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Hybrid Seed Production in Helianthus annuus L. through Male Sterility Induced by Benzotriazole

Research Article Open Access
Surya Mani Tripathi* and KP Singh
Department of Botany, R.B.S. College, Agra-282002, India
*Corresponding author: Surya Mani Tripathi
Department of Botany
R.B.S. College
Agra-282002, India
E-mail: [email protected]
 
Received January 02, 2013; Published March 20, 2013
 
Citation: Tripathi SM, Singh KP (2013) Hybrid Seed Production in Helianthus annuus L. through Male Sterility Induced by Benzotriazole. 2:645 doi:10.4172/scientificreports.645
 
Copyright: © 2013 Tripathi SM, et al. This is an open-access article 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.
 
Abstract
 
The effect of various concentrations of benzotriazole (C6H5N3) on plant morphology, days taken for first flowering, pollen fertility and yield in Helianthus annuus var. MSFH-17 was studied. All the treatments with this chemical hybridizing agent caused reduction in plant height, pollen fertility and yield component. One or two spray of 1% benzotriazole caused insignificant reduction in height and other parameters; however, these treatments induced almost complete pollen sterility among treated plants. On the other hand, the flowering was delayed in benzotriazole treated plants, in comparison to control ones. Plants treated once and twice with 1.0% benzotriazole showed 23.01 and 22.22 g total seed yield/plant, in comparison to 23.68 g total yield/plant produced by control plants. This reduction in yield was insignificant as analyzed by paired student’s‘t’ test. The seeds of 1.5% benzotriazole treated plants showed significant enhancement in total yield in F1 generation from that of control plants due to heterotic effect.
 
Keywords
 
Sunflower; Copper chelating compound; Induced male sterility; Phytotoxicity
 
Introduction
 
Sunflower enjoys fourth position among oil seed crops, after soybean, rapeseed-mustard and ground nut. In economically important crops, attempts to develop hybrid varieties have been hampered by the lack of a suitable and well-functioning male sterility system. Sunflower is predominantly cross-pollinated; although it has genic and structural male sterility systems, but the commercial hybrid seed usage is very limited, because of the cost of required hybrid breeding. An alternative way for practical and more economical production is to use chemically induced male sterile system for breeding purpose. Various chemisterilants have been used to induce male sterility in a large number of plants for hybrid seed production [1-3]. According to Cross and Schulz (1997), benzotriazole is a copper chelating compound, and act as an inhibitor of microscope development. Tapetum, the target site for benzotriazole action, became metabolically inactive due to presence of degenerated cell organelles, and release large amount of sporopollenin [4,5]. The accumulation of unpolymerized sporopollenin precursors increases the osmotic potential of the locular fluid, and drew water out of the microspores, causing them to collapse [6]. Benzotriazole is found to be quite successful in inducing male sterility in a wide range of plants [ 4,7,8].
 
The present communication deals with the effect of benzotriazole (C 6H5N3) on plant height, days taken for first flowering, pollen fertility and yield component in Helianthus annuus L. This study was originally intended to explore the effective dosage of benzotriazole to induce male sterility in sunflower, with least phytotoxic effects.
 
Materials and Methods
 
The seeds of Helianthus annuus var. MSFH-17 and GK-2002 were sown alternately in a randomized row design pattern, maintaining the 25 cm distance between plants and 45 cm between rows. The plants of var. MSFH-17 were sprayed with different concentrations of benzotriazole and distilled water, and act as female parent and control. On the other hand, plants of GK-2002, left untreated between the rows of treated plants, to facilitate cross pollination. MSFH-17 and GK-2002, both are hybrid varieties released by Mahyco Hybrid Seeds Company Ltd., India and Ganga Kaveri Seeds, India, respectively. The MSFH- 17 population have good morphological characteristics and give high yield, but susceptible for fungal diseases. On the other hand, GK-2002 population is resistant for drought and fungal diseases.
 
Aqueous solutions of different concentrations of benzotriazole (1.0, 1.5 and 2.0% w/v) were prepared in distilled water. One or two drops of liquid soap were added as surfactant into these solutions. Fifty plants (var. MSFH-17) were sprayed about a week before the initiation of floral bud (T1), and another fifty plants were sprayed twice, first a week before, and second 5 days after floral bud initiation (T2), individual plants were sprayed with 15 ml of the solution to the runoff. A group of fifty plants were sprayed with distilled water to serve as control.
 
Pollen fertility was checked at regular intervals with Alexander's Stain [9]. Data on plant height, days taken for first flowering, pollen fertility, total yield/plant, and 100 seed weight from treated and controlled plants were collected and analyzed statistically by paired student's 't' test. The data was collected from the F1 plants grown from the seeds of 1.5% benzotriazole treated plants, and compared with control and statistically analyzed.
 
Results
 
Morphological studies
 
Plants of Helianthus annuus sprayed with different concentrations of benzotriazole displayed reduction in height, and this reduction was gradually increased with the increase in concentration and treatment of benzotriazole (Table 1 and Figure 1). However, plant treated once or twice with 1.0% benzotriazole showed insignificant reduction in height from that of control. Leaves of plants sprayed twice with 1.5 and 2.0% benzotriazole showed burning effect and turned brown.
 
Table 1: Effect of benzotriazole on vegetative and reproductive parameters of Helianthus annuus L.
 
 
Figure 1: Effect of benzotriazole on plant height.
 
