Peroxidase and Poly-Phenol Oxidase in Brassica juncea Plants Infected with Macrophomina phaseolina (Tassai) Goid. and their Implication in Disease Resistance

Studies on the peroxidase and poly-phenol oxidase activity in relatively resistant and susceptible strains of Brassica juncea at sequential intervals after inoculation with different isolates of Macrophomina phaseolina revealed that, fungus infected tissues had relatively higher activities of these oxidative enzymes in comparison to healthy plants, and tissues inoculated with ‘Weakly Virulent’ isolates always exhibited higher activity in comparison to ‘Moderately’, ‘Highly’ and ‘MostHighly Virulent’ isolates. At the early stages of the infection on 6th day, resistant plants showed higher activities in comparison to their susceptible counterparts. Very low activity of these enzymes could be recorded in healthy plants. Findings of this, study indicate the possible involvement of these oxidative enzymes in the resistance of this disease.     

Differential Expression of Peroxidase Isoenzymes in Soybean Roots Treated with the Benzothiadiazole

The protection compound benzo-(1,2,3)-thiadiazole-7-carbothioic acid S-methyl ester (BTH) was applied to soybean roots or leaves in a dose of 20 cm³ of a solution containing 25 μg g⁻¹ of the active ingredient. Electrophoretic profiles of chitinase and superoxide dismutase were not altered by the product. Increased activity of two root anionic peroxidases and three differential isoforms of these enzymes were observed in plants with roots treated by BTH, which can be used as biochemical markers of the BTH effect. This revised version was published online in July 2006 with corrections to the Cover Date.     

Resistance to Rhizoctonia solani and Presence of Antimicrobial Compounds in Camelina sativa Roots

Camelina sativa (L.) Crantz was significantly more resistant to Rhizoctonia solani Kühn than [itBrassica napus L. cv Westar. Emergence of C. sativa seedlings was 22 to 33% greater than those of Westar in R. solani-infested soil. The greater resistance of C. sativa seedlings to R. solani appeared to be due to greater amounts of antimicrobial compounds present in C. sativa roots. These antimicrobial compounds inhibited the growth of both weakly virulent and virulent R. solani] isolates to the same extent. Four antimicrobial compounds were purified from C. sativa roots and their structures elucidated. Two were identified as the phytoalexins (camalexin and methoxycamalexin) previously described from C. sativa leaves. This appears to be the first report of elicitation of phytoalexins from roots of crucifers. Two preformed antimicrobial compounds were identified as methyl 1-methylindole-3-carboxylate and 10-methyl sulfinyldecylisothiocyanate.     

Peroxidase and Polyphenol Oxidase Associated with, Induced Resistance of Mung Bean to Rhizoctonia solani Kuhn

Peroxidase and polyphenol oxidase activities and peroxidase isozyme patterns were determined at different stages of hypocotyls of mung bean infected with Rhizoctonia solani. The effect of ethephon (2-chloroethyl phosphonic acid) has been studied. Peroxidase activity increased at 24 h after inoculation as compared with controls followed by a decline later. It increased at 120 h. Polyphenol oxidase activities increased after inoculation. Ethephon treatment increased the resistance to Rhizoctonia solani and enhanced peroxidase and polyphenol oxidase activities. Peroxidase isozyme pattern was found to change as a result of inoculation and ethephon treatment. The results indicated that ethephon-induced resistance was related to peroxidase and polyphenol oxidase activities.     

Rhizoctonia spp. Associated with Container-Grown Ericaceous Plants in Scotland

Fungi with Rhizoctonia-like mycelia were isolated from the foliage, stem-base and roots of ericaceous plants collected from nurseries in Scotland. Isolated fungi were identified as either binucleate Rhizoctonia spp. or Rhizoctonia solani on the basis of hyphal characteristics and nuclear number. The optimum temperature range for growth of binucleate Rhizoctonia spp. and R. solani was 20 and 25 C, resepctively. All isolates tested for pathogenicity caused foliar browning, and webs of mycelial growth were observed on dead and dying foliage. Binucleate Rhizoctonia spp. and R. solani are recorded for the first time on container-grown ericaceous plants in Scotland.     

