RNA interference (RNAi) is one of the key defense mechanisms directed against virus infections in plants and other organisms. In this case in plants infected with viruses, short interfering RNAs (siRNAs) are formed from two-chain replicated forms of virus molecules of RNA. These siRNAs program one of the RNAi basic components, RNA-induced complex of genes silencing (RISC, RNA induced silencing complex) associated with sequence-specific removing virus RNA. Virus protein P19 is a suppressor of RNAi and is capable of trapping the siRNAs being formed before their binding with RISC. Here, it was shown that preliminary entering leaves of plants Nicotiana benthamiana Domin (before virus infecting) of siRNAs eluted from the complex P19/siRNA from the infected plant lowers development of infection symptoms induced by tomato bushy stunt virus (TBSV) in inoculated plants. Exogenous addition of suppressor-associated siRNAs to plants leads to not only lowering virus accumulation but also to survival of infected plants. Thus, it has been established that preliminary addition of virus siRNAs elevates plant tolerance to the virus infection by means of early programming RISC and activation of the defense action of RNAi.

Apples are widely consumed by people all over the world due to their taste and nutritional value. However, apple trees are prone to various environmental stresses, including fungal diseases. Among them, Cytospora canker (or Valsa canker) can cause dieback of branches and twigs. Although Kazakhstan is well known as an origin of apples, very little is known about canker diseases that spread across all commercial orchards. Therefore, an accurate identification of the causal agents of those diseases is needed for further application of informed disease management strategies. In this study, eleven isolates belonging to four Cytospora species were isolated from multiple cultivars, grown in six different orchards within the Almaty region, Kazakhstan. As a result of a multilocus phylogenetic analysis using ITS, LSU and tef1-α marker genes and morphological characterization, these isolates were described as Cytospora parasitica, Cytospora sorbina, Cytospora pruinopsis and Cytospora chrysosperma. Moreover, a pathogenicity test was conducted on detached twigs, and it demonstrated that two of these fungi were highly virulent. Overall, this paper is a first report of the causal agents of apple canker disease in Kazakhstan and could be a trigger for conducting future studies to better understand the disease epidemiology, as well as build management strategies.

Apple (Malus domestica) is a very important crop grown in Kazakhstan. Cytospora species are capable of causing destructive stem cankers on a wide range of woody plants, including apples, and can lead to twig and branch dieback. This study aimed to identify the Cytospora species responsible for canker disease of apple in Kazakhstan and to assess the susceptibility of major apple cultivars to these pathogens. Investigations were conducted in Almaty, Kazakhstan, during 2023 and 2024. Samples from symptomatic trees were collected, and nine Cytospora isolates were obtained from diseased apple trees. Multigene phylogenetic analysis based on combined sequence data of ITS, tef1-α, tub2, and LSU loci, together with morphological characteristics and pathogenicity assays, revealed two Cytospora species: C. leucostoma and C. sorbicola. The reactions of six apple cultivars (Gala, Golden Delicious, Red Delicious, Granny Smith, Fuji, and Jonaprince) to these species were evaluated, and statistically significant differences were found among cultivars (p < 0.05). The largest lesions occurred on Red Delicious and Fuji, indicating that these cultivars are the most susceptible. In contrast, lesion lengths on Jonaprince were significantly smaller than on all other cultivars, suggesting that Jonaprince is resistant to Cytospora species in Kazakhstan. This is the first report of C. leucostoma and C. sorbicola causing apple canker disease in Kazakhstan.