Use of two PGPR strains in the integrated management of blast disease in rice (Oryza sativa) in Southern Spain

Biocontrol capacity of two plant growth-promoting rhizobacteria (PGPR) strains, against blast disease in rice paddy fields in Southern Spain was studied in three cropping seasons. Both strains (Pseudomonas fluorescens Aur 6 and Chryseobacterium balustinum Aur 9) had already shown biocontrol capacity against pathogens, ability to induce systemic resistance against leaf pathogens and against salt stress in different plant species. Bacterial treatments were carried out on seeds and/or on leaves. Strains were inoculated individually and in combination. Protection against natural disease incidence was evaluated, and rice production and quality measured in 2005 and 2006 trials. In 2004, natural disease incidence was low (between 0.1% and 0.35% of damaged leaf surface) due to environmental conditions; under these conditions, both strains significantly protected plants against rice blast. In 2005, disease incidence was higher than in 2004, reaching higher values of affected leaf surface in controls. In these conditions, each strain individually protected rice against rice blast, although the combination of both strains was the most effective treatment. All three treatments (Aur 6, Aur 9 and Aur 6 + Aur 9) reached 50% protection in panicles, with Aur 9 being the most effective. In 2006, the most effective treatment was the combination of both strains on leaves in three physiological stages, suggesting a biocontrol mediated protection. On the other hand, when bacteria were applied to seeds, disease incidence decreased up to 50%, suggesting induction of systemic resistance. Finally, a direct relation between protection mediated by the PGPR and the increase in rice productivity (mT/ha) and quality (weight of 1000 seeds and number of intact grains after milling) was found.     

A quick determination of root resistance to water transport in paddy rice

Hydraulic resistance in plants is one of the most important factors responsible for changes in leaf water potential that is an indicator of plant water stress. Although the hydraulic resistance to passive water transport (R_pa) is a robust index in paddy rice (Oryza sativa), measurement is both time-consuming and labour-intensive. Here, we describe on a quick method to measure hydraulic resistance to osmotic water transport (R_os) by measuring the xylem sap exudation rate and osmotic water potential. In a greenhouse experiment, R_os responded significantly to soil temperature, but under field conditions soil temperature varied considerably less than air temperature. In the field experiment, R_os of six rice cultivars at two growth stages was strongly positively correlated with R_pa. We conclude that measuring R_os could be used to evaluate root water transport capacity in paddy rice under conditions with adequate soil water.     

Rice Blast Resistance of Transgenic Rice Plants with Pi-d2 Gene

Resistance to rice blast of transgenic rice lines harboring rice blast resistance gene Pi-d2 transformed from three different expression vectors of pCB6.3kb, pCB5.3kb and pZH01-2.72kb were analyzed. Nine advanced-generation transgenic rice lines with Pi-d2 gene displayed various resistance to 39 rice blast strains, and the highest disease-resistant frequency reached 91.7%. Four early-generation homozygous transgenic lines with Pi-d2 gene exhibited resistance to more than 81.5% of 58 rice blast strains, showing the characteristic of wide-spectrum resistance. The transgenic embryonic calli selected by the crude toxin of rice blast fungus showed that the callus induction rate of immature embryo from transgenic rice plants decreased as the concentration of crude toxin in the culture medium increased. When the concentration of crude toxin reached 40%, the callus induction rate of immature embryo from transgenic lines was 49.3%, and that of the receptor control was 5%. The disease incidence of neck blast of the transgenic rice lines in fields under induction was 0% to 50%, indicating that the rice blast resistance of transgenic rice lines is much higher than that of the receptor control.     

Occurrence of rice blast (Magnaporthe oryzae) and identification of potential resistance sources in Uganda

