Genome-wide association analysis for grain moisture content and dehydration rate on maize hybrids.

For mechanized maize production, a low grain water content (GWC) at harvest is necessary. However, as a complex quantitative trait, understand the genetic mechanism of GWC remains a large gap, especially in hybrids. In this study, a hybrid population through two environments including 442 F1 was used for genome-wide association analysis of GWC and the grain dehydration rate (GDR), using the area under the dry down curve (AUDDC) as the index. Then, we identified 19 and 17 associated SNPs for GWC and AUDDC, including 10 co-localized SNPs, along with 64 and 77 pairs of epistatic SNPs for GWC and AUDDC, respectively. These loci could explain 11.39-68.2% of the total phenotypic variation for GWC and 41.07-67.02% for AUDDC at different stages, whose major effect was the additive and epistatic effect. By exploring the candidate genes around the significant sites, a total of 398 and 457 possible protein-coding genes were screened, including autophagy pathway and auxin regulation-related genes, and five inbred lines with the potential to reduce GWC in the combined F1 hybrid were identified. Our research not only provides a certain reference for the genetic mechanism analysis of GWC in hybrids but also provides an added reference for breeding low-GWC materials. Supplementary Information: The online version contains supplementary material available at 10.1007/s11032-022-01349-x.

[Effects of drought stress on performance of photosystem II in maize seedling stage].

Maize cultivar Shandan 609 was used to determine the effects of drought stress on photosystem II, dry matter accumulation, protective enzyme activity and proline content at seedling stage in pot experiment. Two drought treatments (moderate drought and severe drought) were tested. The results showed that dry matter accumulation, leaf area and plant height of cultivar shaandan 609 decreased significantly with the increasing drought stress. The less grouped PS II units (L-band > 0), severely damaged OEC (K-band > 0), and the inhibited acceptor side (ψo significantly decreased) resulted in the overall dropped performance of PS II (PI(ABS)). Under the condition of moderate and severe drought stress, the activities of superoxide, peroxidase, catalase and proline content increased significantly, which were 1.3, 1.1, 1.2, 5.8 and 1.1, 3.3, 1.5, 15.0 times of control (CK), respectively. Those results indicated that damage of PS II acceptor and donor side under drought stress led to the decline of PS II performance, which was likely to cause the decline of dry mater accumulation of maize cultivar Shandan 609, while protective enzymes and proline as protective substance in plant played a positive role in drought resistance.

[Effects of low nitrogen stress on source-sink characters and grain-filling traits of different genotypes summer maize].

This paper studied the source-sink characters and grain-filling traits of six genotype summer maize varieties under 2 years (from 2007 to 2008) application of low dosage (105 kg x hm(-2)) and normal dosage (337.5 kg x hm(-2)) fertilizer nitrogen. Under low nitrogen stress, the population yield, leaf area index (LAI), source-sink characters, and grain-filling traits of test varieties differed significantly. The varieties tolerant to low nitrogen, e.g., Xianyu 335 and Zhengdan 958, had longer active grain-filling stage, higher maximum filling rate, longer duration of maximum LAI, and more harmonious sink-source relation; while less tolerant species, e.g., Shaandan 902 and Yuyu 22, had shorter active grain-filling hours, lower maximum filling rate, lower mass increment and LAI under maximum grain-filling rate after silking, and significantly decreased source supply capacity. Low nitrogen stress increased the yield difference among the test varieties significantly.

[Effects of planting date and density on population physiological indices of summer corn (Zea mays L.) in central Shaanxi irrigation area].

By using D-saturation optimum design and the methods of crop population physiology, this paper studied the effects of planting date and density on the population physiological indices of summer maize Shandan 8806 and its yield in central Shaanxi irrigation area. The results showed that in the period from 13 June to 22 July, the delay of planting had negative effects on grain yield, dry matter accumulation (DMA), maximum leaf area index (LAImax), net assimilation rate (NAR), leaf area duration (LAD) and crop growth rate (CGR), with larger effects on LAD and CGR than on LAImax and NAR. Within the range of 45 000-65 918 plants . hm (-2), planting density had positive effects on grain yield, DMA, LAImax, LAD and CGR but negative effect on NAR, with larger effects on LAImax, LAD and CGR than on NAR. The effects of planting date were more significant than those of planting density, and thus, Shandan 8806 should be sowed as early as possible. The regressive model based on the population physiological indices indicated that for the high yield of summer maize Shandan 8806, the optimum planting date was from 10 to 20 June, and the optimum planting density was from 57 767 to 71 706 plants . hm(-2).