Effect of plant growth regulators on growth and yield of chili (Capsicum annuum L.)

Chili (Capsicum annuum L.) is an important food additive with high medicinal value. To investigate the effect of plant growth regulators on chili, seedlings of chili were collected from the local market and grown in the experimental field of the University of Barishal, Bangladesh. Foliar spray of different degrees of plant growth regulators, Gibberellin (50 mg/l, 100 mg/l, 250mg/l, 350 mg/l GA3) and Cytokinin (50 mg/l, 100 mg/l, 250mg/l, 350mg/l Kn) were applied from 15 days of germination. Data on different growth and yield parameters were collected and analyzed statistically. The result reveals that there is a significant difference in growth and yield related traits in chili due to the application of plant growth regulators. An optimum level of PGRs application shows better performance compare with control. Plant height particularly influenced by GA3 whereas other attributes like the number of leaves, branches, flowers and fruits are greatly influenced by the application of kinetin.


INTRODUCTION
Chili (Capsicum annuum L.) is a member of the family Solanaceae, cultivated all year round for variable purposes [1,2]. This crop is famous for its pleasant aromatic flavor, pungency and high colouring substance. The placenta of chili fruits contains phenolic acid compound "capsaicin" which is responsible for the pungency in chili. The pigment "capsanthin" gives the bright red colour of chili at the ripening stage [3].Chili fruit is mainly used as a food additive. In addition, it is also used as traditional medicine, like for the treatment of cough, toothache, sore throat, parasitic infection, wound healing, and also utilized as an antiseptic, antioxidant, and immunemodulator etc. [4,5,6].
The inherent genetic yield potential of the cultivars along with several environmental factors and cultivation practices govern the production of chili. Flower and fruit drop caused by physiological and hormonal imbalance in the plants particularly under unfavorable environments, such as extremes of temperature i.e. too low or high temperatures is one of the major problem in chili production [7,8,9]. Over 60% of the flowers produced in a chili plant are shed. So, yield can be increased by decreasing flower drop. This problem can be solved by selection of breeding lines which retain large proportion of flowers or physiological manipulations by spraying of plant growth regulators (PGRs) which reduces the flower drop [10].
Plant growth regulator is an organic compound, either natural or synthetic, that modifies or controls one or more specific physiological processes within a plant. The plant growth regulators are known to enhance the source sink relationship and stimulate the translocation of photo assimilates thereby helping in better retention of flowers and fruits. Besides this, the growth regulators have the ability to cause accelerated growth in plants. Application of PGR in small amounts modifies the growth of plants usually by stimulating or inhibiting part of the natural growth regulatory system. PGRs are known to enhance the source sink relationship and stimulate the translocation of photo assimilates thereby helping better fruit set.
Among the sixty plant growth regulators which are now commercially available several have reached considerable importance in crop production [10]. Among them gibberellin and cytokinin are very important to stimulate vegetative and reproductive growth of plant. GA 3 , the most common gibberellins, regulate various developmental processes, including stem elongation, germination, dormancy, flowering and fruit development. Cytokinins promote cell division or cytokines is in plant roots and shoots. They are involved primarily in cell growth and differentiation, but also affect apical dominance, axillary bud growth and leaf senescence. Kinetin is a type of cytokinin that promotes cell division.
The average yield of chili in Bangladesh is very low compared to other leading chili growing countries in the world due to improper cultivation management practices. Improvement of existing spice crops through proper cultural management practices need urgent attention to meet increasing demand of edible spices for the fast growing population of Bangladesh.
Therefore, attempt to increase per unit production is necessary. That is why, special attention should be made for increasing the yield per unit area by adopting improved technologies and management practices. To increase the chili production, we need to adapt improve production technology and better agronomic practices and use high yielding adapted varieties.
There are scopes for making breakthrough for improving yield through changes of hormonal behaviors. In this connection, use of plant growth regulators (PGRs) might be a useful alternative to increase crop production. The present study was conducted to select the suitable dose of exact PGR that control the growth and finally increase the chili production in Bangladesh.

