This study investigated the role of vector acquisition and transmission on the propagation of single and co-infections of tomato yellow leaf curl virus (TYLCV,) and tomato mottle virus (ToMoV) (Family: Geminiviridae, Genus: Begomovirus) by the whitefly vector Bemisia tabaci MEAM1 (Gennadius) in tomato. The aim of this research was to determine if the manner in which viruses are co-acquired and co-transmitted changes the probability of acquisition, transmission and new host infections. Whiteflies acquired virus by feeding on singly infected plants, co-infected plants, or by sequential feeding on singly infected plants. Viral titers were also quantified by qPCR in vector cohorts, in artificial diet, and plants after exposure to viruliferous vectors. Differences in transmission, infection status of plants, and titers of TYLCV and ToMoV were observed among treatments. All vector cohorts acquired both viruses, but co-acquisition/co-inoculation generally reduced transmission of both viruses as single and mixed infections. Co-inoculation of viruses by the vector also altered virus accumulation in plants regardless of whether one or both viruses were propagated in new hosts. These findings highlight the complex nature of vector-virus-plant interactions that influence the spread and replication of viruses as single and co-infections.
A new variant of cotton leafroll dwarf virus (CLRDV) (genus: Polerovirus, family: Solemoviridae) was discovered in cotton (Gossypium hirsutum L.) fields that were reported to be infested with aphids and whiteflies in southern Alabama in 2017. Prior to the confirmation of CLRDV, speculation focused on whiteflies as a potential vector of the then-unknown virus. Although the only vector reported to transmit CLRDV to cotton is the cotton aphid, Aphis gossypii (Glover), two recombinant poleroviruses have been reported recently to be transmitted by the whitefly, Bemisia tabaci (Genn.). Due to the emergence of a new CLRDV variant in the U.S., and the recent studies on recombinant poleroviruses, conflicting messages that whiteflies and/or aphids could be transmitting CLRDV have been relayed to growers and stakeholders in the Cotton Belt. The objective of this study was to determine if A. gossypii or B. tabaci (B Mitotype) transmit CLRDV to cotton. The results demonstrated that the CLRDV-AL variant was transmissible by alate and apterous morphs of A. gossypii, but not by B. tabaci. These findings emphasize the importance of screening insect vectors for the transmission of novel plant virus variants to correctly identify the vector(s) and provide growers and stakeholders with appropriate information to make informed management decisions.
This study investigated the role of vector acquisition and transmission on the propagation of single and co-infections of tomato yellow leaf curl virus (TYLCV,) and tomato mottle virus (ToMoV) (Family: Geminiviridae, Genus: Begomovirus) by the whitefly vector Bemisia tabaci MEAM1 (Gennadius) in tomato. The aim of this research was to determine if how viruses are co-acquired and co-transmitted changes the probability of acquisition, transmission and new host infections. Whiteflies acquired virus by feeding on singly infected plants, co-infected plants, or by sequential feeding on singly infected plants. Viral titers were also quantified by qPCR in vector cohorts, in artificial diet, and plants after exposure to viruliferous vectors. Differences in transmission, infection status of plants, and titers of TYLCV and ToMoV were observed among treatments. All vector cohorts acquired both viruses, but co-acquisition/co-inoculation generally reduced transmission of both viruses as single and mixed infections. Co-inoculation of viruses by the vector also altered virus accumulation in plants regardless of whether one or both viruses were propagated in new hosts. These findings highlight the complex nature of vector-virus-plant interactions that influence the spread and replication of viruses as single and co-infections.
