Air potato (
Dioscorea bulbifera
) plants being grown at the Florida Department of Agriculture and Consumer Services Division of Plant Industry Biological Control Laboratory II in Alachua County, ...Florida were observed exhibiting foliar mosaic symptoms characteristic of virus infection. A double-stranded RNA library generated from a symptomatic plant underwent high-throughput sequencing to determine if viral pathogens were present. Sequence data revealed the presence of two viral genomes, one with properties congruent with members of the genus
Potyvirus
(family
Potyviridae
), and the other with members of the genus
Ampelovirus
(family
Closteroviridae
). Sequence comparisons and phylogenetic placement indicate that both viruses represent novel species. The names “dioscorea mosaic virus” and “air potato virus 1” are proposed for the potyvirus and ampelovirus, respectively.
Star jasmine (
Jasminum multiflorum
) plants growing in Hawaii expressing a diverse array of virus-like foliar symptoms were examined for the presence of a causal agent. Symptomatic tissues collected ...from three locations on the island of Oahu, Hawaii consistently harbored double-stranded (ds)RNAs approximately 4.2 and 1.7 kbp in size. Sanger and high-throughput sequencing approaches revealed these dsRNAs were from two distinct virus species co-infecting the same host plant. One of these two viruses was the recently characterized Jasmine virus H (JaVH), and the second we designated as Jasmine mosaic-associated virus (JMaV). Both viruses were subsequently found, by high-throughput sequencing, in a single angelwing jasmine (
J. nitidum
) plant exhibiting similar ringspot symptoms and growing at the U.S. National Arboretum in Washington, DC. Phylogenetic placement, genome organization, and sequence comparisons indicate these two viruses are classifiable as members of the genus
Pelarspovirus
(family
Tombusviridae
). To determine if either of these viruses were associated with the observed symptoms, a PCR-based detection assay was developed to detect and distinguish these two viruses in several Hawaii-grown plants. All 32 samples collected from four Oahu locations displayed symptoms. All 32 samples were positive for JaVH, and 16 were positive for JMaV. An asymptomatic star jasmine plant from the island of Hawaii was negative for both JaVH and JMaV. Both viruses were also found in a symptomatic
J. sambac
sample from Maryland while only JMaV was detected in a symptomatic
Jasminum
sp. sample from California.
The determining number of a graph $G = (V,E)$ is the minimum cardinality of a
set $S\subseteq V$ such that pointwise stabilizer of $S$ under the action of
$Aut(G)$ is trivial. In this paper, we ...provide some improved upper and lower
bounds on the determining number of Kneser graphs. Moreover, we provide the
exact value of the determining number for some subfamilies of Kneser graphs.
Combinatorics is full of examples of real-rooted polynomials. Suppose one has a sequence of real-rooted polynomials, and then wants consecutive pairs to have interlacing roots (on the real line). The ...method of proving the real-rootedness sometimes does not prove the interlacing property. In this work, we prove that if a sequence of real-rooted polynomials satisfies a particular type of recurrence with some conditions, then the sequence also satisfies the interlacing property. We give examples of several interesting combinatorial families of sequences whose interlacingness directly follows from our main result.
Canna yellow mottle virus (CaYMV) is an important badnavirus infecting Canna spp. worldwide. This is the first report of CaYMV in flowering ginger (Alpinia purpurata) in Hawaii, where it is ...associated with yellow mottling and necrosis of leaves, vein streaking, and stunted plants. We have sequenced CaYMV in A. purpurata (CaYMV-Ap) using a combination of next-generation sequencing and traditional Sanger sequencing techniques. The complete genome of CaYMV-Ap was 7,120 bp with an organization typical of other Badnavirus species. Our results indicated that CaYMV-Ap was present in the episomal form in infected flowering ginger. We determined that this virus disease is prevalent in Hawaii and could potentially have significant economic impact on the marketing of A. purpurata as cut flowers. There is a potential concern that the host range of CaYMV-Ap may expand to include other important tropical plants.
