Different responses of two maize cultivars to Spodoptera frugiperda (Lepidoptera: Noctuidae) larvae infestation provide insights into their differences in resistance.

Spodoptera frugiperda (Lepidoptera: Noctuidae), a pest with an amazing appetite, damages many crops and causes great losses, especially maize. Understanding the differences in different maize cultivars' responses to S. frugiperda infestation is very important for revealing the mechanisms involved in the resistance of maize plants to S. frugiperda. In this study, a comparative analysis of two maize cultivars, the common cultivar 'ZD958' and the sweet cultivar 'JG218', was used to investigate their physico-biochemical responses to S. frugiperda infestation by a pot experiment. The results showed that the enzymatic and non-enzymatic defense responses of maize seedlings were rapidly induced by S. frugiperda. Frist, the hydrogen peroxide (H2O2) and malondialdehyde (MDA) contents of infested maize leaves were significantly increased and then decreased to the level of the control. Furthermore, compared with the control leaves, the puncture force values and the total phenolics, total flavonoids, and 2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one contents of infested leaves were significantly increased within a certain time. The superoxide dismutase and peroxidase activities of infested leaves were significantly increased in a certain period of time, while the catalase activities decreased significantly and then increased to the control level. The jasmonic acid (JA) levels of infested leaves were significantly improved, whereas the salicylic acid and abscisic acid levels changed less. Signaling genes associated with phytohormones and defensive substances including PAL4, CHS6, BX12, LOX1, and NCED9 were significantly induced at certain time points, especially LOX1. Most of these parameters changed greater in JG218 than in ZD958. Moreover, the larvae bioassay showed that S. frugiperda larvae weighed more on JG218 leaves than those on ZD958 leaves. These results suggested that JG218 was more susceptible to S. frugiperda than ZD958. Our findings will make it easier to develop strategies for controlling S. frugiperda for sustainable maize production and breeding of new maize cultivars with increased resistance to herbivores.

Multi-trait selection for mean performance and stability of maize hybrids in mega-environments delineated using envirotyping techniques.

Under global climate changes, understanding climate variables that are most associated with environmental kinships can contribute to improving the success of hybrid selection, mainly in environments with high climate variations. The main goal of this study is to integrate envirotyping techniques and multi-trait selection for mean performance and the stability of maize genotypes growing in the Huanghuaihai plain in China. A panel of 26 maize hybrids growing in 10 locations in two crop seasons was evaluated for 9 traits. Considering 20 years of climate information and 19 environmental covariables, we identified four mega-environments (ME) in the Huanghuaihai plain which grouped locations that share similar long-term weather patterns. All the studied traits were significantly affected by the genotype × mega-environment × year interaction, suggesting that evaluating maize stability using single-year, multi-environment trials may provide misleading recommendations. Counterintuitively, the highest yields were not observed in the locations with higher accumulated rainfall, leading to the hypothesis that lower vapor pressure deficit, minimum temperatures, and high relative humidity are climate variables that -under no water restriction- reduce plant transpiration and consequently the yield. Utilizing the multi-trait mean performance and stability index (MTMPS) prominent hybrids with satisfactory mean performance and stability across cultivation years were identified. G23 and G25 were selected within three out of the four mega-environments, being considered the most stable and widely adapted hybrids from the panel. The G5 showed satisfactory yield and stability across contrasting years in the drier, warmer, and with higher vapor pressure deficit mega-environment, which included locations in the Hubei province. Overall, this study opens the door to a more systematic and dynamic characterization of the environment to better understand the genotype-by-environment interaction in multi-environment trials.

Optimizing planting density and nitrogen application to enhance profit and nitrogen use of summer maize in Huanghuaihai region of China.

