Impaginato 457 Adv. Hort. Sci., 2019 33(4): 457­464 DOI: 10.13128/ahsc­8101 Effect of foliar application of boric acid on fruit quality and yield traits of mango Z. Haider 1, N. Ahmad 1 (*), S. Danish 1, J. Iqbal 2, M. Arif Ali 1, U. Khalid Chaudhry 3 1 Department of Soil Science, Faculty of Agricultural Sciences and Technology, Bahauddin Zakariya University, Multan, Punjab, Pakistan. 2 Mango Research Institute, Multan, 60000, Punjab, Pakistan. 3 Department of Agricultural Genetic Engineering, Ayhan Şahenk Faculty of Agricultural Sciences and Technologies, Niğde Ömer Halisdemir University, Niğde, Turkey. Key words: acidity, boron concentration, flowering, Mangifera indica L., TSS. Abstract: Imbalance uptake of boron disturbs the process of pollination that eventually decrease the flowering, fruit setting and yield. Its deficiency also deteriorates the quality of fruit by increasing fruit acidity. Therefore, source, balanced application, method of application and optimum uptake of B is an important aspect and need keen scientific attention. So, a field study was con­ ducted with the hypothesis that foliar application of B would be an effective technique to improve the yield and quality of Mango cv. Summer Bahisht (SB) Chaunsa. The source of B was boric acid (BA) applied twice as foliar spray i.e., 0, 0.1, 0.2 and 0.3%. Results confirmed that as compared to control, a significant improvement in fruit weight at ripening and harvesting stages (36.9%), fruit length (21.9%), fruit width (10.1%), flower (22.1%) and fruit terminals m­2 (40.0%) confirmed the effectiveness of T4 (BA= 0.3%). A significant improve­ ment in average yield (78.6%) validated the efficacious functioning of boric acid (0.3%). In conclusion, boric acid is an important and effective source of B to improve the quality and yield of Mango cv. SB Chaunsa. Similarly, BA (0.3%) is a better option than 0.2 and 0.1% BA to improve the quality and yield of mango. 1. Introduction Mango (Mangifera indica L.) belongs to the genus Mangifera and fami­ ly Anacardiaceae which has 74 genera and 600 species (Mitchell and Mori, 1987; Tian et al., 2010). It is known as ‘King of Fruits’ due to its sweetness, fragrance and nutritional status (Sharma and Singh, 2009). Mango is becoming popular in the western countries and it is originated from Indian sub­continent (Yadav and Singh, 2017). However, in recent years, the productivity of Mango has been reduced due to deficiency of micronutrients especially boron (B) and other environmental stresses (Saran and Kumar, 2011; Adak et al., 2017; Ahmad et al., 2018). Boron deficiency is quite common after zinc micronutrient especially in (*) Corresponding author: niaz.ahmad@bzu.edu.pk Citation: HAIDER Z., AHMAD N., DANISH S., IQBAL J., ARIF ALI M., KHALID CHAUDHRY U., 2019 ­ Effect of foliar application of boric acid on fruit quality and yield traits of mangor. ­ Adv. Hort. Sci., 33(4): 457­464. Copyright: © 2019 Haider Z., Ahmad N., Danish S., Iqbal J., Arif Ali M., Khalid Chaudhry U. This is an open access, peer reviewed article published by Firenze University Press (http://www.fupress.net/index.php/ahs/) and distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Data Availability Statement: All relevant data are within the paper and its Supporting Information files. Competing Interests: The authors declare no competing interests. Received for publication 24 March 2019 Accepted for publication 8 July 2019 AHS Advances in Horticultural Science http://creativecommons.org/licenses/by/4.0/ http://creativecommons.org/licenses/by/4.0/ http://creativecommons.org/licenses/by/4.0/ Adv. Hort. Sci., 2019 33(4): 457­464 458 arid and semi­arid regions (Zhang et al., 2015). The defi­ ciency of B is ubiquitous in acidic sandy, alkaline soils and sandy soils (Camacho­Cristóbal et al., 2018). Boron deficiency is one of the key factors for a reduction in the yield of fruit crops (Davarpanah et al., 2016; Karlidag et al., 2017). Its deficiency symptoms show their effect on younger plant parts, while toxic effects are on older parts of plants (Fernández­Escobar et al., 2016). The deficiency of B in mango plant results in deformed leaves hooked and pre­matured dieback of inflores­ cence, loss of apical dominance, death of apical bud, swelling at internode and retorted growth (Litz, 2009). Contemporary agricultural practices include the additional supply of fertilizers that enhanced the growth of plants and resulted in an improvement of yield (Barker and Pilbeam, 2006). Micronutrients espe­ cially B plays