1816 research outputs found
Sort by
Bacterial Endosymbionts Identified From Leafhopper (Hemiptera: Cicadellidae) Vectors of Phytoplasmas
Full text linkInsects often harbor bacterial endosymbionts that provide them with nutritional benefit or with protection against natural enemies, plant defenses, insecticides, and abiotic stresses. Certain endosymbionts may also alter acquisition and transmission of plant pathogens by insect vectors. We identified bacterial endosymbionts from four leafhopper vectors (Hemiptera: Cicadellidae) of ‘Candidatus Phytoplasma’ species by direct sequencing 16S rDNA and confirmed endosymbiont presence and identity by species specific conventional PCR. We examined three vectors of Ca. Phytoplasma pruni, causal agent of cherry X-disease [Colladonus geminatus (Van Duzee), Colladonus montanus reductus (Van Duzee), Euscelidius
variegatus (Kirschbaum)] – and a vector of Ca. Phytoplasma trifolii, the causal agent of potato purple top disease [Circulifer tenellus (Baker)]. Direct sequencing of 16S identified the two obligate endosymbionts of leafhoppers, ‘Ca. Sulcia’ and ‘Ca. Nasuia’, which are known to produce essential amino acids lacking in the leafhoppers’ phloem sap diet. About 57% of C. geminatus also harbored endosymbiotic Rickettsia. We identified ‘Ca. Yamatotoia cicadellidicola’ in Euscelidius variegatus, providing just the second host record for this endosymbiont. Circulifer tenellus harbored the facultative endosymbiont Wolbachia, although the average infection rate was only 13% and all males were Wolbachia-uninfected. A significantly greater percentage of Wolbachia-infected Ci. tenellus adults than uninfected adults carried Ca. P. trifolii, suggesting that Wolbachia may increase this insect’s ability to tolerate or acquire this pathogen. Results of our study provide a foundation for continued work on interactions between leafhoppers, bacterial endosymbionts, and
phytoplasma
USDA-ARS Plant Introduction lines evaluated for rhizomania and storage rot resistance in Idaho, 2022
Full text linkThirty sugar beet (Beta vulgaris L.) USDA-ARS Plant Introduction (PI) lines and five check cultivars were screened for resistance to Beet necrotic yellow vein virus (BNYVV), the causal agent of rhizomania, and to storage rot. The rhizomania evaluation was conducted at the USDA-ARS North Farm in Kimberly, ID which has Portneuf silt loam soil and had been in barley in 2021. In the spring the field was plowed and fertilized (110 lb N and 160 lb P2O5/A) and roller harrowed on 6 Apr 22. The germplasm was planted (density of 114,048 seeds/A) on 3 May. The plots were one row 10-ft long with 22-in. between-row spacing and arranged in a randomized complete block design with 6 replicates. The crop was managed according to standard cultural practices for southern Idaho. The trial relied on endemic field inoculum for rhizomania and storage rot development. The plots were rated for rhizomania foliar symptom (percentage of plants with yellow, stunted, upright leaves) development on 15 Aug. The plants were mechanically topped and hand harvested on 11-12 Oct. At harvest, ten roots per plot were rated for rhizomania symptom development using a scale of 0 to 9 (0 = healthy and 9 = dead; Plant Disease 93:632-638). At harvest, eight roots per plot were also placed in a mesh-onion bag and kept in an indoor commercial storage facility (temperature set point 34°F) in Paul, ID on 13 Oct. On 14 Mar 23, after 152 days in storage, the roots were evaluated for the percentage of root surface area covered by fungal growth or rot. Except for root ratings, data were analyzed in SAS (Ver. 9.4) using the general linear model (Proc GLM) procedure, and Fisher’s protected least significant difference (α = 0.05) was used for mean comparisons. The root ratings were analyzed in a nonparametric analysis as described by Shah and Madden (Phytopathology 94:33-43)
Beet curly top resistance in USDA-ARS Kimberly germplasm, 2022
Full text linkCurly top caused by Beet curly top virus (BCTV) is a widespread disease problem vectored by the beet leafhopper in semiarid sugar beet production areas. Host resistance is the primary defense against this problem, but resistance in commercial cultivars is only low to intermediate. In order to identify novel sources of curly top resistance, 8 sugar beet lines produced by the USDA-ARS Kimberly sugar beet program were screened in a disease nursery in 2022. The lines were arranged in a randomized complete block design with six replications. A curly top epiphytotic was created by releasing six viruliferous beet leafhoppers per plant at the four- to six-leaf growth stage on 15 Jun. Foliar symptoms were evaluated on 6 July using a scale of 0-9 (0 = healthy and 9 = dead). Curly top symptom development was uniform and no other disease problems were evident in the plot area. The disease pressure in the test was moderately severe with good symptom development in the susceptible checks. Based on the visual rating, five of the entries contain at least some minor resistance since their ratings were lower than the susceptible checks. However, only three entries (KDH13, KDH-39/KDH13, and KDH4-9) were not significantly different from the resistant check. These three entries and the two others with minor resistance will be retested and investigated further for potential release to the general public so they can be utilized to improve BCTV resistance in commercial sugar beet cultivars
Bacterial endosymbionts identified from leafhopper (Hemiptera: Cicadellidae) vectors of phytoplasmas
