High yields of wheat are mainly obtained through a high level of nitrogen and irrigation supplementation.  However, excessive nitrogen and irrigation supplication increase the risk of lodging.  The main objectives of this work were to clarify the capacity of lodging resistance of wheat in response to nitrogen and irrigation, as well as to explore the effective ways of improving lodging resistance in a high-yield wheat cultivar. In this study, field experiments were conducted in the 2015–2016 and 2016–2017 growing seasons.  A wheat cultivar Jimai 22 (JM22), which is widely planted in the northern of Huang-Huai winter wheat region, was grown at Tai’an, Shandong Province, under three nitrogen rates and four irrigation treatments.  The lodging risk was increased with increased nitrogen rate, as indicated by increasing lodging index (LI) and lodging rate across both growing seasons.  With nitrogen increasing, the plant height, the basal internode length and the center of gravity height, which were positively correlated with LI, increased significantly.  While the density of the basal 2nd internode (for culm and leaf sheath) and cell wall component contents, which were negatively correlated with LI, decreased conspicuous along with nitrogen increased.  Increasing irrigation supplementation increased the 2nd internode culm wall thickness, breaking strength and leaf sheath density within limits which increased stem strength.  Among the treatments, nitrogen application at a rate of 240 kg ha^–1 and irrigation application at 600 m3 ha^–1 at both the jointing and anthesis stages resulted in the highest yield and strongest stem.  A suitable plant height ensures sufficient biomass for high yield, and higher stem stiffness, which was primarily attributed to thicker culm wall, greater density of the culm and leaf sheaths and higher cell wall component contents are the characteristics that should be taken into account to improving wheat lodging resistance.

The brown planthopper, Nilaparvata lugens (Stål), is the most serious insect pest of rice. It has developed high resistance to traditional insecticides because of their intensive use. Juvenile hormone (JH) analogs have been used successfully to control this species and other pest insects. However, the molecular mechanism of JH signaling is not well understood. Krüppel-homolog 1 (Kr-h1) is a transcription factor involved in the JH pathway. In this study, the Kr-h1 cDNA was cloned and characterized from N. lugens by rapid amplification of cDNA ends (RACE) and reverse transcription PCR (RT-PCR). Its spatial and temporal expression profiles were examined by real-time quantitative PCR, and its function was also studied by RNA interference (RNAi). The open reading frame of NlKr-h1 is 1 833 bp encoding for 611 amino acids. The protein contains eight conserved zinc-finger motifs. NlKr-h1 was expressed at all life stages, with the highest mRNA level in the 4-day embryo. NlKr-h1 mRNA levels rose during each nymphal molt after the 2nd instar. In the adults, the mRNA level in males was significantly higher than that in females of either the macropterous or brachypterous type. The highest expression was observed in the female midgut. NlKr-h1 was activated by juvenile hormone III (JH III) in the 3rd-5th instar nymphs. Disruption of Nlkr-h1 expression by RNAi caused stunted wing development and malformations of both male and female external genitalia. Our findings suggest that Kr-h1 may be a useful target for pest insect management.