Tiller Mortality Research Articles

Impacts of Improved Switchgrass and Big Bluestem Selections on Yield, Morphological Characteristics, and Biomass Quality

Switchgrass (Panicum virgatumL.) and big bluestem (Andropogon gerardiiV.) are promising warm-season grasses for biomass production. Understanding the morphological and quality-related traits of these grasses can guide breeders in developing strategies to improve yield and quality for bioindustrial applications. Elite selections were made in Southern Quebec from four promising varieties of switchgrass and one of big bluestem. Biomass yield, morphological characteristics, and selected quality traits were evaluated at two sites in 2011 and 2012. Significant variation was detected for all measured characteristics, with differences varying by site and year. In some cases the selection process modified characteristics including increasing height and reducing tiller mortality. Switchgrasses reached a similar tiller equilibrium density in both years of 690 m−2and 379 m−2at a productive and marginal site, respectively. Differences in yield were pronounced at the marginal site, with some advanced selections having a higher yield than their parent varieties. Switchgrass yields were generally greater than those of big bluestem. A delayed spring harvest date greatly reduced yield but reduced moisture content and slightly increased cellulose concentration. Big bluestem had a higher cellulose content than switchgrass, likely due to greater stem content.

Yield and tillering response of super hybrid rice Liangyoupeijiu to tillage and establishment methods

Tillering is an important agronomic trait for rice grain production. To evaluate yield and tillering response, Liangyoupeijiu (super hybrid rice) was grown in Hunan, China during 2011–2012 under different methods of tillage (conventional and no-tillage system) and crop establishment methods (transplanting at a spacing of 20cm×20cm with one seedling per hill and direct seeding at a seeding rate of 22.5kgha−1). Our results revealed that, at maximum tillering (Max.) and at maturity (MA) stages, direct seeding (DS) resulted in 22% more tillers than transplanting (TP) irrespective of tillage system. Tiller mortality reached a peak between panicle initiation (PI) and booting (BT) stages, and was 16% higher under conventional tillage (CT) than under no-tillage (NT). Transplanting required 29% more time for the completion of tillering and less for DS. Tillering rate was 43% higher in DS than TP under either CT or NT. There was a positive correlation between panicle number per m2 and maximum tiller number per m2, but not panicle-bearing tiller rate. The panicle bearing tiller rate was higher under DS than TP and higher under NT than CT. Tiller dry weight gradually increased up to heading (HD) stage, and was 14% higher under TP than DS. Leaf area (cm2tiller−1) gradually increased from Max. to HD stage and then decreased by 34% in conventional tillage transplanting (CTTP) and 45% in no-tillage transplanting (NTTP) from 12DAH–24DAH (days after heading), but was similar (35%) under DS under either CT or NT. Grain yield was higher under CTTP owing to the larger sink size (heavier panicle, more spikelets in per cm length of panicle) than under DS.

Tillering dynamics in Guinea grass pastures subjected to management strategies under rotational grazing

This study was carried out to analyze the tillering profile of Guinea grass (Panicum maximum cv. Tanzania) pastures subjected to two grazing frequencies (time necessary to intercept 90 and 95% of the incoming light) and two post-grazing heights (30 and 50 cm) in the period from November 2005 to October 2006. The experimental design was of completely randomized blocks with three replications, in a 2 × 2 factorial arrangement. At the end of the spring, pastures managed with 90% light interception showed greater tiller appearance rates in relation to pastures managed with 95%, regardless of post-grazing height. In the summer and fall, pastures managed with post-grazing height of 30 cm showed higher tiller appearance rates in comparison with pastures managed at 50 cm, regardless of grazing frequency. Concerning the tiller mortality rates, in the summer, higher values were found for pastures managed at 90/50 and 95/30 (interception/height), intermediate values at 90/30 and lower values in those managed at 95/50. Pastures managed at 90/30, 95/30 and 95/50 in the fall presented greater tiller mortality rates than those managed at 90/50. These differences do not occur in the winter/beginning of spring. The stability index remained above 1 all through the experimental period. All management strategies evaluated are adequate for Guinea grass.