Full text linkInsects often harbor bacterial endosymbionts that provide them with nutritional benefit or with protection against natural enemies, plant defenses, insecticides, and abiotic stresses. Certain endosymbionts may also alter acquisition and transmission of plant pathogens by insect vectors. We identified bacterial endosymbionts from four leafhopper vectors (Hemiptera: Cicadellidae) of ‘Candidatus Phytoplasma’ species by direct sequencing 16S rDNA and confirmed endosymbiont presence and identity by species-specific conventional PCR. We examined three vectors of Ca. Phytoplasma pruni, causal agent of cherry X-disease [Colladonus geminatus (Van Duzee), Colladonus montanus reductus (Van Duzee), Euscelidius variegatus (Kirschbaum)] – and a vector of Ca. Phytoplasma trifolii, the causal agent of potato purple top disease [Circulifer tenellus (Baker)]. Direct sequencing of 16S identified the two obligate endosymbionts of leafhoppers, ‘Ca. Sulcia’ and ‘Ca. Nasuia’, which are known to produce essential amino acids lacking in the leafhoppers’ phloem sap diet. About 57% of C. geminatus also harbored endosymbiotic Rickettsia. We identified ‘Ca. Yamatotoia cicadellidicola’ in Euscelidius variegatus, providing just the second host record for this endosymbiont. Circulifer tenellus harbored the facultative endosymbiont Wolbachia, although the average infection rate was only 13% and all males were Wolbachia-uninfected. A significantly greater percentage of Wolbachia-infected Ci. tenellus adults than uninfected adults carried Ca. P. trifolii, suggesting that Wolbachia may increase this insect’s ability to tolerate or acquire this pathogen. Results of our study provide a foundation for continued work on interactions between leafhoppers, bacterial endosymbionts, and phytoplasma
Experimental sugar beet cultivars evaluated for rhizomania resistance and storability in Idaho, 2021
Full text linkRhizomania caused by Beet necrotic yellow vein virus (BNYVV) and storage losses are serious sugar beet production problems. To identify sugar beet cultivars with resistance to BNYVV and evaluate storability, 9 experimental cultivars were screened by growing them in a sugar beet field infested with BNYVV in Kimberly, Idaho during the 2021 growing season in a randomized complete block design with 6 replications. At harvest on 4-5 October 2021, roots were dug and evaluated for symptoms of rhizomania and also placed in an indoor commercial sugar beet storage building. After 132 days in storage, samples were evaluated for surface rot, weight loss, and sucrose loss. Surface root rot ranged from 14 to 53%, weight loss ranged from 15 to 23%, sucrose losses ranged from 34 to 68%, and estimated recoverable sucrose ranged from 766 to 7,974 lb/A. Given these response ranges, selecting cultivars for rhizomania resistance and combining this resistance with storability will lead to considerable economic benefit for the sugar beet industry
Fargo sugar beet germplasm evaluated for Rhizoctonia crown and root rot resistance in Idaho, 2022
Full text linkRhizoctonia crown and root rot (RCRR) is a serious fungal root disease problem for sugar beets worldwide that is caused by Rhizoctonia solani. In-furrow chemical treatments and host resistance are the primary control measures for RCRR. However, resistance is controlled by a number of genes (quantitative trait) which makes it challenging and time consuming to introgress resistance into commercial hybrids. In order to identify additional sources of resistance, 40 lines from the USDA-ARS Fargo sugar beet program were evaluated along with two check cultivars for resistance to RCRR. The lines were arranged in a randomized complete block design with 6 replicates. The trial was inoculated at the ten-leaf growth stage with 0.02 oz of dried barley inoculum per plant on the 30 June. The roots were evaluated for root rot on 2 August. The rhizoctonia susceptible check had 76% of its root area covered in rot and 5% of its roots were harvestable. On the other hand, the resistant check had only 30% rot and 64% of its roots were harvestable. Lines 17N0043-12 and 17N0043-16 had a level of rhizoctonia resistance similar to the resistant check based on the root rot, disease index, and harvestable roots. These lines will be retested and investigated further for potential release to the general public so they can be utilized to improve RCRR resistance in commercial sugar beet cultivars
Foliar insecticides for the control of curly top in Idaho sugar beet, 2022
Full text linkCurly top caused by Beet curly top virus (BCTV) is a widespread disease problem vectored by the beet leafhopper in semiarid sugar beet production areas. Host resistance is the primary defense against this problem, but resistance in commercial cultivars is only low to intermediate. The neonicotionoid seed treatments currently supplement this resistance to provide early season control. In order to identify other management options seven foliar insecticides were screened in 2022 on a commercial sugar beet cultivar approved for production. The plots were arranged in a randomized complete block design with eight replications. A curly top epiphytotic was created by releasing six viruliferous beet leafhoppers per plant at the eight-leaf growth stage on 15 June. Foliar symptoms were evaluated on 20 July and 15 August using a scale of 0-9 (0 = healthy and 9 = dead). Curly top symptom development was uniform and no other disease problems were evident in the plot area. The disease pressure in the test was severe with good symptom development in the non-treated check. The Poncho Beta seed treatment provided better control than all other treatments based on curly top ratings, root yield, and estimated recoverable sucrose (ERS). The Actara, Asana, Transform, and Violacein treatments all reduced curly top ratings compared to the non-treated check, but the control was not adequate to avoid serious reductions in root yield and ERS. These data show that sugar beet production in areas with curly top would suffer greatly without the neonicotinoid seed treatments and supplemental foliar treatments. Additional evaluations will need to be conducted with other insecticides if alternatives to the neonicotinoid (Poncho Beta) chemical class are to be identified for curly top control
A robust SNP-haplotype assay for Bct gene region conferring resistance to beet curly top virus in common bean (Phaseolus vulgaris L.)