an indispensable role in the growth and development of fruit trees (Davarpanah et al., 2016). Mango fruit drop before maturity is a common issue in most of the mango growing areas (Murti et al., 2008). On the other hand, the potential of foliar application of B has been well documented as an effective amend­ ment for the improvement in mango fruit formation (Saran and Kumar, 2011). Boron is intrinsic for fruit trees in forming higher germinating pollen and elon­ gated pollen tube which sets fruit (El­Sheikh et al., 2007). It is also indirectly involved in the activation of plant hormones and dehydrogenase enzyme (Marschner, 2012). Boron has low adsorption capacity and leaches at a high rate in soil (Raja et al., 2005). Foliar application of fertilizers is more convenient and effective as compared to soil application (Fernández et al., 2013). It has been observed that foliar application of fertilizers moreover confers quick response and alleviate the deficiency symptoms lead­ ing to fruitful returns (Obreza et al., 2010). Scientists have also documented that foliar application of B at different rates enhance mango fruit setting panicle­1, fruit weight and volume (Zhong and Dong, 2000; Bibi et al., 2019). Therefore, the current study was conducted with the aim to examine the effectiveness of the vari­ ous application of boric acid as a source of B on growth and yield of mango. It is hypothesized that foliar appli­ cation of boric acid as a source of B would be an effec­ tive technique for improvement in growth and yield of mango. 2. Materials and Methods Experimental site The study was planned to evaluate the influence of foliar applied boron on yield and quality of mango cultivar Summer Bahisht Chaunsa during the year 2016­17 at experimental mango orchard near Bahauddin Zakariya University, Multan (Fig. 1). Fifteen to twenty years old mango trees were select­ ed for the experimental purpose. The study was car­ ried out in accordance with RCBD design (Randomized Complete Block Design) with four treat­ ments and four replications. Treatment plan There were four different levels of boric acid (BA) i.e., T1 (control) = no boric acid, T2 = 0.1% BA, T3 = 0.2% BA and T4 = 0.3% BA which were applied as foliar application. Each tree was taken as one replica of each treatment (consist of four trees). All treat­ ments were applied twice in a year i.e., firstly at inflo­ rescence stage and secondly at the marble stage (pea size of fruit). Physio‐chemical analysis Soil sampling. The data regarding physio­chemical composition was recorded at harvest stage on ripened fruit. Composite soil samples (0­30 cm) were collected from experimental mango orchard. This depth for soil sampling was selected because the majority of mango feeding roots are present in the depth of 0­30 cm. Sample preparation. Soil samples were initially air dried, after that grinded and finally sieved through 2 mm sieve in the laboratory of Department of Soil Fig. 1 ­ GPS locations of area. Haider et al. ‐ Boron improves Mango fruits quality and yield 459 Science, Faculty of Agricultural Sciences and Technology Bahauddin Zakariya University Multan, Pakistan for determination of different physio­chemi­ cal characteristics of the soil. Soil characterization. For determination of soil texture, hydrometer method was used (Bouyoucos, 1962). Soil pH and electrical conductivity (EC) was assessed by using JENWAY 3510 pH and BANTE DDS­ 12DW Microprocessor EC meter (Abid et al., 2017). Soil cation exchange capacity (CEC) was calculated according to Richards (1954) and Rhoades (1982). For determination of soil organic matter (SOM) Walkley Black method was followed (Jackson, 1975). Olsen et al. (1954) method was adopted for the analysis of soil available P while for soil extractable K Rowell (1994) method was used. Calcium Carbonate (lime) was determined according to Allison et al. (1965). All characteristics of the soil are provided in Table 1. Boron determination in soil and leaves Leaves samples for B determination were collect­ ed twice during 2016­17. Samples were collected prior to foliar application of boric acid and after spraying the mango orchard. Boron (B) concentration from soil was assessed by HCl extraction as described by Ponnamperuma et al. (1981), while for leaves samples method of Gaines and Mitchell (1979) was followed. Growth and yield attributes Different mango parameters were recorded by selecting 15 panicles and labelled on each tree prior to measurements in an experimental mango garden. Flower terminal