Low planting density and irrational nitrogen (N) fertilization are two common practices in conventional cropping of smallholder maize production in Huanghuaihai region of China. A 2-year field experiment was carried out to study the effects of N application and planting density on maize phenology, dry matter accumulation, profit, yield, N uptake and efficiency indices. The experiments included three N application levels (120 kg ha-1, N1; 180 kg ha-1, N2; 240 kg ha-1, N3) and three planting densities (60,000 plants ha-1, D1; 75,000 plants ha-1, D2; 90,000 plants ha-1, D3). Increasing N input and planting density delayed the physiological maturity and enhanced dry matter accumulation. Comparing with the traditional N3 level, grain yield and profit were kept stable at N2 level and decreased at N1 level, partial factor productivity of applied N (PFPN) and nitrogen efficiency ratio (NER) were increased with the decreasing of N level. Comparing with the traditional D1 density, grain yield, profit and PFPN were increased at D2 density and then kept stable at D3 density, NER was kept stable at D2 density and then decreased at D3 density. Based on the predicted maximum profit, the optimal combinations of N application and planting density were 199 kg ha-1 and 81,081 plants ha-1 in 2017, and 205 kg ha-1 and 84,782 plants ha-1 in 2018. The two optimal combinations had an increase of 17.6% for grain yield, 39.8% for PEPN, 3.6% for NRE than the traditional N3D1 treatment. Therefore, an appropriate combination of increased planting density with reduced N application could enhance profit and nitrogen use of summer maize in Huanghuaihai region of China.

Identification of genetic loci associated with rough dwarf disease resistance in maize by integrating GWAS and linkage mapping.

Maize rough dwarf disease (MRDD) is a viral disease that causes substantial yield loss, especially in China's summer planted maize area. Discovery of resistance genes would help in developing high-yielding resistant maize hybrids. Genome-wide association studies (GWASs) have advanced quickly and are now a powerful tool for dissecting complex genetic architectures. In this study, the disease severity index (DSI) of 292 maize inbred lines and an F6 linkage population were investigated across multiple environments for two years. Using the genotypes obtained from the Maize SNP 50K chip, a GWAS was performed with four analytical models. The results showed that 22 SNPs distributed on chromosomes 1, 3, 4, 6, 7 and 8 were significantly associated with resistance to MRDD (P<0.0001). The SNPs on chromosomes 3, 6 and 8 were consistent with the quantitative trait locus (QTL) regions from linkage mapping in an RIL population. Candidate genes identified by GWAS included an LRR receptor-like serine/threonine-protein kinase (GRMZM2G141288), and a DRE-binding protein (GRMZM2G006745). In addition, we performed an allele variation analysis of the SNP loci selected by GWAS and linkage mapping and found that the main alleles of the two SNP loci PZE_101170408 and PZE_106082685 on chromosome 1 differed in terms of disease-resistant materials and disease-susceptible materials. The identified SNPs and genes provide useful information for MRDD-related gene cloning and insights on the underlying disease resistance mechanisms, and they can be used in marker-assisted breeding to develop MRDD-resistant maize.

Transcriptomic profiling of the high-vigour maize (Zea mays L.) hybrid variety response to cold and drought stresses during seed germination.

Abiotic stresses, including cold and drought, negatively affect maize (Zea mays L.) seed field emergence and later yield and quality. In order to reveal the molecular mechanism of maize seed resistance to abiotic stress at seed germination, the global transcriptome of high- vigour variety Zhongdi175 exposed to cold- and drought- stress was analyzed by RNA-seq. In the comparison between the control and different stressed sample, 12,299 differentially expressed genes (DEGs) were detected, of which 9605 and 7837 DEGs were identified under cold- and drought- stress, respectively. Functional annotation analysis suggested that stress response mediated by the pathways involving ribosome, phenylpropanoid biosynthesis and biosynthesis of secondary metabolites, among others. Of the obtained DEGs (12,299), 5,143 genes are common to cold- and drought- stress, at least 2248 TFs in 56 TF families were identified that are involved in cold and/or drought treatments during seed germination, including bHLH, NAC, MYB and WRKY families, which suggested that common mechanisms may be originated during maize seed germination in response to different abiotic stresses. This study will provide a better understanding of the molecular mechanism of response to abiotic stress during maize seed germination, and could be useful for cultivar improvement and breeding of high vigour maize cultivars.

Seed biostimulant Bacillus sp. MGW9 improves the salt tolerance of maize during seed germination.