Piata palisade grass deferred with two distinct initial heights: luminous environment and tillering dynamics

The study was carried out between March 1st and July 1st, 2011, in order to evaluate the tillering pattern of the deferred Piata palisade grass (Brachiaria brizantha cv. Piata). Three sward heights were evaluated in the beginning of the period of deferment: lower (20 cm), medium (30 cm) and higher (40 cm). The experimental design was of completely randomized blocks with three replications. The Piata palisade grass deferred with low initial height presented lower leaf area index, lower light interception and higher leaf angle in relation to the ones deferred with medium and high heights. The advance in the period of deferment increased the leaf area index and the light interception by the sward, in a way that the highest values were recorded in the periods from 91 and 120 days. The leaf angle reduced linearly with the advance in the period of deferment. For basal and aerial tillers, the rates of appearance, mortality and survival of tillers, as well as the balance between appearance and mortality, and the tiller density stability index were not affected by the initial height of the sward. The stability index of the tiller density was lower in the period from 1 to 30 days of deferment in relation to the periods from 31 to 60, from 61 to 90 and from 91 to 120 days. The variation of the initial height of the Piata palisade grass does not influence the tiller density dynamics during the period of deferment. The reduction of the initial height of the Piata palisade grass improves the luminous environment inside the sward, but it does not stimulate the grass tillering during the period of deferment.

Ratooning Induced Rhizospheric Changes Impede Nutrient Acquisition and Growth in Sugarcane Ratoon Crop During Grand Growth Stage in Sub-tropics

Nearly half of the cultivated sugarcane is ratooned, but most often dry matter accumulation in ratoon crops is lesser than plant crops. The aim of present work was to assess ratooning induced rhizospheric changes in plant and ratoon crop for their impact on nutrient acquisition and growth. Significant changes occurred in pH, soil enzymatic activities and phenolic contents of ratoon rhizosphere during the growth stage. The changes also had an impact on ratoon root properties. The cation exchange capacity, root membrane permeability and nitrate reductase activities in vivo of ratoon crop declined significantly as compared to plant crop. These changes were reflected upon significant impediment in nutrient acquisition and their losses through tiller mortality during the growth phase of crop cycle. The NPK uptake reduced in the range 25–35 % while the losses through tiller mortality in NPK contents in ratoon cane ranged from 9 to 10 %. The reduced nutrient acquisition suppressed the development of assimilatory apparatus (27 %) during the grand growth phase and led to reduction in biomass production (15.5 %).

Persistence and production of perennial grasses under water deficits and extreme temperatures: importance of intraspecific vs. interspecific variability

AbstractExtreme climatic events are expected to increase in frequency and magnitude as a consequence of global warming. Grasslands cover a large proportion of the European continent and contribute to both agricultural production and ecosystem services through inter and intraspecific genetic variability. This study analysed the effects of summer droughts and heat waves on the persistence and production of perennial forage grasses. Mediterranean and temperate populations of Dactylis glomerata L. and Festuca arundinacea (Schreb.) were compared at both Mediterranean and temperate sites in France. By manipulating canopy temperatures and water availability, grass swards in the field were subjected to cumulative summer and spring water deficits (CSSWD) ranging from 329 to 707 mm to test different projected climatic conditions and extreme summer events. Under controlled summer heat waves (6–21 days at a mean daily canopy temperature higher than 30–35 °C), there was no increase in membrane damage to surviving aerial tissues. Plant stress was thus mainly generated through greater soil water deficit. Under the greatest CSSWD, annual biomass production was reduced on average by 60% and 30% with temperate and Mediterranean populations, respectively. Thresholds for a significant increase in summer tiller mortality were seen at CSSWD higher than 450 mm for temperate populations and 550 mm for Mediterranean populations. The latter displayed lower predawn leaf water potentials in summer and recovered through intense tillering in the subsequent seasons. Under the most extreme CSSWD, fewer than 20% of tillers of temperate populations survived and their nitrogen uptake ability was drastically altered. The higher potential productivity of Mediterranean populations in winter was associated with greater frost sensitivity. The identification of thresholds for vulnerability and the determination of the role of genetic diversity will improve the management of plant resilience and the design of new plant material to cope with climate change.

