An Investigation into the Effects of Varying Seasons, Indole-3-Butyric Acid (IBA) and Rooting Media on the Rooting and Longevity of Air-layered Water Apples (Syzygium samarangense L.)

Water apple is a non-climacteric and important dry land horticulture tropical fruit crop (Syzygium samarangense L.). It is known by different vernacular names viz., wax apple, rose apple or java apple. It belongs to the family Myrtaceae, having varying chromosome numbers (e.g. 33, 42, 44, 66 and 88). It is widely grown throughout Malaysia and in a few of its neighboring nations including Thailand, Indonesia and Taiwan (Moneruzzaman et al., 2011). The species of Syzygium genus are spread in the tropical and subtropical regions of the world. The fruits are mostly pear-shaped with usually pink, light-red, red, green, sometimes greenish-white, white or cream-colored and in general they are crisp in nature, with sweet taste and aromatic flavor. For every 100 g of fruit weight water apple is found to have 90 per cent water, protein content 0.7 g, fat content 0.2 g, carbohydrates content 4.5 g, fiber content 1.9 g, 253 IU of vitamin A, traces amount of vitamin B1 and B2, 8 mg of vitamin C and 80 kJ/100 g energy (Yassir et al., 2022).

Water apple plants can be propagated through sexual method i.e., seed and asexual methods viz., air layering, grafting and budding. Its inner flesh is white, soft and spongy and it has one or two tiny, spherical, brown seeds (Khandaker et al., 2022). Water apple seeds have a very less viability therefore seedlings produced from seed is very difficult and it has long juvenile period. Seed multiplication results vast genetic diversity in shape and size of fruit and colour of peel. To achieve uniform planting and retain genetic purity, vegetative or asexual methods of propagation like as air layering are required. The lack of good quality seedlings is one drawback which hinders the growth of water apple fruit sector.

Air layering, a vegetative propagation method, is gaining popularity due to its cost-effectiveness, ease of use and improved success rates. However, there is considerable variability in the success rate of air layering and one factor contributing to this variation is the age of the shoots used. Various factors influence the air layering success in water apple including the mother plants condition, layering timing, rainfall, micro climate, humidity, temperature, the choice of rooting and growing media and the plant growth regulators application. To enhance success rates, contemporary practices involve the use of growth regulators during the rainy season in air layering techniques (Tyagi and Patel, 2004). With respect to fruit crops, similar results were stated by Bharanidharan et al., (2023) on West Indian cherry, Chacko et al., (2023) on soursop, Khandaker et al., (2022) on wax apple and Kushwah et al., (2022) on guava.

Currently, the propagation media Sphagnum moss, cocopeat and sawdust are being used widely for the root initiation purpose. But incessant and in discriminate exploiting of epiphytes like Sphagnum spp. as rooting medium is having repercussion on ecological balance of tropical forests, where these plants are grown on tall trees. Layering disrupts the downward movement of organic substances. The rooting capacity of air-layered shoots relies on various factors that differ across crops, cultivars and biochemical components of the clone (Sridevi et al., 2018). These components include levels of carbohydrates, nitrogen, sugars, starch, phenols and auxin, as well as the seasonal climate (such as temperature, relative humidity, amount of rainfall, etc.) at the time of layering (Anandhanambi et al., 2016). More than optimum level of all these factors is needed to attain better rooting of water apple layers.

In water apple there is a huge scope for improving the fruit growth, development and quality. Due to lot of variation observed in the sexual propagation the growth and bearing habit for development of the fruit is very slow it is also because of low photosynthates supply at early growth stages. To overcome this hindrance vegetative propagation method like air layering is the best option. This helps in improving the productivity and quality of the water apple. Considering the importance of air layering in water apple an attempt was made to standardize the air layering technique by evaluating the effect of different season and different planting media on water apple at western tropical wet and dry climate of Tamil Nadu.

The experiment was carried out at North farm, School of Agricultural Sciences (SAS), Karunya Institute of Technology and Sciences (KITS), Coimbatore, Tamil Nadu, India during 2022-23.

