Estimation of genetic variances in flood tolerance of poplar and selection of resistant F1 generations

Five Aigeiros section poplar clones were adopted as parents to produce five full-sib families through cross-breeding. Morphological, ecophysiological, and growth characteristics of the five parents and their 15 superior F1 generations were investigated during 45 days of flooding followed by a 10-day recovery period. Cuttings were subjected to two treatments: watered (control) and flooded to 10 cm above the soil surface. Results showed that flooded cuttings showed significant reduction in growth of height, root-collar diameter and leaf area, and root and total biomass yield. All 20 clones formed hypertrophied lenticels and adventitious roots by day 6-14 of flooding. In flooded cuttings, net photosynthesis, stomatal conductance, transpiration, and chlorophyll fluorescence were decreased significantly compared with the control. After flooding ended, all plants recovered rapidly. Generally, progenies showed higher growth of height, root-collar diameter, root biomass and leaf area than their parents both under flooding and control conditions, showing that heterosis existed in F1 generations, regardless of flooding. However heterosis was lower under flooding conditions than in the control. Under flooding, the highest heterosis of higher-parent in height and root-collar diameter were 68.63 and 20.83%, respectively. Variability of flood tolerance among progenies was clear in growth of height and root-collar diameter. Selection criteria for parents in cross-breeding were different between control and flooding. Relative effect values of the specific combining ability (SCA) and relative effect values of the general combining ability (GCA) of parents were more important than their flood tolerance. Progenies with a higher level of flood tolerance could be obtained, even from parents intolerant to flooding. In terms of breeding, height growth would be most important characteristic to measure in flooding conditions, and root-collar diameter growth was also very useful. Based on all measured values, the tested 20 clones were classified into three groups using hierarchical cluster analysis. Clones Lu, E4, E9, E29, A2, A8, A9, B1, B3, B4, and D8, were flood-tolerant. Clones Lf, Ha, Lm, D1, D7, F9, and F21 were moderately flood-tolerant. Clones Sm and F13 were flood-susceptible.