Cultivar mixtures increase crop diversification and grain yield stability.  Achieving high grain yield and nitrogen use efficiency (NUE) with environmentally friendly practices is a major challenge, but it is currently unclear whether maize cultivar mixtures can improve NUE.  A two-year field experiment was conducted using two maize cultivars with different roots angles and leaf angles planted in monoculture or in mixtures under four nitrogen levels N0 (0 kg N ha^–1), N140 (140 kg N ha^–1), N280 (280 kg N ha^–1) and N340 (340 kg N ha^–1).  Cultivar mixtures significantly increased light interception of the middle canopy, dry matter accumulation and total root length under N0, N140, and N280 conditions.  Light interception of the middle canopy was positively related to dry matter accumulation and thus increased grain yield.  In addition, light interception of the whole canopy was positively related to total lateral root length, while the greater total lateral root length of outer nodal roots significantly improved nitrogen accumulation and NUE.  Thus, cultivar mixtures promoted an optimal canopy structure and good root growth, thereby improving grain yield and NUE.  These findings deepen our understanding of the facilitating effect of canopy structure and root traits of cultivar mixtures on the combined promotion of grain yield and NUE. 

Pyrus pyrifolia Nakai ‘Whangkeumbae’ is a sand pear fruit with excellent nutritional quality and taste.  However, the industrial development of pear fruit is significantly limited by its short shelf life.  Salicylic acid (SA), a well-known phytohormone, can delay fruit senescence and improve shelf life.  However, the mechanism by which SA regulates CONSTANS-LIKE genes (COLs) during fruit senescence and the role of COL genes in mediating fruit senescence in sand pear are poorly understood.  In this study, 22 COL genes were identified in sand pear, including four COLs (PpCOL8, PpCOL9a, PpCOL9b, and PpCOL14) identified via transcriptome analysis and 18 COLs through genome-wide analysis.  These COL genes were divided into three subgroups according to the structural domains of the COL protein.  PpCOL8, with two B-box motifs and one CCT domain, belonged to the first subgroup.  In contrast, the other three PpCOLs, PpCOL9a, PpCOL9b, and PpCOL14, with similar conserved protein domains and gene structures, were assigned to the third subgroup.  The four COLs showed different expression patterns in pear tissues and were preferentially expressed at the early stage of fruit development.  Moreover, the expression of PpCOL8 was inhibited by exogenous SA treatment, while SA up-regulated the expression of PpCOL9a and PpCOL9b.  Interestingly, PpCOL8 interacts with PpMADS, a MADS-box protein preferentially expressed in fruit, and SA up-regulated its expression.  While the production of ethylene and the content of malondialdehyde (MDA) were increased in PpCOL8-overexpression sand pear fruit, the antioxidant enzyme (POD and SOD) activity and the expression of PpPOD1 and PpSOD1 in the sand pear fruits were down-regulated, which showed that PpCOL8 promoted sand pear fruit senescence.  In contrast, the corresponding changes were the opposite in PpMADS-overexpression sand pear fruits, suggesting that PpMADS delayed sand pear fruit senescence.  The co-transformation of PpCOL8 and PpMADS also delayed sand pear fruit senescence.  The results of this study revealed that PpCOL8 can play a key role in pear fruit senescence by interacting with PpMADS through the SA signaling pathway.