A Current Overview of Two Viroids Prevailing in Citrus Orchards: Citrus Exocortis Viroid and Hop Stunt Viroid

Citrus exocortis viroid (CEVd) and hop stunt viroid (HSVd) are the main viroids circulating in all citrus-growing areas worldwide, and causing two well-known diseases on citrus trees; exocortis and cachexia, respectively. These viroids are small, covalently closed single-stranded RNA, allocated to the Pospiviroidae family. CEVd is the first viroid being described on citrus trees in 1948 in California. It is considered the largest citrus viroid at 371 nucleotides. It causes bark scaling disorder on the rootstock of citrus trees grafted on trifoliate orange and its hybrids and can cause dwarfing of trees grown on these rootstocks. HSVd was first observed in 1945 in Florida. It consists of 299 nucleotides. Stunting, chlorosis, bark gumming, stem pitting, decline, and depressions in the wood are the main symptoms of HSVd in mandarin and its hybrids. The introduction and propagation of infected budwoods are the main causes of viroids spread in citrus orchards. These agents are mechanically sap-transmissible and spread by contaminated tools. Neither seed transmission nor vectors have been reported for both viroids. Root transmission, though possible, would be overshadowed by mechanical transmission. Rapid and sensitive molecular-based detection methods specific to both viroids are available. Both diseases are controlled by using viroids-free budwoods for new plantations, launching budwood certification programs, and establishing a quarantine system for new citrus varieties introduction. The most important achievements in CEVd and HSVd researches are outlined in this chapter. This would help to provide a clearer understanding of the diseases they cause and contribute to the development of better control strategies

High-throughput molecular technologies for unraveling the mystery of soil microbial community: challenges and future prospects

Soil microbial communities play a crucial role in soil fertility, sustainability, and plant health. However, intensive agriculture with increasing chemical inputs and changing environments have influenced native soil microbial communities. Approaches have been developed to study the structure, diversity, and activity of soil microbes to better understand the biology and plant-microbe interactions in soils. Unfortunately, a good understanding of soil microbial community remains a challenge due to the complexity of community composition, interactions of the soil environment, and limitations of technologies, especially related to the functionality of some taxa rarely detected using conventional techniques. Culture-based methods have been shown unable and sometimes are biased for assessing soil microbial communities. To gain further knowledge, culture-independent methods relying on direct analysis of nucleic acids, proteins, and lipids are worth exploring. In recent years, metagenomics, metaproteomics, metatranscriptomics, and proteogenomics have been increasingly used in studying microbial ecology. In this review, we examined the importance of microbial community to soil quality, the mystery of rhizosphere and plant-microbe interactions, and the biodiversity and multi-trophic interactions that influence the soil structure and functionality. The impact of the cropping system and climate change on the soil microbial community was also explored. Importantly, progresses in molecular biology, especially in the development of high-throughput biotechnological tools, were extensively assessed for potential uses to decipher the diversity and dynamics of soil microbial communities, with the highlighted advantages/limitations

Viruses of cucurbit crops: current status in the Mediterranean Region

peer reviewedCucurbits are among the most cultivated crops, and the most economically important species are melon (Cucumis melo L.), cucumber (Cucumis sativus L.), watermelon (Citrullus lanatus Thumb.), squash (Cucurbita pepo L.), and pumpkin (Cucurbita spp.). These crops have become important income sources providing export and local consumption commodities in many Mediterranean countries. Increased area of cucurbits has led to the emergence of several viral diseases, which can have impacts on crop production and threaten agricultural sustainability. An overview of the most damaging cucurbit viruses in the Mediterranean area is provided to improve understanding of the diseases they cause and to emphasize effective disease management strategies. An updating of the geographical distribution of these viruses, the symptoms they cause and their means of transmission is also provided. Disease management methods and measures by farmers and phytosanitary authorities to address the virus outbreaks are outlined, including diagnostics, use of tolerant cultivars, and chemical and biological vector control. Mediterranean region farmers have learned many lessons from the damaging pandemics caused by cucurbit viruses, through the extensive published research, and this review provides a basis for managing future outbreaks of newly emerging virus infections