Drought is a major abiotic stress worldwide limiting chickpea yield drastically. Low heritability and high genotype × environment interactions make the trait-based breeding strategy an unreliable approach. This study was planned to identify the drought-tolerant lines by evaluating yield-based selection indices in a recombinant inbred line (RIL) population derived from an inter-specific cross between drought-tolerant genotype GPF 2 (Cicer arietinum L.) and drought-sensitive accession ILWC 292 (C. reticulatum) at two locations in India (Ludhiana and Faridkot). A total of six yield-based selection indices were calculated and significant variation was observed in the RILs and their parents for yield-based selection indices at both locations. A holistic approach across association analysis and principal component analysis identified drought tolerance index, mean productivity, geometric mean productivity and harmonic mean productivity as key selection indices, which could be used for indirect selection of drought-tolerant lines. Overall, on the basis of these approaches, a total of 15 promising RILs were identified for their use in chickpea breeding programme for developing drought-tolerant cultivars.

Emmer wheat (Triticum turgidum ssp. dicoccum) is one of the most promising gene sources for drought tolerance improvement of durum wheat (Triticum turgidum ssp. durum). Achieving desired results requires a conscious choice of crossing parents based on general and specific combining ability (GCA and SCA) and also understanding the genes action involved in controlling the desired traits. In this study a 12 × 12 full diallel cross was performed using four emmer and eight durum wheats. The 132 hybrid progenies along with their parental lines were field evaluated under water-stressed and non-stressed conditions. Based on the Griffing diallel analysis both GCA and SCA effects were highly significant for all measured traits under both water treatments indicating possibility of improvement for drought tolerance. In this respect, the amount of additive effect was higher than the non-additive suggesting the chance for genetic advancement through selection. Based on Hayman's graphical analyses under the two water conditions it was revealed that several grain yield component traits were under the control of partial dominance. In contrary, grain yield and most morphological traits showed either dominance or over-dominance gene action. Grain yield had a significant positive correlation with the number of kernels per spike, kernel diameter, grain weight per spike and harvest index. These traits also had greater share of additive effects, relatively high narrow-sense heritability and high Baker ratio suggesting effective indirect selection for grain yield. Most durum × emmer hybrids had grain yield and drought tolerance indices better than the parents indicating that Iranian emmer wheats have a great genetic potential for drought tolerance improvement of durum wheat.

Cotton fibre yield and quality are markedly influenced by drought and high-temperature stress. We examined the traits of the leaf stomata in 39 cotton genotypes subjected to exogenous phytohormone abscisic acid (ABA) signalling, electrolyte leakage under 40°C thermal stress, and relative GhHsfA, GhbZIP and GhHSP70 expression levels under two treatments. Stomatal density and area ranged from 66 to 182/mm2 and 663 to 1305 μm2, respectively. Under exogenous ABA signalling, the changes in stomatal aperture (ΔSAp) were in the range of 2.5–31.2%; ΔSAp and relative GhHsfA, GhbZIP and GhHSP70 expression levels were significantly correlated, respectively. Electrolyte leakage increased unequally among cotton genotypes after heat stress. The changes in electrolyte leakage (ΔEL) and relative GhHsfA, GhbZIP and GhHSP70 expression levels were very strongly correlated, respectively. Their relative expression levels could be used as references for the rapid identification of stress-tolerant cotton strains. Cluster analysis of the 39 cotton genotypes indicated that Xinluzao36, Shiyang1, shinong98-7 and Zhongmiansuo293 are heat- and drought-resistant. We integrated both analysis of physiological parameters and molecular methods to identify cotton varieties with the drought and heat tolerance, in order to provide a reference for the selection of materials and methods for the research and production of cotton.

