Stem Wilt Research Articles

An In Vitro Assay Method for Resistance to Bacterial Wilt (Ralstonia solanacearum) in Potato

To develop an in vitro assay method for bacterial wilt resistance in potato, resistant and susceptible standard genotypes were grown in vitro, and different conditions of inoculation with Ralstonia solanacearum phylotype I/biovar 4 were examined. The optimal condition was the inoculation of 6–8 leaf stage plants with a bacterial concentration of 102 CFU ml−1 and an incubation temperature of 28 °C. Evaluation of stem wilting was more reliable than that of leaf wilting. Using this method, nine genotypes with different resistance levels in the field were evaluated. Lower disease indices were obtained for genotypes with high resistance levels in the field, suggesting that this assay is useful for evaluating bacterial wilt resistance in a controlled environment.

Diaporthe pseudolongicolla - novi patogen na semenu soje u Srbiji

Seed decay is one of the most important diseases of soybean (Glycine max (L.) Merr.) that has a negative impact on the market grade of soybeans. The disease is mainly caused by Diaporthe longicolla, along with other Diaporthe species. Screening of soybean seeds health status in Vojvodina Province, Serbia, showed cultural and morphological variability among isolates identified as D. longicolla. With the use of DNA sequences of internal transcribed spacer (ITS1-5.8S-ITS2) region and partial translation elongation factor 1-alpha (EF1-α), the new species was determined. BLAST analysis showed 100% identity with D. pseudolongicolla (syn. D. novem) that was described in this study and its taxonomic revision is discussed. Pathogenicity trial showed that both species, D. longicolla and D. pseudolongicolla, are highly pathogenic on soybean stem and seed, causing 100% of stem wilting and more than 82% of seed decay.

Induced systemic resistance and symbiotic performance of peanut plants challenged with fungal pathogens and co-inoculated with the biocontrol agent Bacillus sp. CHEP5 and Bradyrhizobium sp. SEMIA6144

Synergism between beneficial rhizobacteria and fungal pathogens is poorly understood. Therefore, evaluation of co-inoculation of bacteria that promote plant growth by different mechanisms in pathogen challenged plants would contribute to increase the knowledge about how plants manage interactions with different microorganisms. The goals of this work were a) to elucidate, in greenhouse experiments, the effect of co-inoculation of peanut with Bradyrhizobium sp. SEMIA6144 and the biocontrol agent Bacillus sp. CHEP5 on growth and symbiotic performance of Sclerotium rolfsii challenged plants, and b) to evaluate field performance of these bacteria in co-inoculated peanut plants. The capacity of Bacillus sp. CHEP5 to induce systemic resistance against S. rolfsii was not affected by the inoculation of Bradyrhizobium sp. SEMIA6144. This microsymbiont, protected peanut plants from the S. rolfsii detrimental effect, reducing the stem wilt incidence. However, disease incidence in plants inoculated with the isogenic mutant Bradyrhizobium sp. SEMIA6144 V2 (unable to produce Nod factors) was as high as in pathogen challenged plants. Therefore, Bradyrhizobium sp. SEMIA6144 Nod factors play a role in the systemic resistance against S. rolfsii. Bacillus sp. CHEP5 enhanced Bradyrhizobium sp. SEMIA6144 root surface colonization and improved its symbiotic behavior, even in S. rolfsii challenged plants. Results of field trials confirmed the Bacillus sp. CHEP5 ability to protect against fungal pathogens and to improve the yield of extra-large peanut seeds from 2.15% (in Río Cuarto) to 16.69% (in Las Vertientes), indicating that co-inoculation of beneficial rhizobacteria could be a useful strategy for the peanut production under sustainable agriculture system.

Interrelationships between Bacillus sp. CHEP5 and Bradyrhizobium sp. SEMIA6144 in the induced systemic resistance against Sclerotium rolfsii and symbiosis on peanut plants.

Plant-growth-promoting bacteria are often used to enhance crop yield and for biological control of phytopathogens. Bacillus sp. CHEP5 is a biocontrol agent that induces systemic resistance (ISR) in Arachis hypogaea L. (peanut) against Sclerotium rolfsii, the causal agent of root and stem wilt. In this work, the effect of the co-inoculation of Bacillus sp. CHEP5 and the peanut nodulating strain Bradyrhizobium sp. SEMIA 6144 was studied on induction of both systemic resistance and nodulation processes. Bradyrhizobium sp. SEMIA 6144 did not affect the ability of Bacillus sp. CHEP5 to protect peanut plants from S. rolfsii by ISR and the priming in challenged-plants, as evidenced by an increment in phenylalanine ammonia-lyase enzyme activity. Additionally, the capacity of Bradyrhizobium sp. SEMIA 6144 to induce nodule formation in pathogen-challenged plants was improved by the presence of Bacillus sp. CHEP5.