Tiller morphogenesis and mortality were controlled by different loci in rice (Oryza sativa L.)

Productive panicles per plant in hybrids are less than that in pure line cultivars is the main reason why competition heterosis of grain yield is not conspicuous in japonica rice (Oryza sativa L.). In order to improve the trait of hybrids, we detected static loci and dynamic loci affecting tiller numbers by using unconditional and conditional quantitative trait loci (QTL) mapping methods in this study. Tiller numbers were recorded every 14 days until maturity across two environments in 254 recombinant inbred lines (RILs) and parents. Genetic effects for tiller number at different measuring stages were estimated by the best linear unbiased prediction method. Thirteen unconditional additive QTLs were identified at nine stages. For the identical loci detected at various stages, positive alleles came from the identical parent. Seven of the 13 detected conditional additive QTLs were discovered from stage 1 to stage 4, when Xiushui 79 carried positive alleles of tiller number in qTN4 and qTN7.1, and C Bao carried positive alleles in qTN2.1, qTN5.1, qTN5.2, qTN9.1 and qTN10. The remaining six loci (qTN2.2,qTN3, qTN8.1, qTN8.2, qTN11.1 and qTN11.2) were detected between stage 5 and stage 9 when tiller number decreased. Except for qTN8.2, alleles decreasing tiller mortality came from Xiushui 79. For the 13 detected conditional QTLs, the numbers of elite alleles contained in a line had high significant positive correlation with its productive panicles per plant (r = 0.347**). These results indicated that tiller morphogenesis and mortality were controlled by different loci, and it is possible to enhance productive panicles per plant by pyramiding the elite alleles acting at different stages. Key words: Rice (Oryza sativa L.), tiller, morphogenesis, mortality, quantitative trait loci (QTL) mapping.

Grupos funcionais de gramíneas forrageiras tropicais

Foram avaliadas as características morfogênicas e estruturais de gramíneas forrageiras com o objetivo de agrupá-las, de acordo com seu padrão de desenvolvimento, em seus respectivos grupos funcionais. As gramíneas foram plantadas em parcelas de 1,0 m² com 24 plantas, em delineamento de blocos completos casualizados com três repetições. Os dados foram submetidos à análise de fatores, reduzindo as variáveis em quatro fatores: desenvolvimento de massa, mortalidade de perfilhos, estádio de desenvolvimento e longevidade foliar. Os dados foram submetidos à análise de agrupamento por otimização de Tocher adotando-se a distância euclidiana média como medida básica de dissimilaridade. As gramíneas foram agrupadas da seguinte forma: Verão - grupo I (Xaraés, Massai, Mombaça e Marandu); grupo II (Gordura e Aruana); e grupo III (Jaraguá). Outono - grupo I (Mombaça, Massai, Xaraés, Marandu e Gordura); grupo II - (Jaraguá); e grupo III (Aruana). Possivelmente a maior participação do fator mortalidade de perfilhos na formação dos grupos no período de outono influenciou na reorganização dos grupos. Os padrões de desenvolvimento de massa dos diferentes grupos de gramíneas diferiram entre si quanto à forma de utilização dos recursos disponíveis. Houve mudança nos escores de todos os fatores com a mudança do período do verão para o outono. O agrupamento funcional comprova que gramíneas de gêneros e/ou espécies diferentes podem ser enquadradas em um mesmo grupo.

Differences between wheat and barley in leaf and tillering coordination under contrasting nitrogen and sulfur conditions

