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Genetic gains in wheat yield are required to meet future demand. In order to design strategic crosses, it is essential to quantify the genetic variation among elite cultivars on traits responsible for the adaptation and the generation of yield components. We explored the degree of variation within well-adapted commercial cultivars on developmental phases (vegetative, early reproductive and late reproductive), final leaf number and phyllochron, leaf and spikelet plastochron, number of spikelets, florets, and dynamics of floret primordia development. Variation in flowering time among cultivars was minor but they differed in the partitioning of that time into particular phases. Main differences were found for the length of the late reproductive phase, partly linked to those in final leaf number. Variations on number of fertile florets at anthesis were mostly explained by floret survival, due to differential ability of labile florets to maintain normal development between cultivars. These differences were related to the duration of the floret development, but not to the synchrony of development among florets. These findings provide useful information for breeders when selecting genotypes for strategic crosses, as considering floret survival through duration of floret development in one of the parents (for which these processes shall be characterised in the elite germplasm) might increase the likelihood of transgressive segregation towards high-yielding offspring.

The present study was carried out to monitor leaf growth, foliar emission, and the daily photosynthesis behavior of sisal plants cv Ceniza. In a commercial crop, sisal plants were selected and monitored weekly to determine increase in number, length, width, and thickness of the leaves, during a 154 day period. On two occasions during the experimental period, gas exchange rates were also monitored during the light and dark periods. The results allowed determining a phyllochron of 8.65 days. Gas exchange monitoring detected low stomatal conductance rates during the light period. However, starting at 15:30 h, stomatal conductance substantially increased, remaining at maximum levels throughout the dark period, and, subsequently, decreased from 09:30 h, the following light period. A high correlation of stomatal conductance with vapor pressure deficit and leaf temperature was found. Maximum CO2 fixation rates varied between 12.2 and 14.5 µmol m-2 s-1, recorded between 19:19 and 19:26 h. The results corroborate the CAM metabolism of sisal plants cv Ceniza., El presente estudio se llevó a cabo con el objeto de monitorear el crecimiento foliar, la emisión de hojas y el comportamiento diario de la fotosíntesis en plantas de fique cv Ceniza. Para lo anterior, en un cultivo comercial se seleccionaron plantas de fique a las cuales se les realizó un monitoreo semanal para determinar las ganancias en número, longitud, ancho y grosor de las hojas, durante un período de 154 días. En dos oportunidades durante el periodo experimental, se realizó también un monitoreo cada hora a las tasas de intercambio gaseoso durante los periodos de luz y oscuridad. Los resultados de crecimiento permitieron estimar un filocrono promedio de 8,65 días. El monitoreo a las tasas de intercambio gaseoso indicaron una baja conductancia estomática durante el período de luz. Sin embargo, a partir de las 15:30 h, la conductancia estomática se incrementó sustancialmente, manteniéndose a niveles máximos durante todo el período de oscuridad, para posteriormente decrecer a partir de las 09:30 h, del siguiente periodo de luz. Se encontró una alta correlación de la conductancia estomática con el déficit de presión de vapor y la temperatura foliar. Las máximas tasas de fijación de CO2 detectadas variaron entre 12,2 y 14,5 µmol m-2 s-1, las cuales se registraron entre las 19:19 y las 19:26 h, durante el período de oscuridad. Estos resultados corroboran el metabolismo CAM de las plantas de fique cv Ceniza.

