Evaluating Responses of Sugar Beet Cultivars to Fusarium Species in Greenhouse and Field Conditions

Fusarium yellows of sugar beet (Beta vulgaris L.) is becoming an important disease in Minnesota and North Dakota in the United States. One of the best ways to manage Fusarium yellows is to develop and use resistant cultivars. Responses of eight sugar beet cultivars to three Fusarium species were determined in the greenhouse and compared to the responses of the same eight cultivars grown in a field already infected by Fusarium yellows. There were significant and appreciable relationships between greenhouse and field studies for responses of eight sugar beet cultivars on Fusarium yellows. The estimated correlation coefficient for area under disease progress curve (AUDPC) between observations in fields and those in greenhouses was 0.987 (p<0.01). The mean AUDPC were significantly different among cultivars (p<0.01) in the greenhouse and in the field studies. Of the cultivars, Van der Have 46177 was the most susceptible, but Crystal R434 the most resistant. Crystal 820, Van der Have 66561, and Beta 4797R were resistant, and Beta 4818R, Seedex Magnum, and Hilleshog 2463Rz were moderately resistant. There was a strong negative relationship between the AUDPC and recoverable sucrose yield in the field experiments and the estimated coefficient of determination was 0.939 (p<0.01). It was concluded that greenhouse screening can act as a useful and reliable means to evaluate and select beet germplasms and/or accessions for resistance to Fusarium yellows.Peer reviewe

The Influence of Reflective Mulches and Lettuce Types on the Incidence of Aster Yellows and Abundance of its Vector, \u3ci\u3eMacrosteles Fascifrons\u3c/i\u3e (Homoptera: Cicadelidae), in Minnesota

Five commercial lettuce cultivars representing different genetic types were grown through aluminum-coated paper, through black polyethylene film, and on bare soil. For each variety, the aluminum mulch reduced the numbers of Macrosteles fascifrons (St~l), reduced the incidence of aster yellows, and increased yields when compared to uncovered controls. The head lettuce cultivar \u27Minetto\u27 was most susceptible on unmulched plots (74.3%) while the leaf cultivar \u27Grand Rapids\u27 was least susceptible (33.8%). The latter also had the greatest infestation of leafhoppers which may indicate either resistance to the aster yellows agent or shorter feeding times by the vector leafhopper. The abundance of aster leafhoppers on the romaine cultivar \u27Valmaine\u27, the butter head cultivar \u27Buttercrunch\u27, and the bibb cultivar \u27Summer Bibb\u27 was much lower than that of the other two and might explain the lower percentage of aster yellows on these types as compared with \u27Minetto\u27

Grape-vine Yellows - Aetiology, Epidemiology and Diagnosis

Grape-vine Yellows comprise diseases with the same symptoms as Flavescence Doree (FD), a disease severe in Southern France and Italy, and caused by a procaryote. Other members include Bois Noir, Goldgelbe Vergilbung, and Australian Grape-vine Yellows. Yellows diseases have been observed in Europe, Australia, Israel, U.S.A. and Chile. Symptoms include yellow leaves which curl downward, and fall prematurely. Shoots are stunted and remain unlignified, and bunches shrivel and fall at flowering. Baco 22A, Jurancon blanc, Riesling and Chardonnay, are among the most susceptible cultivars. Scaphoideus titanus, the lealbopper vector of FD, is controlled by insecticides and loss from FD is now minimal. The other yellows diseases are of lesser importance and their aetiology is unresolved. Further investigation is needed to clarify the taxonomy of Grape-vine Yellows but the current diagnosis of yellows diseases of grape-vine is dependent on symptoms and at least one of several other features

Use of Aluminum-Foil and Oat-Straw Mulches for Controlling Aster Leafhopper, \u3ci\u3eMacrosteles Fascifrons\u3c/i\u3e (Homoptera: Cicadellidae), and Aster Yellows in Carrots.

Aluminum-foil and oat-straw mulches significantly (P \u3c 0.05) reduced aster leafhopper numbers on carrots compared to an untreated control and a malathion spray treatment during the first half of the growing season. The amount of reflected light was significantly higher in both aluminum-foil and oat-straw mulched plots compared to unmulched treatments. Mulch effectiveness decreased when the closing carrot canopy reduced surface area of reflective mulches and amount of reflected light The percentage of aster yellows-infected plants was significantly lower (P \u3c 0.05) in aluminum-foil and straw mulches and in the malathion spray plots compared to the untreated control. Results demonstrated that aluminum-foil and straw mulches gave control of aster leafhoppers and aster yellows in carrots equal to that of a conventional insecticide spray program

Development of a minigenome cassette for Lettuce necrotic yellows virus: A first step in rescuing a plant cytorhabdovirus

