Neelam Sangwan, B.B.Arora, S.P.Singh1* and Dhiraj Singh1

Genotypic variability for germination and early seedling growth in Indian mustard (brassica juncea L.) in response to IAA application

Neelam Sangwan, B.B.Arora, S.P.Singh1* and Dhiraj Singh1

Department of Crop Physiology, CCS Haryana Agricultural University, Hisar, Haryana

1 Directorate of Rapeseed-Mustard Research, Sewar, Bharatpur, Rajasthan

*Corresponding author:

Abstract

The present experiment was conducted to assess the effect of pre-sowing seed soaking with IAA (50 µM) on germination and seedling growth of 15 Indian mustard (brassica juncea L.) genotypes under controlled laboratory condition. IAA resulted in a significant increase in the germination percentage, mean daily germination (MDG), peak value (PV), germination value (GV), vigour index (VI), shoot and root length of different genotypes. However, a substantial variation existed among genotypes for different tested traits in response to IAA. The mean germination percentage of tested genotypes increased by 14% due to IAA with respect to control. Highest increase in germination percentage with IAA was recorded in NPJ-93 followed by RGN-81, RH-0116, RGN-48 and RH-819. IAA showed an increase of 34% in mean MDG and 41% in mean PV over control. The percent increase in both MDG and PV due to IAA was found highest in NPJ-93 followed by RGN-81, RGN-48 and RH-0116. The GV and VI of four genotypes, RH-819, RH-30, RH0116 and RH-8113 was significantly higher than general mean under IAA treatment, while other varieties showed significantly lower values. The IAA increased mean shoot and root length of genotypes by 31% and 21%, respectively. Highest shoot and root length under IAA treatment was recorded in RH819 followed by RH30.

Key words: Brassica juncea L., germination percentage, germination value, IAA, ,vigour index, peak value

Introduction

Rapeseed-Mustard is an important oil seed crop of the world after soybean (FAO, 2001). In India, it is the second most important oilseed crop after groundnut, cultivated on an area of 6.51 million ha with a total net production of 7.67 million tonnes, and with an average yield of 1179 kg/ha (Anonymous, 2011). It is cultivated in rabi season mainly in northwest India, and contributes nearly 27% to the edible oil pool of the country (Singh et al., 2010).

In crop production, germination and seedling establishment is a critical stage. In order to obtain fast and good establishment of seedlings, seeds with high vigour are needed to provide essential nutrients for seedling establishment and to enable them to photosynthesize independently. Successful seedling establishment depends on the frequency and amount of precipitation, as well as on the ability of seed species to germinate and grow when soil moisture and osmotic potential are low (Ahmad, Jalal 2009). Germination and seedling characteristics are the most viable criteria for cultivar selection.

Growth regulators have been successfully employed for improving the germination and seedling growth in a number of crops (Gopikumar and Moktan, 1994; Sushmita-Bhattacharjee et al., 2000). The growth regulators affect seed germination by acting on different parts of the seed (Srivastava, 2002). The seed development, dormancy and germination are controlled by specific endogenous growth promoting and inhibiting compounds (Hartman et al., 1997) and there is a correlation of hormone concentration with specific developmental stages, effect of applied hormones, and the relationship of hormones to metabolic activities (Pedroza-Manrique et al., 2005). Growth regulators also play important role in ameliorating the adverse effects of several abiotic stresses on germination and seedling growth characteristics (Uma et al., 2007; Singh et al., 1997). The normal hormonal balance of the seed is disturbed when grown under abiotic stresses, which may partly be responsible for the various metabolic disturbances leading to general suppression of germination and seedling growth. Thus, besides increasing the seed yield, growth regulators serve a potential tool to manage the abiotic stresses. IAA is a phytohormone that is needed in small quantities at low concentration to accelerate plant growth and development. It has been documented in several crops that application of IAA manipulates a variety of changes in seed that result to better germination and seedling establishment. However, in mustard little information is available on this aspect. Keeping in view the aforesaid facts present study was undertaken to evaluate the effect of IAA on germination and early seedling growth of 15 genotypes of B. juncea.

