Day Of Anthesis Research Articles

Pollination ecology of Derris trifoliata (Fabaceae), a mangrove associate in Coringa Mangrove Forest, Andhra Pradesh, India

Derris trifoliata is a perennial woody climber. It blooms massively for about two weeks in July/August. The flowers are hermaphroditic, feebly protandrous, self-compatible and display a vector dependent mixed breeding system. They close back by the end of the day of anthesis. The forenoon anthesis and pollen and nectar as rewards attract daytime foragers. The nectar feeding foragers require strength to depress the keel petals in order to collect nectar; only those foragers which have the required strength to do so can collect nectar and in the process trip the floral mechanism and effect pollination. When floral explosion occurs, the pollen is somewhat exposed and the pollen feeding foragers then collect it. Both long- and short-tongued bees trip the flowers, collect nectar and effect pollination. Individual flowers that were not tripped by insects set fruit to negligible level. In open-pollination mode, fruit set rate is up to 30-31% only despite the flowers being visited by insect pollinators. Fruits mature quickly within a month. Each fruit contains 1-3 seeds against 6 linearly arranged ovules in the ovary. The fruits are leathery and possess air cavities, the characteristics of which enable them to float in tidal water. They settle at the parent plant if the site is partly or fully exposed or float for dispersal if the site is inundated with tidal water. Seed release occurs when fruits absorb water and the pericarp breaks. Seeds germinate only when they reach a suitable habitat in mangroves.

Identification of loci contributing to maize drought tolerance in a genome-wide association study

Genome-wide association studies (GWAS) have been used widely to analyze the genetic control of complex traits in crops. In the present study, seven related phenotypic traits were analyzed in combination to study their association with 41,101 SNPs in 201 maize inbred lines that had been evaluated in seven environments (year/location combinations) under water-stressed (WS) or well-watered (WW) regimes. By comparing the association signals with a fixed P value, GWAS showed that the number of association signals identified varied among traits and in different environments. Data that were missing under the severe water stress treatment had a great impact on the results of this GWAS. A total of 206 significant SNPs were associated with 115 candidate genes for drought tolerance and related traits including final grain yield, total number of ears per plot, kernel number per row, plant height, anthesis-silking interval, days to anthesis (DtA), and days to silking (DtS). Among these, four genes were associated with at least two different related traits, and six genes associated with traits were detected in at least two environments under water stress. Nine candidate QTL identified by GWAS were also discovered, three of which co-located to a consensus QTL region meta-analyzed by linkage mapping for drought tolerance. Some regulatory genes related to abiotic stress responses might also make a strong contribution to drought tolerance. The comprehensive information presented here regarding consensus QTL combined with candidate genes derived from GWAS provides an important reference tool for improving maize drought tolerance.

Expanding Maize Genetic Resources with Predomestication Alleles: Maize-Teosinte Introgression Populations.

Teosinte ( subsp. H. H. Iltis & Doebley) has greater genetic diversity than maize inbreds and landraces ( subsp. ). There are, however, limited genetic resources to efficiently evaluate and tap this diversity. To broaden resources for genetic diversity studies in maize, we developed and evaluated 928 near-isogenic introgression lines (NILs) from 10 teosinte accessions in the B73 background. Joint linkage analysis of the 10 introgression populations identified several large-effect quantitative trait loci (QTL) for days to anthesis (DTA), kernel row number (KRN), and 50-kernel weight (Wt50k). Our results confirm prior reports of kernel domestication loci and identify previously uncharacterized QTL with a range of allelic effects enabling future research into the genetic basis of these traits. Additionally, we used a targeted set of NILs to validate the effects of a KRN QTL located on chromosome 2. These introgression populations offer novel tools for QTL discovery and validation as well as a platform for initiating fine mapping.

