Effect of virus infection on the rhizosphere mycoflora of papaya plants

Summary Rhizosphere mycoflora of PLRV (Papaya Leaf Reduction Virus)- infected and healthy papaya plants have been investigated at the pre-flowring, flowering and post-flowering stages of plants. The fungal population per g of soil was higher in rhizosphere of diseased plants at all the three stages than that of healthy ones. The increased C/N ratio in the leaves of PLRV-infected papaya plants is responsible for the increased rhizosphere mycoflora concentration of infected plants.     

Effect of certain chemical fertilizers on the rhizosphere mycoflora ofOryza sativa linn

The present paper deals with the study of the effect of potassium fertilizer (Potassium sulphate) on rhizosphere mycoflora ofOryza sativa. The fertilization improves the microbial activity both in rhizosphere and nonrhizosphere regions. 40 lbs/acre dose of the fertilizer proved best for paddy growth and rhizosphere fungal poulation. The highest fungal population was recorded at the time of flowering of the plants.     

Hummingbirds as vectors of fungal spores in Moussonia deppeana (Gesneriaceae): taking advantage of a mutualism?

Hummingbirds act as vectors of Fusarium moniliforme spores on protandrous flowers of Moussonia deppeana. The resulting interactions between the pathogen and plant-pollinator interactions were investigated in a 4-yr study to determine the pathogen's impact on host flowering phenology, flower longevity, nectar production, and fruit and seed production. We also evaluated hummingbird behavior on healthy and diseased plants and its effectiveness on spore transmission. Individual plants expressed the disease from year to year, and new infected individuals were detected every year. A fraction of the flowers in a plant expressed the disease, and this varied among and within years. Diseased plants produced more inflorescences, buds, and open healthy flowers than did healthy plants. Further, diseased plants bore proportionally fewer pistillate flowers than did healthy plants when considering only healthy flowers. Neither nectar nor fruit production differed between healthy and diseased plants, but healthy plants produced more seeds. Infected flowers were retained longer than uninfected ones, producing an additional 2 mg · μL(-1) · flower(-1) of nectar sugar. Hummingbirds visited more flowers on diseased plants than they did on healthy plants, regardless of number and sexual phase. Most pollen and spores were deposited within plants. These behavioral outcomes may promote geitonogamy and limit fungal spore mixing.     

黑胫病感染对烟草茎秆及根际土壤真菌群落结构的影响

烟草黑胫病是由寄生疫霉烟草变种引起的一种对烟草生产造成巨大经济损失的土传病害。本文以健康烟株与感染黑胫病烟株茎秆和根际土壤为研究对象,通过PCR技术扩增样本中真菌转录间隔区的ITS1区域,采用Illumina Miseq高通量测序技术对扩增片段进行测序,旨在了解黑胫病感染对于烟草茎秆和根际土壤真菌群落结构与多样性的影响。本研究20个测序样品,共获得755 599条高质量序列片段,最短序列为200bp,最长序列为356bp,平均序列长度248bp。结果表明,健康烟株和发病烟株根际土壤的优势真菌为子囊菌门Ascomycota、接合菌门Zygomycota和担子菌门Basidiomycota,所有茎秆样品的优势真菌为子囊菌门、担子菌门。健康烟株与感染黑胫病烟株根际土壤样品相对丰度大于1%的属有镰刀菌属Fusarium、被孢霉属Mortierella、隐球菌属Cryptococcus、链格孢属Alternaria和赤霉菌属Gibberella等,其中,健康烟株根际土壤优势属为镰刀菌属（39.35%）和被孢霉属（14.19%）,发病烟株根际土壤镰刀菌属和被孢霉属相对丰度分别为40.26%和20.77%;健康茎秆样品优势属为隐球菌属（31.12%）、链格孢属（18.28%）、镰刀菌属（15.67%）和红酵母属Rhodotorula（13.34%）;病健交界茎秆样品优势属为镰刀菌属（41.36%）、隐球菌属（28.15%）和链格孢属（22.32%）;发病茎秆优势属为隐球菌属（62.14%）和链格孢属（27.75%）。烟株感染黑胫病后,其根际土壤与茎秆样品真菌优势属种类与健康烟株无明显变化,但属水平的相对丰度变化显著。发病烟株茎秆与根际土壤样品真菌群落Sobs、Chao1、Shannon指数较健康烟株降低,Simpson指数上升,表明烟株发病后根际土壤真菌与茎秆内生真菌群落丰富度与多样性降低。该结果对于研究烟草黑胫病发生的微生态机制及其生物防治具有一定的理论指导意义。     

