The high temperature prevailing during crop season hinders productivity of wheat. Various physiochemical processes are responsible for heat tolerance in wheat varieties. To find out the genetic variation with regards to these parameters among certain varieties in wheat would be of great value to harvest higher yield in the warmer areas. Higher grain yield particularly under high temperature of late sown conditions, indicates presence of genes for heat tolerance. Raj 3765 was found suitable under late sown conditions for grain yield. This indicated that this variety has tolerance to the damage to the high temperature. This genetic resource can be used directly as a commercial variety for the warmer areas or may be useful for improvement of thermo tolerance in wheat. The main morphological characteristics of Raj 3765 are light green, non-waxy leaves, profuse tillering, intermediate and erected ears that turn dusty white at maturity and possess medium bold, amber and lustrous grains. The results obtained are enumerated below.
Late sown-irrigated condition: The analysis of varietal yield evaluation trials over 37 locations (1992-94) revealed that variety Raj 3765 significantly out yielded all check varieties in all the three years except in the third year, where it yielded as good as check PBW 226 (Table 1). The average mean yield of Raj 3765 under three years testing in trials across NWPZ was recorded 4.21 t/ha. This variety yielded 21.3%, 11.9%, 4.5%, 4.9% and 15.4% higher grain yield over Sonalika, HD 2285, PBW 226, Raj 3077 and UP 2338 check varieties, respectively.
The results of agronomic experiments of date of sowing and varieties under three environments (1993- 94) at 6 locations of NWPZ of India exhibited that Raj 3765 variety yielded 3.98 t/ha under late sown conditions. However, mean yield over three environments was recorded 3.80 t/ha, which was numerically higher than all the three cheek varieties (Table 2). Raj 3765 also showed better performance under normal and very late sown conditions. Over all results of agronomical trials suggested that this variety is endowed with inherent mechanism of genetic homeostasis. This enables a higher level of productivity both under optimum and suboptimum environments and permits stability and sustainability of production in NWPZ of India. The studies of morpho- physiological traits revealed that Raj 3765 showed high grain yield and high values of other yield contributing traits like shorter grain filling period (32.9 days), tillers per plant (5.8), flag leaf area (19.9 cm2), spike length (10.6 cm), spike area (33.3 cm2), grains per spike (43.2), grain yield per spike (1.7 g), harvest index (43.6%) and grain yield per plant (9.3 g) under warm condition. Hence, it gave higher grain yield and sustained productivity as compared to the widely cultivated late sown varieties (HD 2285, PBW 226 and UP 2338) under hotter environment. These results confirmed that Raj 3765 is the most stable among the check varieties for warm conditions therefore, it was recommended by AICWIP for late sown condition in 1994.
Very late sown-irrigated condition: The results of varietal yield evaluation trials over 28 locations (1996 -98) revealed superiority of Raj 3765 in grain yield over cheek variety Sonalika during all the three years. However, it yielded as good as checks HD 2285 (Table 1). Over the years Raj 3765 gave maximum yield (2.90 t/ha) as compared to the checks. This variety produced 13.1% and 5.2% grain yield over Sonalika and HD 2285 cheek varieties, respectively. Results clearly exhibited superiority of Raj 3765 over widely cultivated current varieties under very late sown conditions, which were used as checks during experimentation in the trials of NWPZ.
The results of agronomic trials (1997-98) of NWPZ of India indicated that Raj 3765 variety gave significantly higher grain yield over all the checks in both the late and very late sowing conditions (Table 3). This variety gave 20.4% and 13.7% higher yield over Sonalika and HD 2285, respectively, under very late sown condition. The results of yield components exhibited that Raj 3765 had maximum number of tillers per m2 (362.9), grains per spike (41 .4) and 1000-grain weight (34.7 g) as compared to the check varieties (Sonalika and HD 2285) under warm conditions indicated that this variety had better stability through these yield contributing traits to sustain productivity under heat stress environment (Table 3). Mean yield performance of wheat variety Raj 3765 in very late sown trials (1996-98) conducted at different locations of NWPZ and NEPZ of India revealed that this variety gave 15.4% and 8.6% higher grain yield over Sonalika and HD 2285 check varieties, respectively (Table 4). Results further exhibited that out of 28 locations, Raj 3765 was qualified in top group at 14 locations. Thus, these results clearly established that Raj 3765 is an excellent wheat variety, which offered persistent good response under late and very late sown conditions. Physiological studies in AICWIP revealed that the variety remained plastic to changes in climatic factors and found more tolerant to heat with minimum membrane injury, confirming its inbuilt mechanism for stresses. Hence, it was further recommended by AICWIP for very late sown situation in 1998.