Reproductive Biology of <I>Elaeocarpus blascoi</I> Weibel, an Endemic and Endangered Tree Species of Palni Hills, Western Ghats, India

Elaeocarpus blascoi Weibel is a lesser known endemic tree species growing in the Vattakanal shola forest of Palni Hills, Western Ghats, India. A study on reproductive biology of the species was conducted in the natural habitat to study its phenology, floral biology, pollen biology, fruit set and seed germination. Flowers are bisexual, anther dehisces 2-3 hours after anthesis and stigma becomes receptive on the day of anthesis and extends up to 6 days. Breeding experiments confirmed that the species permits autogamy and geitonogamy. Six different pollinators were observed during peak flowering period and Apis dorsata (honey bee) was found to be an effective pollinator and it takes 55 ± 15 sec per flower. Percentage of fruit set observed in the natural habitat was 78% and seed germination rate was found to be less than 5% in the natural habitat. Tests showed that more than 70% of seeds lost their viability after a year and most of the seeds were infested with Fusarium sp., Lasiodiplodia sp. and Penicillium sp. Further, the natural habitat of the species is altered by commercial plantations, tourism and urbanization in the Palni Hills, which leads to their reduction.

NYMPHAEA REVISITED: A PRELIMINARY COMMUNICATION

ABSTRACT A number of pollination syndromes within the genus Nymphaea are examined. Adaptive radiation has created a wide range, from beetle-pollination with production of solid food bodies for the visitors to pollination by small Hymenoptera and syrphid flies with production of a pool of stigmatic fluid in which, on the first day of anthesis when the flower is functionally pistillate, pollinators drown. In the latter category, there is striking sophistication in the features that ensure proper deposition and germination of the pollen grains. In the tropical water lilies examined, the sugar level of the stigmatic fluid was 1%-1.5% which is well below the threshold of perception for honeybees regardless of the nature of the sugar; fructose and glucose were present in roughly equal concentrations. In Nymphaea odorata, a temperate zone water lily, the sugar concentration was about 3%, a considerable part of which was sucrose; glucose and fructose were again present in almost equal concentrations. No obvious b...

Changes in protein quantities of phosphoenolpyruvate carboxylase and Rubisco activase in various wheat genotypes.

In early seedlings of wheat genotypes two isoforms of Rubisco activase with molecular weights of 42 and 46 kDa are expressed. Amounts of both isoforms significantly increase in early seedlings of the durum wheat genotype Barakatli-95 exposed to salt stress. But at the beginning of the tillering stage, the changes in quantities of both RCA isoforms are different in durum and bread wheat genotypes subjected to a 3-day drought stress. In the leaves of the early seedlings of the studied wheat genotypes exposed to drought stress quantities of PEPC subunits increase compared to the control but they remain relatively stable in early roots and germinating seeds. However, quantities of its subunits decrease sharply in roots and germinating seeds of early seedlings under the influence of 100 mM NaCl. In flag leaves and ear elements of the Barakatli-95 genotype grown under normal water supply conditions protein quantities of PEPC subunits change differently depending on time. Changes in protein quantities of RCA, PEPC and Rubisco enzymes have been studied comparatively in ear elements and flag leaves after the fourth day of anthesis.

Is the pollination efficiency of long-lived orchid flowers affected by age?

The long-lived flowers of orchids increase the chances of pollination and thus the reproductive success of the species. However, a question arises: does the efficiency of pollination, expressed by fruit set, vary with the flower age? The objective of this study was to verify whether the flower age of Corymborkis flava(Sw.) Kuntze affects pollination efficiency. The following hypotheses were tested: 1) the fruit set of older flowers is lower than that of younger ones; 2) morphological observations (perianth and stigmatic area), stigma receptivity test by using a solution of hydrogen peroxide and hand-pollination tests are equally effective in defining the period of stigmatic receptivity. Flowers were found to be receptive from the first to the fourth day of anthesis. Fruit set of older flowers (third and fourth day) was lower than that of younger flowers. Morphological observations, the stigma receptivity test and hand-pollinations were equally effective in defining the period of stigmatic receptivity. However, to evaluate the maximum degree of stigma receptivity of orchid species with long-lived flowers, we recommend hand-pollinations, beyond the period of receptivity.

