Genetic and environmental influences on capsule retention following controlled pollination of Eucalyptus globules flowers

Abstract

Summary ‘One-stop’ controlled pollination (CP) and mass supplementary pollination (MSP) are now widely used for commercial production of genetically superior Eucalyptus globules seed. Abortion of pollinated capsules, however, remains a common problem, resulting in reduced yield and greater cost of seed. We studied capsule retention following pollination of 1 072 000 flowers over three commercial CP seasons at a grafted E. globules seed orchard. The aim of our study was to quantify genetic and orchard management effects on capsule retention. We also characterized trends in capsule abortion for 15 mo following pollination to determine associations with weather and orchard management events. Average capsule retention varied between 32% and 46% across the three seasons. Within seasons, capsule retention values for maternal clones varied by 48%. Maternal clone values were highly correlated between seasons (r = 0.83–0.95), suggesting that maternal clone effects can be reliably estimated from a single season. The effect of paternal clone was significant but smaller than the effect of maternal clone. Ramets with poorest health had an average of 17% lower capsule retention than those with the best health score. Ramets that had received an application of the growth hormone paclobutrazol within the previous 5 y had on average 13% lower capsule retention in two of the three seasons. Capsule retention was on average 0.6% lower for each year of ramet age. In two of the three seasons, capsule retention was 1. 7% lower for every 500 flowers pollinated on the tree. The rate of capsule loss from the time of pollination followed different trends in the two years that data were recorded. No maternal or paternal effect was found on the pattern or rate of capsule loss, suggesting overriding environmental effects. Orchard management activities such as irrigation and pruning had no discernible effect. We conclude that the cost of CP and MSP seed can be greatly reduced by careful selection of clones and by eliminating ramets of poor health. The negative association between paclobutrazol application and capsule retention needs to be balanced with the positive effect of paclobutrazol on flower production. Further research is required to understand the physiological bases for capsule abortion, although our results suggest that carbon limitation may be a significant factor.