Growth assessment improves the understanding of the plant’s response to stress conditions. In this study, we aimed to evaluate the response of growth, biomass accumulation and the efficiency of sorghum water use to different continued saline water regimes. The experiment was carried out in municipality of Serra Talhada, Pernambuco, Brazil. The sorghum, cv. Sudan IPA 4202, was sown in pots in a nursery. The plants were laid out in completely randomized design submitted to four water regimes during the entire cycle based on reference evapotranspiration (ET0) (125%, 100%, 75% and 50%.ET0), with 32 repetitions. Over time, data on biometrics, forage biomass and, crop water consumption were collected. The plant was fractionated and its components were measured. Morphophysiological indices were obtained. There was no effect of water regime in most variables of growth, and in the accumulated and dry matter partition. The water use efficiency was maintained, even with the reduction in crop water consumption. Changes in leaf appearance and senescence did not alter the morphophysiological indexes, suggesting maintenance of the photosynthetic rate of the crop in the different water availability. It is concluded that the sorghum, cv. Sudan IPA 4202, has high adaptation to crop environments with wide variation of water regime, recommending water depth of 50%.ET0., A avaliação do crescimento permite melhorar a compreensão da resposta da planta as condições de estresse. Objetivou-se avaliar a resposta do crescimento, acúmulo de biomassa e da eficiência do uso da água do sorgo a diferentes regimes hídricos continuados com água salina. O experimento foi conduzido em Serra Talhada, Pernambuco, Brasil. O sorgo, cv. Sudão IPA 4202, foi semeado em vasos em um viveiro. As plantas foram dispostas em delineamento inteiramente ao acaso submetidas a quatro regimes hídricos durante todo o ciclo com base na evapotranspiração de referência (ET0) (125%, 100%, 75% e 50%.ET0), com 32 repetições. Ao longo do tempo foram coletados dados de biometria, biomassa de forragem e consumo de água da cultura. A planta foi fracionada e seus componentes foram mensurados. Os índices morfofisiológicos foram obtidos. Não houve efeito de regime hídrico na maioria das variáveis de crescimento, acúmulo e partição de matéria seca. A eficiência do uso da água foi mantida, mesmo com a redução no consumo de água pela cultura. As mudanças no aparecimento e na senescência foliar não alteraram os índices morfofisiológicos, sugerindo manutenção da taxa fotossintética da cultura nas distintas disponibilidades de água. Conclui-se que, o sorgo, cv. Sudão IPA 4202, possui alta adaptação a ambientes de cultivo com ampla variação de regime hídrico, recomendando-se lâmina de 50%.ET0.

Growth assessment improves the understanding of the plant’s response to stress conditions. In this study, we aimed to evaluate the response of growth, biomass accumulation and the efficiency of sorghum water use to different continued saline water regimes. The experiment was carried out in municipality of Serra Talhada, Pernambuco, Brazil. The sorghum, cv. Sudan IPA 4202, was sown in pots in a nursery. The plants were laid out in completely randomized design submitted to four water regimes during the entire cycle based on reference evapotranspiration (ET0) (125%, 100%, 75% and 50%.ET0), with 32 repetitions. Over time, data on biometrics, forage biomass and, crop water consumption were collected. The plant was fractionated and its components were measured. Morphophysiological indices were obtained. There was no effect of water regime in most variables of growth, and in the accumulated and dry matter partition. The water use efficiency was maintained, even with the reduction in crop water consumption. Changes in leaf appearance and senescence did not alter the morphophysiological indexes, suggesting maintenance of the photosynthetic rate of the crop in the different water availability. It is concluded that the sorghum, cv. Sudan IPA 4202, has high adaptation to crop environments with wide variation of water regime, recommending water depth of 50%.ET0., A avaliação do crescimento permite melhorar a compreensão da resposta da planta as condições de estresse. Objetivou-se avaliar a resposta do crescimento, acúmulo de biomassa e da eficiência do uso da água do sorgo a diferentes regimes hídricos continuados com água salina. O experimento foi conduzido em Serra Talhada, Pernambuco, Brasil. O sorgo, cv. Sudão IPA 4202, foi semeado em vasos em um viveiro. As plantas foram dispostas em delineamento inteiramente ao acaso submetidas a quatro regimes hídricos durante todo o ciclo com base na evapotranspiração de referência (ET0) (125%, 100%, 75% e 50%.ET0), com 32 repetições. Ao longo do tempo foram coletados dados de biometria, biomassa de forragem e consumo de água da cultura. A planta foi fracionada e seus componentes foram mensurados. Os índices morfofisiológicos foram obtidos. Não houve efeito de regime hídrico na maioria das variáveis de crescimento, acúmulo e partição de matéria seca. A eficiência do uso da água foi mantida, mesmo com a redução no consumo de água pela cultura. As mudanças no aparecimento e na senescência foliar não alteraram os índices morfofisiológicos, sugerindo manutenção da taxa fotossintética da cultura nas distintas disponibilidades de água. Conclui-se que, o sorgo, cv. Sudão IPA 4202, possui alta adaptação a ambientes de cultivo com ampla variação de regime hídrico, recomendando-se lâmina de 50%.ET0.

