ABSTRACT

A field experiment was carried out to screen the best foliar concentration of salicylic acid (SA) out of 25, 50, 75 and 100 mg L^-1 for its effect on various growth and yield parameters like number of leaves, plant height, number of fruits plant^-1, fruit dimensions, leaf chlorophyll content and yield plant^-1 in three chilli cultivars. The selected chilli cultivars included were Sky-Land-II, Sky-Land and 1130. The experiment was conducted in field area of the Department of Horticultural Sciences, The Islamia University of Bahawalpur, Pakistan during 2017. Results indicated that different levels of SA significantly increased plant growth and yield parameters, but the level of SA @ 75 mg L^-1 highly improved the studied parameters in selected cultivars. Moreover, foliar spray of SA significantly increased growth in selected cultivars; however, Sky-Land-II performed better in response to different concentrations of SA. In conclusion, foliar spraying of 75 mg L^-1 SA could be recommended to chilli growers under arid region of Bahawalpur for growing cultivar Sky-Land-II.

INTRODUCTION

Chilli pepper (Capsicum frutescens L.) belongs to Solanaceae family. Chilli crop in Pakistan is produced year round. It is important not only for farm income but also for the nutritional value. It is a superb source of natural colors and various antioxidant (Howard et al., 2000). It is a warm-season and chilling-sensitive tropical crop, cannot tolerate extended period of temperature below 10 °C without serious metabolic disruptions (Decoteau, 2000). A wide range of antioxidants, vitamins, carotenoids, capsaicinoids and phenolic compounds are present in its fruit. Chilli fruits occupy an important place in human diet and are consumed as fresh in salads, and in cooked meals (Maria et al., 2010). This crop is object of much attention for its carotenoids, antioxidants, ascorbic acids and vitamin E, due to possible links in the treatment of certain type of cardiovascular diseases, cancer and delay in ageing process (Simonne et al., 2007). Hot peppers have high content of alkaloid capsaicin, responsible for pungency or heat (Udoh et al., 2005).

Effect of drought, salinity and high temperature are main environmental barrier affecting chilli production worldwide (Ziaf  et al., 2009; Farooq et al., 2009; Ashraf and Haris, 2004). Bot et al. (2000) estimated up to 45% world agricultural land subjected to drought which causes various negative physiological effects in plants like reduction in leaf enlargement, leaf water potential, and stomatal conductance (Jafar et al., 2004; Adejare and Umebese, 2007). The decrease in chlorophyll content under drought condition is considered as an oxidative stress and may be the result of chlorophyll degradation (Anjum, 2011) in vegetables. High temperature has been shown to reduce the number of flowers and fruit set in Solanaceous vegetables (Erickson and Markhart, 2002; Russo, 2003). However, this sensitivity varies according to the type of pepper (hot or sweet) and, within the same cultivar (Tarchoun et al., 2003). Soil salinity is the most common problem in various arid and semi-arid regions of the world, significantly affect physiological processes in plant. It causes reduction in leaf surface area, dry weight, chlorophyll content, stomatal conductance and photosynthesis (Saeed et al., 2016). Sweet pepper (Capsicum annuum L.) is the most widely grown vegetable all over the world; it is susceptible and cannot survive under high soil salinity levels.

A naturally occurring plant hormone, salicylic acid (SA) acts as an important signaling molecule to tolerate various abiotic stresses. It plays a vital role in plant growth, ion uptake and transport. Enzymatic activities were increased by the application of SA, showing synergetic effect with auxins and gibberellins (Zaghlool, 2006). The exogenous application of SA was reported to have an effect on a wide range of physiological processes including increase in cold germination tolerance in pepper and cucumber (Kang and Salveit, 2002). Moreover, Horvath et al. (2007) reported that the application of SA could provide protection against low and high temperature and thus improve chilli production in arid region (Abd et al., 2009). Foliar spray of salicylic acid increased the fresh and dry weight in plant, pod setting and total proteins in leaves and fruits of dry bean (Sanaa et al., 2001). In general, adding SA significantly relieved the harsh effects of drought on okra germination and growth parameters and it seems that SA is able to enhance the tolerant ability of the plant to drought stress (Baghizadeh and Haimohammadadrezael, 2011). However, Magda et al. (2013) reported that effect of different concentration of SA was significant on growth, yield and photosynthetic pigments in arid and drought regions. It was therefore planned to assess different concentrations of SA on plant growth and fruit production in chilli under arid region of Bahawalpur to avoid excessive application of SA for reduction in cost of production without compromising the yield and fruit quality.

