (fine‐silty over sandy or sandy‐skeletal, mixed Typic Hapludoll). Primary tillers formed in the axils of the first and second main shoot leaves (designated T1 and T2, respectively) were labeled with 14C02 on four occasions and the labeled plants sampled at 7‐ to 10‐day intervals. Some labeled tillers were immediately girdled using steam to restrict photoassimilate export and permit estimation of radioactivity losses due to tiller respiration. Knowing the respiratory losses as well as the quantity of radioactivity remaining in a labeled tiller following a given translocation period, the proportional 14C export from the tiller was calculated. These estimates were coupled with changes in tiller dry mass to calculate the photoassimilate dry matter transferred from a tiller between labeling dates, which were summed to give the cumulative dry matter translocated during the entire period of labeling. Nonsurviving T1 tillers translocated 45% of their photoassimilate to other plant parts, which equated to approximately 150 mg of dry matter. These tillers retained 17% and respired 38% of their fixed radioactivity. Nonsurviving T2 tillers exported 57% (approximately 40 mg), retained 20%, and respired 23%. Most photoassimilate exported from nonsurviving tillers was recovered in the main shoot stem, with lesser amounts in the main shoot spike and leaves. Nonsurviving primary tillers may contribute substantial amounts of dry matter for growth of other plant parts, particularly the main shoot. Thus, initiation of such tillers may not be inherently wasteful of plant photoassimilates.

AN EVALUATION OF COMMON SPRING WHEAT GERMPLASM FOR TILLERING

A diverse collection of spring wheat (Triticum aestivum L.) germplasm was evaluated for tillering capacity, spikes m−2, and tiller mortality under both space-planted and solid-seeded conditions. Large genotypic differences were observed for these tillering traits over a 3-yr period. Grain yield did not appear to be associated with tillering capacity or mortality.Key words: Wheat (spring) Triticum aestivum L., germplasm, tillering capacity, tiller mortality, grain yield

Annual replacement of the tillers of Agropyron desertorum following grazing.

The annual replacement of tillers of Agropyron desertorum (Fisch. ex Link) Schult., a grazing-tolerant, Eurasian tussock grass, was examined in the field following cattle grazing. Heavy grazing before internode (culm) elongation seldom affected tiller replacement. Heavy grazing during or after internode elongation, which elevates apical meristems, increased overwinter mortality of fall-produced tillers and reduced the number and heights of these replacement tillers. Unexpectedly, tussocks grazed twice within the spring growing season tended to have lower overwinter tiller mortality, greater tiller replacement, and larger replacement tillers than tussocks grazed only once in late spring. These responses of twice-grazed tussocks, however, were still less than those of ungrazed tussocks or tussocks grazed moderately in early spring. The presence of ungrazed tillers on partially grazed tussoks did not increase the replacement of associated grazed tillers relative to tillers on uniformly grazed plants. This result indicates that resource sharing among tillers, if present, is short-lived or ecologically unimportant in this species. Although A. desertorum is considered grazing-tolerant, tiller replacement on heavily grazed tussocks, particularly those grazed during or after internode elongation when apical meristems were removed, was usually inadequate for tussock maintenance. These observations at the tiller (ramet) level of organization in individual tussocks (genet) may explain the often noted reduction in stand (population) longevity with consistent heavy grazing.

Evaluation of chromosome substitution lines of wheat (Triticum aestivum L.) for freezing injury suffered during the stem elongation stage of development

Eight series of chromosome substitution lines in the Chinese Spring background were subjected to natural freezing stresses during stem elongation. Two of the series were also subjected to an artificial freezing stress at stem elongation. In the series involving the winter cultivar Cheyenne, a major genetic component of the resistance to freezing injury during stem elongation was located in chromosome 5D. Among the seven other series screened in the field, each of the 21 substituted chromosomes was significant in at least one series. Chromosomes most frequently implicated were 3A, 6A, 2D, 4D and 5D. The genetic control of observed tiller mortality following a freezing stress was therefore considered genetically complex.

Effects of Shading on Winter Wheat Yield, Spike Characteristics, and Carbohydrate Allocation1

Light intensity has variable effects on plant morphology, carbohydrate allocation, and yield. This study tested whether shading ‘Vona’ winter wheat (Triticum aestivum L.) altered allocation and spike characteristics that contribute to final grain yield under field conditions (Nunn clay loam, Aridic Argiustolls). The shaded treatment consisted of 50% ambient light reduction from 1 week before booting through the first week of grain fill (6 weeks total). Plants harvested were partitioned into stem, leaf blades by position on culm, and spike components. At maturity, spikes were divided into individual spikelets by position on the rachis. Carbon‐14‐labeled tracer was applied 24 h prior to each harvest. Shading significantly decreased spike weights for the later samplings, but had little effect on leaf or stem weights. Despite high spike sink activity and increasing spike size, when carbohydrates were limiting, photosynthate partitioning to spikes was not increased. Greater tiller mortality resulted in fewer culms per plant (and fewer spikes per plant) in shaded treatments. Shading altered spike morphology by decreasing the number and weight of kernels per spikelet and, therefore, total spikelet and spike weight; the number of grain‐bearing spikelets was unaffected. Spikelets were decreased most at the lower central portion of the spike, contrasting with other studies that found decreases in the upper half or basal portion of the spike. The combined effects of shading resulted in 32% lower yield, due mostly to lower spike density, but also to decreased kernel number and size.

