Biocontrol of Rhizoctonia solani damping-off of sugar beet with native Streptomyces strains under field conditions

A 3-year study was conducted to evaluate the effectiveness of two disease-suppressive Streptomyces spp. to control sugar beet Rhizoctonia solani damping off under field conditions. Streptomyces seed treatments reduced seedling damping off in naturally (2005) and artificially (2006 and 2007) infested soils. All biocontrol agents provided better efficacy than Vitavax to control seedling damping-off. There were no significant differences among Streptomyces isolates. Isolate C increased plant stand by 19.5, 50.5 and 53.75% in 2005, 2006 and 2007, respectively. Evaluation of final harvest revealed that the root yield of the biocontrol agents increased compared to untreated control in these years.     

Evaluation of two Streptomyces spp. and compost for growth promotion and biocontrol potential against Rhizoctonia solani on pepper

The individual and synergistic potentials of two Streptomyces strains and compost for growth promotion and biocontrol against dumping off caused by Rhizoctonia solani on pepper were evaluated. Results showed that the compost can greatly enhance pepper growth while the combination of the two strains and compost was most efficient for the disease suppression.     

Use of DAPI for Anastomosis Group Typing of Strains of the Fungus Rhizoctonia solani

Strains of Rhizoctonia solani, a common soil-borne, pathogenic fungus of plants, are assigned to one of 11 anastomosis groups (AGs) based on the occurrence of imperfect fusions (anastomoses) between hyphae of a non-typed strain and a tester strain of one of the 11 AG's. Imperfect fusion is characterized by the death of one or more cells in each of the hyphae involved in the fusion. Although hyphae from branches of the same strain of JR. solani may fuse with each other (self-fusion), cell death does not occur. Cell death is accompanied by nuclear degradation and granulation, or plasmolysis of the cytoplasm, which often is not visible using bright-field microscopy. When the DNA-binding fluorochrome DAPI (4', 6-diamidino-2-phenylindole) is used and the hyphal fusions viewed under fluorescence microscopy, no nuclei are observed in fused hyphal cells from two strains of the same AG of R. solani Because DAPI reacts only with living nuclei, lack of staining is presumptive evidence that the fused cells are dead as a result of imperfect fusion. The use of DAPI reduces the time required for making AG determinations compared to standard methods because it eliminates the need to assess cell wall dissolution and cytoplasmic fusion. Also, it is not necessary to trace the hyphae involved in the fusion to their respective origins to ensure that self-fusion has not occurred.     

A simple and rapid nuclear staining method for Rhizoctonia solani Kuhn

Abstract

We developed a modified staining technique using acridine orange to stain the nuclei of Rhizoctonia solani. Acridine orange solution was prepared in acetic acid buffer, pH 7.2. Staining for 15 min was critical for observing the nuclei. All of the isolates were found to be multinucleated. The nuclei appeared bright green with light orange background. This method is simple, rapid and reproducible.     

Anastomosis Group Determination of Rhizoctonia solani Kühn (Telemorph: Thanatephorus cucumeris) Isolates from Tomatoes Grown in Aydin,Turkey and their Disease Reaction on Various Tomato Cultivars

In the Province of Aydin‐Turkey most frequently Fusarium spp. and secondly Rhizoctonia solani Kühn were isolated from the roots and crown of tomato plants. Based on affinities for hyphal fusion with test isolates, all R. solani isolates were identified as AG‐4. The tomato cultivars which were grown in soil infested with R. solani AG‐4 exhibited different reactions. From the point of symptom expression and the rate of seedling emergence Sunny 6066 F1 was found to be the most resistant cultivar, whereas Rio Grande, Rio Fuego, NDM 725, Interpeel and Konia were the most susceptible cultivars.     

Induced Resistance in Cucumbers against Fusarium oxysporum f. sp. cucumerinum and Rhizoctonia solani AG2–2 by Infection of the Cotyledons

Localized infection in cucumber cotyledons with Colletotrichum lagenarium induced resistance against infection after challenge inoculation with Rhizoctonia solani AG2–2 and Fusarium oxysporum f. sp. cucumerinum in the roots. The plants were unprotected in soil that was infested heavily with R. solani or in contact with the mycelium, and induced resistance was not observed. Wounding of the root also negated the effect of induced resistance to F. oxysporum .     

