Characterization of Alleppey turmeric(Curcuma longa L.) genotypes

Abstract

Turmeric (Curcuma longa L.) is a major rhizomatous spice grown in India belonging to the Zingiberaceae family. It is recognized as a rich source of curcumin, a bright yellow bioactive polyphenolic pigment that has been extensively studied for its health benefits. India has the highest cultivar diversity of turmeric and Indian turmeric is considered as the best in world market because of its high curcumin content and colour. These are marketed as whole, ground form and as extracts. Among the export type, Alleppey finger turmeric (AFT) is in great demand. AFT is a traded turmeric variety grown in central region of Kerala. During colonial rule, AFT was exported from Alleppey port located in Alleppey district of Kerala and hence the name Alleppey Finger Turmeric was derived. This turmeric is unique to the ideal higher colour value, more flavour and easy to grind. The inner core colour of this rhizome is deep yellow to orange. The curcumin content present in the turmeric ranges from 5 to 6.5 per cent, and the oil ranges from 1.8 to 3.5 per cent. Due to its high curcumin content, it has gained popularity in the global market and is primarily exported to the United States. However, the introduction of high yielding improved varieties for cultivation in Kerala has led to gradual decline in the AFT types. Recently, the members of All India Spices Export Forum raised the issue of non-availability of AFT for exports during the department related parliamentary standing committee meeting held in Kochi during 2022. In view of the non availability of AFT, the present study was carried out to collect, identify and evaluate AFT genotypes based on the growth, yield and quality parameters and thereby increase the production potential for export purposes. The study was conducted at the Department of Plantation, Spices, Medicinal and Aromatic Crops, College of Agriculture, Vellanikkara, Kerala Agricultural University, Thrissur during 2022 to 2024. The study included twenty eight genotypes including check varieties such as Kanthi and Shobha released from Kerala Agricultural University, Thrissur and IISR Alleppey Supreme from Indian Institute of Spices Research Calicut. AFT genotypes were collected from Idukki, Kottayam, Ernakulam, Pathanamthitta, Thrissur and Palakkad. These accessions were evaluated in the field for morphological, biochemical and yield traits. The data analysed showed wide variation in the morphological and biochemical characters. In the case of morphological characters AFT 21, AFT 45 and AFT 50 were found to be superior. AFT 45, AFT 12, AFT 31 and AFT 21 were superior in rhizome characters and contributed highest yield among the genotypes. The principal component analysis of quantitative parameters showed first five principal components with eigen value more than one and it contributed to the 72.92 per cent of variability. Similarly, wide variation was also observed in the biochemical characteristics such as curcumin content, volatile oil content, oleoresin content and starch content. Curcumin, the most important biochemical pigment in turmeric varied from 4.32 to 5.89 per cent in the genotypes. AFT 12 and AFT 21 had the highest curcumin content. Based on these biochemical parameters, AFT 12, AFT 19, AFT 21 and AFT 31 were found as superior. Principal component analysis of biochemical characters revealed that only one principal component had the eigen value more than one and it contributed to 52.73 per cent of cumulative percentage of variance. Among the genotypes diseases such as leaf spot, leaf blotch and rhizome rot were detected and infestation of pest such as shoot borer was also observed in the field. All the genotypes were susceptible to shoot borer and leaf spot. Incidence of leaf blotch was calculated based on per cent disease index (PDI). The PDI ranged from zero to 63.22 per cent. Kanthi, Varna and AFT 40 were highly susceptible to leaf blotch disease. Cluster analysis was done and genotypes were classified into three cluster. First cluster consisted of eleven genotypes and second cluster comprised of six genotypes. Remaining eleven genotypes were included in cluster III. Correlation analysis of AFT genotypes revealed that average rhizome yield was directly correlated with plant height, number of tillers, rhizome weight per plant, length of primary rhizome and width of rhizome. Curcumin content was positively correlated with leaf width, duration of crop, number and weight of mother rhizome. Conversely, it was negatively correlated with rhizome yield, number and weight of secondary rhizomes, length of primary rhizome, internodal length and volatile oil content. Five superior genotypes were selected based on the mean score of transformed values of characters such as rhizome weight per plant, average yield, curcumin content and oleoresin content. Selected genotypes were AFT 12, AFT 19, AFT 21, AFT 31 and AFT 45. The volatile oils of these promising genotypes were collected and subjected to GC-MS. Chemoprofiling of superior turmeric varieties revealed the presence of major compounds such as Ar-turmerone, turmerone, curlone, á-sesquiphellandrene, (ñ)-trans nuciferol, zingiberene, à-curcumene, 2-thujene etc. The Ar-turmerone content ranged from 28.10 (AFT 31) to 31.08 per cent (AFT 12). Turmerone content was superior in AFT 19 with 26.42 per cent and lowest in AFT 45 with 14 per cent. Curlone content varied from 18.07 (AFT 45) to 23.15 per cent (AFT 21). Together, these three compounds account for more than 60 per cent of the total identified compounds. The five genotypes viz., AFT 12, AFT 19, AFT 21, AFT 31, and AFT 45 were found promising genotypes based on rhizome yield and quality. These genotypes could be ideal genotypes for export purposes. However future evaluation on basis of multi location trials to be done to check their stability and future breeding programmes need to be checked out.