14. study on occurrence and safe removal of dormancy in sunflower


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14. study on occurrence and safe removal of dormancy in sunflower

  1. 1. Study on Occurrence and Safe Removal of Dormancy in Sunflower (Helianthus annuus L.) Pallavi H M, Rame Gowda, Shadakshari Y G* and Vishwanath K Department of Seed Science and Technology, University of Agricultural Sciences, GKVK, Bangalore - 65, Karnataka, India *AICRP on Sunflower, University of Agricultural Sciences, GKVK, Bangalore - 65, Karnataka, India e-mail: pallavihm@gmail.com A B S T R A C T A study was conducted on the seed maturation and occurrence of seed dormancy and safe removal method using physical and chemical methods. The study showed that germination per cent was very low (2.0%) at 30 days after pollination (DAP) and increased to 16% after 40 DAP. The dormancy dissipated naturally between 30 to 40 days after harvest (DAH). Maximum germination was recorded at 60 DAH (98.50%) followed by 50 DAH (96.75%). Besides, seed dormancy breaking study revealed that the seeds soaked in water for 24 hours recorded higher germination (82%) followed by dry heating at 80°C for 10 minutes (81%). Seeds treated with GA3 @ 100 ppm recorded higher seedling vigour index (908) followed by ethrel @ 25 ppm (904) and water (902). The smoke treatment with ‘sambrani’ also resulted in significant improvement in germination (80%) over control (24%). Key words: Sunflower, Seed dormancy, Seed treatments, Seed maturation Dormancy is an important component of physiological quality of sunflower seeds. Presence of dormancy causes germination problems in sunflower seeds since it delays the embryo growth and development and is controlled by endogenous action of seeds (Amen 1968). Sunflower require 40-45 days to attain germination capacity, thereby delays the immediate sowing of the seeds for seed and commercial production. Further, dormancy increases when germination takes place under stress (poor field conditions). Dormancy is reported to be innate and is the resultant of interaction between maternal and embryonic genotypes (Zimmerman and Zimmer 1978). Bianco et al. (1994) studied the occurrence of dormancy and found that period of dormancy varied between cultivars ranging from 12 to 40 days after maturity. The degree of maturity of the seeds also influence the dormancy duration. It has reported that seeds harvested early with moisture content of 41-62 per cent showed dormancy for 42-50 days while, seeds harvested at the final maturity stage with moisture content 8-12 per cent possess dormancy only for 22-29 days after harvesting. It has to be safely removed before planting seeds to obtain uniform and better germination. The embryos of sunflower are capable of germinating after 12-16 DAA followed by deep dormancy at 20-30 DAA due to accumulation of Abscisic acid (Le Page et al. 1996) and presence of thick pericarp and seed coat (Subrahmanyam et al. 2002). However, the embryos gained germination capacity at 40 DAA (Ramazunova 1994). At the time of maturity, the balance in promoter- inhibitor is more towards inhibitors, thus imposing dormancy. However, dormant mature seeds of sunflower will eliminate dormancy during storage in under conditions. Seiler (1993) reported that the age of achenes at harvest of wild Helianthus annuus and H. petiolaris had a significant influence on germination and the maximum germination took place by 21 DAA, while, combination of storage temperatures and time could not break dormancy. Further, stated (Singh and Rao 1994) that chemical pre-treatment of wild sunflower achenes with 1mM solution of gibberellic acid (GA3) almost doubled the germination percentage over a non-treated control. The age of the achenes at harvest influenced the germination. Achenes of H. petiolaris, harvested 20 DAF generally had greater germination than those harvested at 40 DAF. Germination of GA3 treated seeds was 81 per cent compared with 38 per cent in control and the enhanced germination was regardless of achene maturity, storage time or storage temperature (Gerald 1998). Seed dormancy of wild sunflowers (H. annuus, H. argophyllus and H. exilis) was found to be controlled primarily by the seed covering (seed coat and pericarp) and embryo dormancy was short-lived (four to eight weeks). Ethylene and its precursor known to enhance the germination by breaking dormancy (Corbineau et al. 1990). The protease activity may be involved in the removal of dormancy by ethylene and the improvement of germination of the sunflower embryo (Borghetti et al. 2002). Since sunflower seeds exhibits 45 to 60 days of dormancy after harvesting, there is a need to identify a simple low cost technique for its safe removal. Several researchers have made an attempt to develop a chemical seed treatment technique for the safe removal of dormancy and succeeded in it. Singh and Rao (1994) Research Journal of Agricultural Sciences 2010, 1(4): 341-344 341
