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Genetic Analysis of Avocado (Persea americana L.) Genotypes for Fruit and Nutritive Traits

Avocado (Persea americana Mill.) or butter fruit is one the important nutritious sub tropical fruit native to Central America. Fruits are rich in nutrients, vitamins and phytochemicals. Fruit pulp is rich in fat and low in sugar content. Avocado exhibits wider variability due to protogyny nature of flower. However exploitation of this variability is very meager. The present study was conducted at Horticultural Research Station, Tamil Nadu Agricultural University, Thadiyankudisai to study and to find out suitable genotypes for further crop improvement programme. A field survey was conducted in Lower Pulney hills area and identified more than 100 genotypes and subjected to fruit characterization by using IPBGR descriptor. Sixteen genotypes were selected out of 100 genotypes based on the fruit characters and did nutritive analysis. Among the sixteen genotypes the avocado genotype TKDPA 93 recorded higher values for fruit length, fruit diameter, peduncle length, peduncle diameter and fruit weight. The genotype TKDPA 87 showed overall superior performance for nutritive traits viz. fat, dietary fibre, carbohydrate, carotene, vitamin C, calcium and phosphorus. The estimates of genetic parameters showed that the highest phenotypic variance was observed with the traits fruit weight, phosphorus content, fat content and peduncle length. Similarly the highest genotypic variance was observed with fruit weight, peduncle length and fat content. The maximum phenotypic co efficient of variance was noted with fruit weight, peduncle length, peduncle diameter, carotene content and pedicle length. The maximum genotypic co efficient of variance was noted with fruit weight, peduncle length, peduncle diameter, carotene content and pedicel length. GCV: PCV values were near unity for the traits fruit weight, peduncle length, peduncle diameter, carotene content, pedicel length and fruit diameter suggested that these traits are less influenced by the environment and can be used as a selection indices for avocado genetic improvement programme.


INTRODUCTION
Avocado (Persea americana Mill.) popularly known as butter fruit belongs to the family Lauraceae, is originated in Mexico, or possibly Central or South America [1] and cultivated in almost all tropical and subtropical regions worldwide. Avocado fruit is rich in lipids, proteins, minerals, vitamins, and other nutrients and phytochemicals (Dreher and Davenport [1] and Galvão et al. [2]). The avocado fruit has a wide range of nutrients and composition of photochemical which is important in a healthy diet. Avocados also are an important nutritional source of folate, which is essential during pregnancy for healthy foetal development. The fruit pulp rich in fat, dietry fibre, energy, minerals (phosphorus, sodium, potassium, calcium, and magnesium) and vitamins (vitamin C, vitamin E, carotene, etc.). The lipid content can comprise 15-30% of the fresh weight of the fruit depending on the cultivar, season, and growing conditions [3]. It is found is that the lipids in avodado fruit contain more than 60% monounsaturated fatty acids and more than 13% essential fatty acids such as oleic acid, palmitic acid, linoleic and linolenic acid, which are beneficial to human cardiovascular health [4,5,6 and 7]. In contrast to lipid content, the sugar content of avocado fruit is relatively low [8] and is recommended for diabetes because it is a high-energy food [9]. Avocado fruit contains more phenolic compounds than other kinds of tropical and subtropical fruits [10,11,9]. Avocado being a cross pollinated crop it exhibits wider variability. Though, the wider variability present in avocado, exploitation of variability is very meager. In Tamil Nadu particularly in lower Pulney hills (1000 m MSL) of Western Ghats avocados are grown as shade tree for coffee plantation. After realization of its importance the avocado cultivation in these areas geared up. However the avocado trees available in these areas are seedling progeny and it exhibits wide variability for different traits like fruit shape, size, peel colour, pulp colour and yield. There is a great scope for exploitation of these variations in avocado to develop a suitable variety with desirable traits. Evaluation of the potentialities of the existing cultivars is essential because it depicts the genetic diversity of the base materials on which depends the promise for further improvement. The success of a breeding programme for the improvement of quantitative attributes depends to a great extent on the magnitude of genetic variability existing in the germplasm. Burton [12] suggested that genetic variability along with heritability should be considered for assessing the maximum and accurate effect of selection. Studies on the variability using genetic parameters like genotypic coefficient of variation (GCV), heritability and genetic advance are essential for initiating an efficient breeding programme. High yield can be achieved by selection of those characters that have high heritability values coupled with high genetic advance. Selection is an indispensable component of the variety development process. Breeders search for dependable parameters that are less affected by the environment. With this aim the present study was conducted.