Growth inhibition of the cereal root pathogens Rhizoctonia solani AG8, R. oryzae and Gaeumannomyces graminis var. tritici by a recombinant 42-kDa endochitinase from Trichoderma harzianum

The objective of this study was to determine the effectiveness of a 42-kDa endochitinase coded by the ThEn42 gene from Trichoderma harzianum as a potential source of transgenic resistance to Rhizoctonia root rot of barley caused by Rhizoctonia solani AG8 and/or R. oryzae. The gene cThEn42 was codon optimized (GC content increased from 53.3 to 65.1%) and then synthesized to produce the modified cThEn42GC in Pichia pastoris for in vitro tests. Two expression vectors were constructed: one with the fungal signal peptide and the fungal activation peptide [FSP-FAP-cThEn(GC)] and the other with barley chitinase 26 signal peptide followed by the fungal signal and activation peptides [SP(HVChi26)-FSP-FAP-cThEn(GC)]. N-terminal sequencing showed that, of two proteins secreted into liquid medium, FSP was cleaved off faithfully in one protein and both FSP and FAP were cleaved from the other protein. Purified endochitinase provided strong in vitro inhibition of both R. solani AG8 and R. oryzae. The enzyme had an intermediate inhibitory activity against Gaeumannomyces graminis var. tritici, and no inhibitory activity against Fusarium graminearum, F. pseudograminearum, and F. culmorum.     

Selective breeding of Steinernema feltiae (Filipjev) (Nematoda: Steinernematidae) for improved efficacy in control of a mushroom fly,Lycoriella solani Winnertz (Diptera: Sciaridae)

A method of selecting a Steinernema feltiae strain that is effective against a mushroom fly, Lycoriella solani, is described in detail. The pest control efficacy of the selected nematode strain was evaluated and compared with the efficacy of two unselected strains. The selection procedure was designed to give preference to nematode individuals with the greatest ability (1) to search effectively for the target insect larvae in their natural habitat, (2) to infect them shortly after application and (3) to reproduce in their haemocoel. Thirty‐four rounds of selection achieved a 4‐fold improvement in nematode ability to find and parasitize third‐ and fourth‐instar larvae of the pest in the mushroom substrate. In 24‐h laboratory experiments, mortality of the insect caused by nematode juveniles rose from 22.5%, recorded for the original unselected isolate, to 92.5% for the selected strain. In a 51‐day experiment conducted on a mixed age mushroom house population of L. solani, the enhanced pest control ability of the selected strain was detected shortly after nematode application and remained high throughout the experimental period. During the first 4 weeks of the trial the selected nematode strain was significantly better than both unselected strains and caused 91.1–92.7% reduction of the fly emergence from the mushroom substrate. No difference was observed between the efficacy of the selected nematodes applied at 1 × 10⁶ and 3 ×10⁶ infective juveniles per m², while the unselected strains performed significantly better at the higher concentration. All the nematodes examined showed good persistence in the mushroom casing apparently due to recycling in the insect host.     

The predatory mite Hypoaspis miles: biological and demographic characteristics on two prey species, the mushroom sciarid fly, Lycoriella solani, and the mould mite, Tyrophagus putrescentiae

The biology of Hypoaspis miles Berlese (Acarina: Hypoaspidae) fed on mushroom sciarid larvae (Lycoriella solani Winnertz) (Diptera: Lycoriidae) and mould mites (Tyrophagus putrescentiae Schrank) (Acari: Acaridae), was investigated by laboratory experiments at 20 °C, 75% r.h. and LD16:D8 hours. H. miles had a significantly shorter development time and a significantly lower juvenile mortality when fed on sciarid larvae than on mould mites, the development time being 14.5 days and the mortality 3.5% on the former prey. The preoviposition and postoviposition periods of H. miles were not uninfluenced by the prey species and were 5–9 and 32–37 days, respectively. Oviposition periods of 53.2 and 68.5 days and female longevities of 82 and 109.6 days were observed on diets of sciarid larvae and mould mites, respectively. Male longevity (168–219 days) was uninfluenced by the prey species. The egg production of H. miles on sciarid larvae was estimated to be 44.4 ± 4.33 eggs per female, as compared to 22.43 ± 1.79 eggs per female on mould mites. The sex-ratio of the offspring was significantly influenced by the prey species, the ratios (/(+)) being 0.66 on sciarid larvae and 0.54 on mould mites. The net reproductive rate (R₀) for H. miles fed on sciarid larvae was approximately 27 which was three times higher than for mites feeding on mould mites. The innate capacity of increase (r_m) was highest (0.0747 day^–1) when sciarid larvae served as food, giving a doubling time of 9.3 days as compared to 12.8 days on mould mites. The generation times were 44.28 on sciarid larvae and 40.67 days on mould mites. The daily food consumption rate of juvenile and adult H. miles was 0.24 and 0.86 sciarid larvae and 10.8 and 21.7 mould mites, respectively. In terms of weight consumed, however, the consumption of sciarid larvae was 2–3.5 times the weight of mould mites. The ratio of females to males influenced the oviposition period and egg production of H. miles, with virgin females laying fewer eggs over a longer period of time as compared with females with access to males. The egg production in relation to the sex-ratio was described by models predicting a maximum number of eggs per female of 22.3 to be attained at a sex ratio of 0.69 (/(+)) and a maximum daily number of eggs per female of 0.33 to be attained at a sex ratio of 0.37 (/(+)).     