Materials and Methods

Seed source, surface sterilization and pre-soaking with IAA

The present experiment was conducted in the Department of Crop Physiology, CCS Haryana Agricultural University, Hisar, India under controlled laboratory conditions in rabi 2012. Seeds of fifteen genotypes of Indian mustard (Brassica juncea L.) were obtained from the Department of Genetics and Plant Breeding of the university. The seeds were surface sterilized using 0.1% (w/v) aqueous mercuric chloride solution for 5 minutes followed by washing with sterilized distilled water for 5 times and then were soaked in 50 µM IAA solution for four hours along with control (water soaked). After soaking treatment, the seeds were removed from the solution and transferred to a tray covered with filter paper in bottom and dried at room temperature till seeds attain original weight.

Sowing and raising the seedlings

The experiment consisted 15 genotypes and 2 growth regulator treatments viz., 50 µM IAA (seed soaking), control (water soaked); their combinations constructing a total of 30 treatments. Thirty seeds of each variety was sown in plastic trays (40 x 29 x 7 cm) filled with 5 kg sandy loam soil (pH -7.8, ECe- 0.12 dS/m) saturated to field capacity. Treatments were replicated three times with three trays per treatment. Seedlings were grown in a seed germinator at 25±1ºC, 70% relative humidity for 10 days. During the experimental period, the pots were weighed on alternate days and water loss was replaced by adding distilled water.

Data collection on germination and seedling growth

Seedling emergence was recorded daily after the first emergence and counted for 10 days after sowing (DAS). A sample of five uniform seedlings from each set was selected per replication and length of root and shoot was measured. Germination percentage, mean daily germination (MDG), peak value (PV), germination value and seedling vigour index were computed by using the following formula:

1. Germination (%) = n / N × 100,

where n is the number of germinated seed at the 10th day; N is the number of total seeds;

2. MDG = Final germination percentage/ Total number of days in a test

3. PV = Final germination percentage/ Number of days required to reach maximum germination percentage

4. GV = MDG x PV

5. Seedling vigour index = Germination (%) x (root length + shoot length in cm)

Results and Discussion

Seed treatment with IAA increased the mean germination percentage of tested genotypes by 14% over control (Table1). The germination percentage in IAA ranged from 83% (PBR-92, RH-0119) to 100% (NPJ-93, RH-0116) as compared to 75% (RGN-81, RH-0119) to 85% (RH-30) in control. Two genotypes, RH-30 and RK-02-03 in control and four genotypes, RH-819, RH-30, RH-0116 and NPJ-93 in IAA showed significantly higher germination percentage than general mean. Among the genotypes, highest increase in germination percentage with IAA was found in NPJ-93(25%) followed by RGN-81(22%), RH-0116, RGN-48(19%) and RH-819, RH-8113, PCR-7 (17%). Phytohormones regulate and integrate the overall growth, development and reproduction in plants by acting as chemical messengers for the communication among cells, tissues and organs (Kucera et al., 2005). They are considered effective molecule in development of seeds. The hormonal control of germination involves a balance between the stimulating and inhibitory components of seeds (Thomas 1980; Pierik 1987). According to Walz et al.(2002), there is a correlation of auxins and cytokinins in plant, known as a A/C=constant that plays important role in germination. The natural IAA can be oxidized by enzyme IAA oxidase, while synthetic auxins are not destroyed by IAA oxidase, so persist longer than natural auxin; this maintain high A/C ratio in seed resulting to better germination. Patil et al.(2012) tested different types and cocentrations of auxins, and found that IAA (10 µM) was most effective in promoting the seed germination of Digitalis purpura L. The present result also get support from the findings of many workers who found stimulatory effect of lower conentration of IAA on seed germination in several crops (Birendra and Bijendra, 1996; Naidu et al., 2000)