MATERIALS AND METHODS
The present study on Genetic Variability of Avocado (Persea americana L.) genotypes in Lower Pulneys for fruit and nutritive traits was conducted at Horticultural Research Station, Thadiyankudisai, Tamil Nadu, India during 2018-2020. Preliminary survey was conducted in lower Pulney hills area to identify suitable avocado genotypes for commercial cultivation. Fruits were collected from identified trees of different location of lower Pulney hills and considered as individual genotypes. Fruit characterization was done by using IBPGR descriptor. Totally 16 avocado genotypes were identified and fruit characterization was done for the traits viz., fruit length (cm), fruit diameter (cm), peduncle length (cm), peduncle diameter (mm), pedicel length (cm) and fruit weight (g). Nutritive analysis for fat (g), dietry fibre (g), carbohydrate, carotene, vitamin C, calcium and phosphorus were done for individual genotypes. The experiment was laid out in a completely randomized block design with four replications. Biometrical observations on fruit length (cm), fruit diameter (cm), peduncle length (cm), peduncle diameter (mm), pedicel length (cm) and fruit weight (g), fat (g), die try fiber (g), carbohydrate, carotene, vitamin C, calcium and phosphorus were taken from randomly selected 10 fruits and were subjected to statistical analysis. Determination of the crude fiber, and fat were carried out according to AOAC procedure [13]. Vitamin C content was determined using the modified. 2, 6-dichlorophenolindophenol method [14].
Total carotenoid content was measured spectrophotometrically at 445 nm using a Shimadzu UV-1800 spectrophotometer. The experiments were carried out in triplicate. Data were subjected to analysis of variance technique to split the total phenotypic variation into casual components. The components of variance were estimated using the method described by Singh and Narayanan [15]. The mean data obtained were used for determining genotypic co-efficient of variation and phenotype co-efficient of variation as suggested by Burton [12], heritability in broad sense was computed as reported by Hanson et al. [16], and the expected genetic advance was calculated by using the formula suggested by Johnson et al. [17].

Fruit Characters
Analysis of variance for different fruit traits (Tables 1 & 2) of avocado revealed that the genotype mean sum of square was highly significant for all the traits indicated that presence of appreciable genetic variability and can be exploited through breeding programme.
Per se performance of avocado genotypes for fruit characters are presented in the Table 3. From the table it was observed that fruit length ranged from 11.10 cm to 18.30 cm. The highest fruit length value was registered by TKDPA 93 (18.30 cm) and it was followed by TKDPA 87 (17.10 cm) and TKDPA 85 (16.20 cm) and TKDPA (16.20 CM). Whereas the lowest fruit length value was registered by TKDPA 83 (11.10 cm). Fruit diameter ranged from 6.20 cm to 12.10 cm. Higher fruit diameter value was registered by TKD PA 93 (12.10 cm) and it was followed by TKDPA 92 and TKDPA 89 (10.80 cm) and TKDPA 87 (10.10 cm). Whereas lower fruit diameter value was registered by TKDPA 86 (6.20 cm). The trait peduncle length ranged from 6.89 cm to 18.40 cm. The highest peduncle length was recorded by TKD PA 93 (18.40 cm) and it was followed by TKDPA 92 (17.30 cm) and TKDPA 97 (14.70 cm). The lowest peduncle length was recorded by TKDPA 82 (6.89 cm). For the trait peduncle diameter the value ranged from 4.70 mm to 9.49 mm. Maximum peduncle diameters was observed by the genotype TKD PA 93 (9.49 mm) and it was followed by TKDPA 92 (9.29 mm) and TKDPA 91 (9.10 mm). While the, minimum peduncle diameter was observed by the genotype TKDPA 97 (4.70 mm). Pedicel length ranged from 0.90 cm to 1.90 cm. The maximum pedicel length was registered by TKDPA 95 (1.90 cm) and it was followed by TKDPA 88 and TKDPA 89 (1.80 cm) and TKDPA 87 (1.70 cm). While the, minimum pedicel length was registered by TKDPA 93 (0.90 cm). Fruit weight ranged from 250.03 g to 780.03 g. The highest fruit weight was observed by the genotype TKDPA 93 (780.03 g) and it was followed by TKDPA 89 (640.03 g) and TKDPA 87 (600.00 g). Whereas the, lowest fruit weight was observed by the genotype TKDPA 84 (250.03 g). From the results it was observed that the genotype TKDPA 93 an oblate fruit registered higher values for all the characters except pedicel length. TKDPA 87 a normally obovate fruit registered higher fruit length, fruit diameter, pedicel length and fruit weight. The genotype TKDPA 89 spheroid in fruit shape registered higher values for fruit diameter, pedicel length and fruit weight. These genotypes can be exploited to develop a new variety with good yield traits.

Nutritive Characters
Mean values of fruit nutritive traits are presented in the Table 4. the results showed that the trait fat content of the fruit pulp ranged from 13.62 g (per 100 g of fruit pulp) to 24.64 g (per 100 g of fruit pulp), The highest fat content was recorded by TKDPA 87 (24.64 g per 100 g of fruit pulp). It was followed by TKDPA 91 (24.19g

Genetic Parameters
The estimates of genetic parameters are presented in the

CONCLUSION
From the results it was evident that the there is a great genetic variability present in the study materials. The traits viz., fruit diameter, peduncle length, peduncle diameter, pedicel length, fruit weight and carotene content can be used as a selection indices in avocado as these traits registered high heritable as well as high genetic advance as percent of mean. However, these study warrants an extensive survey, collection and evaluation of avocado genotypes available at Pulney hills, Dindigul district of Tamil Nadu state, India, since, there is a wide variability present in avocado and has to be commercially exploited.