Gamma Irradiation Effect of

In order to know the influence of 60Co gamma radiation, on the germination of two semitropical species, roselle seeds and sunflower were irradiated at the Transelektro LGI-01 of the InstitutoNacional de InvestigacionesNucleares, At doses 0, 5, 10, 15, 20, 25, 30 and 35 Gy, to determine the radiosensitivity curve and to determine the LD50 of both species, under a randomized complete block design with factorial arrangement, Where the study factors were: radiation doses and species. The results indicate that sunflower is more sensitive to gamma radiation than roselle, so the LD50 for sunflower and roselle was not reached, because the doses of radiation used, did not achieve 0% germination. Thus, the radiosensitivity curves were fitted to a linear model, with a high coefficient of determination. From the present investigation, It can be concluded that to determine the LD50 in the species in question, It is necessary to increase the dose of irradiation, perhaps up to 1000 Gy.

INTRODUCTION Sunflower (Helianthus annuus L.) and roselle (Hibiscus sabdariffa L.), are considered crops of semi-arid zones,and although these present a wide range of adaptability due to their rusticity and phenotypic plasticity,which have been little used to be introduced in tropical areas of the world including Mexico.Sunflower is a plant that originates in northeastern Mexico and southeastern United States (Povereneet al., 2002). This species for many years was used as oilseed,since their seeds are obtained fatty acids with high nutritional value (Gallegos et al., 2003),but nowadays it has gained importance from the ornamental point of view,due to the great size of its foliage and to the beauty of its chapter which has favored,that is used in flower arrangements and as a cut flower (Melgares, 2001).With regard to roselle,is a plant that belongs to the family malvaceae and has its center of origin in Africa specifically in Sudan,although some authors like Vavilov, mention that its origin is the Abyssinian center (López, 2002).This crop for many years has been used as medicinal because of its diuretic properties,although of its stems also is extracted fiber for the elaboration of ropes which are resistant to the salinity and its seeds,a very fine oil is obtained as the one extracted from Luffa cylindrical L.which can be used for the preparation of cosmetics, in addition to possessing antimicrobial properties (Amaya et al., 2000).On the other hand, the genetic improvement of plant species has gone through multiple stages,from selection, introgression, crossing, to the use of potent physical and chemical mutagens, a process called Mutagenesis,to obtain cultivars that meet the characteristics  al., 2012).This type of radiation has a very short wavelength of 10 -12 m, which allows a very high penetration power and is used by geneticists, Causing damage to the DNA molecule causing mutations at the molecular level (Almeida et al., 2004), Which will manifest in the phenotype of organisms in the form of somatic mutations known as "Mosaic".This advantage of generating mutations in the plant, can be of great utility since in the same way, resistance to some adverse environmental conditions such as drought,which is of great help in selecting materials that may present the resistance genes to drought,Or even induce this quality to genotypes with the help of gamma radiations (González et al., 2007).To achieve this, when irradiating seeds or propagules, It is necessary to do studies on the effect of ionizing radiation on these structures, which is known as radiosensitivity curve,which allows us to determine even the average lethal dose known as LD50.For this reason the main objective of the present study was:determine the radiosensitivity and LD50 curve in roselle seeds and sunflower caryopsids under eight 60 Co gamma ray levels.

Location of the experiment.
The present study was carried out in the laboratory of soils of the Universidad Tecnologica de Tehuacan, during the spring of 2015, located in San Pablo TepetzingoTehuacan Puebla, Mexicoat 18º 24 'north latitude, 97º 20' longitude west and 1409 altitude.

Genetic material.
The germplasm of roselle (Hibiscus sabdariffa L.) was collected from an accession on the coast of Oaxaca, Mexico in PinotepaNacional at a location of 16º 21 'north, 98º 02' west and 28 altitude,whose characteristics are: average postage 0.50 to 1.50 m high and red chalices,the sunflower cariopsides (Helianthus annuus L.) cv. Victoria, were donated by the germplasm bank of Ecofisiología de Cultivos of Colegio de Postgraduados,which were irradiated in the Transelektro LGI-01 of the InstitutoNacional de InvestigacionesNucleares (ININ) in Ocoyoacac, Mexico.

Determination of radiosensitivity curve.
This was calculated for both irradiated materials, performing a test of germination,Disinfecting seeds and caryopsids with a solution of 1% sodium hypochlorite and placed in petri dishes with filter paper, depositing 10 seeds per box and equally 10 cariopsides per box, separately for later incubation in a room of growth at constant temperature at 25 o C,And the percentage of germination was calculated using the following expression PG = (Gs / Ss) * 100 where:PG, Percentage of germination; Gs, Germinated seeds; Ss, seed sown (Gil & Miranda, 2008), After determining the percentage of germination, the rediosensitivity curve was calculated by means of a linear regression plotting the percentage of germination vs radiation dose and obtaining the model of adjustment by least squares.From the obtained model an interpolation was made, taking the dependent variable the value of 50% of germination, and clearing the independent variable to determine the LD50 of both species under study (Infante and Zarate, 1990).

