Bulk pollen pollination in maize for efficient construction of introgression populations with high genome coverage

Introgression populations consist of a set of introgression lines or families, constructed by continuous backcrossing to the recurrent parent, while carrying a limited number of chromosome segments from a donor parent in their genomes. Increasing the genome coverage is an important aim when constructing introgression population. In this study, we proposed bulk pollen pollination (BPP) method and used it to increase the genome coverage of a maize introgression population. The results showed that the genome coverage of the introgression population constructed using BPP method reached 100% at BC₃ generation, which accorded with the simulation result. The BPP‐based BC₃F_1:2 population could identify most quantitative trait loci (QTL) detected using the F_2:3 population, especially major QTL. Simulation analysis showed that the genome coverage of introgression population increased with the increase of population size and the number of bulked plants, and decreased with the increase of backcross generation. Our results proved the reliability of the BPP‐based introgression population in increasing genome coverage and detecting QTL, and provided references for constructing high‐coverage introgression populations.     

Dissecting the genetic basis of maize deep-sowing tolerance by combining association mapping and gene expression analysis

Deep-sowing is an important method for avoiding drought stress in crop species, including maize. Identifying candidate genes is the groundwork for investigating the molecular mechanism underlying maize deep-sowing tolerance. This study evaluated four traits (mesocotyl length at 10 and 20 cm planting depths and seedling emergence rate on days 6 and 12) related to deep-sowing tolerance using a large maize population containing 386 inbred lines genotyped with 0.5 million high-quality single nucleotide polymorphisms (SNPs). The genome-wide association study detected that 273 SNPs were in linkage disequilibrium (LD) with the genetic basis of maize deep-sowing tolerance. The RNA-sequencing analysis identified 1 944 and 2 098 differentially expressed genes (DEGs) in two comparisons, which shared 281 DEGs. By comparing the genomic locations of the 273 SNPs with those of the 281 DEGs, we identified seven candidate genes, of which GRMZM2G119769 encoded a sucrose non-fermenting 1 kinase interactor-like protein. GRMZM2G119769 was selected as the candidate gene because its homologs in other plants were related to organ length, auxin, or light response. Candidate gene association mapping revealed that natural variations in GRMZM2G119769 were related to phenotypic variations in maize mesocotyl length. Gene expression of GRMZM2G119769 was higher in deep-sowing tolerant inbred lines. These results suggest that GRMZM2G119769 is the most likely candidate gene. This study provides information on the deep-sowing tolerance of maize germplasms and identifies candidate genes, which would be useful for further research on maize deep-sowing tolerance.     

Genetic relatedness and the ratio of subpopulation‐common alleles are related in genomic prediction across structured subpopulations in maize

Genomic prediction (GP), which could predict the breeding value of crop plants genotyped with molecular markers, has been carried out in multiple species. Prediction accuracy (PA) of GP depends on various factors, including genetic relatedness and genetic basis. In this study, we examined the rationale for the low PA of GP when the training and validation populations were distinct using 170 temperate inbred lines and 210 tropical and subtropical inbred lines, respectively. All inbred lines were evaluated for 17 traits and genotyped with 550K high‐density markers. The results show that: (a) the influences of heritability and marker number on PA reflected variations in phenotypic variance captured by the genetic information; (b) the low PA of GP when the training and validation populations represent structured subpopulation is related to the ratio of subpopulation‐common alleles (RSCA) and the genetic relatedness between the two subpopulations; (c) RSCA and PA increased with the increase of genetic relatedness, suggesting that these three factors were related. Our findings would provide references when performing GP, and guidance when designing breeding populations.     

Current status and predicted impact of climate change on forest production and biogeochemistry in the temperate oceanic European zone: review and prospects for Belgium as a case study

Reviews of the current statuses of forests and the impacts of climate change on forests exist at the (sub)continental scale, but rarely at country and regional levels, meaning that information on causal factors, their impacts, and specific regional properties is often inconsistent and lacking in depth. Here, we present the current status of forest production and biogeochemistry and the expected impacts of climate change on them for Belgium. This work represents a case study for the temperate oceanic zone, the most important bioclimatic zone in northwestern Europe. Results show that Belgian forests are mainly young, very productive, and have a high C-sequestration capacity. Major negative anomalies in tree vitality were observed in the 1990s and—as result of disturbances—in the last decade for sensitive species as poplars and European beech. The most severe disturbances were caused by extreme climatic events, directly (e.g. storms) or indirectly (e.g. insect outbreaks after a mild autumn with an early/severe frost). Because of atmospheric deposition and soil fertilization (due to the previous use of the land), nutrient stocks of Belgian forests are likely to sustain the future enhancement in productivity which is expected to follow the increase in atmospheric CO₂ concentration that will occur in years to come. However, in the long term, such (enhanced) forest production is likely to be limited by nutrient deficiencies at poor sites and by drought for sensitive species such as beech and (particularly) Norway spruce. Drought conditions will likely increase in the future, but adverse effects are expected on a relatively limited number of tree species. The potential impacts of windstorms, insects and fungi should be carefully investigated, whereas fires are less of a concern.     

Quantitative trait locus mapping for seed artificial aging traits using an F2:3 population and a recombinant inbred line population crossed from two highly related maize inbreds

Quantitative trait locus (QTL) mapping for seed longevity is essential for breeding modern cultivars with resistance to deterioration during postharvest storage. The inbred lines X178 and I178 showed large differences in seed vigour after artificial aging treatment, while they had similar performances in terms of most agronomic traits. An F_2:3 population and a recombinant inbred line (RIL) population were generated to map QTL after 5 days under artificial aging conditions. Positive correlations were observed among all investigated traits including the aging germination rate, relative aging germination rate, aging simple vigour index, aging primary root length, aging shoot length and aging total length. Thirteen QTL were identified to locate on five chromosome regions: Chr.1:297 Mb (chromosome 1 region 297 Mb), Chr.3:205 Mb, Chr.4:240 Mb, Chr.5:205 Mb and Chr.7:155 Mb, with 2 to 4 QTL co‐located on a region. In each region, 3–8 previously identified aging‐related QTL were located, confirming the importance of these regions for controlling seed longevity in different maize populations. Taken together, the results of this work provide a foundation for further QTL fine mapping and the molecular‐assisted breeding of aging tolerant maize.