m­2, fruit terminal m­2, total number of flowers per panicles was observed with respect to each treatment and average was computed among all the treatments. The total number of flowers from the selected panicles (in case of each tree) was calcu­ lated to calculate the average one. Fruit weight (FW) after harvest and ripening was measured by selecting 15 fruits from each treatment. Yield of fruits The average yield tree­1 was assessed at the time of harvest by weighing out all fruits of tree regarding each treatment and their average was calculated by multiplying average fruit weight with total number of fruits. Fruit weight after harvest was noted soon after harvesting when fruit was not ripen. When the fruit was ripened, again the weight of fruit was noted and referred to as fruit weight after ripening. Maturity days Maturity days were recorded by estimation of days from flowering period to harvest stage. Length and diameter of fruits Fruit length and diameter were assessed by digital Vernier Caliper after randomly selecting 5 fruits from each treatment. Total soluble solids The total soluble solid percentage was calculated by using a digital refractometer as described by AOAC (2005). Acidity of fruits The acidity of mango was estimated followed by the method as proposed in Souza et al (2015), one drop (mango juice) was retained on the mirror regarding digital refractometer and reading was observed in case of Brix on the screen. Sugar contents Total sugar contents were recorded according to the titrimetric method as described by Raganna (1986). The method proposed by Rusk (1961) was used to estimate the vitamin C content from the juice of mango pulp. Pulp recovery (%) was determined by the following formula Pulp recovery = (Peel weight – stone weight / Fruit weight) × 100 Statistical Analysis For statistical analysis standard statistical proce­ dure was adopted (Steel et al., 1997). The signifi­ cance of treatments was analyzed through analysis of variance (ANOVA). Tukey’s test was applied at p ≤ 0.05 for comparison of treatments by using statistical software “Statistix 8.1”. Textural class Depth (cm) pH ECe (dS m­1) SAR (mmol L­1)1/2 CaCO3 (%) Organic matter (%) Boron concentration in soil (mg kg­1) Boron concentration in leaves (mg kg­1) Phosphorus in soil (mg kg­1) Potassium in soil (mg kg­1) Loam 0­30 8.4 2.04 2.3 6 0.31 0.36 20.49 13 218 Table 1 ­ Pre­experimental characteristics of soil Adv. Hort. Sci., 2019 33(4): 457­464 460 3. Results Fruit weight Effect of various foliar application rates of boric acid remained significant (p≤0.05) for fruit weight at ripening and harvesting stages. No significant change in fruit weight was observed at ripening and harvest stages among control T3 and T2. However, the appli­ cation of T4 was significantly better as compared to control for fruit weight at ripening and harvesting stages (Table 2). The maximum increase of 36.9% in fruit weight was noted where T4 was applied as com­ pared to control at ripening and harvesting stages. Fruit length and width Effect of various foliar application rates of boric acid remained significant (p ≤ 0.05) for fruit length and width. Application of T2, T3 and T4 were statisti­ cally alike to each other but performed significantly better as compared to control for fruit length and width. The maximum increase of 21.9 and 10.1% in fruit length and width was noted respectively where T4 was applied as compared to control. Average yield Effect of various foliar application rates of boric acid remained significant (p ≤ 0.05) for average yield. Application of T3 and T2 did not differ significantly for the average yield of mango fruit as compared to con­ trol. However, the application of T4 was significantly better as compared to control for average yield (Table 2). The maximum increase of 7.86% in average yield was noted where T4 was applied as compared to control. Peel and stone weight Effect of various foliar application rates of boric acid was significant (p ≤ 0.05) for stone and peel yield. Application of T3 and T2 did not differ signifi­ cantly for stone and peel weight of mango fruit as compared to control. However, the application of T4 significantly decreased stone and peel yield as com­ pared to control (Table 2). The maximum decrease of 22.2 and 15.0% in peel and stone yield was noted where T4 was applied as compared to T3 and T2 respectively. Flower and fruit terminal m‐2 Effect of various foliar application rates of boric acid was significant (p ≤ 0.05) for flower and fruit ter­ minals