Evaluation of Cold Tolerance in NERICAs Compared with Japanese Standard Rice Varieties at the Reproductive Stage

New Rice for Africa (NERICA) is a general name for interspecific rice varieties derived from a cross between the high‐yielding Asian rice (Oryza sativa L.) between locally adapted African rice (Oryza glaberrima Steud.). Eight NERICAs were evaluated for cold tolerance (CT) at the reproductive stage and compared with their O. sativa parents and three Japanese standard rice varieties over 3 years. Cold tolerance was evaluated based on the filled grain ratio (FGR) after cold water irrigation. The FGR was greatly reduced by cold water irrigation. NERICA 1, 2 and 7 had higher FGR (51.9–57.9 %), while NERICA 6, 15 and 16 had lower FGR (6.2–14.5 %). NERICA 1, 2 and 7 were less affected by cold stress, with a 31 % mean reduction in FGR, while NERICA 6, 15 and 16 were greatly affected, with their FGRs being reduced by more than 80 %. NERICA 3 and 4 were moderately affected by cold stress, with about 45 % reduction rate in FGR. FGR significantly influenced the grain weights of the varieties with strong positive correlations (r = 0.83–0.91; P < 0.001), and thus, similar trends in grain weights were observed. Grain weights were reduced by 61.7–96.4 % under cold stress. NERICA 1, 2 and 7 showed significantly better performance than NERICA 3 and 4, while NERICA 6, 15 and 16 performed poorly under cold water irrigation. The Japanese varieties Koshihikari (very tolerant) and Ozora (moderately tolerant) were more affected by cold water irrigation than NERICA 1, 2 and 7. On the basis of the mean reduction rate (%) in FGR under cold stress, the varieties were classified as follows: NERICA 1, 2 and 7 as tolerant; NERICA 3 and 4 as moderately tolerant; and NERICA 6, 15 and 16 as susceptible to cold stress. However, NERICA 7 grain yields were lower under cold stress due to both greatly reduced number of panicles per plant and number of spikelets per panicle. Therefore, NERICA 1 and 2 are suitable candidates for production in the highland regions of East Africa and should be promoted for production.     

Genetic characterization of rainfed upland New Rice for Africa (NERICA) varieties

A total of 18 rainfed upland New Rice for Africa (NERICA) varieties were categorized as the heavy panicle and low tillering types and early heading, in compared with 32 different varieties. These chromosome components were clarified using 243 SSR markers which showed polymorphism among NERICA varieties and their parents, CG 14 (O. glaberrima Steud.) and one of the recurrent parents, WAB-56-104 (O. sativa L.). NERICA varieties were classified into three groups, which corresponded with these parents’ continuation including two exceptions, NERICAs 14 and 17, by a cluster analysis using polymorphism data of SSR markers and 14 differential markers among them were selected to classify NERICA varieties. However, three groups: NERICAs, 3 and 4, NERICAs, 8, 9 and 11 and NERICAs, 15 and 16 were not distinguishable. Association analysis was carried out for characterization of NERICA varieties by using SSR markers genotype and phenotype of agronomic traits. A total of 131 quantitative trait loci between SSR markers and 11 agronomic traits were detected. The characteristics of early maturity and heavy panicle of upland NERICA varieties were succeeded from Asian rice varieties and the characteristics of high dry matter production and late heading were introduced from CG 14 and the other varieties.     

Relationship of Fe-tolerance to morphological changes in roots in upland NERICA lines under Fe-treated hydroponic conditions

