Phenotypic characterization and morphological diversity of Tendu (Diospyros melanoxylon Roxb.) genotypes from Southern Rajasthan

Introduction

Tendu (Diospyros melanoxylon Roxb.), a member of Ebenaceae, is an indigenous multipurpose tree species distributed widely across the Indian subcontinent. The species has a diploid chromosome number of 2n = 30 and occurs under a broad range of environmental conditions (Wallnofer, 2001) [14] . Its capacity to persist under dry tropical conditions, together with reported tolerance to drought and frost, contributes to its ecological importance in tropical dry deciduous forests (Hmar et al., 2017) [2] . Tendu is also closely associated with the livelihoods of rural and tribal communities. Its leaves are particularly important as a raw material for the bidi industry, while its fruits, wood and other plant parts have food, medicinal and domestic uses (Jamil et al., 2020) [4] . Although Tendu has considerable socioeconomic and ecological value, much of its genetic resource base remains represented by naturally occurring forest populations, with comparatively limited systematic domestication and orchard development. Habitat degradation, deforestation and unsustainable exploitation reinforce the need to document, conserve and characterize the available diversity (Kala, 2013) [5] . Morphological characterization provides a practical initial approach for identifying phenotypically distinct trees and establishing a foundation for subsequent conservation and utilization programmes (Patel et al., 2021) [10] . Morphological traits, however, are not determined exclusively by genotype. Their expression can vary with environmental conditions, making observations across seasons and multiple traits particularly useful when assessing field populations (Lal et al., 2001) [6] . Southern Rajasthan, encompassing Udaipur, Salumber, Pratapgarh, Banswara and Dungarpur, contains natural Tendu populations distributed across environmentally heterogeneous landscapes (Jain et al., 2005) [3] . Such geographic and environmental variation offers an opportunity to document phenotypic diversity within the species (Malik et al., 2010) [9] . Therefore, the present study was undertaken to characterize morphological variation among Tendu genotypes from southern Rajasthan, with emphasis on leaf and inflorescence descriptors, and to identify contrasting genotypes suitable for further characterization, conservation and utilization.

Materials and Methods

Study period and survey area

The investigation was conducted during two consecutive fruiting seasons, 2023-24 and 2024-25. Field observations were made in Udaipur, Salumber, Pratapgarh, Banswara and Dungarpur districts of southern Rajasthan. The surveyed sites extended approximately from 23.48690 to 24.898640° N latitude and 73.4295820 to 74.78180° E longitude, with elevations ranging from 222 to 736 m above mean sea level. The study area represented the Humid Southern Plains and the Sub-humid Southern Plains and Aravalli Hills agro-climatic regions.

Genotype identification and field observations

Thirty naturally occurring Tendu genotypes were identified and assigned the codes MPUAT-TU1 to MPUAT-TU6, MPUAT-TS7 to MPUAT-TS10, MPUAT-TP11 to MPUAT-TP23, MPUAT-TB24 to MPUAT-TB27 and MPUAT-TD28 to MPUAT-TD30. Representative trees were selected in their natural habitats according to predefined field selection criteria. Observations were recorded during the flowering-to-fruiting period from April to July in each year.

Morphological descriptors and measurements

Qualitative characterization included foliage density, mature leaf colour, leaf lamina surface and pedicel attachment. Foliage density was visually categorized as sparse or dense. Mature leaf colour was assessed under natural daylight according to predominant pigmentation, while lamina surface was assessed visually and by gentle tactile observation and classified as smooth or glabrous. Leaf and inflorescence measurements were obtained from representative samples of each genotype. Leaf length-to-width ratio was calculated using the corresponding mean leaf length and mean leaf width. Inflorescence diameter was measured at the widest point with a digital Vernier caliper, and the inflorescence length-to-diameter ratio was calculated from the corresponding mean measurements. Five mature leaves or representative inflorescences were used for the relevant measurements in each replication. Genotype-wise observations were recorded for both seasons, and pooled values were used to summarize the two-season observations.

