Phenotypic variation of Salix viminalis in well-watered and drought conditions

Abstract: Background and aims Salix viminalis, which is a C3 perennial crop, is one of the promising candidates for bioenergy production. It is easy to propagate by stem cutting and is able to re-sprout after each harvest. In addition, S. viminalis can produce high biomass yield within a short time frame. The broad genetic base of Salix is an advantage for the development of molecular markers for breeding purposes. Although S. viminalis has high water use efficiency, it has relatively high transpiration rate. Hence, it would be ideal if the crop is drought tolerant and able to produce optimal yield despite limited water availability. In order to understand the drought response of S. viminalis between well-watered and drought conditions, we have studied the phenotypic variation of S. viminalis genotypes in well-watered and water stress conditions.Materials and methods A complete randomized block design was used for the greenhouse experiment with three blocks as the control blocks and another three drought-treated blocks. In total, 296 genotypes of S. viminalis and were used for the study. The phenotypic data which included height growth during treatment, crown length, stem dry weight, leaf dry weight and the number of sylleptic shoots was analyzed using ANOVA by JMP software. Two indexes were constructed namely, Drought Response Index (DRI) and Stem Biomass Allocation Index (SBAI). Three statistical models were used to analyze Genotype x Treatment (GxT) interaction effect, heritability and genetic variation. Also, the relationship between the phenotypic traits was examined by Pearson pairwise correlation.Results There was significant difference between the treatments in all the measured traits. Also, there was significant difference among S. viminalis genotypes in response to water stress condition. Though the total biomass was reduced, the biomass allocation to stem seemed to be less influenced by water stress. Height growth during treatment, crown length and dry weights had higher GxT interaction effect among the genotypes. In contrast, the GxT interaction effect was not significant in stem biomass allocation. The number of sylleptic shoots had stable heritability values (H2Genotype) across the treatments while stem biomass allocation had the highest heritability in both treatments. In addition, there was a decrease in the genetic variation within the population for all the traits in drought condition, except for the number of sylleptic shoots which experienced an increase of genetic variation.Conclusion We suggest that the number of sylleptic shoots should receive more attention in Salix breeding because it is positively correlated with the growth traits. Also, stem biomass allocation can be considered in breeding for higher biomass production. It will be challenging if height growth, crown length and dry weight were considered in breeding, because it is harder to estimate the yield since these traits have high GxT interaction effect within the population.Keywords: Salix viminalis, well-watered, drought, Genotype x Environment interaction (GxE), Broad sense heritability (H2), Phenotypic correlation