Twenty-six upland lines of New Rice for Africa (NERICA) were tested with four Oryza sativa varieties in relation to Fe toxicity tolerance under hydroponic culture containing 1.44 mM Fe (+Fe) and 0 mM Fe (-Fe as a control). Three NERICAs, WAB450-IBP-24-HB (P24), WAB450-IBP-82-1-1 (P82), and WAB450-IBP-163-3-1 (P163) among the 30 lines/varieties tested possessed relatively strong tolerance judging from reduction of root length and dry weight and shoot dry weight in +Fe compared to -Fe and from iron toxicity score (ITS) in +Fe. Only P24, P82, and P163 showed emerged lateral roots from pericycle at the root elongation zone, whereas in the other 23 NERICAs and four O. sativa varieties lateral root was not observed in the root elongation or differentiation zones. Less disruption of cortex on root tissues was observed in P24, P82, and P163 than in WAB450-16-2-BL2-DV2 (BL2-DV2), the most susceptible NERICA identified. P24, P82, and P163 showed significantly lower Fe content in the shoots than BL2-DV2, suggesting that the tolerant NERICAs could have some mechanism to inhibit the absorption of Fe. The emergence of lateral roots from the root elongation zone in the three tolerant NERICAs would be closely associated with reducing Fe absorption into the plants.     

Evaluation of Al-tolerance on upland and lowland types of NERICA lines under hydroponic conditions

We evaluated Al-tolerance in 44 interspecific lines (32 upland and 12 lowland) developed from the crosses of Oryza sativa and O. glaberrima called New Rice for Africa (NERICA) with 2 O. glaberrima lines and 13 O. sativa varieties under hydroponic culture containing 0.15, 0.3, 0.6, and 1.2 mM Al (+Al) and 0 mM Al (?Al as a control). Ten upland and four lowland NERICA lines showed strong Al-tolerance judging from their higher relative root and shoot dry weights (percentage ratios of dry weights in the Al treatments to the control) than those of the tolerant O. sativa check of IR 53650. Their tolerance was supported by relatively higher root Al accumulation (dark blue color) opposite performance with common knowledge (shown pale blue color) in root using hematoxylin staining compared to the Al-susceptible genotypes identified based on relative root and shoot dry weights in the study. Net Al concentration was higher in roots than in shoots in all +Al conditions for all genotypes; however, a clear difference in the Al concentration among the Al-tolerant, Al-moderately tolerant, and Al-susceptible genotypes was observed in the shoots. Al concentrations in the shoots of the Al-tolerant and Al-moderately tolerant upland and lowland NERICA lines were significantly lower than those of its Al-susceptible counterparts in the groups under 0.6 and 1.2 mM Al conditions, respectively. Differences in root and shoot growth among the Al-tolerant, Al-moderately tolerant, and Al-susceptible NERICA lines were clearer under strong Al toxic conditions (0.6 and 1.2 mM Al) than under weak Al toxic conditions (0.15 and 0.3 mM Al).     

Mobilization of the active transposon mPing in interspecific hybrid rice between Oryza sativa and O. glaberrima

Miniature Ping (mPing) is the first active miniature inverted-repeat transposable element to be identified in rice, and its mobilization is activated by stress treatments. We have examined the mobilization of mPing in four NERICA (New Rice for Africa) lines and 13 interspecific lines. All 17 lines are inbred progenies derived from crosses between Oryza sativa variety WAB56-104 as the recurrent parent and the O. glaberrima variety CG14 as the donor parent. We found that 16 of the 17 lines studied inherited mPing together with its autonomous partner, Pong, from WAB56-104. Transposon display of mPing disclosed polymorphic banding patterns among these lines. Most importantly, seven of the lines displayed clear polymorphic banding patterns for mPing, indicating that mPing might have been mobilized in these lines. Locus-specific PCR analysis also confirmed the mobilization of mPing. These results signify that interspecific hybridization may activate the transposition of mPing. Based on these results, we discuss the potential use of the mPing system as an efficient tool for gene tagging in interspecific hybrid rice.     

