Bacterization of peanut withPseudomonas fluorescens for biological control ofRhizoctonia solani and for enhanced yield

Severity of stem-rot disease of peanut caused byRhizoctonia solani was reduced by 54.9 and 68% in plants of two cultivars treated in the greenhouse with antagonistic strains ofPseudomonas fluorescens. These strains were selected based on theirin vitro toxicity to mycelial growth and sclerotial germination ofR. solani. In field experiments, bacterization of peanuts withP. fluorescens resulted in taller plants (by 25.7%) and increased yields (by 59.0%).     

Biological control of rice root-knot nematode,Meloidogyne graminicola through mixture of Pseudomonas fluorescens strains

The plant growth promoting rhizobacterium, Pseudomonas fluorescens strains PF1, TDK1, and PY15 were evaluated individually and in combinations for their efficacy against root-knot nematode, Meloidogyne graminicola, in rice plants under in vitro, glass house and field conditions. Culture filtrates of these strains either individually or as mixture inhibited egg hatching and caused mortality of juveniles of M. graminicola in vitro. The efficacy was more pronounced when filtrates of the strain were used as mixtures than as individual strains. Mixtures of P. fluorescens strains signficantly reduced M. graminicola infestation when applied as bacterial suspensions through seed treatment. The higher activity of peroxidase and chitinase enzymes was observed in plants treated with P. fluorescens mixtures than the plants treated with individual strains, two strain mixtures and untreated control. In field trials on rice, talc formulations of the P. fluorescens strains individually as well as mixtures were evaluated as seed treatment, soil treatment and combination of both. A mixture of the three strains was the most effective when applied either as seed + soil treatment or as seed treatment alone. The introduced P. fluorescens strains survived endophytically on rice roots. The application of the P. fluorescens mixture PF1 + TDK1 + PY15 in seed + soil treatment resulted in higher grain yield which provided a 27.3% increase over the control followed by P. fluorescens mixture PF1 + TDK1 + PY15 in seed treatment alone, which increased the grain yield of rice by 24.7% compared to the control.     

Comparison of the efficacy of chitosan with that of a fluorescent pseudomonad for the control of Fusarium head blight disease of cereals and associated mycotoxin contamination of grain

Fusarium culmorum can cause Fusarium head blight (FHB) disease of cereals, resulting in yield loss and contamination of grain with the trichothecene mycotoxin, deoxynivalenol (DON). In this study, we compared the efficacy of a biological control agent (Pseudomonas fluorescens strain MKB 158) with the biochemical chitosan (the deacetylated derivative of chitin) in controlling FHB disease of wheat and barley. Both agents were equally effective in reducing DON contamination of grain caused by F. culmorum. Under both glasshouse and field conditions, treatment with commercially available crabshell-derived chitosan reduced the severity of FHB symptom development on wheat and barley by ?74% (P ? 0.050). While treatment with P. fluorescens reduced the severity of FHB symptom development on these cereals by ?48% (P ? 0.050). Chitosan and P. fluorescens respectively prevented ?58 and ?35% of the FHB-associated reductions in 1000-grain weight in wheat and barley (P ? 0.050). Both agents significantly reduced the DON content of wheat and barley under both glasshouse and field conditions (P ? 0.050) and were equally efficacious in doing so (?74 and ?79% reductions due to chitosan and P. fluorescens, respectively). Crude chitin extracts from crabshells and crude chitosan-based formulations prepared from crabshells and eggshells were also tested under field conditions, but were not as effective as the commercial crabshell-derived preparation in controlling FHB disease. This is the first report on the use of chitosan for the control of Fusarium head blight disease and DON contamination of grain.     