Climate change realities such as high-temperature levels are among the causes of drought episodes affecting the productivity and yield stability of crops worldwide. Breeders, therefore, have a daunting challenge to overcome and a large gap to seal in the agricultural sector arising due to drought through the improvement of new tolerant germplasm. It is in this endeavour that the present study, which included nine winter wheat genotypes grown in the greenhouse, was conducted to evaluate their performance under well-watered and drought stress treatments for the traits: heading time, plant height, above-ground biomass, seed number/plant, grain yield/plant, harvest index, root length and root dry mass. A lower grain yield/plant was observed for each studied genotype under drought stress conditions than for those under well-watered conditions. Additionally, grain yield/plant depression varied from 69.64 to 81.73% depending on the genotype. Positive significant correlations between grain yield/plant and heading time, above-ground biomass, and seed number/plant under the drought stress treatment were obtained. Genotypes that recorded high root dry mass had both high above-ground biomass and seed number/plant under drought stress conditions. Positive correlations between grain yield/plant depression and plant height, seed number/plant, and harvest index depressions were also observed. Grain yield for each genotype under drought stress conditions was recorded, and the varieties ‘Plainsman V.’, ‘GK Berény’ and germplasm ‘PC61’, ‘PC110’ showed the best drought tolerance. These genotypes and germplasm will be used in different drought tolerance experiments and breeding programmes.

A set of durum wheat genotypes from New South Wales (NSW, Durum Breeding Australia (DBA) Northern Program), South Australia (SA, DBA Southern Program and Australian Grain Technology), ICARDA and CIMMYT (International Centre for Research in Dryland Agriculture and International Centre for Maize and Wheat Improvement) was evaluated over 3 years (2012–2014) in field trials containing rainfed and watered blocks in Narrabri, NSW, Australia. Data on yield and other agronomic traits were analysed using a multi-environment trial approach that accommodated the factorial treatment structure (genotype by irrigation regime) within individual trials. Considerable variation was observed in the durum germplasm for productivity and grain quality traits. DBA Bindaroi (NSW) and 101042 (ICARDA) were the top yielders in watered and rainfed blocks, respectively. The yield was positively and strongly related to both harvest index and grains/m2, but grains/m2 was negatively related to thousand grain weight (TGW) and positively related to screenings. TGW and screenings were strongly negatively related and TGW and grains/m2 showed a weak positive relationship. Promising genotypes were identified, with superior traits to both the bread wheat check, EGA Gregory and the durum check, Caparoi. Overall, lines from SA and ICARDA were superior for yield but those from NSW were superior for quality parameters including TGW and screenings. These results suggested the possibility of developing high yielding high-quality durum varieties by crossing NSW lines with SA, CIMMYT and ICARDA lines through simultaneous selection for yield, TGW and low screenings. The results also suggested that productivity in rainfed conditions was positively related to productivity under watering, but further research is required to establish this.

Characterizing the whole genetic architecture of drought tolerance (DT) is a persistent challenge for the breeders. Here we developed a half-sib population comprising of 404 lines of two recombinant inbred line (RIL) populations with M8206 as the joint parent (M8206 × TongShan and ZhengYang × M8206) and tested for its DT under sand culture. The population was sequenced using restriction-site-associated DNA sequencing filtered with minor allele frequency ≥0.01; 55,936 single nucleotide polymorphisms (SNPs) were obtained and assembled into 6137 SNPLDBs (SNP linkage disequilibrium blocks). The restricted two-stage multi-locus genome-wide association analysis characterized with error and false-positive control identified 40 QTLs with 93 alleles on an average of 34.75% of the phenotypic variance (PV) collectively for relative root length (RRL) and relative shoot length (RSL) that served as potential DT indicators. Among these, eight loci corresponded to previously reported QTLs, whereas 32 loci were therefore novel. The identified QTLs with their corresponding alleles for RRL and RSL were organized into QTL-allele matrices, depicting the comprehensive DT genetic architecture of the three parents/half-sib population. From the matrices, we predicted the possible best/optimal genotype with weighted average value (WAV) 1.553 over two indicators, while for the top 10 single crosses among RILs with 95th percentile WAV was 1.218–1.257, transgressive over the parents (0.693–0.794) yet much less than 1.553. From the detected QTL-allele system, 65 potential candidate genes collectively for both indicators explaining on an average of 24.41% PV were annotated and χ2-tested as a DT candidate gene system involving nine biological processes.

