Electronic Nose Differentiation Between Quercus robur Acorns Infected by Pathogenic Oomycetes Phytophthora plurivora and Pythium intermedium

Identification of the presence of pathogenic oomycetes in infected plant material proved possible using an electronic nose, giving hope for a tool to assist nurseries and quarantine services. Previously, species of Phytophthora plurivora and Pythium intermedium have been successfully distinguished in germinated acorns of English oak Quercus robur L. Chemical compound analyses performed by HS-SPME/GC-MS (Headspace Solid-Phase Microextraction/Gas Chromatography–Mass Spectrometry) revealed the presence of volatile antifungal molecules produced by oak seedlings belonging to terpenes and alkanes. Compounds characteristic only of Phytophthora plurivora or Pythium intermedium were also found. Methylcarveol occurred when germinated acorns were infected with Pythium, while neophytadiene (isomer 2 and 3) occurred only when infected with Phytophthora. Moreover, isopentanol was found in acorns infected with Phytophthora, while in control, isopentyl vinyl ether was not observed anywhere else. Among the numerous volatile compounds, isopentanol only occurred in acorns infected with Phytophthora and methylcarveol in acorns infected with Pythium.

Comparative Elimination of Begomoviruses in Cassava Meristems and Axillary Buds

Aim: The production of healthy cuttings from a local cassava cultivar for cassava mosaic control. Study design: The study was carried out at the In Vitro Culture Laboratory using the techniques of thermotherapy and culture of tissues and explants in a specific medium. Place and duration: The study was carried out at the Laboratory of Biological and Agronomic Sciences for Development at the University of Bangui, Central African Republic from December 2017 to June 2018. Methodology: A variety of cassava called six-month very susceptible to mosaic was used for this work. The cuttings used were infected by Cassava Mosaic Begomoviruses (CMBs) with high severity. It were subcultured in a room under the heat of 37 ° C to 40 ° C for two weeks. Explants and meristems were taken from the stems and the apices, respectively. These collected materials were treated and seeded on appropriate culture media. After the plants produced in vitro were acclimatized and the leaves were removed to check their phytosanitary state by the PCR technique. Results: The rate of emergence of the acclimatized plants and the expression of the disease on the microplants were evaluated. The results show that 75% of the weaned vitro plants recovered under acclimatization. In addition, the acclimatized plants left growing in the greenhouse for four months remained asymptomatic. Molecular analysis by PCR showed that begomoviruses were not detected on meristem samples unlike samples from stem fragments. Conclusion: The combination of thermotherapy technique associated with the culture of meristems constitutes an effective means useful for the sanitation of infected plant material.

Pseudomonas syringae pv. actinidiae (bacterial canker of kiwifruit).

Bacterial canker of kiwifruit, caused by Pseudomonas syringae pv. actinidiae (Psa), is a serious threat to kiwifruit production worldwide. At least four related but genetically distinct lineages of Psa are currently known, and more are likely to exist. In 2008, a particularly virulent strain emerged in Italy and spread rapidly to all main global kiwifruit production areas. This strain is variously referred to as the pandemic strain, PsaV or Biovar 3. Different Actinidia species and cultivars show varying susceptibility to Psa, and breeding resistant or tolerant kiwifruit varieties is highly important to the industry. Like all pathovars of Pseudomonas syringae, Psa is present in infected plant material. Transfer of nursery material is a major source of long distance spread, while agronomic techniques such as pruning can contribute to spread within and between orchards. The pathogen can be dispersed in aerosols and can be carried between trees and adjacent orchards in wind-driven rain. Psa is listed on the EPPO Alert List.

Liberibacter asiaticus (Asian greening).

The Asian form of Huanglongbing is considered very invasive due to the cryptic nature of the disease and its ability to be transported either in infected plant material or infective psyllids, in which the disease can persist for up to 3 months (da Graca and Korsten, 2004). Yield losses due to this disease have been estimated to be between 30% and 100%, depending on the proportion of the canopy affected and the age of the trees during inoculation (Gottwald, 2010; Ammar et al., 2011). History has shown that the appearance of the vector in a country will almost guarantee the appearance of the disease in the future, e.g. in Brazil and Florida, USA. The species and its vector are on several alert lists including the EPPO A1 Regulated Quarantine Plant Pests.

