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Posljednjih nekoliko godina, virusne bolesti tikvica i tikvi u Hrvatskoj javljaju se u sve jačem intenzitetu i uzrokuju gubitke u proizvodnji. Cilj rada bio je utvrditi prisutnost virusa mozaika krastavca (CMV), virusa žutog mozaika tikvice (ZYMV) i virusa mozaika lubenice (WMV) na tim kulturama. Tijekom 2019. godine, na 18 lokacija (polja na otvorenom) u šest županija provedeni su vizualni pregledi te je ukupno sakupljeno 43 simptomatičnih uzorka tikvice i 39 uzoraka tikve u svrhu laboratorijske analize na prisutnost CMV, ZYMV i WMV. Analiza je provedena imunoenzimskim testom DAS-ELISA korištenjem komercijalnih seroloških kompleta. Od 82 uzorka, CMV je potvrđen u njih 55 (67%), ZYMV u 50 (61%), a WMV u 10 uzoraka (12%). Pojedinačna zaraza s jednim od tri istraživana virusa utvrđena je u ukupno 38 uzoraka (46%). Mješovite zaraze s dva virusa zabilježene su u 36 uzoraka (44%): 32 uzorka (39%) s kombinacijom CMV + ZYMV te četiri uzorka (5%) s kombinacijom CMV + WMV. Mješovita zaraza sa sva tri virusa (CMV + ZYMV + WMV) utvrđena je u dva uzorka. U šest uzoraka (7%) nije zabilježen niti jedan od tri istraživana virusa. U osam nasada utvrđena je prisutnost jednog virusa, u devet nasada prisutnost dva virusa, a u jednom od 18 pregledanih nasada utvrđena je prisutnost sva tri istraživana virusa., Viral diseases of zucchini and pumpkin have become more severe in recent years, causing significant yield losses. The objective of this study was to determine the presence of cucumber mosaic virus (CMV), zucchini yellow mosaic virus (ZYMV) and watermelon mosaic virus (WMV) in these crops. In 2019, a survey was conducted at 18 sites (open fields) in six counties. Fortythree symptomatic samples of zucchini and 39 symptomatic samples of pumpkin were collected and tested for the presence of CMV, ZYMV and WMV. Samples were tested with commercial serological assays, using doubleantibody sandwich ELISA kits. Out of 82 samples analysed, CMV was detected in 55 (67%), ZYMV in 50 (61%), and WMV in 10 samples (12%). Single viral infection was detected in 38 samples (46%). Mixed infections with two viruses were recorded in 36 samples (44%), CMV + ZYMV combination in 32 samples (39%), and CMV + WMV combination in four samples (5%). Triple viral infection was detected in two samples, while six samples (7%) were determined to be free of all three viruses in the testes. One virus species was recorded at eight locations, two viruses at nine locations, while all three viruses were determined in one out of 18 sampled fields.

Plant-viroid interactions result in systemic infections that are often accompanied by developmental aberration indicative of a general perturbation in phytohormone metabolism and signaling. This chapter provides an overview of the effects of viroid infection, particularly potato spindle viroid disease, on the content of endogenous phytohormones and the expression of phytohormone-related genes in host plants, with a specific focus on salicylic acid, jasmonic acid, brassinosteroids and auxins. The effect of exogenous phytohormones on the development of viroid infections is also described. A summary of recent studies that propose mechanisms of phytohormone signaling involved in plant responses against pathogens and regulatory crosstalk between different signaling pathways is included. A better understanding of the role of phytohormones in plant-viroid interactions could improve our knowledge about host strategies to survive viroid attack and help the development of hormone-based breeding programs aiming to improve plant resistance/tolerance to viroids.

