Abstract
Knowledge about the yield gain over the years due to associated changes in the yield component traits is essential for a critical understanding of yield-limiting factors. To estimate genetic gain in grain yield (GY) and component agronomic traits of wheat varieties released between 1900 and 2016 for northwestern plain zone (NWPZ) of India and to identify agronomic and/or genetic basis of the realized gains, two sets of wheat varieties comprising mega varieties and two recently developed varieties were evaluated under timely sown, tilled, and early sown conservation agriculture (CA) conditions for four consecutive years under irrigated conditions. The average annual genetic gain in GY since 1,905 under timely sown irrigated conditions was found to be 0.544% yr−1 over the average of all varieties and 0.822% yr−1 (24.27 kg ha−1 yr−1) over the first released variety, NP4. The realized mean yield increased from 2,950 kg ha−1 of the variety NP4 released in 1,905–5,649 kg ha−1 of HD3086 released in 2014. Regression analysis revealed a linear reduction in height and peduncle length (PL) over the years with a simultaneous and linear increase in biomass at the rate of 43.9 kg ha−1 yr−1 or relatively at 0.368% yr−1 mainly because of delayed heading and increased crop duration. Regression analysis showed no linear trend for tiller number and thousand-grain weight (TGW). Though harvest index (HI) was found to linearly increase relatively at the rate of 0.198% per annum, polynomial regression improved the fitness of data with the indication of no increase in HI since 1982. Interestingly, genetic gain evaluation under early sown CA conditions for 4 years showed similar relative gain (RG) [a relative improvement in varieties across breeding periods (BP)] (0.544% yr−1) but with a higher absolute value (29.28 kg ha−1 yr−1). Major mega varieties like Kalyan Sona, HD2009, PBW 343, HD2967, and HD3086, which occupied a comparatively larger area, were found highly plastic to the improvements in the production environment under timely sown conditions.
Highlights
Wheat (Triticum aestivum L.), being an important source of carbohydrates, protein, vitamins, and many other essential mineral elements, is the most widely grown crop in the world
The varieties within the period were found significant for dry matter (DM), thousand-grain weight (TGW), grains per spike (GPS), plant height (PH), spikelets per spike (SPS), and coleoptile length (CL)
Like many other earlier studies (Sanchez-Garcia et al, 2013; Zhang et al, 2016), shows a significant difference in grain yield (GY) and related yield component traits in the varieties released in different years and breeding periods (BP)
Summary
Wheat (Triticum aestivum L.), being an important source of carbohydrates, protein, vitamins, and many other essential mineral elements, is the most widely grown crop in the world. To feed the still increasing world population, though, at an unequal rate in different parts of the world, the global average productivity of wheat has to be increased at the rate of 1.3% yr−1 (Rosegrant and Agcaoili, 2010). The recent estimates of genetic gain, the improvement in average phenotypic value due to selection within a population over cycles of breeding (Crespo-Herrera et al, 2017) for a mega wheat-growing environment in the northwestern plains of India are quite assuring. The difference in genetic gain realized across the world can be due to many factors including the available crop growth duration, agronomic practices followed, and prevailing weather and soil conditions. Breeding improved varieties by nicking various agronomic traits has always been the main path to maximize the genetic gain through per unit area yield increments (Zhang et al, 2016; Gao et al, 2017; Mingliang et al, 2020)
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