MATERIALS AND METHODS

A field experiment was carried out in experimental area of Department of Horticultural Sciences University College of Agriculture & Environmental Sciences, The Islamia University of Bahawalpur, Pakistan during spring season 2017 to investigate the response of three cultivars of hot pepper namely Sky-Land-II, Sky-Land and 1130 to foliar spray of SA with five concentrations (0, 25, 50, 75 and 100 mg L^-1). Pepper seedlings (40 days old), collected from Choudhry Abdul Slam Farm, Dahnoot (Lodhran), Pakistan were transplanted on both sides of raised beds (15 cm) prepared 75 cm apart keeping plant to plant distance of 60 cm in sandy loam soil. Seedling beds were fertilized with DAP at the time of field preparation and Urea was applied in two splits with irrigation water using recommended doses. Five levels of salicylic acid (SA) solution were sprayed till every leaf of plant was washed on 50, 70 and 90 days after seedling transplantation. Following parameters were recorded; plant height (cm), number of leaves plant^-1, number of flowers plant^-1, number of fruits set plant^-1, fruit weight, fruit length, fruit diameter, yield plant^-1 and leaf chlorophyll content. Plant height was measured with a meter rod. Numbers of leaves, number of flowers and number of fruit set plant^-1 were counted for three seedlings and average was recorded for each replication. Fruit weight was measured using digital weighing balance. Fruit length and diameter were measured using meter rod and Vernier caliper, respectively. Chlorophyll content were measured by using SPAD Chlorophyll meter.

Statistical Analysis

There were two factors; chilli cultivars and SA concentrations (0, 25, 50, 75 and 100 mg L^-1). Randomized Complete Block Design (RCBD) was used for lay out of the experiment. Recorded data were statistically analyzed through software Statistix 8.1 and the mean values of various treatments were compared using Duncan’s multiple range (DMR) test at 5% level of probability.

RESULTS AND DISCUSSION

Analysis of Variance for Response of Chilli Cultivars to SA Spray

Analysis of variance of recorded data showed highly significant effect of chilli cultivars and SA concentrations on plant height, number of leaves plant^-1, number of fruit set plant^-1, fruit weight, chlorophyll content in leaves and yield plant^-1. Moreover, significant effect of SA was recorded for fruit length. However, interactive effect of SA and chilli cultivars was found non-significant regarding plant height, number of fruit set plant^-1 and fruit diameter. Interactive effects of cultivars and SA on number of leaves, fruit length, fruit weight, chlorophyll content and yield plant^-1 were highly significant (P ˂0.01) and for fruit length it was significant (P ˂0.05) as shown in Table 1.

Table 1: Significance levels of plant growth and yield attributes of chilli cultivars in response to SA spray.

Exogenous application of SA reduced the impact of various abiotic stresses like high temperature in arid regions; thus, improved plant height, number of leaves plant¹, chlorophyll content, and fruit quality and yield as compared to control (Table 2). Our results are in line with Zaghlool et al. (2006) who stated that plant growth and yield related parameters were increased by application of SA. Moreover, Horvath et al. (2007) reported that application of SA could provide protection against low and high temperature and thus improved chilli production in arid region (Abd et al., 2009). In another study, foliar spray of SA increased plant fresh and dry weights and hence increase pod setting in pea (Sanaa et al., 2001).

Table 2: Effect of SA on plant growth and yield attributes.

Individual Effect of SA Concentrations

Significant effect of applied concentrations of SA was recorded on different plant growth and yield attributes as shown in Table 2. Significantly greater plant height (38.77 cm) was recorded in plants sprayed with 75 mg L^-1 SA which was at par with the plants treated with 100 mg L^-1 SA, however, the minimum plant height (31.44 cm) was recorded in plants sprayed with 50 mg L^-1 SA. Significantly high number of leaves plant^-1 (74.88) was recorded in response to 75 mg L^-1 SA which was at par with 100 mg L^-1 SA; however, the least number of leaves were recorded in control and with 25 mg L^-1 spray of SA. Significant effect of different concentrations of SA was recorded on chlorophyll content in leaves with the highest content (40.00 SPAD value) recorded in plants sprayed with 75 mg L^-1 SA, which was statistically at par 50 mg L^-1. However, the least chlorophyll content was recorded in leaves of the plants sprayed with 0 mg L^-1 SA.

