The traditional soil-based rice seedling production methods for mechanical transplanting are resource-intensive, time consuming and laborious. The improvement and optimization of nutrient management in soil-less nursery raising methods like tandem long-mat seedlings (TLMS) are necessary for the resource-efficient cultivation of rice. In the present study, a controlled-release fertilizer (CRF)-polymer-coated compound fertilizer with 3 months release period (PCCF-3M) was applied as seedling fertilizer (SF), and five different dosages of SF (SF-0, SF-10, SF-20, SF-30, and SF-40) were compared with an organic substrate as the control (CK). Among all SF treatments, the best results were obtained with the application of 20 g/tray of SF (SF-20), as the seedling quality and machine transplanting quality were comparable to those of CK. In contrast, the lower dosages (SF-0 and SF-10) resulted in low nitrogen content and reduced shoot growth, while the higher dosages (SF-30 and SF-40) resulted in toxicity (increased malondialdehyde accumulation) and inhibited the root growth. Similarly, SF-20 increased panicle number (5.6–7.0%) and yield (4.3–5.3%) compared with CK, which might be related to the remaining SF entangled in the roots supporting the tiller growth of rice seedlings in the field. Moreover, SF-20 reduced the seedling block weight (53.1%) and cost of seedling production (23.5%) but increased the gross margin, indicating that it was easy to handle and economical. Taken together, our results indicate that SF-20 is a cost-effective way to promote the growth and transplanting efficiency of rice seedlings. To our knowledge, this study is the first to determine the optimum dosage of CRF for the soil-less production of rice seedlings.

Cre/loxP, a site-specific recombination system, has been widely used for various purposes, including chromosomal translocations, generation of marker-free transgenic plants, tissue-specific activation of a reporter gene and efficient heterologous gene expression in plants.  However, stable or transient expression of Cre recombinase in plants can cause chlorosis or necrosis.  Here, we describe a modified Cre/loxP recombination system using a DNA fragment flanked with loxP sites in the same orientation in which necrosis induced by Cre recombinase in Nicotiana benthamiana leaves was alleviated.  The modified system was successfully used to create functional GFP-tagged pepper mild mottle virus (PMMoV) and a chimeric virus with coat protein (CP) substitution assembled from separate pro-vector modules.  Our results provide a new strategy and flexible technique to construct chimeric virus and infectious clones for plant viruses with large genomes.