Differences in temperature responses among phenological processes in diverse Ethiopian sorghum germplasm can affect their specific adaptation to environmental conditions.

BACKGROUND AND AIMS: Main shoot total leaf number (TLN) is a key determinant of plant leaf area and crop adaptation. Environmental factors other than photoperiod can affect TLN in sorghum, implying that leaf appearance rate (LAR) and development rate can differ in response to temperature. The objectives of this study were to determine (1) if temperature effects on TLN can be explained as a consequence of differences in temperature responses across phenological processes and (2) if genotypic differences in these responses can be linked to agroecological adaptation. METHODS: Nineteen sorghum genotypes were sown on 12 dates at two locations in Ethiopia with contrasting altitude, creating temperature differences independent of photoperiod. TLN and temperature were recorded in all experiments and LAR for six sowing dates. KEY RESULTS: Eleven of the genotypes showed a temperature effect on TLN, which was associated with a significantly higher base temperature (Tbase) for LAR than for pre-anthesis development rate (DR). In contrast, genotypes with no effect of temperature on TLN had similar Tbase for LAR and DR. Across genotypes, Tbase for LAR and DR were highly correlated, but genotypes with low Tbase had the greatest difference in Tbase between the two processes. Genotypic differences were associated with racial grouping. CONCLUSIONS: Genotypic and racial differences in responses of phenological processes to temperature, in particular in Tbase, can affect specific adaptation to agroecological zones, as these differences can affect TLN in response to temperature and hence canopy size and the duration of the pre-anthesis period. These can both affect the amount of water used and radiation intercepted pre-anthesis. A multi-disciplinary approach is required to identify genotype × environment × management combinations that can best capture the ensuing specific adaptation.

Maize Leaf Appearance Rates: A Synthesis From the United States Corn Belt.

The relationship between collared leaf number and growing degree days (GDD) is crucial for predicting maize phenology. Biophysical crop models convert GDD accumulation to leaf numbers by using a constant parameter termed phyllochron (°C-day leaf-1) or leaf appearance rate (LAR; leaf oC-day-1). However, such important parameter values are rarely estimated for modern maize hybrids. To fill this gap, we sourced and analyzed experimental datasets from the United States Corn Belt with the objective to (i) determine phyllochron values for two types of models: linear (1-parameter) and bilinear (3-parameters; phase I and II phyllochron, and transition point) and (ii) explore whether environmental factors such as photoperiod and radiation, and physiological variables such as plant growth rate can explain variability in phyllochron and improve predictability of maize phenology. The datasets included different locations (latitudes between 48° N and 41° N), years (2009-2019), hybrids, and management settings. Results indicated that the bilinear model represented the leaf number vs. GDD relationship more accurately than the linear model (R 2 = 0.99 vs. 0.95, n = 4,694). Across datasets, first phase phyllochron, transition leaf number, and second phase phyllochron averaged 57.9 ± 7.5°C-day, 9.8 ± 1.2 leaves, and 30.9 ± 5.7°C-day, respectively. Correlation analysis revealed that radiation from the V3 to the V9 developmental stages had a positive relationship with phyllochron (r = 0.69), while photoperiod was positively related to days to flowering or total leaf number (r = 0.89). Additionally, a positive nonlinear relationship between maize LAR and plant growth rate was found. Present findings provide important parameter values for calibration and optimization of maize crop models in the United States Corn Belt, as well as new insights to enhance mechanisms in crop models.

