Adapting the rice crop to hotter environments: Current and future activities at IRRI

Future climate scenarios are claiming for an increase in global temperature of 2 to 4°C by 2100 in the rice production areas in Asia One of the mandates of the International Rice Research Institute is to predict to what extent the different rice growing areas will be affected, tu analyze consequences on rice production and to provide adaptive strategies. A regional assessment of vulnerability to heat has been conducted by lRRl scientists on rice cropping areas by linking ORYZA2000 with Geographic Information System (GIS). The establishment of a spatio-temporal geo-statistical framework will soon allow identifying regions of risks of heat induced sterility, for which the threshold panicle temperature commonly ranges from 35 to 38°C with respect to the variety. To face this major issue, lRRl scientists are conducting multi-location testing of promising varieties and developing new genetic materials by screening donors from gene bank accessions. Some heat tolerance breeding populations have been developed and dispatched for hotspot screening, and 4 QTL mapping populations have been developed for polymorphism characterization. In addition, anthers of 3 lines contrasted for heat induced sterility were extracted, and some candidate genes are currently being sequenced and will be targeted for transformation. Donors for earlier time of the day of anthesis are investigated for heat induced sterility avoidance: 42 lines among 4000 from the lRRl gene bank accessions appeared to have peaked by 9am and were sent for testing in 5 Asian countries. An integrated phenotyping study for earlier time of the day of anthesis, heat tolerance to sterility and heat tolerance to chalkiness during grain filling, is actually conducted on a set of 212 contrasted accessions in the phytotron. Indeed, lRRl scientists demonstrated under plant temperatures higher than 30°C that genotypes that did not adapt to high temperature produced chalky grains whereas those that sacrificed part of their sink size maintained high quality grains. Similarly, such temperature regimes affect plant growth processes also at earlier stages like for leaf elongation rate. In the case of addressing confounding effects of climatic factors, the correlation observed during the last 15 years in the lRRl farm between the increase in night time temperature from 22 to 24°C and the reduction in grain yield is now confronted with additional data collected in a contrasted night temperature setup in the field. In collaboration with lRRl, scientists from Cirad and NIAES are collecting data in various field environments to quantify panicle temperature and predict its variation with regard to weather conditions, crop architecture and plant cooling ability. At the same time, lRRl scientists are developing the energy balance and exchange routines of OR YZA2000 and adding routines for canopy temperature and spikelet sterility. Considering rice is often grown in humid environments and soon under doubling air [C02], additional routines addressing interactions between temperature, humidity and [C02] will be developed by lRRl collaborators and included into crop models. Such cumulated efforts from rice scientists are necessary to face the challenges of future climate scenarios and make the rice production systems more resilient. (Texte intégral

RootAnalyzer: A Cross-Section image analysis tool for automated characterization of root cells and tissues

The morphology of plant root anatomical features is a key factor in effective water and nutrient uptake. Existing techniques for phenotyping root anatomical traits are often based on manual or semi-automatic segmentation and annotation of microscopic images of root cross sections. In this article, we propose a fully automated tool, hereinafter referred to as RootAnalyzer, for efficiently extracting and analyzing anatomical traits from root-cross section images. Using a range of image processing techniques such as local thresholding and nearest neighbor identification, RootAnalyzer segments the plant root from the image’s background, classifies and characterizes the cortex, stele, endodermis and epidermis, and subsequently produces statistics about the morphological properties of the root cells and tissues. We use RootAnalyzer to analyze 15 images of wheat plants and one maize plant image and evaluate its performance against manually-obtained ground truth data. The comparison shows that RootAnalyzer can fully characterize most root tissue regions with over 90% accuracy

The Frustration with Utilization: Why Have Improvements in Internal Phosphorus Utilization Efficiency in Crops Remained so Elusive?

Despite the attention internal phosphorus utilization efficiency (PUE) of crops has received in the literature, little progress in breeding crop cultivars with high PUE has been made. Surprisingly few studies have specifically investigated PUE; instead, genotypic variation for PUE has been investigated in studies that concurrently assess phosphorus acquisition efficiency (PAE). We hypothesized that genotypic differences in PAE confound PUE rankings because genotypes with higher PAE suffer a lower degree of P stress, resulting in lower PUE. The hypothesis was tested by comparing soil-based screening to a modified technique whereby rice genotypes were grown in individual containers with a single dose of solution P, to eliminate differences in P uptake among genotypes. Genotypic differences in PUE were apparent in root and shoot tissue using the modified nutrient solution technique, but PUE rankings showed no correlation with those from traditional soil-based screening. We conclude that PUE in soil-based screening systems is unavoidably linked with genotypic PAE, resulting in PUE rankings confounded by differences in P uptake. Only screening techniques assuring equal P uptake are suitable for the exploitation of genotypic variation for PUE

RNA catabolites contribute to the nitrogen pool and support growth recovery of wheat

