Estimation of the most important morphological traits affecting apricot seedlings vigor using path analysis

Background and objectives: Acquired morphological traits of seedlings in nurseries are as influential as their originality in their performance and vigor. The evaluation of these traits, including the Dickson quality index (DQI) is considered an efficient method for considering the vigor of various kinds of seedlings, including fruit and forest seedlings. The magnitude of this index for seedlings is a function of the amount and the distribution of dry mass, height, and diameter. Therefore, it is a destructive and time-consuming method for predicting seedling quality in nurseries. Consequently, in order to rank the morphological traits that determine the quality of apricot seedlings, this project was conducted to evaluate the correlation relations between such traits of apricot seedlings of the most important commercial varieties produced in different regions of Iran, based on path analysis and multiple linear regression analysis.

Materials and methods: To evaluate the relationship between the morphological indicators in apricot seedlings, bare-root seedlings of 12 commercial cultivars with three replicates from 8 nurseries in four provinces were lifted during the transplanting seasons of 2020-2021. Sapling height, diameter above grafting line (DAGL), root length, number of roots and branches, shoot and root fresh and dry weights, height to diameter ratio, and DQI were evaluated, and simple correlations between them were estimated. The correlation coefficients were broken down into direct and indirect effects through path analysis, with DQI as the dependent variable.

Results: The indices representing apricot seedling vigor, including DQI and some of its components containing DAGL, total dry mass, height to diameter ratio and shoot to root dry mass ratio were a function of the accumulated growth degree-days (AGDD) in different regions. So that by increasing AGDD from 2700 to about 4500 degree, the average DQI, DAGL and total dry mass were increased and height to diameter ratio was decreased. The shoot to root dry weight ratio of seedlings was also decreased in nurseries located in regions with more than 3400 growth degree days. Among the traits which can be evaluated at the nursery site through non-destructive methods, DAGL had a higher correlation with vigor and the other morphological traits, leading to being considered the most important index in the qualitative evaluation of apricot seedlings, followed by shoot and root dry weights. Although later can be evaluated by destructive methods, they had the highest correlations with seedling vigor. The shoot number, height, sturdiness quotient had the weakest correlations with vigor and other morphological traits.

Conclusion: DAGL is considered the most efficient index in the quality assessment of the apricot seedlings due to having the highest correlation with the DQI and other morphological traits.