Annual Report 2006

digital images of stained cross-sections using
digital microscope and measured root area,
stele area, area and number of xylem vessel.
Association between alleles at 147 RFLP loci
and phenotypic data obtained from 61 varieties
(47 of Indica type and 14 of Japonica type) were
calculated. We discovered one region on
chromosome 4 associated with the stele/root
area ratio.
Microscopic observation showed the
similarity of frequency distribution for root area
and number of xylem vessels between Indica
type and Japonica type cultivars. Japonica rice
was more variable than Indica rice in root traits
such as areas of stele and xylem vessels, xylem
vessel area/no. ratio, and stele/root area ratio,
Fig. 1
Relationship between root area and stele area in 61
rice cultivars (Uga 2005)
and 14 Japonica varieties were divided into two
groups corresponding to small (n=9) and large
(n=5) stele/root area ratios (Fig. 1). We analyzed
genotype frequency at RFLP loci between two
groups divided based on variation in stele/root
area ratio and found one marker (orange box)
associated with stele/root area ratio in long
arm of chromosome 4 (Fig. 2). This region is
suggested to harbor a gene or genes
responsible for size factors of root organs.
Development of Cryopreservation
Protocol for Long-term Storage
of Plant Germplasm
Cryopreservation is becoming a very
important tool for long-term storage of plant
germplasm, especially vegetatively propagated
crops and recalcitrant seed species, with a
minimum of space and maintenance.
Cryopreservation should be considered as a
backup to the collections to insure against loss.
In this, we mean the priority of collections to be
cryopreserved should be given to the at risk
crops that have an increased chance of being
lost from a collection. In our genebank, the
germplasm collection at Tsukuba, which
include about 1,400 accessions with several
species, are processed for long-term preservation.
To date, about 750 accessions of them have
been cryopreserved in liquid nitrogen tanks
Fig. 2
Comparison of graphical genotypes between the two different groups on stele/root area ratios (Uga 2005)
Light blue: Nipponbare (Japonica) type allele;
Pink: Kasalath (Indica) type allele;
White: other type allele;
and Yellow: heterozygous allele.
In each chromosome, each line from left to right indicates genotype of each variety, and each column from top to
bottom indicates a genotype of RFLP markers from a short to a long arm.