Early-maturing provitamin A (PVA) quality protein maize (QPM) hybrids with combined drought and low soil nitrogen (low-N) tolerance are needed to address malnutrition and food security problems in sub-Saharan Africa (SSA). The current study's objectives were to (i) examine combining ability of selected early maturing PVA-QPM inbreds for grain yield and other agronomic traits under drought, low-N, optimal environments and across environments, (ii) determine gene action conditioning PVA accumulation under optimal environments, (iii) classify inbreds into heterotic groups and identify testers and (iv) assess yield and stability of hybrids across environments. Ninety-six hybrids generated from 24 inbred lines using the North Carolina Design II together with four commercial hybrid controls were evaluated under drought, low-N and optimal environments in Nigeria in 2016 and 2017. Fifty-four selected hybrids were assayed for PVA carotenoid and tryptophan content. Additive genetic effects were greater than non-additive effects for grain yield and most agronomic traits under each and across environments. The gene action conditioning accumulation of PVA carotenoids under optimal growing conditions followed a pattern similar to that of grain yield and other yield-related traits. The inbred lines were categorized into four heterotic groups consistent with the pedigree records and with TZEIORQ 29 identified as the best male and female tester for heterotic group IV. No tester was found for the other groups. Hybrid TZEIORQ 24 × TZEIORQ 41 was the highest yielding and most stable across environments and should be further tested for consistent performance for commercialization in SSA.

Drought is the major abiotic constraint to the rice production in the rain-fed areas across Asia and sub-Saharan Africa. Wild species of Oryza offer a wide spectrum of adaptive traits and can serve as potential donors of biotic and abiotic stress tolerance. At the Punjab Agricultural University, we are maintaining an active collection of 1630 accessions of wild species germplasm (AA, CC, BBCC and CCDD) of rice. These accessions were screened to assess genetic variation for drought tolerance under field conditions. Severe water stress was imposed at the late vegetative stage by withholding water initially for 25 d and then extended further to 35 d during kharif season in the years 2013–14 and 2015–16. The tolerance score for drought stress was based on the extent of leaf rolling and leaf drying. Based on the 2 years’ data, seven accessions from Oryza rufipogon, four from Oryza longistaminata and one each from Oryza officinalis and Oryza latifolia were found tolerant to drought stress. These selected accessions were further phenotype for root morphology. The average root length among the selected accessions ranges between 36 and 80 cm and the number of primary roots vary from 30 to 87 cm. The O. rufipogon accession IRGC 106433, O. longistaminata accession IRGC 92656A, O. officinalis accession IRGC 101152 and O. latifolia accession IRGC 80769 showed approximately 2–2.5 times longer root length and number than the indica rice elite cultivar PR121. The results indicated potentiality of selected wild species germplasm for conferring drought tolerance to the elite cultivars.

