1. Introduction

Pathogenic fungi belonging to the genus Monilinia Honey are currently recognized as one of the major limiting factors in fruit production worldwide. These fungi primarily affect fruit-bearing trees and shrubs of the Rosaceae family, causing varying degrees of yield loss and significantly reducing both the quantity and quality of the harvest. Monilinia infections manifest in plants through a range of symptoms, including blossom and twig blight, fruit rot, and leaf damage. In recent years, the geographic distribution of this disease has expanded, making it economically significant not only in European countries but also in Asia, North America, and other regions. For example, in Serbia in 1999, up to 100% of cherry trees were affected during the flowering period and on twigs [1]. In California, fruit losses during storage exceeded 30%, while in Spain, storage-related losses reached up to 59% in certain years. Even as early as the 1950s, complete yield losses of nectarine crops were reported in some areas [2]. These data indicate that Monilinia infections can cause severe economic damage not only in the field but also during postharvest storage.

Brown rot blossom and twig blight, incited by Monilinia laxa (Aderhold & Ruhland) Honey, represents one of the most destructive diseases affecting stone fruit species. The pathogen is considered endemic in Europe and is widespread across major fruit-producing regions characterized by humid and moderately warm climates M. laxa is responsible for blossom, spur, and twig blight, as well as brown rot symptoms on fruits. The sexual (teleomorphic) stage of this fungus is rarely observed. Consequently, the pathogen typically overwinters in infected plant tissues such as twig cankers, blighted blossoms, peduncles, and mummified fruits. During spring, the mycelium within these overwintering structures resumes growth and produces abundant conidia, which serve as the primary inoculum source. When conidia are dispersed and deposited on susceptible tissues including blossoms, spurs, and young twigs – new infections are initiated. As the growing season progresses, especially during the fruit maturation stage, fruits become increasingly susceptible to M. laxa infection. Under favorable environmental conditions, these infections may escalate rapidly, leading to severe epidemics by harvest time. The infected fruits eventually become mummified, remaining attached to trees or on the ground, and act as an important source of inoculum for the subsequent growing season [3,4].

The main objective of this study is to review the research conducted worldwide on the genetic diversity of M. laxa and to assess its distribution in the fruit orchards in Uzbekistan.

2. Materials and Methods

Study object and sample collection

This study was conducted as a bibliographic review incorporating elements of comparative analysis on the genetic diversity of M. laxa populations. Relevant literature was systematically retrieved from international scientific databases, including Scopus, Web of Science, PubMed, Google Scholar, and ScienceDirect, focusing on publications released after 2000. For the experimental component, plant samples infected with Monilinia spp. were collected from fruit orchards located in the Tashkent, Bukhara, Namangan, Surxondaryo, Navoiy, Jizzakh, Sirdaryo, and Khorezm regions of Uzbekistan (Fig. 1).

Figure 1. Study areas across Uzbekistan

During field surveys, symptomatic fruits, leaves, and twigs exhibiting disease symptoms were carefully selected, and corresponding herbarium specimens were prepared. Diseased plant tissues were documented in situ using a Canon EOS 750D digital camera. In the laboratory, collected samples were processed under sterile conditions. Samples were first rinsed with distilled water, then surface-sterilized in a 2% sodium hypochlorite (NaOCl) solution for 1 minute, followed by rinsing with distilled water and air drying. Small fragments (0.1–0.3 mm) were excised from each sample and placed onto pre-sterilized Petri dishes. The dishes were covered with filter paper, and a small volume of distilled water was added. Petri dishes were then placed in desiccators and incubated at 27–28°C.

Mycological analysis and identification

The growth and development of the isolated fungi were monitored under a microscope 2–7 days post-inoculation. Microscopic examinations were performed using Moticam-5 N-300M and Kern Optics OBN-132 microscopes, along with other essential laboratory equipment. Morphological characteristics of the fungi, including the shape, size, and coloration of conidia, as well as the structure of conidiophores, were assessed following internationally accepted mycological identification protocols. Taxonomic identification was conducted using classical morphological criteria and comparative analysis with published literature.

Assessment of disease distribution and severity

The regional distribution and intensity of plant infection were determined based on the methodologies proposed by Dementeva and Sheraliyev [5,6]. Disease incidence (R, %) was calculated using the formula: R = (n/N) × 100 where R – is the disease incidence (%), n – is the number of infected plants, and N – is the total number of plants examined. disease intensity (I, %) was calculated according to the formula: I = (Σ (a × b) / (A × B)) × 100 where a – represents the number of plants assessed at a given disease severity score, b – is the score value, A – is the total number of plants examined, and B – is the maximum score. Using this approach, the distribution, intensity, and host-specific damage caused by the disease across different regions were determined and subjected to statistical analysis.

