Early selection of superior germplasm for oil-producing Eucalyptus maideni F. v. Muell

Eucalyptus maideni F. v. Muell., a rare species cultivated for both oil and timber, yields high-quality wood and economically valuable eucalyptus oil (EO). Previous studies revealed substantial variation in leaf oil content among individual seedlings and families. However, the selection and breeding of superior germplasm for oil production have not yet been initiated. In this study, 15 superior trees were used as seed trees, while commercial seeds served as the controls. Seedlings were sown in family groups, and leaves from seed trees and 480 seedlings (sampled at 180 and 360 days post-sowing) were analyzed. EO was extracted from seed tree leaves by steam distillation and from seedling leaves by headspace solid-phase microextraction, with gas chromatography-mass spectrometry (GC-MS) used for component quantification. Among 249 compounds identified, 1,8-cineole (eucalyptol) consistently exhibited the highest relative content (40.61-71.27%). Significant differences in eucalyptol content were found among families and individuals at both seedling ages, with a coefficient of variation (CV) of approximately 25%. Eucalyptol content at both 180 and 360 days was primarily influenced by within-family variance (56.91% and 62.43%, respectively), exceeding between-family variance (42.13% and 36.73%). Additionally, moderate correlations between eucalyptol concentrations at 180 and 360 days suggest partial temporal stability in essential oil composition across developmental stages. Therefore, the relative eucalyptol content was identified as a key indicator for the preliminary selection of superior germplasm in oil-producing E. maideni. Using the mean + standard deviation (C + σ) as the selection threshold, two superior families (Families 2 and 3) and 56 elite seedlings were preliminarily identified across both growth stages. The selected superior families exhibited an average increase of 29.85% in leaf eucalyptol content, while the elite seedlings showed an average increase of 37.61%. These results demonstrate the feasibility and effectiveness of early selection for superior germplasm in oil-producing E. maideni. The selected superior germplasm provides foundational material for the subsequent propagation of improved varieties, thereby supporting the development of the oil-producing E. maideni industry in Yunnan Province.