First Report of Citrus tristeza virus Infecting Citrus Trees in Georgia, USA

Citrus tristeza virus (CTV) [genus Closterovirus; family Closteroviridae] is one of the most important, economically devastating viruses of citrus worldwide. On citrus trees grafted onto sour orange rootstock, typical CTV symptoms include dieback and defoliation, stunting, curling and chlorotic leaves, stem-pitting, and pinholes below the bud union on the inner face of the bark (Moreno et al. 2008). This single-stranded, positive-sense RNA virus is most efficiently transmitted by the brown citrus aphid (Toxoptera citricida), but it can also be transmitted by other aphid species and through grafting of infected plant material onto healthy plants (Moreno et al 2008; Herron et al. 2006). In Fall 2020, leaf material for virus testing was collected from 13 navel orange trees (Citrus × sinensis) grafted onto Poncirus trifoliata rootstocks (including ‘Flying Dragon’) located in a citrus research orchard in Tifton, GA. Trees ranged in age from 2 to 10 years, with the younger trees having been grafted from cuttings taken from the older trees. The oldest of these trees was derived from cuttings taken in 2009 from an orange tree growing locally in a residential yard in Tifton; this parent tree was more than 15 years old when these cuttings were obtained and was no longer available for sampling as of 2020. Symptoms or other visible signs of disease had not been noted on any of the tested trees, and trees were chosen for testing prior to the further dissemination of this plant material. The presence of CTV was verified via molecular and serological testing. CTV infection was initially confirmed in 8 of 13 tested samples using the ImmunoStrip® for CTV assay (Agdia® Inc., Elkhart, IN, cat no: ISK 78900/0025) according to the manufacturer’s instructions. RNA was extracted from leaf material collected from the 13 sampled trees using the RNeasy Plant Mini Kit (Qiagen, Valencia, CA). Following cDNA synthesis, samples were tested for the presence of CTV by reverse-transcription PCR using primer pair AR18F (5’-ATGTCAGGCAGCTTGGGAAATT-3’) and AR18R (5’-TTCGTGTCTAAGTCRCGCTAAACA-3’) which produces a 511 bp amplicon (Roy et al., 2005). PCR reactions confirmed the presence of CTV, with the same eight samples that had previously tested positive via Immunostrip® producing PCR fragments of the expected size. Amplified products from two of these samples were then sequenced using Sanger sequencing (Retrogen Inc, San Diego, CA, USA) and subjected to BLAST analysis (https://blast.ncbi.nlm.nih.gov/Blast.cgi) for further identification. Sequence analysis revealed that the obtained partial sequences (MW540805) from the p18 gene of both isolates were 100% identical to one another and shared 100% identity to corresponding sequences from CTV strain N4 (MK779711.1). To the best of our knowledge, this is the first report of CTV infecting citrus plants in Georgia. CTV could pose an imminent threat to the emerging citrus industry in Georgia if it were to become established in commercial citrus plantings either via the dissemination of infected plant material or via vector transfer of the virus under field conditions. While the brown citrus aphid is not known to be widespread in Georgia at this time, other CTV vectors are prevalent including the cotton aphid (Aphis gossypii) and the black citrus aphid (T. aurantia). Georgia citrus growers and plant propagators should be aware of this virus and take appropriate control measures to prevent the spread of this viral diseas.

Diplodia sapinea in Swedish forest nurseries

Diplodia sapinea is a common forest pathogen on Pinus spp. in a large part of the world. In 2013, disease caused by this pathogen on Scots pine (Pinus sylvestris) trees in Sweden was reported for the first time. In this study, we report the first detection of D. sapinea on diseased seedlings of P. sylvestris from two Swedish forest nurseries. Infected seedlings were collected July–November 2019. Diplodia sapinea was identified by morphological characteristics of fungal structures on plant tissues and from culture grown on Hagem agar media, followed by sequencing of fungal ITS rDNA. The result emphasizes the susceptibility of P. sylvestris seedlings. More research is needed to better understand the risk for disease spreading within forest nurseries and into the forest through infected plant material.

