Characterization of Rhizoctonia spp. Isolates Associated with Damping-Off Disease in Cotton and Tobacco Seedlings in Greece

Functional Analyses of the Bacillus velezensis HMB26553 Genome Provide Evidence That Its Genes Are Potentially Related to the Promotion of Plant Growth and Prevention of Cotton Rhizoctonia Damping-Off

Bacillus spp. is one kind of the important representative biocontrol agents against plant diseases and promoting plant growth. In this study, the whole genomic sequence of bacterial strain HMB26553 was obtained. A phylogenetic tree based on the genome and ANI (average nucleotide identity), as well as dDDH (digital DNA-DNA hybridization), was constructed, and strain HMB26553 was identified as Bacillus velezensis. Fourteen biosynthetic gene clusters responsible for secondary metabolite were predicted via anti-SMASH, and six secondary metabolites were identified by UHPLC-QTOF-MS/MS (ultra-high-performance liquid chromatography coupled to quadrupole-time-of-flight tandem mass spectrometry). When the phytopathogen Rhizoctonia solani was treated with B. velezensis HMB26553, the mycelial structure changed, ROS (reactive oxygen species) accumulated, and the mitochondrial membrane potential decreased. Characteristics of strain HMB26553 were predicted and confirmed by genomic information and experiments, such as producing IAA, siderophore, extracellular enzymes and biofilm, as well as moving and promoting cotton growth. All these results suggested the mechanisms by which B. velezensis HMB26553 inhibits pathogen growth and promotes cotton growth, which likely provided the potential biocontrol agent to control cotton Rhizoctonia damping-off.

RNA-seq Analysis of Rhizoctonia solani AG-4HGI Strain BJ-1H Infected by a New Viral Strain of Rhizoctonia solani Partitivirus 2 Reveals a Potential Mechanism for Hypovirulence

Rhizoctonia solani partitivirus 2 (RsPV2), in the genus Alphapartitivirus, confers hypovirulence on R. solani AG-1-IA, the causal agent of rice sheath blight. In this study, a new strain of RsPV2 obtained from R. solani AG-4HGI strain BJ-1H, the causal agent of black scurf on potato, wasidentified and designated as Rhizoctonia solani partitivirus 2 strain BJ-1H (RsPV2-BJ). An RNA sequencing analysis of strain BJ-1H and the virus RsPV2-BJ-free strain BJ-1H-VF derived from strain BJ-1H was conducted to investigate the potential molecular mechanism of hypovirulence induced by RsPV2-BJ. In total, 14,319 unigenes were obtained, and 1,341 unigenes were identified as differentially expressed genes (DEGs), with 570 DEGs being down-regulated and 771 being up-regulated. Notably, several up-regulated DEGs were annotated to cell wall degrading enzymes, including β-1,3-glucanases. Strain BJ-1H exhibited increased expression of β-1,3-glucanase after RsPV2-BJ infection, suggesting that cell wall autolysis activity in R. solani AG-4HGI strain BJ-1H might be promoted by RsPV2-BJ, inducing hypovirulence in its host fungus R. solani AG-4HGI. To the best of our knowledge, this is the first report on the potential mechanism of hypovirulence induced by a mycovirus in R. solani.

Characterization and variation of the rhizosphere fungal community structure of cultivated tetraploid cotton