青枯病抗性不同的番茄品种根际拮抗菌拮抗能力差异研究

以植物基因型影响根际微生物的多样性为依据,通过平板拮抗试验,从番茄的感病品种和抗病品种、感病品种的严重发病植株和轻微发病植株根际筛选到36株抬抗菌,不同来源的抬抗菌群落具有不同的特征。严重发病的感病品种植株根际的拮抗菌群落多样性低,仅筛选到1个拮抗菌株,而轻微发病的感病品种和未发病的抗病品种植株根际筛选到的拮抗菌株数较多;抗病品种根际桔抗菌表现出强拮抗能力,而感病品种根际拮抗菌的拮抗能力较弱。测定植株根面和根颈处导管内青枯菌的种群数量、3株拮抗菌的防病效果,发现导管内青枯茵数量与防病效果基本一致,探讨了导管内青枯菌数量作为拮抗菌防病效果指标的可能性。     

Stomatal Conductance, Photosynthetic Rate, and Pigment Content in Ruellia Tuberosa Leaves as Affected by Coal-Smoke Pollution

Study of the effects of air pollution caused by thermal power plant emissions on some foliar traits of Ruellia tuberosa L. has shown that length and width of stomata, length of stomatal pore, stomatal density, photosynthetic rate, stomatal conductance and chlerophyll content were reduced in the polluted plants in pre-flowering, flowering as well as post-flowering phases of plant growth. Intercellular carbon dioxide concentration in the palisade tissue was increased at each stage of plant development. Stomatal index remained almost unchanged at the polluted site, except on the adaxial surface during the preflowering stage where it was higher as compared to the non-polluted plants.     

Effect of foliar spray of hormones on the rhizosphere mycoflora of leguminous weeds

Summary The effect of the foliar spray of two hormonesviz indole acetic acid and gibberellic acid on the rhizosphere mycoflora ofCassia tora L. andCrotalaria medicaginea Lamk., two leguminous weeds, has been studied at different stages of growth of the plants. Three sprays of the aqueous solutions of the hormones were made from the seedling stage onwards and, in all, five samplings of the rhizospheres were made. Estimation of the mycoflora was made by the dilution plate method as described in the text, using dextrose-peptone-agar-rose bengal medium. Statistically significant increase in the total number of fungi was observed in the rhizosphere of sprayed plants. With regard to the total number of species, there was no significant difference between the treated and control plants. It has been concluded that the stimulation of the rhizosphere mycoflora on foliar application of hormones might be due to the enhanced sporulation of fungi in the rhizosphere effected by the exudation of stimulatory factors from the roots.Part of doctoral thesis, Banaras Hindu University (1966).     

Effects of virus infection and light environment on population dynamics of Eupatorium makinoi (Asteraceae)

We studied the effects of virus infection on dynamics of three Eupatorium makinoi populations in contrasting light environments, Gora-dani (a shaded population) and Minou 1 and Minou 2 (open-site populations). Censuses of the plants were taken for 8 yr in Gora-dani and 4 yr in Minou 1 and Minou 2. After the epidemics of virus infection, most plants were virus infected at both sites. The number of plants and the proportion of flowering individuals decreased rapidly and simultaneously in the shaded population in Gora-dani. By contrast, in the open-site populations of Minou, the proportion of flowering plants decreased first, and then the number of plants decreased gradually. Growth analysis of the plants in the Gora-dani population revealed that stem growth was significantly suppressed by infection and that flowering and survivorship of the infected plants decreased with reducing plant height. Since light availability affected plant growth and thereby flowering and survivorship, the differences in population dynamics between the two field sites could be caused by the differences in light environments. Although populations in open sites may persist for considerable periods after virus epidemics, the individual local populations of E. makinoi would eventually become extinct irrespective of light environments.     