Phenology of small cereals as a complex trait, which provides matching plant development with growing conditions, is important factor that influence plant adaptation to particular environment and finally yield. Scales of growth based on plant phenology and scales of development based on apical morphology are very precise, but relationships between them are not always clear. Some morphogenetic features of cereals growth can be predicted on the basis of leaf appearance. That means shoot apex development is coordinated with leaf appearance and total number of formed leaves. The objective of this research was to study relationships among apical development and plant phenology and the variability in phenological development of diverse winter barley cultivars under field conditions. The twelve barley cultivars differed in origin, pedigree and agronomic traits were used in this study over six growing seasons at the Novi Sad location (45o20’N, 15o51’E, altitude 86 m) and under rainfed conditions.

The aim of this study was to analyze traits of leaf appearance and phenological development related to grain yield gain in winter barley cultivars released over the past 50 years. Field trials with 15 six-rowed winter barley cultivars were conducted during two growing seasons. The main leaf appearance and developmental traits were studied. The duration of the emergence-anthesis and emergence-physiological maturity phases decreased by 2.35 and 2.16 GDD yr(1), respectively. The duration of the stem elongation-anthesis phase was 10% longer in modern cultivars. The results showed no clear trend of improvement in final leaf number and phyllochron. The duration of the stem elongation-anthesis phase was positively related with grain number and yield. Constant improvements in grain number and grain weight by fine manipulation of the crop developmental phases could represent an essential strategy for further increases in barley grain yield potential.

The effects of water stress on crop yield through modifications of plant architecture are vital to crop performance such as common bean plants. To assess the extent of this effect, an outdoor experiment was conducted in which common bean plants received five treatments: fully irrigated, and irrigation deficits of 30% and 50% applied in flowering or pod formation stages onwards. Evapotranspiration, number and length of pods, shoot biomass, grain yield and harvest index were assessed, and architectural traits (length and thickness of internodes, length of petioles and petiolules, length and width of leaflet blades and angles) were recorded and analyzed using regression models. The highest irrigation deficit in the flowering stage had the most pronounced effect on plant architecture. Stressed plants were shorter, leaves were smaller and pointing downward, indicating that plants permanently altered their exposure to sunlight. The combined effect of irrigation deficit and less exposure to light lead to shorter pods, less shoot biomass and lower grain yield. Fitted empirical models between water deficit and plant architecture can be included in architectural simulation models to quantify plant light interception under water stress, which, in turn, can supply crop models adding a second order of water stress effects on crop yield simulation.

Accurate predictions of the timing of physiological stages and the development rate are crucial for predicting crop performance under field conditions. Plant development is controlled by the leaf appearance rate (LAR) and our understanding of how LAR responds to environmental factors is still limited. Here, we tested the hypothesis that carbon availability may account for the effects of irradiance, photoperiod, atmospheric CO2 concentration, and ontogeny on LAR. We conducted three experiments in growth chambers to quantify and disentangle these effects for both winter and spring wheat cultivars. Variations of LAR observed between environmental scenarios were well explained by the supply/demand ratio for carbon, quantified using the photothermal quotient. We therefore developed an ecophysiological model based on the photothermal quotient that accounts for the effects of temperature, irradiance, photoperiod, and ontogeny on LAR. Comparisons of observed leaf stages and LAR with simulations from our model, from a linear thermal-time model, and from a segmented linear thermal-time model corrected for sowing date showed that our model can simulate the observed changes in LAR in the field with the lowest error. Our findings demonstrate that a hypothesis-driven approach that incorporates more physiology in specific processes of crop models can increase their predictive power under variable environments.