It is traditionally assumed that barley has a higher tillering capacity than wheat whatever the environmental condition; however, this supposition has not been formally tested under experimental conditions nor analyzed its relationship with leaf appearance. In the present work, leaf appearance and tillering dynamics were studied in wheat and barley genotypes grown under contrasting nitrogen and sulfur levels at sowing. There was no difference in phenology (seedling emergence, first visible node and flowering) between wheat and barley or due to different nutrients. Phyllochron in barley tended to be higher than (or at least equal to) that observed in wheat, without effect of the N or S levels on this trait. Differences in final leaf number were negligible. Tillering dynamics was analyzed considering the tillering appearance rate (TAR), the maximum number of tillers appeared (MTN), the tillering mortality rate (TMR), and the final number of tillers per plant (FTN). TAR was significantly greater in barley than in wheat genotypes in all experiments. In both species, TAR was enhanced as N supply was increased while S promoted TAR only under high N conditions. The MTN was positively and significantly associated with TAR. Although cessation of tillering was similar between both species, the maximum number of tillers was superior in barley than in wheat, due to the differences between species in tiller appearance rate. A high MTN was related to a high tiller mortality rate. In spite of that counterbalance, FTN was closely related to MTN; as a consequence, FTN was pre-defined during the early phase of the tillering process. Barley showed higher values of tiller initiated per leaf appeared (synchrony) than wheat, while N and S deficiencies decreased that synchrony.

Tillering dynamics in pastures of guinea grass subjected to grazing severities under intermittent stocking

This experiment was carried out to analyze the tillering dynamics of the species Panicum maximum cv. Mombaca subjected to three post-grazing heights: residue of 30 cm (30); residue of 50 cm (50); and residue of 50 cm during spring and summer, lowered to 40 cm in the first fall season grazing and to 30 cm in the following grazing cycle, resuming to 50 cm after the first grazing of the following spring season (50-30). Grazings were initiated whenever the swards intercepted 95% of the incident light. The post-grazing heights were allocated in the experimental units in a completely randomized block design with three replications. The density of basal tillers did not vary between the residual heights evaluated. Swards managed with variable residual height (50-30) presented higher rates of appearance and mortality of basal tillers during the summer of 2007, indicating high tiller renovation. Regardless of the post-grazing height evaluated, lower rates of appearance of basal tillers were found in the spring of 2006. The stability index of guinea grass cv. Mombaca was close to 1.0 throughout the experimental period. Swards managed with variable post-grazing present structural changes able to improve the regrowth vigor, which may be important to maximize the use of the forage species in the production system.

Characterization of tropical forage grass development pattern through the morphogenetic and structural characteristics

An experiment was carried out with the objective to evaluate growth pattern of tropical forage grass under free growth by using morphogenetic and structural characteristics with the expectation of using this study for forage grass evaluation protocol. The experimental area was established with two cultivars of Panicum maximum Jacq. (Mombaca and Aruana), a hybrid cultivar of P. maximum Jacq. and P. Infestum BRA-7102 (Massai), two cultivars of Brachiaria brizantha (A. Rich.) Stapf (Marandu and Xaraes) and Molasses grass (Melinis minutiflora Beauv.) and jaragua grass (Hyparrhenia rufa (Nees) Stapf.). The grasses were planted in 1.0-m² experimental units with 24 plants arranged in a completely randomized block design with three replications. Growth pattern of the grasses was evaluated through mass development, tiller mortality, development stage and leaf longevity. Development patterns differed significantly among groups of grasses, indicating that the same available resources can be used in different manners by grasses from the same genus and/or species.

Número de perfilhos do capim-braquiária em regime de lotação contínua

The study was conducted to identify, through assessments of tillering, appropriate management strategies for Brachiaria decumbens cv. Basilisk under continuous stocking with cattle. Two management strategies were studied: pasture with 25 cm throughout the experimental period, and pasture with 15 cm in winter and 25 cm in spring and summer. A split-plot and randomized block design with four replications were adopted. The management strategies represented the primary factor, and the seasons (winter, spring and summer) were the secondary factor. The lowest balance between rates of appearance (TAR) and mortality (TMR) of tillers and the lowest number of vegetative tillers occurred in winter. In spring and summer, the balance and number of vegetative tillers were higher and did not differ. The lowering of pasture in winter resulted in greater balance between TAR and TMR and higher number of tillers in relation to management on sward fixed at 25 cm. There were greater numbers of reproductive and dead tillers in summer and winter, respectively. The pastures with fixed height of 25 cm contained a higher number of dead tiller. Under continuous stocking, the lowering of B. decumbens pasture in winter and its increase to 25 cm in spring and summer optimizes turnover of tillers.

