Seed and seedling nursery characteristics for 10 USDA citrus rootstocks

Authors: BISI, RAYANE - UNIVERSITY OF FLORIDA; ALBRECHT, UTE - UNIVERSITY OF FLORIDA; Bowman, Kim

Submitted to: HortScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/17/2019
Publication Date: 3/5/2020
Citation: Bisi, R., Albrecht, U., Bowman, K.D. 2020. Seed and seedling nursery characteristics for 10 USDA citrus rootstocks. HortScience. 55(4):528-532. https://doi.org/10.21273/HORTSCI14598-19.
DOI: https://doi.org/10.21273/HORTSCI14598-19

Interpretive Summary: Most citrus trees are grown as two part trees, with the fruiting variety grafted on top of a rootstock variety that makes the lower stem and roots of the tree. This provides the opportunity to use a rootstock variety with outstanding traits specifically relating to disease resistance and root strength. Traditionally, citrus rootstocks have been selected to allow for uniform propagation by seeds, as this allows the simplest and most economical propagation. Modern day citrus nursery operations can employ other methods for propagating citrus rootstocks, but it is still often preferred to propagate by seed when practical. Six new disease-resistant hybrid citrus rootstocks were released by USDA in 2014-15 based on stem cutting propagation and before seed propagation could be evaluated. We report in this publication the key seed and seedling characteristics of these six rootstocks, along with four others that were described previously, to guide citrus nurseries and growers in decisions about methods to employ and practicality of seed propagation.

Technical Abstract: The huanglongbing-tolerant rootstocks US-1279, US-1281, US-1282, US-1283, US-1284, and US-1516 were released from the USDA citrus breeding program in 2014-15, to provide increased productivity in disease-endemic areas. Performance of these rootstocks was outstanding from trees propagated by cuttings, but no information was available about nucellar seed propagation, which is the preferred method for commercial propagation of citrus rootstocks. In this study, we examined the suitability of seed propagation for these six new rootstocks, along with standard rootstocks. Among the new rootstocks, seed propagation was found to be suitable for US-1283, US-1284, and US-1516, as they produced plentiful seed that regenerated genetically uniform healthy seedlings. Seed propagation was found not suitable for US-1279, US-1281, and US-1282, despite good seed production, because of the high degree of genetic and morphological variability among seedlings. The use of simple sequence repeat markers (SSR) was described as an effective method for differentiating the rootstock clones and identifying true-to-type or off-type seedlings.