The branch construction of trees is based on phytomers, repetitive subunits defined as node + leaf + axillary meristem + internode. The rate at which phytomers are added to a shoot is termed the phyllochron, which is determined by genetics, endogenous regulation and environmental conditions. The phyllochron is fundamental to understanding the growth of plants. Most phyllochron studies on woody species are of young plants under controlled conditions without consideration for different types of shoots that are present in mature trees. In this 2-year field study, we investigated seasonal patterns of phyllochron development on both proleptic and epicormic shoots of mature peach trees (Prunus persica) exposed to two irrigation treatments. One treatment was not irrigated until significant stress was detected via water potential by pressure bombing. In the second treatment trees were normally irrigated with ~5.84 cm of water each week to match evapotranspirational loss. Midday stem water potential readings were regularly collected to assess the level of water stress experienced by the trees. Measurements of individual leaves and their corresponding internodes were taken along tagged proleptic and epicormic shoots three times per week from the beginning to the end of two growing seasons. Leaf measurements were used to calculate the phyllochron. The phyllochron increased as the season progressed. This increase could not be explained by traditionally accepted effects of temperature or light. The more vigorous epicormic shoots added leaves significantly faster than proleptic shoots on trees in both water deficit and normally irrigated treatments. Additionally, epicormic shoots produced leaves with significantly greater leaf length and leaf area. Midday stem water potentials were more negative in trees in the water deficit treatments only after proleptic shoots stopped growing. The phyllochron did increase while leaf length and leaf area decreased on epicormic shoots of deficit

The branch construction of trees is based on phytomers, repetitive subunits defined as node + leaf + axillary meristem + internode. The rate at which phytomers are added to a shoot is termed the phyllochron, which is determined by genetics, endogenous regulation and environmental conditions. The phyllochron is fundamental to understanding the growth of plants. Most phyllochron studies on woody species are of young plants under controlled conditions without consideration for different types of shoots that are present in mature trees. In this 2-year field study, we investigated seasonal patterns of phyllochron development on both proleptic and epicormic shoots of mature peach trees (Prunus persica) exposed to two irrigation treatments. One treatment was not irrigated until significant stress was detected via water potential by pressure bombing. In the second treatment trees were normally irrigated with ~5.84 cm of water each week to match evapotranspirational loss. Midday stem water potential readings were regularly collected to assess the level of water stress experienced by the trees. Measurements of individual leaves and their corresponding internodes were taken along tagged proleptic and epicormic shoots three times per week from the beginning to the end of two growing seasons. Leaf measurements were used to calculate the phyllochron. The phyllochron increased as the season progressed. This increase could not be explained by traditionally accepted effects of temperature or light. The more vigorous epicormic shoots added leaves significantly faster than proleptic shoots on trees in both water deficit and normally irrigated treatments. Additionally, epicormic shoots produced leaves with significantly greater leaf length and leaf area. Midday stem water potentials were more negative in trees in the water deficit treatments only after proleptic shoots stopped growing. The phyllochron did increase while leaf length and leaf area decreased on epicormic shoots of deficit