Cowpea is a major source of vegetable protein but its production is constrained by drought resulting in yield loss. Developing drought tolerance varieties can enhance yield and reduce the need for supplemental irrigation. Breeding for drought tolerance requires the knowledge of its genetic basis. Genetic basis for some seedling traits in cowpea was investigated. Seven generations (P1, P2, F1, RF1, F2, BC1 and BC2) each derived from two crosses involving two highly drought tolerant (Danilla and IT97K-499-35) and one highly susceptible parents (Tvu7778) were evaluated for drought tolerance in the screen house. Data on Seedling height (SH), Seedling terminal leaflet area (SLA), Seedling Vigour (SV) and Recovery Capacity (RC) were collected. The SV was assessed on a scale of 1 (highly-tolerant) – 9 (highly-susceptible), while RC (%) was evaluated at 5 d interval for 30 d. The hybrids F1 and RF1 showed the best performances in both crosses with SV ranged from 2.50 ± 0.00 in Danilla × IT97K-499-35 cross to 6.50 ± 1.00 in the Danilla × TVU7778 cross. In both crosses, F1 and RF1 had 100.0% RC. Both dominance (46.5–68.6%) and additive (31.4–53.5%) effects were found similar and important in all the traits under water stressed. The six-parameter model indicated few cases of gene interactions, mostly dominance × dominance. Narrow sense heritability ranged from 33.5% for SH to 50.1% for SLA in the cross Danilla × TVU7778 at terminal water stress. Inheritance of these traits in cowpea involved both additive and dominance gene action. However, dominance and/or dominance × dominance effects had a more pronounced effect in genetic control of all characters.

Stress caused by early weed competition is known to delay the rate of maize development which may result in a decrease in kernel number. Kernel number in maize is correlated negatively with the length of the anthesis-silking interval (ASI). A short ASI has been identified as an easily measured, visual trait which may identify enhanced drought tolerance in maize. Field studies were conducted to test whether: (1) delaying weed control would result in a lengthening of ASI in both a drought tolerant and non-drought tolerant maize hybrid and (2) the presence of drought tolerance genetics comes at a physiological cost, resulting in a greater yield reduction under weedy conditions. In this study, the response of a drought tolerant hybrid with its non-drought tolerant near-isoline was compared to seven different timings of weed control using wheat as a surrogate competitor. Results confirmed that there was no treatment by hybrid interaction at any site–yr for any of the parameters evaluated. Delaying weed control reduced plant height, leaf tip number, shifted and reduced biomass accumulation, kernel number and grain yield and lengthened ASI for both hybrids. Although yield losses occurred with the delay in weed control timing, no yield differences were observed between hybrids suggesting that there was no additional physiological cost associated with the drought tolerant traits. The drought tolerant hybrid, however, was found to have a shorter ASI, lower kernel number and higher kernel wt compared to the non-drought tolerant hybrid. This study confirmed that delaying weed control can influence the length of ASI, which is an important drought tolerant trait. The lengthening of ASI by early weed competition resulted in a rate of yield loss of 0.13 T ha−1 growing degree days (GDD)−1 when averaged across both hybrids and all treatments.

Drought remains the most important factor that affects rice productivity, especially in rainfed areas, worldwide. Upland rice is one of the crop choices of farmers in the rainfed environment. Although upland rice varieties require less water than lowland rice varieties, yields often remain limited by drought, particularly in the period of early growth. The aims of this study were to identify the traits related to early drought tolerance in upland rice varieties, and to identify the potential sources of germplasm for early drought tolerance. A total of sixty upland rice varieties were planted in a factorial experiment with a randomized complete block design with 3 replications in the rainy seasons of 2011 and 2012, under greenhouse conditions. Based on the drought tolerance index (DTI), the test germplasm sources were classified into three groups: (i) susceptible; (ii) moderately tolerant; (iii) tolerant to drought stress. Grain yield (GY) showed significant negative correlations with the leaf rolling score (r= − 0.623, P< 0.01), the leaf death score (LDS) (r= − 0.673, P< 0.01) and the recovery score (r= − 0.746, P< 0.01), while leaf dry matter (r= 0.698, P< 0.01) and leaf water potential (r= 0.618, P< 0.01) had significant positive correlations with GY. These findings indicate the suitability of the DTI as the selection criteria for early drought tolerance in a breeding programme. In addition, the upland rice germplasm accessions KKU-ULR011, KKU-ULR012, KKU-ULR125, KKU-ULR199 and KKU-ULR292 were identified as having high levels of stability for drought tolerance in both the 2011 and 2012 experiments, suggesting their potential for further use for rice variety improvement for drought tolerance.

