All India Coordinated Wheat and Barley Improvement Project, Rajasthan Agricultural University, Agricultural Research Station, Durgapura, Jaipur 302 018, Rajasthan, India
Summary
Breeding program for increasing wheat production in the warmer areas of India exhibited that wheat variety Raj 3765 has greater potential for sustaining the green revolution in new paradigms. It was developed from two genetically diverse cultivars (Triticum aestivum L.) through single cross (HD 2402/VL 639). This variety exhibited a higher level of productivity under both late sowing and very late sowing environments. Besides other desirable quality attributes, it possesses superior grain quality along with fairly high degree of resistance to rusts. Genetically, it is blessed with resistance to Lr23+10, Sr2+ rust races. It is a marvelous and reliable wheat variety that offers excellent degree of tolerance to initial and terminal heat under various sowing environments (normal, late and very late) in North Western Plains Zone (NWPZ) of India. Wheat Varietal Release Committee (AICWIP) recommended this variety for late sowing (1994) as well as for very late sowing (1998) in NWPZ of the country. Zonal Research and Extension Advisory Committee (ZREAC) recently recommend this variety for normal sown condition (2000) under mega environment of Rajasthan. The production of this variety can offer an exciting opportunity for overcoming the stagnating yield plateau of wheat in wanner areas of India and also to alleviate the socioeconomic status of the subsistent Indian farmers.
Key words: wheat, cultivars, rust resistance, terminal heat stress, grain yield
Introduction
Over 7 million hectares of wheat grown in approximately 50 countries are subjected to continual heat stressing environments with mean daily temperatures greater than 17.5C in the coolest month of the year (Zhong-Hu and Rajaram 1994; Guha Sarkar et al. 2001). At least as great an area may experience heat stress at the end of the growth cycle, as occurs in the North Western Plains Zone (NWPZ) and North Eastern Plains Zone (NEPZ) of India. Hence, national program leaders identified improving heat tolerance of wheat as being a major research priority. Crop yield is determined by the interaction of genotype, management and environment. Water availability and temperature are the major environmental variables affecting crop yield. Howard (1924) while analyzing the factors controlling wheat production remarked, "wheat production in India is a gamble in temperature". This statement is valid even today. The cultivation of wheat is limited by temperature at both ends of the cropping season and high temperature stress has an adverse effect on wheat productivity. The present day rice-wheat cropping system, keeping in view of monsoonal irregularities, has compelled wheat crop to be subjected to rapidly ascending temperatures coupled with hot dry winds during the post anthesis stage, specially during grain development. These unfavorable environments terminate grain growth prematurely and reduces yield considerably. It has already been established that high temperature stress can be a significant factor in reducing yield and quality of wheat (Stone and Nicolas 1995). Wardlaw (1994) also reported that mean temperature greater than 15-18C following anthesis can result in decrease in grain weight at maturity. Breeding program for heat tolerance is an integral component of wheat breeding program at both national and international level (Acevedo et al. 1990). These programs will not only help in spreading wheat cultivation to nontraditional warmer areas besides, optimizing wheat yield in more tropical environments under the present situation of multiple-cropping system. Approximately, 3.0 million hectare area in northeastern and northwestern plains zone is exposed to terminal heat stress, which at grain filling stage blocks the synthesis and mobilization of photosynthates and results in shriveling of the grains. Hence there is an urgent need for the introduction of wheat varieties tolerant to terminal high temperature stress in India to meet the projected target of production of wheat ie, 105 million tones by 2020 AD.