Performance of Exotic Sweet Orange Genotypes at Dhankuta, Nepal

The study was conducted to evaluate the varietal performance of sweet orange genotypes at National Citrus Research Program, Dhankuta, Nepal during 2015. Twenty exotic as well as local genotypes planted in 2005 were evaluated for their fruit physiochemical characteristics at their 10-years aged. Three genotypes: Malta Blood Red, Dhankuta Local and Valencia Late have resulted as superior genotypes for fruit yield characteristics. Some genotypes Delicious Seedless, Salustiana and Hamlin also exhibited excellent performance for their fruit size and weight; however these genotypes produced lower fruit number per plant. Pineapple, Meisheu-9, and Washington Navel had higher TSS. There was similar fruit maturity period commenced from 14 November to 28 December among the genotypes. Based on the results, the genotypes showing distinct characteristics of fruit yield and quality including fruit maturity period should be promoted to make variety diversity in Nepal.


Introduction
Sweet orange (Citrus sinensis Osbeck) is the high-value fruit crop in the global trade that world production was estimated at 47.8 million metric tons in 2016/17 (USDA, 2018;Grace et al, 2012). It occupies the second position after mandarin in production value among citrus fruits in Nepal (NCRP, 2017;NCDP, 2016;AEC, 2014). The annual production of fresh sweet orange was estimated at 33, 558 t under 5131 ha with 9.7 t/ha productivity in 2016/17 (MoAD, 2016. Nepal has a huge potential of growing sweet orange for area expansion with appropriate varieties. As of now, the cultivars adopted in Nepal are of local origin and exotic varieties have not been adopted. The existing local cultivars have excellent fruit qualities including physio-chemical properties (NCRP, 2016). Nevertheless,

Cite this article as:
A.B. Pun and M.K. Thakur (2018) Int. J. Appl. Sci. Biotechnol. Vol 6(4): 308-312. DOI: 10.3126/ijasbt.v6i4.16023 Dhankuta, Nepal since 2005. The genotypes were collected from different sources including INRA-CIRAD, France; ICAR, India and ICIMOD. The experiments were conducted following a randomized complete block design, with four replications, single plant per replication. The ten trees of each genotype grafted with trifoliate orange have been planted in one block with spacing of 4 m x 4 m. The recommended practices were adopted under rain-fed condition. The experimental site was located between 27°1' north latitude and 87°18' east longitudes with the elevation of 1250 m asl facing south-east aspect. The experimental site comprises sandy loam soil, receiving average annual rainfall at the range of 940-1350 mm. The observations on fruit physio-chemical characteristics were measured from the randomly selected four trees as replications of each genotype at their 10-years of age in 2015. The fruit diameter and fruit weight were measured from 10 fruits per 4 replications, using digital callipers and micro-balance respectively as mentioned in the citrus descriptor (IPGRI, 1999). Similarly, the weight of fruit pulp, juice weight and volume (Cantuarias-Avilés, 2010), TSS °Brix (Total Soluble Solid) and TA% (Titratable acidity) were measured from 10 fruits per 4 replications, respectively using refractor-meter and titrating 2 ml fruit juice with 0.1 M NaOH as mentioned by Hardy and Sanderson (2010). The data were analysed using GenStat and DMRT software.

Fruit Yield Characteristics
The results revealed that variation on the fruit yield characteristics: number of fruits, fruit diameter, fruit weight and fruit yield per plant were highly significant (P < 0.001) among the genotypes ( Taker, and Tamanga had the lowest fruit weight among the genotypes. Genotype: Malta Blood Red produced the significantly highest fruit yield (9.49 kg/plant) followed by Dhankuta Local (6.47 kg/plant) and Valencia Late (5.14 Kg/plant). The genotype Meisheu-9 produced the least fruit yield (0.60 Kg/plant).

Fruit TSS, TA and TSS to TA ratio
The results revealed that there was highly significant variation on TSS, TA and TSS to TA ratio among the genotypes ( Table 2). The significantly higher TSS was observed at Pineapple (11.18 °B), Meisheu-9 (11.16 °B) and Washington Navel (11.13 °B) compared to other genotypes. The least TSS content was observed at Hamlin (8.58 °B), Lue Gim Gong (8.63 °B), and Salustiana (9.28 °B). The Titratable Acidity (TA) was varied, ranging from 1.23% to 4.24%. The highest TA was observed at Caracara Navel (4.24%) followed by Venelle (4.08%) and Malta Blood Red (3.57%). The lowest TA was recorded with Succari (1.25%), corresponding the highest TSS to TA ratio (8.77).

Fruit Maturity
The fruit maturity period commenced from 14 November to 28 December among the genotypes that Tamango, Hamlin and Sevelle Common were found earlier for fruit maturity. Valencia Late, Lue Gim Gong, Blood red and Washington Navel were matured late among the genotypes that they became ready to harvest on 6 December onward. The results revealed that the maturity period among the genotypes was found very short ( Fig. 1).  The fruit diameter among the genotypes was recorded at the range of 52.80 to 92.44 mm that Delicious Seedless had the highest fruit diameter (92.44 mm), while the least was recorded at Tamango (52.80 mm). Khalid et al. (1993) had found similar result as the fruit diameter was found at the range of 62 to 75 cm among the tested varieties of sweet orange. The fruit weight observed at this study was ranged from 75.44 to 165.28 g and this was very lower than those of Khalid et al. (1993)' finding as it was found at the range of 155.00 to 226.70 g.
Similarly, the fruit yield recorded at the present study was very lower than those of other studies. The highest fruit yield recorded at this study was 9.49 kg/plant, while it was 42.7 kg/plant in the observation of Khalid et al., (1993). The juice content observed at the range of 33.61 to 60.36% in this study was similar to those of Chahal and Gill (2015). The genotype Venelle was found to have the highest juice content (60.36%), while genotype Pineapple contained the least juice (33.62%). However, it was statistically at par among the most genotypes except few ones. Moreover, genotypes: Venelle, Tamango, Sevelle Common and Succari were found to have higher juice content among genotypes. The TSS of the following varieties: Pineapple, Blood Red, Salustiana and Hamlin were observed respectively at 11.18, 10.00, 9.28 and 8.58 °B. Khalid et al. (1993) also reported the similar TSS values of the same varieties that were 9.67, 9.53 10.30 and 8.00 °B respectively The genotypes with higher TA% were Caracara Navel (4.24%), Venelle (4.08%) and Malta Blood Red (3.57%).
The similar fruit maturity time of the existing local cultivars is making short harvesting period of sweet orange in Nepal. The harvesting period of sweet orange in Sindhuli and Ramechhap remains only for three months during November to January and beyond this period, Nepal imports fresh fruits in huge amount (AEC/FNCCI, 2014). This brings necessary of adopting distinct varieties of having diverse characteristics including fruit harvesting period. Chahal and Gill (2015) showed that cultivation of narrow genetic pool in citrus may impose market glut including threat in term of diseases and pests outbreak.