Screening the olive tree phyllosphere: Search and find potential antagonists against Pseudomonas savastanoi pv. savastanoi

The Supplementary Material for this article can be found online at: https://www.frontiersin.org/articles/10.3389/fmicb.2020.02051/full#supplementary-materialOlive knot (OK) is a widespread bacterial disease, caused byPseudomonas savastanoipv.savastanoi(Pss), which currently has not effective control methods. The use of naturally occurring microbial antagonists, such as bacteria, as biocontrol agents could be a strategy to manage this disease. The objective of this work was to select bacteria from olive tree phyllosphere able to antagonizePssusingin vitroandin plantaexperiments. The elucidation of their modes of action and the potential relationship between antagonism and bacteria origin has been investigated, as well. To this end, 60 bacterial isolates obtained from the surface and inner tissues of different organs (leaves, twigs, and knots), from two olive cultivars of varying susceptibilities to OK, were screened for theirin vitroantagonistic effect againstPss. A total of 27 bacterial strains were able to significantly inhibitPssgrowth, being this effect linked to bacteria origin. Strains from OK-susceptible cultivar and colonizing the surface of plant tissues showed the strongest antagonistic potential. The antagonistic activity was potentially due to the production of volatile compounds, siderophores and lytic enzymes.Bacillus amyloliquefaciensP41 was the most effective antagonistic strain and their capacity to control OK disease was subsequently assayed usingin plantaexperiments. This strain significantly reduces OK disease severity (43.7%), knots weight (55.4%) and population size ofPss(26.8%), while increasing the shoot dry weight (55.0%) and root water content (39.6%) ofPss-infected olive plantlets. Bacterial isolates characterized in this study, in particularB. amyloliquefaciensP41, may be considered as promising biocontrol candidates for controlling OK disease.This work was funded by FEDER funds through COMPETE (Programa Operacional Factores de Competitividade), national funds through FCT (Fundacao para a Ciencia e a Tecnologia) and by Horizon 2020, the European Union's Framework Programme for Research and Innovation, within the project PRIMA/0002/2018 (INTOMED - Innovative tools to combat crop pests in the Mediterranean), and the Mountain Research Center - CIMO (UIDB/00690/2020 and UIDB/04046/2020)

<span style="font-weight:normal; mso-bidi-font-weight:bold" lang="EN-US">Isolation and characterization of endophytic bacteria associated<span style="mso-bidi-font-family:"AdvTTb8864ccf\.B"; color:#131413;font-weight:normal;mso-bidi-font-weight:bold" lang="EN-US"> with chilli (<i>Capsicum</i> <i>annuum</i>) grown in<span style="font-weight:normal; mso-bidi-font-weight:bold" lang="EN-US"> coastal agricultural ecosystem<span style="mso-bidi-font-family:"AdvTTb8864ccf\.B";color:#131413; font-weight:normal;mso-bidi-font-weight:bold" lang="EN-US"> </span></span></span></span>

247-255The antagonistic potentials of endophytic bacteria isolated from chilli plants were determined in vitro against four pathogens, viz., Sclerotium rolfsii, Fusarium oxysporum, Colletotrichum capsici and Pythium sp. The effect of endophytic bacteria towards these fungi revealed that most of the isolates showed antagonistic activity against Pythium sp. (37.8%), followed by 35.1% isolates against F. oxysporum and C. capsici, and 21.6% to S. rolfsii. The identification of potential bacterial isolates through Microbial Identification System (Biolog) and 16S rDNA sequencing of the isolates revealed the presence of 8 genera. Among them Bacillus species were the dominant antagonists. Characterized by BOX-PCR fingerprints, the 23 antagonistic endophytic bacterial (AEB) isolates represented 19 different cluster types. To explore the antagonistic mechanisms, the agar diffusion method was used to detect cell-wall degrading enzyme activity and siderophore secretion. The isolates BECS7, BECS4 and BECL5 showed clearly the growth promoting activity, reduction of disease incidence and high yield under field conditions. Hence, these isolates are<span style="mso-bidi-font-family:AdvPTimes; mso-bidi-language:KN" lang="EN-US"> promising plant growth promoting isolates showing multiple attributes that can significantly influence the chilli growth. The results of present study provide a strong basis for further development of these strain as bio-inoculants to attain the desired plant growth promoting activity in chilli growing fields.<span style="color:black;mso-bidi-language: KN" lang="EN-US"> </span