  2. 2. also observed that sunflower parental lines, soaked with GA3 recorded in higher germination, however, the MSCS of 70 per cent germination was obtained by soaking in water for 24 hours. Maiti et al. (2005) indicated that sunflower genotypes showed a large variability in dormancy. In general, sunflower hybrids showed greater levels of seed dormancy than the cultivated genotypes. Seed germination was highest under alternating conditions of 12 hours light and 12 hours darkness. The dormancy is mainly due to embryo dormancy and disappears during dry storage in sunflower (Oracz et al. 2008). Endogenous ethylene is involved in sunflower seed alleviation of dormancy. Cyanide is produced during the conversion of 1- aminocyclopropane 1-carboxylic acid to ethylene. While naked dormant sunflower seeds germinated at 10°C when incubated in the presence of 1mM gaseous cyanide. Cyanide stimulated germination of dormant seeds in the presence of inhibitors of ethylene biosynthesis, but its improving effect required functional ethylene receptors. This has not affected ethylene production and the expression of genes involved in ethylene biosynthesis or in the first steps of ethylene signaling pathway. However, the expression of the transcription factor ethylene response factor 1 (ERF1) was markedly stimulated in the presence of gaseous cyanide. The dormancy of the sunflower was overcome by soaking seeds in etherel (25ppm) (Borghetti et al. 2002) and also through hydro priming (Maiti et al. 2005). The physical treatments which does not involve water as a component was under significance to ease the dormancy breaking treatments while handling large mass of seeds at a time. While handling large bulk of seeds, soaking in water is risky since it needs to redry seeds to its original moisture content before packing and shifting. Keeping the above in view is essential to develop a suitable technique which eliminates soaking of seeds in water. MATERIALS AND METHODS Test weight of sunflower seeds recorded at different stages of maturity differed significantly. Maximum seed weight (5.597g) was recorded in seeds harvested at 30 days after pollination (DAP) which was on par with the seeds harvested at 40 DAP (5.567g). Lower dry matter accumulation was observed when seeds harvested at 10 DAP (1.324g). The seed weight increased as the days to maturity increased might be due to the accumulation of food reserves in the cotyledons. Sunflower being an oil seed crop the accumulation of oil in the seed increased only after 10 DAP correspondingly resulted in increased seed weight. The germination of sunflower seeds harvested at 10 DAP was zero and there was no germination till the seeds attained the maximum dry weight (30 DAP). The germination was only 2.0 per cent when harvested at 30 DAP and increased to 18.0 per cent after 40 DAP. The accumulation of food reserves have direct relationship with the germination per cent Table 1 Influence of maturity stages on 100 seed weight (g) and germination (%) in sunflower hybrid KBSH-44 Maturity stages 100 seed weight (g) Germination (%) 10 DAP 1.324 0.00 20 DAP 3.275 0.00 30 DAP 5.597 1.00 40 DAP 5.567 16.0 Mean 3.888 5.00 S. Em± 0.062 - CD (0.05P) 0.13 - CV (%) 2.50 - Freshly harvested matured seeds of sunflower hybrid KBSH-44 were tested for its germination from date of harvest and at weekly interval to check its natural dissipation of dormancy (Table 2). Freshly harvested seeds recorded zero per cent germination. The germination per cent has increased from 0 DAH to 60 DAH. There was gradual decrease in per cent dormancy and increase in germination per cent. Seeds attained maximum germination (100%) at 60 DAH followed by 50 DAH (97.0%). Sunflower requires 40-45 days to attain full germination capacity, thereby delays the immediate sowing of the seeds for commercial crop production. This confirmed the presence of dormancy in freshly harvested seeds of sunflower. However, the seeds attained 85.5 per cent of germination at 40 DAH which is more than the MSCS. Thus, the seeds of sunflower could be safely used for sowing after 30 to 40 days after harvest. However, complete elimination of dormancy was observed only after 60 DAH. The dormancy in sunflower is mainly due to under developed embryo and disappears during dry storage in sunflower (Oracz et al. 2008). Harvest dormancy of sunflower seeds can be released by after-ripening and involves hormonal changes like decrease in ABA biosynthesis and sensitivity (Corbineau et al. 1990, Le Page et al.1992, Le Page et al. 1996). Dry storage of mature or immature seeds strongly improves germination by breaking embryo dormancy and seed coat inhibition (Corbineau et al.1989). RESULTS AND DISCUSSION Safe removal of seed dormancy Freshly harvested seeds of sunflower were treated with different physical and chemical treatments for its safe removal of dormancy and the results are presented in Table 3. Viability (%) The per cent seed viability varied significantly after physical and chemical seed treatments imposed to break the dormancy. Viability decreased significantly when 342 Pallavi et al.