Factors Affecting the Timing of Grassland Regrowth after Fire in the Montane Grasslands of Natal

SYNOPSIS Recent research has indicated that burning Highland Sourveld once growth has been initiated increases grass tiller mortality. Present burning prescriptions could therefore be improved by an insight into the factors controlling the initiation of grass growth in spring. It was hypothesised in this study that early rainfall stimulated early growth in spring. The results indicated, however, that soil moisture was always freely available, even after a long period of drought. There was no correlation between growth and soil moisture, whereas high correlations were found between growth and soil temperature and growth and air temperature. It is concluded that soil temperature is the limiting factor in initiating grass growth in spring in the Natal Drakensberg.

A new selection criterion for yield in wheat

The mortality of young tillers to an extent of 36.5% under optimum cultural conditions was recorded in a field experiment. Attention is drawn to the necessity of minimising this loss and to diverting it towards productive tillers by applying selection pressure. Future yield advances may be achieved by selecting genotypes which tiller moderately in the vegetative phase, most of which survive to produce grains. The character association of each variety under consideration was studied for the suitability towards this objective. A modified selection procedure is suggested which may be advantageously applied to achieve this objective. The proposed new methodology may also be effectively applied to such other cereal crops as barley, triticale and oats.

Tiller appearance and death ofLolium perennein mixed swards grazed by dairy cattle at two stocking rates

Abstract Ryegrass tiller appearance, death, and density were examined in perennial ryegrass — white clover pastures stocked with 2.77 (LSR) or 4.28 (HSR) dairy cows per hectare. Rates of tiller appearance and death were highest between November and January and were low and variable between February and October. Tillering in autumn was low and similar to that in winter (27.8 and 27.7 tillers/m2 per day, respectively). The rate of tiller death (but not appearance) was influenced by stocking rate, and was greater (P<0.01) in LSR than HSR swards during spring (29.5 and 21.2 tillers/m2 per day, respectively) and summer (61.3 and 39.9 tillers/m2 per day, respectively). Higher tiller death rates in LSR swards resulted in lower (P<0.05) tiller density during summer and autumn and reduced heterogeneity of tiller age population. Herbage mass in autumn was composed of more (P<0.05) new tillers in LSR than HSR swards (61.1 and 46.4%, respectively). Herbage mass in winter and spring consisted of a variety of tiller ag...

The effect of plant density on tillering: The involvement of R/FR ratio and the proportion of radiation intercepted per plant

Plants of Paspalum dilatatum and Lolium multiflorum were grown in pots at different densities. Half of the plants at each density received additional red light at their bases by means of light-emitting diodes. Density reduced both the proportion of incident radiation intercepted per plant and the red/far-red ratio of the light at plant bases. Tillering decreased with density in both species. P. dilatatum plants also had fewer reproductive tillers and expanded leaves and a higher mortality of young vegetative tillers in denser stands. In both species the enrichment with red light did not increase tillering of isolated plants, but increased it in stands grown at relatively low densities with small degrees of mutual shading. At these densities P. dilatatum plants achieved the number of tillers of isolated plants. Moreover, red light increased vegetative tiller death in the P. dilatatum dense canopy. These results suggest that low red/far-red ratios might preclude morphogenic responses to density before an important depletion in energy availability takes place.

Effect of seed rate and application of N fertilizer on grain yield and N uptake of rice under intermediate deepwater conditions (15–50 cm)

SUMMARYIn an intermediate deepwater (15–50 cm) situation, the number of tillers increased with increase of nitrogen fertilizer from 0 to 40 and 80 kg/ha and of seed rate from 100 to 200, 300 and 400 seeds/m2. The tiller mortality due to higher water depth was higher under no-N treatment and under higher seed rates. The number of panicles and grain yield increased significantly with increase in N. Similarly, an increase in the seed rate increased the number of panicles and decreased the number of grains per panicle and panicle weight. The grain yields of the different seed rates were similar. The interaction between N levels and seed rates was not significant.

Photoassimilate Partitioning of Main Shoot Leaves in Field‐Grown Spring Barley1

Premature tiller mortality could conceivably limit grain yield production in barley (Hordeum vulgare L.). Knowing photoassimilate partitioning patterns during the vegetative development phase of growth is important for understanding the causes of tiller mortality. A field experiment was conducted to ascertain the 14C translocation patterns of individual main shoot leaf blades during the pre‐anthesis period for three spring barley genotypes differing in tiller production and survival. One of the top three to five leaves was labelled with 14CO2 on each date and above‐ground plant parts were harvested for determining the distribution of 14C after a 24 h translocation period. Also, for two of the leaves, labelled plants were allowed to translocate until anthesis or maturity before the distribution of radioactivity was measured. Most 14C fixed by the first developed leaves on the main shoot was translocated to newly emerging main shoot leaves or to young tillers. The leaf subtending and the leaf above a particular tiller preferentially exported carbon to that tiller. During the early tiller production phase of growth, proportionately more 14C was translocated to tillers of the higher tillering genotypes than for the lower tillering one. During the time when tiller mortality became evident, no differences in partitioning patterns were found between the high or low tiller mortality genotypes. Later formed leaves in all genotypes provided relatively large proportions of labelled photoassimilate to the main shoot stem and inflorescence. A sharp decline in the percentage of 14C translocated to all tillers occurred when the main stem began rapid growth. We conclude that the shift in main shoot photoassimilate translocation away from tillers and to the main shoot stem contributes to the premature abortion of tillers in barley.