Development and growth of leaves in cereals significantly affects grain yield since dry matter accumulation depends on the leaf area that intercepts light. Phyllochron (PHY) is defined as time interval between the emergences of successive leaves on the main stem. The aim of this study was to determine the effect of year and cultivar on phyllochron in winter barley. Twelve cultivars of winter barley differing in origin and time of anthesis were tested during six growing seasons (GS), from 2002/03 to 2007/08. The highest PHY across GSs was determined in the two-rowed cultivar Cordoba (81.6°Cd) and the lowest in the two-rowed cultivar Novosadski 581 (71.0°Cd). The early cultivars had fast leaf development, the medium cultivars medium and the late cultivars slow development, 72.5°Cd, 75.6°Cd and 78.9°Cd, respectively. The tested cultivars showed significant variability in the PHY, which can be used for selecting most adaptable genotypes for specific growing conditions., Razviće i rast listova žita značajno utiče na prinos zrna jer akumulacija suve materije zavisi od lisne površine koja apsorbuje sunčevu svetlost. Filohron se definiše kao vremenski interval između pojave sukcesivnih listova na glavnom stablu. Cilj ovog istraživanja je da se odredi efekat godine i sorte na dužinu filohrona kod ozimog ječma. Dvanaest sorti ozimog ječma različitih po poreklu i vremenu do cvetanja testirano je tokom šest proizvodnih sezona, od 2002/03. do 2007/08. na lokalitetu 'Novi Sad'. Najduži filohron (81.6°Cd) imala je sorta dvoredog ječma 'Kordoba', a najkraći (71.0°Cd) sorta dvoredog ječma 'Novosadski 581'. Rane sote imale su najbrži, srednje rane, srednji i kasne sorte najsporiji porast listova. Kod ranih sorti prosečna vrednost filohrona iznosila je 72.5°Cd, srednje ranih 75.6°Cd i kasnih 78.9°Cd. Testirane sorte pokazale su značajnu varijabilnost u dužini filohrona, što može predstavljati osnovu u izboru najadaptabilnijih genotipova u određenim uslovima spoljne sredine.

Aimed to evaluate the morphogenetic and structural characteristics of the pasture of Brachiaria decumbens, subjected to several intensities and frequencies of cutting and nitrogen fertilization. Experimental design was randomized blocks in split plots, whit a 2 x 2 factorial arrangement relating to combinations of two cutting heights (40 and 50 cm) and two heights of residue (15 and 25 cm) at the plots and nitrogen fertilization (with or without nitrogen) in sub-plots, with four replications. Mophogenetic variables evaluated were: leaf elongation rate (LER), stem elongation rate (SER), leaf appearance rate (LAR), leaf senescence rate (LSR) and phyllochron; and structural features were: number of basal tillers (NBT), total number of leaves (TNL), number of leaves appeared (NLAp), number of dead leaves (NDL), number of alive leaves (NAL) and final leaf length (FLL). 100 kg N/ha allowed increase (p<0.10) on LER of 31.58% and 126.32% respectively for residues 15 and 25 cm. The NBT compared to cutting heights (40 to 50 cm) were affected (p<0.10) only with the use of nitrogen fertilizer, with average of 145.62 tillers/m 2 in 50 cm cut height. Residue height of 25 cm combined with cut height 40 cm increase leaf elongation rate and number of basal tillers, reducing expansion time, without changing other structural characteristics of the pasture., Objetivou-se avaliar as características morfogênicas e estruturais do pasto de Brachiaria decumbens, submetido a intensidades, fre- quências de corte e adubação nitrogenada. O delineamento experimental foi em blocos casualizados em esquema de parcelas subdividi- das, tendo na parcela o arranjo fatorial 2 x 2 referente a combinações entre duas alturas de corte (40 e 50 cm) e duas alturas de resíduo (15 e 25 cm) e nas sub-parcelas a adubação nitrogenada (com ou sem nitrogênio), com quatro repetições. As variáveis analisadas para as ca- racterísticas morfogênicas foram: taxa de alongamento foliar (TAlF); taxa de alongamento de colmo (TAlC); taxa de aparecimento foliar (TApF); taxa de senescência foliar (TSF) e filocrono; e para as características estruturais foram: número de perfilhos basais (NPB); número de folhas totais (NFT); número de folhas aparecidas (NFAp); nú- mero de folhas mortas (NFM); número de folhas vivas (NFV) e comprimento final da folha (CFF). A utilização de 100 kg/ha de N permitiu aumento (p<0,10) na TAlF de 31,58% e 126,32%, respec- tivamente para os resíduos de 15 e 25 cm. O NPB em comparação às alturas de corte (40 e 50 cm) foi afetado (p<0,10) apenas com a utilização da adubação nitrogenada, observando-se média de 145,62 perfilhos/m 2 para a altura de corte 50 cm. A altura de resíduo 25 cm combinada com a altura de corte 40 cm, junto à aplicação de 100 kg/ha de N, promovem maior produção de matéria seca total em menor espaço de tempo (28 dias), permitindo maiores taxas de lotação e facilitando o manejo no sistema de lotação rotacionada.