Disponibilidade de nitrogênio, sobrevivência e contribuição dos perfilhos ao rendimento de grãos do milho

O N influencia os processos de morfogênese e perfilhamento nas espécies da família Poaceae. Contudo, seu efeito sobre o perfilhamento do milho é pouco conhecido. Este trabalho foi realizado com o objetivo de avaliar se a dose de N e a época de aplicação da cobertura nitrogenada interferem na emissão, sobrevivência e contribuição dos perfilhos ao rendimento de grãos de híbridos de milho. O experimento foi instalado no município de Lages (SC), nos anos agrícolas de 2006/07 e 2008/09. O delineamento experimental empregado foi o de blocos casualizados dispostos em parcelas subdivididas. No primeiro ano, as parcelas foram constituídas de dois híbridos de milho (AS 1560 e P30F53); as subparcelas, por três doses de N (0, 100 e 200 kg ha-1 de N); e as sub-subparcelas, por três épocas de aplicação do N (V4, V4+V8 e V8). No segundo ano, avaliaram-se quatro doses de N nas parcelas (0, 50, 100 e 200 kg ha-1 de N) e as mesmas épocas de aplicação usadas no primeiro ano, nas subparcelas. Determinaram-se a percentagem de plantas perfilhadas, o número de perfilhos por planta, o rendimento de grãos e os componentes do rendimento. O híbrido P30F53 teve maior capacidade de perfilhamento e maior rendimento de grãos do que o AS 1560. A aplicação de N em cobertura reduziu a mortalidade dos perfilhos na colheita no primeiro ano, e até a floração, na segunda safra. A realização da cobertura nitrogenada em V4 estimulou o perfilhamento e permitiu maior sobrevivência dos perfilhos na colheita em 2008/09. A aplicação de N em cobertura aumentou o rendimento de grãos nos dois anos de ensaio e incrementou a contribuição direta dos perfilhos à produtividade em 2006/07. A época de aplicação do N em cobertura não interferiu no rendimento de grãos. A capacidade de perfilhamento no milho difere entre híbridos. Os perfilhos contribuem diretamente para o rendimento de grãos do milho em condições de boa disponibilidade de N.

Biomass accumulation in sugarcane: unravelling the factors underpinning reduced growth phenomena

Constant radiation use efficiency throughout the entire sugarcane crop cycle is often assumed for crop yield forecasting and management purposes. However, several examples are known where the linear relationship between cumulative intercepted radiation and biomass accumulation becomes uncoupled at some stage, with the latter declining by 21% in one reported case. This slowdown in growth is commonly referred to as the reduced growth phenomenon (RGP). In certain instances, this phenomenon appears to be related to the timing of crop initiation and harvesting. Summer-initiated sugarcane crops do not always resume expected growth rates after the transition from winter to spring, despite conditions being favourable for vigorous growth. Possible factors underlying the failure of sugarcane crops to realize full yield potential are reported and interrogated in this review. The potential involvement of lodging, flowering, and tiller mortality have been reviewed and the data suggest that, while such factors may contribute, they are unlikely to be the major causes of sugarcane RGPs. Similarly, reports indicate that temperature cannot account for reduced growth, as rates remain low despite the onset of favourable conditions in spring. In contrast, a decline in specific leaf nitrogen, potential initiation of sugar-mediated source-sink feedback inhibition of photosynthesis, and increased rates of maintenance respiration that occur during sugarcane development and maturation appear to be likely factors contributing to RGPs. An evaluation of areas of sugarcane biology and agronomy that would benefit from further research towards overcoming yield restriction imposed by reduced growth phenomena is provided.

