Dragon fruit is an exotic fruit crop commonly referred to as Pitaya, is perennial in naturewith a life span of 20 years

Abstract

Dragon fruit is an exotic fruit crop commonly referred to as Pitaya, is perennial in naturewith a life span of 20 years. The production of dragon fruit is on the increase in Kerala due to its wide adaptability and high nutritional properties. As it is an exotic fruitcrop, the information on flowering, phenology and ideal genotypes under Kerala condition is lacking. So information on genotypes and reproductive biology of dragon fruit will be aboon to farmers and also to the researchers for future breeding programmes. The current investigation entitled “Reproductive biology and evaluation of dragon fruit (Hylocereus spp.) genotypes” conducted in the college orchard of the Department of Fruit Science, Vellanikkara during the period of 2021- 2023 throws light on this aspect. Two experiments were conducted as a part of the study, one for assessing the yield and quality of different dragon fruit genotypes,and the other for investigating the reproductive biology and phenology of different dragon fruitgenotypes. Five dragon fruit genotypes, namely Cambodian Red, Malaysian Red, Oregano Red, Srilankan Red and Cambodian White were evaluated during this research study. In the first experiment, when the different parameters related to stem, yield and quality were studied, significant variations could be observed among the genotypes. With regard to quantitative stem characteristics, Cambodian White exhibited highest stem segment width (33.05 mm), arch height (4.62 cm) and distance between areoles (35.08 mm) and the least number of spines per areole (2.13). When qualitative stem characteristics were considered, Oregano Red exhibited strong waxiness with a flat margin and prominent dark brown colouredspines on areoles making it distinctly different from the other genotypes. When the quantitative fruit characteristics were observed Oregano Red produced fruits having highest fruit width (8.62 cm), fruit girth (27.84 cm) and number of bracts on fruit (28.07cm), whereas minimum fruit width (6.65 cm) and fruit girth (22.34 cm) were recorded in Malaysian Red. The highest bract width was recorded in Cambodian White (35.00) with less number of bracts in fruits (19.21), and lowest bract width was observed in Malaysian Red (25.52). The length of apical bract was highest in Cambodian Red (42.66 mm), whereas it wasabsent in Oregano Red. Among the fruit parameters studied, highest fruit weight (411.33 g), peel weight (134.82g) and pulp weight (276.47g) were recorded in Oregano Red and lowest in Malaysian Red. Cambodian Red recorded the highest number of seeds (2045 per 50 g of fruit pulp) but small in size, whereas Oregano Red had the least number of seeds (820.00 per 50 g of fruit pulp) but larger in size. The pulp to fruit weight ratio was highest in Cambodian Red (0.74) followed by Srilankan Red (0.72), indicatingthe presence of thin peel in these genotypes. On contrary, Cambodian White had the lowest pulp to fruit weight ratio (0.63) indicating the presence of thick peel in this genotype. Regarding the number of fruits per pole, Malaysian Red recorded the maximum numberof fruits per pole (17.60), followed by Cambodian Red (11.8). However, the fruit yield (kg per pole), of both Cambodian Red (3.79 kg) and Malaysian Red (3.68 kg) were found to be on par.This result revealed that Malaysian Red produced smaller fruits when compared to Cambodian Red. The number of fruits per pole were least in Oregano Red (3.6 fruits per pole) and was onpar with Srilankan Red (4.6 fruits per pole) resulting in reduced yield in Oregano Red (1.29 kg/pole) followed by Srilankan Red (1.54 kg per pole). Oregano Red and Cambodian White were distinct from the other genotypes with respectto fruit morphological features. With regards to the position of the fruit bract towards the peel,the bracts were slightly held out in Cambodian White, while bracts were strongly held out in Oregano Red. Considering the peel and pulp colour, Cambodian White had medium pink colour with white flesh, whereas, Oregano Red exhibited red coloured peel and dark pink pulp.Regarding the shape of the fruit, Cambodian White produced oblong fruits, while the fruits of Oregano Red were spherical in shape. Biochemical analysis of the fruits clearly indicated that there exists significant variationsamong the dragon fruit genotypes with respect to total soluble solids (TSS), TSS/acid ratio and anthocyanin content. Srilankan Red and Cambodian