MATERIALS AND METHODS
The present study was undertaken at the experimental field of Department of Botany, University of Barishal to study the effect of various growth regulators on growth responses of chili. The soil of the experimental pot will be thoroughly mixed with recommended doses of urea, Triple Super Phosphate (TSP), Muriate of Potash (MP), gypsum and cow dung for the cultivation of chili in Bangladesh. Locally grown chili plantlets were used as plant material in the present experiment. The experiment was laid out in randomized block design with three replication and five treatments. Intercultural operations like irrigation, weeding, mulching and pest control were followed as and when necessary for normal growth and developments of chili plants.
Foliar application of GA 3 (50 mg/l, 100 mg/l, 250 mg/l, 350 mg/l) and Kinetin (50 mg/l, 100 mg/l, 250 mg/l, 350 mg/l) were applied at 15 days after transplantation and repeat it twice a week up to harvest stage. The spray was done by hand sprayer at morning. The collected data were analyzed statistically and the mean difference was adjudged by Duncan's Multiple Range Test (DMRT).

RESULT AND DISCUSSION
Findings of the study of effect of plant growth regulators on growth and yield of chili are as follows-

Plant Height
The effect of varying concentration of plant growth regulators on plant height has been presented in Table 1 The increase in height of GA 3 treated plant might be due to rapid elongation, increased cell division and cell enlargement, which would have increased inter nodal distance. Table 2 represents the effect of PGRs on number of leaf of chili plants used in the present investigation. From table-2 it is observed that there is a significant difference in leaf number with the different degrees of GA 3 and Kn. At 30 DAT highest number of leaf found in T 2 (100 mg/l GA 3 ) whereas highest number of leaf found in T 6 (100 mg/l Kn) at 15 DAT and 90 DAT of plant age. Over all the highest number of leaf found in T 6 (100 mg/l Kn)i.e 57.1 followed by T 4 (350 mg/l GA 3 ) i.e 42.9 and T 2 (100 mg/l GA 3 ) i.e

Number of Branches
A significant difference found in number of branches with the application of PGRs, which has been shown in Table 3.
After 30 days highest number of branch (7.75) was found in T 2 (100 mg/l GA 3 ) whereas maximum number of branches 12.5 and 18.5 was found in T 6 (100 mg/l Kn) at 60 and 90 DAT respectively. In the mean, the highest number (12.75) was found in T 6 (100 mg/l Kn) followed by 11.5 in T 2 (100 mg/l GA 3 ) and the lowest number found 7.42 in T 4 (350 mg/l GA 3 [20] where they drew attention to the fact that under the influence of kinetin many buds form on a single tobacco tissue fragment without seeming to inhibit each other's growth.

Number of Flower
Effect of PGRs on flowering of chili is shown in Fig. 1

Number of Fruit
Number of fruit is also significantly differing when plant growth regulators applied. From Table 4 it is found that better fruit setting response was found in T 6 (100 mg/l Kn). In    T0  T1  T2  T3  T4  T5  T6  T7  T8  mean  overall expression highest number was 10.42 that found in T 6 (100 mg/l Kn) followed by 7.33 in T 7 (250 mg/l Kn) and 7.25 in both the T 2 (100 mg/l GA 3 ) and T 3 (250 mg/l GA 3 ). This result go with the findings of Lou et al. (2012) in Eriobotrya japonica [22], Mukherjee and Kumar (2007) in Cajanus cajan L. [23] where they found a better fruit setting after application of kinetin.

CONCLUSION
Result of the present study suggests that the application of optimum degree of plant growth regulators GA 3 and Kn improve the growth and reproduction of chili. Particularly kinetin has a great positive impact on growth and yield of chili.

AUTHOR CONTRIBUTION STATEMENT
All of the authors conceived and designed the program. Anolisa and Md. Al-Imran conducted the experiments including statistical analyses and wrote the manuscript. Subroto K. Das mainly supervised the experiments. Subroto K. Das, Riyad Hossen and A.T.M. Rafiqul Islam co-ordinate the study and gave suggestion in preparing manuscript.