Rice blast caused by Magnaporthe oryzae continues to be the most destructive disease of rice worldwide, and is a number one disease of rice in Uganda. We present the footprints of M. oryzae importance, distribution, incidence and severity in the rice growing agro-ecologies of Uganda for 2009/2010, and the potential mitigation measures. Our data show that rice blast affects more than 50% of the cultivated rice area on average, and ranks as the most important disease encountered in the field. Between and within agroecologies, both incidence and severity varied (P < 0.05) reflecting the contribution of different cropping practices on rice blast epiphytotics. The highest blast incidence and severities were recorded in Bugiri, Butaleja, Mbale and Lira farmlands, which are the ancestral rice cultivation areas in Uganda. These areas showed mean yield reductions of >30% relative to other locations, suggesting that rice production history played a significant role in rice blast outbreaks. Broadcasting and drill seeding yielded 42.4% less than transplanted rice. Growing two rice crops per year is one of the methods suggested to increase rice production in Uganda, but there was a higher disease incidence in the late season than in the early season, indicating the need for improved resistant varieties. Four blast resistance genes (Pi9, Piz-t, Pi19 and Piz-5) and the cultivar Tetep had the lowest (≤4) blast severity scores in all the test locations. It could be suggested that these genes are potential resistance sources for developing varieties, which would be more relevant for the double cropping systems.     

Improvement of Bacterial Blight Resistance in Rice Cultivars Jyothi and IR50 via Marker-Assisted Backcross Breeding

Abstract

In pathogen population analysis of 208 Xanthomonas oryzae pv. oryzae(Xoo) strains that were assembled from different parts of India, 21 pathotypes were identified on the basis of disease reactions on near-isogenic lines (NILs) and 13 pathotypes, on rice differentials. Rice cultivars, Jyothi and IR50, which are high yielding but highly prone to bacterial blight (BB) caused by pathogen populations of Xanthomonas oryzae pv. oryzae in India, were chosen. To improve the BB resistance of these two varieties, a pyramid line, NH56, containing four R-genes, Xa4, xa5, xa13, and Xa21, was selected as the R-donor based on resistance to existing pathogen population. The four R-genes were successfully transferred to cultivars through a traditional backcross method and their presence was documented with marker-aided selection (MAS). Thirty BC₄F₂ plants derived from JxNH56 (cv. Jyothi) and 45 BC₄F₂ plants derived from IR50xNH56 (cv. IR50) had all four resistance genes (Xa4, xa5, xa13, and Xa21), which should be useful resistance donors for breeding other BB-resistant elite indica varieties.     

Resistance responses of rice to rice blast fungus after seed treatment with the endophytic Achromobacter xylosoxidans AUM54 strains

In the present investigation, we studied resistance imparted by seed treatment with an endophytic strain of Achromobacter xylosoxidans, AUM54, against rice blast caused by Magnaporthe oryzae. In vitro studies showed that A. xylosoxidans AUM54 was able to inhibit mycelial growth of M. oryzae by 11% and was able to increase rice germination and seedling vigor index of rice by 31 and 114%, respectively. AUM54 also showed better survivability in the spermosphere and spermoplane and was able to move systemically through the roots and stem. Among the evaluated carriers, liquid formulation amended with 2% glycerol sustained the maximum bacterial population (7.4 log cfu ml⁻¹) after six-months-storage at room temperature. Plants treated with A. xylosoxidans AUM54 followed by inoculation with M. oryzae showed a significant increase in the activities of defense related enzymes such as polyphenol oxidase (PPO), peroxidase (POD), phenylalanine ammonia-lyase (PAL) and chitinase. A. xylosoxidans AUM54 treatment was able to reduce blast disease incidence by 39% in treated rice plants. Additionally, inoculation with A. xylosoxidans AUM54 significantly enhanced the growth (3–13% plant height), and yield (11–31%) of inoculated rice plants under no-disease and disease conditions in the greenhouse experiments.     

空间诱变育成抗稻瘟病和白叶枯病水稻突变体浙101

 早籼浙9248经卫星搭载诱变处理，种子的发芽率及当代植株的性状均没有明显的变化，但对秧苗的生长表现出一定的刺激作用；SP2在株高、生育期、穗长、每穗粒数、千粒重、结实率及抗病性等性状上出现了较大的分离。经病区多代筛选培育成的突变体浙101，在熟期、抗病性和产量等性状上比原亲本有明显改良，2001~2002年经浙江省多点稻瘟病和白叶枯病联合鉴定，叶瘟平均级分别为1.4和1.7级，最高级为5.0级；穗瘟平均级分别为1.6和1.3级，最高级为3.0级；抗谱频率分别为70%和60%；对白叶枯病抗性平均级为1.4级，最高级为5.0级。抗病性比原亲本和对照有显著提高。试验表明，浙101是一个高抗稻瘟病兼抗白叶枯病的水稻突变体，可作为水稻品种改良的新抗源。     