3. Results and Discussion

The assessment of genetic diversity within and among populations of fungal species has been a central topic in plant pathology research. Various molecular techniques, including inter-simple sequence repeat (ISSR), restriction fragment length polymorphism (RFLP), amplified fragment length polymorphism (AFLP), and randomly amplified polymorphic DNA (RAPD) fingerprinting, have been widely applied to analyze the genetic variability of fungal pathogens [7,8,10,11,12]. Within the Monilinia genus, studies on genetic diversity have primarily focused on M. fructicola [9,10,12], whereas similar investigations on M. laxa have been comparatively limited [7,8,9]. These studies collectively highlight the usefulness of molecular fingerprinting techniques for understanding population structure, evolutionary relationships, and the epidemiology of Monilinia species.

In studies examining the genetic diversity of Monilinia laxa, Fulton et al. reported population-level variation that appeared to be randomly distributed on a global scale based on RAPD marker analyses [4]. In one of the first extensive investigations of M. laxa populations, Gell et al. (2007) demonstrated that the grouping of M. laxa isolates was independent of their geographical origin, indicating no clear pattern related to whether isolates originated from the same or different orchards [7]. Furthermore, the authors found no relationship between the clustering of isolates and the year of collection or host species.

In contrast, Gril et al. (2008) identified significant genetic differentiation between isolates obtained from apple trees and those collected from other host plants. However, no additional grouping related to other host species was detected. Their study, which utilized an AFLP marker system, provided further insight into the genetic diversity and host-related variation within M. laxa populations [8].

During rainy spring seasons, M. laxa can lead to significant crop losses in stone fruit orchards [3]. The severity of blossom blight can often be managed in conventionally grown orchards through one to three applications of protective or systemic fungicides during the flowering period, depending on local weather conditions [13]. However, under favorable environmental conditions, controlling brown rot remains challenging [2,3]. One of the main difficulties in disease management stems from the limited understanding of the genetic structure of M. laxa populations [14,7]. To date, only a few studies have explored the relationship between fungicide treatments and the genetic composition of plant pathogen populations [4].

Fazekas et al. (Hungary) showed that the clustering of M. laxa isolates was independent of host species, corroborating earlier observations by Gell et al., who reported no grouping according to peach, almond, or apricot [4]. In contrast, Gril et al. (2008) found host-specific differentiation between apple and other hosts, although no further clustering among stone fruits was detected, consistent with the Hungarian results [8]. The study also demonstrated that most fungicides effectively inhibited M. laxa mycelial growth regardless of geographic origin or host, with some isolates exhibiting reduced sensitivity to boscalid – piraclostrobin, elementary sulphur, cyprodinil, fenhexamid, and prochloraz. Reduced efficacy was generally associated with frequent application in seasonal programs, except for elementary sulphur, whose inherently low activity against Monilinia spp. is well documented. In conclusion, the Hungarian M. laxa population displays high genetic diversity independent of location, host, inoculum source, or fungicide sensitivity. This variation likely arises from pathogen migration among orchards and hosts, underscoring the key role of sanitation practices in the management of brown rot at both local and regional scales [4].

As a result of mycological investigations conducted across various regions of Uzbekistan, samples of fruit trees infected with by M. laxa were collected. Based on these samples, the distribution characteristics of the disease, the degree of plant infection, and specific symptomatic features were analyzed. For each crop species and cultivar, the incidence of M. laxa, morphological manifestations of the disease, and infection severity were evaluated. The results indicated that the pathogen is widely distributed in certain fruit tree species, while in some cases, severe damage to fruits and vegetative parts was observed. Detailed observations on disease incidence and symptomatic features for each crop species are presented below.

Apricot (Prunus armeniaca L.)

Apricot brown rot caused by M. laxa is a highly destructive fungal disease that significantly reduces yield and fruit quality. The pathogen actively develops from the flowering stage and affects both generative and vegetative plant organs. Initial disease symptoms appear after flowering and are characterized by unexpected reddening, wilting, and dark necrotic lesions on flowers (Fig. 2).

Figure 2. Apricot blossoms infected with monilial blight

Infected twigs, leaves, and young buds quickly desiccate, resembling a “burnt” appearance. The disease is particularly severe during cool and humid weather conditions, which favor spore germination, infection of plant tissues, and rapid disease spread. Consequently, reproductive organs are destroyed, leading to a substantial reduction in yield. These findings emphasize the ecological and phytosanitary significance of M. laxa infection in apricot-growing regions and highlight the necessity of developing integrated disease management strategies.

The study also revealed differential susceptibility of apricot cultivars to M. laxa. High susceptibility was observed in the “Shalakh”, “Qora orik”, and “Gulungi luchchak” cultivars, with disease incidence (R) ranging from 35–45% and disease intensity (I) from 45–55%. Moderate susceptibility was recorded in the “Navoi”, “Korsodiq”, and “Khurmoi” cultivars, with R = 25–35% and I = 35–45%. Low susceptibility was characteristic of the “Isfarak”, “Ruhi juvanon”, and “Sibir orik” cultivars, with R = 10–20% and I = 15–30%.

Regional comparisons indicated the highest infection levels in Samarkand (R = 38%, I = 50%) and Namangan (R = 36%, I = 48%), whereas the lowest levels were observed in Sirdaryo (R = 18%, I = 25%) and Khorezm (R = 15%, I = 20%). These results demonstrate the differential response of apricot cultivars to M. laxa, as well as the direct influence of ecological and agroclimatic factors on disease distribution.

