Browsing by Author "Machado, J."
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- Chemical characterization and antimicrobial activity of 6 plant essential oils against Pseudomonas syringae pv. actinidiae and P. syringae pv. actinidifoliorumPublication . Silva, M. Nunes da; Machado, J.; Mazzaglia, A.; Balestra, G. M.; Vasconcelos, M. W.; Carvalho, S. M. P.Introduction: Kiwifruit bacterial canker (KBC), caused by Pseudomonas syringae pv. actinidiae (PSA), is currently the most destructive disease of kiwifruit worldwide. It was introduced in Portugal in 2010, leading to drastic production losses and plant mortality. Conversely, a closely related pathovar, P. syringae pv. actinidifoliorum (PSAF), only causes necrotic spots, not being associated with plant mortality. Current control techniques are expensive, consisting in the application of copper- and antibiotics-based compounds, with serious risks of environmental contamination and development of resistant bacteria. Therefore, the aim of this work was to characterize six plant essential oils against (anise, basil, cardamom, cumin, fennel and laurel) by gas chromatography–mass spectrometry (GC-MS) and evaluate their antimicrobial potential against different strains of PSA and PSAF. Methods: 1. Two highly virulent PSA strains (CFBP 7286 and 1F, isolated from Italy and France, respectively) and two less virulent PSAF strains (ICMP 18804 and ICMP 19441, isolated from New Zealand and Australia, respectively) were grown overnight in LB broth at 27 ᵒC and with shaking. 2. Bacterial inoculum (1-2x107 CFU.mL-1) was plated onto Nutrient Sucrose Agar medium and 20 μL droplets of each essential oil concentration were placed in 5 mm diameter paper discs (N = 3). 3. Plates were incubated at 28 ᵒC for 48 h, after which the inhibition zone was measured. 4. Essential oils chemical characterization was performed by GC-MS. Conclusions: Plant essential oils differed in their composition; however, compounds such as 3-carene, eucalyptol, camphor, fenchone and 4-terpineol were detected transversely in all oils. Although cumin presented the most simple composition, it showed MIC as low as 0.1 % for PSA 19441. In general, basil, cardamom and fennel had higher MICs, whereas anise had the lowest. PSAF strain 19441 was the most sensitive to almost all essential oils tested.
- Exploring the expression of defence-related genes in Actinidia spp. after infection with Pseudomonas syringae pv. actinidiae and pv. actinidifoliorum: first stepsPublication . Silva, M. Nunes da; Machado, J.; Balestra, G. M.; Mazzaglia, A.; Vasconcelos, M. W.; Carvalho, S. M. P.Kiwifruit bacterial canker (KBC), caused by Pseudomonas syringae pv. actinidiae (PSA), is currently the most destructive disease of kiwifruit worldwide. Conversely, a closely related bacterial strain, P. syringae pv. actinidifoliorum (PFM), only causes necrotic spots and has not been associated with plant mortality. Moreover, there is some evidence on the higher susceptibility of the Actinidia chinensis var. deliciosa kiwifruit species to KBC, compared with A. arguta, but the reasons behind it are still largely unknown. In this work, micropropagated plants of Actinidia chinensis var. deliciosa 'Hayward' and A. arguta var. arguta 'Ken's Red' were inoculated with PSA or with PFM (10(7) CFUs mL(-1)). Disease development was monitored 1, 2 and 5 days post inoculation (dpi) through the determination colony forming units (CFUs) and the expression analysis of six plant defence-related genes (APX, CAT, SOD, LOX1, SAM and TLP1). At 5 dpi, CFUs in plant tissues inoculated with PSA and PFM were, respectively, 17.4-fold and 2.8-fold higher in A. chinensis compared with A. arguta. Expression of antioxidant enzyme-related genes was very distinct between the two kiwifruit species: SOD expression was drastically increased in A. chinensis (up to 2.1-fold, 5 dpi), whereas in A. arguta CAT was the most upregulated gene (up to 1.7-fold, 2 dpi). LOX1, involved in jasmonic acid biosynthesis, was upregulated in both species, however reaching the highest values at 2 dpi in A. chinensis (2.2 fold) and 1 dpi in A. arguta (1.9-fold). It is concluded that A. arguta is much more tolerant to PSA than A. chinensis and that the molecular mechanisms between the two kiwifruit species involve specific defence pathways being triggered at distinct moments after plant infection.