Days taken to first flowering
 
In benzotriazole treated plants, first flowering was delayed in comparison to control plants (Table 1 and Figure 2). Single treatment with 1.0% benzotriazole caused insignificant enhancement in days taken for first flowering from control plants. Plants treated once or twice with 2.0% benzotriazole took maximum days (69 days) for flowering.
 
Figure 2: Effect of benzotriazole on days taken to first flowering.
 
Pollen fertility
 
Benzotriazole was found to be quite effective in inducing complete pollen sterility in this important oilseed crop (Table 1 and Figure 3). All the concentrations and treatments induced 100% pollen sterility, except single treatment of 1.0% benzotriazole, which induced 97.0% pollen sterility. Sterility induced by benzotriazole was of permanent nature and persistent throughout the flowering period.
 
Figure 3: Effect of benzotriazole on pollen sterility.
 
Yield
 
Plants treated once and twice with 1.0% benzotriazole showed insignificant reduction in total yield, along with 97-100% pollen sterility (Table 1 and Figure 4). These plants produced 23.01 and 22.22 g seeds per plant, in comparison to 23.68 g seeds produced by control plants. On the other hand, both the treatments of 1.5 and 2.0% benzotriazole caused significant reduction of yield in treated plants. Seed index (100 seed weight) also showed insignificant reduction with single and double treatments of 1% benzotriazole, which was 5.96 and 5.89 g, respectively, as compared to 6.23 g of that in control plants (Figure 5). The seeds of plants sprayed with higher concentration of benzotriazole were smaller and light weighted.
 
Figure 4: Effect of benzotriazole on total yield/plant.
 
Figure 5: Effect of benzotriazole on 100 seed weight.
 
Performance in F1 generation
 
Plants grown from the seeds obtained from 1.0% benzotriazole (T2) treated plants showed significant vigrosity in vegetative and reproductive parameters (Table 2). The plant height was insignificantly enhanced in F1 generation, as compared to height in control plants. However, days taken for first flowering and pollen sterility showed insignificant difference in both F1 and control plants. On the other hand, total yield (124.58%) and 100 seed weight (111.08%) showed significant enhancement over control in F1 generation plants. This 2013increase in different parameters showed the superiority of F1 plants over their parents due to heterosis. From the foregoing observations, it is evident that different concentrations of benzotriazole were found to be successful in inducing complete pollen sterility in Helianthus annuus. It is interesting to note that one and two spray of 1.0% benzotriazole, along with inducing 97-100% pollen sterility, caused insignificant reduction in yield components. This emphasized its suitability as a successful chemical hybridizing agent for Helianthus annuus.
 
Table 2: Performance of F1 generation plants obtained from the seeds of 1.5% benzotriazole treated plants of Helianthus annuus L.
 
Discussion
 
Benzotriazole has a toxic effect on plants [10]. Studies have shown that benzotriazole causes morphological changes in tomatoes [11], and has toxic effects on cucumber seedlings and bush beans [12,13] reported that triazoles are visibly toxic to plants, inhibiting root growth and plant development at concentrations greater than 100 mg/L 5-methyl benzotriazole. Benzotriazole has been shown to be an effective nitrification inhibitor [14].
 
Benzotriazole has also been shown to impact wheat yields via chelation of soil copper, causing resulting in male plant sterility and other Cu deficiency symptoms [15]. Benzotriazole act as an inhibitor of microspore development, and thus, causing male sterility in plants. It was also found to be a suitable chemical hybridizing agent for some other economically important crops like Brassica juncea [4], Vicia faba [7], Datura alba [8], Capsicum annuum, Gossypium arboreum and Raphanus sativus [16]. Lower concentration of benzotriazole caused insignificant reduction in yield components among all these crops.
 
Benzotriazole was not biodegradable, and tend to persist in the environment for a very long time due to their UV stability and resistance to oxidation. These properties of benzotriazole make it an effective CHA for a long time period. Thus, the male sterility induced by benzotriazole was of permanent nature and long lasting. Kaul [12] confirmed the phytotoxicity and stability of benzotriazole in soil solution. Another report by Klingensmith [13] noted that some triazoles, including 5-methyl benzotriazole, may be degraded by plant (Helianthus annuus) enzymatic reactions, when present at levels below the phytotoxic threshold. This may lead that although benzotriazole has some phytotoxic properties, but these effects were not found to be effective in sunflower plants, and failed to cause any damage on shoot apices, leaves, buds, etc.
 
The above observations and discussion conclude that lower dosage of benzotriazole caused poor phytotoxic effects, nearly 100% pollen sterility and insignificant reduction in yield parameters in Helianthus annuus. This is also supported by enhancement in yield components of 1 generation plants over their parent plants, due to heterotic effect. The experiment suggests that benzotriazole was found to be a suitable chemical hybridizing agent for sunflower, and double treatment with 1.0% benzotriazole can be effectively used at commercial scale. The encouraging results from benzotriazole based male sterility call for further evaluation on a larger scale.
 
Acknowledgements
 
Dr. Tripathi is grateful to CSIR, New Delhi for the financial assistance in the form of JRF and SRF, and the facilities provided by the Department of Botany, School of Life Sciences, Dr. B.R. Ambedkar University, Agra, India, throughout the period of the investigation, and for the successful completion of the present study as part of his Ph.D. research programme.
 
 
References