Influence of cucumber mosaic virus infection on the growth response of Portulaca oleracea (purslane) and Stellaria media (chickweed) to nitrogen availability

The study characterized the influence of cucumber mosaic virus (CMV) on the growth response of two annual weeds to nitrogen. Plants were grown individually along a N gradient from 4 to 32 mmol l⁻¹ and data were interpreted using growth analysis. Plant biomass increased with N concentration and was significantly higher for healthy than infected plants at the two highest N concentrations. Healthy plants of Portulaca oleracea L. were characterized by lower biomass allocation to leaves and higher biomass allocation to roots than infected plants; no change in biomass allocation was recorded for Stellaria media Vill. Relative growth rate ( rgr ), net assimilation rate ( nar ) and specific leaf area ( sla ) of plants increased with increasing N concentration. Healthy plants of P. oleracea were characterized by a higher rgr and nar and a lower sla than infected plants, whereas healthy S. media had a higher rgr but a similar nar and sla or leaf weight ratio ( lwr ) compared with infected plants. The consequences of these results on the population dynamics of weeds and virus spread are discussed.     

Influence of Bud Position and Plant Ontogeny on the Morphology of Branch Shoots in Pea (Pisum sativum L. cv. Alaska)

The morphology of axillary shoots of pea plants (Pisum sativumL. cv. Alaska) was analysed as a function of the position ofthe bud on the plant axis and the stage of plant developmentwhen the buds began to grow. Buds from the three most basalnodes were stimulated to develop by decapitating the main shootwhen buds were still growing (4 d plants), shortly after budsbecame dormant (7 d plants) or after the initiation of floweringon the main shoot (post-flowering plants, about 21 d after sowing).Branch shoots were scored for node of floral initiation (NFI),shoot length, and node of multiple leaflets (NML), a measureof leaf complexity. Shoots that developed spontaneously fromupper nodes (nodes 5-9) on intact post-flowering plants werescored for NFI. NFI for basal buds on 4 and 7 d plants variedas a function of nodal position and ranged from 5 to 6·7nodes. NFI on these plants was not influenced by bud size orwhether a bud was growing or dormant when the plant was decapitated.NFI for shoots derived from basal buds on decapitated post-floweringplants and upper nodes on intact post-flowering plants was about4. Reduced NFI on post-flowering plants may be due to depletionof a cotyledon-derived floral inhibitor. Basal axillary shootson 4 d plants were about 20% longer than those on 7 d plantsand about five times longer than those on post-flowering plants.These differences may be due to depletion of gibberellic acidsfrom the cotyledons. NFI and NML for the main shoot and forbasal axillary shoots were similar under some experimental conditionsbut different under other conditions, so it is likely that eachdevelopmental transition is regulated independently.Copyright1995, 1999 Academic Press Apical dominance, bud development, garden pea, initiation of flowering, Pisum sativum L., shoot morphology     

Effects of nitrogen deficiency on photosynthetic traits of maize hybrids released in different years

