1. KAUTIR (Kerala Agricultural University Theses Information and Retrieval)

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Author: search.filters.author.Aiswarya Raj, P T.Subject: search.filters.subject.Genetics and Plant Breeding

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    Genetic improvement through physical mutagenesis in Gladiolus grandiflorus L.
    (Department of Genetics and Plant Breeding, College of Agriculture, Vellayani, 2024-11-28) Aiswarya Raj, P T.; Beena Thomas
    The present study entitled “Genetic improvement through physical mutagenesis in Gladiolus grandiflorus L.” was carried out in the Department of Genetics and Plant Breeding, College of Agriculture, Vellayani during 2022-24. This study aimed to develop novel ornamental characters in gladiolus through physical mutagenesis. The research programme involved two experiments. The first experiment was the determination of LD50 for gamma rays and the second was the induction of physical mutation through gamma irradiation in gladiolus. Corms of gladiolus varieties, Arka Amar and Arka Thilak were irradiated with gamma ray of doses 25, 40, 55 and 70 Gy using a gamma chamber with 60Co as the radiation source. Each dosage was applied to eight corms of both varieties. The survival rate of the plants decreased significantly with increasing radiation doses. The LD50 values were determined as 58.22 Gy for Arka Amar and 58.31 Gy for Arka Thilak through probit analysis. Based on the LD50 value, effective doses were fixed. Along with control, 45, 50, 55, 60 and 65 Gy were decided as treatments for both varieties. Corms of gladiolus varieties were then treated with effective doses of gamma radiation as estimated from the first experiment to induce physical mutagenesis. Six treatments of each varieties were evaluated in FCRD with three replications. The observations on quantitative characters and qualitative characters were recorded. All the characters exhibited significant differences among treatments. Most of the characters showed significant differences among varieties and in their interactions with treatments. The characters like number of leaves per plant, plant height, length and diameter of the floret, and rachis internodal length were the highest in Arka Thilak treated with 45 Gy. In Arka Amar, length of leaf blade and field life were the maximum at 45 Gy, and a greater number of florets per spike was observed at 50 Gy. Among the treatments, lower doses (45- 50 Gy) promoted better growth and development, whereas higher doses (60-65 Gy) had detrimental effects. 99 Among the varieties, Arka Amar exhibited variations in the predominant flower colour, resulting in the production of novel colour mutants at higher doses of gamma radiation. Corms treated with 50 Gy produced a dark pink flower with white colour in the central portion. Also, corms treated with 55 Gy showed a pink colour with light yellow shade in the central portion and a dark pink colour flower with golden yellow shade in central portion was observed in 60 Gy and 65 Gy treatments. High phenotypic coefficient of variation (PCV) and genotypic coefficient of variation (GCV) were observed for the number of spikes per plant, number of cormels per corm, number of florets per spike, days to sprouting, plant height and number of leaves per plant. Low PCV and GCV were recorded in days to spike initiation and field life. High heritability along with high genetic advance was observed in days to sprouting, number of leaves per plant, length of leaf blade, width of leaf blade, plant height, days to full emergence of spike, spike length, length of the floret, diameter of the floret, number of florets per spike, rachis internodal length, corm weight and number of cormels per corm. This indicates that additive gene action plays a significant role in the expression of these traits. Hence, selection for these traits would be effective. The correlation studies showed a significant positive correlation for spike length with number of florets per spike, length of floret, diameter of floret, plant height, number of leaves per plant, length of leaf blade, corm weight, field life and rachis internodal length. However, days to sprouting and days to spike initiation showed a significant negative correlation with spike length. Path analysis revealed that the length of the floret and number of florets per spike exhibited the highest direct effect on spike length. A high indirect effect on spike length was shown by diameter of the floret through length of the floret. In conclusion, novel colour mutants were obtained in Arka Amar, and also ornamental traits such as length and diameter of the floret, number of spikes per plant, spike length, rachis internodal length, field life, and number of florets per spike were improved with novel variations through gamma irradiation. Lower doses, such as 45 Gy and 50 Gy, were found to be more effective for the development of novel ornamental traits in gladiolus. 100 These treatments can be used in future breeding programmes to improve economically important floral traits. The best treatment combination obtained in this study was Arka Amar with 50 Gy as it produced novel colour mutants along with more number of flowers and more number of spikes per plant. These colour mutants can be multiplied through in vitro techniques.