Reproductive biology and evaluation of kokum (garcinia indica (thouars) choisy) genotypes

Abstract

Kokum (Garcinia indica (Thouars) Choisy) is a valuable yet underutilized perennial fruit tree. It is gaining importance due to multifarious uses mainly in the preparation of pleasant and attractive beverages which have rich medicinal properties. Kokum is one of the native species exhibiting a complex nature of flowering and fruiting behaviour. In the present investigation, twenty nine genotypes of kokum maintained at College Orchard, Department of Fruit Science as well as ICARNBPGR, Regional Station, Vellanikkara were studied systematically for phenological growth stages, floral characters, growth, yield and quality parameters during the period 2019-2021. In kokum, a total of 7 principal growth stages and 35 secondary growth stages were identified and described by using extended Biologische Bundesantalt, Bundessortenamt and Chemische Industrie (BBCH) scale (Meier, 2001). The principal growth stage 0- the vegetative bud development recorded 17 days, stage 1- the leaf development stage took 48 days, stage 3- the shoot development extended for 65 days, stage 5- the reproductive bud development took 32 days, stage 6- flowering lasted for 11 days, stage 7- which represented the fruit development had the longest duration of 103 days and stage 8- the fruit maturity and ripening took 5 days. Among the twenty nine genotypes studied for floral characters, twelve genotypes were female, fifteen were male and one genotype produced bisexual flowers. Male flowers were of two types, type I male flowers were present in all the fifteen male trees, whereas type II male flowers were present in seven male trees. Variation was observed among the genotypes for qualitative characters of flower viz., position of inflorescence (axillary, terminal or both), calyx colour (greenish yellow to yellowish green), corolla colour (yellow to yellowish orange), nature of stamens (free in all male and bisexual flowers), presence of pistillode (present in type II male flower and absent in type I male flower), staminodes were observed in female flowers only and it ranged from 3.7 to 11.8 in number, stigmatic rays was tuberculate and it found to be similar in all the female genotypes. The genotypes varied significantly with respect to quantitative characters of flowers such as number of flowers per m2 (10.90 to 25.20), length (3.48 mm to 6.64 mm) and breadth (4.78 mm to 8.05 mm) of flower. Majority of the female trees produced solitary or in groups of two to three, whereas male and bisexual trees produced flowers in clusters. Female flowers were sessile or with small pedicels, whereas in male flowers, pedicel length ranged from 3.41 to 5.73 mm. The time of anthesis in all three types of flowers found to occur from 19.30 to 21.00 hours. The anther dehiscence in male and bisexual flowers were found to start simultaneously from 19.00 hours and it continued till 20.30 hours. Stigma receptivity was observed at the time of anthesis and it remained receptive for about 12 to 14 hours. Both type I and type II male flowers had round shaped pollen which measured about 5 µm diameter. The pollens of bisexual flowers were elongated with prominent ridges on the surface and showed same size as that of male pollen. Acetocarmine test revealed that 84.07 to 98.49 per cent of pollen were found to be viable in male and bisexual flowers of kokum. Controlled pollination was performed in different combinations, female tree as receptors and male (type I and type II flowers) as well as bisexual trees as donors for understanding pollination and fruit set behaviour in different sex form of kokum. Female trees crossed with type II male and bisexual flowers recorded 100 per cent fruit set. Female trees crossed with type I male flower recorded 60 per cent of fruit set, whereas bisexual flowers on selfing exhibited 50 per cent fruit set. In the present study, variation was noticed among the kokum genotypes with regard to the growth and leaf characters. Fruit characters were recorded from thirteen bearing genotypes and all these genotypes were found to vary significantly for the fruit characters. Fruit weight ranged from 12.17 to 40.14 g, fruit volume varied from 34.22 to 45.60 cm3 , fresh weight of rind varied from 7.15 to 21.01 g, dry weight of rind ranged from 1.09 to 3.07 g, rind to seed ratio ranged from 0.81 to 1.77 and rind thickness varied from 2.46 to 3.41 mm. Genotype, IC552528-3 recorded maximum number of fruits per m2 (71.10), ACC.FSC-9 had produced the highest number of fruits per tree (2258) and fruit yield per tree (60.64 kg). Kokum genotypes differed significantly for all the biochemical parameters except moisture content. Moisture content ranged from 82.91 to 90.34 per cent, titratable acidity ranged from 2.30 to 4.47 per cent, total sugars varied from 4.32 to 10.60 per cent, TSS ranged from 5.65 to 14.15 0Brix and anthocyanin content varied from 11.12 to 25.01 mg per 100 g. Genotypes were ranked based on the biochemical composition of the fruit rind. Genotypes, IC552528-3 and IC136687-3 which had significantly high TSS and low acidity were ranked as superior quality genotypes and these genotypes can be utilised for value addition. Based on the yield and quality parameters nine genotypes were selected for organic acid profiling of kokum rind. The Liquid Chromatography Mass Spectrometry (LCMS) analysis revealed that eleven major constituents are present in kokum rind. Total organic acids in the genotypes varied from 47.12 (IC342319-2) to 759.29 mg/g (ACC.FSC-1). Among the different organic acids, hydroxycitric acid (HCA) was predominant (1908.48 mg/g) followed by citric acid (1254.89 mg/g). Significantly the highest HCA (652.52 mg/g) was recorded in ACC.FSC-6. It has antiobesic, anticholesterol and UV protecting properties and hence, genotypes which are found rich in HCA can be utilised by the pharmaceutical industries. Cluster analysis of kokum genotypes based on organic acids formed five different clusters. Genotypes under the same cluster showed more similarity in bioactive compounds. Principal component analysis distinguished distribution of organic acid constituents into two axes. The axes first two principal components explained 63.03 per cent of total variance. The knowledge on variability of chemical constituents has vital role in identification of chemotypes which pave way for investigation on therapeutic potential of genotypes.