Rapid growth in trade of agricultural products has increased the risk of introduction of exotic pests into new area. In order to fulfill quarantine obligations, several treatments are in practice: fumigation with methyl bromide (MB), application of extreme temperatures, controlled atmospheres, and combinations of them. Although MB was most effective and widely applied for quarantine treatment, its use was banned by the Montreal Protocol. Ionizing irradiation phytosanitary treatments – gamma radiation, electron beam, and X-ray are being used as an alternative to MB currently. For applying ionizing irradiation as a quarantine treatment, there is a research protocol which should be followed, International Standards for Phytosanitary Measure 18 [ISPM #18] and Phytosanitary Treatment Regulation of Korea (Notice 2014-35). We have evaluated the effect of gamma radiation, electron beam, and X-ray on H. armigera as quarantine treatments. In this presentation, ISPM #18 and Notice 2014-35 will be talked with the example of H. armigera.

Ionizing radiation directly and indirectly affects gene expression within the plant genome. To access the physiological response of rice to different types of ionizing radiation, rice seeds were exposed to gamma-ray and ion beam radiation. Exposure to ionizing radiation dramatically decreased the shoot length compared with non-irradiated plants. Fluorescence-activated-cell-sorting (FACs) was used to measure DNA contents. There were significant correlations of dose-dependent between irradiated plant and non-irradiated plant. The radicals induced by the ionizing radiation in the plant could be observed by electron spin resonance (ESR). It was confirmed that the number of free radicals in cell was greatly increased all irradiated plants than non-irradiated plant. A significant positive correlation was shown between ionizing radiation dose and signal intensity. In order to determine the Genetic diversity, AFLP analysis was conducted with the irradiated plant and non-irradiated plant. Based on band patterns, the cluster analysis was conducted to evaluate the genetic variation by using the UPGMA (Unweighted Pair Grouping Method of Averages). Genetic diversity of irradiated plants by low dose ion beam was the closest non-irradiated plant and irradiated by high dose gamma-ray was the furthest from non-irradiated. We describe the detailed methods of ionizing irradiation and discuss its applications in genetic research as well as plant breeding.

To define whole genome-level of structural variation by ionization energies and radiation doses in plant, the seeds of Ilpum rice cultivar were acutely irradiated with gamma rays (100Gy, 200Gy, and 400Gy) and ion-beams (20Gy, 40Gy, and 80Gy), respectively. Six M1 rice plants were re-sequenced by Hi-Seq2500 with Ilpum cultivar as control. The average sequencing coverage of the individuals was 10.6X, and the average mapping rate to the rice reference genome (IRGSP-1.0) sequence was 96.95%. The individual plants were irradiated with gamma-400Gy and ion-50Gy had highest variation of SNP with 471,837 and 469,147, respectively. The number of insertion/deletion was 77,500 and 77,106, the synonymous and frame-shift were 7,859 and 7,763 in above two individuals. Although high genome variation shown between Ilpum cultivar and irradiated individuals, there were non-correlation between number of variation and radiation doses. However, five individuals, except ion-20Gy, showed 33 common variant blocks (CVBs) spanning 6 Mb in whole rice genome (1.6%). The CVBs were distributed on 12 rice chromosomes, Chromosome 6 had biggest CVB (5 blocks, 1.3Mb), whereas chromosome 9 had smallest CVB (0.01Mb). Total five hundred fifty one genes were in CVBs which can regard radiation sensitive genes or may be regarded as radiation hot spots in rice genome. This study will contribute to the improvement of the radiation mutation breeding research in genetic and genomic aspect.