could be due to some mutation in the embryogenic callus
line used to make the somatic hybrids. Another somatic
hybrid of Hamlin ? Flying Dragon performed well initially
(Table 4), but had poor survival at some field locations,
precluding its further potential as a commercial
rootstock. As mentioned, the sour orange ? Rangpur
somatic hybrid performed very well in trials where it was
grown as rooted cuttings (Table 4), and it produces fruit
that are seedy. Unfortunately, it has been shown that the
seedlings are of zygotic origin and therefore cannot be used
for standard nursery propagation, which relies on nucellar
embryony to yield uniform rootstock seedlings. The evaluation
of additional somatic hybrid rootstocks has resulted
in the identification of several promising selections for tree
size control that do not exhibit the deficiencies mentioned
above, and some of these are described in Table 5. These
somatic hybrid rootstocks have yield efficiencies higher
than the standard industry dwarfing rootstock Flying Dragon
trifoliate orange, and produce adequate nucellar seed
for standard nursery propagation. Due to their parentage,
they are expected to have better soil adaptation than Flying
Dragon, which does not perform well on high pH, calcareous
soils. Following additional testing, we expect to
release some of these somatic hybrid rootstocks for commercial
use.