Abstract
Although the grain yield of wheat is finally determined after anthesis, the yield potential is largely dependent on early growth and development. At the specific stage from double ridge to terminal spikelet, spikelet initiation occurs and can affect the number of grains per spike and the grain yield. A factorial experiment using a randomized complete blocks design with six replicates was used to study the effect of three growth regulators (3‑indoleacetic acid [IAA], gibberellic acid [GA3], and 6‑benzylaminopurine [6‑BAP]) on two bread wheat (Triticum aestivum L.) cultivars (Rijaw and Azar‑2), at the Campus of Agriculture and Natural Resources of Razi University, in Kermanshah, Iran, during the 2013–2014 and 2014–2015 cropping seasons. The effect of the hormones was not significant for spikelet initiation number or spikelet initiation rate based on days and growing degree days (GDDs), but apical meristem length and rate of elongation of the apical meristem were affected by exogenous application of hormones in both years. The Rijaw genotype was better than Azar‑2 with respect to apical meristem traits. As well, biplot diagrams showed that the treatment combination 6‑BAP × Rijaw was the best in terms of shoot apex length and rate of shoot apex elongation and that the treatment combination GA3×Rijaw was the best in terms of spikelet number and rate of spikelet initiation. It is concluded that each hormone can improve specific apical meristem characteristics and that the rate of each hormone’s effect depends on the plant’s genetic feature and on the environmental conditions.
Highlights
Bread wheat (Triticum aestivum L.) is a main food crop and a strategic cereal crop around the world
The application of different exogenous plant hormones during the stage from double ridge to terminal spikelet had no significant effect on spikelet number and rate of spikelet initiation in both years of the experiment, whereas apical meristem length and rate of apical meristem elongation were affected by hormone application (Tables 2 and 3)
In both years of the experiment, apical meristem length and rate of elongation of the apical meristem in the Rijaw genotype were highest when the wheat plants were treated with 6-BAP (Figures 4b, c, and 5b, c), As well, the highest and lowest measured apical meristem lengths at the terminal spikelet stage were associated with the application of 6-BAP to the Rijaw genotype (4.2 and 3.7 mm in the first and second years) and the application of distilled water to the Azar-2 genotype (3.2 and 3.3 mm in the first and second years), respectively (Figures 4b and 5b)
Summary
Bread wheat (Triticum aestivum L.) is a main food crop and a strategic cereal crop around the world. Great successes have been achieved in improving the yields of crops, especially wheat, through crop breeding methods, we have a long way to go before we reach the theoretical wheat yield potential (20 t/ha) that is estimated by cereal physiologists (Evans, 1993). Studies show that gaining adequate knowledge of the formation and physiology of crop yield, being able to distinguish changes created by different factors in the life cycle of the crop, and identifying the relationship between the impacts of these factors on the formation of yield components can be effective in making genetic achievements to improve grain yield (Pedrό et al, 2012; Reynolds et al, 2012)
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