BACKGROUND AND AIMS: New maize (Zea mays) hybrids outperformed old ones even at reduced N rates. Understanding the mechanisms of the differences in performance between newer and older hybrids under N deficiency could provide avenues for breeding maize cultivars with large yield under N deficiency, and reduce environmental pollution caused by N fertilizers. METHODS: N deficiency effects on grain weight, plant weight, harvest index, leaf area and photosynthetic traits were studied in the field for six maize hybrids released during the past 50 years to compare their tolerance and to explore their physiological mechanisms. KEY RESULTS: N deficiency decreased grain yield and plant weight in all hybrids, especially in the older hybrids. However, there was no significant difference in harvest index, rate of light-saturated photosynthesis (Psat) 20 d before flowering, leaf area or plant weight at flowering between the N-deficient and control plants of all hybrids. Dry matter production after flowering of the N-deficient plants was significantly lower than that of the control plants in all hybrids, especially in the older hybrids, and was mostly due to differences in the rate of decrease in photosynthetic capacity during this stage. The lower Psat of the older hybrids was not due to stomatal limitation, as there was no significant difference in stomatal conductance (gs) and intercellular CO2 concentration (Ci) between the hybrids. N deficiency accelerated senescence, i.e. decreased chlorophyll and soluble protein contents, after anthesis more for the earlier released hybrids than for the later ones. N deficiency decreased phosphoenolpyruvate carboxylase (PEPCase) activity significantly more in older hybrids than newer hybrids, and affected the maximal efficiency of PSII photochemistry (Fv/Fm) only in the old hybrids and at the late stage. CONCLUSIONS: Compared with older (earlier released) hybrids, newer (later released) hybrids maintained greater plant and grain weight under N deficiency because their photosynthetic capacity decreased more slowly after anthesis, associated with smaller non-stomatal limitations due to maintenance of PEPCase activity, and chlorophyll and soluble protein content.     

水肥菌一体化番茄基质栽培系统青枯病病株和健株根际微生物群落结构的差异

[目的]探究水肥菌一体化基质栽培系统番茄青枯病害发生与根际群落结构的相互关系.[方法]通过田间病情调查,统计番茄青枯病发病率和病情指数,进而利用高通量测序技术比较分析感染青枯病和健康番茄植株根际基质细菌群落结构多样性和组成.[结果]番茄植株在生殖生长期(移栽后60 d)的发病率(6.17％)和病情指数(5.11)均大于...     

Foliar responses ofPeristrophe bicalyculata to coal smoke pollution

Study of the foliar responses ofPeristrophe bicalyculata (Reth) Nees to the pollution caused by thermal power plant emissions revealed that the stomatal size, pore length, density, and index, as well as the photosynthetic rate and total chlorophyll content were reduced inP. bicalyculata plants at the polluted site in pre-flowering, flowering as well as post-flowering stage of plant growth. Contrary to this, stomatal conductance increased at each stage. The intercellular level of carbon dioxide was raised in the pre-flowering and flowering stages but decreased later at the polluted site.     

Regulation of ADPglucose pyrophosphorylase in cucumber plants infected with the cucumber mosaic virus

ADPglucose pyrophosphorylase level and mechanisms regulating its activity were studied in cucumber plants infected with the cucumber mosaic virus at the stage of chronic infection. Studies carried out with partially purified preparations of the enzyme have shown that there was no substantial difference in the regulatory influence of the ratio 3-PGA/P₁, or in the number of binding sites of the effectors on the enzyme, but that the virus infection reduced the level of the enzyme in the tissues to 74% of the control and the 3-PGA/P₁ ratio to one half which resulted in a further decrease in ADPglucose pyrophosphorylase activity. In crude homogenate prepared from diseased plants, activity of the enzyme was reduced to 42% of the healthy control. The level of UDPglucose pyrophosphorylase was three times higher in cucumber leaf tissues than the level of ADPglucose pyrophosphorylase which was inhibited by both 3-PGA and P₁. Inhibitory effects of both these effectors were cumulated. The enzyme isolated from healthy plants was inhibited by inorganic phosphate more strongly than the enzyme isolated from diseased plants. UDPglucose pyrophosphorylase activity was increased in crude homogenate of diseased plants to 127% of the healthy control when the level of the enzyme was the same in the tissues of both healthy and diseased plants which was presumably connected with the enhanced rate of sucrose catabolism.     

Post-Flowering Nitrate Uptake in Wheat Is Controlled by N Status at Flowering,with a Putative Major Role of Root Nitrate Transporter NRT2.1

