Amino acid, sugar, phenolic, and terpenoid profiles are capable of distinguishing Citrus tristeza virus infection status in citrus cultivars: Grapefruit, lemon, mandarin, and sweet orange

Complex interplay: The interactions between citrus tristeza virus and its host

Citrus tristeza virus (CTV) is one of the largest and most economically important RNA viruses infecting plants. CTV's interactions with various citrus hosts can result in three diseases: quick decline, stem pitting, or seedling yellows. Studying CTV poses several challenges owing to its significant genetic diversity and the highly specific occurrence of disease symptoms when different genotypes infect different citrus hosts. Considerable progress has been made to functionally characterize the virus-host interactions involved in the induction of CTV's three diseases, revealing that the four CTV ORFs (p33, p18, p13 and p23) play significant roles in determining the pathogenicity of CTV infections. These ORFs are unique to CTV and are not conserved among other members of the family Closteroviridae. This minireview aims to capture the complexity of the factors that have been shown to be involved in CTV disease induction and highlights recent work that provides novel insights into this pathosystem.

Citrus Yellow Vein Clearing Virus Infection in Lemon Influences Host Preference of the Citrus Whitefly by Affecting the Host Metabolite Composition

Plant viruses have been known to alter host metabolites that influence the attraction of insect vectors. Our study investigated whether Citrus yellow vein clearing virus (CYVCV) infection influences vector attractiveness, focusing on the citrus whitefly, Dialeurodes citri (Ashmead). Free choice assays showed that citrus whiteflies exhibited a preference for settling on CYVCV-infected lemon plants versus healthy control plants. Using chromatography techniques, we found that the levels of sugars were similar in leaves and stems of both plant groups, while the contents of several amino acids in leaf or stem samples and non-volatile phenolic compounds in the leaf samples of CYVCV-infected and healthy plants differ drastically. In addition, volatile terpenes/terpenoids decreased significantly in virus-infected plants compared to healthy controls. Several of the identified volatile compounds such as α-phellandrene, α-terpinolene, p-cymene, linalool, and citral are known for their whitefly repellent properties. Further Y-tube olfactometer bioassays revealed that emissions of volatile organic compounds (VOCs) from infected plants attracted more citrus whiteflies, but not alate spirea aphids, Aphis spiraecola Patch, than those from healthy plants, suggesting that the VOCs released from CYVCV-infected lemon plants may specifically affect citrus whiteflies. Therefore, we suggest that, in addition to the visual cue of yellow vein symptoms, the preference of citrus whiteflies that settled on CYVCV-infected lemon plants was attributed to a reduction in the levels of repellent volatile compounds.

Applying infectious clones and untargeted metabolite profiling to characterize citrus tristeza virus-induced stem pitting in citrus

Citrus tristeza virus (CTV) causes economically important stem pitting in sensitive citrus types however the exact mechanisms of stem pitting development in citrus remain unclear. In this study, CTV infectious clones were used to study stem pitting induction in 'Duncan' grapefruit and 'Mexican' lime. A panel of open reading frame (ORF) replacement clones was generated focusing on the CTV ORFs implicated in stem pitting development and pathogenicity, namely p33, p18, p13 and p23. ORF replacements from severe- and mild-pitting CTV isolates were introduced into a mild-pitting infectious clone (genotype T36) to determine if stem pitting could be induced. A broad range of stem pitting outcomes were observed with ORF p18 (from isolate T3-KB) and ORF p23 (from isolate GFMS12-1.3) associated with enhanced stem pitting development. Metabolomic trends underlying the different stem pitting outcomes were further assessed by untargeted metabolite profiling. In each citrus host, the metabolite profiling identified statistically significant compounds that differed between stem pitting groups. These compounds were mainly phenolic acids and phenolic glycosides and are known to function as antioxidant and stress-signaling molecules. These metabolites can serve as targets for future time-course observations to potentially use mass spectrometry profiling to inform CTV management practices.

Pre-inoculation water deficit effects on grapevine physiology, Xylella fastidiosa titers, and Pierce's disease progression

Drought and Pierce's disease are common throughout many grapevine-growing regions such as Mexico and the United States. Yet, how ongoing water deficits affect infections of Xylella fastidiosa, the causal agent of Pierce's disease, is poorly understood. Symptoms were observed to be significantly more severe in water-stressed plants one month after X. fastidiosa inoculation, and, in one experiment, titers were significantly lower in water-stressed than well-watered grapevines. Host chemistry examinations revealed overall amino acid and phenolic levels did not statistically differ due to water deficits, but sugar levels were significantly greater in water stressed than well-watered plants. Results highlight the need to especially manage Pierce's disease spread in grapevines experiencing drought.

Effect of natural products use prior to infection with COVID-19 on disease severity and hospitalization: A self-reported cross-sectional survey study

Background: Managing coronavirus disease 2019 (COVID-19) using available resources is essential to reduce the health burden of disease. The severity of COVID-19 is affected by nutritional status. In this study the effect of natural product use prior to infection with COVID-19 on disease severity and hospitalization was explored.

Methods: This was a cross-sectional study. Between March and July 2021, a self-administered survey was conducted in Jordan. Individuals who recovered from COVID-19 and were ≥18 years old were the study population. Study measures included the use of natural products, COVID-19 severity, and hospitalization status. A multivariate regression model was used for statistical analysis.

Results: The mean age (mean ± SD) of the study sample (n=2,148) was 40.25 ± 15.58 years old. Multivariate logistic regression showed that the regular intake of carnation (OR [0.56], CI [0.37–0.85]), onion (OR [0.69], CI [0.52–0.92]), lemon (OR [0.68], CI [0.51–0.90]), and citrus fruits (OR [0.66], CI [0.50–0.89]) before infection were associated with a substantial reduction in COVID-19 severity (P<0.01). Also, the consumption of carnation (OR [0.55], CI [0.34–0.88]), lemon (OR [0.57], CI [0.42–0.78]), and citrus fruits (OR [0.61], CI [0.44–0.84]) were associated with a significant decrease in the frequency of COVID-19-induced hospitalization (P<0.01).

Conclusions: Regular consumption of carnation, lemon, and citrus fruits before infection was associated with better outcomes for COVID-19. Studies on other populations are required to confirm these findings.