Sweet Cherry (Prunus avium L.)

In sweet cherry, Monilinia laxa infects flowers, young shoots, and leaves. Infected tissues typically develop light brown discoloration, which serves as a clear visual indicator of the disease. Blossom blight symptoms, characterized by necrotic and wilted flowers, are common not only in cherry but also in other fruit trees such as almond, peach, plum, and apricot. Disease development is most pronounced during spring under cool and rainy conditions, which promote spore germination and rapid infection of susceptible tissues.

Peach (Prunus persica L.)

M. laxa is one of the major pathogens causing blossom and twig blight in peach cultivars. The first symptoms of the disease usually appear in early spring. During our observations, the initial signs of infection were detected in late March to early April, when the pathogen penetrated through the floral openings or wounds on the plant tissues [15]. The period of highest susceptibility was recorded from the bud swelling stage to the full opening of the petals. Once the flowers are completely infected, both the blossoms and certain young fruit tissues turn light brown, which clearly indicates the development of the disease.

The study of M. laxa distribution among different peach cultivars revealed that the morphological structure of the varieties directly affects their resistance to the pathogen. Traditional “hairy peach” cultivars exhibited moderate susceptibility to infection, with a disease incidence of R = 25–35% and an intensity of I = 35–45%. In contrast, nectarine varieties, which possess a smooth fruit surface that facilitates rapid spore spread, showed slightly higher rates of infection (R = 30–40%, I = 40–50%).

Regional analysis demonstrated that the highest infection levels were observed in Namangan (R = 35%, I = 45%) and Samarkand (R = 33%, I = 42%) regions. The lowest levels were recorded in Syrdarya (R = 18%, I = 25%) and Khorezm (R = 15%, I = 20%) regions. These findings confirm that fruit pubescence and skin thickness have a direct influence on pathogen penetration. According to the regional assessment, M. laxa infection is most active in areas of moderate humidity such as Samarkand, Namangan, and certain parts of Kashkadarya, whereas its spread remains limited in dry and hot regions like Bukhara, Syrdarya, and Khorezm.

Almond (Prunus amygdalus Batsch)

Similar to its manifestation in apricot, cherry, and peach, the disease is characterized by blossom blight, and the infection of young shoots and fruits [15]. In almond trees, the spring form of moniliosis appears during the flowering period. The disease is expressed by the reddening and wilting of blossoms, followed by the drying of leaves and young shoots (monilial blight). The most susceptible stage of the plant is during flowering, when blossoms suddenly wither and turn brown. Infected fruits initially develop small brown spots, which rapidly enlarge and cover the entire fruit surface within a few days (Fig. 3).

Figure 3. Almond fruits infected with monilial blight

The distribution and incidence levels of M. laxa among almond cultivars were investigated, and the results are presented in table 1.

Table 1. Distribution of M. laxa in almond cultivars in Uzbekistan

Studies on M. laxa across multiple countries have revealed substantial genetic diversity within populations, largely independent of geographic origin, host species, or year of collection. Molecular markers such as RAPD and AFLP have proven effective in elucidating population structure and host-related variation, underscoring the complex nature of pathogen populations in local orchards.

4. Conclusions

Based on the results of field and laboratory studies, it can be concluded that disease development varies among apricot, cherry, peach, and almond cultivars and is strongly influenced by climatic conditions, relative humidity, and cultivar-specific traits. In Uzbekistan, disease incidence generally ranges from 15% to 45%, although periods of high spring humidity can increase infection rates to 50–55%. Regions such as Samarkand and Namangan, characterized by moderate temperatures and high humidity, exhibit the highest disease prevalence, whereas dry and hot regions including Bukhara, Syrdarya, Navoiy, and Khorezm tend to restrict pathogen spread.

Among the cultivars studied, apricot varieties such as “Shalax,” “Qora orik,” and “Gulungi luchchak,” as well as cherry varieties “Valeriy Chkalov” and “Savri Surkhoni,” showed high susceptibility, while cultivars including “Isfarak,” “Ruhi juvanov,” “Bahor,” “Sariq Drogana,” “Bostanliq,” and “Nikitin” exhibited relative resistance. For peaches, susceptibility is largely influenced by fruit surface morphology, with smooth-skinned nectarines being more prone to infection compared to hairy peaches.

Disease development is most intense in spring and declines as fruits mature under high temperature and low humidity. Selecting resistant cultivars is a key strategy for managing brown rot in Uzbekistan. When combined with strict orchard sanitation measures – such as removal of mummified fruits, pruning of blighted twigs, and control of infected blossoms – resistant cultivars provide an effective foundation for disease control.

Overall, understanding the genetic diversity and population structure of M. laxa is crucial for predicting outbreaks and designing sustainable management strategies. Regular monitoring of pathogen populations, including assessment of fungicide sensitivity, supports targeted fungicide rotation programs, reduces the risk of resistance development, and enhances long-term control of brown rot in stone fruit orchards.