Introduction of a fungal NADP(H)-dependent glutamate dehydrogenase (gdhA) improves growth,grain weight and salt resistance by enhancing the nitrogen uptake efficiency in forage rice

We report the effect of the introduction of a fungal glutamate dehydrogenase gene (gdhA) into forage rice (cv. Momiroman) by analyzing the transgenic rice plants in terms of growth, source function, and nitrogen contents. NADP (H)-dependent glutamate dehydrogenase activities in the gdhA-transgenic lines were markedly higher than those in non-transgenic control plants. Plant growth analysis at the seedling stage revealed that the leaf area and shoot and root dry weights of the high gdhA-expressors were higher than those of control plants under both high (high N) and low nitrogen (low N) conditions. These results suggested that the source ability was enhanced by the gdhA introduction. This was supported by the fact that the net photosynthesis rate at the heading stage was also higher in transgenic than in control leaves. Furthermore, under both high and low N conditions, the nitrogen contents in the shoots and roots, at seedling and grain-harvest stages, were significantly higher in high gdhA-expressors than in control plants, indicating that nitrogen uptake was higher in transgenic than in control plants. At the harvest stage, the high gdhA-expressors exhibited greater panicle and spikelet numbers per plant compared with control plants, resulting in higher grain weight, under the high N conditions. In addition, gdhA expression in forage rice significantly enhanced their tolerance to salt stress compared to control plants. The present study showed that the introduction of a fungal gdhA into forage rice could lead to higher source ability, better growth and higher grain weight by enhancing nitrogen uptake efficiency.     

Differences in Leaf Senescence among Reciprocally Grafted Plants of Two Soybean Cultivars,Enrei and Tachinagaha

Abstract

The effect of porous hydrated calcium silicate (PS) application on the resistance of rice plants ( Oryza sativa L.) to rice blast (Pyricularia olyzae) was evaluated. Experiments were conducted in Andisol at the experimental farm of Tohoku University from 1993 to 1995. The blast infection in the PS plot was much less than that in the control plot. On the other hand, slag (commercial slag silicate fertilizer) used in our experiment had no effect on blast infection. The number of silicified bulliform cells, the main invasion site for rice blast, was increased 320-980% by PS application, but only 80% by commercial slag. These results imply that PS application is effective in preventing fungal infection through silicification of bulliform cells. The number of silicified bulliform and trichome cells increased exponentially with increasing content of the silicon in the leaf blade, whereas the number of silicified short cells, which are smaller than bulliform cells and trichomes, had no relation to the silicon content in the rice leaf blade. We may conclude that the application of porous hydrated calcium silicate for rice plants is effective in increasing rice blast resistance because PS increase the number of silicified bulliform cells.     

Effects of rice-water chestnut intercropping on rice sheath blight and rice blast diseases

Both sheath blight and blast are important rice diseases worldwide. The exploration of environmentally sound practices to control these diseases will help to reduce fungicide application. Effects of rice (Oryza sativa) intercropping with water chestnut (Eleocharis dulcis) on rice sheath blight and rice blast disease as well as the extracts of different plant parts and root exudates from water chestnut on pathogens of rice sheath blight (Rhizoctonia solani) and rice blast disease (Magnaporthe oryzae) were investigated using pot experiments and bioassay tests. The results from pot tests showed that rice-water chestnut intercropping system suppressed sheath blight and blast and improved land equivalent ratio (LER). The results from bioassay tests indicated that extracts and root exudates from water chestnut had significant effects to inhibit the expansion of these pathogens. The scales of these inhibitions were time and concentration dependent. The antifungal activities of the extracts from aboveground parts and pulp of water chestnut were significantly higher than the extracts from other parts and root exudates. The water extracts of aboveground parts showed the highest antifungal activity on both pathogens according to EC₅₀ values. The antifungal activities of the same extracts from water chestnut on R. solani were significantly higher than on M. oryzae. The result suggests that water chestnut possesses bioactive substances to suppress rice sheath blight disease and rice blast disease. The rice-water chestnut intercropping system can be used as an environment-friendly method for diseases control in rice field.     