Results

Qualitative phenotypic variation

The surveyed Tendu germplasm exhibited clear qualitative differences among genotypes. Both sparse and dense foliage types were observed. Mature leaf colour varied between green and dark green, while smooth and glabrous lamina surfaces were recorded. Among the 30 genotypes, 20 (66.66%) possessed dark green leaves and 10 (33.33%) possessed green leaves. Calyx-lobe type pedicel attachment was recorded for all genotypes. These descriptors provided readily observable characters for preliminary discrimination of the surveyed material. 2.

Discussion

The observed qualitative and quantitative differences confirm appreciable phenotypic heterogeneity within the surveyed Tendu germplasm. Variation in leaf colour, lamina characteristics and foliage density offers practical descriptors for preliminary fieldlevel discrimination. The predominance of dark green foliage, recorded in two-thirds of the genotypes, may reflect differences in pigment-associated phenotypes; however, leaf pigmentation can also respond to environmental variables such as light, temperature, nutrient availability and developmental stage (Taiz et al., 2015; Li et al., 2023) [12,8] . Variation in leaf dimensions was reflected in the leaf length-towidth ratio, which extended from 1.40 to 2.48 on a pooled basis. MPUAT-TU1 displayed the most elongated leaf proportion, whereas MPUAT-TB27 exhibited the lowest ratio. Similar variability in Tendu leaf morphology has been reported previously (Toppo et al., 2020) [13] . Leaf form is influenced by both genetic constitution and environmental factors, including light regime, temperature, water availability and nutrient status (Lambers et al., 2008; Ren et al., 2020) [7,11] . Consequently, the repeated observation of contrasting phenotypes over two seasons supports their usefulness as preliminary descriptors, although evaluation under a common environment would be required to strengthen conclusions concerning genetic control.

Reproductive morphology also differed substantially among the genotypes. Pooled inflorescence diameter ranged from 1.21 to 1.91 cm, while the length-to-diameter ratio ranged from 1.14 to 2.01. MPUAT-TB24 was characterized by the largest pooled inflorescence diameter, whereas MPUAT-TP13 combined the smallest diameter with the highest length-to-diameter ratio. Such contrasting combinations suggest differences in reproductive architecture among the surveyed trees. At the same time, flowering and inflorescence development can be modified by genotype, temperature, light, moisture, nutrient availability and genotype × environment interaction (Taiz et al., 2015) [12] . Morphological characterization should therefore be viewed as an initial layer of germplasm assessment rather than definitive evidence of genetic relatedness. Integrating field descriptors with molecular approaches can improve the resolution of diversity analysis. Morphological descriptors are accessible for preliminary classification, whereas molecular markers can provide complementary evidence of genetic relationships because they are less directly influenced by the immediate environment. SSR and other PCR-based marker systems have been used effectively for diversity assessment in Diospyros and other fruit crops (Gajera et al., 2018) [1] . The contrasting genotypes identified in the present investigation can consequently serve as candidate material for subsequent molecular characterization and conservation-oriented studies.

Conclusion

The 30 naturally occurring Tendu genotypes surveyed across southern Rajasthan showed substantial qualitative and quantitative phenotypic diversity. Differences were evident in foliage density, mature leaf colour, lamina surface, leaf proportions and inflorescence architecture. On a pooled basis, leaf length-to-width ratio ranged from 1.40 to 2.48, inflorescence diameter from 1.21 to 1.91 cm and inflorescence length-todiameter ratio from 1.14 to 2.01. MPUAT-TU1, MPUAT-TB27, MPUAT-TB24, MPUAT-TP13 and MPUAT-TP19 represented particularly contrasting phenotypes for the major descriptors. The study establishes a useful baseline for morphological characterization of Tendu germplasm in southern Rajasthan and identifies material suitable for further molecular validation, conservation and utilization. Because quantitative morphological traits may respond to environmental conditions, controlled or replicated common-environment evaluation should precede definitive breeding or domestication selections.

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