Quantitative trait loci controlling rice seed germination under salt stress

Salt tolerance of rice (Oryza sativa L.) at the seed germination stage is one of the major determinants for the stable stand establishment in salinity soil. One population of recombinant inbred lines (RILs, F_2:9), derived from a cross between a japonica rice landrace tolerant to salt stress and a sensitive indica rice variety, was used to determine the germination traits including imbibition rate and germination percentage under control (water) and salt stress (100 mM NaCl) for 10 days at 30 °C. The multiple interval mapping (MIM) were applied to conduct QTL for the traits. The results showed that seed germination was a quantitative trait controlled by several genes, and strongly affected by salt stress. A total of 16 QTLs were detected in this study, and each QTL could explain 4.6–43.7% of the total phenotypic variance. The expression of these QTLs might be developmentally regulated and growth stage-specific. In addition, only one digenic interaction was detected under salt stress, showing small effect on germination percentage with R² 2.7%. Among sixteen QTLs detected in this study, four were major QTLs with R² > 30%, and some novel alleles of salt tolerance genes in rice. The results demonstrated that the japonica rice Jiucaiqing is a good source of gene(s) for salt tolerance and the major or minor QTLs identified could be used to improve the salt tolerance by marker-assisted selection (MAS) in rice.     

Cold tolerance at the early growth stage in wild and cultivated rice

The present study was conducted to understand the pattern of variation and the genetic bases for cold tolerance at the early growth stage in Asian rice. The genetic variation was investigated at the germination, plumule and seedling stages among 57 strains including cultivated rice (Oryza sativa ssp. indica and ssp. japonica) and its wild progenitor (Oryza rufipogon). The significant differentiation of cold tolerance was observed among the taxonomically divided groups. At the germination stage, both indica and japonica subspecies tended to be more tolerant than O. rufipogon, whereas at the plumule and seedling stages, ssp. japonica tended to be more tolerant than ssp. indica and O. rufipogon. Furthermore, in cold tolerance at the plumule stage, the clinal variation across the latitude of origins was observed within O. rufipogon and ssp. japonica, suggesting that the current pattern of variation seems to have been shaped by both their phylogenetic histories and on-going adaptation to the local environments. QTL analysis between O. sativa ssp. japonica (tolerant) and O. rufipogon (susceptible) revealed five putative QTLs for cold tolerance at the plumule and seedling stages but not at the germination stage. Substitution mapping was also carried out to precisely locate the two major QTLs for cold tolerance at the plumule stage, which could be used for improvement of tolerance to cold stress in ssp. indica.     

Variability in Osmotic Stress Tolerance of Starch Potato Genotypes (Solanum tuberosum L.) as Revealed by an In Vitro Screening: Role of Proline,Osmotic Adjustment and Drought Response in Pot Trials

Solanum tuberosum (potato) as a drought sensitive plant is also one of the most promising plants to meet the demands for food and starch of a growing population. Distinguishing genotypes into tolerant and susceptible is therefore of utmost interest. We subjected eighteen potato genotypes and two wild species, S. tarijense and S. chacoense, to osmotic stress applied in vitro by addition of 0.2 m sorbitol to a solid medium. Here, we report that a ratio of root:shoot dry mass (DM) together with the SSI (stress susceptibility index, equivalent to drought susceptibility index by Fischer and Maurer, Aust. J. Agron. Res., 29, 1978) of shoot DM were found to be relevant parameters to characterize genotypes in vitro for their osmotic stress tolerance. Drought stress data from pot trials in a rainout shelter (2013 and 2015) correlated poorly with the data obtained in in vitro experiments. However, the most tolerant and most sensitive genotypes in vitro were also categorized to be more tolerant or sensitive than the average to drought stress in vivo. Both, under in vitro and in vivo conditions, proline displayed an increase under osmotic stress conditions in nearly all potatoes tested, but no direct correlations were found to stress tolerance. However, a genotype classified as tolerant displayed earlier proline accumulation. Proline is thought of as one factor for plants to withstand stressful conditions, but cannot be used to distinguish potato genotypes for their stress tolerance to osmotic stress in vitro. Analysis of the osmotic potential of in vitro and in vivo stressed plants displayed a general increase compared to the control.     