m­2. It was observed that T4 and T2 did not dif­ fer significantly but differed significantly better as compared to control for flower terminals m­2. Application of T3 also performed significantly better for flower terminals m­2 as compared to control (Table 3). For fruit terminals, m­2 T3 and T4 were sta­ tistically alike to each other but differed significantly as compared to control. Application of T4 also dif­ fered significantly better for fruit terminals m­2 as compared to control (Table 3). The maximum increase of 22.1 and 40.0% in flower and fruit termi­ nals m­2 was noted respectively where T4 was applied as compared to control. Total number of flowers, male and hermaphrodite flower Effect of various foliar application rates of boric acid was significant (p≤0.05) for total number of flowers, Table 2 ­ Effect of various levels of boric acid on yield attributes of mango Table 3 ­ Effect of various levels of boric acid on flowering related attributes of mango Treatments Fruit weight after ripening (g) Fruit weight after harvest (g) Fruit length (cm) Fruit width (cm) Average yield (kg tree­1) Peel weight (g) Stone weight (g) T1 (control) 250.72 b 270.93 b 10.46 b 5.74 b 132.25 b 40.48 ab 51.18 ab T2 0.1% boric acid 281.62 b 301.74 ab 11.82 a 6.10 a 135.75 b 47.20 a 58.30 a T3 0.2 % boric acid 304.29 ab 334.28 ab 12.01 a 6.11 a 138.43 ab 47.72 a 51.27 ab T4 0.3 % boric acid 343.34 a 371.16 a 12.75 a 6.32 a 142.65 a 37.15 b 49.53 c Mean values followed by the different letter in the same column are statistically different (p ≤ 0.05). Mean values followed by the different letter in the same column are statistically different (p ≤ 0.05). Treatments Flower terminal m­2 Fruit terminal m­2 Total number of flowers panicle­1 Male flower (%) Hermaphrodite flowers (%) Maturity days T1 (control) 21.50 c 7.32 c 895.43 c 548.475 b 346.525 ab 195 b T2 0.1% boric acid 25.08 ab 8.75 b 933.54 b 618.45 ab 314.55 b 197 a T3 0.2 % boric acid 24.25 b 9.25 a 1017.5 a 633.225 ab 384.275 a 196 b T4 0.3 % boric acid 26.25 a 10.25 a 1001.75 a 672.525 a 329.225 b 198 a Haider et al. ‐ Boron improves Mango fruits quality and yield 461 results are in accordance with Silva et al. (2014) that supply of boron is intrinsic to enhance the length and diameter of mango fruit with foliar application. Moreover, it was revealed that boron is less mobile in the plant, therefore, it piles up in older plant leaves and becomes unable for the sturdy growth of fruit development (Oldoni et al., 2018). Contrarily male and hermaphrodite flower. Application of T3 and T4 did not differ significantly with each other but remained significant for total number of flowers in mango as com­ pared to control (Table 3). However, the application of T2 also significantly improved total number of flowers in mango as compared to control. In the case of male flow­ ers, only T4 remained significantly better from control (Table 3). For hermaphrodite flowers, application of T3 remained significantly better as compared to control. The maximum increase of 11.9, 22.6, and 22.2% in total number of flowers, male and hermaphrodite flower was noted where T4, T4 and T3 were applied as compared to control, control and T2 respectively. Maturity days Effect of various foliar application rates of boric acid was significant (p≤0.05) for fruit maturity days. Application of T2 and T4 remained statistically alike to each other but remained significantly better as com­ pared to control for maturity days. No significant change was noted among T3 and control for maturity days. The maximum increase of 1.51% in maturity days was noted where T4 was applied as compared to control. Acidity and boron concentration The foliar application was effective in case of quality traits of mango. It was observed that with the applica­ tion of boric acid treatments acidity of fruit was decreased. Minimum acidity was noted in T3 treatment while T2 and T4 treated plots exhibited the same response for the acidity of fruit (Fig. 2). The pulp recov­ ery, vitamin C, total soluble solids and total sugar con­ tents tend to increase with an increasing application rate of foliar boric acid (0.3% boric acid) (Fig. 3). Boron concentration in leaves Foliar application of B was found effective in term of improvement in leaves B concentration (Fig. 4). Higher application of foliar B 0.3% (T4) enhanced the B concentration in leaves as compared to T1. Lowest B concentration was noted in T1. No significant change was noted among T4 and T3 for B concentra­ tion in leaves. Similarly, T3 and T2 were statistically alike to each other for B concentration in leaves. 