inoculum sources
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2021 ◽  
Author(s):  
Eduardo S. G. Mizubuti ◽  
Jaqueline K. Yamada ◽  
Thais R. Santiago ◽  
Carlos A. Lopes

Dispersal of Ralstonia spp. cells by water and contaminated plant material and the importance of weeds as inoculum sources have been poorly investigated. Water of rivers, soil from fields of diverse crops and areas of natural vegetation both from the Amazonia, Cerrado and Mata Atlantica biomes, besides soil of the rhizosphere of weeds present in tomato fields with records of bacterial wilt were sampled and analyzed to detect Ralstonia spp. Seeds of tomato plants artificially and naturally infected with Ralstonia spp. were also processed. All samples were enriched a priori in selective medium South Africa (SMSA) and colonies were isolated in plates containing solid SMSA. Detection of Ralstonia spp. was confirmed by polymerase chain reaction with specific primers. The Co-operational PCR (CO-PCR) was also used to detect Ralstonia spp. Colonies were obtained from soil samples and from a commercial substrate sample. Five soil samples from eggplant fields, one from coffee field, one substrate from potato seed tuber production, two soil samples from the rhizosphere of Amaranthus spp., one from Bidens pilosa and one from Solanum americanum tested positive for Ralstonia spp. Besides these soil samples, five water samples of rivers were positive for CO-PCR detection: two samples from Amazonia, one from Cerrado and two samples from irrigation water collected from tomato fields located in the Mata Atlantica biome. Ralstonia spp. were not detected in tomato seeds. These results revealed potential inoculum sources, especially weeds, in areas with historical records of bacterial wilt. Additionally, rivers may act as dispersal agents of inoculum of Ralstonia spp.


Plants ◽  
2021 ◽  
Vol 10 (12) ◽  
pp. 2716
Author(s):  
Karima Bencherif ◽  
Frédéric Laruelle ◽  
Yolande Dalpé ◽  
Anissa Lounès-Hadj Sahraoui

(1) Background: Soil degradation is an increasingly important problem in many parts of the world, particularly in arid and semiarid areas. Arbuscular mycorrhizal fungi (AMF) isolated from arid soils are recognized to be better adapted to these edaphoclimatic conditions than exogenous ones. Nevertheless, little is known about the importance of AMF inoculum sources on Tamarix articulata development in natural saline soils. Therefore, the current study aims at investigating the efficiency of two AMF-mixed inoculums on T. articulata growth, with consideration of its rhizosphere microbiota. (2) Methods: indigenous inoculum made of strains originating from saline soils and a commercial one were used to inoculate T. articulata in four saline soils with different salinity levels under microcosm conditions with evaluation of rhizosphere microbial biomasses. (3) Results: Our findings showed that indigenous inoculum outperforms the commercial one by 80% for the mycorrhizal rate and 40% for plant biomasses, which are correlated with increasing shoot phosphorus content. Soil microbial biomasses increased significantly with indigenous mycorrhizal inoculum in the most saline soil with 46% for AMF, 25% for saprotrophic fungi and 15% for bacterial biomasses. (4) Conclusion: Present results open the way towards the preferential use of mycorrhizal inoculum, based on native AMF, to perform revegetation and to restore the saline soil microbiota.


Plant Disease ◽  
2021 ◽  
Author(s):  
Abigail Justine Stack ◽  
Stephen Mark Marek ◽  
Thomas Gordon ◽  
Richard M. Bostock

Previous research determined that Fusarium acuminatum and Fusarium avenaceum are important causal agents of a canker disease in bareroot-propagated fruit and nut trees in California that emerges during cold-storage or after transplanting. The disease largely disappeared after 2001, but it reemerged in 2011 in almond trees in at least one nursery. This motivated further study of the etiology and epidemiology of the disease by undertaking studies to determine distribution of the pathogens throughout almond nursery propagation systems and trace possible sources of inoculum. Research initiated in 2013 detected pathogenic Fusarium spp. throughout the almond propagation system, including in healthy trees, in soils, on wheat rotation crops, on equipment, and in the cold storage facility air. In addition to the two Fusarium spp. implicated previously, Fusarium brachygibbosum and a new Fusarium species, Fusarium californicum, were found to be pathogenic on almond trees. Multi-locus sequence typing and somatic compatibility testing confirmed that isolates within a species collected from different materials in the nursery were all highly genetically similar and likely of one clonal lineage. These findings affirm that equipment surfaces, wheat rotation crops, soil, cold storage facility air, and asymptomatic almond tree materials (i.e., rootstock cuttings, budwood, and scions) can potentially contribute inoculum to increase disease prevalence and severity.


Plant Disease ◽  
2021 ◽  
Author(s):  
Frank Hay ◽  
Daniel Winter Heck ◽  
Audrey Klein ◽  
Sandeep Sharma ◽  
Christine Anne Hoepting ◽  
...  

