LIBRO-CONGRESO-CITRUS

S01
Aurantioideae genera has historically been associated with the use of the related taxa as rootstocks for Citrus
spp. However, the use of Citrus spp as rootstocks for related taxa can be useful in maintaining germplasm
accessions, in propagating specimen trees or specific commercial taxa, and biological indexing in a sanitation
program. One of the largest collections of taxa related to Citrus is maintained by the University of California
and the United States Department of Agriculture in Riverside, California. This paper reviews historical
observations made in Riverside of graft compatibility between Aurantioideae genera and updates them with
current observations. Specific combinations have been observed to be incompatible whereas others have
shown either short- or long-term compatibility and survival.
S01P04
Fertility relationships among Citrus and its relatives in the subfamily Aurantioideae
Siebert T., Ellstrand N., and Kahn T.
University of California, Riverside, Botany and Plant Science, United States. tsiebert@ucr.edu
Data on fertility relationships between crop species and their relatives is of immediate practical value because
they can be used to predict the ease of introgression of valuable traits into cultivars. Likewise, those data
are of evolutionary significance as evidence of phylogenetic relationships. Here, we review what is known
regarding the relative cross-compatibility of various Citrus taxa with each other as well as with members
of other genera in the Rutaceae subfamily Aurantioideae. For the most part these data were collected as
collateral information from breeding studies and therefore are uneven within the group. We compare how
the extant fertility relationship data support the various molecular phylogenies of the Aurantioideae. We
conclude with the identification of significant gaps in the data that could be filled with a series of strategic and
feasible crosses for the purposes of better defining the systematic relationships of the group as well as guiding
future citrus improvement by breeding.
S01P05
Characterization of seed and embryo abortion during fruit development in several citrus cultivars
pollinated by ‘Nishiuchi Konatsu’ (Citrus tamurana) and preliminary trial of embryo rescue of
aborting embryos
Honsho C. 1 , Tsuruta K. 1 , Ryuto K. 1 , Sakata A. 1 , Kuroki S. 2 , Nishiwaki A. 2 , and Tetsumura T. 1
1 University of Miyazaki, Faculty of Agriculture, Japan; and 2 University of Miyazaki, Field Science Center, Japan.
chitose@cc.miyazaki-u.ac.jp
‘Hyuganatsu’ (HY; Citrus tamurana) is a late-season citrus grown in several specific prefectures in Japan.
Although it is self-incompatible, its bud mutation, ‘Nishiuchi Konatsu’ (NK), is self-compatible, and interestingly
most of the seeds in harvested fruits are aborted. In our previous study we revealed that NK produces a
proportion of unreduced 2N pollen grains, resulting in unusual seed development. In this study, we have
focused on seed and embryo development when pollen from NK was used to pollinate HY, NK, and ‘Hassaku’
(HS; Citrus hassaku), which is compatible with both HY and NK. When NK pollen was used to pollinate HY or
NK, most of the seeds aborted, whereas all seeds developed successfully from crossing using HS pollen. The
seeds from NK-pollinated fruits were found to be significantly smaller than those from HS-pollinated fruits 10-
12 weeks after pollination during periodic samplings of fruits, suggesting that the seed abortion phenotype
is expressed during this time period. Embryo development was observed using differential interference
contrast or stereo microscopy. Embryos that had formed from NK self-pollination had aborted at 10 weeks
after pollination, whereas control embryos had reached the globular or heart-shaped stage. In the cross HS
× NK, both normal and aborted seeds were present in the resulting fruit. Embryo development was found to
cease at 12 weeks after pollination, and at 14 weeks after pollination, normal and aborted seeds were easily
distinguishable. In addition to the characterization of seed development, preliminary attempts at embryo
rescue have been made to recover triploid seedlings. After making the crosses HY × NK or NK × NK, aborting
embryos were placed on MT media supplemented with 500 mg/L malt extract, 50 g/L sucrose, and 5 mM
GA3. As a result, several triploid plantlets confirmed by flow cytometry were recovered from both pollination
combinations, although the success rate was not high.
30 - VALENCIA CONFERENCE CENTER, 18th-23rd NOVEMBER 2012