Cyrtopodium paranaense is a tropical terrestrial orchid, which propagates mainly through sexual seed germination. In this study, we document the asexual morphogenesis of the root tip to protocorm-like body (PLB) conversion in Cyrtopodium paranaense. Protocorm-like bodies sporadically developed from root tips of flask-grown seedlings in the absence of any exogenous plant growth regulators (PGRs). The compact PLBs ultimately gave rise to normal plantlets. Histological observations revealed that the root cap became dissociated from the root apex at an early stage followed by dispersed extension of root vascular strands into nascent PLBs. Protocorm-like bodies also developed from the root central stele tissue. In root tip segment cultures, PLBs were not formed without providing PGRs but were efficiently formed from root tips in Murashige and Skoog (MS) medium supplemented with 10.2 μM indole-3-acetic acid (IAA) and 9.0 μM thidiazuron (TDZ). Both IAA and TDZ promoted the formation of PLBs; however, TDZ did not induce PLB formation in the absence of IAA, indicating a synergistic effect of the two PGRs. Protocorm-like bodies were proliferated and subsequently plants regenerated in PGR-free MS medium. Root tip culture may be used as an alternative method for the propagation of Cyrtopodium paranaense.
Efficient nitrogen (N) fertilizer management is crucial for ensuring the maximum economic yield and reducing the risk of environmental pollution. The objective of this study was to determine the effect of N fertilizer management on root yield and N uptake of radish in southern China by using 15N isotope tracing. A 2-year field experiment was conducted with three N rates (0, 60, and 120 kg N/ha) and two different application proportions, viz, A [50% at basal, 20% at 15 days after seeding (DAS), 30% at 30 DAS] and B (30% at basal, 20% at 15 DAS, 50% at 30 DAS) for each N rate, which were expressed as N0, N60A, N60B, N120A, and N120B, respectively. The results showed that root yields were significantly increased with N rates increasing from 0 to 120 kg N/ha. The root yields for N120A and N120B were 67.60 t·ha−1 and 72.50 t·ha−1 at harvest, 64.07% and 66.67% higher than those for the treatments of N60A and N60B, respectively. Mean radish recovery of N fertilizer ranged from 25.90% at N120A to 32.60% at N60B, and N fertilizer residual rate in the soil ranged from 11.50% at N120A to 14.90% at N60B. About 17.50% to 35.70% of total uptake of 15N derived from basal fertilizer was absorbed at seeding stage. However, 61.87% to 80.18% of total uptake of 15N derived from topdressing fertilizer absorbed at root expanding stage. Therefore, appropriate nitrogen application with increasing topdressing nitrogen amount could increase root yield of radish and the nitrogen recovery efficiency. Nitrogen fertilizer application recommended was 120 kg N/ha with 30% for basal, 20% for 15 DAS and 50% for 30 DAS in this study.