Components of resistance of cassava to African cassava mosaic virus

Components of resistance of cassava (Manihot esculenta) to African cassava mosaic virus (ACMV) and their interrelationships were confirmed and quantified in a series of experiments at Adiopodoumé (Ivory Coast, West-Africa). The response to virus infection and toBemisia tabaci infestation of a large collection of cassava, including local cultivars and others derived from inter-specificM. glaziovii hybrids was assessed. A consistent correlation was found between virus titre, symptom intensity, disease incidence and non-systemicity (recovery) which suggests that they are different expressions of the same genetic resistance. By contrast, there was no correlation between whitefly infestation and incidence of ACMV, suggesting that resistance to virus and vector are determined by two distinct genetic mechanisms. Several improved cultivars derived from inter-crossing cassava withM. glaziovii as well as some local cultivars were highly resistant and combined low susceptibility, low symptom intensity, low virus content and high level of recovery. Although yield losses ranged from 10% to 30% in such resistant cultivars, the combined effect of high field resistance and high rate of recovery lead to low disease incidence and limited yield losses, even in areas of high infection pressure such as Adiopodoumé.     

Symptom severity of cassava mosaic disease in relation to concentration of African cassava mosaic virus in different cassava genotypes

The concentration of African cassava mosaic virus (ACMV) was assessed by enzyme-linked immunosorbent assay in relation to symptom severity among resistant, moderately resistant and susceptible cassava genotypes. Resistant genotype NR 8083 had significantly lower symptom severity scores ( P  < 0·05) than the susceptible genotype TMS 91934, but the two genotypes contained similar levels of virus concentration. The moderately resistant genotypes TMS 30572 and NR 8082 expressed significantly lower symptom severities ( P  < 0·05) than the susceptible genotypes TMS 91934 and TME 117, but they contained significantly higher virus concentrations ( P  < 0·05) than TMS 91934 and similar virus concentration as in TME 117. However, two other resistant genotypes, TME 1 and TME 8, had low symptom severity scores and virus concentrations. There was significant interaction ( P  ≤ 0·05) between cropping season and virus concentration in all the genotypes except TMS 30572. The resistant and moderately resistant genotypes that had high virus concentrations sustained storage root yield losses. The severity of symptoms expressed was not necessarily a reflection of the virus concentration in some of the genotypes. In addition to the use of symptom severity scores to group genotypes into resistant classes, it is recommended that virus concentration should also be considered. Genotypes displaying mild symptoms, but with high levels of virus accumulation, could be an important source of inoculum in the spread of ACMV by the whitefly vectors. This suggests that each genotype should be tested for virus accumulation prior to its release to the farmers.     

Cassava common mosaic virus infection causes alterations in chloroplast ultrastructure,function, and carbohydrate metabolism of cassava plants

Cassava common mosaic virus (CsCMV) is a potexvirus that causes systemic infections in cassava plants, leading to chlorotic mosaic and producing significant yield losses. To date, the physiological alterations and the mechanism underlying biotic stress during the cassava–CsCMV compatible interaction remains unknown. In this study, we found that CsCMV infection adversely modified chloroplast structure and had functional effects on chloroplasts in source leaves during the course of viral infection. Extrusion of the chloroplast membrane with amoeboid-shaped appearance and disorganized grana stacks were observed in infected mesophyll cells. These alterations were associated with up to 35% reduction of relative chlorophyll content, and a decline of CO₂ fixation (13.5% and 24.2% at 90 and 210 days after planting, respectively). The effects of CsCMV infection on the performance index on absorption basis dropped up to 37%. The analysis of chlorophyll a fluorescence showed a progressive loss of both oxygen evolving complex activity and “connectivity” within the tripartite system (core antenna-LHCII-reaction centre). Here, we report the latter phenomenon for the first time in a viral infection. The oxidative stress process was observed in CsCMV-infected plants (20.8% reduction of antioxidant capacity with respect to noninfected plants). Other effects of the pathogen included reduction of starch and maltose content in source leaves, and a significant increase (24.7%) of the sucrose:starch ratio, which indicates an altered pattern of carbon allocation. Our results suggest that CsCMV induces chloroplast distortion associated with progressive chloroplast function loss and diversion of carbon flux in source leaf tissue, leading to the loss of cassava tuber yield.     

Quercetin influences response in Nicotiana megalosiphon infected by satellite-associated cucumber mosaic virus

Journal of Plant Diseases and Protection - Quercetin is a prominent flavonoid with a remarkable spectrum of biochemical activities. Its impact on human health, as well as its role in the normal...     

The reaction of two lettuce cultivars to mixed infection by beet western yellows virus, lettuce mosaic virus and cucumber mosaic virus

The interaction of beet western yellows virus (BWYV), lettuce mosaic virus (LMV) and cucumber mosaic virus (CMV) has been studied in lettuce cultivars Little Gem and Saladin. LMV infection alone or in combination with BWYV and or CMV caused the most severe symptoms and yield losses in both cultivars. BWYV caused more severe reactions in Little Gem than in Saladin; the reactions caused by CMV were mild in both cultivars. The interaction between BWYV and CMV infection resulted in a significantly greater yield loss in both cultivars than that caused by BWYV or CMV infection alone.     