White recorded the highest and lowest values respectively for both TSS (13.78 °Brix and 10.18 °Brix) and TSS/acid ratio (107.66 and79.55). Oregano Red recorded the highest anthocyanin concentration (0.27 mg/g), whereas Cambodian White (0.01 mg/g) recorded only very low concentration of anthocyanin. Other biochemical parameters, such as acidity, ascorbic acid content, reducing sugar and total sugardid not exhibit any significant variation among the genotypes. In the second experiment, flower characteristics such as flower bud length and girth, pericarpel width, length of perianth, distance of anther below stigma, number of stigma lobes,number of flower flushes and the number of flowers per pole varied among the genotypes. Withregards to flower production, Malaysian Red produced highest number of flowers (23.0 flowersper pole) while Srilankan Red produced less number of flowers (4.8 flowers per pole). The number of flower flushes per year varied among the genotypes, where Cambodian Red and Malaysian Red recorded seven flower cycles per year, Srilankan Red and Cambodian White exhibited five flower cycles per year, while in Oregano Red only four flower flushes were observed per year. In terms of qualitative flower characteristics, Cambodian White and Oregano Red were found to significant vary from the other genotypes. Both Oregano Red and Cambodian White exhibited circular bud shape with rounded apex. Regarding the flower colour, the primary colour of sepals and petals of both genotypes were green and white, respectively, whereas the secondary colour of sepal in Oregano Red exhibited a strong red edge on sepals, and that of Cambodian White featured no red colour on the sepals. The sex form, nature of stamen and shape of the bract did not differ among all the genotypes. Hermaphrodite sex form with free stamen was observed in all the dragon fruit genotypes under study. Phenological parameters clearly indicated that there exists variation among the genotypes. Early bud initiation was recorded in Malaysian Red (291.6 days) and late bud initiationobserved in Oregano Red (388.0 days). From the observation recorded, the genotype OreganoRed was observed to take maximum number of days for flowering (18.00), fruit set (4.06) and harvest (28.22 days) when compared to other genotypes. Cambodian White (26.34 days) took only minimum number of days for fruit harvest from fruit set. During the study period flowering season was observed to start from the month of May for Malaysian Red and Cambodian Red and in Oregano Red flowering was delayed and found to start only in the last week of June. The fruiting season of Cambodian Red and Malaysian Red started from June and continued up to last weekof October while in other genotypes flowering started from July and continued till October. In the pollen study, the highest pollen viability of 100% was observed in Oregano Red, Srilankan Red and Cambodian White. The genotypes did not significantly vary for pollen sizeand length of pollen tube, as it ranged from 0.08 to 0.09 mm and 0.203 to 0.250 mm respectively. In the compatibility study, all self and cross pollinations resulted in successful fruit set (100%), except for Oregano Red which exhibited only 33.3% self compatibility. Cluster analysis of stem, flower and fruit qualitative characters provided four clusters at 70 % similarity coefficient and it could be inferred that, Cambodian Red and Malaysian Red were closely related to each other, indicating a possibility of belonging to the same species. The other clusters were found to exhibit variations among them, even though, they originated from the same species, indicating the presence of more than one genotype in the same species. Based on the current research, it can be inferred that the best genotype with the highest yield and largest fruits was Cambodian Red. Oregano Red was found to have the highest anthocyanin concentration and Srilankan Red recorded the highest total soluble solids, makingboth suitable for value addition. Despite being members of the same species (H. costaricensis),the morphological characteristics of Malaysian Red, Srilankan Red and Cambodian Red differed from one another. Oregano Red (H. polyrhizus) and Cambodian White (H. undatus) displayed wide genetic variation as they belong to different species. Morphological, biochemical and phenological characterization of five dragon fruit (Hylocereus spp.) genotypes revealed the presence genetic variations among them which could be used as a key trait for distinguishing three different species.