Different continuous cropping spans significantly affect microbial community membership and structure in a vanilla-grown soil as revealed by deep pyrosequencing.

In the present study, soil bacterial and fungal communities across vanilla continuous cropping time-series fields were assessed through deep pyrosequencing of 16S ribosomal RNA (rRNA) genes and internal transcribed spacer (ITS) regions. The results demonstrated that the long-term monoculture of vanilla significantly altered soil microbial communities. Soil fungal diversity index increased with consecutive cropping years, whereas soil bacterial diversity was relatively stable. Bray-Curtis dissimilarity cluster and UniFrac-weighted principal coordinate analysis (PCoA) revealed that monoculture time was the major determinant for fungal community structure, but not for bacterial community structure. The relative abundances (RAs) of the Firmicutes, Actinobacteria, Bacteroidetes, and Basidiomycota phyla were depleted along the years of vanilla monoculture. Pearson correlations at the phyla level demonstrated that Actinobacteria, Armatimonadetes, Bacteroidetes, Verrucomicrobia, and Firmicutes had significant negative correlations with vanilla disease index (DI), while no significant correlation for fungal phyla was observed. In addition, the amount of the pathogen Fusarium oxysporum accumulated with increasing years and was significantly positively correlated with vanilla DI. By contrast, the abundance of beneficial bacteria, including Bradyrhizobium and Bacillus, significantly decreased over time. In sum, soil weakness and vanilla stem wilt disease after long-term continuous cropping can be attributed to the alteration of the soil microbial community membership and structure, i.e., the reduction of the beneficial microbes and the accumulation of the fungal pathogen.

First Report of Stem Wilt and Root Rot of Schlumbergera truncata Caused by Fusarium oxysporum f. sp. Opuntiarum in Southern Italy.

Schlumbergera truncata (Haw.) Moran, belonging to the Cactaceae, is a very common ornamental cactus in southern Italy. In November 2011, sudden stem wilt and root rot was observed in about 45% of vegetatively propagated plants cultivated as potted ornamental plants in a commercial greenhouse in Cerignola (Foggia Province, Apulia, Italy). The roots and collars of the plants showed brown rot. Yellow sunken lesions that were similar to cortical cankers were detected at basal level of the stem. Ten plants with these symptoms were analyzed by fungal isolation techniques. Small (0.5 cm) tissue portions from root, collar, and basal stem were plated on potato dextrose agar (PDA) after disinfection with 75% ethanol for 1 to 2 min, 0.2% NaOCl for 1 to 2 min, and a wash with sterile distilled water. A fungal isolate that was morphologically similar to Fusarium sp. was isolated from 85% of these tissue samples. It had nucleotide sequences of the internal transcribed spacer region (ITS1-5.8S-ITS2) of ribosomal DNA (GenBank Accession No. KC196121) 100% identical to those of the comparable sequences of Fusarium oxysporum (HQ651161). The nucleotide sequences of its translation elongation factor 1-α (EF-1α) gene (KC196120) showed 100% identity to sequences of F. oxysporum f. sp. opuntiarum (DQ837689, AF246881) retrieved from GenBank. Pathogenicity tests were performed at 22 ± 3°C on 18 45-day-old plants of S. truncate by adding of a 5-ml aliquot of conidial suspension adjusted to 5 × 106 conidia/ml to soil of each plant. Six non-inoculated plants were used for a control treatment and sprayed with 5 ml of sterilized water. Plants were maintained in greenhouse at 22 ± 3°C. After 10 days, nine of the inoculated plants showed wilting, and after 45 days, all of them were dead, with root and collar rot and lesions on the basal stem. Control plants were symptomless. Koch's postulates were fulfilled as the pathogen was reisolated from all of the symptomatic tissues and identified as Fusarium sp. On the basis of 3-septate macroconidia (mean 31.75 × 3.21 μm; range, 26 to 35 μm long, 3.0 to 4.2 μm wide), aseptate microconidia, single chlamydospores, and monophialide conidiophores on carnation leaf agar, and molecular analyses, the fungus was identified as F. oxysporum f. sp. opuntiarum (Speg) (1,2,3). In Italy, F. oxysporum f. sp. opuntiarum was reported as basal stem rot of Echinocactus grusoni (4). To our knowledge, this is the first report of stem wilt and root rot of S. truncata caused by F. oxysporum f. sp. opuntiarum in Italy.

