Studies on the Effects of Ultraviolet Irradiation on Pea (Pisum sativum L.)

Abstract

Pea (Pisum sativum L.) is one of the earliest domesticated cool season annual legume crop produced worldwide, mainly in temperate regions. In common with other grain legumes, pea plays an important role in food and nutritional security of humans as well as livestock. Pea is an annual plant which exhibits mainly self-pollination, although cross pollination through insects also occurs in nature. The improvement of pea through plant breeding requires considerable genetic variations in the key quantitative traits and the expression of those polygenic traits also depends on the environmental interactions. Therefore, UV irradiations have been employed in the present study to assess the genotypic sensitivity of the pea cultivar for possible application in mutation breeding of pea. Seed germination and seedling growth at different duration of exposures were calculated for estimating the effect of UV irradiations stress on pea. The findings of the present study conclude that the UV irradiation can be useful as non-ionizing physical mutagen for induction of selectable macromutations in local pea cultivars and the exposure to the increasing UV stress in the nature will be detrimental for the crop productions. Introduction Pea (Pisum sativum L.) is generally considered to have originated in the Near East region and domesticated as early as 7000-6000 BC [1]. In India, it is grown in an area of 1.10 million ha with an annual production of 1.02 million tones and average productivity of 927.2 kg/ha. The major producers are Canada, China, India, Russian Federation, the USA, and France. Dry pea seeds are rich in protein (18-33%), starch (35-50%) and digestible nutrient content and low in fibre (4-7%), which make it an excellent livestock feed also. Most of the pea growing area in developing countries, including India, is occupied by traditional varieties, with narrow genetic base, which suffers from some abiotic and biotic constraints like late maturity, lodging, susceptibility to rust etc. Genetic bottleneck, mostly in Indian cultivars, accumulated due to traditional breeding methods over the years, is one of the major constraints commonly limiting the breeder’s efforts. The availability as well as accessibility to the genetic variation within the genepool of a crop species is the prerequisite for initiating an improvement programmed. Induce mutagenesis has proved to be a powerful complimentary breeding tool for creating new genetic blend within a short period of time without disturbing overall genetic architecture of the crop. Thus, it allows the plant breeders to screen and select desirable combination of expressed economic traits for further introgression into the proper breeding stock. UV radiation, first described by Johann Wilhelm Ritter in 1801, is light energy emitted between the wavelengths of 100 and 400 nm, i.e. between the electromagnetic spectra of X-ray and visible light. UV radiation, in comparison γand X-rays, is of relatively low energy and is not ionizing, i.e. does not dislodge electrons. Based on the wavelength, UV radiation is further divided into Ultraviolet A (UVA) 315-400 nm, Ultraviolet B (UVB) 280315 nm and Ultraviolet C (UVC) 100-280 nm. UVC is the most energetic and biologically damaging, it is not found in sunlight as it is absorbed by the ozone layer; UVB is the major mutagenic fraction of sunlight; and UVA also has deleterious effects primarily because it creates oxygen radicals, which can indirectly damage DNA. However, due to continuous depletion of ozone layer, the strength of UV radiation reaching Earth’s surface increasing everyday which have deleterious effects on both animals and plants. Enhanced UV radiation can alter plant growth and development as Citation: Khan TU, Rafiul Amin Laskar RA, Debnath B (2018) Studies on the Effects of Ultraviolet Irradiation on Pea (Pisum sativum L.). Int J Genom Data Min: IJGD126. DOI: 10.29011/ 2577-0616. 000026 2 Volume 2018; Issue 02 Int J Genom Data Min, an open access journal ISSN: 2577-0616 well as reproduction [2]; this has serious implications for plant yields and agricultural economies. [3] discovered the mutagenic effect of UV radiation on polar cap cells of fruit fly eggs. The mutagenic potential of these rays has since been confirmed in many organisms in which germ tissue could be easily exposed to the low-penetrating ultraviolet light. Since, UV wavelengths are absorbed by bases in DNA molecules and by aromatic amino acids of proteins, it reacts with DNA and other biological molecules to induce mutagenic effects in the organism. Induced mutations are highly effective in enhancing natural genetic resources and have been used in developing improved cultivars of cereals, pulses, fruits and other crops [4]. These mutations provide beneficial variation for practical plant breeding purpose. The technology is simple, relatively cheap to perform and equally usable on a small and large scale [5]. Expression