Chestnut blight fungus in Croatia: diversity of vegetative compatibility types,mating types and genetic variability of associated Cryphonectria hypovirus 1

In order to improve understanding of its diversity, 338 isolates of Cryphonectria parasitica, the causal agent of chestnut blight, were sampled from 10 chestnut populations throughout chestnut‐growing coastal and continental areas of Croatia. Eighteen vegetative compatibility (VC) types were identified. The VC type EU‐1 was the most widespread, comprising 42·9% of the isolates, followed by EU‐2 (21%) and EU‐12 (14·2%). In respect to the occurrence of the main VC types, the C. parasitica populations in Croatia combined features of both northwestern and southeastern European populations. Perithecia and mating‐type ratios of approximately 1 : 1 were found in all populations, suggesting that sexual reproduction of the fungus is common in Croatia. Natural hypovirulence was also evident in all populations, with incidence of hypovirus‐infected isolates ranging from 12·7% in Istria‐Buje to 66·6% in the continental part of the country. A total of 36 hypovirus‐infected isolates sampled throughout Croatia were analysed in ORF‐A and ORF‐B by RT‐PCR/RFLP analysis. All viral isolates belonged to the Italian subtype of Cryphonectria hypovirus 1 (CHV‐1) and were closely related to the isolates found in other European countries. The RFLP patterns found were also identical or similar to the patterns of three isolates collected in Croatia 22 years ago, suggesting a slow evolution of the hypovirus.     

Biological control of green mould on <Emphasis Type="Italic">Agaricus bisporus</Emphasis> by a native <Emphasis Type="Italic">Bacillus subtilis</Emphasis> strain from mushroom compost

Fifty bacterial isolates obtained from compost were tested in vitro against the causal agents of green mould in Agaricus bisporus. Isolate B-38 which induced 48.08% in vitro growth inhibition of T. harzianum T54 and 52.25% of T. aggressivum f. europaeum T77 was identified as Bacillus subtilis, based on 16S rDNA sequence and used in mushroom growing room experiments. B. subtilis B-38 did not decrease mycelial growth rate of Agaricus bisporus A15 in mushroom compost in glass tubes. After applying prochloraz-manganese, B. subtilis B-38 and B. subtilis QST 713, no significant differences in BE values among treatments were found concerning both total yield and the weight of healthy mushrooms. Statistical analyses showed that only inoculation significantly influenced the healthy mushroom yield. In plots inoculated with T. harzianum T54 disease incidence was significantly lower after treatments with prochloraz-manganese (11.81%), B. subtilis QST 713 (12.26%) and B. subtilis B-38 (14.19%) compared to the control (28.16%), as well as in plots inoculated with T. aggressivum f. europaeum T77 11.88%, 12.2% and 15.03%, respectively, in comparison with the control (23.47%). Statistically significant differences were not found among the efficacy values of tested bio-fungicides based on B. subtilis and the commercial fungicide prochloraz-manganese suggesting the use of B. subtilis B-38 and B. subtilis QST 713 as good alternatives to chemical fungicides.     

Viruses affecting tomato crops in Serbia

In a two-year survey (2011–2012), 3220 samples were collected and analyzed in order to determine the presence and distribution of viruses in tomato crops at 56 localities of 18 districts in Serbia. Out of 12 viruses tested, Cucumber mosaic virus (CMV), Potato virus Y (PVY), Alfalfa mosaic virus (AMV), Tomato spotted wilt virus (TSWV), Tomato mosaic virus (ToMV) and Tobacco mosaic virus (TMV) were detected in 42.1, 40, 11, 8.6, 2.3 and 1.3% of the total tested samples, respectively. The results revealed that CMV was prevalent in 2011 and PVY in 2012. CMV and PVY, apart from being predominant, were also the most widespread viruses. In general, single infections were the most frequent type of infection. Additionally, the most common mixed infections were double infections and the most prevalent combination was CMV and PVY. In 2011, the incidence of diseases and the percentage of all infection types were significantly higher than in 2012. Furthermore, in 2011, regardless of total single infections being prevalent compared to mixed infections, two prevailing viruses were commonly detected in mixed infections. The additional molecular testing of ELISA-negative samples using virus specific primers did not reveal the presence of Pepino mosaic virus (PepMV), Tomato yellow leaf curl virus (TYLC), Tomato infections chlorosis virus (TICV) and Tomato chlorosis virus (ToCV).     

Biochemical and physiological responses to long‐term Citrus tristeza virus infection in Mexican lime plants

Reactions that occur when a plant is subjected to Citrus tristeza virus (CTV) infection often result in triggering of numerous defence mechanisms to fight the infection. The reactions vary according to virus strain, host genotype, time of exposure to the infection and environmental conditions. To date, no study has examined in detail the consequences of 10‐year exposure to CTV infection on the biochemical and physiological status of susceptible Mexican lime plants (Citrus aurantifolia). To understand the reaction of such plants, changes in nutrient status, total proteins, enzyme activity involved in scavenging of reactive oxygen species, photosynthetic and transpiration rates, chlorophyll content, membrane permeability and water content were analysed in plants infected with different CTV isolates and in healthy plants. The activity of superoxide dismutase and polyphenol oxidase significantly decreased in the infected leaves, and membrane permeability was lower in the infected plants. Macro‐ and micronutrient elements were significantly changed: concentrations of leaf nitrogen, zinc, magnesium and iron were elevated but potassium concentration depressed in comparison to noninfected control leaves. Levels of other analysed nutrient elements, enzymes, photosynthesis and stomatal conductance, chlorophyll content and relative water content were unchanged. Clear physiological changes were found among infected and noninfected control plants but none between plants infected with different CTV isolates. The data suggest that some of the defence mechanisms investigated here were suppressed due to the continuous and long‐term pressure of biotic stress.     

First report of invasive brown marmorated stink bug Halyomorpha halys (Stål, 1855) in Croatia

The brown marmorated stink bug, Halyomorpha halys (Stål, 1855) (Hemiptera: Heteroptera: Pentatomidae), has been spreading over Europe since the first documented records from Liechtenstein in 2004 and Switzerland in 2007. It is considered to be a pest in many agricultural crops and a household nuisance. In 2017 the species was observed in Croatia for the first time, in the city of Rijeka on the north Adriatic coast. Halyomorpha halys has already been recorded in three nearby countries (Italy, Hungary and Serbia), and therefore the arrival of this species had been expected from neighbouring populations or from distant sources via trading goods. To identify the pathway of entry, the haplotypes of H. halys (Stål, 1855) individuals were analysed by comparing a part of the mitochondrial COI gene with other haplotypes present in the GenBank database. Individual specimens shared the most common haplotype with nearby Italian and Hungarian populations.