Pollination Activity ofElaeidobius kamerunicus(Coleoptera: Curculionoidea) on Oil Palm on Hainan Island

Abstract Elaeidobius kamerunicus Faust (Coleoptera: Curculionidae), the pollinating weevil, is the most efficient insect pollinator of oil palm, Elaeis guineensis Jacq. (Arecales: Arecaceae). In this experiment, the pollinating activity of E. kamerunicus was observed in an oil palm field in Hainan, China, in order to further understand the dynamics of the weevil's behavior on inflorescences. Both male and female inflorescences emitted an anise-like fragrance. Female inflorescences appeared to reward the weevils with copious nectar production, whereas male inflorescences appeared to do so with both nectar and pollen. The number of weevils visiting an inflorescence was assessed by the use of a sticky trap encircling it, and by counting the weevils present on samples of spikelets of inflorescences. The weevil population peaked on the 3rd day of anthesis on male inflorescences, and on the 2nd day of anthesis on female inflorescences. Weevil activity recorded on the day of highest abundance during anthesis rev...

Mapping-by-sequencing of Ligon-lintless-1 (Li 1 ) reveals a cluster of neighboring genes with correlated expression in developing fibers of Upland cotton (Gossypium hirsutum L.).

Mapping-by-sequencing and SNP marker analysis were used to fine map the Ligon-lintless-1 ( Li 1 ) short fiber mutation in tetraploid cotton to a 255-kb region that contains 16 annotated proteins. The Ligon-lintless-1 (Li 1 ) mutant of cotton (Gossypium hirsutum L.) has been studied as a model for cotton fiber development since its identification in 1929; however, the causative mutation has not been identified yet. Here we report the fine genetic mapping of the mutation to a 255-kb region that contains only 16 annotated genes in the reference Gossypium raimondii genome. We took advantage of the incompletely dominant dwarf vegetative phenotype to identify 100 mutants (Li 1 /Li 1 ) and 100 wild-type (li 1 /li 1 ) homozygotes from a mapping population of 2567 F2 plants, which we bulked and deep sequenced. Since only homozygotes were sequenced, we were able to use a high stringency in SNP calling to rapidly narrow down the region harboring the Li 1 locus, and designed subgenome-specific SNP markers to test the population. We characterized the expression of all sixteen genes in the region by RNA sequencing of elongating fibers and by RT-qPCR at seven time points spanning fiber development. One of the most highly expressed genes found in this interval in wild-type fiber cells is 40-fold under-expressed at the day of anthesis (DOA) in the mutant fiber cells. This gene is a major facilitator superfamily protein, part of the large family of proteins that includes auxin and sugar transporters. Interestingly, nearly all genes in this region were most highly expressed at DOA and showed a high degree of co-expression. Further characterization is required to determine if transport of hormones or carbohydrates is involved in both the dwarf and lintless phenotypes of Li 1 plants.

Ultrastructure of the stigma and style of Cabomba caroliniana Gray (Cabombaceae).

Cabomba Aubl. is a genus that presents a range of features that have made it to be considered a potential genetic model for studies of early angiosperm evolution. Therefore, any study that expands our knowledge of this genus is potentially useful for the understanding of the evolution of early angiosperms. This paper reports the study of the anatomy and the ultrastructure of the stigma and the style of Cabomba caroliniana Gray during the 2 days of anthesis using bright-field microscope, fluorescence microscope and transmission electron microscope. The stigma is dry and has pluricellular papillae. The style is hollow with a central canal coated by an epithelium. The papillae have fewer organelles than those typical of glandular cells, and they are covered by a cuticle that is broken when pollen germinates. The ultrastructure of epithelial cells indicates that the cells lining the canal are secretory. The canal is filled with a fibrillar and granular substance. The pollen tubes grow inside the canal through this substance. The results are discussed in the context of what is known for other species of angiosperms.

