Tree peonies native to China are a precious crop with ornamental, medicinal and edible oil properties, of which flare tree peony (Paeonia rockii) is one of the most significant germplasms in Paeonia.  The development and application of expressed sequence tag-simple sequence repeat (EST-SSR) markers are very valuable for genetic and breeding applications, but EST-SSR resources for the genus Paeonia are still limited.  In this study, we first reported the development of SSRs within transcription factors (TFs) in P. rockii based on next-generation sequencing (NGS) and single-molecule long-read sequencing (SMLRS).  A total of 166 EST-SSRs containing six nucleotide repeat types were identified from 959 candidate TFs associated with yield, with an average of one SSR per 5.83 unigenes.  In total, 102 (61.45%) pairs of primers produced amplification products in the two RNA-seq cultivars.  Among them, 58 (56.86%) pairs of primers from 18 gene families (AP2, bHLH, HSF, etc.) were identified to be polymorphic both in the parents of a linkage mapping population and in eight randomly selected accessions of P. rockii.  Further, the 58 EST-SSRs indicated a high level of informativeness with PIC values ranging from 0.32 to 0.91 (mean 0.70) after assessment in 37 tree peony accessions.  Transferability studies indicated that the amplification ratio of the 58 pairs of primers ranged from 89.66 to 100% across seven species of Paeonia.  In addition, a genetic relationship study was performed in 62 accessions.  Cluster analysis using the neighbour-joining (NJ) tree demonstrated that major clusters corresponded to the known pedigree trees.  Taken together, these newly developed EST-SSRs have a potential use in the conservation of tree peony germplasm and marker-assisted selection (MAS) breeding.

Salt stress can be alleviated by straw layer burial in the soil, but little is known of the appropriate form of the straw layer for optimal regulation of soil water and salinity because of the uncontrollability of field tests.  Here, the following four straw forms with compaction thickness of 5 cm buried 40–45 deep were studied: no straw layer (CK), segmented straw (SL, 5 cm in length), straw pellet (SK), and straw powder (SF).  The three straw forms (SL, SK and SF) significantly delayed the infiltration of irrigation water down the column profile by 71.20–134.3 h relative to CK and the migration velocity of the wetting front under SF was the slowest.  It took longer for the wetting front to transcend SK than SL but shorter for it to reach the bottom of soil column after water crossed the straw layer.  Compared with CK, the average volumetric water content in the 0–40 cm soil layer increased by 6.45% under SL, 1.77% under SK and 5.39% under SF.  The desalination rates at the 0–40 and 0–100 cm soil layers increased by 5.85 and 3.76% under SL, 6.64 and 1.47% under SK and 5.97 and 4.82% under SF.  However, there was no significant difference among straw forms in the 0–40 cm soil layer.  Furthermore, the salt leaching efficiency (SLE, g mm^–1 h^–1) above the 40 cm layer under SL was 0.0097, being significantly higher than that under SF (0.0071) by 37.23%.  Salt storage under SL, SK and SF in the 40–45 cm layer accounted for 4.50, 16.92 and 7.43% of total storage in the 1-m column profile.  Cumulative evaporation under SL and SF decreased significantly by 41.20 and 49.00%, with both treatments having the most significant inhibition of salt accumulation (resalinization rate being 36.06 and 47.15% lower than CK) in the 0–40 cm soil layer.  In conclusion, the different forms of straw layers have desalting effects under high irrigation level (446 mm).  In particular, SL and SF performed better than SK in promoting deep salt leaching and inhibiting salt accumulation on the soil surface.  However, SL was simpler to implement and its SLE was higher.  Therefore, the segmented 5 cm straw can be recommended as an optimum physical form for establishing a straw layer for managing saline soils for crop production.