Evolution of Plant RNA Viruses and Mechanisms in Overcoming Plant Resistance

Plant RNA viruses are one of the most destructive pathogens that cause a significant loss in crop production worldwide. They have evolved with high genetic diversity and adaptability due to the short replication cycle and high mutation rate during genome replication, which are characteristics of RNA viruses. Plant RNA viruses exist as quasispecies with high genetic diversity; thereby, a rapid population transition with new fitness can occur due to selective pressure resulting from environmental changes. Plant resistance can act as selective pressure and affect the fitness of the virus, which may lead to the emergence of resistance-breaking variants. In this paper, we introduced the evolutionary perspectives of plant RNA viruses and the driving forces in their evolution. Based on this, we discussed the mechanism of the emergence of variant viruses that overcome plant resistance. In addition, strategies for deploying plant resistance to viral diseases and improving resistance durability were discussed.

​Screening of Pigeonpea Varieties through Nylon Bag No-choice Bioassay for Host Plant Resistance to Helicoverpa armigera

Background: The legume pod borer, Helicoverpa armigera (Hübner), is one of the most damaging crop pests, including pigeonpea. Host plant resistance is a component of pest management and therefore, we standardize a nylon bag No-Choice Bioassay technique to screen for resistance to H. armigera under field conditions. Methods: Pigeonpea plants were infested with 24 h old 1, 2, 3, 4 and 5 larvae per plant inside the nylon bag. Observations were recorded on pod damage, larval survival, larval weight, pupation, adult emergence, and fecundity after 10 days. Result: Pigeonpea varieties AL-201, H03-41 and PAU-881 exhibited lower pod damage (15.89 to 19.77%) and larval weight (12.02 to 13.82 mg). The expression of resistance to H. armigera was associated with trichome density, pod wall thickness and higher amount of phenolic compounds and condensed tannins. Lower trichome density and thin pod walls and higher amounts of sugars rendered the varieties Paras, Manak and Pussa-992 more susceptible to H. armigera. Nylon bag assay can be used to screen and select pigeonpea cultivars for resistance to H. armigera.

Resistance and Not Plant Fruit Traits Determine Root-Associated Bacterial Community Composition along a Domestication Gradient in Tomato

Soil bacterial communities are involved in multiple ecosystem services, key in determining plant productivity. Crop domestication and intensive agricultural practices often disrupt species interactions with unknown consequences for rhizosphere microbiomes. This study evaluates whether variation in plant traits along a domestication gradient determines the composition of root-associated bacterial communities; and whether these changes are related to targeted plant traits (e.g., fruit traits) or are side effects of less-often-targeted traits (e.g., resistance) during crop breeding. For this purpose, 18 tomato varieties (wild and modern species) differing in fruit and resistance traits were grown in a field experiment, and their root-associated bacterial communities were characterised. Root-associated bacterial community composition was influenced by plant resistance traits and genotype relatedness. When only considering domesticated tomatoes, the effect of resistance on bacterial OTU composition increases, while the effect due to phylogenetic relatedness decreases. Furthermore, bacterial diversity positively correlated with plant resistance traits. These results suggest that resistance traits not selected during domestication are related to the capacity of tomato varieties to associate with different bacterial groups. Taken together, these results evidence the relationship between plant traits and bacterial communities, pointing out the potential of breeding to affect plant microbiomes.

Functional Genomics and Comparative Lineage-Specific Region Analyses Reveal Novel Insights into Race Divergence in Verticillium dahliae

Deciphering the gene-for-gene relationships during host-pathogen interactions is the basis of modern plant resistance breeding. In the Verticillium dahliae -tomato pathosystem, two races (races 1 and 2) and their corresponding avirulence ( Avr ) genes have been identified, but strains that lacked these two Avr genes exist in nature.