Efficacy of Pseudomonas fluorescens and Paecilomyces lilacinus against Meloidogyne graminicola infecting rice under system of rice intensification

The talc-based formulations of the plant growth promoting rhizobacterium, Pseudomonas fluorescens and egg parasitic fungi, Paecilomyces lilacinus, were evaluated as seed treatment, soil application and combination of both for the management of M. graminicola in fields of rice grown under system of rice intensification. Both the bioformulations significantly reduced the root invasion and soil populations of M. graminicola but P. fluorescens was most effective when applied as seed cum soil application and seed treatment alone. Effect of these treatments was comparable with the standard chemical carbofuran application. The introduced P. fluorescens survived significantly in rice roots when applied as seed cum soil application and seed application alone than as soil application. There was significant increase in phenol, peroxidase and chitinase accumulation in plants treated with P. fluorescens. Application of bioagents had positive influence on growth parameters such as plant height, root length, shoot weight, root weight and number of tillers per hill. Application of P. fluorescens as seed cum soil treatment resulted in higher grain yield, which was 20.6%–26.9% increase over control followed by P. fluorescens as seed treatment alone that increased grain yield of rice by 10.7%–11.2% than control. However, economic returns per investment was higher when P. fluorescens was applied as seed treatment alone (1:8.8–1:12.0 incremental cost benefit ratio) followed by the P. fluorescens as seed cum soil treatment (1:6.2–1:9.7 incremental cost benefit ratio).     

Interactions between Heterodera avenae and Pratylenchus neglectus on Wheat

In a long-term field experiment, differential population densities of Heterodera avenae were produced by frequent cropping with resistant (cv. Panema) or susceptible (cv. Peniarth) oat. The two oat cultivars were equally good hosts of Pratylenchus neglectus in a glass house experiment with field soil. On wheat crops grown after oats in field experiments, P. neglectus population densities in roots were higher in plots where H. avenae had been controlled than in plots with moderate infestations (40 H. avenae eggs/g soil). The field observations indicated that the reduction in population densities of P. neglectus coincided with the development in roots of sedentary stages of the cyst nematode. Evidence for an indirect effect of H. avenae on P. neglectus was found in vitro in a split-root experiment. In the same field, grain yields of two wheat cultivars susceptible or resistant to H. avenae, but both susceptible to P. neglectus, was not reduced by P. neglectus. Alternation of H. avenae resistant and susceptible cultivars is a possible way of exploiting the inverse relationship between these nematodes, whilst controlling cyst nematode -populations in intensive cereal production systems.     

A comparative screening of hybrid,modern varieties and local rice cultivar for brown leaf spot disease susceptibility and yield performance

Five rice cultivars, one hybrid (WR96), three modern (BR16, BR26, and BRRI Dhan27) and one local (Pari) were screened for reaction to brown leaf spot disease caused by Cochliobolus miyabeanus and performance of yield-related characters. The severity of brown leaf spot varied with growth stages of rice plant as well as different cultivars tested under field condition. Low disease severity was observed at maximum tillering stage compared to moderate to high at dough stage, with hybrid cultivar WR96 showing highest disease, while local cultivar Pari had the lowest. Brown spot disease severity in different cultivars under induced epiphytic condition also followed the similar trend. The results also revealed that most of the yield-contributing characters examined showed wide variations among the cultivars. Modern cultivar BR16 produced the highest panicle length, number of grain per panicle and grain yield per hectare. At the same time as local cultivar Pari generated the lowest number of tiller per plant, panicle length, grain number per panicle and grain yield per hectare. Moreover, hybrid cultivar WR96 produced the highest percentage of spotted grain per panicle and seed yielding C. miyabeanus, and also the lower percentage of seed germination, while the reverse was observed in local cultivar Pari. These findings may allow producers and breeders to select rice cultivar, resistant or tolerant to brown leaf spot disease and to avoid significant reductions in grain yields.     

Effect of arbuscular mycorrhizal fungi and Pseudomonas fluorescens on root-rot and wilt,growth and yield of Coleus forskohlii