Identification of four genes for stable hybrid sterility and an epistatic QTL from a cross between Oryza sativa and Oryza glaberrima

To further understand the nature of hybrid sterility between Oryza sativa and Oryza glaberrima, quantitative trait loci (QTL) controlling hybrid sterility between the two cultivated rice species were detected in BC₁F₁ and advanced backcross populations. A genetic map was constructed using the BC₁F₁ population derived from a cross between WAB450-16, an O. sativa cultivar, and CG14, an O. glaberrima cultivar. Seven main-effect QTLs for pollen and spikelet sterility were detected in the BC₁F₁. Forty-four sterility NILs (BC₆F₁) were developed via successive backcrosses using pollen sterility plants as female and WAB450-16 as the recurrent parent. Seven NILs, in which the target QTL regions were heterozygous while the other QTL regions as well as most of the reminder of the genome were homozygous for the WAB450-16 allele, were selected as the QTL identification materials. BC₇F₁ for the seven NILs showed a continuous variation in pollen and spikelet fertility. The four identified pollen sterility QTLs were located one each on chromosomes 1, 3, 7 and 7. Pollen sterility loci qSS-3 and qSS-7a were on chromosomes 3 and 7, respectively, which coincides with the previously identified S19, and S20, while loci qSS-1 and qSS-7b on chromosomes 1 and 7L appear distinct from all previously reported loci. An epistatic interaction controlling the hybrid sterility was detected between qSS-1 and qSS-7a.     

Increasing biodiversity of irrigated rice in Africa by interspecific crossing of Oryza glaberrima (Steud.) × O. sativa indica (L.)

The African rice Oryza glaberrima, traditionally cultivated since more than 3.500 years, is of poor agronomic performance but resistant/tolerant to various stresses and diseases. The introduction of these characters into O. sativa cultivars is difficult since crossing barriers cause spikelet sterility in F1. Backcrossing can restore fertility and recently facilitated the development of fertile O. glaberrima × O. sativa ssp. japonica hybrid progenies for rain fed systems. With the objective to gain access to African rice germplasm for improvement of irrigated rice, crosses were performed with eighteen O. glaberrima and twenty O. sativa ssp. indica accessions. In total about one hundred F1-hybrid grains were obtained. The F1 plants were all completely sterile and backcrossing (BC) to O. sativa was performed in order to restore spikelet fertility. Monitoring of Tog5681 × IR64 hybrid progenies under field conditions revealed a broad genetic diversity within the BC₁ and BC₂ populations. Some BC₁ and BC₂ progeny plants outperformed the O. sativa parent, indicating that the heterozygocity level and complementary gene action after two backcrosses are still sufficient to positively influence plant vigor. Spikelet fertility of progenies was highly variable, but almost complete fertility was already observed within the BC₁F₂ population. High spikelet fertility was preserved in one out of two analyzed BC₁F₃ families and inmost of the BC₂F₃ families. The ability to restore spikelet fertility within few generations and the potential of the genetic diversity present in interspecific progenies facilitates the development of plant types specifically designed for the African irrigated and lowland environment. This revised version was published online in August 2006 with corrections to the Cover Date.     

Genetic studies on the interspecific cytoplasm substitution lines of an Asian perennial strain of Oryza rufipogon Griff. and O. glaberrima Steud.

Summary It is shown that the restorer gene Rf _j extracted from the Japanese rice variety Akebono is effective on pollen restoration in the cytoplasm substitution line having the nucleus of Oryza glaberrima and japonica or indica cytoplasm of O. sativa, and is of the sporophytic type.The Asian perennial type of the wild rice species O. rufipogon is considered to be the progenitor of O. sativa. Two substitution lines having the cytoplasm of a perennial strain of O. rufipogon from Sri Lanka and the nucleus of O. glaberrima with or without the gene Rf _j in homozygous condition have been bred by means of successive backcrosses. These lines have now reached the BC₅ generation. Plants of the lines resemble morphologically the recurrent parent, but do not show pollen restoration, indicating that the cytoplasm of the rufipogon strain induced male sterility and that the gene Rf _j does not act as the restorer.     

