Morphological Variability Between Geographical Provenances of Walnut Fruit (Juglans Mandshurica) in the Eastern Liaoning Province, P.R
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Pol. J. Environ. Stud. Vol. 30, No. 5 (2021), 4353-4364 DOI: 10.15244/pjoes/131806 ONLINE PUBLICATION DATE: 2021-05-21 Original Research Morphological Variability between Geographical Provenances of Walnut Fruit (Juglans mandshurica) in the Eastern Liaoning Province, P.R. China Lijie Zhang1,2, Xiujun Lu1,2, Qiang Zhou1, Jifeng Deng1,2* 1College of Forestry, Shenyang Agricultural University, Shenyang, Liaoning Province, People’s Republic of China 2Key Laboratory of Forest Tree genetics and Breeding of Liaoning Province, Shenyang, Liaoning Province, People’s Republic of China Received: 5 October 2020 Accepted: 18 December 2020 Abstract The eastern Liaoning Province of China has rich morphological diversity in walnut fruit, which is beneficial for selecting promising characters for marketability purposes. However, only a few reports have addressed morphological diversity in this region. In this study, J. mandshurica nuts and kernels from six geographical provenances were assessed for morphological traits, such as nut longitudinal diameter, nut lateral diameter, nut transverse diameter, mean diameter, nut weight, kernel weight, shell thickness, nut sutural thickness, kernel percentage, and index of roundness. Morphological traits proved to be quite variable and showed differences both within and among the geographical provenances. The frequency distribution of the traits had single peaks and followed a normal distribution. Principal component analysis revealed that 81.062% of the total variance was explained by the first three components. An unweighted PGM with averaging cluster analysis divided the geographical provenances into two groups; cluster I, containing five geographical provenances, and cluster II, containing only one. The study highlighted that the traits related to nut weight were of importance for discrimination, and Fushun is the optimal geographical provenance for breeding and selection. This study could provide a basis and reference for further understanding of the genetic resources of Juglans mandshurica fruit types. Keywords: Phenotypic diversity, Juglans mandshurica, Eastern Liaoning Province, variation, principal component analysis *e-mail: [email protected] 4354 Zhang L., et al. Introduction J. mandshurica resources in recent years [23]. At present, the yield of J. mandshurica walnut fruits Geographical provenance (a distinct geographical has declined sharply, and the timber yield accounts place to obtain seeds or propagating materials, which for less than 1% of the total timber output in the originated from the same tree species) variation of eastern mountainous areas of Liaoning, China [26]. forest trees plays an important role in tree breeding Therefore, there is an urgent need for development studies and is of great significance for efficient and sustainable utilization of J. mandshurica. Previous utilization of their germplasm resources [1-2]. The studies on germplasm resources of J. mandshurica fruit facilitates species reproduction and has relatively from northeastern China revealed that J. mandshurica stable reproduction characteristics, which show strong is a monoecious plant with different flowers and has adaptability in complex and changeable environments two mating types, which are randomly distributed in [3]. Morphological traits are specific and genetically the population. The reproductive characteristics of J. stable external reproductive characteristics, which are mandshurica during its dioecious maturation lead to the result of interactions between genetic variation and the rare flowering of male and female flowers, which environmental factors [3]. Variations in morphological seriously affects the pollination and fruit setting rate, traits reflect the variability of genotypes, populations, thus affecting its yield and quality [26-27]. Though ecotypes, and geographical provenance [4-5]. Over J. mandshurica has been extensively studied, most the last few decades, scientists have found that studies have focused on its pharmacological properties there are considerable variabilities in morphological [28-33] and population dynamics [34]. Few reports, traits within and among geographical provenances to our knowledge, have addressed the morphological under the influence of eco-environmental stress, and variability of walnut fruits in the eastern Liaoning fruit morphological traits may vary greatly among Province, P.R. China, which has the greatest natural individuals, even within the same geographical distribution of J. mandshurica. Therefore, the aim provenance [6-8]. Some fruits show strong adaptability of the present study was to utilize morphological and have more flexible survival strategies [9-10]. characteristics to assess the differences in geographical Therefore, studying the phenotypic variations of fruit is provenances of J. mandshurica naturally grown in the helpful to understand the effects of environmental and eastern Liaoning region. This is the first report, to our genetic factors on species and how well plants adapt knowledge, on the morphological variability of walnut to environmental changes in distributed areas through fruits grown throughout this area and would provide long-term selection and evolution. Moreover, it provides a basis for effective management and sustainable the basis for forest improvement and breeding, ex situ utilization of J. mandshurica. conservation, seed selection, seed production, and genetic diversity protection [11-16]. Juglans mandshurica is commonly known as Materials and Methods “hickory” and is included in the “three hard and broad tree species” along with Fraxinus mandshurica Field Survey and Phellodendron amurense, which are tree species distributed in the northeastern forest region of China Based on geographical distribution, climate [17-18]. J. mandshurica is a tertiary relict species and differences, and local heterogeneity in the eastern is a national class II and class III protected rare plant Liaodong region, six representative natural geographical and endangered tree species in China [19]. Natural provenances of J. mandshurica were selected along J. mandshurica forests are mainly distributed in the Changbai mountain ranges: Benxi, Dandong, the Xiaoxinganling Mountains, Wanda Mountains, Xinbin, Qingyuan, Huanren, and Fushun (Table 1). Changbai Mountains, and the eastern mountainous The plots were determined in the spring of 2017; for areas of the Liaoning province in China, and partly each provenance, three 100×100 m plots were set up in far eastern Russia, North Korea, and Japan [20- as replicates, and for each plot, the topography was 21]. J. mandshurica has substantial economic value, flat and without human interference. No major natural because of its nutritional, medicinal, and collection disasters such as fire, pests, or disease occurred in values. In general, the nut kernels contain 57%-65% the selected regions over the last decade. In the early fat, of which 3%-6% are saturated fatty acids; 1950s, a large-scale fire almost destroyed the original 15%-29% protein; and 5%-7% fiber, of which 25% is forest, resulting in the natural regeneration of the site soluble. The kernels also contain small amounts of plant to a secondary forest, which was composed of Fraxinus sterols and other phytochemicals. Moreover, walnuts mandshurica, J. mandshurica, and Quercus mongolica are the only nut that is rich in ALA Omega-3s, which in the tree layer. In the early 1960s, patches of the F. are essential fatty acids to various body processes [20, mandshurica and Q. mongolica forests were partially 22-25]. However, the existing J. mandshurica resources cleared. The selected plots were located on slopes are distributed mostly as natural forests, and due to between 18° and 23° and at elevations ranging from 400 excessive logging, the imbalance between harvesting to 550 m asl. The soil in all stands was typical brown and breeding has led to imminent danger for the natural forest soil. The forest stands were all half-mature, Morphological Variability between Geographical... 4355 Table 1. Topographical and climatological data of the geographical provenances. Average Average Maximum Lowest air Frost-free Geographical annual annual air Latitude Longitude temperature period Provenance temperature precipitation temperature (ºC) (d) (ºC) (mm) (ºC) Benxi 40°49′–41°35′ 123°34′–125°46′ 5.85 876.25 33.0 –32.0 127 Dandong 39°43′–41°09′ 123°22′–125°42′ 7.43 931.20 36.0 –17.0 173 Xinbin 41°14′–41°58′ 124°15′–125°57′ 5.47 898.60 29.0 –12.0 150 Qingyuan 41°47′–42°28′ 124°20′–125°28′ 4.97 775.59 37.0 –38.0 120 Huanren 40°25′–41°34′ 124°43′–125°47′ 5.66 946.55 28.0 –19.0 153 Fushun 41°14′–42°28′ 123°39′–125°28′ 6.04 800.64 38.0 –33.0 145 stand canopy density was above 0.6, and the height ...where, LonD is nut longitudinal diameter, TD is nut of the secondary forests was 15-20 m. Superior trees transverse diameter, LatD is nut lateral diameter, and (based on the diameter at breast height, tree height, MD is mean diameter. height under living branches, crown width, and shape) were simultaneously investigated from late August IR = (TD+ LatD ) (2× LonD ) (2) to early September (surveyed 6 times per month) for morphological diversity analysis based on their mature ...where, IR represents index of roundness. period. Fruit Appearance Morphological Data Nuts from our sample trees were preliminarily For each provenance, 10 sample trees were selected classified as 12 shape forms: spherical, spherical with in every plot; in total, 180 sample trees were selected one-side saddle-backing,