► We examine rice peduncle elongation, anther dehiscence and spikelet sterility under drought. ► Forty-five rice genotypes were grown in upland field and exposed to drought stress 10–15 days before ...heading. ► The average yield in the drought treatment was only 20% of that of the control. ► Yield was highly associated with spikelet fertility, peduncle elongation and leaf water status. ► Peduncle elongation affects yield through regulation of spikelet fertility by plant water status.
Reproductive stage drought stress results in dramatic reduction of spikelet fertility and grain yield of upland rice (
Oryza sativa L.). The hypothesis investigated here is that spikelet sterility under pre-anthesis drought is triggered by deficient plant water status that inhibits peduncle elongation, panicle exsertion and anther dehiscence. A set of 45 rice genotypes was grown in an upland field under well-watered and drought-stressed conditions. Irrigation was applied using a drip irrigation system, and the drought stress treatment was initiated differentially for each genotype at 10–15 days before heading. Drought stress substantially reduced grain yield, and the average yield in the drought treatment was only 20% of that of the control. Peduncle elongation rate (PER) was significantly inhibited by drought, simultaneously with the decrease of plant water status parameters. Yield was highly associated with spikelet fertility (
r
=
0.74***), PER (
r
=
0.47***), leaf water potential (LWP) (
r
=
−0.4**), and peduncle water potential (PWP) (
r
=
−0.38**). The sensitivity of anther dehiscence to drought stress, as determined by the anatomic structure of anther walls, did not differ among genotypes. Path analysis revealed that spikelet fertility and PER had a major positive effect on yield, while peduncle length and LWP had negative effects. PWP had a small direct effect, but had a high negative indirect effect on yield through spikelet fertility reduction. PER had a high and positive indirect effect on yield under drought through spikelet fertility. It is concluded that PER is key parameter that affects rice yield through the regulation of spikelet fertility by plant water status under drought.
Drought stress is one of the major factors affecting nitrogen fixation by legume-rhizobium symbiosis. Several mechanisms have been previously reported to be involved in the physiological response of ...symbiotic nitrogen fixation to drought stress, i.e. carbon shortage and nodule carbon metabolism, oxygen limitation, and feedback regulation by the accumulation of N fixation products. The carbon shortage hypothesis was previously investigated by studying the combined effects of CO2 enrichment and water deficits on nodulation and N2 fixation in soybean. Under drought, in a genotype with drought tolerant N2 fixation, approximately four times the amount of 14C was allocated to nodules compared to a drought sensitive genotype. It was found that an important effect of CO2 enrichment of soybean under drought was an enhancement of photo assimilation, an increased partitioning of carbon to nodules, whose main effect was to sustain nodule growth, which helped sustain N2 rates under soil water deficits. The interaction of nodule permeability to O2 and drought stress with N2 fixation was examined in soybean nodules and led to the overall conclusion that O2 limitation seems to be involved only in the initial stages of water deficit stresses in decreasing nodule activity. The involvement of ureides in the drought response of N2 fixation was initially suspected by an increased ureide concentration in shoots and nodules under drought leading to a negative feedback response between ureides and nodule activity. Direct evidence for inhibition of nitrogenase activity by its products, ureides and amides, supported this hypothesis. The overall conclusion was that all three physiological mechanisms are important in understanding the regulation of N2 fixation and its response of to soil drying.
•988 IRRI Genebank accessions were screened for yield under drought.•Most drought-resistant accessions originated from E. India and Bangladesh.•Disease evaluation was conducted of the top-yielding ...lines.•Kataktara Da2, Dular, Shada Shaita, and DA 28 are recommended for drought breeding.
Genebanks are stewards of the world's crop diversity, and represent large potential for sources of stress tolerance. In this study, selected accessions from the Genebank of the International Rice Research Institute (IRRI) were screened under upland and lowland field conditions to identify accessions that could be drought tolerance donors for use in breeding. Accessions that performed well under drought stress were retained and screened again in succeeding years along with additional new accession entries under well-watered and different drought stress treatments. A total of 988 accessions were screened in this study. High biomass production and short growth duration (flowering in less than 100 days after sowing) were related to high grain yield under drought stress. Accessions Binuhangin, Dharia Boalia, Gul Murali, and Kalia produced the highest yields under drought stress in both upland and lowland environments. Accessions Kataktara Da2, L201, Gopal, Gathi Kama Nangarhar, and Kotteyaran exhibited the highest grain yields in both well-watered and drought stress conditions. Most drought-tolerant accessions identified in this study originated from eastern India and Bangladesh. Based on yield results under drought and well-watered conditions across crop seasons combined with a disease-resistance evaluation, accessions Kataktara Da2, Dular, Shada Shaita, and DA 28 are recommended for use in drought breeding programs.
