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
Drought stress causes yield loss in rice by inhibiting panicle exsertion which is driven by peduncle elongation near flowering. To elucidate the mechanism of peduncle elongation, we examined the ...drought sensitivity of corresponding genes encoding xyloglucan endotransglycosylase/hydrolase (XTH), a cell wall-loosening enzyme essential for cell elongation in the peduncle elongation zone at heading stage. When drought was imposed 6 days before heading, peduncle elongation rate (PER) was inhibited significantly at heading and 1 day after heading. Eleven
OsXTH
genes were isolated and their expression in rice peduncle determined. The expression of 11
OsXTH
genes showed different patterns of response to drought stress.
OsXTH3
was completely suppressed by drought. Transcript levels for
OsXTH19
, -
20
, -
24
, -
27
and -
28
genes were markedly down-regulated at a series of drought stresses. By contrast,
OsXTH5
was up-regulated. Also, the behavior of leaf gas exchange and peduncle abscisic acid (ABA) level was determined under drought conditions. The results indicated that stomatal conductance was 83% lower than that in control plants and peduncle ABA increased ninefold with drought stress. Peduncle ABA content correlated highly with leaf stomatal conductance and PER (
r
= 0.85** and 0.88**). The expression in
OsXTH5
, -
19
, -
20
, -
24
and -
28
, corresponded to changes in PER and ABA. We conclude that ABA could be involved in inducing the retardation of PER and changes of expression of
OsXTH
genes.
OsXTH5
, -
19
, -
20
, -
24
and -
28
genes may play a role in rice peduncle elongation. In addition, interactions among genes may affect PER under drought.
More than 400 million people in the developing world depend on dryland agriculture for their livelihoods. Dryland agriculture involves a complex combination of productive components: staple crops, ...vegetables, livestock, trees and fish interacting principally with rangeland, cultivated areas and watercourses. Managing risk and enhancing productivity through diversification and sustainable intensification is critical to securing and improving rural livelihoods. The main biophysical constraints are natural resource limitations and degradation, particularly water scarcity and encroaching desertification. Social and economic limitations, such as poor access to markets and inputs, weak governance and lack of information about alternative production technologies also limit the options available to farmers. Past efforts to address these constraints by focusing on individual components have either not been successful or are now facing a declining rate of impact, indicating the need for new integrated approaches to research for development of dryland systems. This article outlines the characteristics of such an approach, integrating agro-ecosystem and livelihoods approaches and presents a range of empirical examples of its application in dryland contexts. The authors draw attention to new insights about the design of research required to accelerate impact by integrating across disciplines and scales.
The AP2/EREBP genes play various roles in developmental processes and in stress-related responses in plants. Genome-wide microarrays based on the gene expression profiles of the AP2/EREBP family were ...analyzed under conditions of normal growth and drought stress. The preferential expression of fifteen genes was observed in specific tissues, suggesting that these genes may play important roles in vegetative and reproductive stages of growth. A large number of redundant genes were differentially expressed following phytohormone treatments (NAA, GA3, KT, SA, JA, and ABA). To investigate the gene expression responses in the root, leaf, and panicle of three rice genotypes, two drought stress conditions were applied using the fraction of transpirable soil water (FTSW) under severe (0.2 FTSW), mild (0.5 FTSW), and control (1.0 FTSW) conditions. Following treatment, transcriptomic analysis using a 44-K oligoarray from Agilent was performed on all the tissue samples. We identified common and specific genes in all tissues from two near-isogenic lines, IR77298-14-1-2-B-10 (drought tolerant) and IR77298-14-1-2-B-13 (drought susceptible), under drought stress conditions. The majority of the genes that were activated in the IR77298-14-1-2-B-10 line were members of the AP2/EREBP gene family. Non-redundant genes (sixteen) were found in the drought-tolerant line, and four genes were selected as candidate novel reference genes because of their higher expression levels in IR77298-14-1-2-B-10. Most of the genes in the AP2, B3, and B5 subgroups were involved in the panicle under severe stress conditions, but genes from the B1 and B2 subgroups were down-regulated in the root. Of the four subfamilies, RAV exhibited the highest number of up-regulated genes (80%) in the panicle under severe stress conditions in the drought-tolerant line compared to Minghui 63 under normal conditions, and the gene structures of the RAV subfamily may be involved in the response to drought stress in the flowering stage. These results provide a useful reference for the cloning of candidate genes from the specific subgroup for further functional analysis.
Increasing N
2
fixation tolerance to drought has been hindered by the labor and costs of quantifying N
2
fixation using
15
N methodologies. The relative abundance of ureides (RAU) in plant tissues ...has been used for estimating N
2
fixation in soybean
Glycine max
(L.) Merr. grown under well‐watered conditions, but it has not been evaluated for drought conditions. The present research evaluated the response of N accumulation to N fertilization, the ability of the RAU technique to predict N
2
fixation under drought conditions, and the response of yield to N fertilization under well‐watered and drought conditions. Under drought, shoot N accumulation rate during vegetative growth approximately doubled as the amount of N fertilizer was increased from 10 to 200 kg N ha
−1
, indicating a greater sensitivity of N
2
fixation to drought than uptake and assimilation of inorganic N. Under well‐watered conditions, the relationship between estimates of N
2
fixation made by
15
N‐dilution and RAU agreed within 15% of published reports. Under drought conditions, however, this relationship was greatly different (13 to 43%) from published reports. Fertilization with inorganic N in 1 yr increased grain yield 15 to 25% for the drought treatment and 12 to 15% for the well‐watered treatment. In a second year, N fertilization increased yield of both drought and well‐watered treatments approximately 9%. This research indicates that the RAU technique for estimating N
2
fixation under drought conditions may be invalid without further refinement, that N
2
fixation is more sensitive to drought than the uptake and assimilation of inorganic soil N, and that increasing the tolerance of N
2
fixation to drought would likely result in yield increases.