BASE GROWTH TEMPERATURE AND PHYLLOCHRON FOR KIKUYU GRASS (Cenchrus clandestinas; Poaceae) / Temperatura base de crecimiento y filocrono para el pasto kikuyo (Cenchrus clandestinus; Poacea)

ABSTRACT In order to estimate the base temperature (Bt) of growth through the appearance of leaves and calculate the phyllochron for kikuyu grass, three plots were established on three farms in the Provincia of Ubaté (Cundinamarca, Colombia) located at different altitudes (2560, 2640, 3143 m. a. s. l.). Measurements were made in four cycles in a period of eight months. The Bt was estimated by the least coefficient of variation method using a second order regression model and the model obtained was validated by the cross-validation method. The Bt values for the first, second, third and fourth leafwere 4.02, 3.68, 3.93, and 3.62 °C, respectively. For the appearance of the first leaf, the kikuyu required more thermal time (TT) (97.5 accumulated growing degree days (AGDD)) than for the second (74.2 AGDD), third (73.8 AGDD) and fourth leaf (76.0 AGDD) (p <0.05). There were no differences in TT among farms (p> 0.05). There was a tendency to a greater number of days required to reach each leaf stage in the farm located at higher altitude and with lower mean temperature. The validation showed an adequate adjustment (r2 = 0.94) and a substantial concordance (CCC = 0.97) between the observed values and the predicted values for the estimated TT with the Bt value obtained for each leaf stage. The results ofBt for kikuyu grass obtained, will allow to make more precise predictions about the phyllochron and generate growth models close to reality.

RESUMEN Con el fin de estimar la temperatura base (Tb) de crecimiento a través de la aparición de hojas y calcular el filocrono para el pasto kikuyo, se establecieron tres parcelas en tres fincas de la provincia de Ubaté (Cundinamarca, Colombia) ubicadas a diferente altitud (2560, 2640, 3143 m. s. n. m.). Se realizaron cuatro ciclos de mediciones en un tiempo total de ocho meses. La Tb se estimó por el método de mínimo coeficiente de variación utilizando un modelo de regresión de segundo grado y el modelo obtenido se validó por el método de validación cruzada. La Tb para la primera, segunda, tercera y cuarta hoja fue 4,02, 3,68, 3,93 y 3,62 °C, respectivamente. El kikuyo requirió mayor tiempo térmico (TT) para la aparición de la primera hoja (97,5 grados día de crecimiento acumulados (GDCA)) que para la segunda (74,2 GDCA), tercera (73,8 GDCA) y cuarta hoja (76,0 GDCA) (p<0,05). No hubo diferencias en el TT entre fincas (p > 0,05). Hubo tendencia a un mayor número de días calendario requeridos para alcanzar cada estado de hoja en la finca ubicada a mayor altitud y con menor temperatura media. La validación mostró un adecuado ajuste (r2 = 0,94) y una concordancia sustancial (CCC= 0,97) entre los valores observados y los valores predichos para el TT estimado con los valores de Tb obtenidos para cada estado de hoja. Los resultados de Tb de crecimiento del pasto kikuyo obtenidos permiten realizar predicciones más precisas sobre el filocrono y generar modelos de crecimiento cercanos a la realidad.

Wheat Developmental Traits as Affected by the Interaction between Eps-7D and Temperature under Contrasting Photoperiods with Insensitive Ppd-D1 Background.

Earliness per se (Eps) genes are important to fine tune adaptation, and studying their probable pleiotropic effect on wheat yield traits is worthwhile. In addition, it has been shown that some Eps genes interact with temperature and therefore determining the likely Eps × temperature interaction is needed for each newly identified Eps gene. We studied two NILs differing in the newly identified Eps-7D (carrying insensitive Ppd-D1 in the background) under three temperature regimes (9, 15 and 18 °C) and two photoperiods (12 and 24 h). Eps-7D affected time to anthesis as expected and the Eps-7D-late allele extended both the period before and after terminal spikelet. The interaction effect of Eps-7D × temperature was significant but not cross-over: the magnitude and level of significance of the difference between NILs with the late or early allele was affected by the growing temperature (i.e., difference was least at 18 °C and largest at 9 °C), and the differences caused due to temperature sensitivity were influenced by photoperiod. The rate of leaf initiation was faster in NIL with Eps-7D-early than with the late allele which compensated for the shorter duration of leaf initiation resulting in similar final leaf number between two NILs. Eps-7D-late consistently increased spike fertility through improving floret primordia survival as a consequence of extending the late reproductive phase.