Changes in physicochemical attributes of sweet pepper (Capsicum annum L.) during fruit growth and development

Changes in physicochemical attributes of sweet pepper var. ‘BARI Misti Morich-1’ during fruit growth and development were studied. Capsicum flowers were tagged on the day of anthesis and fruits were harvested at three days interval started on 33 days after anthesis (DAA) until 48 DAA, when turned to light green colour. Length, diameter, and weight of fruits were linearly increased from 33 DAA to 48 DAA. Dry matter content, TSS, firmness, and shelf life of fruits were also gradually increased with lengthen the harvesting time from flower anthesis and reached from 5.1 to 7.3%, 4 to 5%, 7.1 to 14.5 kgf cm-2 and 9.6 days to 21.3 days, respectively, from 33 DAA to 48 DAA. However, ascorbic acid content of fruits was sharply decreased from 68 to 56 mg/100g from first harvest to last harvest, respectively. Hue angle declined with time while chroma and lightness values increased with fruit maturity. Considering all physical and nutritional characteristics and shelf life along with sensory evaluation scores, fruits of BARI Misti Morich-1 was found suitable to harvest after 45 days of anthesis, when they attained length 12.2 cm, diameter 8.8 cm, and weight 191g. Moreover, fruits were crispier, glossy with attractive colour and flavour and contained 58 mg/100g ascorbic acid at this maturity stage. DOI: http://dx.doi.org/10.3329/bjar.v39i2.20446 Bangladesh J. Agril. Res. 39(2): 373-383, June 2014

Morphological strategies of Cabomba (Cabombaceae), a genus of aquatic plants

This paper describes the vegetative and reproductive morphology of Cabombaceae species in Brazil, discussing its strategies for survival in an aquatic habitat. Through studies in the field, in cultivation and in the herbarium, we examined the following species: Cabomba aquatica, C. caroliniana, C. furcata and C. haynesii. In cultivation, only C. aquatica, C. furcata and C. haynesii produced flowers. In those three species, the flowers opened during the day on two consecutive days, submerging during the night, although the stigmata of the first two were receptive only on the first day, their anthers dehiscing on the following day. The flowers of C. haynesii remained unreceptive on the first day of anthesis, the stigmata and anthers maturing only on the second day, at different times. Fruit developed when the flowers were submerged. The data provided here are useful for the identification of these species, as well as laying the groundwork for future taxonomic and ecological studies.

Nectar secretion dynamic links pollinator behavior to consequences for plant reproductive success in the ornithophilous mistletoe Psittacanthus robustus

The mistletoe Psittacanthus robustus was studied as a model to link flower phenology and nectar secretion strategy to pollinator behaviour and the reproductive consequences for the plant. The bright-coloured flowers presented diurnal anthesis, opened asynchronously throughout the rainy season and produced copious dilute nectar as the main reward for pollinators. Most nectar was secreted just after flower opening, with little sugar replenishment after experimental removals. During the second day of anthesis in bagged flowers, the flowers quickly reabsorbed the offered nectar. Low values of nectar standing crop recorded in open flowers can be linked with high visitation rates by bird pollinators. Eight hummingbirds and two passerines were observed as potential pollinators. The most frequent flower visitors were the hummingbirds Eupetomena macroura and Colibri serrirostris, which actively defended flowering mistletoes. The spatial separation between anthers, stigma and nectar chamber promotes pollen deposition on flapping wings of hovering hummingbirds that usually probe many flowers per visit. Seed set did not differ between hand-, self- and cross-pollinated flowers, but these treatments set significantly more seeds than flowers naturally exposed to flower visitors. We suggest that the limitation observed in the reproductive success of this plant is not related to pollinator scarcity, but probably to the extreme frequency of visitation by territorial hummingbirds. We conclude that the costs and benefits of plant reproduction depend on the interaction strength between flowers and pollinators, and the assessment of nectar secretion dynamics, pollinator behaviour and plant breeding system allows clarification of the complexity of such associations.

