Rice is the staple food in Asia and is the single biggest user of fresh water Amudha et al., 2009). The declining availability of water threatens the traditional way of irrigated rice production and necessitates water use efficiency in rice production. Aerobic rice system is the cultivation of high yielding varieties in unpuddled, unsaturated soil (Bouman, 2001). Aerobic ice is targeted to water short areas where irrigation water supply is insufficient for growing lowland rice in flooded condition and to rainfed areas where rainfall is sufficient to frequently bring the soil water close to field capacity. China started aerobic rice research from 1980 onwards and developed varieties like Han Dao 297, Han Dao 277, Han Dao 502, Danjing 5, Danjing 8 etc. Screening trials at IRRI, Philippines identified Magat, UPLRi -7, APO and CT-6510-24-1-2 for aerobic culture. CNA 8557 and BRS Talento had been identified as rice varieties suited for aerobic condition in Brazil. Rice varieties under aerobic system should have better input use efficiency, weed competitiveness and drought tolerance to attain high yield. Experiments to study the physiological traits of aerobic rice genotypes revealed that root characteristics (root volume, root number and root length, proline content and relative water content are the major factors that influence drought tolerance of aerobic rice. Rice variety, PMK 3 with high proline content, high relative water content and favorable root characteristics, performed better in aerobic condition (Sritharan and Vijayalakshmi, 2007). Genotypes for aerobic system can be developed through hybridizing weed competitive, drought tolerant upland varieties with high yielding, input responsive lowland varieties (Amante et al., 2010). Combination breeding and heterosis breeding are mainly adopted to achieve this goal. Huaqi et al., (2010) reported that in China, combination breeding resulted in the development of a group of new-generation elite aerobic varieties such as Han Dao 297 (Mujiao 78-595 x Khaoman), Han Dao 277 (Qiuguang x BanLi) and Han Dao 502 (Qiuguang x Hongkelaoshuya). These elite varieties showed breakthroughs in traits such as stronger drought tolerance, reduced plant height, increased lodging resistance, erect upper leaves, higher yields, stronger resistance to blast and better grain quality. MAS 946-1 and MAS 26 are the varieties developed through marker assisted selection from UAS, Bangalore (Hittalmani et al., 2012). qDTY6. 1 is a major QTL associated with grain yield in aerobic environment and is closely linked to two SSR markers viz., RM 510 and RM 19367 (Venuprasad et al., 2012). At TNAU, Coimbatore, hybrids for aerobic condition were developed using six drought tolerant male sterile female lines and seven male parents. Four heterotic hybrids for yield viz., IR 67684 A x CT-6510-24-1-2, IR 68885 A x IR 73718-3-1-3-3, IR 70369A x IR 73718-3-1-3-3 and IR 70372 A x PSBRC 80 showed better adaptability to aerobic condition (Amudha et al., 2010).
Prof. Dr. Bilal BİLGİN