Aimed to evaluate the morphogenetic and structural characteristics of the pasture of Brachiaria decumbens, subjected to several intensities and frequencies of cutting and nitrogen fertilization. Experimental design was randomized blocks in split plots, whit a 2 x 2 factorial arrangement relating to combinations of two cutting heights (40 and 50 cm) and two heights of residue (15 and 25 cm) at the plots and nitrogen fertilization (with or without nitrogen) in sub-plots, with four replications. Mophogenetic variables evaluated were: leaf elongation rate (LER), stem elongation rate (SER), leaf appearance rate (LAR), leaf senescence rate (LSR) and phyllochron; and structural features were: number of basal tillers (NBT), total number of leaves (TNL), number of leaves appeared (NLAp), number of dead leaves (NDL), number of alive leaves (NAL) and final leaf length (FLL). 100 kg N/ha allowed increase (p<0.10) on LER of 31.58% and 126.32% respectively for residues 15 and 25 cm. The NBT compared to cutting heights (40 to 50 cm) were affected (p<0.10) only with the use of nitrogen fertilizer, with average of 145.62 tillers/m 2 in 50 cm cut height. Residue height of 25 cm combined with cut height 40 cm increase leaf elongation rate and number of basal tillers, reducing expansion time, without changing other structural characteristics of the pasture., Objetivou-se avaliar as características morfogênicas e estruturais do pasto de Brachiaria decumbens, submetido a intensidades, fre- quências de corte e adubação nitrogenada. O delineamento experimental foi em blocos casualizados em esquema de parcelas subdividi- das, tendo na parcela o arranjo fatorial 2 x 2 referente a combinações entre duas alturas de corte (40 e 50 cm) e duas alturas de resíduo (15 e 25 cm) e nas sub-parcelas a adubação nitrogenada (com ou sem nitrogênio), com quatro repetições. As variáveis analisadas para as ca- racterísticas morfogênicas foram: taxa de alongamento foliar (TAlF); taxa de alongamento de colmo (TAlC); taxa de aparecimento foliar (TApF); taxa de senescência foliar (TSF) e filocrono; e para as características estruturais foram: número de perfilhos basais (NPB); número de folhas totais (NFT); número de folhas aparecidas (NFAp); nú- mero de folhas mortas (NFM); número de folhas vivas (NFV) e comprimento final da folha (CFF). A utilização de 100 kg/ha de N permitiu aumento (p<0,10) na TAlF de 31,58% e 126,32%, respec- tivamente para os resíduos de 15 e 25 cm. O NPB em comparação às alturas de corte (40 e 50 cm) foi afetado (p<0,10) apenas com a utilização da adubação nitrogenada, observando-se média de 145,62 perfilhos/m 2 para a altura de corte 50 cm. A altura de resíduo 25 cm combinada com a altura de corte 40 cm, junto à aplicação de 100 kg/ha de N, promovem maior produção de matéria seca total em menor espaço de tempo (28 dias), permitindo maiores taxas de lotação e facilitando o manejo no sistema de lotação rotacionada.