Anther characteristics and spikelet fertility in rice (Oryza sativaL.) under high temperature stress at anthesis

The effect of high temperature at anthesis on spikelet fertility was studied in 22 rice genotypes selected from 98 heat tolerant genotypes. Genotypes were grown in field under natural conditions in Randomized Block Design replicated twice till vegetative stage. Before booting stage, few plants were transferred to pots and placed in polyhouse for high temperature treatments. On the first day of anthesis (i.e. the appearance of anthers), plants were transferred into polyhouse with temperatures gradually increasing from 29°C to 40°C and maintained at 40°C until 15 h, with a relative humidity of 75 percent. Seven genotypes viz., IR 86970-145-1, IR 86977-140-2, IR 86977-141-3, IR 86977-95-1, IR 86970-126-3, IR 86977-92-3 and IR 86977-104-1 exhibited 20 to 40 per cent spikelet fertility after exposure to high temperature of 40°C.The pollen fertility ranged from 39.0 to 90.5 per cent. The genotype IR 86970-145-1 had significant value for anther length (2.125) and anther breadth (0.320). Anther dimensions seem to have an influence on anther dehiscence, pollen and spikelet fertility. All other genotypes were found to be sterile with no seed set. Exposure to high temperature during heading has significantly reduced the spikelet fertility but there were genotypic differences.

Effect of pistil age on pollen tube growth, fruit development and seed set in Cucurbita pepo L.

The effects of pistil age on pollen tube growth, fruit development and seed set were studied in <em>Cucurbita pepo</em> L., the flower of which opens for only six hours. Stigma receptivity lasts four days, from one day before until two days after anthesis. Style receptivity lasts three days, from the day before to the day after anthesis. Ovule receptivity lasts two days: the day of anthesis and the day before. The rate of pollen tube growth varies in different parts of the pistil and in relation to pistil age. In the stigmatic and stylar region, the tubes grow faster if pollination occurs the day before anthesis; in the ovary they grow faster when pollination occurs at anthesis. In the receptacle region, where the transmitting tissue is reduced, the growth rate decreases independently of the time of pollination. The fruits are larger and heavier with more seeds when pollination occurs at anthesis. There is a positive correlation between seed number and fruit weight when pollination occurred at anthesis and the day before.

English

To provide theoretical basis for artificial pollination in Lagerstroemia indica L., pollen viability and stigma receptivity were tested and the morphological change of stigma was observed. Pollen viability tested by in vitro culture, stigma receptivity examined by benzidine-H2O2 testing and fruit set estimated by field artificial pollination were analyzed in this study. The maximum pollen viability was observed at 10:00 am one day of anthesis (DA), of which ‘Hong Wei’ (46.2%) was significantly lower than that of ‘Yin Wei’ (56.8%) and ‘Zi Wei’ (62.5%). The stigma receptivity of the three crape myrtle cultivars was sustained for eight days, which was 95.7 to 96.9% at 1 DA to two days after anthesis (DAA), then declined to 75.5 to 79.9% at 3 to 4 DAA and 50.6 to 59.7% at 5 to 6 DAA, and only 29.5% at 7 DAA. Higher stigma receptivity was associated with columnar style, upward stigma, green and wet papillae and copious exudates at stage 1 (1 DA to 2 DAA). Frequencies of fruit set at stage 1 (74.4%) and stage 2 (3 to 4 DAA) (78.9%) were significantly higher than that at stage 3 (5 to 6 DAA) (21.9%). So, selecting pollen at 10:00 am 1 DA and stigma of 1 DA to 4 DAA was a strategy to enhance fruit set in the future artificial hybridizations for crape myrtle.   Key words: Lagerstroemia indica L., dimorphic pollen, pollen viability, stigma receptivity, fruit set.