Mycoparasitism of Pythium ultimum by Antagonistic Binucleate Rhizoctonia Isolates in Agar Media and on Capsicum Seeds

Hyphal interactions between two antagonistic binucleate Rhizoctonia isolates (BNR) and the seedling dampingoff pathogen, Pythium ultimum var. sporangiiferum, were observed by both light-and scanning electron microscopy (SEM), on agar media and on capsicum seeds in sterilized potting mix. Both BNR isolates displayed similar mycoparasitic behaviour towards P. u. sporangiiferum on agar media. This included parallel growth along the pathogen hyphae, formation of hook-shaped hyphal tips and coils on the surface of P. u. sporangiiferum hyphae and penetration and growth within pathogen structures. Disruption of cytoplasmic streaming and disorganisation of pathogen cytoplasm were also observed. SEM observations revealed alterations in P. u. sporangiiferum cell wall structure and the presence of penetration holes apparently due to digestion by the BNR. P. u. sporangiiferum was also parasitised by both BNR isolates on capsicum seed coats, with parallel growth, hook formation and coils commonly observed. The above observations indicated that mycoparasitism is a possible mode of action of BNR against P. u. sporangiiferum.     

Peroxidase Isoenzymes in Development of Tall and Dwarf Cultivars of Rice

Four cultivars of rice, Hansraj (tall), Jamuna, Padma and Sabarmati(all dwarf) were analysed for variation in isoperoxidase patternsduring development by horizontal starch-gell electrophoresis.The samples were taken at weekly intervals, starting with soakedseeds (12 h) until the post panicle stage. There is a distinctpattern of peroxidase isoenzymes in the tall and dwarf cultivarsstudied. Some isoenzymes appear at a particular developmentalstage while others disappear while some remain fairly constantonce they are activated. Hansraj showed more qualitative fluctuationsin peroxidase than did the three dwarf varieties. A few isoperoxidaseswere specific to some varieties such as bands A₃ and A₇ forHansraj and band A₄ for Sabarmati. These specific bands of peroxidasemay have some role to play in development of Hansraj (tall)and Sabarmati (with aroma). Besides this, greater fluctuationsin peroxidase activity in the tall variety may be due to loosecontrol in the regulation of peroxidase activity. The significanceof controlling elements of enzyme activity is discussed.     

Peroxidase Isozymes from Meloidogyne spp. and Their Origin

Two peroxidase isozymes (Ef 0.43 and 0.53) were detected by electrophoretic analysis in homogenates of Meloidogyne arenaria, M. hapla, M. javanica, and M. incognita females reared on tomato. No peroxidase isozymes were detected electrophoretically in homogenates of adult males, preparasitic larvae, or eggs. Peroxidase isozymes from females reared on bean, eggplant, or tobacco differed from those from females reared on tomato. Bean and eggplant populations had a single peroxidase isozyme each, respectively Ef 0.21 and 0.28. No peroxidase isozymes were detected in tobacco populations under the conditions used, although total activity assays did reveal low levels of peroxidase activity in homogenates of tobacco populations. The peroxidase isozymes detected in females reared on tomato or bean appear similar to the peroxidase isozymes present in root-knot galls, adjacent ungalled roots, and roots from uninoculated plants of the corresponding hosts. The probability is discussed that most of the peroxittase activity associated with Meloidogyne spp. females is of host origin.     

苦参和苦豆子的过氧化物酶同工酶谱分析和比较

采用聚丙烯酰胺凝胶电泳技术分析和比较了5个不同产地的苦参和1种苦豆子的过氧化物酶同工酶活性。结果表明：不同产地苦参品种和苦豆子的过氧化物酶同工酶谱迁移率在0.14～0.28之间,共6条酶谱带。聚类分析表明,苦参和苦豆子的亲缘关系较远,而不同产地的苦参种质也存在一定的差异,可分为3类：甘肃成县栽培的苦参与甘肃岷县栽培的苦参为一类,河南卢氏野生苦参单独为一类,河北承德野生苦参和甘肃成县野生苦参为一类。     

Effect of Crop Rotation on Meloidogyne spp. and Pratylenchus spp. Populations in Strawberry Fields in Taiwan