In bread wheat (Triticum aestivum L.), the simultaneous improvement of both yield and grain protein is difficult because of the strong negative relationship between these two traits. However, some genotypes deviate positively from this relationship and this has been linked to their ability to take up nitrogen (N) during the post-flowering period, regardless of their N status at flowering. The physiological and genetic determinants of post-flowering N uptake relating to N satiety are poorly understood. This study uses semi-hydroponic culture of cv. Récital under controlled conditions to explore these controls. The first objective was to record the effects of contrasting N status at flowering on post-flowering nitrate (NO₃ ^-) uptake under non-limiting NO₃ ^- conditions, while following the expression of key genes involved in NO₃ ^- uptake and assimilation. We found that post-flowering NO₃ ^- uptake was strongly influenced by plant N status at flowering during the first 300–400 degree-days after flowering, overlapping with a probable regulation of nitrate uptake exerted by N demand for growth. The uptake of NO₃ ^- correlated well with the expression of the gene TaNRT2.1, coding for a root NO₃ ^- transporter, which seems to play a major role in post-flowering NO₃ ^- uptake. These results provide a useful knowledge base for future investigation of genetic variability in post-flowering N uptake and may lead to concomitant gains in both grain yield and grain protein in wheat.     

Size-dependent flowering behavior and heat production of a sequential hermaphrodite, Symplocarpus renifolius (Araceae)

We examined the flowering performance in a population of the protogynous perennial herb Symplocarpus renifolius (Araceae), with special consideration of plant size. Flowering of S. renifolius occurred in very early spring, soon after snow melt. The spadices generated heat throughout the pistillate (female) and bisexual phases, but heat production decreased quickly after the beginning of the staminate (male) phase. During the flowering season, the sex ratio within the population dramatically changed from a dominance of females to a dominance of males. The duration of the female phase was negatively correlated with the onset time of flowering, and the duration of the male phase was positively correlated with plant size. Larger plants began blooming earlier, produced more heat, made the transition from female to male phase more rapidly, and lasted longer as males than smaller ones. Such size-dependent flowering performance caused unidirectional pollen flow from large to small plants. The number of seeds produced per spadix was positively correlated with the duration of the female phase, although it was not correlated with plant size. However, the estimated number of seeds sired during the male phase was positively correlated with plant size. Early flowering, rapid gender change, and higher heat production of the spadices by larger plants were factors considered to promote the higher success of the male function without decreasing the success of the female function.     

Bread Wheat (Triticum aestivum L.) Grain Protein Concentration Is Related to Early Post-Flowering Nitrate Uptake under Putative Control of Plant Satiety Level

The strong negative correlation between grain protein concentration (GPC) and grain yield (GY) in bread wheat complicates the simultaneous improvement of these traits. However, earlier studies have concluded that the deviation from this relationship (grain protein deviation or GPD) has strong genetic basis. Genotypes with positive GPD have an increased ability to uptake nitrogen (N) during the post-flowering period independently of the amount of N taken up before flowering, suggesting that genetic variability for N satiety could enable the breakage of the negative relationship. This study is based on two genotypes markedly contrasted for GPD grown under semi-hydroponic conditions differentiated for nitrate availability both before and after flowering. This allows exploration of the genetic determinants of post-flowering N uptake (PANU) by combining whole plant sampling and targeted gene expression approaches. The results highlights the correlation (r² = 0.81) with GPC of PANU occurring early during grain development (flowering–flowering + 250 degree-days) independently of GY. Early PANU was in turn correlated (r² = 0.80) to the stem-biomass increment after flowering through its effect on N sink activity. Differences in early PANU between genotypes, despite comparable N statuses at flowering, suggest that genetic differences in N satiety could be involved in the establishment of the GPC. Through its strong negative correlation with genes implied in N assimilation, root nitrate concentration appears to be a good marker for evaluating instantaneous plant N demand, and may provide valuable information on the genotypic N satiety level. This trait may help breeders to identify genotypes having high GPC independently of their GY.     