Australian rice varieties vary in grain yield response to heat stress during reproductive and grain filling stages

Climate change may lead to an increase in both day and night time temperatures in rice (Oryza sativa L) growing regions, but the impact of such temperature increases on yields of Australian rice varieties is not known. We evaluated the biomass and grain yield response of eleven Australian rice varieties including long, medium and short grain types, and the Californian cultivar M205, to heat stress during the reproductive phase and grain filling stages. Heat stress (day/night = 35/25°C) was applied at one of three stages: from panicle exertion to anthesis (PE), from anthesis to 10 days after anthesis (EGF) and from 10–20 days after anthesis (LGF) periods after which the effect on biomass and grain yield was compared to control plants. When heat stress was applied at PE and early grain filling stages, mean grain yield losses across rice varieties were 83% and 53%, respectively, though significant genotype × heat stress treatment interactions were observed. Notably, three varieties—YRM 67, Koshihikari and Opus—appeared to possess greater tolerance to heat stress at these growth stages. A significant genotype × heat stress treatment interaction was also observed in the LGF treatment, where significant yield reductions were only observed in Opus (21% loss) and YRM 67 (25% loss). A lack of effect of heat stress on total grain yield in most varieties at late grain filling appeared to be due to late tiller grain yields which were either unaffected by the heat stress or increased significantly compared to control plants. While genetic variation for tolerance to heat stress across the three growth stages was observed, there was no rice genotype that was consistently tolerant (in terms of yield under stress) across all three heat stress treatments. In the absence of a genotype that showed broad heat stress tolerance during reproductive growth, we suggest screening of a wider pool of more diverse rice germplasm is warranted.     

Evaluation of seedling cold tolerance in rice cultivars: a comparison of visual ratings and quantitative indicators of physiological changes

Rice (Oryza sativa L.) is sensitive to prolonged exposure to low temperature, which at the seedling stage can result in significant chilling injury and mortality. The objective of this study was to quantify physiological and biochemical changes in rice seedlings undergoing chilling stress and compare those changes with visual evaluation of tolerance. Seedlings from the cultivars M-202 (tolerant) and IR50 (sensitive) were subjected to 9°C for 14 days in a controlled environment chamber. Leaf tissues were harvested at various time points for determination of electrolyte leakage, proline, malondialdehyde, ascorbic acid and reduced glutathione. Significant differences between M-202 and IR50 were detected in electrolyte leakage, proline, and ascorbic acid starting at 7 days with IR50 exhibiting higher levels of these indicators. Most IR50 seedlings were dead at 14 days. A set of fifty rice accessions including M-202 and IR50 was evaluated at 10 days of cold treatment to examine the correlation of visual ratings with the physiological indices. Visual ratings were most highly correlated with electrolyte leakage and least correlated with proline content. Based on visual ratings and the physiological indices, we identified several cultivars that outperformed M-202 in cold tolerance while IR50 had the lowest tolerance of the cultivars tested.     

Identification and crop performance of acid sulfate soil-tolerant rice varieties

The present study aims to: 1) identify acid sulfate soil (ASS)-tolerant rice varieties from the genetic stock of Korean rice (Oryza sativa L.) varieties under ASS conditions; 2) to evaluate their yield performance, and elucidate the physiological mechanism for ASS tolerance with the identified tolerant varieties. Two hundred sixty-six rice varieties were screened for ASS tolerance, and we identified two japonica-indica hybrid varieties, Geumgang (GG) and Pungsan (PS), as having high tolerance under ASS paddy conditions (pH 3). We first conducted a yield trial of GG and PS grown in Wagner pots to determine their potential yields under ASS conditions. A yield trial under paddy field condition followed. In the pot experiment, the ASS-tolerant varieties, GG and PS, showed significantly higher yields than PT-1, which is a local reference variety in mildly improved soil pH conditions (pH 4.1–4.6). Al and Fe content in GG and PS were significantly lower than that of PT-1, so there might be some mechanism that inhibits the absorption of toxic metal ions in the tolerant varieties. In the paddy conditions, the grain yields more than 5 t ha⁻¹ of the two tolerant varieties under mildly improved soil pH condition were significantly higher than PT-1. Dry matter weights of above ground parts also showed the same trend as grain yield. The study demonstrated that the ASS-tolerant japonica-indica rice varieties with high yielding potential could contribute to the improvement of rice yield in ASS regions, and will be good materials for the development of acid soil-tolerant rice varieties.     