Species/defoliation/drought interactions on tuft survival and tiller and phytomass production in four sourveld grass species in KwaZulu-Natal, South Africa

Productivity and mortality of grass plants following drought may be controlled by interactions between defoliation and severity of the drought. Prudent grassland management might mitigate deleterious changes in species composition in multispecies grasslands. This study, conducted in a horticultural tunnel, explored the interactions of drought duration, and the period of uninterrupted postdrought growth before defoliation, on phytomass, tiller production and mortality of Aristida junciformis, Eragrostis curvula, Hyparrhenia hirta and Themeda triandra. Pretreatment tiller production was highest for Aristida and Eragrostis, followed by Hyparrhenia and then Themeda. Mortality was positively related to tuft size and drought duration. Tiller mortality was controlled by a species × drought interaction and the covariate tuft-size. All species lost tillers following a 28-day drought, with the highest loss in Eragrostis and lowest in Themeda. Phytomass production was positively related to recovery, and inversely related to drought duration. Species-specific differences in production were apparent only in the no-drought treatment, where Hyparrhenia produced more phytomass than Themeda and Eragrostis. Aristida had the lowest phytomass production and showed little plasticity across drought treatments. Results indicated that postdrought rest is important for phytomass production, and that species may exhibit a tradeoff between productivity and survival.

Growth and potential reproduction of Poa crymophila in response to season precipitation shortage in the Eastern Tibetan Plateau, China

The growing season in 2006 existed a quite less precipitation than previous years in the eastern of Tibetan Plateau, China. In order to explore the response strategies of the grass to drought year, the variations of growth and potential reproduction of Poa crymophila between rich (2005) and poor rainfall year (2006) were studied. Reproductive shoot biomass, above- and below-ground biomass pronounced decreased in the poor rainfall year, but the ratio of above-/below-ground biomass and vegetative shoot biomass increased. Carbon content in inflorescence increased significantly in 2006, but decreased significantly in root. Nitrogen contents and the C/N ratios in plant components were not significantly different. Sexual reproduction in 2005 and 2006 was not different. Season precipitation shortage could result in the higher mortality of vernal budding shoots or tillers. The results suggested that P. crymophila response to poor rainfall year (drought) by a smaller plant body, allocating more proportional biomass to above-ground, altering more carbon to inflorescence, and altering its reproductive way to sexual.

Effects of fire, post-fire defoliation, drought and season on regrowth and carbohydrate reserves of alpine snowgrass Poa fawcettiae (Poaceae)

Following defoliation, grasses regenerate foliage from basal buds. We used a combination of field, glasshouse and growth-room experiments to investigate the role of carbohydrate reserves in regrowth of Poa fawcettiae Vickery following fire or mock grazing, and the effect on reserve dynamics of post-fire defoliation, drought and seasonal factors. Fructan reserves of burnt plants were depleted during foliage regeneration, and remained below those of unburnt plants for up to 10 months in the field, and for up to 3 months in the glasshouse. Plants were resilient to occasional mechanical clipping of foliage, but experienced significant depletion in fructan reserves and high tiller mortality when clipped at frequent intervals. Cold treatment led to fructan concentrations almost double those in plants growing at a warm temperature, explaining peak autumn levels in field plants, whereas a short drought treatment doubled the concentration of ethanol-soluble carbohydrates. Taken together, these data show how the dynamics of carbohydrate reserves, and specifically tiller-base fructan reserves, explain the vegetative regeneration capacity of P. fawcettiae.

Características morfogênicas, estruturais e acúmulo de forragem do capim-tanzânia submetido a duas alturas e três intervalos de corte

Avaliaram-se as características morfogênicas e estruturais e o acúmulo de forragem do capim Panicum maximum, cv. Tanzânia, submetido a duas alturas de corte (25 e 50 cm) e três intervalos de corte (correspondentes ao surgimento de duas, três e quatro folhas por perfilho). Utilizou-se um arranjo fatorial 2 × 3 em delineamento de blocos completos casualizados, com três repetições. A taxa de aparecimento de folhas diminuiu e o filocrono aumentou com a redução da frequência de desfolhação. De modo geral, o comprimento final da folha foi menor na altura de corte 25 cm que na de 50 cm. A taxa de senescência de folhas e a taxa de alongamento de colmos tenderam a aumento quando o intervalo de corte variou de duas para três folhas por perfilho. A taxa de mortalidade de perfilhos aumentou ao longo do período de avaliação. As altas taxas de mortalidade e de aparecimento de perfilhos caracterizaram um padrão intenso de renovação (turnover) da população de perfilhos. A altura pré-desfolhação diminuiu com o aumento da frequência de corte, enquanto a massa de forragem tendeu a ser maior nas menores frequências de corte. O acúmulo de colmos só variou entre as alturas de corte no segundo corte e foi menor no intervalo de duas folhas em comparação aos de três e quatro folhas surgidas por perfilho, também no mesmo corte. O intervalo de cortes do capim-tanzânia não deve exceder o tempo necessário para o aparecimento de duas a três folhas por perfilho.