Rhizosphere fungal communities exert important influencing forces on plant growth and health. However, information on the dynamics of the rhizosphere fungal community structure of the worldwide economic crop cotton (Gossypium spp.) is limited. In the present study, next-generation sequencing of nuclear ribosomal internal transcribed spacer-1 (ITS1) was performed to characterize the rhizosphere fungal communities of G. hirsutum cv. TM-1 (upland cotton) and G. barbadense cv. Hai 7124 (island cotton). The plants were grown in field soil (FS) that had been continuously cropped with cotton and nutrient-rich soil (NS) that had not been cropped. The fungal species richness, diversity, and community composition were analyzed and compared among the soil resources, cotton genotypes, and developmental stages. We found that the fungal community structures were different between the rhizosphere and bulk soil and the difference were significantly varied between FS and NS. Our results suggested that cotton rhizosphere fungal community structure variation may have been primarily influenced by the interaction of cotton roots with different soil resources. We also found that the community composition of the cotton rhizosphere fungi varied significantly during different developmental stages. In addition, we observed fungi that was enriched or depleted at certain developmental stages and genotypes in FS and NS, and these insights can lay a foundation for deep research into the dynamics of pathogenic fungi and nutrient absorption of cotton roots. This research illustrates the characteristics of the cotton rhizosphere fungal communities and provides important information for understanding the potential influences of rhizosphere fungal communities on cotton growth and health.

Characterization of Rhizoctonia solani Associated with Black Scurf in Cyprus

During 2011, 96 sclerotial isolates of Rhizoctonia solani were collected from potato tubers from all main potato-cultivating regions of Cyprus. All isolates were found to be multinucleate. Characterization of anastomosis groups (AG) based on hyphal anastomosis reactions showed that 91 isolates belonged to AG3 and 5 to AG4. Sequence analysis of the internal transcribed spacer (ITS) regions (ITS1 and ITS2) of ribosomal DNA (rDNA) of 68 isolates confirmed the prevalence of AG3. In addition, phylogenetic analysis found that AG3 isolates were of the potato type, distinctly separated from the AG3 tobacco type, while AG4 isolates were separated into two different subgroups (HGI and HGII). Temperature studies showed that isolates belonging to both AG4 subgroups had significantly higher optimum growth temperatures compared with AG3. In vitro sensitivities to the fungicide pencycuron, in terms of concentrations where 50% growth inhibition was observed, ranged from 0.012 to 0.222 μg/ml. Pathogenicity and aggressiveness of the isolates was determined on 'Annabelle' potato sprouts and seedlings of a number of selected hosts, based on crop rotations followed in Cyprus. The majority of the isolates were pathogenic to potato sprouts, with disease severity (DS) values ranging from 0 to 88%. Mean DS values were statistically different among AG and subgroups, with AG4-HGI (69.25%) and AG4-HGII (3.12%) being the most and least aggressive, respectively. However, AG4-HGII isolates were the most aggressive in all rotational hosts tested, while AG3 isolates were the least aggressive. More specifically, the highest DS levels by AG4-HGI were recorded to barley, by AG4-HGII to lettuce and melon, and by AG3 isolates to vetch. This is the first comprehensive study to elucidate the AG composition, pathogenicity and other biological aspects of R. solani isolates associated with potato black scurf in Cyprus.

Rhizoctonia Web Blight-A New Disease on Mint in Israel

Mentha longifolia is produced in and exported from Israel with annual revenue of US$16 million. In 2010, a severe epidemic of unknown etiology reduced growers' returns up to 50%. Disease symptoms included water-soaked lesions, necrosis, and web-like mycelia on plants. Two isolates (JV-1 and BS-1) from randomly selected symptomatic plants were identified as members of Rhizoctonia solani anastomosis groups 1-IB and 4HG-I, respectively. The fitness of JV-1 and BS-1 interacted with temperatures between 17 and 35°C: JV-1 grew faster and was more aggressive (P < 0.05) at lower temperatures (<24°C), BS-1 grew faster and was more aggressive at higher temperatures (>30°C), and the two isolates performed similarly at intermediate temperatures. Disease developed fastest at 24 to 28°C. Yield was reduced between 46 and 100%. In all, 77.5% fewer plants recovered from disease developing at 24 to 28°C than at 17 to 23 or 30 to 35°C. The relationship of disease to relative humidity (RH) fit a quadratic model (P < 0.0015, R² = 0.98). Disease was most severe at 100% RH, decreasing by 1.3-, 1.9-, 3-, 4.5-, and 10.5-fold with the reduction of RH from 100% to 88, 76, 69, 55, or 49%, respectively. This is the first report of Rhizoctonia web blight in mint in Israel.