Double-seed sowing (two seeds per hole) is the dominant pattern of peanut sowing in China, but within-hole plant competition usually limits their growth and yield formation.  Besides, the traditional double-seed sowing method does not facilitate mechanization during sowing.  The objective of this study was to determine if single-seed sowing at a proper seeding rate yielded better than traditional double-seed sowing pattern and the differences of physiological metabolism of roots.  A field experiment was conducted in two consecutive years to compare pod yields of single-seed sowing at 180 000 (S180), 225 000 (S225), and 270 000 seeds ha^–1 (S270) with that of double-seed sowing at 270 000 seeds ha^–1 (D270) using a completely randomized block design with four replications.  And the root bleeding sap rate, nutrient content, and the main hormone contents in root bleeding sap were also comparatively investigated.  Although the pod yields of single-seed sowing at the three densities were higher than that of traditional double-seed sowing (D270), S225 yielded better than the other two single-seed sowing treatments (S180 and S270).  The increased pod yield in single-seed sowing at 225 000 seeds ha^–1 was mainly due to the higher pod dry weight per plant and harvest index.  The improved pod dry weight and shoot growth had closely relationship with the enhanced root physiological traits such as the increased root bleeding sap rate, content of free amino acids, soluble sugars, K⁺, Mg^2+, Zn²⁺, and Ca²⁺ of the individual plant root.  The improved activity of root reductive, nitrate reductase (NR) and ATPase and higher zeatin and zeatin riboside (Z+ZR) content of root bleeding sap were also crucial to the pod and shoot growth of peanut.  Single-seed sowing at a moderate seeding rate (S225) is a potential practice to increase pod yield and to save seed cost.

 

The growth and yield of peanut are negatively affected by continuous cropping.  Arbuscular mycorrhizal fungi (AMF) and calcium ions (Ca²⁺) have been used to improve stress resistance in other plants, but little is known about their roles in peanut seedling growth under continuous cropping.  This study investigated the possible roles of the AMF Glomus mosseae combined with exogenous Ca²⁺ in improving the physiological responses of peanut seedlings under continuous cropping.  G. mosseae combined with exogenous Ca²⁺ can enhance plant biomass, Ca²⁺ level, and total chlorophyll content.  Under exogenous Ca²⁺ application, the F_v/F_m in arbuscular mycorrhizal (AM) plant leaves was higher than that in the control plants when they were exposed to high irradiance levels.  The peroxidase, superoxide dismutase, and catalase activities in AM plant leaves also reached their maximums, and accordingly, the malondialdehyde content was the lowest compared to other treatments.  Additionally, root activity, and content of total phenolics and flavonoids were significantly increased in AM plant roots treated by Ca²⁺ compared to either G. mosseae inoculation or Ca²⁺ treatment alone.  Transcription levels of AhCaM, AhCDPK, AhRAM1, and AhRAM2 were significantly improved in AM plant roots under exogenous Ca²⁺ treatment.  This implied that exogenous Ca²⁺ might be involved in the regulation of G. mosseae colonization of peanut plants, and in turn, AM symbiosis might activate the Ca²⁺ signal transduction pathway.  The combination of AMF and Ca²⁺ benefitted plant growth and development under continuous cropping, suggesting that it is a promising method to cope with the stress caused by continuous cropping.