Tiller dynamic and production on a SW Atlantic Spartina alterniflora marsh

We used non-destructive methods to study the bi-monthly changes in standing stock, turnover, and net aerial primary productivity (NAPP) of Spartina alterniflora in the Bahía Blanca Estuary, Argentina, from 2005 to 2007. Tillers were tagged and counted bimonthly and a weight:height relationship developed for the live and dead stems in a regularly flooded zone (low marsh, LM) and an irregularly flooded one (high marsh, HM). The annual tiller natality in year one compared to year two decreased from 440 ± 68 to 220 ± 58 new individuals m –2 yr –1 in the HM and from 500 ± 103 to 280 ± 97 new individuals m −2 yr −1 in the LM ( μ ± 1 SE). Tiller mortality averaged 670 ± 70 individuals m −2 yr −1. Living biomass was present throughout the year in both the sites, but flowering occurred only at the HM where it began in December. The live biomass in the LM was significantly greater than in the HM in the first year, but decreased in the second year from 455 ± 66 to 266 ± 31 g m −2 in the HM and from 572 ± 76 to 277 ± 78 g m −2 in the LM ( μ ± 1 SE). The highest levels of standing dead material were in the HM (55%) and the lowest in the LM (24%). The average total (live + dead) aboveground biomass in the HM was significantly greater than in the LM in the first year, but decreased in the second year from 1033 ± 120 to 556 ± 33 g m −2, and in the LM from 679 ± 57 to 355 ± 61 g m −2 ( μ ± 1 SE). The annual NAPP, calculated as the sum of positive growth in individual tillers between intervals, showed no significant differences between years and sites, and averaged 628 ± 94 g m −2 yr −1 ( μ ± 1 SE). The dead biomass output (DBO), calculated as the sum of negative increments in NAPP between sampling intervals, was 956 ± 121 g −2 yr −1, and was not statistically different between sites. The productivity at this site is not different from that estimated for other marshes, when similar methods are used. The production at this site, however, may be limited by high salinity levels, and the differences observed between years related to climate changes between years, e.g., the 2006–2007 was an ENSO period.

Evaluation of Resistance to Chinch Bug in Pearl Millet in Temperate and Subtropical Environments

Pearl millet inbreds and hybrids were evaluated for resistance to chinch bug at Lincoln, NE, and Tifton, GA, in 2003 and 2004. Insect feeding damage expressed as plant mortality, stunting, leaf sheath necrosis, and tiller mortality was observed over time. Resistance was expressed by a slower rate of plant damage to resistant genotypes compared to susceptible ones. Across experiments, inbreds 59464B and 59668M-1 were most frequently identified as resistant. Inbred Tift 99B was susceptible in every experiment and by every assessment criterion. The experiments revealed information on the genetic expression of resistance. When insect damage among hybrids made with Tift 454 was compared, resistance tended to be dominant or overdominant in expression. Evidence for location-specific resistance caused by environmental conditions or genetic differences in the insect populations between the two locations was observed. Inbreds 03GH707 and Tift 454, developed at Tifton, were resistant only in some assessments at Tifton, but not at Lincoln. 16RmR1, developed at Lincoln, was susceptible in both Lincoln experiments, but not at Tifton. 03GH706 was susceptible in some Tifton assessments, but was not among the most susceptible inbreds in the Lincoln experiments. Evaluations are needed at multiple locations to effectively identify resistance to damage caused by chinch bug feeding in pearl millet. Accepted for publication 14 October 2008. Published 12 January 2009.