Impaginato 215 Adv. Hort. Sci., 2017 31(3): 215-221 DOI: 10.13128/ahs-20460 Commercial advantages on basil architecture by ultraviolet-B irradiation A. Ciurli 1, T. Huarancca Reyes1 (*), L. Guglielminetti 1, 2 1 Dipartimento di Scienze Agrarie, Alimentari e Agro-Ambientali, Università di Pisa, Via Mariscoglio, 34, 56124 Pisa, Italy. 2 Centro interdipartimentale di ricerca “Nutraceutica e alimentazione per la salute”, Università di Pisa, Via del Borghetto, 80, 56124 Pisa, Italy. Key words: fresh market advantages, Ocimum basilicum, plant architecture, UV-B. Abstract: Sweet basil (Ocimum basilicum L.) is one of the most important herbs widely used for its medicinal properties and as food ingredient. The marketing of this product highlights the problem that these plants have long and slender stems, which are easy to break off and thus making difficult their market distri- bution. In this work, two cultivars of basil (Genovese and Profumo) at the ade- quate development stage for sale were used. We evaluated the effect of sup- plemental ultraviolet (UV)-B irradiation (15 W m-2; 3 h day-1) on plant growth and market quality. Both cultivars of basil plants under UV-B irradiation result- ed in increased leaf size and biomass, and decreased shoot length in compari- son to that of under control growth conditions. These results indicate that the application of UV-B irradiation beneficially influenced plant architecture in basil improving their greenhouse production for fresh market. 1. Introduction Many species in the genus Ocimum (Labiatae) are ranked among the most important herbs for their medicinal properties, that are associated to high content of secondary metabolites including essential oils and caf- feic acid derivatives (Gülҫin et al., 2007). The most significant species of the genus is sweet basil (Ocimum basilicum L.), which originated from tropical areas, such as India, Africa and southern Asia. Sweet basil is an annual herbaceous species that is usually cultivated as an aromatic plant. The minimum temperature for the growth of sweet basil has been deter- mined to be 10.9°C (Vågen et al., 2003; Chang, 2004). It is typically used in Italian and Asian cuisines because of the pronounced scent of its leaves, which depends on genotype (Chang et al., 2009), nitrogen nutrition (Sifola and Barbieri, 2006) and harvesting system (May et al., 2008). Sweet basil is not only cultivated for the use of aroma additives in food but also for other house-hold purposes, pharmaceuticals, cosmetics and folk medi- cine. Numerous different chemo-types exist in both wild and cultivated (*) Corresponding author: thais.huarancca@agr.unipi.it Citation: CIURLI A., HUARANCCA REYES T., GUGLIELMINET- TI L., 2017 - Commercial advantages on basil architecture by ultraviolet-B irradiation. - Adv. Hort. Sci., 31(3): 215-221 Copyright: © 2017 Ciurli A., Huarancca Reyes T., Guglielminetti L. This is an open access, peer reviewed article published by Firenze University Press (http://www.fupress.net/index.php/ahs/) and distribuited 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 10 March 2017 Accepted for publication 22 June 2017 AHS Advances in Horticultural Science Adv. Hort. Sci., 2017 31(3): 215-221 216 basil. For instance, sweet basil contains high levels of phenylpropanoids, e.g. eugenol and methyleugenol, a n d t e r p e n o i d s e . g . l i n a l o o l a n d 1 , 8 - c i n e o l e (Lachowicz et al., 1997). In recent years, the consumption of fresh basil has b e e n e x p a n d e d i n s u p e r m a r k e t s w h e r e y o u n g seedlings are directly sold in pots obtained from greenhouses. These plants are intended for family use, which after to be transplanted, are placed on balconies, vegetable gardens or gardens. The market- ing of fresh basil highlights the problem that these plants have long and slender stems, which are easy to break off and thus making difficult their market distributions. Therefore, the objective of this study was to facilitate the sale of fresh basil in pots result- ing not only in plants more compact and resistant to movements along the supply chain, but also healthy products in the market because of the avoidance of chemicals to control the plant height (Körner and Van Straten, 2008; Nagashima et al., 2011). The interest on the effects of ultraviolet (UV) irra- diation on plants has considerably increased in the last ten years due to the continuous depletion of the ozone layer (Ballaré et al., 2011). The stratospheric ozone layer completely absorbs solar UV-C (200-280 nm) which is extremely active and