Studies of gamma irradiation on morphological characters in gladiolus

Introduction

Gladiolus is a high-value, commercially significant geophyte crop, extensively cultivated for the cut flower industry in both domestic and global markets. The substantial demand necessitates ongoing genetic enhancement programs to develop novel cultivars with superior ornamental and agronomic traits. Mutation breeding is a well-established methodology for inducing genetic variability in highly heterozygous, vegetatively propagated ornamental species like gladiolus. The application of physical mutagens, such as gamma irradiation, provides a promising approach to create stable, new phenotypes (mutants) by altering the plant's genetic material. Previous research has demonstrated that varying doses of gamma radiation can induce a spectrum of physiological and morphological changes, ranging from detrimental effects at higher doses (e.g., inhibited mitosis, reduced plant height, delayed flowering) to beneficial or stimulatory effects at lower doses (e.g., enhanced photosynthetic efficiency, altered flower colour, increased corm production). Therefore, the present investigation was specifically conducted to quantitatively assess the dose-dependent impact of gamma radiation exposure on the key morphological and phenological parameters of gladiolus germplasm.

Plant Height

The general trend indicated that low-dose irradiation treatments enhanced plant height while high doses were inhibitory. Specifically, optimal vegetative growth, characterized by maximum plant height at 30 DAP (43.16 cm in Year 1 and 37.73 cm in Year 2), was associated with control treatment and exposure of 35 Gy. Conversely, the maximum radiation dose of 65 Gy consistently induced a significant reduction in height (36.30 cm in Year 1 and 30.15 cm in Year 2), demonstrating a potent depressive effect on cellular division and elongation. Furthermore, inherent genetic variability among the Gladiolus cultivars resulted in statistically significant differences in height. 'Pusa Suhagin' emerged as the tallest cultivar (mean of 42.14 cm), while 'Arka Naveen' was categorized as a dwarf phenotype (mean of 36.65 cm). The statistically significant interaction effect underscored the genotype-by-treatment response. Significantly maximum plant height was recorded in cv. Pusa Suahgin in control treatment (45.17 cm) which was at par with cv. Pusa Suhagin treated with 35 Gy gamma rays (44.13 cm) where as minimum plant height was recorded in cv. Arka Naveen treated with 65 Gy gamma rays (32.38 cm) in first year where as The interaction effect of varieties (V) and different irradiation doses (G) on plant height of gladiolus after 30 DAP was found to be non-significant in second year. These results confirm a dose-dependent radiosensitivity that varies significantly among different Gladiolus genotypes. Interaction among gamma irradiation and variety showed that, the number of leaves/plant of gladiolus were found to be non-significant for first year. For second year significant result was found for Interaction effect of irradiation doses (G) and variety (V). The maximum number of leaves were found in cv. Pusa Suhagin in control treatment (5.12) and minimum number of leaves were recorded in cv.Arka Naveen at 65 Gy gamma irradiation treatment (3.16).

The data analysis and represents in table 3. revealed a nonsignificant influence of gamma irradiation dosage, cultivar genotype, and their interaction on the morphological parameter of length of leaf across two consecutive cultivation seasons (2021-22 and 2022-23). The general trend indicated that low-dose irradiation treatments enhanced length of leaf were inhibitory. The significantly maximum length of leaf was recorded in cv. Pusa Suhagin (29.76 and 29.22 cm) which was at par with cv. Punjab Dawn (29.15 and 29.13 cm) and the minimum length of leaf was recorded in cv. Arka Naveen (25.20 and 24.84 cm).

The data analysis confirmed a non significant, inhibitory effect of high-dose gamma irradiation on the length of leaf of Gladiolus. Specifically, in the maximum applied dose of 65 Gy consistently resulted in reduction in length of leaf 24.12 and 22.27) of across two consecutive cultivation cycles.

The results on length of leaves reduction with increase in gamma radiation doses was reported by Raghava et al.

(1988) [12] and Banerji et al. (1994) [3] .

The data presented in Table 4 indicate that, during the first year, significant varietal differences were observed for leaf width at 30 DAP. The widest leaves were recorded in cv. Pusa Suhagin (2.67 cm), which remained statistically at par with cv. Punjab Dawn (2.48 cm) and cv. Dhanvantari (2.41 cm), whereas cv. Arka Naveen (1.96 cm) exhibited the narrowest leaves. In the second year, a similar varietal response was noted, with cv. Pusa Suhagin (2.18 cm) registering the maximum leaf width, statistically comparable to cv. Punjab Dawn (2.12 cm), while cv. Arka Naveen (1.51 cm) again recorded the minimum leaf width. A significant effect of irradiation dosage on leaf width was also evident. In the first year, treatment G₁ (2.98 cm) resulted in the maximum leaf width, followed by G₂ (2.79 cm), while G₅ (1.62 cm) produced the minimum width.

During the second year, G₁ (2.54 cm) again recorded the highest leaf width, remaining at par with G₂ (2.22 cm), whereas G₅ (1.29 cm) consistently exhibited the lowest values.

The interaction effect (G × V) on leaf width at 30 DAP was found to be significant in the first year, indicating that varietal responses to irradiation were not uniform. The maximum leaf width was obtained in cv. Dhanvantari under the control treatment (3.26 cm), which was statistically comparable to cv. Pusa Suhagin under the control treatment (3.17 cm) and cv. Pusa Suhagin treated with 35 Gy (3.09 cm). The minimum interaction mean was observed in cv. Dhanvantari treated with 65 Gy (1.30 cm). In contrast, during the second year, the G × V interaction for leaf width at 30 DAP was non-significant, indicating a more uniform varietal response to irradiation doses under that year's environmental conditions. A comprehensive study conducted by Patil (2010) [9] on three gladiolus cultivars viz. American Beauty, Nova Lux, and Eurovision-aimed at inducing genetic variability through gamma irradiation. Corms were exposed to doses of 1, 2, 3, 4, 5, 6, and 7 kR. Lower doses ranging from 1 to 3 kR were found to be insufficient to cause adverse effects and, in some instances, even exerted a stimulating influence on growth. However, doses ≥ 4 kR resulted in a marked reduction in leaf length and suppressed vegetative growth parameters in gladiolus. Similar findings were reported by Pranom et al. (1986) [11] and Banerji et al. (1994) [3] , who observed reduced plant height and fewer leaves with increasing gamma irradiation levels. The adverse effects of higher irradiation doses may be attributed to disturbances in auxin metabolism, including the inactivation of auxin (Datta and Datta, 1953) [4] , destruction of enzyme systems (Bairagi, 1969) [2] , or inhibition of auxin synthesis (Gordon, 1954) [5] . Additionally, gamma irradiation may impede plant growth through suppression of mitotic activity, chromosomal aberrations, and associated secondary physiological damage (Gunckal, 1957) [6] . The observed reductions in plant height, leaf length, and number of leaves likely result from a decrease in the number of vertical cell layers, shorter internodal length, fewer internodes, or a combination of these structural modifications.

References

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