Although structurally simple, viroids can trigger numerous changes in host plants and cause loss of yield in agronomically important crops. This study investigated changes in the endogenous status of phytohormones and antioxidant enzyme activity in Solanum tuberosum cv. Désirée in response to Potato spindle tuber viroid (PSTVd) infection. Phytohormone analysis showed that the content of endogenous jasmonic acid (JA) and its precursor cis-OPDA significantly increased in leaves, while the content of castasterone (CS) increased in both leaves and tubers of systemically infected plants compared to mock- inoculated control plants at 8 weeks post- inoculation. The indole-3-acetic acid content moderately increased only in tubers, while no differences in salicylic acid and abscisic acid content were observed between infected and control plants. Changes in endogenous phytohormone content were associated with upregulated expression of genes involved in the biosynthesis of JA and brassinosteroids, and the metabolism of auxins. Additionally, PSTVd infection provoked overproduction of hydrogen peroxide, which coincided with increased activity of guaiacol peroxidase in leaves and ascorbate peroxidase in potato tubers. The activity of catalase decreased in leaves, while superoxide dismutase activity remained steady regardless of the treatment and organ type. Total ascorbate and glutathione did not change significantly, although a shift towards oxidized forms was observed. Results suggest the existence of organ-specific differences in phytohormone and antioxidative responses in potato upon PSTVd infection. Possible effects of the observed changes on symptom development are discussed.

To better understand the role of phytohormones and antioxidative responses in plant-viroid interaction, changes in endogenous phytohormone contents and activities of key antioxidant enzymes during latent infection of Solanum laxum by potato spindle tuber viroid (PSTVd) were examined. The results showed that endogenous jasmonic acid (JA) and castasterone (CS) content significantly increased, whereas abscisic acid content significantly decreased in symptomless leaves of systemically infected plants compared to that of mock-inoculated control plants. Regarding endogenous salicylic acid and indole-3-acetic acid content, there were no differences between infected and control plants. PSTVd infection also caused excessive production of hydrogen peroxide and enhanced the activity of ascorbate peroxidase (APX) and superoxide dismutase but not the activity of peroxidase and catalase (CAT). When expressed on a protein-weight base, only APX activity increased while CAT activity decreased almost by half in systemic leaves of infected plants. Furthermore, there was a fall in total glutathione content but also a rise in the content of oxidized forms of both ascorbate and glutathione, indicating that the regeneration of glutathione is insufficient. Results of this study strongly suggest the involvement of JA, CS and enzymatic and non-enzymatic antioxidants in the physiological response of S. laxum during latent infection by PSTVd.

Viroids of the genus Pospiviroid are able to induce diseases in a wide range of host plants including important crop species. Although occasional disease outbreaks of Potato spindle tuber viroid (PSTVd) and closely related pospiviroids have been reported in potato and tomato, recent studies found an increase in number of latent infections in ornamental solanaceous species. In order to verify the presence of PSTVd and other pospiviroids in Croatia, a survey was conducted between 2009 and 2012. A total of 182 samples belonging to five ornamental species and two solanaceous crops were analyzed. Eight plants belonging to two different species (Solanum jasminodes and Lycianthes rantonnetii) were found infected by PSTVd and, in addition, one S. jasminoides plant infected by Tomato apical stunt viroid (TASVd). Viroid infection was confirmed by mechanical inoculation on tomato plants to observe symptom expression and molecular tests. Molecular characterization of the isolates was done and complete viroid sequences were submitted to the GenBank. This is the first evidence of the presence of PSTVd and TASVd and their variability in Croatia.

Virus pjegavosti i venuća rajčice (Tomato spotted wilt virus, TSWV) u Hrvatskoj je na krizantemi prvi put utvrđen 2012. godine u Splitu. Tijekom 2016. zabilježene su epidemijske pojave TSWV-a na krizantemi u Primorsko-goranskoj županiji. U radu su prikazani simptomi koje TSWV uzrokuje na krizantemi i glavne mjere zaštite od TSWV-a., Tomato spotted wilt virus (TSWV) on chrysanthemum was detected for the first time in Croatia near Split in 2012. During 2016, epidemic occurrence of TSWV on chrysanthemum was recorded in Primorje Gorski Kotar County. Symptoms caused by TSWV on chrysanthemum are described and the basic principles of TSWV management are presented.