Morphogenetic characteristics of two accesses of Bromus catharticus Vahl. (Agros-tologia and Platano) were studied during the establishment period. The experiment was carried out in greenhouse at UFPEL, Animal Science Department, using pots in a completely randomized design with eight replications, from June 19th to August 11th, in 2006. Plants were evaluated with intervals from two to three days in a week. Length and number of the leaf blades in the main tillers were measured, with scale and marked with a colour wire. Leaf appearance rate and phyllochron did not differ significantly (p>0.05) for both accesses, however, leaf elongation rate of Platano was higher (p, As características morfogênicas de dois acessos de Bromus catharticus Vahl. (Agrosto-logia e Platano) foram estudados na fase de estabelecimento. O experimento foi realizado em casa de vegetação do Departamento de Zootecnia-UFPel, em vasos plásticos, em delineamento completamente casualizado com 8 repetições, no período de 19 de junho a 11 de agosto de 2006. Usou-se a técnica de perfilhos marcados medindo-se o comprimento e número de lâminas a intervalos de 2 a 3 dias, com início em 10 de julho. Foram calculadas a taxa de aparecimento e expansão foliar e filocrono. A taxa de aparecimento foliar e filocrono não diferiram significativamente (p>0,05), entretanto, a taxa de expansão foliar do acesso Platano (p

Morphogenetic characteristics of two accesses of Bromus catharticus Vahl. (Agros-tologia and Platano) were studied during the establishment period. The experiment was carried out in greenhouse at UFPEL, Animal Science Department, using pots in a completely randomized design with eight replications, from June 19th to August 11th, in 2006. Plants were evaluated with intervals from two to three days in a week. Length and number of the leaf blades in the main tillers were measured, with scale and marked with a colour wire. Leaf appearance rate and phyllochron did not differ significantly (p>0.05) for both accesses, however, leaf elongation rate of Platano was higher (p, As características morfogênicas de dois acessos de Bromus catharticus Vahl. (Agrosto-logia e Platano) foram estudados na fase de estabelecimento. O experimento foi realizado em casa de vegetação do Departamento de Zootecnia-UFPel, em vasos plásticos, em delineamento completamente casualizado com 8 repetições, no período de 19 de junho a 11 de agosto de 2006. Usou-se a técnica de perfilhos marcados medindo-se o comprimento e número de lâminas a intervalos de 2 a 3 dias, com início em 10 de julho. Foram calculadas a taxa de aparecimento e expansão foliar e filocrono. A taxa de aparecimento foliar e filocrono não diferiram significativamente (p>0,05), entretanto, a taxa de expansão foliar do acesso Platano (p

Extensive research shows temperature to be the primary environmental factor controlling the phyllochron, or rate of leaf appearance, of wheat (Triticum aestivum L.). Experimental results suggest that soil temperature at crown depth, rather than air temperature above the canopy, would better predict wheat leaf appearance rates. To test this hypothesis, leaf appearance in spring wheat ('Nordic') was measured in a 2-year field experiment (Nunn clay loam soil; fine, smectitic, mesic Aridic, Argiustoll) with three planting dates and two soil temperature treatments. One temperature treatment (denoted +3C) consisted of heating the soil at crown depth to 3 °C above the ambient soil temperature (denoted +OC). Main stem cumulative leaf number was measured at least weekly until flag leaf emergence. Leaf appearance was essentially linear with both air and soil growing degree-days (GDD), although there was a stronger linear relationship with soil GDD in the +OC plants than in +3C plants. A weak positive relationship between planting date and the phyllochron was observed. Unexpectedly, we found that heating the soil did not increase the rate of leaf appearance, as the paradigm would predict. To explain these results, we propose extending the paradigm in two ways. First, three processes are involved in leaf appearance: (1) cell division at the shoot apex forms the primordium; (2) cell division in the intercalary meristem forms the cells that then (3) expand to produce the leaf. Cell division is predominately controlled by temperature, but cell expansion is considerably more affected by factors other than temperature, explaining the influence of other factors on the phyllochron. Secondly, the vertical distribution of the two meristems and region of cell expansion occur over a significant distance, where temperature varies considerably, and temperature at a specific point (e.g. crown depth) does not account for the entire temperature regime under which leaves are developing.