Suppression of Fusarium Wilt Caused by Fusarium oxysporum f. sp. lactucae and Growth Promotion on Lettuce Using Bacterial Isolates.

This study was carried out to explore a non-chemical strategy for enhancing productivity by employing some antagonistic rhizobacteria. One hundred eighteen bacterial isolates were obtained from the rhizospheric zone of various crop fields of Gangwon-do, Korea, and screened for antifungal activity against Fusarium wilt (Fusarium oxysporum f. sp. lactucae) in lettuce crop under in vitro and in vivo conditions. In broth-based dual culture assay, fourteen bacterial isolates showed significant inhibition of mycelial growth of F. oxysporium f. sp. lactucae. All of the antagonistic isolates were further characterized for the antagonistic traits under in vitro conditions. The isolates were identified on the basis of biochemical characteristics and confirmed at their species level by 16S rRNA gene sequencing analysis. Arthrobacter sulfonivorans, Bacillus siamensis, Bacillus amyloliquefaciens, Pseudomonas proteolytica, four Paenibacillus peoriae strains, and Bacillus subtilis were identified from the biochemical characterization and 16S rRNA gene sequencing analysis. The isolates EN21 and EN23 showed significant decrease in disease severity on lettuce compared to infected control and other bacterial treatments under greenhouse conditions. Two bacterial isolates, EN4 and EN21, were evaluated to assess their disease reduction and growth promotion in lettuce in field conditions. The consortium of EN4 and EN21 showed significant enhancement of growth on lettuce by suppressing disease caused by F. oxysporum f. sp. lactucae respectively. This study clearly indicates that the promising isolates, EN4 (P. proteolytica) and EN21 (Bacillus siamensis), can be commercialized and used as biofertilizer and/or biopesticide for sustainable crop production.

Biological Control of Bacterial Fruit Blotch of Watermelon Pathogen (Acidovorax citrulli) with Rhizosphere Associated Bacteria.

Bacterial fruit blotch (BFB), which is caused by Acidovorax citrulli, is a serious threat to watermelon growers around the world. The present study was conducted to screen effective rhizobacterial isolates against 35 different A. citrulli isolates and determine their efficacy on BFB and growth parameters of watermelon. Two rhizobacterial isolates viz. Paenibacillus polymyxa (SN-22), Sinomonas atrocyanea (NSB-27) showed high inhibitory activity in the preliminary screening and were further evaluated for their effect on BFB and growth parameters of three different watermelon varieties under greenhouse conditions. The greenhouse experiment result revealed that SN-22 and NSB-27 significantly reduced BFB and had significant stimulatory effect on total chlorophyll content, plant height, total fresh weight and total dry weight compared to uninoculated plants across the tested three watermelon varieties. Analysis of the 16S ribosomal RNA (rRNA) sequences revealed that strains SN-22 belong to P. polymyxa and NSB-27 to S. atrocyanea with the bootstrap value of 99% and 98%, respectively. The isolates SN-22 and NSB-27 were tested for antagonistic and PGP traits. The result showed that the tested isolates produced siderophore, hydrolytic enzymes (protease and cellulose), chitinase, starch hydrolytic enzymes and they showed phosphate as well as zinc solubilizing capacity. This is the first report of P. polymyxa (SN-22) and S. atrocyanea (NSB-27) as biocontrol-plant growth promoting rhizobacteria on watermelon.

Three New Records of Mortierella Species Isolated from Crop Field Soil in Korea.

Three new fungal species of the genus Mortierella, Mortierella zychae, Mortierella ambigua, and Mortierella indohii, have been reported in Korea. The fungi were encountered during a study on the fungal community of soil samples collected from different locations in Korea. The species were identified based on molecular and morphological analyses. This study presents detailed descriptions of the morphological observations and molecular phylogenetic analysis of these three fungi. All three species were found to be sensitive to triphenyltetrazolium chloride staining. M. zychae demonstrated the highest intensity of mycelial staining, indicating that this species has the highest potential to produce arachidonic acid of the three species. The staining results indicated that the newly recorded species could potentially be useful for arachidonic acid production.

A New Record of Gongronella butleri Isolated in Korea.

We report the isolation of a Gongronella butleri species and describe it based on the analysis of the internal transcribed spacer region of rDNA and morphological characteristics. G. butleri has been reported as a high chitosan producer in the literature. This is the first record of G. butleri isolated from crop field soil in Korea.

Penicillium menonorum: A Novel Fungus to Promote Growth and Nutrient Management in Cucumber Plants.

The present study is the first report on the isolation of Penicillium menonorum from rhizosphere soil in Korea and its identification based on morphological characteristics and internal transcribed spacer gene sequence. The fungal isolate was named KNU-3 and was found to exhibit plant growth-promoting (PGP) activity through indole acetic acid (IAA) and siderophore production, as well as P solubilization. KNU-3 produced 9.7 mg/L IAA and solubilized 408 mg of Ca3PO4/L, and inoculation with the isolate significantly (p < 0.05) increased the dry biomass of cucumber roots (57%) and shoots (52%). Chlorophyll, starch, protein, and P contents were increased by 16%, 45%, 22%, and 14%, respectively, compared to plants grown in uninoculated soil. The fungus also increased soil dehydrogenase (30%) and acid phosphatase (19%) activities. These results demonstrate that the isolate KNU-3 has potential PGP attributes, and therefore it can be considered as a new fungus to enhance soil fertility and promote plant growth. Moreover, the discovery of PGP ability and traits of this fungus will open new aspects of research and investigations. In this study, plant growth promotion by P. menonorum KNU-3 is reported for the first time in Korea after its original description.

A New Record of Volutella ciliata Isolated from Crop Field Soil in Korea.

During a survey of fungal species in South Korea, a species of Volutella ciliata was isolated and described based on the analysis of the internal transcribed spacer region of its rDNA and its morphological characteristics. This is the first record of Volutella ciliata isolated from crop field soil in Korea.

Discovery of Two New Talaromyces Species from Crop Field Soil in Korea.

Two new fungal species of the genus Talaromyces, Talaromyces purpurogenus and Talaromyces trachyspermus from the Trichocomaceae family, were recovered during an investigation of fungal communities in soil collected from the Gangwon-do and Jeollanam-do provinces of Korea. These two species have not been previously officially reported from Korea. In this study, detailed descriptions of internal transcribed spacer rDNA and beta-tubulin gene regions of these two fungi are presented. Morphological features of the two fungi in five agar media, potato dextrose, oatmeal, malt extract, czapek yeast extract, and yeast extract sucrose, are also reported. The species were identified on the basis of molecular and morphological analysis, and herein we present data with detailed descriptions and figures.

First Report of Mortierella alpina (Mortierellaceae, Zygomycota) Isolated from Crop Field Soil in Korea.

A new recorded species of Mortierella was recovered during the investigation of fungal communities in soil samples collected from different locations of Gangwon-do, Korea. The species was identified and described as Mortierella alpina on the basis of phylogenetic analysis of internal transcribed spacer sequences and morphological characteristics. This species has not been officially reported from Korea thus far.

Three new records of penicillium species isolated from insect specimens in Korea.

Three Penicillium species have been isolated from insect specimens in Korea; Penicillium sp., P. steckii, and P. polonicum. Penicillium sp. (KNU12-3-2) was isolated from Lixus imperessiventris, while P. polonicum (KNU12-1-8) and Penicillium steckii (KNU12-2-9) were isolated from Muljarus japonicas and Meloe proscarabaeus, respectively. The identification was based on the morphological characteristics of the fungi and in internal transcribed spacer analysis. This is the first report on the isolation of these three species of Penicillium from insects in Korea.