Experimental design.
The design used was complete random blocks with three replicates and factorial arrangement following the mathematical model:Yijk = μ + Aj + Bk +βi + (AB)jk + εijkwhere: Yijk is the response variable of the i-th radiation dose in the j-th species of the k-th block;µ, is the true overall mean;Ai, is the effect of the i-th radiation dose;Bj, is the effect of the j-th species under study; Βk, is the effect of the k-th block; (AB)ij, is the effect of the interactiondosis of radiation i on the species j under study and εijk, is the experimental error of the i-th radiation dose on the j-th species in the k-th block,thus the study factors were integrated by: the radiation dose and the species under study.The experimental unit consisted of a roselle seed and a sunflower.

Response variable.
This was only constituted by the percentage of germination in both study factors and when it was significant, the Tukey test was applied to a level of significance of 5% of probability of error.

III.
RESULTS. The analysis of variance and the comparison test of means for dose and species, showed highly significant differences for: treatments, both study factors as well as repetitions.Radiation x species interaction was only significant.Regarding the coefficient of variation, this oscillated between 6.34% for radiation dose, whereas for the species it was 10.50%,indicating that the experimental data were very reliable during the development of the experiment (Table 1). For the radiation factor, the highest percentage of germination occurred in the control and the dose of 5 Gy with 96.50 and 92.02%, respectively,being also statistically equal.Levels 10, 15, 20 and 25 Gy of radiation were found to be statistically equal but differ  figure 1.In it is observed that the mathematical model was linearly adjusted in a decreasing way, whose coefficient of determination turned out to be highly significant 0.98 **, and whose slope was -0.37 indicating that for each Gy of radiation, supplied to roselleseeds, there was a decrease of 0.37% germination.On the other hand the germination of sunflower caryopsids, submitted to different levels of radiation, maintained a tendency similar to roselle, keeping the linear model decreasing. For this case the coefficient of determination was 0.92* and slope -0.50, for each unit of radiation the germination of sunflower caryopsids is reduced by 0.50% (Figure 2).   The mean lethal dose,to be derived from the mathematical models of adjustment for both species under study,was not reached,due to the fact that in none of the species did germination reach 0.0%, as can be seen in Figures 1 and  2.Thus in this way,the lowest percentages of germination occurred with 35 Gy,for the species in question with 81.00% germination for roselle and 72.00% for sunflower.This indicates,that roselle has a lower sensitivity to gamma radiation than sunflower,that is to say,11.11% less sensitivity to gamma radiation than 60Co than sunflower ( Table 2).  In the interaction radiation x species, we can see that both species interacted in a decreasing way with respect to radiation,in the range of 0 to 25 Gy,that is to say, as the radiation increased the germination of both decreased,to then decrease drastically from 25 to 30 Gy in sunflower,while roselle does not experience a change of slope keeping the same trend. From 30 at 35 Gy,roselle experienced a steady slope,indicating that in this radiation range,the species presents insensitivity to gamma rays ( Figure 3). IV. DISCUSSION Germination decreased as the radiation dose increased,both in Jamaican seeds and in sunflower caryopsids,the latter presenting a reduction of 11.11% in germination compared to roselle.This response coincides with that observed and reported by Díazet al. (2003),who worked with Tigridiapavonia (L.f) D.C. And mention a progressive reduction in the budding of the bulbs of this species,when subjected to gamma rays of 60 Co in a range of 5 to 30 Gy despite being different species.On the other hand, Ramírezet al. (2006), mention that dose 500 Gy,result in a significant decrease in the germination of tomato hybrids of up to 23%,data that differ from those reported in this present study,the above may be due to the differences between species in which both studies were carried out and the high germination percentage of the tomato hybrids,as well as the different doses of radiation used.The results presented in this study,indicate that both structures are sensitive to gamma radiation of 60 Co,and are of great importance for being the basis for establishing doses of radiation,when it is desired to improvement genetic using the mutagenesis technique and thus eliminate the doses that are lethal when killing more than 50% of the study population,which was not reached in this investigation.For this reason the establishment of radiosensitivity curves is of great importance in this type of studies.

V.
CONCLUSIONS From the present investigation carried out, under the conditions of the valley Tehuacan-Cuicatlan, the following conclusions were derived:  In the low doses of gamma irradiation of 60 Co, both species presented an equal germination, statistically speaking.  Sunflower presented the lowest germination than Jamaican, when applying high dose of gamma rays.  Sunflower prove be more susceptible to gamma radiation, as it decreased its germination, compared to roselle.  The germination vs radiation adjustment models were linear with high determination coefficients for both species.  The LD50 could not be determined, because in both species the zero germination percentage was never reached.  For further studies, where it is intended to establish the LD50 of the species in question, it will be necessary to irradiate up to 1 kGy to obtain a positive response.