Reliable and relevant qualitative descriptors for evaluating complex architectural traits in olive progenies

Architectural characteristics play an important role in the agronomic performance of fruit tree genotypes. However quantifying such traits in large numbers of individuals represents an important challenge, and little is known regarding their diversity and inheritance. This study evaluates the occurrence, variability, relevance and robustness of visual descriptors, which we propose and test for assessing ten major plant architectural traits in a large number of young olive seedlings and their parents. Our results revealed high phenotypic plant architecture diversity in the studied 825 seedlings from directed crosses, as well as significant parent genotype influence. From ten initially proposed traits, five ('Main vertical axis', 'Preferential distribution of lateral shoots', 'Dominant length of lateral shoots', 'Branch orientation' and 'Branch bending') were found to have the most relevant descriptors for olive seedling architecture based on the high capacity to indicate diversity, strong influence of parent genotype, lack of correlation with each other, and demonstrated value for agronomical performance. All of the descriptors of these five most relevant traits were then combined to generate 105 plant phenotypes, eight of which predominated and showed a clear dependence on parental characteristics. Validity of the results obtained from visual evaluation was verified by their correspondence to quantitative measurements at different stages of analysis. The synthetic characterization of plant-form provides new insights regarding olive seedling description, variability, and parent genotype influence, and represents a significant advance for measuring complex plant architectural traits. © 2012 Elsevier B.V.