Root-rot and wilt caused by Fusarium chlamydosporum affects the cultivation of Coleus forskohlii, a medicinal plant grown for its roots, which contain a pharmaceutically important compound called forskolin. In this study, management of this disease under low and high inoculum levels was assessed with four arbuscular mycorrhizal (AM) fungi and a strain of Pseudomonas fluorescens. The AM fungus Glomus fasciculatum and P. fluorescens were the most effective treatments that reduced the severity of root-rot and wilt of C. forskohlii by 56–65% and 61–66%, respectively, under lower and higher levels of pathogen F. chlamydosporum. G. fasciculatum increased the dry shoot and root weight by 108–241% and 92–204%, respectively, while in plants treated with P. fluorescens, an increase of 97–223% and 97–172% in dry shoot and root weight, respectively, was observed. Although P. fluorescens was effective, it gave higher root yields only under lower inoculum level of the pathogen. G. fasciculatum performed equally well under both lower and higher inoculum levels. Increase in yields with both the biocontrol agents was accompanied by increase in P uptake (230–303%) and in K uptake (270–335%). The forskolin content of the roots was significantly increased (14–21%) by G. fasciculatum, P. fluorescens or G. mosseae under lower inoculum level of pathogen.     

Variation of weed-suppressing potential of Vietnamese rice cultivars against barnyardgrass (Echinochloa crus-galli) in laboratory,greenhouse and field screenings

Abstract

A total of 73 different varietal groups and cultivars of Vietnamese rice (Oryza sativa L.) were evaluated for the allelopathic potential on barnyardgrass (Echinochloa crus-galli) in laboratory, greenhouse and field screenings. In a bioassay, Y1, U17, Nep Thom and Lua Huong, cultivars showed the highest weed-suppressing ability against the length of shoot and root of barnyardgrass. Y-1, Nhi Uu and Khau Van exerted significant inhibitory effects in greenhouse screening. In the field study, Phuc Tien obtained the highest weed-suppressing potential. The allelopathic activity of Vietnamese rice showed cultivar-dependence and varietal group-dependence, of which hybrid group cultivars (H) showed the highest inhibition, followed by the local non-sticky cultivars (LNS), foreign (F), traditional sticky (TS), and traditional upland sticky (TUS), while the least were the local upland non-sticky (LUNS) cultivars. The inhibition exerted in both bioassay and greenhouse was lower than the observed weed suppression in the field by 15–20%; however, rice cultivars against the growth of barnyardgrass in greenhouse screening showed more correlation to the results obtained in the field than that of the laboratory, but both laboratory and greenhouse screenings may arduously reflect the actual weed-suppressing ability of rice exhibited in the field. The obtained data might be useful for the enhancement of the weed-suppressing ability of rice in this country.     

Effects of Canavalia ensiformis and Mucuna pruriens intercrops on Pratylenchus zeae damage and yield of maize in subsistence agriculture

Host status of four leguminous cover crops [Canavalia ensiformis (L.) DC. (Jack bean), Crotalaria ochroleuca G. Don (Sunnhemp), Lablab purpureus L. (Hyacinth bean) and Mucuna pruriens (L.) DC. (velvet bean)] to Pratylenchus zeae Filipjev and effects of intercropping C. ensiformis and M. pruriens with Pan5195, H627 and Emap11 maize cultivars on P. zeae population and disease severity on maize were determined in greenhouse and field tests. Pratylenchus zeae significantly (P<0.05) reduced growth of C. ochroleuca by 36% but had no effect on C. ensiformis, M. pruriens and L. purpureus. While C. ensiformis, M. pruriens and L. purpureus reduced P. zeae population, C. ochroleuca increased it. In the greenhouse test, intercropping maize with C. ensiformis significantly (P<0.05) improved maize growth by up to 34%, Nematode populations in the roots of maize intercropped with either C. ensiformis or M. pruriens were significantly (P<0.05) reduced by up to 32% while nematode disease severity in these intercropping systems was reduced by up to 26%. In the field test, intercropping Emap11, Pan5195 and H627 with C. ensiformis significantly (P<0.05) increased maize grain yield by 190, 29 and 22%, respectively. Intercropping H627 with M. pruriens significantly (P<0.05) increased maize grain yield by 12%, but grain yields of Pan5195 and Emap11 declined by 79 and 40%, respectively. Root necrosis and soil nematode populations in the C. ensiformis–maize intercrop declined by up to 50 and 30%, respectively. Under pure maize stands, soil nematode populations increased by up to 35% in 90 days relative to the initial nematode population of three nematodes g⁻¹ of fresh soil. Section Editor: P. A. M. Bakker     