Full text linkBeet curly top virus (BCTV), which is synonymous with curly top virus (CTV),
causes significant yield loss in common bean (snap and dry beans) cultivars and
several other important crops. Common bean cultivars have been found to be
resistant to CTV, but screening for resistance is challenging due to the cyclical
nature of epidemics and spotty feeding by the leafhopper that vectors the virus.
We used an SNP dataset for the Snap Bean Association Panel (SnAP) agroinoculated
with CTV-Logan (CA/Logan) strain to locate the Bct gene region to a
1.7-Mb interval on chromosome Pv07 using genome-wide association study
(GWAS) analysis. Recombinant lines from the SnAP were used to further narrow
the Bct region to a 58.0-kb interval. A missense SNP (S07_2970381) in candidate
gene Phvul.007G036300 Exonuclease V (EXO5) was identified as the most likely
causal mutation, and it was the most significant SNP detected by GWAS in a dry
bean population (DBP) naturally infected by the CTV-Worland (Wor) strain. Tmshift
assay markers developed for SNP S07_2970381 and two linked SNPs,
S07_2970276 and S07_2966197, were useful for tracking different origins of
the Bct EXO5 candidate gene resistance to CTV in common bean. The three
SNPs identified four haplotypes, with haplotype 3-1 (Haplo3-1) of Middle
American origin associated with the highest levels of CTV resistance. This SNPhaplotype
assay will enable breeders to track resistance sources and to develop
cultivars with better CTV resistance
Microbial responses to biochar soil amendment: A three-level meta-analysis
Full text linkBiochar is a multifunctional soil conditioner capable of enhancing soil health and crop production while reducing greenhouse gas emissions. Understanding how soil microbes respond to biochar amendment is a vital step towards precision biochar application. Here, we synthesized 3899 observations of 24 microbial responses from 61 primary studies, applied a three-level mixed-effects model to estimate biochar effects, and evaluated the importance of biochar characteristics (feedstock, pyrolysis temperature), soil properties (pH, C:N, cation exchange capacity, bulk or rhizosphere), and treatment protocols (application rate, fertilization, duration, field or laboratory). Biochar significantly boosts microbial abundance (microbial biomass carbon > CFU), nitrite reductase gene (nirS), the activity of C- and N-cycling enzymes (dehydrogenase > cellulase > urease > invertase), and potential nitrification rate. Biochar characteristics, soil properties, and treatment protocols strongly determine the direction and extent of microbial response changes. Feedstock, pyrolysis temperature, application rate, and soil pH are important predictors most frequently included in the final models. Our study highlights the promise of purpose-driven biochar production and application such that biochar production parameters can be tuned to elicit the desired microbial responses and application protocols could be optimized to invoke multiple benefits. It also underlines current knowledge gaps and future research needs
Modification of the RZWQM2-P model to simulate labile and total phosphorus in an irrigated and manure amended cropland soil
Full text linkWith the expansion of the dairy industry, phosphorus (P)-enriched dairy manure has increasingly been used to replace chemical fertilizer to meet crop nutrient demand. This practice could lead to excessive total P accumulation in the soil and increase the risk of P pollution in the environment. The newly-developed RZWQM2-P model uses the soil P pool structure from the EPIC model, which is not sensitive to total soil P. Therefore, we modified the P module in RZWQM2-P to increase its sensitivity to total soil P. We subsequently assessed the ability of the modified model to simulate labile soil P, total soil P, plant P uptake, and crop yield using a dataset collected from an irrigated field treated with dairy manure and inorganic fertilizer at eight rates. We simulated the long-term soil P dynamics under three P-application scenarios. The results suggested that the modified RZWQM2-P model simulated field-measured annual total soil P, plant P uptake, and crop yield well. Labile soil P was simulated less accurately, but the results were acceptable as the model responded well to P treatments. Long-term simulation results showed that it took 14 years for the labile soil P level to return to the initial level after eight years of manure-P applications at a rate of 65.5 kg P/ha/year. The modified RZWQM2-P model can be used to simulate total soil P and labile soil P contents and to assess P management practices in irrigated cropland amended with manure