Objectives We investigated the variation characteristics of different wheat cultivars from aspect of spikelet development and dry matter accumulation and transportation under drought stress.
Methods A pot experiment was conducted in an artificial chamber, a conventional wheat cultivar “Jimai 22 (JM22)” and a drought-resistant cultivar “Zhongmai 36 (ZM36)” were used as materials. Drought stress lasted from late spikelet stage to maturity (WS, the soil moisture was 40%−45% of the field water capacity), and full soil moisture (80%−85% of field water capacity) was used as control. The floret primordia development at different spike positions, the dry matter accumulation before and after anthesis in different organs, and the grain-filling rate were determined, and the yield of superior and inferior grains at different spike positions was investigated.
Results 1) Drought stress accelerated the development of floret primordia in the central and apical spikelets, and reduced the number of floret primordia in the apical and basal spikelets of JM22, resulting in unbalanced spike development in JM22. However, drought stress had no significant effect on the development of floret primordia of ZM36. 2) For the drought resistant cultivar ZM36 under drought stress, the transportation amount and efficiency of pre-anthesis dry matter stored in vegetative organs (Pre-DT, and Pre-DTE) were significantly decreased by 34.8% and 33.2%, which severely reduced its contribution rate to grain (Pre-DCR), however, the post-anthesis dry matter accumulation (Post-DA) and its contribution rate to grain (Post-DCR) increased by 5.1% and 25.7%, respectively, for the conventional cultivar JM22, the Pre-DCR was increased by 32.1% while the Post-DA and Post-DCR decreased by 40.4% and 21.3%. So the post-anthesis dry matter accumulation dominant grain yield in ZM36, and pre-anthesis vegetative organ dry matter translocation decides the grain yield of JM22 under drought stress. The decrease of Pre-DCR in stem of ZM36 was higher than those in the other organs, while the increase of Pre-DCR in spike axis+glume of JM22 was the highest, which was 1.4 times of that in control. 3) Drought stress inhibited the dry matter transportation of leaf sheath, stem and spike axis+glume of JM22, resulting in a reduction of grain-filling rate, but drought stress only inhibited the dry matter transportation of steam and spike axis+glume of ZM36, without impacting its grain-filling rate. The decrease in grain number, single-grain weight and yield at different spike positions in JM22 caused by drought stress (7.6%, 15.9% and 24.3%) were higher than those of ZM36 (3.3%, 9.5% and 16.3%). The adverse effect of drought stress on JM22 was mainly happened in the superior grains, but on ZM36 was mainly in the inferior grains.
Conclusion Drought stress decreases the grain yield of JM22 as it causes unbalanced development of floret primordia in different spike position, blocks the post-anthesis dry matter accumulation and translocation from leaf sheath, stem and spike axis+glume to superior grains in apical and central spikelet position, resulting in a significant decrease in the grain-filling rate. For cultivar ZM36, drought stress reduces the pre-anthesis vegetative organ dry matter translocation to grain, but increases the post-anthesis vegetative organ dry matter accumulation, so the adverse impact to yield mainly happened on the inferior grains, not reducing grain yield severely. Therefore, the study of drought stress is very important to ensure stable and high yield of wheat.
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