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Murviel-lès-Montpellier, France

Clerget B.,ACIRAD | Clerget B.,International Rice Research Institute | Bueno C.,International Rice Research Institute
Functional Plant Biology | Year: 2013

Rice has generally been reported to yield less in aerobic soil conditions than in flooded soil conditions, in association with delayed anthesis and a reduction in height. A greenhouse experiment was conducted and repeated twice with four rice varieties grown in either flooded or nearly-saturated aerobic soil, in either large or small pots. The rate of leaf appearance was recorded weekly until heading time, when plants were harvested for shoot and root biomass. The kinetics of leaf appearance was generally trilinear with longer phyllochrons in the May sowing. Pot size had only a small effect whereas aerobic soil conditions slowed down the rate of leaf initiation, which consequently delayed panicle initiation and heading date and thus increased the duration of the tillering phase and finally the number of tillers. Surprisingly, the four varieties showed a significant response to sowing date, especially IR72, which headed 21 days later and after the expansion of two more leaves in the May sowing. The aerobic soil conditions and sowing date have thus changed the rate of development of rice plants and this trait has appeared to be the initial link of a chain of consequences in a series of traits known to be affected by these factors. © 2013 CSIRO.

Gutjahr S.,ACIRAD | Clement-Vidal A.,ACIRAD | Soutiras A.,ACIRAD | Sonderegger N.,ACIRAD | And 4 more authors.
Functional Plant Biology | Year: 2013

Sugar accumulation in sorghum (Sorghum bicolor (L.) Moench) stems is a complex trait that is particularly plastic in response to photoperiod. This study investigated sucrose accumulation in a sterile (no grain filling) and fertile near-isogenic line of the photoperiod-sensitive cultivar IS2848 in two greenhouse experiments. Variable phenology was induced by applying a short (12-h PP) and a long (13-h PP) photoperiod. Dynamics of plant growth, phenology, sugar accumulation and related enzyme activities in internodes were investigated. Under 13-h PP, plants flowered 28 days later and attained threefold higher sucrose concentration at anthesis compared with those under 12-h PP. Sucrose accumulation in individual internodes was driven by organ physiological age, not by plant phenology. Competition with grain filling was marginal but greater under 12-h PP (i.e. when sucrose accumulation in internodes occurred after flowering). Enzyme activities showed marked developmental patterns but contributed little to explaining differences between treatments and genotypes. The study demonstrates that sucrose storage physiology in sweet sorghum resembles that of sugarcane (Saccharum spp.) but is more complex due to photoperiod effects on phenology. It confirms the field results on 14 sorghum genotypes contrasting for phenology and photoperiod sensitivity presented in a companion paper. Perspectives for developing sorghum ideotype concepts for food and fuel crops are discussed. © 2013 CSIRO.

Combres J.-C.,ACIRAD | Pallas B.,Montpellier SupAgro | Rouan L.,ACIRAD | Mialet-Serra I.,CIRAD - Agricultural Research for Development | And 4 more authors.
Functional Plant Biology | Year: 2013

For oil palm, yield variation is in large part due to variation in the number of harvested bunches. Each successively-produced phytomer carries a female (productive), male or aborted inflorescence. Since phytomer development takes 3-4 years and nearly two phytomers are produced per month, many inflorescences develop in parallel but have different phenological stages. Environment-dependent developmental rate, sex and abortion probability determine bunch productivity, which, in turn, affects other phytomers via source-sink relationships. Water deficit, solar radiation, temperature and day length are considered key external factors driving variation. Their impact is difficult to predict because of system complexity. To address this question we built a simple model (ECOPALM) to simulate the variation in number of harvested bunches. In this model, trophic competition among organs, expressed through a plant-scale index (Ic), drives sex determination and inflorescence abortion during specific sensitive phases at phytomer level. As a supplemental hypothesis, we propose that flowering is affected by photoperiod at phytomer level during a sensitive phase, thus, contributing to seasonal production peaks. The model was used to determine by parameter optimisation the influence of Ic and day length on inflorescence development and the stages at which inflorescences are sensitive to these signals. Parameters were estimated against observation of number of harvested bunches in Ivory Coast using a genetic algorithm. The model was then validated with field observations in Benin and Indonesia. The sensitive phases determined by parameter optimisation agreed with independent experimental evidence, and variation of Ic explained both sex and abortion patterns. Sex determination seemed to coincide with floret meristem individualisation and occurred 29-32 months before bunch harvest. The main abortion stage occurred 10 months before harvest-at the beginning of rapid growth of the inflorescence. Simulation results suggest involvement of photoperiod in the determination of bunch growth dynamics. This study demonstrates that simple modelling approaches can help extracting ecophysiological information from simple field observations on complex systems. © 2013 CSIRO.

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