Stemphylium leaf blight (SLB) caused by Stemphylium vesicarium is the dominant foliar disease affecting large-scale onion production in New York. The disease is managed by fungicides, but control failures are prevalent and recently attributed to fungicide resistance. Little is known of the relative role of inoculum sources in initiation and spread of SLB epidemics. Plate testing of 28 commercially available organic onion seedlots from 2016 and 2017 did not detect S. vesicarium. This finding suggests that although S. vesicarium has been reported as seed transmitted, this is unlikely to be a significant inoculum source in commercially available organic seed lots and even less so in fungicide-treated seed used to establish conventional fields. The spatial and spatiotemporal dynamics of SLB epidemics in six onion fields were evaluated along linear transects in 2017 and 2018. Average SLB incidence increased from 0 to 100% throughout the cropping seasons with an average final lesion length of 28.3 cm. Disease progress was typical of a polycyclic epidemic and the logistic model provided the best fit to 83.3% of the datasets. Spatial patterns were better described by the beta-binomial than binomial distribution in half of the datasets (50%) and random patterns were more frequently observed by the index of dispersion (59%). Geostatistical analyses also found a low frequency of datasets with aggregation (60%). Spatiotemporal analysis of epidemics detected that the aggregation was influenced by disease incidence. However, diseased units were not frequently associated with the previous time period according to the spatiotemporal association function of SADIE. Variable spatial patterns suggested mixed inoculum sources dependent upon location, and likely an external inoculum source at the sampling scale used in this study. A small-plot replicated trial was also conducted in each of two years to quantify the effect of S. vesicarium-infested onion residue on SLB epidemics in a field isolated from other onion fields. SLB incidence was significantly reduced in plots without residue compared to those in which residue remained on the soil surface. Burial of infested residue also significantly reduced epidemic progress in one year. The effect of infested onion residue on SLB epidemics in the subsequent onion crop suggests rotation or residue management may have a substantial effect on epidemics. However, the presence of an inoculum source external to fields in onion production regions as indicated by a lack of spatial aggregation may reduce the efficacy of in-field management techniques.


2021 ◽  
Author(s):  
Frank Hay ◽  
Daniel Heck ◽  
Audrey Klein ◽  
Sandeep Sharma ◽  
Christy Hoepting ◽  
...  

Stemphylium leaf blight (SLB) caused by Stemphylium vesicarium is the dominant foliar disease affecting large-scale onion production in New York. The disease is managed by fungicides, but control failures are prevalent and recently attributed to fungicide resistance. Little is known of the relative role of inoculum sources in initiation and spread of SLB epidemics. The spatial and spatiotemporal dynamics of SLB epidemics in six onion fields were evaluated along linear transects in 2017 and 2018. Average SLB incidence increased from 0 to 100% throughout the cropping seasons with an average final lesion length of 28.3 cm. Disease progress was typical of a polycyclic epidemic and the logistic model provided the best fit to 83.3% of the datasets. Spatial patterns were better described by the beta-binomial than binomial distribution in half of the datasets and random patterns were more frequently observed by the index of dispersion. Geostatistical analyses of spatial pattern also found a low frequency of datasets with aggregation. Spatiotemporal analysis of epidemics detected that the aggregation was influenced by disease incidence. However, diseased units were not associated with the previous time period according to the spatiotemporal association function of SADIE. Variable spatial patterns suggested mixed inoculum sources dependent upon location, and likely an external inoculum source at the sampling scale used in this study. Plate testing of 28 commercially available organic onion seedlots from 2017 and 2018 did not detect S. vesicarium. This finding suggests that although S. vesicarium has been reported as seed transmitted, this is unlikely to be a significant inoculum source in commercially available organic seed lots and even less so in fungicide-treated seed used to establish conventional fields. A small-plot replicated trial was also conducted in each of two years to quantify the effect of S. vesicarium-infested onion residue on SLB epidemics in a field isolated from other onion fields. SLB incidence was significantly reduced in plots without residue compared to those in which residue remained on the soil surface. Burial of infested residue also significantly reduced epidemic progress in one year. The effect of infested onion residue on SLB epidemics in the subsequent onion crop suggests rotation or residue management may have a substantial effect on epidemics. However, the presence of an inoculum source external to fields in onion production regions as indicated by a lack of spatial aggregation may reduce the efficacy of in-field management techniques.


2021 ◽  
Author(s):  
Eduardo de la Lastra ◽  
José I. Marín‐Guirao ◽  
Francisco J. López‐Moreno ◽  
Teresa Soriano ◽  
Miguel de Cara‐García ◽  
...  

Plant Disease ◽  
2021 ◽  
Author(s):  
Juliana Silveira Baggio ◽  
Marcus Vinicius Marin ◽  
Natalia A. Peres

Phytophthora crown rot, caused mainly by Phytophthora cactorum, and also by the recently reported P. nicotianae, is an important disease in the Florida strawberry annual production system. Mefenoxam is the most effective and widely used fungicide to manage this disease. However, due to pathogen resistance, alternatives to chemical control are needed. Phytophthora spp. were rarely recovered during the summer from soil of commercial farms where the disease was observed during the season. In a more detailed survey on research plots, neither of the two species was recovered one month after the crop was terminated and water was shut off. Therefore, Phytophthora spp. does not seem to survive in the soil over summer in Florida. In a field trial, asymptomatic nursery transplants harboring quiescent infections were confirmed as the major source of inoculum for these pathogens in Florida. Heat treatment of P. cactorum zoospores at 44oC for as little as 5 min was effective in inhibiting germination and colony formation; however, oospore germination was not inhibited by any of the tested temperatures in vitro. In the field, thermotherapy treatment of inoculated plants was shown to have great potential to serve as a non-chemical approach for managing Phytophthora crown rot in production fields and reducing mefenoxam-resistant populations in nursery transplants.


2021 ◽  
Vol 87 (3) ◽  
pp. 127-136
Author(s):  
Zoë E. Dubrow ◽  
Adam J. Bogdanove

AbstractXanthomonas campestris pv. campestris, the causal agent of black rot of crucifers, was one of the first bacterial plant pathogens ever identified. Over 130 years later, black rot remains a threat to cabbage, cauliflower, and other Brassica crops around the world. Recent genomic and genetic data are informing our understanding of X. campestris taxonomy, dissemination, inoculum sources, and virulence factors. This new knowledge promises to positively impact resistance breeding of Brassica varieties and management of inoculum sources.


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