Higher plants use RNA silencing to defend against viral infections. As a counter defense, plant viruses have evolved proteins that suppress RNA silencing. Mealybug wilt of pineapple (MWP), an ...important disease of pineapple, has been associated with at least three distinct viruses, Pineapple mealybug wilt associated virus -1, -2, and -3 (PMWaV-1, -2, and -3). Selected open reading frames (ORFs) of PMWaV-1 and PMWaV-2 were screened for their local and systemic suppressor activities in Agrobacterium-mediated transient assays using green fluorescent protein (GFP) in Nicotiana benthamiana. Results indicate that PMWaV-2 utilizes a multiple-component RNA silencing suppression mechanism. Two proteins, p20 and CP, target both local and systemic silencing in N. benthamiana, while the p22 and CPd proteins target only systemic silencing. In the related virus PMWaV-1, we found that only one of the encoded proteins, p61, had only systemic suppressor activity. Of all the proteins tested from both viruses, only the PMWaV-2 p20 protein suppressed local silencing induced by double-stranded RNA (dsRNA), but only when low levels of inducing dsRNA were used. None of the proteins analyzed could interfere with the short distance spread of silencing. We examined the mechanism of systemic suppression activity by investigating the effect of PMWaV-2-encoded p20 and CP proteins on secondary siRNAs. Our results suggest that the PMWaV-2 p20 and CP proteins block the systemic silencing signal by repressing production of secondary siRNAs. We also demonstrate that the PMWaV-2 p20 and p22 proteins enhanced the pathogenicity of Potato virus X in N. benthamiana.
Mealybug wilt of pineapple (MWP) is a disease of pineapple that has a long history in Hawaii, but is present throughout the world where pineapples are grown in tropical regions. The disease has an ...interesting etiology that is poorly understood but involves an association with virus particles, mealybug vectors, and ants which spread the mealybug vectors. Several distinct pineapple mealybug wilt-associated virus (PMWaV) species have been identified thus far with potential further member species yet to be characterized. Pineapple mealybug wilt-associated viruses are member species of the Ampelovirus genus of the Closteroviridae family. Ampeloviruses are split into two subgroups, subgroup I and subgroup II. PMWaV-2 is a subgroup II member, and these have a longer and more complex genome with additional genes on the 3’ terminus of the RNA genome compared to subgroup I ampeloviruses. PMWaV-2, along with the presence of mealybug vectors, have been shown to be necessary factors in symptom development in Hawaii. Some of these extra genes in the 3’ of PMWaV-2 have recently been shown to function as silencing suppressors, and may play a role in the virulence of PMWaV-2 and symptom development. In other regions of the world, reports of symptomatic plants without PMWaV-2 infection, but with PMWaV-1, -3 or some combination, contradict the requirement of PMWaV-2 for symptom development in MWP. It is possible that further, uncharacterized PMWaVs may be present in symptomatic pineapple plants that test negative for PMWaV-2, explaining the inconsistency in symptom development. More research is necessary to explore the confusing etiology of the MWP disease, and to perhaps shed light upon the symptom development.
Banana bract mosaic virus (BBrMV) has never been reported in banana plants in Hawaii. In 2010, however, it was detected in a new host, flowering ginger (
Alpinia purpurata
). In this study, we ...characterize the
A. purpurata
isolate and study its spread in flowering ginger in Hawaii. A laboratory study demonstrated that BBrMV could be transmitted from flowering ginger to its natural host, banana, therefore raising a serious concern about the potential risk to the rapidly growing banana industry of Hawaii. To quickly monitor this virus in the field, we developed a robust immunocapture reverse transcription loop-mediated isothermal amplification (IC-RT-LAMP) assay. Deep sequencing of the BBrMV isolate from
A. purpurata
revealed a single-stranded RNA virus with a genome of 9,713 nt potentially encoding a polyprotein of 3,124 aa, and another predicted protein, PIPO, in the +2 reading-frame shift. Most of the functional motifs in the Hawaiian isolate were conserved among the genomes of isolates from one found in the Philippines and India. However, the
A. purpurata
isolate had an amino acid deletion in the Pl protein that was most similar to the Philippine isolate. Phylogenetic analysis of an eastern Pacific subpopulation that included
A. purpurata
was closest in genetic distance to a Southeast Asian subpopulation, suggesting frequent gene flow and supporting the hypothesis that the
A. purpurata
isolate arrived in Hawaii from Southeast Asia.
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