Changes in population levels of Meloidogyne hapla, M. incognita, Pratylenchus coffeae, and P. penetrans were studied in 12 strawberry fields in the Dahu region of Taiwan. Ten potential rotation crops and two cultural practices were evaluated for their effect on nematode populations and influence on strawberry yield. Rotation with rice or taro and the cultural practice of flooding and bare fallowing for four months were found to reduce nematode soil populations to two or fewer nematodes per 100 ml soil. Average strawberry yields increased between 2.4% to 6.3% following taro compared to the bare fallow treatment. Corn suppressed M. incognita and M. hapla populations and resulted in an increased in strawberry yield compared to bare fallow. Other phytopathogens also present in these fields limited taro as the rotation choice for nematode management. Results of this research and economic analysis of the input requirements for various rotation crops, corn and bare fallow were recommended as the most appropriate rotation strategies for nematode management in strawberry in this region.     

Antagonism of Rhizoctonia spp. to Pythium oligandrum and Damping-Off Fungi

In paired cultures on corn-meal agar, Rhizoctonia solani, R. cerealis and R. fragariae caused vacuolation, disappearance of cytoplasm, and apparent lysis of hyphae of Pythium oligandrum, P. ultimum, and Aphanomyces cochlioides. Hyphae of Phoma betae were not injured by the Rhizoctonia spp. When sugar-beet seeds dressed with mycelium of R. cerealis, R. fragariae, or an isolate of R. solani nonpathogenic to sugar-beet were planted in soil naturally infested with P. ul-timum, the level of biological control of damping-off was similar to that obtained with captan dressing. In soil artificially infested with P. ultimum, biological dressings were slightly less efficacious than the chemical dressing.     

Rhizoctonia spp. Causing Root and Hypocotyl Rot in Phaseolus vulgaris in Cuba

Sixty isolates of Rhizoctonia spp. were obtained from Cuban bean fields during the period 2004–2007. Isolates were characterized with different techniques, including nuclei staining, pectic zymogram, PCR–RFLP analysis of the rDNA–ITS region and sequencing of the rDNA–ITS region. The majority of the isolates were identified as multinucleate Rhizoctonia solani isolates, representing two different anastomosis groups (AGs), AG 2‐2 WB and AG 4 HGI; the remaining isolates were binucleate Rhizoctonia isolates and belonged to AG F and AG A. AG 4 HGI isolates were equally distributed in all soil types; AG 2‐2 isolates were more frequently isolated from cambisols, whereas AG F isolates were related to calcisols. Pathogenicity experiments in vitro and in the greenhouse, revealed that binucleate isolates only caused root rot, whereas R. solani isolates were able to cause root rot and hypocotyl rot. Furthermore, differences in virulence level were observed between R. solani and binucleate isolates and among different AGs. Isolates of R. solani AG 4 HGI and R. solani AG 2‐2 WB were the most aggressive, binucleate isolates of AG F were intermediate aggressive, whereas a binucleate isolate of AG A was weakly aggressive. In contrast with other reports about R. solani in bean, web blight symptoms were never observed during this study.     

The Glycoprotein Nature of Indoleacetic Acid Oxidase/Peroxidase Fractions and their Development in Pea Roots

IAA oxidase/peroxidase active fractions were separated using concanavalin A-sepharose into glycoprotein and non-glycoprotein fractions. No IAA oxidase peak was separable from peroxidase activity. The development of these fractions were followed in pea roots over a four day period. Initially the nonglycosylated IAA oxidase/peroxidase was the dominant fraction with the IAA oxidase/peroxidase ratio remaining close to unity. The glycosylated fraction developed later with IAA oxidase the dominant activity. Differential carbohydration of IAA oxidase/peroxidase fractions may determine the intracellular sites of activity of this molecular species.     

Biocontrol of Rhizoctonia crown and root rot of sugar beet by binucleate Rhizoctonia spp. and Laetisaria arvalis

Two isolates of Laetisaria arvalis and 10 of binucleate Rhizoctonia spp. (BNR) from the Ohio sugar beet production area, were tested in the greenhouse and field for biocontrol of Rhizoctonia crown and root rot of sugar beet, caused by Rhizoctonia solani anastomosis group 2, type 2. L. arvalis was ineffective in standard greenhouse tests, and the single isolate used in the field was generally ineffective. Seven of 10 BNR isolates effectively controlled crown and root rot in greenhouse tests. Delayed application of biocontrol agents to plants 5 – 10 wk old was generally more effective than applications made at planting. A BNR isolate significantly reduced % plant loss and disease ratings and increased yield in a 1985 field test as compared with the control infested with R. solani alone. Two BNR isolates were effective in a 1986 field test and increased yields c. 22% in comparison to a L. arvalis treatment, which did not differ from the R. solani-infested control. The Ohio binucleate Rhizoctonia isolates appear to have considerable potential as applied biocontrol agents and may play a role in the natural ecology of R. solani in the sugar beet production area of Ohio.     