Number of fruits per plant were significantly affected by the application of SA. Significantly higher number of fruits (12.22) was recorded with 75 mg L^-1 SA spray, which was statistically similar with 100 and 25 mg L^-1 spray of SA. The least number of fruit set (7.11) was noted in plants sprayed with only distilled water (0 mg L^-1 SA). Individual fruit length was significantly affected by different concentrations of SA with the highest fruit length (55.22 mm) recorded with 75 mg L^-1 SA spray, which was statistically at par with 25 mg L^-1 SA. However, the least fruit length (50.66 mm) was recorded in control plants. Significantly greater fruit diameter (6.94 mm) was recorded in plants sprayed with 75 mg L^-1 SA, which was statistically similar with spray of 100 and 25 mg L^-1 SA. The least diameter was recorded in control plants and in those sprayed with 50 mg L^-1 SA. Fruit weight was significantly affected by foliar spray of SA with the highest fruit weight (8.03 g) recorded in plants sprayed with 75 mg L^-1 SA which was at par with 100 mg L^-1 SA. However, the least fruit weight (6.14 g) was recorded in control plants sprayed with distilled water. There was significant effect of SA concentrations on yield plant^-1 with the highest yield (20.28 g) in plants sprayed with 75 mg L^-1 SA which was at par with 100 and 25 mg L^-1 SA. However, the least yield plant^-1 (12.37 g) was recorded in control plants sprayed with distilled water.

All applied concentrations of SA showed significant impact on various growth and yield parameters of chilli crop grown in arid region of Bahawalpur. Results are in accordance with Magda et al. (2013) who reported that impact of different concentrations of SA was significant on growth, yield and photosynthetic pigment content in barley. Moreover, Shafeek et al. (2014) reported that foliar spray of high level of SA significantly increased growth, yield and pod quality in bean plants. Exogenous application of SA improved vegetative growth and yield attributes in vegetables (Shokar et al., 2014) because SA provides resistance against various biotic and abiotic stresses in plants (Yuan and Lin, 2008).

Individual Effect of Cultivars

There was significant difference among selected chilli cultivars regarding plant height and number of leaves with more plant height and leaves (41.06 cm and 103.2) in Sky-Land-II followed by 1130 and Sky-Land. Significantly high chlorophyll content (43.91 SPAD value) was recorded in Sky-Land-II followed by Sky-Land and 1130 (Table 3).

Table 3: Effect of cultivars on plant growth and yield attributes.

Fruit set plant^-1, fruit length, fruit diameter, fruit weight and yield plant^-1 were significantly higher (13.26, 56.26 mm, 7.11 mm, 8.80 g and 31.22 g, respectively) in Sky-Land-II as shown in Table 3. Significantly least fruit set plant^-1, fruit weight and yield plant^-1 (6.33, 5.70 g and 8.86 g, respectively) were recorded in Sky-Land. However, statistically, the least fruit length (49.86 mm) was recorded in chilli cultivar 1130 as shown in Table 3.

Significant variation was recorded in selected chilli cultivars with comparatively better performance of Sky-Land-II regarding growth and yield characters. Similar results were published by Zhigila et al. (2014) who recorded variation among different chilli cultivars for 33 morphological characters. Chilli cultivars had great variability in its various plant and fruit characters like form, size, colour and position of flowers and fruits (Moscone et al., 2007). Fresh fruit weight of various genotypes of Capsicum frutescens L. ranged from 0.23 g to 4.04 g (Jarrett et al., 2007), which is lower than our selected cultivars like Sky-Land-II.