Crop performance is seriously affected by high salt concentrations in soils. To develop improved seed pre-sowing treatment technologies, it is crucial to improve the salt tolerance of seed germination. Here, we isolated and identified the strain Bacillus sp. MGW9 and developed the seed biostimulant MGW9. The effects of seed biopriming with the seed biostimulant MGW9 in maize (Zea mays L.) under saline conditions were studied. The results show that the strain Bacillus sp. MGW9 has characteristics such as salt tolerance, nitrogen fixation, phosphorus dissolution, and indole-3-acetic acid production. Seed biopriming with the seed biostimulant MGW9 enhanced the performance of maize during seed germination under salinity stress, improving the germination energy, germination percentage, shoot/seedling length, primary root length, shoot/seedling fresh weight, shoot/seedling dry weight, root fresh weight and root dry weight. Seed biostimulant MGW9 biopriming also alleviated the salinity damage to maize by improving the relative water content, chlorophyll content, proline content, soluble sugar content, root activity, and activities of superoxide dismutase, catalase, peroxidase and ascorbate peroxidase, while decreasing the malondialdehyde content. In particular, the field seedling emergence of maize seeds in saline-alkali soil can be improved by biopriming with the seed biostimulant MGW9. Therefore, maize seed biopriming with the seed biostimulant MGW9 could be an effective approach to overcoming the inhibitory effects of salinity stress and promoting seed germination and seedling growth.

Comparative analysis of the SPL gene family in five Rosaceae species: Fragaria vesca, Malus domestica, Prunus persica, Rubus occidentalis, and Pyrus pyrifolia.

SQUAMOSA promoter-binding protein-like (SPL) transcription factors are very important for the plant growth and development. Here 15 RoSPLs were identified in Rubus occidentalis. The conserved domains and motifs, phylogenetic relationships, posttranscriptional regulation, and physiological function of the 92 SPL family genes in Fragaria vesca, Malus domestica, Prunus persica, R. occidentalis, and Pyrus pyrifolia were analyzed. Sequence alignment and phylogenetic analysis showed the SPL proteins had sequence conservation, some FvSPLs could be lost or developed, and there was a closer relationship between M. domestica and P. pyrifolia, F. vesca and R. occidentalis, respectively. Genes with similar motifs clustering together in the same group had their functional redundancy. Based on the function of SPLs in Arabidopsis thaliana, these SPLs could be involved in vegetative transition from juvenile to adult, morphological change in the reproductive phase, anthocyanin biosynthesis, and defense stress. Forty-eight SPLs had complementary sequences of miR156, of which nine PrpSPLs in P. persica and eight RoSPLs in R. occidentalis as the potential targets of miR156 were reported for the first time, suggesting the conservative regulatory effects of miR156 and indicating the roles of miR156-SPL modules in plant growth, development, and defense response. It provides a basic understanding of SPLs in Rosaceae plants.

The Pentatricopeptide Repeat Gene Family in Salvia miltiorrhiza: Genome-Wide Characterization and Expression Analysis.

The pentatricopeptide repeat (PPR) gene family is one of the largest gene families in plants and plays important roles in posttranscriptional regulation. In this study, we combined whole genome sequencing and transcriptomes to systematically investigate PPRs in Salvia miltiorrhiza, which is a well-known material of traditional Chinese medicine and an emerging model system for medicinal plant studies. Among 562 identified SmPPRs, 299 belong to the P subfamily while the others belong to the PLS subfamily. The majority of SmPPRs have only one exon and are localized in the mitochondrion or chloroplast. As many as 546 SmPPRs were expressed in at least one tissue and exhibited differential expression patterns, which indicates they likely play a variety of functions in S. miltiorrhiza. Up to 349 SmPPRs were salicylic acid-responsive and 183 SmPPRs were yeast extract and Ag⁺-responsive, which indicates these genes might be involved in S. miltiorrhiza defense stresses and secondary metabolism. Furthermore, 23 salicylic acid-responsive SmPPRs were co-expressed with phenolic acid biosynthetic enzyme genes only while 16 yeast extract and Ag⁺-responsive SmPPRs were co-expressed with tanshinone biosynthetic enzyme genes only. Two SmPPRs were co-expressed with both phenolic acid and tanshinone biosynthetic enzyme genes. The results provide a useful platform for further investigating the roles of PPRs in S. miltiorrhiza.