Mutation-induced variability for improved yield and rust resistance in wheat in hot irrigated environments Abdelbagi M. Ali1, 2, Izzat S.A. Tahir2, Abdalla M.A. Kurmut2, Sufian M. Suliman2, Nasrein M.K. Omer2 , TahaniY. Elagib2 and Brian Forster1 Wheat production under dry and hot environments, such as Sudan, is challenged by drought and heat stresses and biotic stresses including rust diseases. Wheat improvement in such stressful environments is constrained by a paucity of genetic variability. Gamma-ray irradiation was used to induce variability in two local wheat varieties (Tagana and Khalifa) to improve grain yield and rust resistance under hot (30-38°C during the grain filling period) and irrigated environments of Sudan. Seeds were exposed to six treatments of gamma irradiation (0, 100, 200, 300, 400 and 500 GY) and the M1 seeds were grown in the field (Gezira Research Station, GRS) in 2008/9 (Fig 1). The LD50-60 was 150 and 200 Gy for Khalifa and Tagana, respectively, indicating that Khalifa was more sensitive to irradiation than Tagana (Fig. 1). The mutant populations (20,000 lines) were advanced to M4 with preliminary evaluation of grain yield. Based on M4 field plot grain yields, 500 M5 lines from the two populations were selected and tested for stem and leaf rust resistance at New Half Research Station (NHRS) and grain yield under the heat stress condition of the GRS in 2012/13 (Table 1). Fifty of the top yielding M5 lines were also evaluated in a replicated preliminary yield trail at Shambat Research Station (SRS). Mutant lines showed variable reactions to stem and leaf rust diseases at NHRS ranging from highly resistant to susceptible (Table 1, Fig. 2). About one hundred of the M5 lines showed very good to excellent agronomic performance as evaluated by visual scoring of which 34 lines had stable good to excellent performance at both GRS and NHRS sites. Grain yield was significantly different (P = 0.01-0.06) among lines and parents in the SRS trail, with means ranging from 3.2 to 7.6 ton/ha. Seven M5 lines had significantly higher grain yields (6.7-7.6 ton/ha) than the parents, Tagana (6.0 ton/ha ) and Khalifa (6.5 ton/ha). Some of these lines combined resistance to diseases with early maturity and high grain yield. Screening nursery Table 1. Visual and diseases scores for M5 lines in two populations at the two testing sites; Wad Medani and New Halfa.   Visual Scores 1 Wad Medani New Halfa Disease1 Scores  Stem rust Leaf rust Poor 221 277 R-trR 256 6 √ Acceptable 136 125 trR-MR 154 45 * Good 73 62 MR-MS 68 84 ** Very good 61 32 MS-S 19 311 *** Excellent 7 2 S 3 54 Total 498 500 Stem rust Leaf rust 1R= resistant, tr= trace infection, MR= moderately resistant, MS= Moderately susceptible, S= susceptible Visual scoring in both sites while the diseases scoring was at New Halfa Research Station 0 R R-MR MR MS MS-MSS S Peterson et al. 1972 Mutagenic treatment M0 seeds M3 and M4 phenotyping M2 Plants M1 Plants Fig 1. Scheme mutation induction and phenotyping of mutant populations of Tagana and Khalifa Fig. 2. Rust diseases screening nursery with humidifier (top), leaf and stem rust infected plants (middle) and screening scale for adult plant infection response to stem rust resistance (bottom) Conclusion Useful genetic variability was generated in two wheat varieties, Tagana and Khalifa, using gamma rays. Mutant lines with high yield under heat stress, resistant to rust diseases and earlier in maturity than the parents were identified. These lines will be advanced to multi-location trails to verify their performance before submission for official release as new mutant varieties for hot irrigated environments of Sudan. Acknowledgement This work is partially supported by the IAEA TC projects SUD5/30 and SUD 5/33. The follow up and management of the material at the GRS, Wad Medani by the senior technician, Mohamed Jiha is highly appreciated. Plant Breeding and Genetics Laboratory, Joint FAO/IAEA Division of Nuclear Techniques in Food and Agriculture, Department of Nuclear Sciences and Applications, International Atomic Energy Agency - P.O. Box 100, A-1400 Vienna, Austria Agricultural Research Corporation, PO Box 126, Wad Medani, Sudan a.mukhtar-ali-ghanim@iaea.org