biologically lethal. UV-B (280-320 nm) is the most susceptible to ozone layer depletion because it is efficiently absorbed although small proportion is transmitted to the Earth surface. UV-A (320-400 nm) is hardly absorbed by ozone and thus passes almost unaltered through the s t r a t o s p h e r i c l a y e r r e a c h i n g t h e E a r t h s u r f a c e (Houghton et al., 2001; Solomon et al., 2007). Despite the small proportion of UV-B in the natural daylight and higher energy than UV-A, UV-B has sub- stantive effects on plant growth and metabolism (Kolb et al., 2001). Moreover, plants are differently sensitive to UV-B levels which strongly depend on the latitude, hours of direct sunlight and variation in the thickness of the ozone layer (Ballaré et al., 2011). For instance, plant species grown in Mediterranean and Tropical environments and/or at high altitudes have developed defensive mechanisms to protect them- selves against UV radiation (Zheljazkov et al., 2008). Many studies found that UV-B irradiation signifi- cantly affects secondary compounds such as the biosynthetic pathway of phenylpropanoids, which are antioxidant agents (Korkina, 2007) that also act as protection against UV (Johnson et al., 1999; Ioannidis et al., 2002). Previous studies reported that UV-B irradiation also increases essential oils and total phenolic compounds content in plants (Kumari et al., 2009; Kumari and Agrawal, 2011). Moreover, it has been demonstrated that the UV-B irradiation stimu- lates the production of volatiles organic compounds in fresh herbs which usually are depleted when plants grown under glass or plastic greenhouses con- ditions in the absence of natural levels of UV-B (Johnson et al., 1999; Ioannidis et al., 2002). In the case of plant morphology, several studies have been demonstrated the role of UV-B in controlling the growth of various plants such as Lycopersicon escu- lentum Mill. and Salvia splendens L. (Garner and Björkman, 1996; Giannini et al., 1996; Del Corso and Lercari, 1997). Additional techniques to control plant growth have been proposed: temperature manipula- tion, induction of mild water or mechanical stress, and the use of chemical compounds, however all these methods present many drawbacks (Moe and Mortensen, 1992; Garner and Björkman, 1996; Barreiro et al. 2006; Sun et al., 2008). Therefore, we focused on the role of UV-B as a growth regulator of potted basil intended for fresh consumption. 2. Materials and Methods Plant material and growth conditions Two cultivars of basil were used in this study, Genovese and Profumo. Basil seeds were sowed into peat-based growing medium in 8 cm diameter pots (10 seeds each pot). Pots were covered with non- woven fabric and incubated in a growth chamber at 23±1°C, relative humidity 60-65%, 12 h light (150 μmol m-2 s-1). After one week of incubation, the cov- erage was removed and half of the pots were kept at the same conditions while the other half were under supplementary UV-B irradiation (fluorescent tubes with UV-B 10%, 15 W m-2, Exo Terra). UV-B was applied for 3 h starting 1 h before darkness, and lamps were placed at 0.5 m above plants. Basil plants were regularly irrigated. Control and UV-B treated plants were sampled 11 and 22 days after the onset of UV treatment. Morphological analysis Leaf length and width, shoot length, fresh and dry weight of shoot and leaves were determined upon treatment completion. All measurements were the mean of three independent experiments. Analysis of pigments Pigments were extracted and analysed from full expanded leaves as previously described (Pompeiano et al., 2013). All the analyses were conducted in trip- Ciurli et al. - Commercial advantages on basil architecture by UV-B 217 licate. Statistical analysis The statistical analyses of biometric and physio- logic traits were subjected to an analysis of variance (ANOVA). Differences between treatments were assessed using the F-test, and the least significant dif- ference (LSD) was calculated at P≤0.05. All computa- tions were performed with R 2.14.2 R Development Core Team 2012. 