Aspergillus flavus is an opportunistic fungus that affects many crops including corn. A. flavus colonizes the ear of the corn, causing a disease known as Aspergillus ear rot (AER). AER contributes to yield loss in two ways; through fungal infection, which results in decreased kernel weight, and through contamination of the grain with aflatoxins. A. flavus has the ability to produce toxic secondary metabolites called aflatoxins which are harmful to humans and animals when consumed. Contamination with aflatoxin can result in reduced price, or rejection of grain depending on FDA regulatory limits. Due to their ability to compete with and displace toxigenic strains, atoxigenic (non‐toxin producing) strains of A. flavus have been used as a biological control, such as the Syngenta product Afla‐Guard®. The evaluation of local populations of A. flavus strains enables researchers to gather information about what is present in the field (atoxigenic or toxigenic) and can help make more informed management recommendations. Therefore, the purpose of this research was to evaluate the characteristics of an unknown isolate of A. flavus isolated from corn in West Tennessee in comparison to known atoxigenic (1 isolate from Afla‐Guard®) and toxigenic isolates (2 isolates). Each isolate was grown on barley seed and plated onto MDRB media three times (i.e. 3 replications) along with a negative control (autoclaved barley) (total of 15 plates). Radial growth and colony morphology of each isolate were evaluated at 3‐ and 5‐days after plating in a laboratory setting. Based on observations of the activity of the TN field collected isolate, it was predicted to grow slower than the Afla‐Guard®/atoxigenic isolate. Preliminary results demonstrate that the Afla‐Guard®/atoxigenic isolate did outgrow the TN strain as hypothesized. Additional research is required to determine the toxicity of the TN strain, as well as evaluation of other naturally occurring strains in TN in relation to potential use as biological controls.
Cotton (Gossypium hirsutum L.) is used as a non-host of tomato yellow leaf curl virus (TYLCV) (family Geminiviridae, genus Begomovirus) in many studies (Ghanim and Czosnek 2000; Legarrea et al. 2015; Zeidan and Czosnek 1991), but only one reports methods used to determine host-status (Sinisterra et al. 2005), and there is one contradictory report from China stating cotton is a host of TYLCV (Li et al. 2014). In October 2018, cotton was screened for the presence of begomoviruses in Elmore, Escambia and Macon Counties, AL, where infestations of its whitefly vector (Bemisia tabaci Genn.) occurred in August. DNA was extracted from fully expanded leaves from the upper 1/3 of the canopy using a DNeasy® Plant Mini Kit (QIAGEN, Hilden, Germany) and amplified with primers V324/C889 targeting a 575 bp coat protein fragment of begomoviruses (Brown et al. 2001). Five out of 200 cotton samples tested positive, and sequences recovered from three samples revealed 98-99% identity to TYLCV isolates in NCBI (Accession Nos. MT947801-03); sequences from the other two samples were of low quality and inconclusive. These samples were not available for additional tests, therefore, we proceeded to confirm host status using a monopartite clone of TYLCV-Israel (Reyes et al. 2013) reported in the US (Polston et al. 1999). All experiments were conducted in growth chambers with 16:8 light:dark cycle at 25.0℃ and 50% RH. Cotton seedlings (DeltaPine 1646 B2XF) at the 2-3 true leaf stage and tomatoes (Solanum lycopersicum L., var. ‘Florida Lanai’) at the 4 true leaf stage were agroinoculated at the stem tissue between the apical meristem and the first node (Reyes et al. 2013). Tomato served as a positive control; tomato and cotton mock inoculated with an empty vector were negative controls. A hole-punch was used to collect 4 leaf discs along midveins of the three, uppermost fully expanded leaves. DNA was extracted 28 days after inoculation as described above. A 390 bp segment of the intergenic region of TYLCV-A was amplified using primers PTYIRc287/PTYIRv21 (Nakhla et al., 1993). PCR results from agroinoculated plants confirmed (2/18) cotton plants, (5/5) tomatoes and (0/10) mock inoculated controls were infected with TYLCV. Whitefly transmission to cotton was confirmed using a leaf-disc bioassay for rapid testing (Czosnek et al. 1993). Bemisia tabaci MEAM-1 reared on eggplant (non-host of TYLCV) were placed on agroinoculated TYLCV-infected tomato/span> plants for a 96-h acquisition access period. Cohorts of 10 viruliferous B. tabaci were aspirated into 30mL cups each containing a 2.5cm healthy cotton leaf disc set in plant agar. After a 48-h inoculation access period, adults and their eggs were removed from the leaf discs. Leaf discs were held another 96-h before they were tested for TYLCV using the methods described above. TYLCV-infection was confirmed in (9/20) cotton leaf discs, demonstrating the viral load delivered by whiteflies was high enough to initiate local infection in cotton. No obvious begomovirus symptoms were observed on cotton plants in the field or laboratory. Field collection of samples was prompted by symptoms attributed to cotton leafroll dwarf virus (Avelar et al. 2017). TYLCV infection of cotton does not appear to be of economic importance. Additional information is needed to determine the frequency of infection in the field, specificity of TYLCV isolate x cotton genotype interactions leading to successful infection, and underlying causes of conflicting host-status reports in previously published studies.
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