Novel cytopathological structures induced by mixed infection of unrelated plant viruses

A Survey of Main Pepper Crop Viruses in Different Cultivation Systems for the Selection of the Most Appropriate Resistance Genes in Sensitive Local Cultivars in Northern Spain

Viral diseases have become one of the main phytosanitary problems for pepper growers in the Basque Country (northern Spain). In 2014, a survey was carried out to determine the prevalence of the most common viruses found in Gernika pepper and Ibarra chili pepper landraces. A total of 97 plots were surveyed and classified according to the crop system. Within these plots, 1107 plants were sampled and tested for tobacco mosaic virus (TMV), tomato mosaic virus (ToMV), tobacco mild green mosaic virus (TMGMV), pepper mild mottle virus (PMMoV), paprika mild mottle virus (PaMMV), potato virus Y (PVY) and tomato spotted wilt virus (TSWV) applying a DAS-ELISA test. PaMMV was verified by the non-radioactive molecular hybridization technique and it was found to be negative. All viruses were detected, but the most prevalent viruses were PVY and TMGMV (19.8% and 10.6% of tested plants, respectively). Differences among cultivation systems were found for most of the tested viruses. PVY had a higher level of infection under open field conditions (27.3%) than under greenhouse conditions (12.3%). Inversely, the viruses belonging to the Tobamovirus genus and TSWV prevailed under greenhouse conditions (28.9% and 5.2%) when compared to open field (11.2% and 1.1%), respectively. Single (28%) and multiple infections (8.9%) were found. All PMMoV isolates were classified as pathotype P1.2. Survey results indicated that tobamovirus and PVY resistance genes would be the most appropriate to be included in breeding programs with these sensitive pepper landraces.

Additive interactions of unrelated viruses in mixed infections of cowpea (Vigna unguiculata L. Walp)

This study was carried out to determine the effects of single infections and co-infections of three unrelated viruses on three cowpea cultivars (one commercial cowpea cultivar "White" and 2 IITA lines; IT81D-985 and TVu 76). The plants were inoculated with Cowpea aphid-borne mosaic virus (CABMV), genus Potyvirus, Cowpea mottle virus (CMeV), genus Carmovirus and Southern bean mosaic virus (SBMV), genus Sobemovirus singly and in mixture (double and triple) at 10, 20, and 30 days after planting (DAP). The treated plants were assessed for susceptibility to the viruses, growth, and yield. In all cases of infection, early inoculation resulted in higher disease severity compared with late infection. The virus treated cowpea plants were relatively shorter than buffer inoculated control plants except the IT81D-985 plants that were taller and produced more foliage. Single infections by CABMV, CMeV, and SBMV led to a complete loss of seeds in the three cowpea cultivars at 10 DAP; only cultivar White produced some seeds at 30 DAP. Double and triple virus infections led to a total loss of seeds in all three cowpea cultivars. None of the virus infected IITA lines produced any seeds except IT81D-985 plants co-infected with CABMV and SBMV at 30 DAP with a reduction of 80%. Overall, the commercial cultivar "White" was the least susceptible to the virus treatments and produced the most yield (flowers, pods, and seeds). CABMV was the most aggressive of these viruses and early single inoculations with this virus resulted in the premature death of some of the seedlings. The presence of the Potyvirus, CABMV in the double virus infections did not appear to increase disease severity or yield loss. There was no strong evidence for synergistic interactions between the viruses in the double virus mixtures.

Virus diseases in lettuce in the Mediterranean basin

Lettuce is frequently attacked by several viruses causing disease epidemics and considerable yield losses along the Mediterranean basin. Aphids are key pests and the major vectors of plant viruses in lettuce fields. Lettuce mosaic virus (LMV) is probably the most important because it is seed-transmitted in addition to be transmissible by many aphid species that alight on the crop. Tomato spotted wilt virus (TSWV) is another virus that causes severe damage since the introduction of its major vector, the thrips Frankliniella occidentalis. In regions with heavy and humid soils, Lettuce Mirafiori big-vein virus (LMBVV) can also produce major yield losses.

Immediate reduction of Salmonella enterica serotype typhimurium viability via membrane destabilization following exposure to multiple-hurdle treatments with heated, acidified organic acid salt solutions

The antimicrobial activity of organic acids in combination with nonchemical treatments was evaluated for inactivation of Salmonella enterica serotype Typhimurium within 1 min. It was observed that the effectiveness of the multiple-hurdle treatments was temperature (P ≤ 0.05) and pH (P ≤ 0.05) dependent and corresponded to the degree of organic acid lipophilicity (sodium acetate being least effective and sodium propionate being the most effective). This led to the hypothesis that the loss in viability was due at least in part to cell membrane disruption. Evaluation of osmotic response, potassium ion leakage, and transmission electron micrographs confirmed treatment effects on the cell membrane. Interestingly, all treatments, even those with no effect on viability, such as with sodium acetate, resulted in measurable cellular stress. Microarray experiments explored the specific response of S. Typhimurium to sodium acetate and sodium propionate, the most similar of the tested treatments in terms of pK(a) and ionic strength, and found little difference in the changes in gene expression following exposure to either, despite their very different effects on viability. Taken together, the results reported support our hypothesis that treatment with heated, acidified, organic acid salt solutions for 1 min causes loss of S. Typhimurium viability at least in part by membrane damage and that the degree of effectiveness can be correlated with lipophilicity of the organic acid. Overall, the data presented here indicate that a combined thermal, acidified sodium propionate treatment can provide an effective antimicrobial treatment against Salmonella.