  3. 3. the seeds were dry heated at high temperatures. Among the different treatments, lowest per cent of viability was recorded when seeds were dry heated at 100°C for 5 minutes (T10-19%) followed by micro wave exposure for 60 seconds (T16-26%). The reduced activity of dehydrogenase might have caused seeds to become nonviable. Seeds treated with chemicals did not show any reduction in viability per cent. However, highest (99%) was recorded in seeds treated with Ethrel (25 ppm), thiourea (100 ppm) and KNO3 (2%) followed by chemically treated seeds. Table 2 Natural dissipation of seed dormancy in sunflower hybrid KBSH-44 Days after harvest R1 R2 R3 R4 Mean 0 7 5 8 6 6.50 7 16 24 18 22 20.00 14 34 32 33 36 33.75 20 36 32 38 36 35.50 30 59 62 58 64 60.75 40 85 86 88 84 85.75 50 96 98 96 97 96.75 60 100 100 98 96 98.50 Mean 54.13 54.88 54.63 55.13 Germination (%) The influence of various dormancy breaking methods on germination percentage varied significantly. In general seeds treated with chemicals recorded higher germination when compared to physical treatments. Among the treatments, seeds soaked in water for 24 hours recorded maximum germination (82 %) followed by dry heating at 80°C for 10 minutes (81%), Ethrel @ 25 ppm (80 %), smoke for 3h (80%) and GA3 @ 100 ppm (79 %) as against the control where it was only 24 per cent. Similar results have been reported by (Singh and Rao 1994, Gerald 1998, Borghetti et al. 2002, Fabian et al. 2002) opined that the protease activity might be involved in breaking dormancy by ethylene and there by improvement in germination of sunflower embryo was seen. The causal mechanism of breaking dormancy/ enhancing germination induced by chemical treatments might be due to some chemical changes in the seed during the change from solution to gel stage by soaking and drying process. This might be associated with the washing away of the inhibitor, ABA and further during the process, the porosity of the seed coat might have increased and resulted in increased germination per cent (Maiti et al. 2005). The increased germination in dry heat treatments could be due to the denaturation of inhibitors and also enhanced after ripening process. Table 3 Influence of different physical and chemical seed treatments on seed quality parameters and release of dormancy in sunflower hybrid (KBSH-44) Treatments Viability (%) Germination (%) % increase over control Seedling dry weight (mg) SVI T1: Control 96 24 --- 11.50 276 T2: Water (24 hrs) 98 82 241.6 11.00 902 T3: Dry heating (60°C,15 min) 54 54 125.0 11.40 615 T4: Dry heating (60° C, 30 min) 55 50 108.3 09.50 475 T5: Dry heating (60° C, 60 min) 47 46 91.66 09.15 420 T6: Dry heating (70°C, 15 min) 49 48 100.0 10.85 520 T7: Dry heating (70°C, 30 min) 48 47 95.83 07.55 354 T8: Dry heating (80° C, 15 min) 46 43 79.16 10.10 434 T9: Dry heating (80°C, 10 min) 87 81 237.5 08.75 708 T10: Dry heating (100° C, 5 min) 19 15 -37.50 08.15 122 T11: Dry heating (100° C, 2 min) 50 50 108.3 09.20 460 T12: Microwave (80%, 30 sec.) 55 55 129.1 09.30 511 T13: Microwave (80%, 60 sec.) 43 43 79.16 09.05 389 T14: Microwave (100%, 20 sec.) 46 45 87.50 10.85 488 T15: Microwave (100%, 30 sec.) 35 34 41.66 7.70 261 T16: Microwave (100%, 60 sec.) 26 26 8.333 5.10 132 T17: Smoking (3 hours) 97 80 233.3 10.50 840 T18: GA3 (100 ppm) 98 79 229.1 11.50 908 T19: Thiourea (100 ppm) 99 66 175.0 09.50 532 T20: Ethrel (25 ppm) 99 80 233.3 11.30 904 T21: KNO3 (2%) 99 76 216.6 11.00 836 Mean 64.09 52.19 - 10.14 520.56 S.Em± 1.90 4.58 - 0.989 74.36 CD (0.05P) 3.96 9.54 - 2.058 154.64 CV (%) 3.32 3.5 - 2.6 4.48 343 Study on Occurrence and Safe Removal of Dormancy in Sunflower