Rhabdoviruses are enveloped negative-sense RNA viruses that have numerous biotechnological applications. However, recovering plant rhabdoviruses from cDNA remains difficult due to technical difficulties such as the need for concurrent in planta expression of the viral genome together with the viral nucleoprotein (N), phosphoprotein (P) and RNA-dependent RNA polymerase (L) and viral genome instability in E. coli. Here, we developed a negative-sense minigenome cassette for Lettuce necrotic yellows virus (LNYV). We introduced introns into the unstable viral ORF and employed Agrobacterium tumefaciens to co-infiltrate Nicotiana with the genes for the N, P, and L proteins together with the minigenome cassette. The minigenome cassette included the Discosoma sp. red fluorescent protein gene (DsRed) cloned in the negative-sense between the viral trailer and leader sequences which were placed between hammerhead and hepatitis delta ribozymes. In planta DsRed expression was demonstrated by western blotting while the appropriate splicing of introduced introns was confirmed by sequencing of RT-PCR product

A Semipersistent Plant Virus Differentially Manipulates Feeding Behaviors of Different Sexes and Biotypes of Its Whitefly Vector.

It is known that plant viruses can change the performance of their vectors. However, there have been no reports on whether or how a semipersistent plant virus manipulates the feeding behaviors of its whitefly vectors. Cucurbit chlorotic yellows virus (CCYV) (genus Crinivirus, family Closteroviridae) is an emergent plant virus in many Asian countries and is transmitted specifically by B and Q biotypes of tobacco whitefly, Bemisia tabaci (Gennadius), in a semipersistent manner. In the present study, we used electrical penetration graph (EPG) technique to investigate the effect of CCYV on the feeding behaviors of B. tabaci. The results showed that CCYV altered feeding behaviors of both biotypes and sexes of B. tabaci with different degrees. CCYV had stronger effects on feeding behaviors of Q biotype than those of B biotype, by increasing duration of phloem salivation and sap ingestion, and could differentially manipulate feeding behaviors of males and females in both biotype whiteflies, with more phloem ingestion in Q biotype males and more non-phloem probing in B biotype males than their respective females. With regard to feeding behaviors related to virus transmission, these results indicated that, when carrying CCYV, B. tabaci Q biotype plays more roles than B biotype, and males make greater contribution than females

Efficient Protein Expression and Virus-Induced Gene Silencing in Plants Using a Crinivirus-Derived Vector.

Plant virus-based vectors are valuable tools for recombinant gene expression and functional genomics for both basic and applied research. In this study, Lettuce infectious yellows virus (LIYV) of the genus Crinivirus was engineered into a virus vector that is applicable for efficient protein expression and virus-induced gene silencing (VIGS) in plants. We examined gene replacement and “add a gene” strategies to develop LIYV-derived vectors for transient expression of the green fluorescent protein (GFP) reporter in Nicotiana benthamiana plants. The latter yielded higher GFP expression and was further examined by testing the effects of heterologous controller elements (CEs). A series of five vector constructs with progressively extended LIYV CP sgRNA CEs were tested, the longest CE gave the highest GFP expression but lower virus accumulation. The whitefly transmissibility of the optimized vector construct to other host plants, and the capability to accommodate and express a larger gene, a 1.8 kb β-glucuronidase (GUS) gene, were confirmed. Furthermore, the LIYV vector was also validated VIGS by silencing the endogenous gene, phytoene desaturase (PDS) in N. benthamiana plants, and the transgene GFP in N. benthamiana line 16c plants. Therefore, LIYV-derived vectors could provide a technical reference for developing vectors of other economically important criniviruses

Phytoplasmas associated with grapevine yellows in Virginia belong to group 16SrI, subgroup A (tomato big bud phytoplasma subgroup), and group 16SrIII, new subgroup I

Grapevine yellows disease in Virginia closely resembles flavescence doree and other grapevine yellows diseases, but the phytoplasmas infecting grapevines in Virginia are distinct from other grapevine yellows pathogens. RFLP analysis of PCR-amplified 16S rDNA indicated that a Virginia grapevine yellows phytoplasma, designated VGYIII was distinct from all other phytoplasmas studied, but was most closely related to spirea stunt (SP1), walnut witches' broom (WWB), and poinsettia branch-inducing (PoiB 1) phytoplasmas in subgroups E, G, and H, respectively, of 16S I RNA group 16SrIII. RFLP analysis also indicated the existence of sequence heterogeneity between the two rRNA operons in the genomes of SP 1 and WWB. Based on the results from RFLP and sequence comparisons with other group 16SrIII phytoplasmas, the VGYIII phytoplasma was classified in a new subgroup, designated 16SrIII-I. A second phytoplasma (VGYI) was detected in cultivated grapevines(Vitis vinifera L.) and in wild grapevines(V. riparia Michx.) and identified as a member of subgroup 16SrI-A. There was no evidence of flavescence doree, bois noir, or Australian grapevine yellows phytoplasmas in Virginia