ReDivia - Repositorio Digital de l'Instit Valencià d'Investigacions Agràries
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Tomato trichomes are deadly hurdles limiting the establishment of Amblyseius swirskii Athias-Henriot (Acari: Phytoseiidae)
Get PDFAmblyseius swirskii is a predatory mite widely used for the control of very important pest species, such as whiteflies and thrips, in organic farming and conventional agriculture. However, this species cannot establish on tomato crops, probably due to the toxic effects of plant trichomes and their exudates. We evaluated tomato plants for effects on: a) A. swirskii preference mediated by plant volatiles, b) A. swirskii development, predation capacity and reproductive performance, c) the dispersal and survival of mites as affected by stem trichomes, and d) mite survival as a function of secondary metabolites secreted by tomato trichomes. The results showed that A. swirskii mites which gained experience foraging on tomato plants, tend to avoid them. The survival of A. swirskii eggs and juveniles on tomato leaves was not different from that on sweet pepper. However, adult survival was significantly lower when tested on whole plants. This was ostensibly due to the impact of trichomes and their secondary metabolites that are abundant on the stems and which negatively impacted mite dispersal on the plant. Among the secondary metabolites detected in tomato trichomes, the strongest negative effects were associated with acyl sugars. Acyl sugars were highly toxic to the mites and also, physically accumulated on their bodies after walking on tomato stems. Altogether, our results reveal why A. swirskii is not an efficient biocontrol agent on tomato crops
Sex, males, and hermaphrodites in the scale insect Icerya purchasi
Get PDFAndrodioecy (the coexistence of males and hermaphrodites) is a raremating system for which the evolutionary dynamics are poorly
understood. Here, we investigate the cottony cushion scale, Icerya purchasi, one of only three reported cases of androdioecy in
insects. In this species, female-like hermaphrodites have been shown to produce sperm and self-fertilize. However, males are
ocassionally observed as well. In a large genetic analysis, we show for the first time that, although self-fertilization appears to
be the primary mode of reproduction, rare outbreeding events do occur in natural populations, supporting the hypothesis that
hermaphrodites mate with males and hence androdioecy is the mating system of I. purchasi. Thus, this globally invasive pest insect appears to enjoy the colonization advantages of a selfing organism while also benefitting from periodic reintroduction of genetic variation through outbreeding with males
Zeolites functionalised with essential oils as new fungicidal materials for citrus fruits
Get PDFPostharvest diseases produced by fungi are one of the main problems affecting the quality of agricultural products during storage. In citrus fruits, the largest economic losses are caused by wound pathogens, in particular, by Penicillium digitatum (PD), Penicillium italicum (PI) and Geotrichum citri-aurantii (GC), causing citrus green mould, blue mould and sour rot, respectively
Regulation of carotenoid and chlorophyll pools in hesperidia, anatomically unique fruits found only in Citrus
No full textDomesticated citrus varieties are woody perennials and interspecific hybrid crops of global economic and nutritional importance. The citrus fruit “hesperidium” is a unique morphological innovation not found in any other plant lineage. Efforts to improve the nutritional quality of the fruit are predicated on understanding the underlying regulatory mechanisms responsible for fruit development, including temporal control of chlorophyll degradation and carotenoid biosynthesis. Here, we investigated the molecular basis of the navel orange (Citrus sinensis) brown flavedo mutation, which conditions flavedo that is brown instead of orange. To overcome the limitations of using traditional genetic approaches in citrus and other woody perennials, we developed a strategy to elucidate the underlying genetic lesion. We used a multi-omics approach to collect data from several genetic sources and plant chimeras to successfully decipher this mutation. The multi-omics strategy applied here will be valuable in driving future gene discovery efforts in citrus as well as in other woody perennial plants. The comparison of transcriptomic and genomic data from multiple genotypes and plant sectors revealed an underlying lesion in the gene encoding STAY-GREEN (SGR) protein, which simultaneously regulates carotenoid biosynthesis and chlorophyll degradation. However, unlike SGR of other plant species, we found that the carotenoid and chlorophyll regulatory activities could be uncoupled in the case of certain SGR alleles in citrus and thus we propose a model for the molecular mechanism underlying the brown flavedo phenotype. The economic and nutritional value of citrus makes these findings of wide interest. The strategy implemented, and the results obtained, constitute an advance for agro-industry by driving opportunities for citrus crop improvement
Comparación de los protocolos de PCR en tiempo real para la detección de Xylella fastidiosa en diferentes hospedadores vegetales
Get PDFLas técnicas de detección son herramientas clave para prevenir la introducción de enfermedades emergentes, especialmente cuando no se dispone de tratamientos eficaces contra el organismo patógeno que las causa. En el caso de Xylella fastidiosa, especie bacteriana capaz de afectar a más de 595 especies vegetales diferentes, el protocolo actual de la European Plant Protection Organization (EPPO) para su diagnóstico describe diferentes protocolos de PCR en tiempo real, técnica considerada como gold standard en detección