This review uses production and climate data to examine global and local production trends that can be related to events such as drought. UK grain quality data is also available and provides an overview of trends in protein content. Literature surveys show a consistent reduction in grain size due to the effects of temperature and/or drought. A review of gene expression studies showed that most genes involved in starch synthesis are down regulated under heat stress. Net protein production is also reduced under heat and/or drought stress but apparently to a lesser degree as the reduction in grain mass is larger, resulting in an increase in protein concentration. Modelling has suggested that adaptation could be achieved by moving production to more extreme latitudes but other research suggests that simply transferring germplasm from one region to another is unlikely to be successful. Another review has identified drought tolerance phenotypes that could be used to breed more drought tolerant crops. At the time of the review, the authors concluded that phenotypic selection was generally preferable to forms of marker-assisted breeding and have used the approach to produce drought tolerant wheat cultivars. Transgenic approaches have also been shown to improve drought tolerance under controlled environment conditions but there are no results to show how well these results translate into improved crop performance under field conditions. The recent advances in genomic data and detecting marker–trait associations suggest that marker-assisted breeding will play a much more important role in breeding drought tolerant cereals in the future.

The regions of north-eastern Ethiopia are known for their high levels of sorghum genetic diversity, and for being drought prone. For centuries, sorghum has been developed and maintained by farmers for its adaptation to the marginal and heterogeneous environment of these regions. The objective of this study was to examine the genetic diversity and population structure of 200 sorghum landraces collected from seven lowland districts, using 30 microsatellite markers sampled from all linkage groups of the sorghum genome. Both distance-based and model-based analytical approaches were used to analyse the data. The data analysis revealed that there was a large variation among all the markers under study. The values of polymorphic information content ranged from 0.26 to 0.88, with a mean value of 0.61, reflecting the high discriminating ability of the markers studied. The mean value of total gene diversity was 0.69, which partitioned 86% among the landraces and 14% within the landraces. Gene diversity among the landraces was largely due to the variation among the genotypes within the geographic origins. Landraces sampled from different collection sites appeared to cluster together, indicating the existence of a high level of gene flow among the sites of collection. This indicates that a relatively small, random collection of landraces would capture the bulk of genetic diversity in the target area. A moderately high level of genetic differentiation and a relatively low level of gene flow were observed between sorghum races and maturity groups. Given that the target area is marginal, drought prone and heterogeneous, the study of genetic diversity among sorghum landraces could serve as an important indicator of valuable alleles for drought tolerance in future sorghum improvement programmes.

The landscape of the upper Rio Negro basin (North Amazon) exhibits distinctive habitats that are associated with differential soil characteristics and topographical conditions as well as species composition (Herrera et al. 1978). The mixed forests thrive on well-structured oxisols on slightly more elevated areas. The valleys with sandy podzols are occupied by the ‘Amazon caatinga’ complex with three distinct zones: the bottom valley and the gentle slopes, both of which have closed forests, and the sandy domes with open forests (‘bana’ or sclerophyllous forest; Breimer 1985). From the mixed forest towards the caatinga valley-slope-dome habitats, the leaf δ15N signatures become increasingly negative, suggesting a trend in N limitation in the same direction (Sobrado 2010). Thus, negative leaf δ15N signatures depleted in 15N compared with the soil indicate a very tight N cycle in all of the habitats. Water availability follows a similar pattern from the top of the oxisol towards the flooded valley bottom of the caatinga, with extreme water-table fluctuations in the sandy domes (Klinge 1978). Thus, parallel variation in nutrient and water availabilities exist in this area that are associated with soil characteristics and topography. Under such contrasting habitats, species-specific responses would be linked to particular conditions of the habitat at a local scale (Comita & Engelbrecht 2009, Engelbrecht et al. 2007). A number of studies in these habitats have shown that this is the case for soil fertility (Coomes 1997, Medina et al. 1990, Sobrado 2010, Sobrado & Medina 1980). Similarly, the hydraulic characteristics and long-term water use are species specific and related to particular conditions of the habitat at the local scale (Sobrado 2010). In this report, it was hypothesized that the leaf tissue water relations of species thriving in different habitats may reflect the water availability at the particular sites as well. The leaf tissue water relations of species thriving in the extreme nutrient and water-supply conditions of the sandy domes from the caatinga complex have been previously studied in detail (Sobrado 2009a). However, these data are currently not available for the species that thrive in the surrounding area of the closed forests, and importantly, such information would allow for a comparison across habitats. Therefore, the present study assessed the minimum leaf water potential (midday) under field conditions as well as the leaf tissue water relations by using pressure-volume analysis of dominant tree species in the top canopy of these high-stature forests.