Modeling the sensitivity of CERES-Rice model: An experience of Nepal

The experiment was conducted with four levels of nitrogen (40, 80,120 and 160 kg/ha) and 3 different cultivars (Prithivi hybrid), Masuli (HYV) and Sunaulo Sugandha (Aromatic).RMSE value (747.35 kg/ha, 1.106 days, 2.58 days and 0.004 kg/ha) and D-stat value (0.793, 0.99, 0.99 and 0.633) for grain yield, anthesis days, maturity days, and individual grain weight respectively. The objective of this study was to identify whether CSM-CERES-Rice model can be used in Nepalese condition and to evaluate the sensitivity of model with impact of climate change on rice production. Eight different climate scenarios were built by perturbing maximum and minimum temperature (± 4°C), CO2 (± 20ppm), solar radiation (±1MJ/m2/day) using interactive sensitivity analysis mode in DSSAT. Among the scenario evaluated, temperature (± 40°C), CO2 concentration (+20 ppm) with change in solar radiation (±1MJ m-2 day-1) resulted maximum increase in yield (by 62, 41 and 42%) under decreasing climatic scenarios and sharp decline in yield (by 80, 46 and 40%) was observed under increasing climate change scenarios, in Prithivi, Masuli and Sunaulo Sugandha cultivars respectively.Not surprisingly, increasing yield by (48, 25 and 27 %) and decrease in yield by(77, 41 and 34) by perturbing only maximum and minimum temperature by (± 4) shows that the temperature is most sensitive for yield potentiality of cultivars than other. CERES-Riceversion 4.0 was well calibrated in Chitwan Nepal condition. The model applications show that model could be a tool for precision decision-making. There was variation in yield in response to the change in climatic scenario in the study. RMSE value (747.4 kg/ha, 1.11days, and 2.58 days), and d-stat (0.79, 0.99 and 0.99) for grain yield, anthesis, and maturity days confirm the possibility of CERESRiceuse in Nepalese agriculture. The finding showed that there was sharp decrease in rice yield due to change in temperature, CO2 and solar radiation. Climatic scenario developed by CERES-Rice model in sensitivity analysis resulted yield reduction up to 80%. Among the cultivar, hybrid rice shows more vulnerability with climate change. Decrease in yield were mainly associated with lowering growth duration along with increasing temperature, where as there is very less counter effect of increasing carbon dioxide concentration and solar radiation. Agronomy Journal of Nepal (Agron JN) Vol. 3. 2013, Page 11-22 DOI: http://dx.doi.org/10.3126/ajn.v3i0.8982

Comparative anatomy of the floral elaiophore in representatives of the newly re-circumscribed Gomesa and Oncidium clades (Orchidaceae: Oncidiinae)

Recently, molecular approaches have been used to investigate the phylogeny of Oncidiinae. This has resulted in the transfer of taxa previously considered to be species of Oncidium Sw. into Gomesa R. Br. and the re-circumscription of both genera. In this study, the structure of the floral elaiophore (oil gland) is described and compared for Gomesa echinata (Barb. Rodr.) M.W. Chase & N.H. Williams, G. ranifera (Lindl.) M.W. Chase & N.H. Williams, Oncidium amazonicum (Schltr.) M.W. Chase & N.H. Williams and O. oxyceras (Königer & J.G. Weinm.) M.W. Chase & N.H. Williams in order to determine whether phylogenetic revision is supported by differences in its anatomy. The floral elaiophore structure was examined and compared at three developmental stages (closed bud, first day of anthesis and final stage of anthesis) for all four species using light microscopy, fluorescence microscopy, scanning electron microscopy, transmission electron microscopy and histochemistry. In all species investigated, the floral elaiophore occurs on the labellar callus and is of the epithelial type, comprising cuboidal to palisade-like, secretory epidermal cells and a layer of sub-epidermal cells, both tissues enclosing ground parenchyma supplied with collateral vascular bundles and containing idioblasts, often with raphides or phenolic contents. A bi-layered cuticle comprising an outer, lamellate and an inner, reticulate layer is present, and sub-cuticular accumulation of secreted material results in distension of the cuticle. Secretion-filled cavities are present at anthesis in the elaiophore cell walls and, in most species, the outer, tangential walls of the elaiophore have small, peg-like projections that protrude into the cytoplasm. In all taxa examined, the elaiophore organelle complement, especially the smooth endoplasmic reticulum (SER), is typical of lipid-secreting cells. In terms of location, morphology, anatomy and ultrastructure, the floral elaiophores of both Gomesa and Oncidium species examined are very similar, and distinction between these genera is not possible based on elaiophore features alone. Furthermore, many of these elaiophore characters are shared with representatives of other clades of Oncidiinae, including the Ornithocephalus clade. Consequently, elaiophores are considered homoplasious and of limited value in investigating the phylogeny of this subtribe.