Suppression of Cyst Nematode by Natural Infestation of a Nematophagous Fungus

Penetration of cabbage roots by Heterodera schachtii was suppressed 50-77% in loamy sand naturally infested with the nematophagous fungus Hirsutella rhossiliensis. When Heterodera schachtii was incubated in the suppressive soil without plants for 2 days, 40-63% of the juveniles had Hirsutella rhossiliensis spores adhering to their cuticles. Of those with spores, 82-92% were infected. Infected nematodes were killed and filled with hyphae within 2-3 days. Addition of KCl to soil did not increase infection of Heterodera schachtii by Hirsutella rhossiliensis. The percentage of infection was lower when nematodes were touched to two spores and incubated in KCl solution than when nematodes naturally acquired two spores in soil.     

Biology and Nymph Host Range of Anchocoema bidentata and Astroma saltense (Orthoptera: Proscopiidae), Potential Biocontrol Agents for Creosotebush, Larrea tridentata (Zygophyllaceae) in the U.S.A.

Two stick-like acridids (Orthoptera: Proscopiidae) from Argentina, Anchocoema bidentata Mello-Leitao and Astroma saltense Mello-Leitao, were evaluated as potential biological control agents of creosote bush (Larrea tridentata (DC.) Coville) in the southwestern United States. Their biology, behavior and geographic distribution of those species were studied. The host plant ranges for both insects were established through nymph feeding preference and development tests in the laboratory and in the field. A total of 33 species of plants belonging to 13 families were tested. Anchocoema bidentata and A. saltense are mimetic species, having as many as three generations a year, and exhibit strong sexual dimorphism; females are larger and less mobile than males. In both species, females laid egg masses in the soil. First instars appeared in the field at the end of the spring, the second generation at mid-summer, and a third at the end of the summer. Adults of A. bidentata and A. saltense appeared in the field at the beginning of the spring. The laboratory multiple-choice feeding test showed that A. bidentata preferred Larrea divaricata Cav., whereas A. saltense preferred L. divaricata and L. cuneifolia Cav. In the nymph development test (no choice), A. bidentata was able to complete its development only on L. divaricata and L. cuneifolia, while Astroma saltense completed its development on six plant species: L divaricata, L. cuneifolia, Bulnesia retama (Gillies ex Hooker et Arnott), B. schickendantzi Hieron (all Zygophyllaceae), Zuccagnia punctata Cav., and Prosopis torquata (Cav. Ap. Lag.) (both Fabaseae). We concluded that A. bidentata could be a biocontrol agent for L. tridentata because the first instar can complete its development only on Larrea spp. Regarding A. saltense, this species showed a wide host range and should not be considered as a biological control agent of L. tridentata.     

Developmental Host-Specificity of Mozena obtusa (Heteroptera: Coreidae), a Potential Biocontrol Agent for Prosopis Species (Mesquite) in Australia

Mozena obtusa Uhler (Heteroptera: Coreidae) was examined in quarantine for its potential as a biological control agent of Prosopis species (mesquite) in Australia. Trials were conducted on 16 nontarget plant species to estimate its developmental host range. Complete development occurred on all Prosopis species that have become naturalized in Australia as well as on four Australian native species (Neptunia species and Paraserianthes lophantha), although reproductive diapause prevented assessment of subsequent fecundity. Development through the first feeding nymphal instar also occurred on other plant species representing two subfamilies. Nymphal performance was highly variable on both target and nontarget species, possibly because variation in plant nitrogen composition affected plant quality. The correlation between environment, plant nitrogen, and plant quality is likely to be sufficiently strong to determine whether a plant species can support development. Plant quality should therefore be considered when predicting the field host range of M. obtusa and of sap-sucking coreids generally. Nonetheless, our preliminary results suggest that M. obtusa may not be sufficiently specific for release in Australia, although insufficient understanding of its oviposition behavior in the field and the effect of plant quality on development means that its rejection would be premature.