First Report of Fusarium oxysporum Causing Wilt on Iceland Poppy (Papaver nudicaule) in Italy.

During fall 2011, symptoms of a wilt disease were observed in a commercial nursery near Ventimiglia as well as in the Research Center of Floriculture of Sanremo (northern Italy) on plants of Papaver nudicaule (Iceland poppy) of a local unnamed cultivar. In the commercial nursery, 15 to 20% of plants were affected, while about 3% of plants were affected at the Research Center. Symptoms consisted of chlorosis, premature leaf drop, and foliar wilting, followed by the stem wilting, bending, and eventually rotting from the base. Brown discoloration was observed in the stem vascular tissue. Using Komada's Fusarium-selective agar medium (2), a fungus was consistently and readily isolated from symptomatic vascular tissue of plants collected from both sites. The isolates were purified and subcultured on potato dextrose agar (PDA), on which medium both isolates produced pale violet, abundant, aerial mycelium, felted in old cultures, with pale purple pigments in the agar medium. The isolate generated short monophialides with unicellular, ovoid-elliptical microconidia of 3.9 to 6.7 × 1.4 to 3.0 (average 5.4 × 2.3) μm. On carnation leaf agar (CLA) (1), isolates produced pale orange sporodochia with macroconidia that were 3-septate, slightly falcate with a foot-shaped basal cell and a short apical cell, and 26.0 to 43.5 × 3.1 to 4.4 (average 35.3 × 3.7) μm. Chlamydospores were abundant, terminal, and intercalary, rough walled, mostly singles but sometime in short chains or clusters, and 5.2 to 10.1 μm in diameter. Such characteristics are typical of Fusarium oxysporum (3). The internal transcribed spacer (ITS) region of rDNA was amplified from the isolates using the primers ITS1/ITS4 (4), and sequenced. BLASTn analysis of the 507-bp ITS sequence of one isolate from P. nudicaule collected from the commercial nursery (GenBank Accession No. JX103564) showed an E-value of 0.0 and 100% identity with the ITS sequence of F. oxysporum (HQ649820). To confirm pathogenicity of one of the Iceland poppy isolates, tests were conducted on 2-month-old plants of the same cultivar on which symptoms were first observed. Plants (n = 14) were inoculated by dipping roots in a 1 × 107 CFU/ml conidial suspension of the isolate of F. oxysporum prepared from 10-day-old cultures grown in potato dextrose broth (PDB) on a shaker (90 rpm) for 10 days at 22 ± 1°C (12-h fluorescent light, 12-h dark). Non-inoculated control plants (n = 14) were dipped in sterilized water. All the plants were transplanted into pots filled with steamed potting mix (sphagnum peat/perlite/pine bark/clay at 50:20:20:10), and maintained in a glasshouse at 24 to 28°C. Inoculated plants showed typical symptoms of Fusarium wilt after 10 days. The stems then wilted and plants died. Non-inoculated plants remained healthy. F. oxysporum was reisolated from inoculated plants but not from control plants. The pathogenicity test was conducted twice with the same results. Since Fusarium wilt has not previously been described on Iceland poppy at any location, this is first report of F. oxysporum on P. nudicaule in Italy and anywhere in the world.

First Report of Phomopsis Seed Decay of Soybean Caused by Phomopsis longicolla in South China