- Kiwifruit bacterial canker: novel insights on an old problemPublication . Silva, M. Nunes da; Machado, J.; Balestra, G. M.; Mazzaglia, A.; Vasconcelos, M. V.; Carvalho, S. M. P.Framework: Kiwifruit bacterial canker (KBC), caused by Pseudomonas syringae pv. actinidiae (PSA), is currently the most destructive disease of kiwifruit worldwide. It was introduced in Portugal in 2010, inducing production losses up to 80 %. Conversely, a closely related pathovar, P. syringae pv. actinidifoliorum (PSAF), only causes necrotic spots, not being associated with plant mortality. There is some evidence on the higher susceptibility of green kiwifruit (Actinidia deliciosa) cultivars to KBC, compared with the berry kiwi (A. arguta), but the reasons behind it are still largely unknown. The aim of this work was to evaluate how kiwi plants with reported distinct tolerance to the disease responded to artificial infection in terms of defence-related genes expression. Methods: Micropropagation of A. deliciosa cv. ‘Hayward’ and A. arguta cv. ‘Ken’s Red’ plants. Plant inoculation with a virulent Pseudomonas syringae pv. actinidiae strain (PSA) and with a low virulent P. syringae pv. actinidifoliorum strain (PSAF). Bacterial colony forming units (CFUs) determination in plant tissues 1, 2 and 5 days post inoculation (dpi). Defence-related gene expression analysis by reverse transcription polymerase chain reactions (qRT-PCR) at 1, 2 and 5 dpi. Conclusions: A. deliciosa cv. ‘Hayward’ seems to be much more susceptible to PSA infection than A. arguta cv. ‘Ken’s Red’. SOD expression was drastically increased in ‘Hayward’, whereas C AT was the most upregulated antioxidant-encoding gene in ‘Ken’s Red’. Jasmonic acid and ethylene precursors, LOX and SAM, were upregulated 2 dpi in ‘Hayward’ and already at 1 dpi in ‘Ken’s Red’. LOX1 and SAM transcriptional levels were higher in PSA-inoculated plants, compared with PSAF.
- Tomato responses to nitrogen, drought and combined stresses: shared and specific effects on vascular plant anatomy, nutrient partitioning and amino acids profilePublication . Machado, J.; Fernandes, A. P. G.; Bokor, B.; Vaculík, M.; Kostoláni, D.; Kokavcová, A.; Heuvelink, E.; Vasconcelos, M. W.; Carvalho, S. M. P.Crops are often subjected to various abiotic stresses and interactions between them may occur, but how plants cope with them remains poorly understood. This study explored how combined nitrogen and drought stress impact tomato vascular stem anatomy, nutrient partitioning and amino acids profile. Tomato seedlings were exposed to control (CTR; 100N + 100%W), N stress (N; 50%N), drought stress (W; 50%W), or combined stress (N + W; 50%N+50%W) for 27 days. All treatments similarly reduced the phloem and xylem areas. Plants under N + W stress exhibited increased root synthesis of asparagine and arginine (up to 230% compared to W stress and 66% compared to N stress) and showed a higher reallocation and synthesis of osmolytes such as K+ and proline, respectively. This, along with the specific increase in other amino acids related to osmoregulation (alanine, tyrosine and phenylalanine), contributed to an enhanced stomatal closure and lower transpiration rate compared to W stressed plants. Conversely, N stressed plants responded mainly through N remobilization from the photosynthetic machinery, leading to decreased chlorophyll content (up to 32%) and photosynthetic rate (up to 57%). Under single W stress, plants invested more in the root system as a strategy to increase W and nutrients' uptake, compared to those grown under N + W stress, and maintained the photosynthetic rate at the level of CTR plants. It is concluded that tomato plants employed distinct mechanisms for reallocating nitrogen and regulating osmosis to withstand either single or combined stresses and that amino acids and nutrients’ homeostasis have an important role in these processes.