Soil is a multifunctional ecosystem that supports the global exchange of materials and energy and is home to various microorganisms [1, 2]. Microorganisms perform diverse functions in the soil, such as participating in biogeochemical cycles, dissolving nutrients, stabilizing soil particles, and controlling pests and diseases [3, 4]. Yeast, a common species found in the soil, plays an important role in maintaining the ecological functioning of the soil, promoting plant growth, and protecting plants from pests and diseases [5]. For example, yeasts isolated from soil (e.g., Filobasidium magnum, Naganishia albida, and Lipomyces spp.) are known to produce extracellular polymeric substances that protect themselves from adverse environmental conditions, as well as promote the formation of soil aggregates to enhance the stability of the soil structure [6–8]. Plant roots support the survival of yeast species by secreting carbohydrates and organic acids (i.e., amino acids and carboxylic acids). Yeast, in turn, contributes to plant growth and development by producing substances, such as Indole-3-acetic acid (IAA), and by dissolving large amounts of nutrients, such as phosphorus and calcium [2, 9–11]. Some soil yeasts are also present as antagonists of pathogens, such as Verticillium dahliae and Pythium aphanidermatum, and thus protect the plant from diseases [11, 12]. Additionally, several functional yeasts, such as oleaginous yeast and producing high level of 3-hydroxypropionic acid yeast, which are widely used in agriculture, industry, and pharmaceutical production, can be isolated from the soil by culture-dependent methods [13–15]. The size, diversity, and structure of the soil yeast community are known to be influenced by factors, such as soil type, plant species, and geographic location [5]. Moreover, special ecological environments can help yeast species develop tolerance to conditions, such as high/low temperatures, drought, salinity, etc [16]. Therefore, it is vital to study the diversity, community structure, and adaptation strategies of yeast in soils in special environments, which can provide more information regarding yeast resources.
Xinjiang is located in the hinterland of Eurasia, a transition zone between the dry summer zone of Europe and the humid summer belt of East Asia [17]. The special climatic conditions of this region, such as large differences in temperature between day and night and its long hours of daylight, promote the richness of melon and fruit resources [18]. Rich sugar sources in orchard ecosystems promote yeast survival. Moreover, the harsh natural environment of dry summer and cold winter is known to drive yeast evolution, resulting in improved species diversity of yeast [17]. Some studies have used culturable methods to identify 12 genera and 26 species of yeast in the soils from 52 vineyards in 28 autonomous prefectures or counties in Xinjiang, and isolated and identified 12 genera and 17 species of yeast in the soils of peach orchards in northern Xinjiang, followed by the screening of 23 strains of yeast with selenium-rich and protease-producing functions [17, 19]. Saccharomyces cerevisiae with excellent fermentation properties was also isolated from pear orchards, pomegranate orchards, and several vineyards in Xinjiang [20–24]. However, little is known about the yeast species in the soil of melon crops in Xinjiang. Hami melons are popular worldwide and are considered to be a national geographic product and the king of melons in China due to their pleasant aroma, crisp taste, sweetness, and color [25]. The central production areas of Hami melon are the Turpan-Hami Basin, northwest and southwest of Tarim Basin, as well as the north slope of Tianshan Mountain. These areas provide more than 100 varieties of Hami melon [26, 27]. Currently, the research on Hami melon yeast is mainly focused on the screening of antagonistic yeast to prevent postharvest diseases and control the bacterial fruit blotch disease [28–32]. However, the diversity and composition of the yeast community in the soil of Hami melon orchards in different areas of Xinjiang are unclear; this has created a bottleneck for the in-depth understanding of the adaptation mechanism of Hami melon soil yeast species, its beneficial functions, and consequently for the development of yeast resources in Xinjiang.
In recent years, research on the yeast species from orchard soils has been done using the culture-dependent method. This method is useful for isolating diverse yeast cultures, enriching the resources bank of yeast strains, screening of useful strains for food, industry, medicine, etc.; however, only a few yeast species have been identified in soil samples using culture-dependent methods, and the possibility for studying microbial population dynamics in an individual environment is limited compared with culture-independent methods [33, 34]. Illumina MiSeq high-throughput sequencing is an emerging technology, which allows comprehensive and accurate detection of the species composition, generates large data volume with greater coverage and detects low-abundance species in various habitats compared with traditional culture methods [35]. The aim of this study was to quantitatively analyze the diversity and structure of rhizosphere soil yeast communities in Hami melon orchards in different regions of Xinjiang using Illumina MiSeq high-throughput sequencing technique and to explore the factors that influenced the differences in the formation of yeast community structures in different regions. To the best of our knowledge, this is the first study to analyze the yeast diversity in the soil rhizosphere in Hami melon of Xinjiang using high-throughput sequencing. Our results offer new insights into the in-depth understanding of the diversity and structure of yeast communities in the soil of Hami melon orchards in different regions of Xinjiang, providing supplemental information on the yeast resources in Xinjiang orchards.