Location and climate

Coimbatore, situated in the western region of Tamil Nadu, can be found at coordinates of approximately 11°00'19.98" N latitude and 76°57'58.03" E longitude, elevation of 432 MSL. The annual rainfall per year in Coimbatore is around 660 mm. The monsoon season typically begins in the third week of July and continues until the second week of September in 2022, with the majority of the rainfall coming from the South West monsoon. The environmental conditions during the study were given in the Table 1.



Plant materials

Red cultivar of water apple (Syzygium samarangense L.) mature shoots were used for this air layering study and  chosen from mini orchard maintained at North farm, SAS, KITS, Coimbatore. In mother block, two-year-old plants planted at close spacing of 5 m × 5 m were headed back during the month of March. After 4-5 months, the new shoots were ready for layering operations. Totally nine plants were selected for this study, trees are divided into three equal parts to carry out the research in three different months i.e. August, September and October. Three trees in a particular month indicate three different replications and each treatment was imposed to five randomly selected shoots. Totally thirty shoots in each plant were used to impose six different treatments in a single tree, similar method had been followed in other two trees for replicating the treatments.

Treatment details

The experiment was laid out in factorial randomized complete block design (FRCBD). The air layering was done in three months i.e., August (S₁), September (S₂) and October (S₃) with three different concentrations of IBA i.e., 2000 mg/L (I₁), 3000 mg/L (I₂) and 4000 mg/L (I₃) with two different rooting media i.e., Cocopeat (M₁) and Sphagnum moss (M₂). Six layers were prepared for each treatment combination which was replicated three times. There were 18 treatments which comprised of combination of three seasons of air layering, three concentrations of IBA and two different rooting media.

Preparation of different concentration of IBA

To prepare a 2000 mg/L lanolin paste containing 200 milligrams of IBA powder, first, accurately weigh 200 milligrams of IBA powder using a chemical balance and transfer it into a beaker. Next, add 5 milliliters of 95% ethyl alcohol to the powder and vigorously shake it until it completely dissolves. Then, take 100 grams of lanolin paste in another beaker and heat it. Once the lanolin paste has melted, add the dissolved growth regulator to it and swirl the mixture well with a magnetic stirrer or your hands until the ethanol evaporates. This ensures the creation of a homogeneous mixture of IBA and lanolin paste.

Recording the observations

Number of days taken for appearance of roots (No.), number of days taken for bulk appearance of roots (No.) and number of days taken for detachment of layers (No.) in air layers were recorded by periodic observation of air layers by observation through transparent polythene sheet of each treatment. The values for air layers for each treatment was noted and mean expressed in number.

The length of primary roots was measured in centimeters along each layer, starting from the collar region and extending to the tip of the primary root. These measurements were recorded using a measuring scale.

The diameter of primary roots was measured between center of collar region and tip of primary roots by using vernier caliper and measured in millimeters (mm).

Three rooted layers were randomly sampled from each treatment at the time of transfer to rooting media. The polythene sheet and the rooting media were removed carefully using forceps and care was taken to avoid damage to roots. Mean numbers were counted in each rooted layer for number of primary roots (No.), secondary roots (No.) and total roots (No.) per layer.

Observing roots that were visible through the white polythene. Subsequently, the percentage of rooted layers was calculated for different treatment conditions after 45 days. The total count of rooted layers was recorded for each treatment after detachment of layers.

Design of experiment

A factorial randomized complete block design (FRCBD) was employed for this study, with three replicates for each treatment. ANOVA was conducted to analyze all the data and when the F test indicated significance at a p-value of 0.05, Fisher’s protected least significant difference (LSD) test was used to differentiate the means.

The significant differences were observed between season of air layering done, concentrations of IBA and rooting media on the parameters highlights the importance of considering all three factors in promoting successful root initiation were given in Table 2. The ranges (Season - IBA - Media) seen in various parameters viz., days taken for the appearance of roots (21.91 - 22.20 - 19.83), days taken for bulk appearance (42.18 - 43.09 - 40.81), days taken for detachment (71 - 80 - 90), length of the primary root (9.53 - 10.28 - 9.18), diameter of the root (2.36 - 2.52 - 2.40), number of primary roots (25.29 - 26.70 - 24.47), number of secondary roots (52.34 - 42.94 - 49.78), number of roots (78.87 - 82.93 - 74.36), number of rooted layers (108 - 108 - 161) and percentage of rooting in layers (100% - 100% - 99.38%) were observed.



