Industrial cultivation of nut crops in the Republic of Kazakhstan is promoted by favourable soil and climate conditions, especially in the southern region, which makes it possible to obtain high yields of this valuable plant in the future. Significant damage to the yield of nut crops is caused by diseases, protection of plantations from which is one of the main measures aimed at increasing their productivity. The most important issue in cultivation of nut crops is its protection from bacterial and fungal pathogens. In Kazakhstan purposeful researches on studying species diversity of diseases and pests of nut crops have not been carried out. The novelty of the conducted research is in the fact that for the first time in Kazakhstan fungal and bacterial diseases of walnut in the conditions of the southern zone of fruit growing on the basis of microbiological and molecular-genetic methods were identified. The results of research showed that the majority of isolated pathogens are fungi, as well as several species of bacteria causing diseases of walnut. In total, 4 genera of fungi were isolated: Alternaria, Fusarium as causative agents of fungal diseases; Aspergillus, Penicillium as secondary infestation; also 2 genera of bacteria: Pantoea, Pseudomonas as causative agents of bacterial diseases. Molecular identification of fungal and bacterial pathogens by PCR based on genomic DNA showed that the studied walnut samples were identified as phytopathogenic fungi: Alternaria alternata, Fusarium solani, as well as phytopathogenic bacteria: Pantoea agglomerans, Pseudomonas syringae, Pseudomonas oryzahabitans. The conducted research results will allow to make up a system of protection of walnut from harmful diseases in order to increase the productivity of plantations.

Walnut (Juglans regia L.) is a significant nut crop in the southern regions of Kazakhstan; however, its productivity is substantially limited by fungal and bacterial diseases. Therefore, a phytopathological investigation was conducted in 2023–2024 in the Almaty and Turkestan regions, including field monitoring, pathogen isolation, molecular identification, and pathogenicity testing. Field monitoring revealed that symptoms of brown spot, walnut canker, walnut blight, bacterial blight, and crown gall were widespread. The overall disease incidence ranged from 8% to 30%, while the disease severity index varied from 15% to 70% across the surveyed sites. Pure cultures of pathogens were isolated from 69 samples, and their morphology was characterized. Molecular identification through sequencing of universal genetic loci (the internal transcribed spacer for fungi and 16S ribosomal RNA for bacteria) revealed the presence of the fungal species Alternaria alternata and Fusarium incarnatum, as well as the bacterial species Pantoea agglomerans and Xanthomonas arboricola pv. juglandis. Pathogenicity testing confirmed the virulence of the identified pathogens, which induced characteristic symptoms of brown spot, walnut canker, and walnut blight, consistent with those observed in the field. These findings have considerable practical significance for improving phytosanitary monitoring and protection systems in walnut plantations, thereby facilitating disease outbreak prediction and the development of effective quarantine measures.

Walnut blight is a harmful disease that affects nut crops. It is caused by the bacterium Pantoea agglomerans and has become widespread in recent years, posing a serious threat to walnut plantations. The disease not only destroys more than half of the crop, but also causes bark cracking and slow crown desiccation, which can lead to further infections. One of the most important requirements for modern varieties of agricultural plants, including nut crops, is an increased level of resistance to diseases. In Kazakhstan, there is currently no data on the spread of diseases of nut crops and resistance of varieties to harmful diseases. This makes it difficult to recommend a suitable variety for industrial and private nut orchards. Ipmroving the breeding process and increasing the productivity of walnut plantations, it is extremely relevant to assess the resistance of varieties to the most dangerous pathogens. For the first time in Kazakhstan, a two-year monitoring study was conducted to assess the resistance of promising walnut varieties and forms to the Pantoea agglomerans, taking into account the prevailing weather and climatic conditions. The study was carried out on 23 varieties and forms in the main fruit-growing regions of the country. It was found that the walnut blight caused by the bacterium Pantoea agglomerans annually damages walnut plants, and the degree of disease damage depends on the prevailing weather and climatic conditions. The research results revealed that the Moldavian variety - Kazaku showed high resistance to walnut blight. Other resistant varieties are Miroslava, Ovidiu, Germisara, Yarivski, Peshanski, Kogylnichanu, 185, Lipin 2, Liaohe, Fernor, Plin, and Kishinevski. These varieties showed minimal damage, not exceeding 2 points, during the years of observation. These varieties are recommended as suitable varieties for increasing the productivity of industrial and private nut orchards and improving the breeding process.