Brassinosteroids regulate grain filling in rice

Genes controlling hormone levels have been used to increase grain yields in wheat (Triticum aestivum) and rice (Oryza sativa). We created transgenic rice plants expressing maize (Zea mays), rice, or Arabidopsis thaliana genes encoding sterol C-22 hydroxylases that control brassinosteroid (BR) hormone levels using a promoter that is active in only the stems, leaves, and roots. The transgenic plants produced more tillers and more seed than wild-type plants. The seed were heavier as well, especially the seed at the bases of the spikes that fill the least. These phenotypic changes brought about 15 to 44% increases in grain yield per plant relative to wild-type plants in greenhouse and field trials. Expression of the Arabidopsis C-22 hydroxylase in the embryos or endosperms themselves had no apparent effect on seed weight. These results suggested that BRs stimulate the flow of assimilate from the source to the sink. Microarray and photosynthesis analysis of transgenic plants revealed evidence of enhanced CO₂ assimilation, enlarged glucose pools in the flag leaves, and increased assimilation of glucose to starch in the seed. These results further suggested that BRs stimulate the flow of assimilate. Plants have not been bred directly for seed filling traits, suggesting that genes that control seed filling could be used to further increase grain yield in crop plants.     

Field inoculation of sorghum and rice withAzospirillum spp. andHerbaspirillum seropedicae

Two field experiments were carried out at the UAPNPBS experimental station, Seropédica, with two sorghum and one rice cultivars. The establishment, and inoculation effects, ofAzospirillum spp. andHerbaspirillum strains marked with antibiotic resistance were investigated. One grain sorghum (BR 300) and one sugar sorghum (Br 505) cultivar were used.Azospirillum lipoferum strain S82 (isolated from surface sterilized roots of sorghum) established in both cultivars and comprised 40 to 80% of theAzospirillum spp. population in roots and stems 60 days after plant emergence (DAE).Azospirillum amazonense strain AmS91 (isolated from surface-sterilized roots of sorghum) reached only 50%. At 90 DAE, S82 almost disappeared (less than 30% of establishment) while the establishment of AmS91 remained constant in roots and stems. No establishment ofH. seropedicae strain H25 (isolated from surface-sterilized roots of sorghum) orA. lipoferum strain S65 (isolated from the root surface of sorghum) could be observed on inoculated roots. Inoculation with S82, AmS91 or S65 but not withH. seropedicae H25, increased plant dry weight of both cultivars and total N in grain of the grain sorghum. In rice,A. lipoferum Al 121 andA. brasilense Sp 245 (isolated from surface sterilized rice and wheat roots respectively) established in the roots but there was no increase inAzospirillum spp. numbers due to inoculation. None of the strains affected plant growth or rice grain yield.Azospirillum amazonense, A82 andH. seropedicae Z95, which did not establish in roots, significantly enhanced seed germination.     

Reproductive and Damage Potential of Ditylenchus destructor on Peanut

The reproductive and damage potential of Ditylenchus destructor on peanut, Arachis hypogaea cv. Sellie, was determined in greenhouse tests. Final nematode population densities (Pf) in roots, hulls, and seeds increased (P = 0.01) as a function of increasing initial population (Pi). Final population densities were higher in hulls than in seeds and roots. Final densities in hulls and seeds were positively (P = 0.01) correlated. Fresh root and hull weight and number of pods and seeds per plant were not affected by D. destructor. Second generation germination and pod and seed disease severity increased (P = 0.01), whereas fresh seed weight decreased (P = 0.01) as a function of increasing Pi, and Pf in seeds and Pf in hulls. At Pi 250 and higher, 10-25% of seeds germinated into second generation seedlings before harvest. At Pi 250 and higher, fresh weight of harvested seed was suppressed 20-50%. At Pi 50 or Pf greater than 20 per seed, pod disease severity was 3-7 (on a scale of 1 to 10) and 15-80% of seeds were blemished or unsound.     