Marker-Assisted Breeding of Thermo-Sensitive Genic Male Sterile Line 1892S for Disease Resistance and Submergence Tolerance

Rice line 1892S is an elite thermo-sensitive genic male sterile(TGMS)line for two-line hybrid rice production.However,1892S is susceptible to rice blast,bacterial blight and submergence.Here we reported the introduction of blast resistance(R)gene Pi9,bacterial blight R gene Xa21 and submergence tolerance gene Sub1A into 1892S genetic background through backcrossing and marker-assisted selection.The improved TGMS line 31892S and its hybrids conferred disease resistance to rice blast and bacterial blight,and showed submergence tolerance for over 14 d without significant loss of viability.The sterility-fertility conversion of 31892S was similar to that of 1892S.31892S and its derived hybrid rice had similar agronomic traits and grain quality with 1892S and the control hybrid rice,respectively.The newly developed 31892S provided an improved TGMS line for two-line hybrid rice production with disease resistance to rice blast and bacterial blight,and submergence tolerance with no yield penalty or change in grain quality.     

Effects of Powdered Rice Chaff Application on Si and N Absorption,Lodging Resistance and Yield in Rice Plants (Oryza sativa L.)

Abstract

Rice chaff, a major by-product of rice cultivation, is generally known for its high content of Si. Pot and small field plot (concrete plot) experiments were conducted to ascertain the effects of rice chaff in powdered form (Cp) and normal rice chaff (Ch) with or without bio-decomposer application on lodging resistance, yield, Si and N absorption of rice ( Oryza sativa L. cv. Hatsushimo). The results showed that the absorption of Si by plants could be promoted by Gp supplied together with a bio-decomposer, although the N content in plants was not increased. In the concrete plot experiment, lodging resistance was improved by Cp applied under a lightly-fertilized condition due to the high breaking strength and strong bending stress caused by the high Si content in the plants. Cp application tended to increase under a lightly-fertilized condition, but decreased the yield under a heavily-fertilized condition. It was suggested hat Cp application is effective on rice growth under a lightly-fertilized condition, and that Cp may be useful as an alternative of inorganic Si fertilizer and contribute to a sustainable Si recycle system in rice cultivation.     

Light and plant growth‐promoting rhizobacteria effects on Brachiaria brizantha growth and phenotypic plasticity to shade

This is the first report on the effect of light intensity and plant growth‐promoting rhizobacteria (PGPR) on the growth of a tropical forage grass, being a relevant study to improve pasture management in conventional farming and integrated crop‐livestock‐forestry systems. In this study, our aim was to evaluate the effects of light intensity and Burkholderia pyrrocinia and Pseudomonas fluorescens inoculation on Brachiaria brizantha cv. BRS Piatã growth, and phenotypic plasticity to shade. The experiment was conducted in a semi‐controlled environment. Seedlings of B. brizantha were allocated to full sun and shade. P. fluorescens and B. pyrrocinia were inoculated individually or co‐inoculated by soil drench, 14 days after seedling emergence. We evaluated morphogenesis, structural and growth parameters. Irrespective of the light regime, co‐inoculated plants had greater leaf area and SPAD index (chlorophyll content). Increase in total biomass production in co‐inoculated plants was over 100% and 300%, under full sun and shade respectively. Co‐inoculated P. fluorescens and B. pyrrocinia increased shade tolerance in B. brizantha, improving plant performance. Co‐inoculation promoted growth in B. brizantha under both sun and shade, indicating its potential as a bio‐fertilizer in conventional and integrated systems, especially in silvopastoral systems, where light availability to pasture growth may be limited.     

CRISPR/Cas9-Targeted Knockout of Rice Susceptibility Genes OsDjA2 and OsERF104 Reveals Alternative Sources of Resistance to Pyricularia oryzae

Rice genes OsDjA2 and OsERF104, encoding a chaperone protein and an APETELA2/ ethylene-responsive factor, respectively, are strongly induced in a compatible interaction with blast fungus, and also have function in plant susceptibility validated through gene silencing. Here, we reported the CRISPR/Cas9 knockout of OsDjA2 and OsERF104 genes resulting in considerable improvement of blast resistance. A total of 15 OsDjA2 (62.5%) and 17 OsERF104 (70.8%) T₀ transformed lines were identified from 24 regenerated plants for each target and used in downstream experiments. Phenotyping of homozygous T₁ mutant lines revealed not only a significant decrease in the number of blast lesions but also a reduction in the percentage of diseased leaf area, compared with the infected control plants. Our results supported CRISPR/Cas9-mediated target mutation in rice susceptibility genes as a potential and alternative breeding strategy for building resistance to blast disease.     