Season

August is found to be appropriate time for layering, considering seasonal variations in variables that influence the environment, such as temperature, moisture and light intensity, which can influence root development. August received maximum rain fall of 363.0 mm for 18 days and with higher relative humidity (88.80%), which favoured root initiation. Agro-climatic conditions of the experimental area also have a greater influence on the success. August and September were favorable seasons for carrying out air layering. Similar findings were recorded by Chauhan et al., (2008) and Dhillon and Mahajan (2000) in their research.

IBA concentration

The findings of this investigation indicate that treating the air layers with 4000 mg/L of IBA resulted in the highest root numbers. This suggests that an optimal IBA concentration enhances the amyloplasts breakdown within the cell wall and stimulates cambium activities, thereby facilitating the mobilization of photosynthates from the source to the sites where roots form in air layers, ultimately it helps in promoting root formation. The application of exogenous IBA encourages callus formation, accelerates the dedifferentiation of interfascicular cambium and generates numerous cells that differentiate into root primordia and root cells, consistent with the results of Singh et al., (2015). External application of IBA played a crucial role in breaking down starch and reducing amyloplast levels. This specific mechanism was identified as a facilitator for the rooting process (Shahzad et al., 2019) and potentially increasing the speed of carbohydrate translocation from leaves to the stem or air layering site, thereby promoting their growth and development (Shekhawat and Manokari, 2016). The results also highlight the significant role of IBA concentrations and appropriate media in promoting root initiation. This might be due to the influence of auxin signalling and root-inducing processes.

Media

The early root appearance in sphagnum moss might be due to favourable conditions like- maximum water holding capacity, proper aeration available to the air-layers which helps in faster growth of callus resulted in early root emergence. Similarly, Rymbai et al., (2012) revealed that the sphagnum moss had found superior over cocopeat for rooting.

Interaction effect

The interaction effect between season of air layering done, concentrations of IBA and rooting media on the parameters highlights the importance of considering all three factors in promoting successful root initiation were given in Table 3. The best result was observed under the S₁I₃M₂ treatment combination, which involved layering in the first fortnight of August along with 4000 mg/L IBA in sphagnum moss as rooting media. The ranges seen in various parameters viz., days taken for the appearance of roots (16.20), days taken for bulk appearance (37.17), days taken for detachment (71), length of the primary root (11.19), diameter of the root (3.32), number of primary roots (32.67), number of secondary roots (69.67), number of roots (107), number of rooted layers (18) and percentage of rooting in layers (100 %) were observed. In terms of interaction effect, Rymbai and Reddy (2010) found that the combined impact of several treatment combinations produced noticeable changes. They discovered that the optimum treatment combinations for air layering of guava cv. L-49 in Andhra Pradesh were IBA @ 4000 mg/L + Sphagnum moss + 15^th August (86%). The similar findings were stated by Khandaker et al., (2022) in wax apple, Mozumder et al., (2017) in plum, Patel et al. (2012) in pomegranate and Gowda et al., (2006) in apple.

The investigation indicates that the use of external IBA had a significant positive impact on both the rooting and vegetative growth of air layers. This effect was particularly pronounced when applying IBA at a concentration of 4000 mg/L. Among the different rooting media tested, sphagnum moss emerged as the most effective in rapid root development in air layers. The treatment combining 4000 mg/L IBA with sphagnum moss had the highest success rate for root initiation, achieving a 100% success rate in water apple air layering. This discovery aids in determining the optimal conditions, including season, dosage and combination (4000 mg/L IBA with sphagnum moss applied in August), for successful air layering in water apple. Ultimately, this information facilitates the production of high-quality planting materials.
 

The authors are thankful to the School of Agricultural Sciences, Karunya Institute of Technology and Sciences for their support and providing required facilities to carrying this work.

All authors declared that there is no conflict of interest.