Qisheng Li

This paper aims to clarify the effects of different exogenous phytohormones on the physiological traits of rice (Oryza sativa L.) at the early stage of irrigation under low-temperature stress. In this study, two types of rice varieties with different temperature sensitivities screened out previously, namely, a cold-tolerant variety (Nan Jing 9108) and a low-temperature-sensitive variety (Hui Liang You 898), were used in pots to simulate the process of low-temperature stress in rice at the early stage of grouting (6–9 days after anthesis) with artificial low-temperature treatments. The experimental treatments were 450 mg L⁻¹ Methyl jasmine acid (MJ), 46 mg L⁻¹ Melatonin (MT), 69 mg L⁻¹ Salicylate (SA), 40 mg L⁻¹ Erythromycin (GA₃), 25 mg L⁻¹ Zeatin (Z), 145 mg L⁻¹ Spermidine (SPD), and 5 mg L⁻¹ Abscisic acid (ABA) sprayed on rice before low-temperature stress, while low-temperature treatment without spraying (DK) and conventional planting without spraying (CK) were added as the control. The results showed that compared with the room temperature control (CK, sprayed with deionized water), the low-temperature control (DK, low-temperature treatment, and sprayed with deionized water) all significantly reduced the rice grain yield. Different exogenous hormones sprayed before low-temperature stress could increase rice yield, among which, Z and SPD spraying treatments had a better effect on the yield of Hui Liang You 898, while different exogenous hormone treatments increased the yield of Nan Jing 9108 in an average manner. The Z and SPD treatments increased the yield of Hui Liang You 898 by 24.87% and 26.16% and that of Nan Jing 9108 by 15.87% and 17.80%, respectively. This was mainly attributed to the significant increase in thousand-grain weight and fruiting rate, while there was no significant difference in the number of spikes and number of grains. The different exogenous hormone treatments were able to delay leaf senescence, enhance the photosynthetic production capacity of plants by increasing leaf chlorophyll content, and thus increase the accumulation of photosynthetic assimilation products and population growth rate after flowering. Among them, both Z and SPD treatments resulted in a population growth rate of more than 30% from spike flushing to maturity, which led to a higher dry matter accumulation of the plant at maturity. In addition, in the dry matter distribution of the plant at maturity, the seeds occupied a higher accumulation amount and proportion compared with the respective DK; the SPD treatment resulted in the maximum distribution rate of seeds at maturity of Hui Liang You 898, with an increase of 8.27%, and the Z treatment resulted in the maximum distribution rate of seeds at maturity of Nan Jing 9108, with an increase of 7.34%. At the same time, the Z treatment significantly increased the activities of adenosine diphosphate glucose phosphorylated enzyme (AGP) and starch branching enzyme (SBE) in the grains of both varieties, which resulted in the accumulation of more starch and ultimately increased the rice grain yield. The results verified that different exogenous phytohormones could be used to regulate the insufficiency of grouting caused by low-temperature stress during the grouting and fruiting stages of rice and enriched their agronomic and physiological traits in response at the same time.

With the rapid development of ecological agriculture and organic products, there is an urgent need to reduce the use of fertilizers and pesticides by producing bio-nursery substrates containing multifunctional microbial communities. In this study, beneficial Pseudomonas strains were screened from the rhizosphere of muskmelon (Cucumis melo L.) pre-inoculated with Bacillus velezensis R1-3. The ability of the strain to dissolve phosphorus and produce indole-3-acetic acid (IAA), the effect of the strain on seed germination rate, and the antagonism with R1-3 were determined. Four strains of beneficial Pseudomonas strains that had no antagonistic effect against R1-3 were obtained and formed a Bacillus–Pseudomonas community. The seedling effect of biological substrates containing the Bacillus–Pseudomonas community was evaluated using a seedling pot experiment and a pot experiment. The results showed that the phosphorus solubilization range of all Pseudomonas strains was 86.32–459.48 mg L⁻¹ and the IAA production range was 2.98–11.86 mg L⁻¹. There was a significant negative correlation between the amount of phosphorus dissolved in the fermentation solution and pH. Combined with the results of the seed germination rate and antagonism test, the strains R1-3 + HY-S7, R1-3 + HY-S25, R1-3 + HY-S36, and R1-3 + HY-S70 were selected for the seedling pot experiment and the pot experiment. The results of the two-season seedling culture and two-season pot experiments showed that the bio-nursery substrates containing the bacterial community R1-3 + HY-S70 significantly promoted the growth of muskmelon seedlings, improved plant height, maximum leaf length, and fresh weight, and were significantly better than single bacterial and control treatments at increasing plant height and fresh weight. Finally, the bacterial community R1-3 + HY-S70 was established as the optimal combination for developing biological seedling substrates. Based on 16S rDNA gene sequence analysis, the strain HY-S70 was preliminarily identified as Pseudomonas moraviensis.