Cowpea is an important grain legume crop in sub-Saharan Africa (SSA) where, on a worldwide basis, the bulk is produced and consumed. The dry savanna area of SSA is where cowpea is mostly grown under rain-fed conditions. The crop is therefore prone to drought which may occur early, mid and/or late in the cropping season. Compared with many other crops, cowpea is drought tolerant, even though drought is still a major constraint limiting its productivity in SSA. Increasing the level of drought tolerance in existing cowpea varieties grown by farmers would enable them to obtain more and stable yield from their cowpea fields. As a first step towards enhancing drought tolerance in existing cowpea varieties, 1288 lines were selected randomly from cowpea germplasm collections maintained at the International Institute of Tropical Agriculture, and evaluated for their drought tolerance at Ibadan. Drought was imposed by withdrawal of irrigation from 5 weeks after sowing. On average, drought reduced the number of days to flower by 12 d, and the mean grain yield per plant was also reduced by 67.28%. A few of the cowpea lines stayed green for up to 6 weeks after irrigation was stopped, even though some of these produced no pods when the study was terminated. Further evaluation in the screenhouse of 142 selected drought-tolerant lines helped to identify six lines that could be potential parents for developing breeding lines with enhanced drought tolerance.

Flooded savannas in south-west Venezuela consist of seasonal, marshy and flooded grassland communities, the distribution of which depends on soil level. Seasonal grasslands are dominated by tuft-forming, rhizomatous C4-grasses (exemplified by Paspalum chaffanjonii in this study), while flooded grasslands are dominated by stoloniferous grasses which develop rooted, floating culms during the rainy season (Leersia hexandra and Hymenachne amplexi-caulis). The interface between these two communities is a marshy grassland dominated by stoloniferous grass species which tolerate flooding to a depth of 10 to 25 cm (Panicum laxum and Leersia hexandra). All perennial grass species in flooded grasslands behave as typical C3 plants, while marshy grasslands are dominated by Panicum laxum, a species with reduced photo-respiration, low RuBP/PEP-carboxylase ratios, and low absolute RuBP-carboxylase activity compared to C3 grasses. It also has lower photosynthetic rates than the other grass species. Hymenachne amplexicaulis appears to be the least drought tolerant from the species selected, in accordance with its distribution in the wettest side of the flooding gradient studied. The other species showed marked reduction in relative water content and pronounced increase in leaf proline content in drought experiments lasting 6 to 30 days. Alcohol dehydrogenase increased markedly in response to anaerobiosis in the root environment in the tuft forming grasses, while the stoloniferous species with ascending culms were least affected by this treatment, probably as a result of better aeration inside the culms and also to the production of adventitious roots in upper nodes. Nitrate reductase activity increased as a result of anaerobiosis in the roots but not in the leaves, of all species except Leersia hexandra. No difference among the species was found in malate accumulation, or the activity of malic enzyme.