•200 O. sativa (IR64)×O. glaberrima (RAM) introgression lines were evaluated.•Field drought experiments were conducted in Tanzania and the Philippines.•Root growth correlated with canopy temperature ...but not grain yield under drought.•The highest-yielding lines can be donors for improving rice in sub-Saharan Africa.
Rainfed rice ecosystems account for more than 80% of the total rice area in sub-Saharan Africa, and large parts of this region frequently experience drought stress. One potential approach to improve the drought resistance and local adaptation of high-yielding rice varieties in rainfed regions of sub-Saharan Africa is to cross them with the African rice species Oryza glaberrima. In this study, 200 introgression lines (ILs) from crosses of O. sativa (IR64) and O. glaberrima (RAM90 and RAM54) were evaluated in three field experiments under different rainfed drought scenarios in Tanzania and the Philippines. The objectives of the study were to select ILs for yield and traits associated with drought resistance, and to analyze the genetic variation in water uptake, root growth, and drought response that were observed among the ILs in a previous greenhouse lysimeter study. Several ILs showed improved yield under drought stress and well-watered conditions compared with the recurrent parent IR64. One cluster of ILs that showed the highest yield across all environments included genotypes with the lowest canopy temperature under drought. In 10 selected ILs, root length density was negatively correlated with canopy temperature and soil moisture, and positively related to shoot biomass, but not significantly correlated with grain yield under drought. Although root growth in the field correlated well with root growth in the previous lysimeter study, only some of the highest-yielding lines under drought in the field were those that showed more water uptake in lysimeters. These results confirm the complex relationship among grain yield, root growth, and additional physiological mechanisms underlying crop growth and productivity in the field. The high-yielding ILs under both drought and well-watered conditions in this study can be used as donors to improve drought resistance in target rainfed rice environments in sub-Saharan Africa.
Symbiotic N2 fixation response to drought Serraj, Rachid; Sinclair, Thomas R.; Purcell, Larry C.
Journal of experimental botany,
02/1999, Letnik:
50, Številka:
331
Journal Article
Recenzirano
Odprti dostop
Symbiotic nitrogen fixation is highly sensitive to drought, which results in decreased N accumulation and yield of legume crops. The effects of drought stress on N2 fixation usually have been ...perceived as a consequence of straightforward physiological responses acting on nitrogenase activity and involving exclusively one of three mechanisms: carbon shortage, oxygen limitation, or feedback regulation by nitrogen accumulation. The sensitivity of the nodule water economy to the volumetric flow rate of the phloem into the nodule offers a common framework to understand each of these mechanisms. As these processes are sensitive to volumetric phloem flow into the nodules, variations in phloem flow as a result of changes in turgor pressure in the leaves are likely to cause rapid changes in nodule activity. This could explain the special sensitivity of N2 fixation to drying soils. It seems likely that N feedback may be especially important in explaining the response mechanism in nodules. A number of studies have indicated that a nitrogenous signal(s), associated with N accumulation in the shoot and nodule, exists in legume plants so that N2 fixation is inhibited early in soil drying. The existence of genetic variation in N2 fixation response to water deficits among legume cultivars opens the possibility for enhancing N2 fixation tolerance to drought through selection and breeding.
► Hybrids and inbred parents were tested under increasing levels of drought severity. ► A variable response to drought stress was observed among hybrid lines. ► Our results point to the importance of ...screening hybrids and parents under drought. ► HI and tillering efficiency were associated with drought response of hybrids.
Hybrid rice provides an option for achieving high yield potential under favorable conditions, but the performance of hybrids under drought stress has not yet been fully evaluated. This study explored the feasibility of using hybrid rice technology in drought-prone rainfed lowland fields. Hybrid lines, parental inbreds, and cultivated varieties as checks were screened for yield potential in well-watered fields and for drought resistance in drained fields at different stress levels. Nineteen out of 45 hybrid lines showed a yield advantage (on average 20%) over check lines in the three well-watered environments. Classifications of drought stress levels were based on the yield reduction relative to the well-watered environments, with moderate, severe, and very severe stress levels resulting in 54%, 77% and 89% reductions in yield, respectively. The relationship between yield advantage of hybrids and drought severity differed among lines; some hybrids showed more of an advantage under severe drought, whereas others had a greater yield advantage under moderate stress. Some hybrids did not perform as well as parents under drought. In general, the harvest index of hybrids was greater than those of inbred parents and checks, and showed strong correlation with grain yield in the different stress environments. Total dry matter yield of hybrids was correlated with improved yield in all stress environments during dry seasons, and some drought-tolerant hybrids also showed greater tillering efficiency and thousand-grain weight. Twenty-four selected hybrid lines were divided into seven clusters on the basis of yield trends across different drought stress environments. Among the hybrid rice lines, one cluster including IR81954H, IR81955H, and IR81956H stood out as combining high yield potential in both well-watered and drought stress environments. Hybrid IR81954H showed an 8% yield advantage over other hybrids across all studies, as well as stable yield in all the stress environments having an average yield advantage of 22% over other hybrids averaged across drought environments. These results highlight the variability among hybrids in their drought response, and the need for screening of hybrids and parents under drought stress conditions.