  4. 4. Seedling dry weight (mg) and Seedling vigour index The mean seedling dry weight differed significantly due to dormancy breaking treatments. The seeds treated with GA3 @ 100 ppm recorded higher seedling dry weight (11.50mg) and it was lower in micro wave exposure for 60 sec (5.10mg). Though the seeds dry heated at 80°C had recorded higher germination (81%), the seedling dry weight was lower (8.75mg) due to the shortened seedling length. Similarly, higher seedling vigour index was recorded when seeds were treated with GA3 @ 100 ppm (908) followed by ethrel 25 ppm (904) and water (902). However, the seedling vigour index was greatly affected in dry heat at 100°C for 5 minutes (122) followed by microwave exposure for 60 seconds (132). When seeds exposed to high energy treatments might have affected the enzyme activation resulting in reduced seedling growth and vigour index. Seeds exposed to sambrani smoke for 3 hours had also stimulated germination (80%), better seedling dry weight (10.5mg) and vigour (840) compared to control. Tieu et al. (2001) opined that ethylene in the smoke was responsible for the stimulation of germination (Brown and Staden 1997). Thus both smoke treatment and drying treatments can be commonly exploited for removal of seed dormancy in sunflower. However, the protocol needs to be refined further. LITERATURE CITED Amen R D. 1968. A model of seed dormancy. Botanical Review 34: 131 Bianco J Garello G and M T Le Page-degivry. 1994. Release of dormancy in sunflower embryos by dry storage: involvement of gibberellins and abscisic acid. Seed Science and Research 4: 57-62 Borghetti F, Noda F N and De Sa C M. 2002. Possible involvement of proteasome activity in ethylene-induced germination of dormant sunflower embryos. Brazilian Journal of Plant Physiology 14: 125-131 Brown N A C and Staden J Van. 1997. Smoke as a germination cue: a review. Plant Growth Regulation 22: 115-124 Corbineau F, Bagniol S and Come D. 1990. Sunflower (Helianthus annuus L.) seed dormancy and its regulation by ethylene. Israel Journal of Botany 39: 313-325 Corbineau F, Rudnicki R M and Comes D. 1989. ACC conversion to ethylene by sunflower seeds in relation to maturation, germination and thermodormancy. Plant Growth Regulation 8: 105-115 Fabian B, Nakamura N F and Martins de Sa Cezar. 2002. Possible involvement of protease activity in ethylene- induced germination of dormant sunflower embryos. Brazilian Journal of Plant Physiology 14: 125-131 Gerald J Seiler. 1998. Seed Maturity, Storage Time and Temperature, and Media Treatment Effects on Germination of Two Wild Sunflowers. Agronomy Journal 90: 221-226 Le Page-degivry M T and Garello G. 1992. In situ Abscisic acid synthesis: a requirement for induction of embryo dormancy in Helianthus annuus L. Plant Physiology 98: 1386-1390 Le Page-degivry M T, Bianco J, Barthe P and Garello G. 1996. Change in hormone sensitivity in relation to the onset and breaking of sunflower embryo dormancy. In: Lang GA, ed. Plant dormancy: physiology, biochemistry and molecular biology. Wallingford, CAB International, pp221-231 Maiti R K, Vidyasagar P, Shahapur S C and Seiler G J. 2005. Genotypic variability in seed dormancy in sunflower (Helianthus annuus L.) genotypes and the effects of priming in breaking dormancy and improving seedling vigour. Crop Research 30(2): 291-298 Oracz Krystynael-Maarour-Bouteau, Hayatbogatek, Renatacorbineau, Francoisebailly and Christophe. 2008. Release of sunflower seed dormancy by cyanide: cross-talk with ethylene signaling pathway. www.pubmedcentral.nih.gov/articlerender.fcgi Ramazunova. 1994. The nature of sunflower seed dormancy and its control by environmental factors. Sel Skokhozyiastvenneya Biologia 3: 89-97 Seiler G J. 1993. Wild sunflower species germination. Helia 16(18): 15-20 Singh B G and Rao G R. 1994. Effect of chemical soaking of sunflower seeds on vigour index. Indian Journal of Agricultural Sciences 63: 232-233 Subrahmanyam S V R, Kumar S S R and Ranganatha A R G. 2002. Genotypic differences for seed dormancy in sunflower (Helianthus annuus L.). Seed Research 30: 325-327 Tieu A, Dixon K W, Meney K A and Sivasithamparam K. 2001. The Interaction of Heat and Smoke in the Release of Seed Dormancy in Seven Species from Southwestern Western Australia. Annuals of Botany 88: 259-265 Zimmerman D C and Zimmer D E. 1978. Influence of harvest date and freezing on sunflower seed germination. Crop Science 18: 479-481 344 Pallavi et al.