The main stem diameter, number of branches, and number of nodes were significantly different among different growing periods and different seeding patterns . However, only the growth stage had a significant effect on the main stem height , whereas the seeding pattern showed no significant effect on it . The monoseeding treatment resulted in the thickest main stem diameter and the highest number of branches and nodes compared with those in the triple-seeding treatments . Non-significant differences were observed in the main stem diameter, number of branched and the number of nodes between the double- and triple-seeding treatments. The effect of the growth stage, treatment, and interaction between year and growth stage, and growth stage and treatment, was significant for the main stem height, main stem diameter, number of branches, and number of nodes , whereas only the year had a significant effect on the main stem height, main stem diameter, and number of nodes . However, the interaction of year × growth stage × treatment had no significant effect on the main stem height, main stem diameter and number of branches but did affect the number of nodes .

The present study revealed that monoseeding might be a useful strategy to minimize the SAR of peanut at the same population density as used for the traditional seeding methods and thus increase peanut yield. Monoseeding decreased the main stem height but increased the main stem diameter, number of branches and nodes, SPAD values, and Pn, which is similar to the results in both herbaceous and woody species . Higher yield was achieved through increasing the number of pods per plant, 100-pod weight, and shelling percentage in the monoseeding treatment. Furthermore, the expression levels of SAR genes were also found to be associated with monoseeding. Many researchers have found that yield can be increased by minimizing the SAR in crops . Here, main stem height decreased but main stem diameter, number of branches, and number of nodes increased compared to the traditional seeding patterns , which reduces the competition among plants. Similarly, another study revealed that monoseeding reduces the competition among individuals at the same population density . Moreover, the leaf and root dry biomass were simultaneously reduced in the multiple seeding groups as a result of the reallocation of resources due to the low R/FR ratio.

We found that the dry matter of different organs in the monoseeding treatment was higher than that in the double- and triple-seeding treatments. This result may be due to the increased reallocation of assimilates to the organs rather than stem elongation compared with that under the traditional seeding patterns. Leaf chlorophyll content reduction is another phenomenon of SAR . When the R/FR ratio is low, chlorophyll synthesis decreased and the plant accumulates less chlorophyll, which is partly mediated by phytochromes. The response of phytochromes to FR and Rradiation plays an important role in adjusting the SAR at high population density . Phytochromes are encoded by a small gene family in angiosperms, which interact with bHLH transcription factors to control many aspects of photomorphogenesis . Under shaded conditions, the pool of PIFs increases, which regulates the gene expression that promotes the SAR . However, the expression of PIF 1 and PIF 4 under monoseeding signifificantly decreased compared to that in the double- and triple-seeding treatments in our study. This result indicated that monoseeding might reduce the shade for peanut neighbors, enabling plants to absorb more R light and thereby inhibiting the SAR at the same population density as used for the traditional seeding patterns. The decrease in PIFs observed at high PAR was accompanied by an increase in Phy B, which plays a major role in SAR inhibition . We also found that expression of Phy B was increased and PIF 1 and PIF 4 expression levels were decreased in the monoseeding treatment, thereby inhibiting the SAR in peanut.

These results are in accordance with those of Franklin regarding Arabidopsis. Therefore, the regulation of SAR under monoseeding could be due to the decreased expression of PIF 1 and PIF 4 and the increased expression of Phy B. However, in the double-seeding treatment with low R/FR, the phytochrome photo-equilibrium shifted to the inactive Pr forms, which no longer interact with PIF 4 and promote the SAR. Phy A is the only phytochrome to rapidly decrease at a high R/FR ratio . Previous research indicated that Phy A can reduce the SAR at a low R/FR ratio . In our study, the expression of Phy A significantly decreased in the monoseeding treatment compared to that in the double-seeding treatment, indicating that plants under monoseeding might receive more R radiation from sunlight and convert it into the biological active Pfr form, which interacts with PIF 4, triggering additional phosphorylation and alleviating SAR. PAR was detected initially as an early repressed gene in the photoreceptor signaling pathways and acts as a negative factor of the SAR . At a low R/FR ratio, the expression of PAR 1 and PAR 2 increases, which suppresses several auxin-mediated SARs .