Genetic aspects of polyacrylic-acid-induced resistance to tobacco mosaic virus and tobacco necrosis virus in Nicotiana plants

Among the Nicotiana tabacum cultivars and hybrids tested, polyacrylic acid (PAA) only induced resistance to tobacco mosaic virus (TMV) and tobacco necrosis virus (TNV) in the cultivars Xanthi-nc (NN) and Xanthi (nn) respectively. This varietal response to the PAA treatment could be sexually transmitted. The complete genetic analysis of the inheritance of the PAA response is reported for the first time, demonstrating that the response is a dominant character with a Mendelian segregation which occurs independently of either the N gene responsible for resistance to TMV or the PRb-protein genes. Possible relationships between the N gene, the gene for the PAA response and the PRb genes are discussed.     

Elucidation of turnip yellows virus (TuYV) spectral reflectance pattern in Nicotiana benthamiana by non-imaging sensor technology

Journal of Plant Diseases and Protection - Turnip yellows virus (TuYV), belonging to the genus Polerovirus of the family Solemoviridae, is an aphid transmissible, pathogenic virus causing...     

芜菁花叶病毒对寄主植物叶片PSⅡ功能的影响

 芜菁花叶病毒(Turnip mosaic virus,TuMV)是十字花科蔬菜作物上最重要的病原病毒之一,TuMV在青菜、榨菜、芥菜、油菜等作物上的主要发病症状为花叶和畸形,研究植物病毒致花叶症状的机理有助于建立新的病毒控制理论。     

Exogenous salicylic acid treatment delays initial infection and counteracts alterations induced by Maize dwarf mosaic virus in the maize proteome

The phytohormone salicylic acid (SA) was applied to healthy and Maize dwarf mosaic virus (MDMV)-infected maize plants, and differential proteomic analysis was simultaneously performed to evaluate the physiological effects and the SA-maize-virus interaction in the early pathogenesis cycle. MDMV infection reduced photosynthetic rates, while SA increased them, together with plant height and roots in healthy plants. In infected plants, SA increased RuBisCo and stabilized chlorophyll a-b binding protein expression, increased plant height and root volume, delayed symptom expression, and reduced infection rate. Results highlight biochemical pathways involved in the maize-MDMV pathosystem and signal SA as key to maize disease management programs.     

Cassava common mosaic virus infection affects growth and yield components of cassava plants (Manihot esculenta) in Argentina

Cassava is an important crop with great economic and social significance in many countries. Most of its biomass is usable: storage roots can be destined for industry or fresh consumption, leaves are a source of protein, vitamins, and minerals, and stems can be used as propagation material. Due to its vegetative propagation, cassava yield is greatly constrained by viral diseases. Cassava common mosaic virus (CsCMV), one of the most widely spread viruses in Latin America, is the only cassava-infecting potexvirus able to cause disease in a single infection: cassava common mosaic disease (CCMD). Here, we evaluated the effect of an Argentinian strain of CsCMV on several agronomic traits. Field trials were established in north-eastern Argentina for three successive cropping seasons, 2016/17, 2017/18, and 2018/19. CsCMV presence was confirmed by PCR or ELISA tests in mechanically inoculated cassava plants. The evaluated traits were plant height (PH), total fresh weight (TFW), shoot fresh weight (SFW), diameter and FW of tuberous root per plant (TRD and FWTR), FW of each individual tuberous root (FWiTR), length and number of tuberous roots (TRL and TRN), harvest index (HI), and estimated yield of tuberous root (EY) in both infected and noninfected plants. Significant yield losses were recorded in infected plants. The most affected traits were EY and FWTR (both showing 44.3% of losses), followed by TFW, SFW, TRN, and FWiTR (37.8%, 33.5%, 29.9%, and 24.8% of losses, respectively). These losses are extremely high for Argentina, where this crop provides food security and demand for the raw material is unsatisfied.     

Inverse correlation between mRNA levels in GFP-silenced transgenic Nicotiana benthamiana and resistance to Potato virus X engineered to contain GFP sequence

Nicotiana benthamiana was transformed with a green fluorescent protein (GFP) gene driven by cauliflower mosaic virus 35S promoter. A GFP-silenced line and a nonsilenced line were selected after ultraviolet irradiation. GFP short-interfering RNAs (siRNAs) were detected in the silenced line but not in the nonsilenced line. T₁ progeny of the silenced line varied in GFP suppression patterns and were grouped into three types (I, II, III) based on the GFP suppression pattern. With Northern blot analysis, different levels of GFP mRNA accumulated, from a very low level in type I and II to an intermediate level in type III, in contrast to a much higher level in the nonsilenced line. Plants were also inoculated with Potato virus X engineered to contain the GFP sequence to evaluate the levels of virus resistance. None to a few GFP spots were observed on inoculated leaves in types I and II, whereas numerous spots and systemic infection appeared in type III. These results showed that virus resistance was inversely correlated with the levels of mRNA, suggesting that the strength of RNA silencing determines the extent of virus resistance.