Ureides accumulate in soybean (Glycine max L. Merr.) petioles during drought under greenhouse conditions despite decreased N2 fixation and ureide production. Field experiments with water-deficit ...treatments were established to examine the possibility of ureide accumulation under natural drought-stress conditions. Tissue ureide concentration of drought tolerant 'Jackson' were compared with either 'Hutcheson' or 'Biloxi'. For mild water-deficit conditions, petiole ureide levels were greater than a well-watered treatment at ten sampling dates for Hutcheson compared to three dates for Jackson. At only two dates were there significant differences between genotypes in petiole ureide concentration, in which case petiole ureide concentration of Hutcheson was greater than Jackson. Under more severe water-deficit conditions, there were greater and more consistent increases in petiole ureide concentration for Jackson and Biloxi. Jackson, however, had lower petiole ureide concentration than Biloxi throughout the measurement period for both well-watered and water-deficit treatments. Ureide catabolism in leaves during reproductive development was found to be negatively associated with petiole ureide concentration of Hutcheson (r = -0.37, P = 0.01), but not in Jackson (r = -0.12, P = 0.44). These results indicated that increased ureide accumulation in response to water deficits experienced under field conditions was negatively associated with drought tolerance of N2 fixation in these cultivars, and that petiole ureide accumulation may result from decreased ureide catabolism
Abstract
The sensitivity of N2 fixation to drought stress in soybean (Glycine max Merr.) has been shown to be associated with high ureide accumulation in the shoots, which has led to the hypothesis ...that N2 fixation during drought is decreased by a feedback mechanism. The ureide feedback hypothesis was tested directly by measuring the effect of 10 mm ureide applied by stem infusion or in the nutrient solution of hydroponically grown plants on acetylene reduction activity (ARA). An almost complete inhibition of ARA was observed within 4 to 7 d after treatment, accompanied by an increase in ureide concentration in the shoot but not in the nodules. The inhibition of ARA resulting from ureide treatments was dependent on the concentration of applied ureide. Urea also inhibited ARA but asparagine resulted in the greatest inhibition of nodule activity. Because ureides did not accumulate in the nodule upon ureide treatment, it was concluded that they were not directly inhibitory to the nodules but that their influence mediated through a derivative compound, with asparagine being a potential candidate. Ureide treatment resulted in a continual decrease in nodule permeability to O2 simultaneous with the inhibition of nitrogenase activity during a 5-d treatment period, although it was not clear whether the latter phenomenon was a consequence or a cause of the decrease in the nodule permeability to O2.
Crop tolerance to salinity is of high importance due to the extent and the constant increase in salt-affected areas in arid and semi-arid regions. Pearl millet (Pennistum glaucum), generally ...considered as fairly tolerant to salinity, could be an alternative crop option for salt affected areas. To explore the genotypic variability of vegetative-stage salinity tolerance, 100 pearl millet lines from ICRISAT breeding programs were first screened in a pot culture containing Alfisol with 250 mM NaCl solution as basal application. Subsequently, 31 lines including many parents of commercial hybrids, selected from the first trial were re-tested for confirmation of the initial salinity responses. Substantial variation for salinity tolerance was found on the basis of shoot biomass ratio (shoot biomass under salinity/ non-saline control) and 22 lines with a wide range of tolerance varying from highly tolerant to sensitive entries were identified. The performance of the genotypes was largely consistent across experiments. In a separate seed germination and seedling growth study, the seed germination was found to be adversely affected (more than 70% decrease) in more than half of the genotypes with 250 mM concentration of NaCl. The root growth ratio (root growth under salinity/control) as well as shoot growth ratio was measured at 6 DAS and this did not reflect the whole plant performance at 39 DAS. In general, the whole plant salinity tolerance was associated with reduced shoot N content, increased K⁺ and Na⁺ contents. The K⁺/Na⁺ and Ca⁺⁺/Na⁺ ratios were also positively related to the tolerance but not as closely as the Na⁺ content. Therefore, it is concluded that a large scope exists for improving salt tolerance in pearl millet and that shoot Na⁺ concentration could be considered as a potential non-destructive selection criterion for vegetative-stage screening. The usefulness of this criterion for salinity response with respect to grain and stover yield remains to be investigated.
The success of the Green Revolution in closing the gap between world population and food production was principally achieved by increasing crop productivity in favorable areas. However, this success ...has been limited in the rainfed systems, which are prone to frequent droughts and other abiotic stresses. Worldwide, drought affects approximately 23 million hectares of rainfed rice. Varieties combining improved drought resistance with high yield under favorable conditions and quality characteristics preferred by farmers are the most promising and deliverable technologies for alleviating poverty in communities dependent on rainfed rice production.This book describes some of the recent advances in the genetics and physiology of drought resistant rice varieties and the integration of highly efficient breeding and genetic analysis techniques with functional genomics. Harnessing recent scientific breakthroughs, Drought Frontiers Project (seeds.irri.org/drought) is launched as a major assault on the problem of improving drought resistance in rice. Featuring contributions from leading international experts, case studies are discussed to present perspectives on the various multidisciplinary facets of drought resistance in rice, along with the involvement of natural resource management practices and the socioeconomic implications that entail. Readers will be better informed of this highly relevant and complex topic of improving rice drought resistance in a global environment characterized by increased water scarcity.
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