Phenology and Floret Development as Affected by the Interaction between Eps-7D and Ppd-D1.

Earliness per se (Eps) genes may play a critical role in further improving wheat adaptation and fine-tuning wheat development to cope with climate change. There are only few studies on the detailed effect of Eps on wheat development and fewer on the interaction of Eps with the environment and other genes determining time to anthesis. Furthermore, it seems relevant to study every newly discovered Eps gene and its probable interactions as the mechanisms and detailed effects of each Eps may be quite different. In the present study, we evaluated NILs differing in the recently identified Eps-7D as well as in Ppd-D1 at three temperature regimes (9, 15 and 18 °C) under short day. The effect of Eps-7D on time to anthesis as well as on its component phases varied both qualitatively and quantitatively depending on the allelic status of Ppd-D1 and temperature, being larger in a photoperiod-sensitive background. A more noticeable effect of Eps-7D (when combined with Ppd-D1b) was realised during the late reproductive phase. Consequently, the final leaf number was not clearly altered by Eps-7D, while floret development of the labile florets (florets 2 and 3 in this case, depending on the particular spikelet) was favoured by the action of the Eps-7D-late allele, increasing the likelihood of particular florets to become fertile, and consequently, improving spike fertility when combined with Ppd-D1b.

Relationship between Vessel Formation and Seasonal Changes in Leaf Area of Evergreen and Deciduous Species with Different Vessel Arrangements.

To discuss the diversity of morphological traits and life strategies of trees, the functional relationship between leaf expansion and vessel formation must be clarified. We compared the temporal relationship among tree species with different leaf habits and vessel arrangements. Twigs, leaves, and trunk core samples were periodically acquired from 35 sample trees of nine species in a temperate forest in Japan. We quantitatively estimated leaf expansion using a nonlinear regression model and observed thin sections of twigs and trunks with a light microscope. Almost all of the first-formed vessels in twigs, which formed adjacent to the annual ring border, were lignified with a leaf area between 0% and 70% of the maximum in all species. The first-formed vessels in trunks lignified between 0% and 95% of the maximum leaf area in ring-porous deciduous Quercus serrata and ring-(radial-)porous evergreen Castanopsis cuspidate. Their lignification occurred earlier than in diffuse-porous deciduous Liquidambar styraciflua, diffuse-porous evergreen Cinnamomum camphora and Symplocos prunifolia, and radial-porous evergreen Quercus glauca and Quercus myrsinifolia. The timing varied in semi-ring-porous deciduous Acanthopanax sciadophylloides and diffuse-porous evergreen Ilex pedunculosa. The observed differences in the timing of vessel formation after leaf appearance were reflected in their differing vessel porosities and were connected to the different life strategies among tree species.

Experimental and modeling evidence of carbon limitation of leaf appearance rate for spring and winter wheat.

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 phyllochron of well-watered and water deficit mature peach trees varies with shoot type and vigour.

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 irrigated trees in the 2010 growing season. The phyllochron of both shoot types gradually increased over the season, which was primarily due to an endogenous rank or shoot ageing effect. Differences between shoot types indicate that the phyllochron is variable among shoots on the same tree and is associated with shoot vigour. Water deficit increased the phyllochron and over all shoot growth rate.