To investigate the wheat transcriptional profile under drought stress, a drought-tolerant variety of wheat (Triticum aestivum), Hanxuan 10, was treated with polyethylene glycol (PEG6000) and samples were collected at 0, 1, 6 and 24 h. Complementary DNA was labelled with fluorescent dye and hybridized with the BGI-RiceChip, a whole genome rice gene chip platform, which contains over 60 000 oligos based on the rice genome sequence. Data analysis detected 166, 207 and 328 differentially expressed genes (DGs), respectively, at 1, 6 and 24 h, indicating that the number of DGs increased with the length of the PEG treatment. Functional category analysis showed that the number of DGs related to energy metabolism pathways increased – 4.2%, 8.2% and 16.8%, respectively, as a proportion of the total number of DGs. Most of the photosynthesis-related genes were up-regulated. It is interesting to note that Psbr and ribulose-bisphosphate carboxylase (Rubisco)-coding genes were down-regulated, suggesting their potential role in the response to drought tolerance.

Drought tolerance (DT) is a very complex trait. For the purpose of developing DT rice cultivars, a research programme was initiated in 1997 in China, consisting of four coherent parts: the development of a DT field screen facility and evaluation standard; the collection, evaluation and enhancement of DT rice resources; DT gene/quantitative trait locus (QTL) discovery; and DT rice breeding. More than 2000 rice accessions, mostly from China, were collected and evaluated in a new DT screening facility with a powerful water management system. Eighty-six entries were selected to serve as a core DT collection. A set of 187 recombinant inbred lines was developed for the genetic mapping of DT and high yield-related QTL under drought conditions. Several DT rice cultivars adapted to southern and central China were released. DT rice CMS lines were developed and distributed to most parts of China to encourage the development of DT or water-saving hybrid rice.

The diversity of chironomid larvae in relation to flooding and drought phases in a marginal fluvial wetland of the Middle ParanáRiver floodplain was analyzed. Four sampling stations in the right bank of the Tiradero Viejo River towards the interior of themarginal wetland were established: one at the riverside, and three more at 10, 30 and 40 m from the river. Bottom sedimentsamples were extracted during the hydrosedimentological cycle of 2001. A total of 25 taxa of Chironomidae were recorded. Thevalues of taxonomic richness, density and diversity were higher in the marginal fluvial wetland than in the riverside, increasingwhen the wetland is disconnecting from the river. Polypedilum (Tripodura) spp., Polypedilum (Polypedilum) spp., Ablabesmyia(Karelia) spp., Coelotanypus sp., Monopelopia cf. boliekae, Goeldichironomus holoprasinus and Chironomus gr. decorus spp.were dominant in marginal wetlands. The results indicate that the variations in the hydrosedimentological regime, the degree ofdisconnection with the river and the progressive desiccation at each one of the stations of the marginal fluvial wetland arelimitant factors in the distribution and abundance of aquatic chironomids. The different assemblages of Chironomidae werestrongly conditioned by temporal changes related to the gradient of inundation-drought and to the hydroperiod dynamics.

We used regression models and information-theoretic model selection to assess the relative importance of environment, local dispersal and historical contingency as controls of the distributions of 26 common plant species in tropical forest on Barro Colorado Island (BCI), Panama. We censused eighty-eight 0.09-ha plots scattered across the landscape. Environmental control, local dispersal and historical contingency were represented by environmental variables (soil moisture, slope, soil type, distance to shore, old-forest presence), a spatial autoregressive parameter (ρ), and four spatial trend variables, respectively. We built regression models, representing all combinations of the three hypotheses, for each species. The probability that the best model included the environmental variables, spatial trend variables and ρ averaged 33%, 64% and 50% across the study species, respectively. The environmental variables, spatial trend variables, ρ, and a simple intercept model received the strongest support for 4, 15, 5 and 2 species, respectively. Comparing the model results to information on species traits showed that species with strong spatial trends produced few and heavy diaspores, while species with strong soil moisture relationships were particularly drought-sensitive. In conclusion, history and local dispersal appeared to be the dominant controls of the distributions of common plant species on BCI.