Phomopsis seed decay of soybean (Glycine max (L.) Merr.) causes poor seed quality and suppresses yield in most soybean-growing areas in the world. The disease is caused primarily by Phomopsis longicolla Hobbs. During the spring of 2010, soybean seeds without symptoms were planted in the fields but emergence was poor and the emergence rates ranged from 30 to 70% in south China. Approximately 3,000 symptomless seeds were randomly collected from seven fields at three locations in Guangzhou, Nanchang, and Wuhan. Seeds were surface disinfected with 1% sodium hypochlorite for 12 min, rinsed in sterile distilled water three to four times, and placed on 2% agar. Plates were then incubated at 26°C under 16/8-h photoperiod for 3 to 4 days. About 10 to 20% of the seeds produced white hyphae that spread rapidly and covered the whole seed. The hyphae from fungal isolates were transferred to potato dextrose agar (PDA) and incubated at 26°C in the dark. After 3 to 4 weeks, conidia were elliptical with two oil drops at both ends and hyaline (6.2 to 7.2 × 2.6 to 3.2 μm). The cultural and morphological characteristics of the isolates corresponded with the description of P. longicolla (2). Colonies on PDA were floccose, dense, and white. Stromata were large, black, and spreading. To confirm the morphological identification, the ribosomal internal transcribed spacers (ITS1-5.8S-ITS2) from three isolates were sequenced (GenBank Accession Nos. JQ899030, JQ899031, and JQ899032). BLAST analysis indicated that the isolates had 99% nucleotide sequence identity with P. longicolla (GenBank Accession Nos. AY857868.1, EF026104, and HQ130441.1). Pathogenicity tests were conducted on 2-week-old soybean seedlings (3). A mycelial plug (3 mm in diameter) from the margin of 1-week-old PDA culture of the Wuhan isolate was individually placed mycelial side down directly on the top of cut stem 1 to 2 cm above cotyledon node of the soybean seedling. PDA plugs without the fungus was used as the negative control. All seedlings were kept in a growth chamber at 26°C with 92 to 94% relative humidity. After 2 weeks, all inoculated seedlings showed browning, stem wilt, and the lesions were 0.3 to 2.0 cm long. No symptoms were observed in the control plants. P. longicolla was reisolated from the infected seedlings. The pathogenicity test was repeated three times. Soybean stem blight caused by P. longicolla has been reported in northeast China (1). To our knowledge, this is the first report of P. longicolla causing Phomopsis seed decay of soybean in south China. This report will establish a foundation for developing a program for screening germplasm for resistance to this disease in south China.

A root drench in unsaturated hydrogel solution reduced stress in transplanted Eucalyptus pilularis cuttings but was ineffective for seedlings: a glasshouse experiment

Summary Available soil moisture and quality of planting material are two important criteria affecting survival during plantation establishment. It has been observed that in northern NSW most seedling deaths occur within the first four weeks of planting. Reducing the rate that plants become stressed is important as less-stressed plants are more capable of exploiting available soil moisture required for survival beyond this four-week period. The health (leaf gas exchange, visual symptoms of leaf and stem wilt) and survival of Eucalyptus pilularis Smith seedlings and cuttings were examined following the application of water in the form of either a hydrogel solution or as irrigation. The main findings were that the rate at which stress developed was slower for cuttings than for seedlings; and that supplying more water, either as hydrogel or irrigation, reduced transplant stress and prolonged survival. Differences in morphology between seedlings and cuttings may explain why cuttings developed stress more slowly than did seedlings. Compared with seedlings, cuttings had reduced leaf area, an increased root: shoot ratio and lower leaf area: root dry mass ratio, all of which are traits that enhance water uptake and reduce water loss. The most effective treatments for reducing stress of seedlings and cuttings were either removing individual seedlings or cuttings from nursery trays and dipping the root ball into a 100% saturated hydrogel solution which coated it with a layer of saturated hydrogel, or supplying the equivalent volume of water as irrigation when transplanting the plants. Drenching nursery trays in 25% and 50% unsaturated hydrogel solutions prior to the removal of the plants delayed stress of transplanted cuttings to a similar extent as the 100% saturated hydrogel solution, but these solutions were ineffective in delaying stress in seedlings. It is thought the more open structure of the soil medium used for cuttings allowed the unsaturated hydrogel solutions to enter the root-ball during root drenching, and because the hydrogel solutions are more viscous than water the drainage of the solutions after removing the nursery trays from the root drench was reduced.

Peanut priming induced by biocontrol agents

Selected strains of rhizobacteria induce systemic resistance in plant (ISR), enhancing the capacity to mobilize infection-induced cellular defense responses (priming). Bacillus sp. CHEP5 and Pseudomonas sp BREN6 strains reduced root and stem wilt disease severity caused by Sclerotium rolfsii in Arachis hypogaea L. Strains inoculation increased the activity of phenylalanine ammonia-lyase and peroxidase, after pathogen-challenge, indicating priming. CHEP5 primes plants to produce more ethylene upon stimulation with ACC. A. hypogaea L is an ISR-positive plant and BREN6 and CHEP5 strains enhance the plant’s defense capacity by priming for potentiated activity of defense proteins and ACC-converting capacity.