Characterization and Pathogenicity of Rhizoctonia spp. from Onion in Amasya, Turkey

Forty‐two isolates of Rhizoctonia spp. were obtained from onion in Amasya, Turkey. Of these, 29% were Rhizoctonia solani (AG‐4), 69% were Waitea circinata var. zeae (Rhizoctonia zeae) and 2% were binucleate Rhizoctonia (AG‐B). Most of the isolates were recovered from rhizosphere soil. In pathogenicity tests on onion, R. solani AG‐4 caused the greatest disease severity, those of W. circinata var. zeae were moderately virulent but binucleate Rhizoctonia isolates were of low virulence. This is the first report of binucleate Rhizoctonia AG‐B and W. circinata var. zeae occurring on onion in Turkey.     

Interaction of Pratylenchus penetrans and Rhizoctonia fragariae in Strawberry Black Root Rot

A split-root technique was used to examine the interaction between Pratylenchus penetrans and the cortical root-rotting pathogen Rhizoctonia fragariae in strawberry black root rot. Plants inoculated with both pathogens on the same half of a split-root crown had greater levels of root rot than plants inoculated separately or with either pathogen alone. Isolation of R. fragariae from field-grown roots differed with root type and time of sampling. Fungal infection of structural roots was low until fruiting, whereas perennial root colonization was high. Isolation of R. fragariae from feeder roots was variable, but was greater from feeder roots on perennial than from structural roots. Isolation of the fungus was greater from structural roots with nematode lesions than from non-symptomatic roots. Rhizoctonia fragariae was a common resident on the sloughed cortex of healthy perennial roots. From this source, the fungus may infect additional roots. The direct effects of lesion nematode feeding and movement are cortical cell damage and death. Indirect effects include discoloration of the endodermis and early polyderm formation. Perhaps weakened or dying cells caused directly or indirectly by P. penetrans are more susceptible to R. fragariae, leading to increased disease.     

Characterisation of antagonistic soil microbes against Rhizoctonia spp. and Sclerotium hydrophilum

Rhizoctonia solani, R. oryzae-sativae and Sclerotium hydrophilum are responsible for sheath diseases of rice. Soil treatment measures with antagonist microbes have produced good results against various soil-borne fungi. The objective of this study included to find out the potential antagonist microbes from the paddy field soil. Ten different soil samples were collected from the disease-prone area of paddy field soil. Antagonist microbes were identified by 16S rRNA sequence analysis. Subsequent screening of antagonist microbes yield B. subtilis B37 and P. aeruginosa B258 as the potential antagonist microbes to control sheath diseases of rice in Myanmar. Bacillus subtilis strains induced the competition between antagonist and the tested fungi at the margin of the bacterial growth itself. However, P. aeruginosa induced the competition at a long range formed by the antibiotic of antagonist microbe. Bacillus subtilis B37 and P. aeruginosa B258 could be applicable in the control strategy of causal agents of rice sheath diseases in Myanmar.     

Isoenzyme Polymorphism in Flowering Plants. IV. The Peroxidase Isoenzymes of Maize (Zea mays)

Twenty-four peroxidase isoenzymes were identified by starch gel electrophoresis of 250 varieties of maize. Twelve of these bands corresponded in electrophoretic mobility to bands observed in commercial horseradish peroxidase. Maize tissues varied greatly in isoenzyme pattern, many tissues having a characteristic and distinguishing complement. Ontogenetic variations were observed for the leaf blade, leaf sheath, and internodes during maturation, and were related to the rates of tissue enlargement. Genetic studies of two isoenzymes, C10 and C20, indicated that they were conditioned by alleles of a single locus, here designated Px₁.