Optimal levels of water and salt in the growth of giant sweet clone cactus forage

Forage cactus is perennial growth plant, resistance to drought adaptation to hot climate regions, being considered important for the development of livestock. In this study objective was estimate the morphometrics measures of forage cactus Giant Sweet clone associate the optimal levels water and salt. Design used was completely randomized, composed of four levels of water replacement, using the crop evapotranspiration (25, 50, 75 and 100%.Etc) and four levels of salinity (0, 2, 4 and 8 dS/m), obtained through the concentrations of (NaCl) salts corresponding to 0, 1.16, 2.32 and 4.64 g/L, respectively. The morphometric measures of cladodes were evaluated 20 times during the experimental period. Response surface was used to estimate the optimal levels water and salt that maximizing the morphometric measures of the cladodes. Water level in range of 54% and 64%, and 3.5 to 5.3 dS/m of saline level promote greater development of the Giant Sweet clone without changing the morphological characteristics of plant, generating greater phytomass yield.

Phytopathological and nutraceutical evaluation of cauliflower plants treated with high dilutions of arsenic trioxide

Introduction: This research aimed at verifying the effects of highly diluted (HD) treatments on cauliflower (Brassica oleracea L.) plants both healthy and inoculated by the fungus Alternaria brassicicola, causing the dark leaf spot disease. In vitro spore germination assays (A), growth chamber experiments (B) and field trials (C) were performed. Material and Methods: (A): spore suspensions were prepared in HD treatments and their inhibiting effect on germination was recorded microscopically after incubation at 25°C for 5 h. (B): the same treatments were tested in plants artificially inoculated with the fungus. The infection level on leaves was blindly evaluated by a previously defined infection scale. (C): the field was divided into plots according to a complete randomized block design. In the first trial (i), plants were artificially inoculated and weekly treated; the infection level was evaluated on cauliflower heads. The second trial (ii) was performed on the same field with the aim to induce a natural infection, mediated by infected crop residues. Measurement endpoints concerned the evaluation of some physiological parameters along with the glucosinolate content on cauliflower heads. Results: (A): arsenic trioxide (As 35x and 35x diluted 1:5000) and Cuprum 5x induced highly significant inhibition of germination rate (-60%) vs. control. (B): As 35x and Cu 3 g/l induced a significant decrease of mean infection level (-50%). (C): in (i), a significant reduction of disease symptoms on heads was recorded for As 35x and Cu 3 g/l (-45%). In (ii) natural fungal infection did not occur due to dry weather conditions; physiological and nutraceutical analyses of healthy heads demonstrated that As 35x induced a significant increase of both head size and glucosinolate content. Discussion: Some evidences on the efficacy of arsenic, at different decimal and centesimal HD, in fungal and viral disease control were previously reported [1]. In the present study the efficacy of HD arsenic in dark leaf spot control in field has been shown for the first time: since fungal inoculation was performed on the leaves before flowering, we can hypothesize that this treatment induced an increase of plant resistance to fungal infection. Conclusions: This research showed the possibility of using HD arsenic in agriculture (“agrohomeopathy”), as it increased both plant resistance to fungal infection and the content of glucosinolates, ie secondary metabolites involved in plant resistance mechanisms [2] and considered as “plant food protection agents” [3]. Acknowledgments: Authors declare there is no conflict of interest. This research has been supported by Marche Region. A grateful acknowledgement to Dr. Leonardo Valenti for his support to this research. The authors thank Laboratoires Boiron srl for the grant awarded to one of the author Dr. Grazia Trebbi. Finally, authors are grateful to Cemon srl for financial support of glucosinolate analyses. We had full access to all the data in this study and we take responsibility for the integrity of the data and the accuracy of the data analysis Keywords: cauliflower, arsenic trioxide, Alternaria brassicicola, glucosinolates References [1] Betti L, Trebbi G, Majewsky V, Scherr C, Shah-Rossi D, Jäger T, et al. Use of homeopathic preparations in phytopathological models and in field trials: a critical review. Homeopathy 2009; 98: 244-266. [2] Ménard R, Larue J-P, Silué D, Thouvenot D. Glucosinolates in cauliflower as biochemical markers for resistance against downy mildew. Phytochemistry 1999; 52: 29-35. [3] Talalay P, Fahey JW. Phytochemicals from Cruciferous plants protect against cancer by modulating carcinogen metabolism. J Nutr. 2001; 131:3027S- 3033S.