4. Discussion and Conclusions The current study depicted the beneficial role of foliar application of boric acid as a source of B for improving mango yield and quality traits. Similarly, the effective role of foliar application has been reported previously (Anees et al., 2011; Singh et al., 2017; Ahmad et al., 2018; Oldoni et al., 2018). Our Fig. 2 ­ Effect various levels of boric acid on acidity of mango fruit. Fig. 3 ­ Effect of various levels of boric acid on pulp recovery, vitamin C, total soluble solids and total sugar contents in mango fruits Fig. 4 ­ Effect of various levels of boric acid on boron concentra­ tion in mango leaves. 462 Adv. Hort. Sci., 2019 33(4): 457­464 foliar application was reported to supplement boron supply to the growing plant organs which ultimately enhanced mango fruit diameter (Bhatt et al., 2012). It was further strengthened by the findings of Singh et al. (2017) that B application increases fruit size due to the better mobilization of food material from pro­ duction sites to storage organs and rapidly fruit development. It was noted that foliar application was significantly effective for improvement in mango fruit weight. Our results were inlined with findings of Dutta (2004). The possible reason behind the increase in fruit weight might be due to increased cell expansion and cell division. Moreover, boron contri­ bution in hormonal metabolism and boron is a key player in the rapid mobilization of sugar and water in fruits (Haq et al., 2013). Increase in yield after boron application was correlated to an increase in carbohy­ drates metabolism (Perica et al., 2001 a). The higher yield was also associated with the greater number of flower formation due to boron absorption and they also set a greater number of fruits (Usenik and Stampar, 2007; Sarrwy et al., 2012). The similar result regarding an increase in fruit yield was also reported in almond (Nyomora et al., 1999), Kinnow (Ullah et al., 2012), guava (Rawat et al., 2010), persimmon (Khayyat et al., 2007) and peach (Ali et al., 2014). Mango flowering is influenced by physiological events taking place throughout the course of its growth. We observed that improvement in flowering is due to the synthesis of flower promoters synthe­ sized in leaves and their translocation to sprouts via phloem (Ramírez and Davenport, 2012). Foliar appli­ cation increases bud formation by the synthesis of essential hormones and metabolite translocation to the bud of the tree (Usenik and Stampar, 2002). Perica et al. (2001 b) reported the similar findings that boron foliar spays resulted in a higher percent­ age of perfect flowers. It was well acknowledged that boron concentration obtained higher in pollen grains and flowers as compared to leaves. This improved flowering is due to the readily available boron required for reproductive organs (Dell and Huang, 1997; Blevins and Lukaszewski, 1998). Therefore, these results are in agreement with other fruits, where boron concentration at bud initiation, repro­ ductive tissues, flowers and fruits were favourable (Nyomora et al., 1999). It was well documented the role of boron application considerably enhanced the emerging flowers and fruits (Perica et al., 2001 b). Mango quality traits were improved due to boron application was reported (Ahmad et al., 2018). Increase in sugar contents due to boron was also reported from earlier studies (Hassan, 2000; Shaaban, 2010). It is due to the development of stor­ age and accumulation in sugar content with the con­ version of polysaccharide and starch into simple sugar (Kahlon and Uppal, 2005). It is evident that boron is responsible for declining acidity of fruit (Baiea et al., 2015). This result was further supported by (Anees et al., 2011; Sarker and Rahim, 2012; El­ Razek et al., 2013). Other quality traits improvement reports were found accordingly with our results (Bhatt et al., 2012; Haq et al., 2013). The higher rate of boron accumulation in leaves is due to the direct absorption by the leaves (Khan et al., 2012). Foliar application increased boron concentration with high­ er application rate (Perica et al., 2001 b). This result was endorsed by previous studies in olive (Hegazi et al., 2018), apricot (Karlidag et al., 2017) and straw­ berry (Kitir et al., 2018). It was concluded that foliar application of boric acid is an effective source to alleviate B deficiency in mango trees. 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