Spatial Distribution of Calibrated WOFOST Parameters and Their Influence on the Performances of a Regional Yield orecasting System

We investigate in this study (i) a redefinition of crop variety zonations at a spatial scale of 10x10 km, and (ii) the influence of recalibrated crop parameters on regional yield forecasting of winter wheat and grain maize in western Europe. The baseline zonation and initial crop parameter set was derived from the operational European crop growth monitoring system (CGMS) which involves the agrometeorological model WOFOST. Air temperature data from 325 weather stations over the 1992-2007 period were used to define new zonations in a 300 x 300 km test site. Two parameters which influenced mostly the phenological development stages (i.e. TSUM1 and TSUM2, the effective air temperature sums from emergence to anthesis, and from anthesis to maturity, respectively) were chosen and calibrated. The CGMS was finally run based on these new recalibrated parameters and simulated crop status indicators were compared with official statistics over the 2000-2007 period. Our results showed that the days of anthesis and maturity were simulated with coefficients of determination (R2) ranging from 0.22 to 0.87 for both crops over the study site. A qualitative assessment of maximum leaf area index and harvest index also revealed a more consistent spatial pattern than the initial zonation in the simulation results. Finally, recalibrated TSUM1 and TSUM2 led to improved relationships between official yield and simulated crop indicators (significant R2 in 17 out of 28 and in 14 out of 59 NUTS3 regions with respect to the best predictor for grain maize and winter wheat, respectively).

Predicting temperature induced sterility of rice spikelets requires simulation of crop-generated microclimate

Extreme temperatures cause spikelet sterility in rice and thus yield losses. Predicting sterility is difficult because organ temperature may differ from air temperature. Four rice genotypes were planted under irrigated flooded conditions in a similar replicated design in four environments: the relatively humid dry season in the Philippines, the summer season in southern France and the cold-dry and hot-dry seasons in northern Senegal. Panicle temperature was measured by IR photography on ca. 4000 images, complemented with simultaneous monitoring of micro-climatic variables on the floodwater-canopy-air continuum. Spikelet sterility was observed at the population scale at grain maturity, and canopy morphology was also characterized (plant height, leaf area index, panicle position within the canopy and panicle exertion). The period and time of day of anthesis (TOA) was estimated using a model developed on the same experiments as described in a previous paper. Panicle temperature varied between 9.5°C below and 2°C above air temperature at 2m. During TOA it was on average slightly warmer than the air in the Philippines and significantly colder in Senegal. Spikelet sterility was disaggregated into three components caused by chilling at microspore stage, incomplete panicle exertion at anthesis and high panicle temperature at anthesis. Chilling caused up to 100% and heat up to 40% sterility, the former mainly in the Senegal cool-dry season and the latter in the Philippines. All genotypes avoided heat sterility in the hot-dry season in Senegal despite air temperatures up to 40°C, by a combination of escape (early TOA) and avoidance (transpiration cooling). Only one genotype had no chilling induced sterility due to physiological tolerance. It is concluded that heat stress causing sterility is more likely to occur in warm-humid than hot-arid environments due to humidity effects on transpiration cooling. Models predicting global warming effects on sterility losses need to consider microclimate and organ temperature, and research is now needed on the genetic control of panicle transpiration cooling