White lupin (Lupinus albus) variation for adaptation to severe drought stress

This study aimed to reduce the gap of knowledge on white lupin drought tolerance variation, by assessing the grain yield of 21 landraces from major historical cropping regions, one variety and two breeding lines in a large phenotyping platform that imposed controlled severely stressed or moisture‐favourable conditions after an initial stage of favourable growth. Drought stress reduced grain yield by 79%. Genetic correlation coefficients indicated moderate consistency of genotype responses across conditions for grain yield (r_g = 0.76), fairly high consistency for straw yield (r_g = 0.85) and harvest index (r_g = 0.91), and high consistency for flowering time (r_g = 0.99). However, low genetic correlation for yield (r_g = 0.31) occurred among a subset of genotypes with early phenology. Specific adaptation to either condition implied significant (p = 0.05) genotype × condition interaction of crossover type between well‐performing genotypes. Early flowering was an important stress escape mechanism, but intrinsic drought tolerance could be inferred from responses of a few genotypes. Various landraces out‐yielded the improved germplasm under stressed or favourable conditions.     

Analysis of population structure and genetic diversity reveals gene flow and geographic patterns in cultivated rice (<Emphasis Type="Italic">O. sativa</Emphasis> and <Emphasis Type="Italic">O. glaberrima</Emphasis>) in West Africa

To fully exploit the diversity in African rice germplasm and to broaden the gene pool reliable information on the population genetic diversity and phenotypic characteristics is a prerequisite. In this paper, the population structure and genetic diversity of 42 cultivated African rice (Oryza spp.) accessions originating from West Africa (Benin, Mali and Nigeria, Liberia etc.) were investigated using 20 simple sequence repeats (SSR) and 77 amplified fragment length polymorphisms (AFLP). Additionally, field trials were set up to gain insight into phenotypic characteristics that differentiate the genetic populations among rice accessions. The analysis revealed considerably high polymorphisms for SSR markers (PIC mean?=?0.78) in the germplasm studied. A significant association was found between AFLP markers and geographic origin of rice accessions (R?=?0.72). Germplasm structure showed that Oryza sativa accessions were not totally isolated from Oryza glaberrima accessions. The results allowed identification of five O. glaberrima accessions which grouped together with O. sativa accessions, sharing common alleles of 18 loci out of the 20 SSR markers analyzed. Population structure analysis revealed existence of a gene flow between O. sativa and O. glaberrima rice accessions which can be used to combine several interesting traits in breeding programs. Further studies are needed to clarify the contributions of this gene flow to valuable traits such as abiotic and biotic stresses including disease resistance.     

Silicon Application in Cultivated Rices (Oryza sativa L and Oryza glaberrima Steud) Alleviates Iron Toxicity Symptoms Through the Reduction in Iron Concentration in the Leaf Tissue

Iron (Fe) toxicity is a constraint commonly encountered in waterlogged conditions. Under anaerobic conditions, reduced Fe is massively absorbed by plants and may induce the generation of reactive oxygen species. This oxidative stress is responsible for physiological perturbations, growth reduction and yield losses. Rice is known as a silicon (Si) accumulator. Although Si is not considered as essential, it is known to play a beneficial role in the resistance to biotic and abiotic stresses through diverse and sometimes unknown mechanisms. The aim of this study was to determine the alleviation of Fe toxicity through Si application in different genotypes. Therefore, cultivars of both cultivated rice species (Oryza sativa and Oryza glaberrima) and lines from a segregating population issued from a cross between IR64 (O. sativa subsp. indica) and Azucena (O. sativa subsp. japonica) were grown in hydroponics under standard or excessive Fe(II) conditions, with or without the addition of Si. The application of Si on Fe‐treated plants strongly alleviated Fe toxicity symptoms. The reduced Fe uptake by Si‐treated plants suggested that an avoidance mechanism would be involved in this alleviation. Moreover, an additive effect of the Si and Fe treatments on the absorption of other nutrients by plants was revealed. These promising results gave insights into the understanding of rice resistance mechanisms to Fe toxicity, opening new perspectives in its management through Si fertilization. Finally, plant response to Si application was greatly influenced by the genotype. Thus, selection of stronger Si‐accumulating varieties could also be of valuable interest in the improvement of rice resistance to Fe toxicity.     