The most widespread and effective method of protecting walnut trees from diseases is through chemical treatments. With the increasing variety of fungal pathogens affecting walnut trees in the southern zone of fruit production in Kazakhstan, there is a need to study the effectiveness of fungicides against these pathogens. Therefore, laboratory and field studies were carried out to evaluate the effectiveness of several fungicides against the most common diseases of walnut trees caused by Fusarium and Alternaria fungi. The effectiveness of fungicides with different mechanisms of action was studied for the first time. The fungicides evaluated were Score (difenoconazole, 250 g/l), Horus (cyprodinil, 750 g/kg), Stroby (kresoxim-methyl, 500 g/kg), Luna Tranquility (fluopyram, 125 g/l + pyrimethanil, 375 g/l) against walnut diseases in the southern zone of fruit cultivation in Kazakhstan. The results of both laboratory and field experiments showed that the most effective fungicide against fungal pathogens on walnut was Score (difenoconazole, 250 g/l). Stroby (kresoxim-methyl, 500 g/kg) also demonstrated over 80% biological efficacy against Alternaria alternata. The results of this study will assist local growers in managing various fungal diseases in walnut plantations.

Apple (Malus domestica Borkh.) production is increasingly threatened by fungal diseases under conditions of intensive horticulture and ongoing climate change. In southeastern Kazakhstan, symptoms associated with Alternaria spp. have become more frequent in commercial orchards; however, molecularly confirmed data on the pathogen associated with these symptoms remain limited. This study aimed to identify, using multigene molecular phylogenetic analysis, an Alternaria isolate obtained from infected apple leaves and fruits, to confirm its pathogenicity experimentally, and to compare the susceptibility of apple cultivars to this pathogen. For molecular identification, nucleotide sequences of four genetic markers—the ITS region of rDNA, SSU, tef1-α, and RPB2—were obtained by PCR and sequencing. The sequences were compared with reference data from the GenBank database using BLASTn, and phylogenetic relationships were inferred using the maximum likelihood method based on a concatenated dataset of the four loci. The isolate KZ17 clustered within the A. alternata clade, with the broader node uniting this group with A. gossypina and A. longipes receiving a bootstrap value of 78%. A total of 20 fungal isolates were obtained from 112 symptomatic apple leaf and fruit samples. Among them, one representative isolate, KZ17, was selected for multilocus molecular identification and pathogenicity testing. The pathogenicity of isolate KZ17 was confirmed in inoculation experiments on apple microshoots under controlled conditions. Artificial inoculation of detached leaves and ripe fruits of 14 apple cultivars revealed significant cultivar-dependent differences in susceptibility. Lesion diameters ranged from 12.3 ± 0.20 to 19.2 ± 0.35 mm on detached leaves and from 15.0 ± 1.2 to 30.0 ± 2.4 mm on ripe fruits. The least susceptible cultivars were ‘Granny Smith’, ‘Zaman’, and ‘Maksat’, whereas ‘Voskhod’, ‘Saltanat’, and ‘Kamila’ showed the greatest susceptibility. These differences were statistically significant (p < 0.001). This study provides the first multigene-based confirmation of the association of A. alternata with apple leaf and fruit lesions in southeastern Kazakhstan and demonstrates cultivar-dependent differences in susceptibility to this pathogen. These findings contribute to improved pathogen diagnostics, germplasm screening for resistance, and the development of plant protection strategies for commercial apple orchards.

The walnut (Juglans regia L.) is an economically important crop in southern Kazakhstan, where brown spot disease, caused by the fungus Alternaria alternata, poses a serious threat to yield. The objective of this study was to determine whether A. alternata isolates obtained from walnut leaves in orchards located in different climatic zones (Almaty and Turkestan regions) exhibit pathogenic properties in all cases. The fungus was identified based on morphological characteristics and confirmed by PCR analysis. Pathogenicity was assessed through artificial inoculation of walnut leaves under controlled conditions. The results demonstrated that A. alternata exhibits pathogenicity under diverse climatic conditions, inducing brown spot symptoms, including chlorosis and necrosis of leaves. These findings confirm the wide distribution and threat of brown spot and provide a scientific basis for further research aimed at developing effective plant protection strategies.