Turn-over of RNA and catabolism of nucleotides releases one to four ammonia molecules; the released nutrients being reassimilated into primary metabolism. Preliminary evidence indicates that monocots store high levels of free nucleotides and nucleosides but their potential as a source of internal organic nitrogen for use and remobilization is uncharted. Early tillering wheat plants were therefore starved of N over a 5-day time-course with examination of nucleic acid yields in whole shoots, young and old leaves and roots. Nucleic acids constituted ∼4% of the total N pool of N starved wheat plants, which was comparable with the N available from nitrate (NO3 -) and greater than that available from the sum of 20 proteinogenic amino acids. Methods were optimized to detect nucleotide (purine and pyrimidine) metabolites, and wheat orthologs of RNA degradation (TaRNS), nucleoside transport (TaENT1, TaENT3) and salvage (TaADK) were identified. It was found that N starved wheat roots actively catabolised RNA and specific purines but accumulated pyrimidines. Reduced levels of RNA corresponded with induction of TaRNS2, TaENT1, TaENT3, and TaADK in the roots. Reduced levels of GMP, guanine, xanthine, allantoin, allantoate and glyoxylate in N starved roots correlated with accumulation of allantoate and glyoxylate in the oldest leaf, suggesting translocation of allantoin. Furthermore, N starved wheat plants exogenously supplied with N in the form of purine catabolites grew and photosynthesized as well as those plants re-supplied with NO3 -. These results support the hypothesis that the nitrogen and carbon recovered from purine metabolism can support wheat growth.Vanessa Jane Melino, Alberto Casartelli, Jessey George, Thusitha Rupasinghe, Ute Roessner, Mamoru Okamoto and Sigrid Heue

Effects of hotter, drier conditions on gaseous losses from nitrogen fertilisers

Global warming is expected to cause hotter, drier summers and more extreme weather events including heat waves and droughts. A little understood aspect of this is its effects on the efficacy of fertilisers and related nutrient losses into the environment. We explored the effects of high soil temperature (>25 °C) and low soil moisture (<40% water filled pore space; WFPS) on emissions of ammonia (NH3) and nitrous oxide (N2O) following application of urea to soil and the efficacy of urease inhibitors (UI) in slowing N losses. We incubated soil columns at three temperatures (15, 25, 35 °C) and three soil moisture contents (20, 40, 60% WFPS) with urea applied on the soil surface with and without UIs, and measured NH3 and N2O emissions using chambers placed over the columns. Four fertiliser treatments were applied in triplicate in a randomised complete block design: (1) urea; (2) urea with a single UI (N-(n-butyl) thiophosphoric triamide (NBPT); (3) urea with two UI (NBPT and N-(n-propyl) thiophosphoric triamide; NPPT); and (4) a zero N control. Inclusion of UI with urea, relative to urea alone, delayed and reduced peak NH3 emissions. However, the efficacy of UI was reduced with increasing temperature and decreasing soil moisture. Cumulative NH3 emission did not differ between the two UI treatments for a given set of conditions and was reduced by 22–87% compared with urea alone. Maximum cumulative NH3 emission occurred at 35 °C and 20% WFPS, accounting for 31% of the applied N for the urea treatment and 25%, on average for the UI treatments. Urease inhibitors did not influence N2O emissions; however, there were interactive impacts of temperature and moisture, with higher cumulative emissions at 40% WFPS and 15 and 25 °C accounting for 1.85–2.62% of the applied N, whereas at 35 °C there was greater N2O emission at 60% WFPS. Our results suggest that inclusion of UI with urea effectively reduces NH3 losses at temperatures reaching 35 °C, although overall effectiveness decreases with increasing temperature, particularly under low soil moisture conditions

High temperature tolerance in a novel, high-quality phaseolus vulgaris breeding line is due to maintenance of pollen viability and successful germination on the stigma

The common bean (Phaseolus vulgaris L.) is an important nutritional source globally but is sensitive to high temperatures and thus particularly vulnerable to climate change. Derived from a breeding program at CIAT (Colombia), a heat-tolerant breeding line, named heat-tolerant Andean-type 4 (HTA4), was developed by a series of crosses of parents with a small-bean tepary genotype (Phaseolus acutifolius L.) in their pedigree, which might be the donor of heat stress (HS) tolerance. Importantly, in HTA4, the large, commercially desirable Andean-type beans was restored. To assess underlying tolerance mechanisms, HTA4, together with a heat-sensitive Colombian variety (Calima), was exposed to HS (31 °C/24 °C HS vs. 26 °C/19 °C day/night) under controlled environment conditions. Vegetative growth and photosynthetic performance were not negatively impacted by HS in either genotype, although senescence was delayed in Calima. HS during the reproductive stage caused an increase in pod number in Calima but with few fully developed seeds and many pods aborted and/or abscised. In contrast, HTA4 maintained a similar filled pod number under HS and a higher seed weight per plant. Pollen showed high sterility in Calima, with many non-viable pollen grains (24.9% viability compared to 98.4% in control) with a thicker exine and fewer starch granules under HS. Calima pollen failed to adhere to the stigma and germinate under HS. In HTA4, pollen viability was significantly higher than in Calima (71.1% viability compared to 95.4% under control), and pollen successfully germinated and formed pollen tubes in the style under HS. It is concluded that HTA4 is heat tolerant and maintains a high level of reproductive output due to its ability to produce healthy pollen that is able to adhere to the stigma