Synthesis, Structure and Biological Activities of 2-(1 H-1, 2, 3-Benzotriazol-1-yl)-1-(4-methylphenyl)-2-(1 H-1, 2, 4-triazol-1-yl)-1-ethanone

The title compound was synthesized and characterized by IR, 1 H NMR, elemental analysis and single crystal X-ray diffraction analysis. Its biological activities were also tested. The results show that the title compound reveals inhibiting activities towards wheat gibberellin, apple ringspot, tomato early blight, peanut cercospora arachidicola and stem wilt of asparagus.

Characterization and pathogenicity of isolates of Leptosphaeria maculans from Aguascalientes and Zacatecas, Mexico1

Blackleg of crucifers caused by Leptosphaeria maculans is the most important disease of broccoli and cauliflower in central Mexico, causing up to 70% yield loss in cauliflower crops. The pathogen was isolated from broccoli crops near Aguascalientes, Ags., and Zacatecas, Zac., and culture characteristics and pathogenicity on cauliflower were examined. Colony appearance and mycelial growth on V8-juice agar, germ tube growth on water agar, and the absence of pigment production in Czapek-Dox medium were characteristic of isolates belonging to the aggressive strain. No pseudothecia formed when the Mexican isolates were paired nor when they were crossed with a tester isolate for mating type +, suggesting that all of the Mexican isolates were of mating type +. This was indirectly confirmed by the absence of the MAT-2 gene, which is associated with mating type –. Reliable inoculation techniques, based on inoculation of wounded plants with pycnidiospores, were developed for cauliflower. In seedlings whose cotyledons were wound-inoculated, the fungus progressively destroyed the cotyledons, then the petioles, the cotyledonary node, and eventually the stem, resulting in dieback and a wire stem. In stem-inoculated plants, the fungus caused wire stem and leaf wilt. The Mexican isolates were aggressive to oilseed rape and belonged to pathogenicity group 2.

Susceptibility of Clematis Varieties and Species to Stem Infection by Phoma Clematidina as an Indicator for Resistance to Wilt

The susceptibility to stem rot and wilt caused by Phoma clematidina was tested for a range of clematis varieties and species widely grown in Europe, and compared with their susceptibility to wilt in practice as judged by amateur and commercial growers in two postal surveys. Most small flowering clematis species did not die back when unwounded stems were inoculated with spores of P. clematidina, and were also reported in the surveys as being very resistant to wilt. In contrast, large flowering hybrids were found to be highly susceptible both to stem infection by P. clematidina and to wilt in practice according to growers. A significant positive linear relationship existed between the susceptibility scores for disease in the stem inoculation test and those for wilt from the surveys. Fungal isolations were made from the stems of naturally wilted clematis plants from British nurseries and private gardens. Unlike the many other fungal species isolated, P. clematidina occurred very frequently, especially in stems of large flowering varieties. Together with the results from the grower surveys and stem inoculation trial, this indicates that this fungus is a regular cause of clematis wilt. The stem inoculation test with P. clematidina described in this study would be useful for European breeders and growers to determine the susceptibility of new clematis varieties to wilt before they are marketed.

MANAGEMENT OF TAPERING DISORDER IN COCONUT

The tapering stem wilt of coconut was amply proven to be a physiological disorder, with relevance to physiological and bio chemical investigations of the 14th frond analysis. The experiments, in a rainfed garden, revealed that the occurrence of this malady was mainly due to deficiency of iron, associated with copper and manganese at lower level. The management of this malady was possible by root feeding of micronutrient mixture (Fe+Cu+Mn+B) for two years at six monthly interval. The synergistic effect of Fe, Cu, Mn has indirectly acted on the improvement of tapering disorder, as they are part of metabolic enzymes.

Basal Stem Rot and Wilt of Sunflower in Nigeria Caused bySclerotium rolfsii

Basal Stem Rot and Wilt of Sunflower in Nigeria Caused by<i>Sclerotium rolfsii</i>

Control of stem wilt of broad bean by the seed disinfection with some chemicals or dry heat treatment

Control of stem wilt of broad bean by the seed disinfection with some chemicals or dry heat treatment

Bud Rot of Areca Palms in Mysore

IN Hirethota, a village near Thirthahalli, Mysore State, a serious disease of areca palms has been rampant for the past fifty years. Locally the disease goes by the name 'hidimundige', which literally means the thinning out or tapering of the crown, gradually dwindling in diameter. But actually the disease in no way resembles the tapering stem wilt, better known as the 'pencil point disease' of coco-nuts so well known in the West Indies. A preliminary report of the investigations carried out is presented here.