A loss‐of‐function allele of OsHMA3 associated with high cadmium accumulation in shoots and grain of Japonica rice cultivars

Excessive cadmium (Cd) accumulation in rice poses a risk to food safety. OsHMA3 plays an important role in restricting Cd translocation from roots to shoots. A non‐functional allele of OsHMA3 has been reported in some Indica rice cultivars with high Cd accumulation, but it is not known if OsHMA3 allelic variation is associated with Cd accumulation in Japonica cultivars. In this study, we identified a Japonica cultivar with consistently high Cd accumulation in shoots and grain in both field and greenhouse experiments. The cultivar possesses an OsHMA3 allele with a predicted amino acid mutation at the 380^th position from Ser to Arg. The haplotype had no Cd transport activity when the gene was expressed in yeast, and the allele did not complement a known nonfunctional allele of OsHMA3 in F₁ test. The allele is present only in temperate Japonica cultivars among diversity panels of 1483 rice cultivars. Different cultivars possessing this allele showed greatly increased root‐to‐shoot Cd translocation and a shift in root Cd speciation from Cd―S to Cd―O bonding determined by synchrotron X‐ray absorption spectroscopy. Our study has identified a new loss‐of‐function allele of OsHMA3 in Japonica rice cultivars leading to high Cd accumulation in shoots and grain.     

Evaluation of Cultivars,Experimental Lines and Plant Introduction Collection of Sainfoin for Resistance to Meloidogyne hapla Chitwood

Stands of several cultivars and experimental lines of sainfoin (Onobrychis viciifolia) were severely reduced (92% average loss) in a field naturally infested with Meloidogyne hapla. Stands of two alfalfa cultivars included in the test were unaffected. In studies conducted in the greenhouse with plants inoculated at the time of seeding, average mortality was 55% for sainfoin entries and 7% for Ladak alfalfa. Little mortality occurred when plants were inoculated after establishment. Three months after inoculation, all sainfoin entries were heavily galled (range of 3.3-3.7 on a scale of 1-4) while roots of Ladak were only slightly galled (rating of 1.6). Intermating of plants selected in the field plots for resistance to M. hapla showed a slight increase in resistance. Of the 147 plant introduction lines tested in the greenhouse, none were resistant to M. hapla.     

Expression of Tolerance for Meloidogyne graminicola in Rice Cultivars as Affected by Soil Type and Flooding

The effects of different water regimes on the pathogenicity of Meloidogyne graminicola on six rice cultivars were determined in two soil types in three greenhouse experiments. Two water regimes, simulating continuous flooding and intermittent flooding, were used with five of the cultivars. All cultivars were susceptible to the nematode, but IR72 and IR74 were more tolerant than IR20 and IR29 under intermittent flooding. All were tolerant under continuous flooding. UPLRi-5 was grown under multiple water regimes: no flooding; continuous flooding; flooding starting at maximum tillering, panicle initiation, or booting stage; and flooding from sowing until maximum tillering or booting. In sandy loam soil, M. graminicola reduced stem and leaf dry weight, root dry weight, and grain weight under all water regimes. In clay loam soil, the nematode reduced root weight when the soil was not flooded or flooded only for a short time, from panicle initiation, or booting to maturity, and from sowing to maximum tillering. In clay loam soil, stem and leaf dry weight, as well as grain weight, were reduced by the nematode under all water regimes except continuous flooding or when the soil was flooded from sowing to booting stage. These results indicate that rice cultivar tolerance of M. graminicola varies with water regime and that yield losses due to M. graminicola may be prevented or minimized when the rice crop is flooded early and kept flooded until a late stage of development.     

Bacterial biosynthesis of 1-aminocyclopropane-1-caboxylate (ACC) deaminase,a useful trait to elongation and endophytic colonization of the roots of rice under constant flooded conditions

