Modern varieties of wheat are well adapted to control cultural practices, but they are generally not highly tolerant to extreme environmental stresses, such as high temperature. The varieties of one region are generally not suitable for the others, and separate breeding objectives will be needed for each situation (Rajaram 1988). Since plant tolerance to temperature stress is heritable, selection and breeding can be used to improve this trait. The objective of the present study was to establish a pure line for release as a commercial variety for warmer areas of India. Keeping this scenario in view, a specific breeding program was initiated for the development of high yielding and disease resistant varieties. A new wheat variety Raj 3765 has been developed in India, which has genetic potential for excellent performance under different environments (late and very late planting) in the major wheat-growing zone (NWPZ) of the India. Farmers can enjoy the rich harvest with Raj 3765 every year in warmer areas under different prevailing crop rotations particularly in rice-wheat farming system. This paper describes the development, performance, resistance to rusts and quality parameters of this new wheat variety.

Materials and methods

Wheat improvement for heat tolerance depends on intensive hybridization using heat tolerant donors and high yielding cultivars. For meeting immediate varietal needs, two genotypes (parents) namely, HD 2402 and VL 639 were selected from National Germplasm Screening Nursery on the basis of desirable developmental traits for heat tolerance. The parent HD 2402 was selected for earliness (perhaps favored the plant to escape the losses due to rise in temperature) and profuse tillering (contributor to grain yield). Whereas, the parent VL 639 was selected on the basis of higher grains per spike, biomass, harvest index and test weight. In the breeding program, attempts were made to incorporate genes for tolerance to heat and yield contributing traits along with resistance to various prevailing rust races. The varietal developmental program was initiated at Rajasthan Agricultural University, Agricultural Research Station, Durgapura, Jaipur, Rajasthan, India. Hybridization between the chosen parents (HD 2402/VL 639) was attempted. The expanded pedigree of this cross is BJ 66 SIB/NAD/63/LR 64 A/5/SL SIB/ NP 852/4/PJ SIB/P14/KT 54 B/3/K 65/VL 639. Conventionally segregating generations of this cross were handled by pedigree selection program under late sown conditions (50th meteorological week) only. In this breeding method superior individual plants were selected in successive generations (F2- F5) under artificial epiphytotic conditions of rusts and a complete record of parent progeny relationship was maintained. For screening homozygous heat tolerant lines from advanced materials (F₆), sowing was done both in late and very late sown conditions to expose the crop to terminal heat stress. On the basis of various developmental traits for heat tolerance like earliness, high tillering, high number of spikelets per spike, high number of grains per spike, 1000-grain weight, grain yield per plant, reaction to important diseases and grain quality parameters, the most promising, homozygous line was screened out and named Raj 3765. Based on multi-location station trials in Rajasthan under late and very late sown conditions, this variety exhibited higher grain yield, resistance to rusts and desirable quality parameters. Hence, this variety was included into different varietal yield evaluation trials for normal sown (46th meteorological week), late sown (50th meteorological week) and very late sown (52nd meteorological week) conditions for three years at different locations of NWPZ of India under the All India Coordinated Wheat Improvement Project (AICWIP). In first year (Initial varietal trial) the trial was conducted in double lattice design and onwards (Advance varietal trial) in randomized block design was conducted under varietal testing programs at all locations across the zone (NWPZ). The mean averaged over locations for different traits has been given only for Raj 3765 and check varieties for interpretation of the results in this paper, although a number of other varieties were also tested in the coordinated trials.

To assess the adaptability in different date of sowings of this variety, the agronomical coordinated trials were planted under irrigated conditions at 46th (normal), 50th (late) and 52nd (very late) meteorological week. The experiment was laid out in split plot design with four replications. The sowing was done in rows, 23 cm apart in normal sowing and 18 cm apart in late and very late sowings by drill method. Besides other recommended practices, six irrigations (at crown root initiation, late tillering, late jointing, flowering, milk stage and dough stage) were applied to raise the crop.

The resistance of Raj 3765 to rusts was tested with the help of AICWIP pathologists at several locations under epiphytotic conditions in the country. The standard inoculation and post-inoculation procedures and practices (Joshi et al. 1982; Nagarajan and Nayar 1986) were followed to generate comparable information. Host- pathogen interactions were scored into various grades following Stakman et al. (1962) for black rust, Johnston (1963) for brown rust and Jhonson et al. (1972) for yellow rust.

Quality laboratory under coordinated program assisted in screening varieties for different quality parameters required at the time of release of the variety. The evaluation of different quality parameters of the variety was made as suggested by Hanslas (1986).