Interactive Effect of SA Concentrations and Chilli Cultivars

Significant interaction between cultivars and SA concentrations was recorded for plant height with the highest value (44.3 cm) recorded in Sky-Land-II sprayed with 75 mg L^-1 SA, which was at par with Sky-Land-II treated with 100 mg L^-1 SA and sprayed with 0 mg L^-1 SA (control). However, the least plant height was recorded in the cultivar 1130 sprayed with 0 mg L^-1 SA and in Sky-Land sprayed with 50 and 25 mg L^-1 SA as shown inTable 4. Number of leaves plant^-1 were significantly higher (105.0) in Sky-Land-II sprayed with 75 mg L^-1 which was at par with Sky-Land-II sprayed with 100, 50, 25 and 0 mg L^-1 SA, followed by the cultivar 1130 sprayed with 75 and 100 mg L^-1 SA. However, the least number of leaves (41.6) were counted in Sky-Land sprayed with 50 mg L^-1 SA. Significant differences in leaf chlorophyll content of different cultivars sprayed with different concentrations of SA were recorded. The highest chlorophyll content (56.3 SPAD value) was recorded in Sky-Land-II sprayed with 75 mg L^-1 SA which was at par with Sky-Land-II receiving 100 mg L^-1 SA. However, the least chlorophyll content (18.0 SPAD value) was recorded in the cultivar 1130 treated with 0 mg L^-1 SA (control) as shown in Table 4.

Table 4: Interactive effect of SA and cultivars on plant growth and yield attributes.

Significant interactive effect of cultivars and SA concentrations was recorded for number of fruit set plant^-1 with the highest value (15.6) recorded in Sky-Land-II and followed by the cultivars 1130 and Sky-Land-II sprayed with 75 and 100 mg L^-1 SA, respectively. However, the least number of fruit set plant^-1 (3.3) were recorded in Sky-Land receiving 0 mg L^-1 SA. Significantly greater fruit length (60.0 mm) was recorded in Sky-Land-II that received 75 mg L^-1 SA, which was at par with Sky-Land-II sprayed with 25 mg L^-1 SA and distilled water. Significantly least fruit length (44.3 cm) was recorded in the cultivar 1130 sprayed no SA which was at par with the same cultivar sprayed with 100 mg L^-1 SA (Table 4 ). Significantly greater fruit diameter (7.5 mm) was recorded in Sky-Land-II received 75 mg L^-1 of SA which was statistically similar with Sky-Land-II treated with 25 mg L^-1 SA and Sky-Land-II received 100 mg L^-1 SA. However, the least fruit diameter (5.4 mm) was recorded in Sky-Land received 100 mg L^-1 SA. Fruit weight was significantly high (10.5 g) in Sky-Land-II sprayed with 75 mg L^-1 SA, which was at par with 100 mg L^-1 in the same cultivar. However, the least fruit weight (4.8 g) was recorded in Sky-Land sprayed with 25 mg L^-1 SA, which was at par with the same cultivar received 50 mg L^-1 SA and also with some others. Significant interaction effect of chilli cultivars and SA concentrations was also recorded for fruit yield plant^-1 with the highest fruit yield (37.5 g) measured in Sky-Land-II treated with 75 mg L^-1 SA which was at par with Sky-Land-II sprayed with 100, 50 and 25 mg L^-1 SA. However, the least yield plant^-1 (7.3 g) was recorded in Sky-Land sprayed with distilled water.

Significant impact of SA concentrations and chilli cultivars for plant height, fruit dimension and fruit weight in our selected cultivars was in line with the finding of Chartzoulakis and Klapaki (2000), who stated that greenhouse hybrid pepper responded differently for plant height, fruit length, fruit weight and yield plant^-1. Moreover, Aliu et al. (2017) stated that different pepper genotypes of Kosovo showed highly significant differences for various morphological traits like plant height, fruit dimension and fruit weight as proved in our studied cultivars. Bozokalfa et al. (2009) proved phenotypic variation in pepper cultivars in response to various cultural practices in Turkey.

CONCLUSION

Life zone for capsicum species is 7 to 29 °C with an annual precipitation of 0.3 to 4.6 meters, however, average summer temperature and rainfall in arid region of Bahawalpur is ≥ 38 °C and ≤ 0.2 meters, respectively; thus it is recommended to spray 75 mg L^-1 SA on chilli cultivar (Sky-Land-II) after 50, 70 and 90 days of seedlings transplantation for better plant and fruit growth and high yield. Other cultivars are needed to be introduced in this region through screening and standardizing the production technology against various salinity and drought stresses.

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