Productivity and morphological characteristics of buffel grass intercropped with butterfly pea under shade conditions / Características morfológicas e produtivas do capim buffel em consórcio com cunhã sob sombreamento

Forage production in the Brazilian semiarid region can be enhanced by irrigation and shading to maximize water use. We evaluated the productivity and morphological characteristics of buffel grass (Cenchrus ciliaris) intercropped with butterfly pea (Clitoria ternatea) under shade conditions using an irrigated area with an artificial shading system (26, 39, 55%, or full sunlight). Butterfly pea was implemented in half of the land parcels in a randomized block using a split plot design with three replications. One hundred twenty days after planting was designated as the uniformity cut and the cutting was performed every 45 days for four consecutive cycles. The morphological analysis was performed during the first and fourth cycle, and the herbage mass was determined. The shadow had a quadratic effect on the leaf appearance rate in the first cycle, while shading had a quadratic deviation effect on the leaf elongation rate in the second cycle and an increased linear effect on the length of the sheet in the first cycle. Shading had a quadratic effect on the herbage mass in the third cycle and decreased linearity in the fourth cycle. The highest percentage of buffel grass was found in the single system in the first and second cycles. In addition, we observed a decreased linear effect of shade in the first cycle and the quadratic deviation effect of shade in the second cycle. A quadratic effect of shade was observed in the third and fourth cycles. The survival of the butterfly pea had a quadratic effect with a minimum rate level of 21% shading. The crude protein content showed a system effect in four cycles with higher crude protein in the intercropping system in the first and second cycles. There was also a quadratic effect of shade in the third cycle and linear increase in the fourth cycle. In conclusion, shading increased the leaf appearance rates and elongation at intermediate levels. In addition, a high level of shading increased the leaf length and survival of butterfly pea while it decreased the mass of the forage produced.

A produção de forragem na região semiárida brasileira pode ser intensificada com a irrigação e o sombreamento, maximizando o uso da água. Com o objetivo de avaliar as características produtivas e morfológicas do Capim Buffel (Cenchrus ciliaris) consorciado com Cunhã (Clitoria ternatea), sob sombreamento, foi utilizada uma área irrigada com sistema de sombreamento artificial (26, 39, 55% ou pleno sol). Foi implantada Cunhã em metade das parcelas em delineamento de blocos casualizados em esquemas de parcelas subdivididas com três repetições. Após 120 dias foi realizado o corte de uniformização e a cada 45 dias foram realizados os cortes por quatro ciclos consecutivos, sendo realizadas análises morfológicas e determinada a massa de forragem no 1.º e 4º ciclos. Houve efeito quadrático para sombra na taxa de aparecimento foliar no 1º ciclo, efeito de desvio da quadrática para sombreamento na taxa de alongamento foliar no 2º ciclo e efeito linear crescente para sombreamento no comprimento da folha no 1º ciclo. A massa de forragem apresentou efeito quadrático para sombreamento no 3º ciclo e efeito linear decrescente no 4º ciclo. O maior percentual de Capim Buffel foi encontrado no sistema solteiro no 1º e 2º ciclos. Foi observado efeito linear decrescente para sombra no 1º ciclo e de desvio da quadrática para sombra no 2º ciclo. Já no 3º e 4º ciclos houve efeito quadrático para sombra. A sobrevivência da Cunhã apresentou efeito quadrático com taxa mínima em 21% de sombreamento. O teor de proteína bruta apresentou efeito de sistema nos quatro ciclos, sendo encontrados maiores teores de proteína bruta no sistema consorciado no 1º e 2º ciclos. Houve ainda efeito quadrático para sombra no 3º ciclo e efeito linear crescente no 4º ciclo. Conclui-se que o sombreamento promove aumento nas taxas de aparecimento e alongamento foliar em níveis intermediários. Além disso, alto nível o sombreamento promove aumento do comprimento foliar, eleva a sobrevivência da Cunhã e diminui a produção de massa de forragem.

Effects of nitrogen and vapour pressure deficit on phytomer growth and development in a C4 grass.

