Getting To The Root Of The Weevil Problem
August 1, 2007 
A primary research objective of the Citrus Research and Education Center variety improvement program is the development of improved rootstocks than can handle the P/D complex. The solution for rootstock improvement programs is to package resistance genes against Phytophthora into appropriate hybrids that also exhibit wide soil adaptation.
Citrus rootstock improvement is a daunting task because a large number of traits must be combined in any successful new rootstock, including resistance/tolerance to blight, citrus tristeza virus, Phytophthora spp., nematodes, Diaprepes, salinity, adaptation to challenging soils, tree size control, nucellar embryony for seed propagation, good nursery performance, the ability to consistently produce high yields of quality fruit, and now tolerance of greening.
Recent research has provided data aimed at developing complex rootstock hybrids that have the capacity to tolerate mechanical damage caused by weevil feeding and recovery by exhibiting vigorous root growth in challenging soils inoculated with Phytophthora nicotianae and P. palmivora. Data from seven screening experiments has been evaluated, along with progress from screening experiments.
Promising Selections
Test material, featuring a high level of genetic diversity, has been selected from tetrazygs obtained from 2000-2004 crosses of selected somatic hybrids, open-pollinated seedlings, somatic hybrids, and diploid hybrids. Weevil larvae fed on all candidate rootstocks; however, it was evident that the average amount of mechanical damage from feeding per candidate rootstock was quite variable.
Seed trees of some of the hybrids showing promise are demonstrating that they are amenable to traditional propagation. Trees on these rootstocks grafted with sweet orange scion are growing off well in field trials, as good as or better than control trees.
The hybrids performing well in these studies should be tolerant to the P/D complex, but they must still be propagated for replicated field trials and evaluated in a real-world setting to determine their long-term horticultural performance. Simultaneously, seed trees are being grown in the field to determine if these selections are amen-able to traditional nucellar seed propagation. This approach is expected to greatly reduce the time required for rootstock improvement.
Encouraging results were obtained from continued development of selections, as several are amenable to traditional propagation, while the initial field performance of grafted trees is quite good. Continued research is expected to identify superior rootstocks for use against the complex.
For More Information
The results of the studies performed by Grosser and his research team have been highlighted by both the Citrus Research and Education Center and the Florida State Horticultural Society. For more information on this and similar research trials, go to www.crec.ifas.ufl.edu and click on “Research” or “Publications.”
Subscribe Today For