Quantitative effects of cultural practices on growth and yield of forage rice having short panicles

Cultivation of forage rice for whole-crop silage has been increasing in Japan and will be important in Asia. In this study, effects of cultural practices on growth and yield of a forage rice cultivar “Tsukisuzuka” having short panicle 1 allele were analysed quantitatively using linear mixed model. The contribution of basal dressing to dry yield per 1 g/m² nitrogen fertilizer was larger than that of topdressing. In addition, topdressing 30 and 20 days before heading was considered to have the disadvantage of increasing risk of lodging and panicle weight respectively. Effects of weather elements on growth of forage rice were also speculated. In tested fields, high solar radiation at seedling and tillering stage was considered important for the high yield. As the number of continuous cropping cycles increased, growth of forage rice got worse. And application of compost improved growth of forage rice. Elemental analysis of soil and plants revealed that this continuous cropping obstacle was likely to attributed to deficiency of potassium. In addition, potassium deficiency increased panicle weight of a forage rice cultivar having short panicle 1 allele. Therefore, control of potassium nutrition will be useful for both sustaining productivity (sufficient application of potassium) and seed production (restriction of potassium). These findings will be useful for improvement of cultivation method of forage rice.     

Improvement of nitrogen management in rice paddy fields using chlorophyll meter (SPAD)

Optimum rate and timing application of nitrogen (N) fertilizer are most crucial in achieving high yield in irrigated lowland rice. In order to assess leaf N status, a semidwarf rice cultivar (Khazar) was grown with different N application treatments (0, 40, 80, and 120 kg N ha⁻¹ splited at transplanting, midtillering, and panicle initiation stages) in a sandy soil in Guilan Province, Iran, in 2003. The chlorophyll meter (SPAD 502) readings were recorded and leaf N concentrations were measured on the uppermost fully expanded leaf in rice plants at 10-day internals from 19 days after transplanting to grain maturity. Regression analysis showed that the SPAD readings predicted only 23% of changes in the leaf N concentration based on pooled data of leaf dry weight (N _dw) for all growth stages. However, adjusting the SPAD readings for specific leaf weight (SPAD/SLW) improved the estimation of N _dw, up to 88%. Specific leaf weight (SLW), SPAD readings, leaf area and weight as independent variables in a multiple regression analysis predicted 96% of the N _dw changes, while SPAD readings independently predicted about 80% of leaf N concentration changes on the basis of leaf area (N _a). It seems that chlorophyll meter provides a simple, rapid, and nondestructive method to estimate the leaf N concentration based on leaf area, and could be reliably exploited to predict the exact N fertilizer topdressing in rice.     

Modeling the effects of N application on growth,yield and plant properties associated with the occurrence of chalky grains of rice

The objective of this study was to propose a model for explaining rice responses to a wide range of N application rates in various growth attributes associated with the occurrence of chalky grains. We improved the sub-model for N uptake process of a previous rice model which was originally developed for explaining genotypic and environmental variations in the whole growth processes, considering the difference in the rate of N loss from the plant-soil system between indigenously supplied soil mineral N and fertilizer N. A total of 80 growth datasets of cultivar ‘Koshihikari’ grown at Shiga prefecture, Japan, in 2010 was utilized for the calibration and validation of the model. The rice growth model well explained the above-ground biomass growth (RMSD = 78.7 g m^?2) and rough dry grain yield (RMSD = 83.2 g m^?2) for the validation data-set, simultaneously. The simulated carbohydrate content available per single spikelet was negatively correlated with the observed percentage of the milky-white grain which includes white-cored grain (r = ?.77, p < .001) for all the data-sets of calibration and validation. On the other hand, the observed percentage of the sum of white-back and white-base grains was closely correlated with the simulated plant N content available per single spikelet (r = ?.59, p < .001). It was suggested that the present rice growth model would rationally explain the effects of N application on the occurrence of the chalky grains through the dynamic change of the carbohydrate content and plant N content available per single spikelet.     