3. Results In this study, we analyzed the plant architecture and photosynthetic pigments content of two basil cultivars, Profumo and Genovese, at time zero (T0) and after treatment. Two different time points of treatment were analyzed: 11 and 22 days after UV-B treatment (UV) and their respective control (C) condi- tions. Morphological analysis was determined on leaves and shoots of both basil cultivars (Fig. 1, 2). Length and width of cotiledonary leaves did not show differ- ences between cultivars at T0, and also between treated and control plants during all the experimen- tal time (Fig. 1). The first true leaves, which appeared at the first time point of the experiment, showed a significant increased size from 11 to 22 days at con- trol conditions in both cultivars (Fig. 1). It was also o b s e r v e d t h a t U V t r e a t e d p l a n t s s i g n i f i c a n t l y increase, about two times, the leaf expansion in both cultivars in comparison with their respective control (Fig. 1). Interestingly, only 22 days UV treated seedlings showed the second leaves pair without morphological differences between the cultivars (Fig. 1). In the case of shoot length evaluation, no differ- e n c e s w e r e o b s e r v e d b e t w e e n c u l t i v a r s a t T 0 , although ‘Genovese’ showed longer shoot than ‘Profumo’ at 11 and 22 days control conditions (Fig. 2). Moreover, the UV irradiated plants showed a con- siderably shorter shoots than that of control plants at both 11 and 22 days after treatment, and in all cases ‘Genovese’ still longer than ‘Profumo’ (Fig. 2). The effect of UV irradiation on basil biomass of both cultivars was also analyzed (Fig. 3). At T0, no dif- ferences were exhibited in fresh weight (FW) and dry weight (DW) leaves (only cotyledon) between culti- vars, while FW and DW shoots were almost double in ‘Genovese’ in comparison with ‘Profumo’ (Fig. 3 A-B). Fig. 1 - Effect of UV-B radiation on the morphology of basil leaves. Two cultivars of basil were use: (A, C) cv. Profumo and (B, D) cv. Genovese. (A, B) Length and (C, D) width of basil leaves were measured at time zero (7 days old basil seedlings, T0) and after treatment. Two different time points of treatment were evaluated: 11 and 22 days (d) after UV-B treatment (UV) or control (C) conditions. Cotyledonary (white bars), first (grey bars) and second leaves (black bars) were measured sepa- rately. Each value is the mean ± SD of three indepen- dent experiments. Asterisk indicates significant differ- ences among treatments (P≤0.05). Fig. 2 - Effect of UV-B radiation on the length of basil shoots. Two cultivars of basil were use: (A) cv. Profumo and (B) cv. Genovese. Shoot length of basil cultivars was mea- sured at time zero (7 days old basil seedlings, T0) and after treatment. Two different time points of treatment were evaluated: 11 and 22 days (d) after UV-B treat- ment (UV) or control (C) conditions. Each value is the mean ± SD of three independent experiments. Asterisk indicates significant differences among treatments (P≤0.05). Adv. Hort. Sci., 2017 31(3): 215-221 218 At 11 days after treatment, no differences were reported in FW and DW of shoot or leaves (cotyledon plus first pair) between cultivars (Fig. 3 C-D). Both cultivars treated with UV irradiation showed signifi- cant increase of FW and DW leaves in comparison with that of the control conditions, while no differ- ences were reported in shoots (Fig. 3 C-D). At 22 days after treatment the biomass in both cultivars was increased in comparison with that of 11 d, while simi- lar pattern was maintained when it was compared the biomass before and after UV irradiation (Fig. 3 E- F). The photosynthetic pigments analyzed in both cultivars include chlorophyll a, chlorophyll b and carotenoids (Fig. 4). All pigments were detected at T0 without differences among cultivars. Then, the amount was dramatically reduced after 11 days under control conditions as well as UV irradiation, showing no statistical differences even between cul- tivars (Fig. 4). At 22 days after treatment, the level of chlorophyll b was maintained similar to that of 11 days and no differences were registered between control and UV conditions (Fig. 4). Chlorophyll a and carotenoids levels at 22 days under control condi- tions were increased in respect to that of 11 days, and no differences were detected when compared with that of after UV treatment (Fig. 4). 