of traits is a complex process which involves many interdependent genes and the responses of each gene varies towards different mutagens [6]. Therefore, selection of mutagens and their optimal doses is very crucial for unleashing the huge possibilities in mutation breeding. The germination and seedling growth inhibition percentage of the treated seeds has been considered as one of the most dependable indexes to estimate the sensitivity of any crop genotype towards any mutagens. Keeping in view the economic value of pea and mutagenic potential of UV irradiation, the present study was designed to estimate the impact of UV irradiation stress on pea genotype for understanding the future threat of increasing UV incidence on agricultural production and to assess the mutagenic potency of UV irradiation at different treatment durations for possible genetic improvement of local pea cultivars through UV irradiation based mutation breeding. Materials and Methods Dry (moisture content 10-12%) and healthy seeds of the local pea cultivar, obtained from Seed Store, Hailakandi, Assam, were used for mutagenic treatments of ultraviolet radiation (UV). A germicidal ultraviolet lamp which emits high intensity ultraviolet radiation concentrated around the wavelength of 253.7 nm (i.e., UV-C radiation) was used in the present experiment. The seeds were divided into three sets of 15 seeds each and seeds from each set were distributed in three petriplates with 5 seeds each. Therefore, three replications of each seed set were prepared for the experiment. Two sets were used for UV radiation treatment of different durations and the remaining one set was considered as control. UV radiation treatment of two durations (30 mins and 60 min) per day for 7 days was employed and distance of 30 cm was maintained between lamp and petriplates. Therefore, C, T1 and T2 abbreviations for Control, UV (30mins/day/7days) and UV (60mins/day/7days), respectively, will be used in the following texts of the study. In between the treatments, the petriplates were kept in the B.O.D. incubator at 27±1oC temperature in Department of Botany, S. S. College, Hailakandi, for seed germination and seedling growth. The seeds were allowed to grow for 14 days with initial 7 days under UV stress for genotypic sensitivity assessments. Statistical analysis, namely, Mean (X), Standard Error (SE), Standard Deviation (SD), Coefficient of variation (CV %) were done using IBM SPSS statistics 20. Following parameters were studied from the M1 generation. Seed Germination After recording germination counts, the percentage of seed germination was calculated on the basis of total number of seeds sown in the petridishes and in the field. Germination (%) = 100 sown seeds of No. germinated seeds of No. × Seedling Height Seedling height was recorded after 14 days by measuring the root and shoot lengths for each treatment and control. Seedling emergence reduction (%) = [1 (Average number of seedlings in a treated combination/Average number of seedlings in the control) X 100 Seedling growth reduction (%) = [1 (Average length of seedlings in a treated combination / Average length of seedlings in the control)] X 100 Seedling vigour index = Average seed germination (%) X Average seedling height Results Seed Germination Percentage The comparative data recorded on seed germination are presented (Table 1) and (Figure 1). Citation: Khan TU, Rafiul Amin Laskar RA, Debnath B (2018) Studies on the Effects of Ultraviolet Irradiation on Pea (Pisum sativum L.). Int J Genom Data Min: IJGD126. DOI: 10.29011/ 2577-0616. 000026 3 Volume 2018; Issue 02 Int J Genom Data Min, an open access journal ISSN: 2577-0616 Parameters Treatments Mean Std. Error Std. Deviation CV% 95% Confidence Interval for Mean Minimum Maximum Lower Bound Upper Bound Seed germination (%) C 93.33 6.67 11.55 12.37 64.65 122.02 80 100 T1 86.67 6.67 11.55 13.32 57.98 115.35 80 100 T2 60 11.55 20 33.33 10.32 109.68 40 80 Total 80 6.67 20 25 64.63 95.37 40 100 Seedling shoot length (cm) C 13.78 0.45 0.77 5.6 11.86 15.7 12.98 14.52 T1 16.26 0.34 0.58 3.59 14.81 17.71 15.76 16.9 T2 8.77 0.39 0.68 7.71 7.09 10.45 8.11 9.46 Total 12.93 1.12 3.36 25.95 10.35 15.51 8.11 16.9 Seedling root Length (cm) C 8.2 0.36 0.62 7.55 6.67 9.74 7.63 8.86 T1 10.57 0.36 0.63 5.95 9.01 12.13 9.98 11.23 T2 5.13 0.38 0.65 12.68 3.51 6.74 4.48 5.78 Total 7.97 0.81 2.43 30.44 6.1 9.83 4.48 11.23 Seedling total length (cm) C 21.98 0.09 0.16 0.71 21.6 22.37 21.84 22.15 T1 26.82 0.7 1.21 4.51 23.82 29.83 25.74 28.13 T2 13.89 0.03 0.05 0.32 13.78 14.01 13.85 13.94 Total 20.9 1.9 5.69 27.23 16.53 25.27 13.85 28.13 # C=Control, T1=UV (30mins/day/7days) and T2=UV (60mins/day/7days). Table 1: Estimates of mean ( X ), Standard Error (S.E.), Standard Deviation (S.D.) and coefficient of variance (CV %) of seed germination (%), seedling shoot, root and total height in UV treated M1 generation of pea. Figure 1: Comparative effect of UV irradiation doses on seed germination and seedling growth of pea (Pisum sativum L.)