Unravelling Citrus Huanglongbing Disease
Get PDFHuanglongbing (HLB) or citrus greening is a disease caused by the unculturable, fastidious, phloem-restrictive, Gram-negative bacterium Candidatus Liberibacter spp. Currently, there are three species linked to the disease. The Asian form associated with Candidatus Liberibacter asiaticus (CLas) is heat-tolerant and can survive well above 30°C. The African (Candidatus Liberibacter africanus) and American forms are heat-sensitive and develop between 22 and 25°C (Candidatus Liberibacter americanus) (Bové, 2006). Huanglongbing is vector-transmitted mainly by the African citrus psyllid Trioza erytreae Del Guercio (Hemiptera: Triozidae) and the Asian citrus psyllid (ACP) Diaphorina citri Kuwayama (Hemiptera: Psyllidae), with two other psyllids also reported as vectors, D. communis Mathur and Cacopsilla citrisuga (Yang & Li) (Hemiptera: Pysllidae). The disease was first described in 1929 and reported in China in 1943. The African variation was reported in South Africa in 1947. The disease was reported in Brazil (São Paulo) in 2004 and the United States (Florida) in 2005. More than 20% of citrus trees in Brazil and 90% in Florida are currently affected, with symptomatic trees present in Texas and California. Huanglongbing is present and affects several citrus-producing countries of Asia, sub-Saharan Africa, and America (except for Bolivia, Chile, Perú, and Uruguay). The Mediterranean Basin and Australia are still free of HLB. The threat to HLB-free countries is constant due to the proximity of the disease and its vectors and the unstoppable increase in international trade.
Candidatus Liberibacter asiaticus can infect most citrus species, cultivars, and hybrids. Leaves of infected trees develop a blotchy mottle symptom (yellowing vein and an asymmetrical chlorosis). Infected branches suffer substantial leaf drop, resulting in severe canopy thinning. Fibrous root density decreases nearly 30%, directly affecting water and nutrient uptake, severely reducing fruit yield, and demanding more frequent irrigation and improved mineral nutrition practices. Fruit from HLB-affected trees are often lopsided, poorly colored, and contain aborted seeds, with low commercial value due to small size and quality. The juice from affected fruit present low soluble solids content, high acidity, and bitterness.
There is no cure for the disease yet. Current management strategies focus on either delaying infection or managing infected trees. Methods of delaying infection include removal of symptomatic trees, planting and resetting using HLB-free nursery trees, protection of grove edges and intensive monitoring and control of the vectors mainly using physical, chemical, and biological control methods. Management of infected trees includes adjusting soil pH, enhancing nutritional programs, and improving irrigation management based on altered tree capacities and needs when affected by HLB. Research has evolved rapidly to address this devastating challenging, and several recent alternatives based on psyllid management, bactericides, cultural practices (thermotherapy and vector exclusion using netting), and genetic transformation have been tested. While most attempts at management have focused on a single component of the disease pyramid, most do not explicitly consider multiple elements at the same time.
This Research Topic is a collection of 9 articles from 49 co-authors and present the latest advances in managing the HLB pathosystem, focusing on assessments of near-term feasible practices in the context of the vector, pathogen, host plant, and environment
Biological control of the citrus leafminer 25 years after its introduction in the Valencia citrus growing area (Spain): a new player in the game
Get PDFNatural enemies have been the key factor for the regulation of the citrus leafminer populations, Phyllocnistis citrella, since its introduction in Spain in 1993. The use of various broad-spectrum insecticides in citrus has been banned in recent years. This has led to an increase in the abundance and importance of the complex of generalist predators that inhabit the citrus canopy. In this work, we hypothesize that the incidence of P. citrella and the impact of its natural enemies would have changed due to the greater presence of generalist predators. Following the same protocols used in previous studies, three orchards located in Valencia, the major citrus-growing area of Spain, were monitored during 2017-2018. The incidence of P. citrella has decreased from 1.8-2.4 mines per leaf in 2006 to 0.93-1.98 in 2017-2018. This decrease could be attributed to the 43.0% increase of mortality by natural enemies compared to 2006. Currently, predation is the most important mortality factor. Predation resulted in 50.6% of the mortality caused by natural enemies compared to 34.6% in 2006. The first larval instar was the most susceptible to predation. Among the predators collected, the density of Pilophorus clavatus, a zoophytophagous mirid recently detected in Spanish citrus, was positively correlated with P. citrella predation. In the laboratory, females of P. clavatus preyed actively on second-instar P. citrella. Our results show the importance of conservation biological control in Spanish citrus and suggest that P. clavatus is occupying an important niche for the biological control of P. citrella