Characterization of Cochin ginger (Zingiber officinale Rosc.) genotypes

Abstract

Ginger (Zingiber officinale Rosc.) is a globally cherished rhizomatous spice acclaimed for its unique flavour, aroma, and therapeutic properties. It is a rich source of zingiberene, a monocyclic sesquiterpene that forms the primary component of its essential oil and imparts ginger’s unique flavour. India has the highest cultivar diversity of ginger in the world. Indian ginger is considered as the best in world market because of its high zingiberene and fibre content. These are marketed as whole, powder and in dried form. Among the export type ginger, Cochin Ginger (CG) has a great demand. The CG is a traded ginger variety grown in central region of Kerala. The CG is renowned for its quality features in the global market viz., α-zingiberene content, β-sesquiphellandrene, camphene, citral, starch and crude fibre content etc. The inner core colour of this rhizome is bright yellow. According to the specifications of the export industry, traded Cochin ginger should have zingiberene content ranging from 28 to 31 per cent, the volatile oil from 1.8 to 3 per cent and citral content from 0.29 to 0.7 per cent. Due to its high zingiberene content, Cochin ginger has gained popularity in the global market and is primarily exported to the USA and Europe. As the farmers in the state preferred cultivation of the high rhizome yielding varieties which fetches higher price by selling vegetable ginger and whole ginger, the cultivation of the local cultivars of the ginger such as Cochin ginger with a comparative lower rhizome yield but higher volatile oil and zingiberene content, is on the decline. The declining area of cultivation of the local Cochin ginger types has caused unavailability of the quality rhizomes for export purpose. This alarming situation was revealed by the All-India Spices Export forum in Kochi and subsequently raised as a query in the parliament demanding immediate solutions. The proposed research was thus conceived this pressing issue. The research thus focused on collecting, identifying pure Cochin ginger genotypes from the local genotypes and evaluating these on basis of yield and quality parameters. Thus, it will increase the production potential for meeting the export demands. The study was carried out from 2022 to 2024 at the Department of Plantation, Spices, Medicinal, and Aromatic Crops, College of Agriculture, Vellanikkara, Kerala Agricultural University, Thrissur. The study was centered on twenty-six genotypes, including a check variety (KAU Chithra) suitable for dry ginger. The CG genotypes were collected from ginger growing tracts of Idukki, Kottayam, Ernakulam, Thrissur, and Palakkad. These genotypes were evaluated for the morphological, biochemical, and yield traits. On analysis of the genotypes, considerable variation both in case of morphological and biochemical characteristics was observed. Among the morphological traits, CG 47, CG 44, CG 53, and CG 22 were identified as superior. Additionally, CG 47, CG 46, CG 53, and CG 52 excelled in rhizome traits and contributed the highest yield among the genotypes. Similarly, there was considerable variation in biochemical characteristics such as zingiberene, volatile oil, oleoresin, crude fiber, and starch content. Zingiberene, the most crucial biochemical compound in ginger, ranged from 21.30 per cent to 35.90 per cent across the genotypes. The CG 52 and CG 46 exhibited the highest zingiberene content. Based on these biochemical traits, CG 47, CG 46, CG 53, and CG 52 were identified as superior genotypes. Principal component analysis of the quantitative parameters revealed six principal components with eigen values exceeding one, collectively accounting for 79.79 per cent of the variability. Among the genotypes, diseases such as leaf spot and rhizome rot were detected and shoot borer infestation was also observed in the field. All genotypes were vulnerable to the shoot borer, except for CG 40, CG 44, CG 47, and CG 53. The incidence of leaf spot and rhizome rot was assessed using the per cent disease index (PDI). The PDI of leaf spot ranged from 0.00 to 68.44 per cent, while rhizome rot ranged from 0.00 to 64.20 per cent. On basis of the PDI, CG 29 was found to be highly susceptible to rhizome rot, and CG 44 showed susceptibility to leaf spot disease. The cluster analysis of the genotypes revealed four clusters. The cluster I contained four genotypes, the cluster II included five genotypes, and the cluster III consisted of four genotypes. The remaining thirteen genotypes were grouped into cluster IV. Correlation analysis of CG genotypes indicated that average rhizome yield was positively correlated with factors such as the number of leaves, leaf length, plant height, rhizome inter-node pattern, rhizome length, number of primary and secondary rhizomes, weight of primary and secondary rhizomes, as well as total rhizome weight per plant. Zingiberene content showed a positive correlation with dry recovery and volatile oil content. Fiber content was positively correlated with the number of tillers, rhizome length, and oleoresin content but was negatively correlated with the weight of the primary rhizome and rhizome width. Five top-performing genotypes were chosen based on the mean scores of transformed values for traits such as plant height, rhizome weight, average yield, volatile oil content, zingiberene, and fiber content. The selected genotypes were CG 27, CG 46, CG 47, CG 52, and CG 53. The volatile oil profiling from these promising genotypes were collected and analyzed using GC-MS. Chemoprofiling of the superior Cochin ginger genotypes revealed the presence of key compounds such as zingiberene, α-sesquiphellandrene, α-bisabolene, α-curcumene, α-citral, α-farnesene, and 1,8-cineol. Zingiberene content ranged from 29.61 per cent (CG 53) to 35.90 per cent (CG 52). α-sesquiphellandrene was highest in CG 52 at 16.85 per cent and lowest in CG 47 at 14.74 per cent. α-curcumene content varied from 5.18 per cent (CG 52) to 10.30 per cent (CG 53). Citral compounds were present in varying amounts, ranging from 0.71 per cent (CG 52) to 5.53 per cent (CG 47). The five promising genotypes CG 27, CG 46, CG 47, CG 52, and CG 53 were identified based on their rhizome yield and quality. The rhizome yield of these genotypes ranged from 12.08 t/ha (CG-52) to 30.92 t/ha (CG-47). As these genotypes meet the specifications of the export industry, they may be suitable genotypes for export purposes. Future research should focus on the molecular characterization of CG genotypes to identify key genetic markers and traits. Multi-location trials of the ideal genotypes will offer valuable data on their performance and adaptability across different environmental conditions. The superior CG genotypes may be taken up for large-scale multiplication in the niche areas to ensure a consistent supply of elite CG types. Securing a GI (Geographical Indication) tag for these genotypes may also increase their market value and recognition, preserving their unique identity and contributing to regional economic growth.