Phytomers are basic morphological units of plants. Knowledge of phytomer development is essential for understanding morphological plasticity, functional-structural modelling of plant growth and the usage of leaf characteristics to indicate growth conditions at the time of production (e.g. stable isotope signals). Yet, systematic analysis on the process of phytomer development is unavailable for wild or perennial C4 grasses. Also, effects of environmental factors, such as nitrogen nutrition or vapour pressure deficit (VPD), on coordination events of developmental processes of C4 grasses have not been studied. This study investigates phytomer growth and development in Cleistogenes squarrosa, a predominant C4 grass in the Eurasian steppe, grown at low (0.63 kPa) or high (1.58 kPa) VPD with low or high nitrogen supply in controlled environments. Elongation of phytomers on marked tillers was measured daily for 13 days. Then lengths of immature and mature phytomer components (blade, sheath and internode) of all phytomers were measured following dissection. Nitrogen nutrition and VPD had no effects on coordination of growth within and between phytomers: phytomer tips emerged when phytomers reached 26 % of their final length, coincident with the acceleration phase of its elongation; blade elongation stopped when phytomers reached ∼75 % of their final length and elongation of the preceding phytomer was confined to the internode. The relationship between fraction of final phytomer length and days after tip emergence for all treatments was well described by a sigmoidal function: y = 1/{1 + exp[(1.82 - x)/1.81]}. C. squarrosa exhibited little morphological plasticity at phytomer-level in response to nitrogen supply and VPD, but a clear increase in tillering under high N supply. Also, the invariant coordination of elongation within and between phytomers was a stable developmental feature, thus the quantitative coordination rules are applicable for predicting morphological development of C. squarrosa under contrasting levels of nitrogen nutrition or VPD.

Estimated phyllochron in low tunnel cultivated strawberry cultivars / Estimativa de filocrono em cultivares de morangueiro conduzidas em túnel baixo

ABSTRACT: The aim of this study was to determine phyllochron in strawberry cultivars, from two origins during two crop years, conducted in low tunnel. Experiments were conducted at the Universidade Federal de Santa Maria, campus Frederico Westphalen (CESNORS/UFSM), Brazil, evaluating 'Camarosa', 'Camino Real' and 'Albion' strawberry cultivars. During the 2012 crop year, seedlings from Chile and Pelotas/RS, Brazil were evaluated, for the 2013 crop year, only seedlings from Chile were submitted to evaluations. In order to determine the phyllochron, twice a week the numbers of leaves (NL) of the main crown were counted and a regression between NL and accumulated thermal time (ATT) was held. The experimental design was a complete randomized block, with three repetitions with the evaluation of 12 plants per experimental unity, consisting of a factorial. For 2012 and 2013 crop years, it is possible to conclude that 'Camarosa' and 'Camino Real' cultivars required higher accumulation of degree-days (ºC day-1) to issue each successive leaf than cv. 'Albion', which, in turn, presented higher rates of leaf emergence, being considered earlier. Regarding to origin, seedlings from cv. 'Albion' from Chile presented lower total phyllochron values and for samples from Pelotas, no difference among cultivars was observed.

RESUMO: O objetivo deste trabalho foi determinar o filocrono, em cultivares de morangueiro, de duas procedências e em dois anos agrícolas, conduzidas em túnel baixo. Os experimentos foram conduzidos em área da Universidade Federal de Santa Maria, campus Frederico Westphalen (CESNORS/UFSM), constando da avaliação das cultivares 'Camarosa', 'Camino Real' e 'Albion'. Para o ano de 2012, avaliaram-se mudas procedentes do Chile e da região de Pelotas/RS e, para o ano de 2013, apenas mudas chilenas. Na determinação do filocrono, foi realizada contagem, duas vezes por semana, do número de folhas (NF) da coroa principal e, posteriormente, realizou-se regressão linear entre o NF e a soma térmica acumulada (STa). O delineamento experimental foi o de blocos casualizados, com três repetições, sendo cada unidade experimental composta por 12 plantas de avaliação, em esquema fatorial. Para os anos de 2012 e 2013, os resultados obtidos mostram que as cultivares 'Camarosa' e 'Camino Real' necessitam de maior acúmulo de graus dia para emissão de cada folha sucessiva do que a cv. 'Albion', que, por sua vez, apresenta maiores taxas de emissão de folhas, podendo ser considerada como mais precoce. Com relação à procedência, verifica-se que as mudas da cv. 'Albion' provenientes do Chile apresentam menores valores de filocrono total. Para a procedência Pelotas, não foi observada diferença entre as cultivares.