Rice yield and its relation to root growth and nutrient-use efficiency under SRI and conventional cultivation: an evaluation in Madagascar

While plant growth and productivity are known to derive from the interaction between genetic potential (G) and environmental factors (E), efforts to improve rice production have usually proceeded assuming a standard E that is created by conventional rice-growing practices. Genotypes have been assessed for their performance in continuously flooded paddy soils, with optimally dense plant populations, with reliance on inorganic fertilization to raise yields. The System of Rice Intensification (SRI) developed in Madagascar and now becoming accepted in much of Asia proposes that GxE interactions can be made more productive with different management practices: optimally sparse populations, established with very young seedlings carefully transplanted, intermittent flooding of paddies, with active soil aeration and with soil organic matter enhanced as much as possible. This article evaluates the effects of alternative SRI cultural practices on grain yield with particular attention to their impact on the growth and functioning of rice plant roots and on associated nutrient-use efficiencies that could be contributing to the observed higher grain yields. On-station experiments and on-farm surveys were conducted in Madagascar to evaluate SRI practices in comparison with standard cultural methods, considering how rice plants’ expression of their genetic potential was affected by different crop management practices. Controlling for both soil and farmer effects, rice plants cultivated with SRI methods produced average yields more than double those from standard practice (6.26 vs. 2.63 t ha⁻¹). The most evident phenotypic difference was in plant root growth, assessed by root-pulling resistance (RPR), a summary measure of root system development. On average, uprooting single SRI plants required 55.2 kg of force plant⁻¹, while pulling up clumps of three conventionally grown plants required 20.7 kg hill⁻¹, or 6.9 kg plant⁻¹. SRI plants thus offered 8 times more resistance per plant to uprooting. Direct measurements confirmed that SRI methods induced both greater and deeper root growth, which could be contributing to increased nutrient uptake throughout the crop cycle, compared with the shallower rooting and shorter duration of root functioning under continuous flooding. Rice plants grown with SRI methods took up more macronutrients than did the roots of conventionally managed plants, which was reflected in the higher SRI yields. When grain yield was regressed on nutrient uptake to assess nutrient-use efficiency, SRI plants achieved higher grain yield per unit of N taken up, compared to plants grown with conventional methods. The internal efficiency (IE) of SRI plants in utilizing macronutrients was 69.2 for N, 347.2 for P, and 69.7 for K, while the IE in plants conventionally grown was 74.9, 291.1, and 70.4 for these three macronutrients, respectively. Although no significant differences in IE were observed for N and K, the uptake of P was significantly greater, indicating more efficient use of P by SRI plants for grain production. More research needs to be done on such relationships, but this study indicates that productive changes in the structure and functioning of rice plants, particularly their roots, can be induced by alternative management methods.     

Characterization of a Maize Sucrose–phosphate Synthase Protein and Its Effect on Carbon Partitioning in Transgenic Rice Plants

Abstract

We obtained transgenic rice (Oryza sativa L. cv. Nipponbare) plants with the gene for maize sucrose-phosphate synthase (EC 2.4.1.14, SPS). Some of the transgenic plants over-expressed maize SPS (over-expressing plants) and some had reduced levels of native SPS protein (co-suppressed plants). There was a positive correlation between the amounts of maize SPS protein and SPS activities. However, apparent Km values for uridine diphosphoglucose (UDPG) were higher in over-expressing plants than in control rice plants. These results suggest that overproduced maize SPS protein was not fully activated. The sucrose contents did not differ significantly between control and over-expressing rice plants, but they were lower in co-suppressed plants than in control plants. The starch contents were negatively and the sucrose/starch ratios were positively correlated with SPS activities. Thus, carbon partitioning in the transgenic rice was changed, even though rice is predominantly a sucrose-former.     

杂交稻抗瘟性遗传表达特征的研究

本文报导我国主要三系及其组合的抗瘟性和抗瘟性遗传的表达特征,讨论了提高杂交水稻抗瘟性的有关问题。