Morphological physicochemical and molecular characterisation of mango Mangifera indica L genotypes of Upper Brahmaputra Valley of Assam

Abstract

To study the extent of variation among the different mango genotypes of Assam, the present investigation entitled Morphological, physico-chemical and molecular characterisation of mango (Mangifera indica L.) genotypes of Upper Brahmaputra Valley of Assam was carried out during 2021-23 in Golaghat, Jorhat, Sivasagar and Tinsukia districts of Assam. A total of 100 accessions were surveyed out of which 33 accessions were finally selected based on acceptability. All the morphological characteristics were studied as per descriptor of IPGRI, Rome (2006). Results revealed significant variation in qualitative as well as quantitative traits. Tree height (tall, medium and dwarf) varied significantly among the accessions. Leaf features did not significantly differ between accessions, but flower color (yellowish green, yellow, and pink), panicle location (axillary, terminal, and terminal), and the presence of leafy bracts showed significant variations. Substantial differences in fruit shape (roundish, oblong, obovoid, elliptic) and fruit apex shape (round, obtuse, acute) were also observed. Stone and seed characteristics varied among the accessions with respect to type of veins on stone, quantity of fibre on stone, adherence of fibre to stone, seed shape and type of embryony. Quantitative characteristics of leaf, panicle, stone, seed and fruits also varied significantly among the accessions. Highest length:breadth ratio of leaf was observed in AMG-5 (8.89) and lowest in AMS-2 (2.78). Panicle length:breadth ratio was highest in AMS-7 (3.13) and lowest in AMJ-13 (1.04). The number of secondary rachis per panicle, sex ratio, number of fruits per panicle, per cent fruit drop and per cent fruit retention also varied. Study of physical characteristics of fruits revealed that accession AMG-2 had highest fruit weight 1206.48 g and 1197.92g both at harvest and at ripening respectively, whereas, fruit weight at harvest and ripening was lowest in AMG-5 86.31g and 75.67g, respectively. Similarly, significant variations were observed in characters like shape index, lenticels density, stone per cent, pulp: stone ratio, waste index and pulp percent. Study also revealed significant differences in chemical characteristics of fruit. TSS was highest in AMS-6 (18.80°Brix) and lowest in AMJ-13 (10.26°Brix). TSS: Acidity ratio was highest in AMJ-11 (91.00) and lowest in AMG-7 (24.50). Ascorbic acid content was highest in AMT-1(52.70 mg/100g) and lowest in AMJ-14 (22.63 mg/100g). Other chemical characteristics of fruits like total sugar, sugar:acid ratio, carotenoid content, moisture content also significantly varied among the accessions. The PCA for 55 quantitative characters in mango accessions revealed considerable variation among the accessions. 15 components displayed a total variation of 89.55% and were consequently considered to exhibit notable variance. 35 characters contributed to the 18.21% variation in PC1. Cluster analysis revealed maximum Euclidean distance of 17.10 that was observed between the two accessions of Golaghat, AMG-2 and AMG-8, and minimum Euclidean distance of 6.131 was observed between the two accessions of Sivasagar, AMS-3 and AMS-6 indicating that variation was influenced by genetic factor. Despite SSR markers demonstrating that there was no polymorphism, the occurrence of diversity in morphological and physiological traits necessitated additional molecular level studies using a wider array of markers. It can be concluded from the study of the accessions that there is considerable variation among them, and that accessions with distinguished characteristics can be exploited in mango improvement programmes.