Mean daily germination (MDG) and peak value (PV) differed non significantly among mustard genotypes in control (Table1), however in IAA, significant differences were observed. IAA resulted in an increase of 34 and 41% in mean MDG and PV, respectively over control. The maximum percent increase in both MDG and PV due to IAA was found in NPJ-93 followed by RGN-81, RGN-48 and RH-0116. The mean germination value (GV) and vigour index (VI) of tested varieties increased by 17 and 45%, respectively with IAA application (Table2). Among genotypes, percent increase in GV due to IAA varied from 0.7(RM-101) to 42% (NPJ-93) and in VI from 19.3 (PBR-92) to 121% (RH-0119). Six genotypes, RH-819, RH-30, RH-0116, RH-8113, RM-11, PCR-7 showed significantly higher GV over general mean under both control and IAA treatment. However, GV value of above varieties was 9 to 18% higher under IAA than control. Two genotypes, RGN-48 and NPJ-93 which had significantly lower GV than general mean under control showed significantly higher GV under IAA and recorded 17 and 42% increase, respectively. The VI of six genotypes, RH-819, RH-30, RH0116, RH-8113, RK-02-03 and NPJ-93 was significantly higher than general mean in both control and IAA treatment. However, above varieties recorded 33 (RH-8113) to 78% (RH-0116) higher VI in IAA as compared to control. In the interpretation of Brown and Mayer (1988), PV is an expression of speed and totality of germination, and their interaction. The values of PV and MDG can be counterbalanced, resulting in equal values for GV for samples or treatments with different behaviour in relation to germination process. Patil et al. (2012) evaluated different concentrations of IAA, NAA and 2,4-D and found that IAA (10 µM) was most effective in increasing the germination speed (GS), GV and VI of Digitalis purpura L. The IAA in combination with zeatin has been found promotive for seed germination, vigour index and and related traits in terrestial orchid species (Vejsadova, 2006). Our results are also in accordance with findings of other studies (Pedroza- Manrique et al., 2005; Zeng et al., 2012).

Application of IAA resulted in significant increase in shoot length and root length (Table 3). The IAA increased mean shoot length of genotypes by 31% as compared to 21% in root length. In control, the shoot length of varieties ranged from 0.31(NPJ-92) to 3.74 cm (RH-819) and in IAA, from 0.68 (ONK-1) to 4.78cm (RH-819). Four varieties, RH-819, RH-30, RK-02-03 and NPJ-93 recorded significantly higher shoot length over general mean in control as well as IAA treatment. The varieties exhibited large variability in the increase in shoot length in response to IAA that ranged from 0 to 184%; highest increase was observed in RGN-48 (184%) followed by PBR-92 (154%), RGN-81(140%) and NPJ-92 (129%). The root length of varieties varied from 2.05 (RH-0119) to 7.90 cm (RH-819) in control and 4.21(PB-92) to 9.80 cm (RH-819) in IAA. The genotypes RH-819, RH-30, RH-0116 and RH-8113 showed significantly higher root length over general mean in IAA treatment. The percent increase in root length in these varieties due to IAA ranged from 13 (RH-30) to129% (RH-0116). The promotive effect of presowing IAA treatment on shoot and root length may be attributed to their indirect effect through change in permeability. The differential increase in shoot length and root length in present experiment due to IAA is well supported by earlier studies (Vejsadova, 2006; Shen et al., 2011). Increase in shoot and root length with IAA may be more effective for seedling establishment especially in the varieties that had relatively lower shoot and root length (RH-0119, RM-101, ONK-1, PBR-92, RGN-81, PCR-7) in control. However, it is equally important for the varieties that have higher initial shoot length and root length (Control); even slight increase in above traits in these genotypes may give better seedling establishment resulting to higher seed yield and better adaptation under adverse environmental conditions. A similar promotive effect of plant growth hormones on seedling growth of Vigna mungo(Black gram) and Macrotyloma uniflorum (Horse gram) were reported by Chauhan et al. (2009).

It is deduced from the experiment that pre-sowing seed soaking with 50 µM IAA can be used as a potential tool for enhancing the germination and seedling growth of mustard. A substantial variation existed among genotypes for different tested germination traits in response to IAA. Among 15 genotypes, RH-819, RH-30, RH-0116, RH-8113, RK-02-03 and NPJ-93 showed relatively more beneficial effect of IAA. However, further study is necessary to assess the advantage of improved germination and seedling establishment on crop yield.

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