Combination of stem elongation ability with submergence tolerance in rice

Summary A study was conducted with six F₂ populations to test the possibility of combining submergence tolerance and stem elongation ability into a single genotype of rice (Oryza sativa L.). Submergence tolerance and stem elongation ability could be combined in the same genotype if strongly submergence tolerant genes are present in submergence tolerant parents.     

Genotype-by-environment interaction analysis of rice (Oryza spp.) yield in a floodplain ecosystem in West Africa

West Africa has large areas of river floodplains, most of which are not currently used for farmland. Rice (Oryza spp.) is a promising crop for farming in floodplains because of its high adaptability to a wide range of water environments. On the other hand, there is great variation in soil fertility and water availability even in a small area within a floodplain. Hence, we evaluated 27 rice genotypes in four fields in three years in a floodplain of the Northern Region of Ghana to investigate genotype × environment (G × E) interactions for rice yield and to identify stable, high-yielding genotypes. The genotypes consisted of O. sativa, O. glaberrima and New Rice for Africa (NERICA), and many were selected for their reported submergence resistance because of the anticipated submergence damage in the floodplain. There were large variations in yield, which ranged from 0.14 to 5.35 t ha⁻¹ depending on the location within a floodplain, genotype and year, and there were significant genotype, environment and G × E interaction effects on yield, accounting for 24.8%, 20.2%, and 28.2%, respectively, of the total variation. The results suggested that selection of suitable location with high soil fertility and low risk of submergence is necessary to achieve high yield in a floodplain. In addition, early sowing would be effective high-yielding crop management, which reduced the risk of submergence-induced damage just after sowing and secured sufficient growth duration to achieve high yield. Genotype IR42 showed the highest average yield among environments, but its yield stability was low. On the other hand, several genotypes including Amankwatia, a local aromatic cultivar adapted to irrigated and lowland environments, and IRBL9-W[RL], a blast-tolerant variety containing the Sub1 gene for submergence tolerance, showed high, stable yield. To put these results to practical use in other floodplain areas in West Africa, physiological mechanisms causing G × E interaction for rice yield should be further studied.     

Salicylic Acid and Abiotic Stress Responses in Rice

Among plant species rice (Oryza sativa L.) leaves can be characterised with a very high level of salicylic acid content; however, its exact role is still poorly understood. In the present work, rice genotypes with different levels of drought tolerance have been subjected to PEG‐induced drought or cold stress at 10 °C in order to find relationship between the salicylic acid metabolism and the level of stress tolerance; and between the salicylic acid level and other protective mechanisms. Although the drought‐sensitive genotypes usually contained slightly higher amount of salicylic acid than the tolerant ones, there was no strong correlation between the salicylic acid contents and the degree of drought tolerance. Because the expression pattern of the chorismate synthase and isochorismate synthase genes did not correlate with the level of salicylic acid, but there was a correlation between the levels of salicylic acid and ortho‐hydroxy‐cinnamic, it is assumed that the salicylic acid synthesis via ortho‐hydroxy‐cinnamic acid may play a more decisive role than the chorismate–isochorismate–salicylic acid pathway in rice. While the activity of the glutathione reductase enzyme did not show correlation with drought tolerance, the glutathione S‐transferase activities were usually higher in the leaves of the drought‐tolerant varieties than in the sensitive ones. The salicylic acid contents in the leaves were not substantially affected by the applied stress conditions; however, other stress‐related compounds polyamines showed marked, stress‐specific responses. Correlation data suggest that there is no direct link between the abiotic stress‐induced polyamine changes and the salicylic acid metabolism in rice.