4. Discussion and Conclusions Results of the present study pointed towards a positive impact of supplementary UV-B irradiation on basil architecture, resulting on the reduction of stem e l o n g a t i o n , i n c r e a s e o f l e a f l e n g t h a n d w i d t h , increase of biomass, induction of second leaf sprout- Fig. 3 - Effect of UV-B radiation on fresh and dry biomass of basil. Two cultivars of basil were use: (A, C, E) cv. Profumo and (B, D, F) cv. Genovese. Measurements were monitored at (A, B) time zero (7 days old basil seedlings) and after treatment. Two different time points of treatment were evaluated: (C, D) 11 days and (E, F) 22 days after UV-B treatment (UV) or control (C) conditions. S: shoot, L: leaf, FW: fresh weight, DW: dry weight. Each value is the mean ± SD of three indepen- dent experiments. Asterisk indicates significant differ- ences among treatments (P≤0.05). Fig. 4 - Effect of UV-B radiation on photosynthetic pigments in basil leaves. Two cultivars of basil were use: (A) cv. Profumo and (B) cv. Genovese. Measurements were monitored at time zero (7 days old basil seedlings, T0) and after treatment. Two different time points of treat- ment were evaluated: 11 and 22 days (d) after UV-B treatment (UV) or control (C) conditions. Chlorophyll a (white bars), chlorophyll b (grey bars) and carotenoids (black bars) content are expressed as mg g FW-1. Each value is the mean ± SD of three independent experi- ments Ciurli et al. - Commercial advantages on basil architecture by UV-B 219 ing and with a similar trend of photosynthetic pig- ments content in comparison to that of plants under control conditions. These UV-B effects on plants are in accordance with previous studies (Giannini et al., 1996; Del Corso and Lercari, 1997). The reduction of stem elongation found in our research was also reported previously in other species such as wheat (Yuan et al., 1998). This phe- nomenon could be related to the impact of UV-B radiation on phytohormones metabolism, such as photo-oxidation of indole-3-acetic acid which plays an important role in stem elongation and lateral shoots (Ros and Tevini, 1995; Mark and Tevini, 1996). In addition, effects of UV-B radiation on leaf thicken- ing, leaf elongation and biomass accumulation are highly dependent on UV-B dose and source, experi- mental parameters and species of study (Kakani et al., 2003). Therefore, in this study, we used growth chamber instead of open fields and greenhouses in order to control all the environmental conditions, making this condition replicable in any situation and avoiding the influence of environmental and seasonal variations. Our results showed also an increase of leaf thick- ening, leaf elongation and biomass after UV-B irradia- tion, which could be related to a morphological archi- tecture strategy to protect plants to deleterious effects of UV-B radiation (Maffei and Scannerini, 2000; Jansen, 2002; Santos et al., 2004; Chang et al., 2009). Moreover, the generation of second leaves in basil plants was earlier promoted after UV-B treat- ment which may also involve phytohormones metab- olism changes; this effect was also previously report- ed (Barnes et al., 1988). Thus, structural changes on l e a v e s i n r e s p o n s e t o t h e a p p l i e d U V - B w e r e observed, although no changes on the content of chloroplast pigments was registered between UV treated and control plants. Photosynthetic pigments are useful indicators of UV-B tolerance or sensitivity (Kataria et al., 2014). Lower pigments content was obtained at 11 days of treatment in comparison with T0, which could be due to the stress arising from the removal of the non-woven fabric that protected plants from excessive light. However, this phenome- non was recovered in a tendency to the start point T0, suggesting the acclimatization of plants, as observed similarly in previous report (Teramura and Sullivan, 1994; Radyukina et al., 2012). Therefore, our data suggest that Genovese and Profumo basil culti- vars are tolerant to the supplementary UV-B irradia- tion (15 W m-2; 3 h day-1) at chlorophyll level, but pro- ducing other strategy to prevent UV-B penetration to the mesophyll cell at plant architecture level. Although the impacts of UV-B radiation on plant growth and development have been widely studied (Strid et al., 1994; Ballaré et al., 1995; Giannini et al., 1996; Del Corso and Lercari, 1997; Santos et al., 2004; Zu et al., 2004; Körner and Van Straten, 2008), the detailed mechanism of how UV-B radiation affects plant morphogenesis is still unclear. However, previous evidences found that UV-induced morpho- logical changes are associated with the induction of the phenylpropanoids pathway resulting in accumu- lation of flavonoids (Jansen et al., 1998). Moreover, it has been demonstrated that flavonoids regulate auxin transport affecting plant architecture (Jansen, 2002; Robson et al., 2015). In conclusion, the results of this work have practi- cal implications for greenhouse production of pot basil. In fact, supplementary UV-B radiation reduced plant height but increased biomass and leaf number, width and length with no significant effect on photo- synthetic pigments. 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