This study was conducted to investigate the role of 1-aminocyclopropane-1-carboxylate (ACC) deaminase in Pseudomonas fluorescens strain REN₁ and its ability to reduce ethylene levels produced during stress, endophytically colonize and promote the elongation of the roots of rice seedlings under gnotobiotic conditions. We isolated 80 bacteria from inside roots of rice plants grown in the farmers’ fields in Guilan, Iran. All of the isolates were characterized for plant growth promoting (PGP) traits. In addition, the colonization assay of these isolates on rice seedlings was carried out to screen for competent endophytes. The best bacterial isolate, based on ACC deaminase production, was identified and used for further study. 16S rDNA sequence analysis revealed that the endophyte was closely related to Pseudomonas fluorescens. The results of this study showed ACC deaminase containing P. fluorescens REN1 increased in vitro root elongation and endophytically colonized the root of rice seedlings significantly, as compared to control under constant flooded conditions. The trait of low amount of indole-3-acetic acid (IAA) production (<15 μg mL⁻¹) and the high production of ACC deaminase by bacteria may be main factors in colonizing rice seedling roots compared to other PGP traits (siderophore production and phosphate solubilization) in this study. Endophytic IAA and ACC deaminase-producing bacteria may be preferential selections by rice seedlings. Therefore, it may be suggested that the utilization of ACC as a nutrient gives the isolates advantages in more endophytic colonization and increase of root length of rice seedlings.     

Effect of chemical forms of cadmium,zinc, and lead in polluted soils on their uptake by cabbage plants

Sorghum (Sorhum bicolor L. Moench) is an important cereal crop of the world. Performance of sorghum in acid infertile soils that are common to the tropics is rather poor. Research was undertaken in greenhouse and field conditions to evaluate the differences in growth, grain yield, and nutrient efficiency ratio (NER) of sorghum genotypes grown at three levels of Al saturation. The growth of shoots and roots and the grain yields showed significant differences with respect to Al-saturation, genotypes and their interactions. The shoot weights, root weights, and visual scores of the greenhouse study were highly related to grain yields obtained in field. The greenhouse technique adapted in this study appears to be a reliable method for separation of genotypes into Al-tolerant and intolerant types. The NER values helped differentiate genotypes into efficient and inefficient utilizers of the absorbed nutrients. The sorghum entries showed intraspecific genetic diversity in growth and NER values for the essential elements in the presence or absence of toxic levels of Al. We concluded that selection of acid soil tolerant genotypes and further breeding of acid soil (Al) tolerant cultivars is feasible in sorghum.IICA/EMBRAPA/World Bank     

Numerical taxonomy of fluorescent Pseudomonas associated with tomato roots

The phenetic taxonomy of 110 fluorescent bacterial strains, isolated from the roots of tomatoes and other plants was numerically studied through 97 features including 69 assimilation tests. Thirty-two reference strains of various Pseudomonas spp. were additionally included. The strains clustered into 16 clusters at the 74% similarity level when using Jaccard similarity coefficients. Almost all field strains belonged to the P. fluorescens/P. putida-complex while none clustered with P. syringae and allied bacteria. The biovar II branch, as well as the newly described biovar VI of P. fluorescens, made up 55% and 20% respectively, of the field strains; two % were allocated to P. fluorescens biovar I and three % to biovar IV. Eleven % of the root associated strains were designated P. putida; six strains were biovar A, three strains biovar B while four strains could not be referred to any known biovar. The continuum within the P. fluorescens/P. putida-complex as well as the taxonomic status of the six biovars of P. fluorescens and the three biovars of P. putida are discussed.     

Occurrence of Aphelenchoides besseyi in Louisiana Rice Seed and Its Interaction with Sclerotium oryzae in Selected Cultivars

Aphelenchoides besseyi, the nematode causal agent of white-tip disease of rice, was recovered from 5.5% of 474 seed samples obtained from rice seed warehouses in Louisiana. Laboratory tests in which A. besseyi-infested rice seed was treated with Phostoxin®, a compound used for control of insects in stored grain, indicate that it also has nematicidal properties. In 18-week-duration greenhouse tests, populations of A. besseyi increased 4-5-fold on the cultivars Saturn and Melrose and 3-fold on Nova ''76. Green weights of Nova ''76 plants inoculated with A. besseyi and Sclerotium oryzae, the causal agent of rice stem rot, were significantly reduced below those of plants inoculated with either organism alone or with distilled water. Weights of Melrose plants were reduced significantly by treatments with A. besseyi alone and A. besseyi plus S. oryzae, but not by S. oryzae alone. Saturn plant weights were not reduced significantly by either organism alone or by the two in combination.