Nitrogen dioxide accelerates flowering without changing the number of leaves at flowering in Arabidopsis thaliana.

A negative correlation has consistently been reported between the change in flowering time and the change in leaf number at flowering in response to environmental stimuli, such as the application of exogenous compounds, cold temperature, day length and light quality treatments in Arabidopsis thaliana (Arabidopsis). However, we show here that the application of exogenous nitrogen dioxide (NO2) did not change the number of rosette leaves at flowering, but actually accelerated flowering in Arabidopsis. Furthermore, NO2 treatment was found to increase the rate of leaf appearance. Based on these results, reaching the maximum rosette leaf number earlier in response to NO2 treatment resulted in earlier flowering relative to controls.

Filocrono, área foliar e produtividade de frutos de berinjela conduzidas com uma e duas hastes por planta em estufa plástica / Phyllochron, leaf area, and fruit yield in eggplants grown with one and two stems per plant in plastic greenhouse

Os objetivos deste trabalho foram estimar o filocrono, relacionar a área foliar com o número de folhas e determinar a produtividade de frutos em plantas de três genótipos de berinjela conduzidas com uma e duas hastes dentro de estufa plástica. O experimento foi conduzido na área experimental do Departamento de Fitotecnia da Universidade Federal de Santa Maria, Santa Maria, Rio Grande do Sul (RS). Foram utilizados três genótipos de berinjela: Nápoli, Comprida Roxa e Ciça. O transplante das mudas foi realizado com cinco folhas definitivas no dia 29 de outubro de 2007. O delineamento experimental foi o de blocos ao acaso com quatro repetições, compostas de duas fileiras de oito plantas. Em quatro plantas de cada repetição, foram realizadas observações do número de folhas na haste principal e na secundária. Em duas plantas de cada repetição, foi medida a largura das folhas na haste principal e na secundária. O filocrono foi estimado pelo inverso do coeficiente angular da regressão linear entre o número de folhas acumuladas na haste e a soma térmica acumulada após o transplante. A emissão de folhas na berinjela foi mais rápida nas plantas conduzidas com duas hastes. A área foliar da berinjela pode ser estimada por meio do número de folhas acumuladas. A produtividade de frutos de berinjela foi maior nas plantas conduzidas com duas hastes, sendo o genótipo Ciça aquele que apresentou maior produtividade de frutos.

The objective of this study was to estimate the phyllochron, to associate the leaf area to the leaf number and to determine fruit yield of eggplants grown with one and two stems inside a plastic greenhouse. An experiment was carried at the experimental area of the Plant Science Department of the Federal University of Santa Maria, Santa Maria, RS, Brazil. Three eggplant genotypes were used: Nápoli, Comprida roxa, and Ciça. Five-leaf seedlings were transplanted on 10/29/2007. The experimental design was a complete randomized blocks with four replications composed by two rows with eight plants. The number of leaves on the main stem and secondary branches was counted in four plants of each replication. Leaf width was measured on two plants per replication. The phyllochron was estimated as the inverse of the slope of the linear regression between the leaf number and the accumulated thermal time after transplanting. Eggplant fruit yield was greater in plants grown with two stems than and Ciça had the higher fruit yield among genotypes. The time for leaves emergence in eggplant was reduced in plants with two stems than in plants with only the main stem. Leaf area of eggplant can be estimated as function of the accumulated number of leaves. Eggplant fruit yield was greater in plants conducted with two stems than with only the main stem, and Ciça presented the greatest yield among genotypes.