A simple technique for separation of Cowpea chlorotic mottle virus from Cucumber mosaic virus in natural mixed infections

A simple technique was developed to separate Cowpea chlorotic mottle virus (CCMV) from Cucumber mosaic virus (CMV) in natural mixed infections. Sap from cowpea leaves infected naturally with a mixture of CCMV and CMV was inoculated mechanically on the first tri-foliolate leaf of cowpea seedlings. Both inoculated and non-inoculated upper leaves were sampled 3 or 8 days post-inoculation and tested by reverse transcription polymerase chain reaction (RT-PCR) using primers specific to CCMV and CMV. RT-PCR analysis showed the presence of only CCMV in the inoculated leaf and both viruses in the non-inoculated systemically infected upper leaves. Total RNA from the inoculated leaves positive to CCMV only was further confirmed upon re-inoculation to cowpea seedlings. Typical CCMV symptoms were produced within 1 week and RT-PCR analysis showed only the presence of CCMV in both inoculated and non-inoculated systemically infected upper leaves. Systemically infected upper leaves of the same plants were used for CCMV purification. RT-PCR analysis of the purified virion and RNA extracted from the virion further confirmed the absence of CMV contamination. To our knowledge, this is the first report of a method separating CCMV directly from mixed infections with CMV in cowpea.

Viral Interactions Lead to Decline of Blackberry Plants

Blackberry yellow vein disease (BYVD) poses a new threat to the blackberry industry in the United States. Blackberry yellow vein associated virus (BYVaV) was originally thought to be the sole cause of this disease. However, BYVaV has been found in several asymptomatic blackberry cultivars. An unusual member of the family Potyviridae was identified recently from symptomatic plants and named Blackberry virus Y (BVY). BVY has been shown to spread in the field and cause BYVD when co-infected with BYVaV. Both viruses are asymptomatic in single infections but are readily detectable in asymptomatic plants by reverse transcription-polymerase chain reaction (RT-PCR). However, in mixed infections, the titer of BYVaV is repressed, sometimes to levels undetectable by RT-PCR, while the concentration of BVY is increased several fold. Electron microscopy revealed a variety of viral inclusions in symptomatic leaf samples, but none could be found in single infections with either BVY or BYVaV. Although BYVaV has been consistently associated with BYVD in different geographical regions, the detection of BVY has thus far been restricted to northwest Arkansas. It has been hypothesized that BYVaV is the synergistic determinant of BYVD that causes symptoms in different cultivars at various locations during co-infection with other viruses.

Synergistic pathogenicity of a phloem-limited begomovirus and tobamoviruses, despite negative interference

In contrast to previous observations on phloem-limited geminiviruses supported in movement andaccumulation by RNA viruses such as cucumo- and tobamoviruses, tissue infiltration by Abutilon mosaic virus (AbMV) was enhanced by neither Tobacco mosaic virus nor Tomato mosaic virus (ToMV) in two different hosts, Nicotiana benthamiana and tomato. Both tobamoviruses exerted a negative effect on the DNA virus, resulting in a decrease in AbMV accumulation and significantly reduced infectivity in N. benthamiana. Despite these unexpected molecular observations, a striking synergistic enhancement in pathogenicity occurred with respectto stunting and necrosis. In situ hybridization revealed that this was not due to any alteration of tissue infiltration by AbMV, which also remained limited to the phloem in the mixed infections. Transgenically expressed ToMV 30K movement protein was not able to induce phloemescape of AbMV in tomato plants and did not lead to any obvious change in begomovirus symptomatology.

Synergism of a DNA and an RNA virus: enhanced tissue infiltration of the begomovirus Abutilon mosaic virus (AbMV) mediated by Cucumber mosaic virus (CMV)

Replication of the begomovirus Abutilon mosaic virus (AbMV) is restricted to phloem nuclei, generating moderate levels of virus DNA. Co-infection with Cucumber mosaic virus (CMV) evidently increased AbMV titers in Nicotiana benthamiana, tobacco, and tomato, resulting in synergistic symptom enhancement. In situ hybridization revealed that in double-infected leaves an increased number of nuclei contained elevated amounts of AbMV. Additionally, the begomoviral phloem-limitation was broken. Whereas CMV 3a movement protein-expressing tobacco plants did not exert any similar influence, the presence of CMV 2b silencing suppressor protein lead to enhanced AbMV titers and numbers of infected vascular cells. The findings prove that AbMV can replicate in nonvascular cells and represent the first report on a true synergism of an RNA/ssDNA virus combination in plants, in which CMV 2b protein plays a role. They indicate considerable consequences of mixed infections between begomo- and cucumoviruses on virus epidemiology and agriculture.