Abstract. Tomato is one of the economically important crops in Bulgaria. Low tomato yields in the country are mostly due to lack of knowledge on sustainable agronomic practices, lack of improved varieties, which are well suited for high yield and resistance to diseases, and also due to damage caused by pests and diseases. Many viruses infect the tomato crop. The object of this research was to identify viruses infecting tomato crops in Bulgaria. The presence or absence of a viral infection in tomato plants was carried out with DAS-ELISA serologic assays with specific polyclonal immunoglobulin G for the relevant plant virus. Most of the tomato plants were infected with one or two viruses and in rare cases with more than two viruses. We found that mixed viral infections caused more severe necrotic damages in the tomato fruits and increased the economic loss compared with mono infections.

Tomato leaf curl virus disease caused by whitefly-transmitted begomoviruses is a serious tomato production constraint in tropical and subtropical regions of the world. Use of genetic resistance for diseases caused by begomoviruses is an important component of sustainable disease management approaches. To date, six introgressions (Ty genes) derived from different tomato wild species that confer resistance to tomato leaf curl disease have been identified. Among these, dominant Ty-2 and partially dominant Ty-3 are important for the development of resistant hybrids because of their gene action. In the present study we report marker assisted selection of tomato lines carrying Ty-2 and Ty-3 genes and the effect of combining these in tomato hybrids using agroinoculation. The response of lines and hybrids with the Ty-2 gene indicated ineffectiveness of Ty-2 to infection by a bipartite tomato leaf curl virus. The Ty-3 gene showed dosage effect with partial resistance in heterozygous state. However, the level of resistance in hybrids with the combination of Ty-2 and Ty-3 genes was higher and similar to homozygous Ty-3 plants. The Ty-2 gene in either homozygous or heterozygous state enhanced the level of resistance of plants with heterozygous Ty-3. Thus, tomato hybrid breeding programs can be benefited by using tomato lines carrying Ty-2 and Ty-3 resistance genes. The combined results of evaluation of horticultural performance, field resistance and agroinoculation tests demonstrated that the set of tomato lines developed in this study could be useful resources for achieving higher level of resistance in tomato hybrids.

Disease caused by Tomato yellow leaf curl virus (TYLCV) brings serious production losses of cultivated tomato worldwide. In our previous study, two novel amino acid derivatives exerted satisfactory antiviral activities against TYLCV. In this study, the variation of TYLCV, the transcriptional expression level of Ty-1 and the enzyme activities of POD and PPO in tomato were monitored after treatment with two amino acid derivatives to illustrate the antiviral mechanism. The results showed the symptom severity caused by TYLCV was reduced significantly by two compounds and was associated with the inhibition of viral DNA level at the early stage. Among three levels of concentration, the highest inhibition rate of CNBF-His was 40.66 % at 1000 mg/L, for CNBF-Asn, the highest inhibition rate was 36.26 % at 2000 mg/L 30 days post-inoculation. Two compounds could also enhance the activities of PPO and POD and the transcriptional expression level of Ty-1 which correlates with plant resistance in tomato. In the field test, two compounds increased the yields of tomato and the maximum increase of yield was 37.66 %. This is the first report of novel amino acid derivatives inducing resistance in tomato plant against TYLCV. It is suggested that amino acid derivatives have the potential to be an effective approach against TYLCV in tomato plant.

Fusarium wilt of tomato (Lycopersicon esculentum) caused by Fusarium oxysporum f. sp. lycopersici is a recent dangerous disease in tomato growing areas. In this study, biocontrol agent Trichoderma was isolatedfrom tomato fields. The effect of Trichoderma isolates on resistance induction in tomato was evaluated in vitro and in vivo conditions. Results obtained showed that, in dual culture study all Trichoderma isolates inhibitory effect on growth of test fungus and were effective in controlling the growth of the pathogen. Disease incidence was reduced when Trichoderma isolates applied in combination with soil + seedling treatment. This result has important practical implications for biocontrol of tomato diseases under commercial conditions.

This study was conducted to evaluate the efficacy of yeast strain TA-2 for controlling rice blast, cabbage black leaf spot, and tomato bacterial wilt diseases. Microscopic and phylogenetic analyses based on rDNA-internal transcribed region (ITS) and rDNA-D1/D2 sequences indicated that yeast strain TA-2 is Meyerozyma guilliermondii . Pretreatment with TA-2 by soil drenching significantly reduced the severity of black leaf spot disease caused by Alternaria brassicicola and leaf blast disease caused by Magnaporthe oryzae . Symptom development of tomato bacterial wilt caused by Ralstonia solanacearum in both soil drench and needle inoculation tests was significantly reduced in TA-2-pretreated plants under soil drenching. Disease severity and R. solanacearum growth were significantly reduced in tomato plants pretreated with yeast culture, cell suspension, or culture filtrate of TA-2 under soil drenching. TA-2 does not produce antibiotics. The present study indicates that disease suppression is systemic, as the roots were treated with TA-2 and the pathogens were inoculated onto leaves or stems, thereby separating the two spatially. M. guilliermondii TA-2 could become a promising natural antimicrobial agent against rice blast, cabbage black leaf spot, and tomato bacterial wilt diseases and might be useful as an eco-friendly control measure, contributing to sustainable agriculture.