The NAC (NAM, ATAF1/2 and CUC2) genes are plant-specific transcriptional factors known to play diverse roles in various plant developmental processes. We describe the rice (Oryza sativa) OsNAC genes ...expression profiles (GEPs) under normal and water-deficit treatments (WDTs). The GEPs of the OsNAC genes were analyzed in 25 tissues covering the entire life cycle of Minghui 63. High expression levels of 17 genes were demonstrated in certain tissues under normal conditions suggesting that these genes may play important roles in specific organs. We determined that 16 genes were differentially expressed under at least 1 phytohormone (NAA, GA3, KT, SA, ABA, and JA) treatment. To investigate the GEPs in the root, leaf, and panicle of three rice genotypes e.g., 2 near-isogenic lines (NILs) and IR64, we used two NILs from a common genetic combination backcross developed by Aday Selection and IR64. WDTs were applied using the fraction of transpirable soil water at severe, mild, and control conditions. Transcriptomic analysis using a 44K oligoarray from Agilent was performed on all the tissue samples. We identified common and specific genes in all tissues from the two NILs under both WDTs, and the majority of the OsNAC genes that were activated were in the drought-tolerant IR77298-14-1-2-B-10 line compared with the drought-susceptible IR77298-14-1-2-B-13 or IR64. In IR77298-14-1-2-B-10, seventeen genes were very specific in their expression levels. Approximately 70 % of the genes from subgroups SNAC and NAM/CUC3 were activated in the leaf, but 37 % genes from subgroup SND were inactivated in the root compared with the control under severe stress conditions. These results provide a useful reference for the cloning of candidate genes from the specific subgroup for further functional analysis.
The successful use of gene technology for complex crop traits and responses to stress environments remains a challenging approach despite its potential. Stable crop yield in drought prone ...environments has been one of the most studied complex traits in recent years and transgenic crops with better performance have been repeatedly reported. We reviewed the experimental approach of contrasting case studies that report the enhancement of drought resistance in rice using various strategies. If the overall gene technology method is very similar in the different studies analyzed, the limited number of transgenic lines evaluated remains often a pitfall from a breeding perspective since it does not provide a robust assessment of the strategy. The protocols for plant evaluation and the parameters used to assess stress resistance are very different, which is a major limitation to literature mining. This clearly emphasizes the urgent need to define or redefine the major steps and criteria to meet better crop performance in the field, in particular for less favorable environments. We summarized some of these key parameters and we proposed some enabling solutions that can address crop breeding challenges.
The rapid progress in rice genotyping must be matched by advances in phenotyping. A better understanding of genetic variation in rice for drought response, root traits, and practical methods for ...studying them are needed. In this study, the OryzaSNP set (20 diverse genotypes that have been genotyped for SNP markers) was phenotyped in a range of field and container studies to study the diversity of rice root growth and response to drought. Of the root traits measured across more than 20 root experiments, root dry weight showed the most stable genotypic performance across studies. The environment (E) component had the strongest effect on yield and root traits. We identified genomic regions correlated with root dry weight, percent deep roots, maximum root depth, and grain yield based on a correlation analysis with the phenotypes and aus, indica, or japonica introgression regions using the SNP data. Two genomic regions were identified as hot spots in which root traits and grain yield were co-located; on chromosome 1 (39.7-40.7 Mb) and on chromosome 8 (20.3-21.9 Mb). Across experiments, the soil type/ growth medium showed more correlations with plant growth than the container dimensions. Although the correlations among studies and genetic co-location of root traits from a range of study systems points to their potential utility to represent responses in field studies, the best correlations were observed when the two setups had some similar properties. Due to the co-location of the identified genomic regions (from introgression block analysis) with QTL for a number of previously reported root and drought traits, these regions are good candidates for detailed characterization to contribute to understanding rice improvement for response to drought. This study also highlights the utility of characterizing a small set of 20 genotypes for root growth, drought response, and related genomic regions.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
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