Desenvolvimento vegetativo em diferentes hastes da planta de mandioca em função da época de plantio / Vegetative development on different stems of cassava as a function of planting date

Estudos sobre o desenvolvimento vegetativo da mandioca cultivada nas condições subtropicais do Brasil são escassos. O objetivo deste trabalho foi determinar o filocrono e o número final de folhas na haste principal e nas ramificações simpodiais de uma variedade de mandioca em diferentes épocas de plantio, em condições de clima subtropical. Um experimento de campo foi conduzido em Santa Maria, Rio Grande do Sul (RS), com quatro datas de plantio: 26/09/2006, 18/10/2006, 08/11/2006 e 28/11/2006. A variedade usada foi a FEPAGRO RS13, com caule do tipo simpodial tricotômico, no delineamento experimental inteiramente casualizado, com quatro tratamentos (datas de plantio) e quatro parcelas de 4,0 x 9,0m, com cinco fileiras e espaçamento 0,80 x 0,80m. Em seis plantas por parcela selecionadas aleatoriamente, foi feita a contagem semanal do número de folhas visíveis (NF) e do número final de folhas (NFF) da haste principal (HP) e das ramificações simpodiais de primeira (RS1) e de segunda (RS2) ordem. O filocrono (°C dia folha-1) foi estimado para HP, RS1 e RS2 pelo inverso do coeficiente angular da regressão linear entre NF e soma térmica acumulada, considerando a temperatura base de 14°C. O filocrono aumentou na seqüência HPRS1>RS2. Ambos filocrono e NFF variaram com a época de plantio, sendo o fotoperíodo uma possível causa da variação. Dentro das ramificações simpodiais RS1 e RS2, o filocrono e o NFF não são diferentes entre as hastes.

Studies on the vegetative development of cassava grown in subtropical conditions of Brazil are scarce. The objective of this study was to determine the phyllochron and the final leaf number on the main stem and on sympodial branches of a cassava variety grown in different planting dates in a subtropical climate. A field experiment was conducted in Santa Maria, RS, with four planting dates: 09/26/2006, 10/18/2006, 11/08/2006 and 11/28/2006. The variety FEPAGRO RS13, with tricotomic growth habit, was used in a complete randomized design with four treatments (planting dates) and four 4.0 x 9.0m plots with five rows and 0.8 x 0.8m spacing in each planting date. On the main stem (MS) and on the first order (BR1) and second order (BR2) sympodial branches of six plants per plot randomly selected, the number of visible leaves (NL) on a weekly basis, and the final leaf number (FLN) were measured. The phyllochron on MS, BR1 and BR2 was estimated by the inverse of the slope of the linear regression of NL against accumulated thermal time, assuming a base temperature of 14°C. Phyllochron increased in the sequence MSBR1>BR2. Both phyllochron and FLN varied according to planting date, with photoperiod being a possible cause of such variation. Within BR1 and BR2 sympodial branches, phyllochron and FLN were not different among stems.

Estimativa do filocrono em calêndula / Estimating the phyllochron in calendula

O objetivo deste trabalho foi estimar o filocrono em plantas de calêndula (Calendula officinalis L.) cultivadas em diferentes épocas de semeaduras. Realizaram-se três épocas de semeaduras: 06/04/2005, 23/06/2005 e 03/10/2006, no interior de uma estufa plástica com área de 240m2, instalada no campus da Universidade Federal de Santa Maria, UFSM. A semeadura foi realizada em vasos plásticos com capacidade volumétrica para cinco litros. O delineamento experimental foi inteiramente casualizado com 320 vasos em cada época, sendo distribuído em quatro fileiras de 80 vasos cada. Em uma planta de oito vasos de cada quatro fileiras, fez-se a contagem, semanalmente, do número de folhas emergidas da haste principal e na primeira haste lateral. Os dados do número de folhas foram correlacionados com a soma térmica diária acumulada, considerando-se uma temperatura base de 8°C. Constatou-se que o filocrono variou com a época de semeadura, sendo o menor valor igual 15,9°C dia folha-1, obtido na 2ª época de semeadura e o maior, igual a 24,5°C dia folha-1, na 1ª época na haste principal e 48,9°C dia folha-1 na semeadura de outubro na primeira haste lateral.