Influence of Riparian Habitat and Ground Covers on Threecornered Alfalfa Hopper (Hemiptera: Membracidae) Populations in Vineyards

Grapevine red blotch virus (GRBV) is the causal agent of grapevine red blotch disease, which affects wine grapes and leads to reduced crop yield and quality. While some virus spread can be attributed to the propagation of infected plant material, a greenhouse assay recently demonstrated that the threecornered alfalfa hopper (Membracidae: Spissistilus festinus Say) can transmit GRBV between grapevines. While S. festinus is not considered an economic pest of wine grapes, this species is present in California vineyards and their feeding can cause petiole girdling. Recent surveys have noted a correlation between S. festinus populations and GRBV-positive vines in vineyard areas adjacent to riparian habitat. Here, S. festinus populations were monitored over a 2-yr period at multiple vineyard sites adjacent to riparian habitats. At each site, insects were sampled from ground covers and the vine canopy at the vineyard edge and interior, and vines in both locations were evaluated for petiole girdling. Results indicate that there was no difference in abundance of S. festinus at the vineyard edge and interior. Populations in the vine canopy were highest in the late spring and early summer, and this was followed by the appearance of petiole girdling, indicating a key period of potential GRBV transmission. Furthermore, activity in the vine canopy appears to be amplified when the quality of ground covers is reduced as the season progresses. That said, overall populations of S. festinus were relatively low and additional work is needed to characterize the timing and efficiency of transmission under field conditions.

Controlling water hyacinth infestation in Lake Tana using Fungal pathogen from Laboratory level upto pilot scale

ABSTRACTWater hyacinth (Eichhornia crassipes) is one of the most dangerous aquatic weeds for Lake Tana and other water body in Ethiopia. To reduce its invasion biological, chemical and physical control methods can be used. Use of natural biological enemies of the weed to discourage its propagation is one of the best recommended options by scientfic society. Among them, there are more fungi naturally a pathogen for water hyacinth and other plants. To use those patogenes to manage water hyacinth infestation in Lake Tana infected plant material by fungi were collected from three weredas (Amba Gyorgese, Dabat and Debarke) around Gondar at 20 Peasant associations (PAs) since Novmber 2015. The collection was done from infected Faba bean leaves and roots. All isolated fungus was attempted to infect the collected healthy water hyacinth in laboratory and green house. Among isolated fungus species Rhizoctonia solani, Aspergillus flatus, Tricothcium roseum, Fusarium spp and Aspergillus niger fungi show high moderate disease severity on the healthy water hyacinth at temporarey green house and laboratory. Disease severity scale was recorded using modified NAHEMA et al. (200). By following those experiments to show its efficiency, the effective pathogens on laboratory and green house were released to 16 m2 open ponds since September 2016, in University of Gondar. In this study, we have recorded scientific data that shows the fungi were high potencial to attack healthy water hyacinth at above 26 oc and at less than 25 % humidity. From this research also we have observed the most infected water hyacinth by fungi have not produced flower and it can not re generate by seed in the next propagation sesaon.Finally, before directly release the fungi on Lake Tana its impacts were studied in the Goregora, at Kuame Michel kebela for a year in open ponds and in controlled wet land areas that not linked to the Lake by taking some common aquatic plants and fish from the Lake. Fortunatelly, those fungi have not impact on aquatic plant like Echinochloa and Cyperus papyrus grass, water quality and fish.

SPECIFIC FEATURES OF THE STUDY AND MAINTENANCE OF A POTATO COLLECTION THREATENED BY VIRUSES AND VIRUS¬LIKE DISEASES

Background. The article deals with the problems faced while studying and maintaining a collection of plant genetic resources against a strong virus infection background.Materials and methods. The data obtained during 8 years of monitoring over 1000 potato accessions for the incidence of virus diseases are presented. The work was carried out at Pushkin and Pavlovsk Laboratories of VIR and at the Polar Experiment Station of VIR (Khibiny, Arctic Circle). Visual control of the symptoms of the infection was combined with an enzyme-linked immunosorbent assay (ELISA) for potato mosaic viruses Х, S, M and Y.Results and conclusions. For many years, the global collection of VIR has been studied and maintained under a threat of strong virus infections. Among the viruses that have the widest distribution and cause significant damage to potato, there are viruses M and Y in Pushkin, and Х in Khibiny. Among the infected plant material, accessions with a latent virus infection, manifesting tolerance to the pathogens, have constantly been observed. The conventional point-based principle of scoring field resistance of potato cultivars and hybrids to viruses requires a significant revision. A new alternative approach is proposed for virus resistance assessment, when the clonal reproduction type of the tested accessions is taken into account.