Molecular identification and biocontrol activity of sugarcane rhizosphere bacteria against red rot pathogen Colletotrichum falcatum

A total of 226 sugarcane rhizosphere-associated bacterial strains from the six different cultivars were screened against three pathogenic strains of C. falcatum (cfNAV, cfCHA, and cf8436) for the suppression of red rot disease. On the basis of mycelial growth inhibition in dual culture assay, 26 bacteria were selected for further characterization of morphology, biochemical activity, plant-growth-promoting (PGP) activity, antifungal potential and molecular identity by 16S rRNA gene sequence. On the basis of the 16S rRNA gene sequencing, it was found that the isolates belonged to proteobacteria (13), Firmicutes (10), and Bacteroides (3). The antagonistic bacteria tested for PGP traits revealed that 10 strains were able to solubilize tricalcium phosphate, 11 strains were able to produce siderophore, and 14 strains were able to grow in the N-free medium. The quantitative estimation of indole-3-acetic acid production was ranged from 21.58 to 66.31 μg/mL. On the basis of PGP and biocontrol traits, five strains Ochrobactrum intermedium (TRD14), Acinetobacter sp. (PK9), Bacillus sp. (RSC29 and KR91) and Escherichia sp. (VRE34) were further chosen for pot trial under greenhouse conditions on highly susceptible variety CoC671. The results showed that the pathogen-inoculated sugarcane plants were able to germinate but died within one month. However, the CoC671 inoculated with selected biocontrol strains found protected from disease and an increase in plant growth parameters on par with carbendazim fungicides. This study proves that the isolates identified in this study could be used as an alternative to chemical fungicides to control red rot pathogen of sugarcane plants. Keywords: Antagonism, Biocontrol, Carbendazim, Colletotrichum falcatum, Red rot, Sugarcan

Prevalence and magnitude of acidosis sequelae to rice-based feeding regimen followed in Tamil Nadu, India

Background and Aim: In Tamil Nadu, a southern state of India, rice is readily available at a low cost, hence, is cooked (cooking akin to human consumption) and fed irrationally to cross-bred dairy cattle with poor productivity. Hence, a study was carried out with the objective to examine the prevalence of acidosis sequelae to rice-based feeding regimen and assess its magnitude. Materials and Methods: A survey was conducted in all the 32 districts of Tamil Nadu, by randomly selecting two blocks per districts and from each block five villages were randomly selected. From each of the selected village, 10 dairy farmers belonging to the unorganized sector, owning one or two cross-bred dairy cows in early and mid-lactation were randomly selected so that a sample size of 100 farmers per district was maintained. The feeding regimen, milk yield was recorded, and occurrence of acidosis and incidence of laminitis were ascertained by the veterinarian with the confirmative test to determine the impact of feeding cooked rice to cows. Results: It is observed that 71.5% of farmers in unorganized sector feed cooked rice to their cattle. The incidence of acidosis progressively increased significantly (p<0.05) from 29.00% in cows fed with 0.5 kg of cooked rice to 69.23% in cows fed with more than 2.5 kg of cooked rice. However, the incidence of acidosis remained significantly (p<0.05) as low as 9.9% in cows fed feeding regimen without cooked rice which is suggestive of a correlation between excessive feeding cooked rice and onset of acidosis. Further, the noticeable difference in the incidence of acidosis observed between feeding cooked rice and those fed without rice and limited intake of oil cake indicates that there is a mismatch between energy and protein supply to these cattle. Among cooked rice-based diet, the incidence of laminitis increased progressively (p<0.05) from 9.2% to 37.9% with the increase in the quantum of cooked rice in the diet. Conclusion: The study points out the importance of protein supplementation in rice-based feeding regimen to set right the mismatched supply between nitrogen and fermentable organic matter in the rumen. This research has practical implications for animal health, welfare, nutrition, and management