Late blight, caused by Phytophthora infestans, has emerged as the most destructive disease of potato and tomato in South India since 2008. One hundred and fifty‐seven isolates of Phytophthora infestans, 63 from potato and 94 from tomato, were collected from major potato and tomato production areas of South India between 2010 and 2012. Their phenotypic and genotypic characteristics were determined and compared with reference isolates. Isolates were characterized based on mating type, in vitro metalaxyl sensitivity, mitochondrial DNA haplotype, RG57 DNA fingerprinting patterns, SSR markers and aggressiveness on potato and tomato, in order to monitor population changes in P. infestans. All isolates were A2 mating type, metalaxyl resistant, mtDNA haplotype Ia and had RG57 and SSR fingerprints almost identical to the 13_A2 clonal lineage reported in Europe. Variation at the D13 and SSR4 loci allowed discrimination of minor variants, designated as 13_A2_3, 13_A2_3b, 13_A2_3c and 13_A2_1. A comparison of the lesion diameters caused by 157 isolates on detached leaflets of three potato and tomato cultivars showed all isolates to be equally aggressive, confirming that the same clonal population is infecting both hosts. This study demonstrates that the 13_A2 lineage was responsible for severe late blight outbreaks on potato and tomato in South India and has replaced the prior population represented by the US‐1 and other genotypes. Revised management strategies will be required to combat this destructive 13_A2 clonal lineage and monitoring of the population across other potato‐ and tomato‐growing regions of India is warranted.

Biological control of the bacterial wilt disease of tomato has been developed on the last several years in Indonesia. Two isolates of biocontrol agents have been tested for their antagonistic activities toward R. solanacearum in vitro were Bacillus subtilis AB89 (PGPR) and endophytic bacteria, Staphylococcus epidermidis BC4. This experiment was conducted to evaluate the effectiveness of those two bacteria, singly or in combination, in the experimental plots and in the field, and also to observe their relationship. Application of S. epidermidis BC4 singly relatively caused the lowest AUDPC value of tomato bacterial wilt, while application of S. epidermidis BC4 and B. subtilis AB89 in combination caused the increasing of AUDPC values. Application of the biocontrol agents, single or in combination, were significantly increasing the total fresh weight of tomato fruits during harvest compared with those in control.

MAIN CONCLUSION : We demonstrate here that the reduction of InsP ₃ , the key component of the phosphoinositol pathway, results in changes in ROS-scavenging machinery and, subsequently, increases the tolerance of tomato plants to light stress. Different plant stress signaling pathways share similar elements and, therefore, ‘cross-talk’ between the various pathways can exist. Links between the phosphoinositol signaling pathway and light signaling were recently found. Tomato plants expressing InsP 5-ptase and exhibiting reduction in the level of inositol 1,4,5-triphosphate (InsP₃) demonstrated enhanced tolerance to stress caused by continuous light exposure. To understand the molecular basis of observed stress tolerance in tomato lines with decreased amount of InsP₃, we monitored the expression of enzymatic antioxidants as well as important factors in light signaling associated with non-enzymatic antioxidants (secondary metabolites). Here, we demonstrated that InsP 5-ptase transgenic plants accumulate less hydroxide peroxide and maintain higher chlorophyll content during stress caused by continuous light exposure. This observation can be explained by documented activation of multiple enzymatic antioxidants (LeAPX1, SICAT2, LeSOD) at levels of gene expression and enzymatic activities during continuous light exposure. In addition, we noticed the up-regulation of photoreceptors LePHYB and LeCHS1, key enzymes in flavonoid biosynthesis pathway, transcription factors LeHY5, SIMYB12, and early light-inducible protein (LeELIP) genes in transgenic tomato seedlings exposed to blue or red light. Our study confirmed the existence of a correlation between phosphoinositol signaling pathway modification, increased tolerance to stress caused by continuous light exposure, activation of ROS-scavenging enzymes, and up-regulation of molecular activators of non-enzymatic antioxidants in InsP 5-ptase expressing tomato lines.