The objective of this study was to estimate the phyllochron in calendula (Calendula officinalis L.) grown in different sowing dates. Three sowing dates (06/04/2005, 23/06/2005 and 03/10/2006) were performed inside a 240m2 plastic greenhouse at the Campus of the Federal University of Santa Maria, RS, Brazil. Sowing was in five liter plastic pots. The experimental design was a completely randomized with 320 pots on each sowing date and rows with 80 pots. The number of leaves in the main stem and oi the first lateral branch was counted on a weekly basis in one plant of eight pots. The number of leaves data was regressed against accumulated thermal time, assuming a base temperature of 8oC. The main stem phyllochron varied with sowing date, with the lowest value (15.9°C day leaf -1) obtained on the second sowing date, and the greatest value (24.5°C day leaf -1) obtained on the first sowing date. The greatest phyllochron on the first order lateral branch was 48.9°C day leaf -1 in the October sowing date.

Emissão de folhas e início de acumulação de amido em raízes de uma variedade de mandioca em função da época de plantio / Leaf emergence and beginning of starch accumulation in roots of a cassava variety as a function of planting date

O número de folhas acumulado (NF) na haste principal está associado com o aparecimento de vários estádios de desenvolvimento da cultura da mandioca. O início de acumulação de amido (IAA) nas raízes tuberosas da mandioca marca o início da translocação dos fotoassimilados para o principal órgão de reserva nessa espécie. O objetivo deste trabalho foi estimar o filocrono e identificar um indicador morfológico baseado no NF para o IAA em mandioca plantada em diferentes épocas. Um experimento a campo foi conduzido em Santa Maria, RS, Brasil, com quatro épocas de plantio (28/09; 11/10; 16/11 e 27/12/2005). A variedade de mandioca usada foi a "RS 13", plantada em baldes de 12 litros, enterrados no espaçamento com 2,0 x 0,8m. O delineamento experimental foi o inteiramente casualizado com 11 repetições. A soma térmica diária (STd, °C dia) foi calculada a partir da emergência e acumulada por: STa = sigmaSTd. O IAA foi determinado nas plantas de cada balde quando uma raiz atingia um diâmetro de 1cm. O NF na data do IAA e o número final de folhas (NFF) até o primeiro simpódio também foram determinados. O filocrono variou de 20,3 a 29,5°C dia folha-1 e seus valores foram maiores quanto mais tardio foi o plantio. O NFF variou entre as épocas de plantio, aumentando com o atraso do plantio. O NF no IAA foi similar nas quatro épocas de plantio e ocorreu quando, em média, o NF corresponde a 20,9 (±1,0) folhas.

The accumulated number of leaves (NF) on the main stem is related to the appearance of several developmental stages in cassava. The beginning of starch accumulation (IAA) in the fibrous roots of cassava switches the source/sink ratio because of the translocation of photoassimilates to the major storage organ in this species. This study was aimed at estimating the phyllochron and identifing a morphological indicator based on NF for IAA in cassava grown in several planting dates. A field experiment was carried out in Santa Maria, RS, Brazil, with four planting dates (28/09, 11/10, 16/11 and 27/12/2005). The variety RS 13 was used and planted in 12 l pots, buried in the soil in a 2.0 x 0.8m spacing. The experimental desing was a completely randomized with 11 replications. Daily degree-days (STd, °C day) were calculated starting at emergency and accumulated by STa = sigmaSTd. IAA was determined on the plants when one root reached a diameter of 0.01m. NF on the date of IAA and the main sterm final leaf number (NFF) up to the first sympodial branches were determined. The plyllochron varied from 20.3 to 29.5°C day leaf -1, with larger values in the two latest planting dates. The NFF varied among planting dates, increasing as planting was delayed. The NF at IAA was similar for the four planting dates and occurred when NF was on average 20.9 (± 1.0) leaves.