Influence of rice black streaked dwarf virus on the ecological fitness of non-vector planthopper Nilaparvata lugens （Hemiptera： Delphacidae）

Rice black streak dwarf virus （RBSDV） is transmitted by the small brown planthopper （SBPH）, Laodelphax striatellus （Fallen）. Non-vector rice brown planthopper （BPH）, Nilaparvata lugens （Stal）, shares the same host rice plants with SBPH in paddy fields. The changes in nutritional composition of rice plants infected by RBSDV and the ecological fitness of BPH feeding on the infected plants were studied under both artificial climate chamber and field conditions. Contents of 16 detected amino acids and soluble sugar in RBSDV infected rice plants were higher than those in the healthy ones. On the diseased plants BPH had significantly higher nymphal survival rates, nymphal duration of the males, weight of the female adults, as well as egg hatchability compared to BPH being fed on healthy plants. However, there was no obvious difference in female nymph duration, longevity and fecundity. Defense enzymes （superoxidase dismutase, SOD and catalase, CAT） and detoxifying enzymes （carboxylesterase, CAE and glutathione S-transferase, GST） in BPH adults fed on diseased plants had markedly higher activities. The results indicate rice plants infected by RBSDV improved the ecological fitness of the brown planthopper, a serious pest but not a transmitter of the RBSDV virus.     

广东连州自然分布的3种植物体内及根际环境中稳定性碳和氮同位素的分析

以广东连州自然分布的3种国家重点保护野生植物南方红豆杉〔Taxus chinensis var.mairei(Lemée et Lévl.)Cheng et L.K.Fu〕、半枫荷(Semiliquidambar cathayensis Chang)和金荞麦〔Fagopyrum dibotrys(D.Don)Hara〕为研究对象,分析了根、茎和叶片及根际土壤和岩石的C、N含量和C:N比以及δ13 C和δ15 N值的差异;在此基础上,通过δ13 C和δ15 N值的散点图比较了3种植物生态位的差异.结果表明:在同种植物中,根、茎和叶片的C和N含量及C:N比总体高于根际土壤和岩石,其中,叶片中C和N含量均最高,茎的C:N比最高;而根际土壤和岩石的δ13 C和δ15 N值总体高于根、茎和叶片.在供试的3种植物间,根际土壤和岩石中C和N含量总体上无明显差异,但根、茎和叶片中C和N含量以及根、茎和叶片及根际土壤和岩石的C:N比、δ13 C和δ15 N值均有一定差异;其中,金荞麦根中C含量显著(P<0.05)低于南方红豆杉和半枫荷,其根、茎和叶片中N含量和δ15 N值均极显著(P<0.01)高于后二者,其根、茎和叶片的C:N比和δ13 C值均极显著低于后二者,其根际土壤和岩石的C:N比和δ13 C值总体上也低于后二者;南方红豆杉和半枫荷的叶片中C和N含量以及茎和叶片的δ13 C值、根际土壤和岩石的δ13 C和δ15 N值均存在显著差异,但二者的整体差异相对较小.从散点图上看,金荞麦的生态位远离南方红豆杉和半枫荷,而后二者的生态位有交集.综合分析结果显示:草本植物金荞麦与木本植物南方红豆杉和半枫荷的C和N含量以及δ13 C和δ15 N值的差异不仅与植物自身的生活型有关,而且与各自生境中的光照和土壤因子等相关.另外,供试3种植物的根、茎和叶片的δ13 C值变幅为-31.69‰~-26.46‰,符合C3植物的δ13 C值范畴.     

Zinc Accumulation and Tolerance in Solanum nigrum are Plant Growth Dependent

Zinc tolerance, accumulation, and organic acid production by Solanum nigrum, a known Zn accumulator, was studied during pre- and post-flowering stages of development. The plants, when challenged with Zn concentrations lethal to plantlets, showed an increase in tolerance from pre-flowering to post-flowering, which was accompanied by a reduction of Zn translocation to the aerial plant parts. Treatment with Zn induced a differential response in organic acids according to the plant organ and developmental stage. In the roots, where Zn concentrations were similar in pre- and post-flowering plants, a general decrease in organic acid in pre-flowering roots contrasted with the increase observed in post-flowering plants. In the stems, Zn induced a generalized increase in organic acids at both growth stages while in the leaves, a slight increase in malic and shikimic was observed in pre-flowering plants and only shikimic acid levels were significantly increased in post-flowering plants. This work shows that Zn accumulation and tolerance in S. nigrum vary during plant development – an observation that may be important to improve the efficiency of phytoremediation approaches. Furthermore, the data suggest the involvement of specific organic acids in this response.