Red rice

• Binomial: Oryza longistaminata• Also called longstamen or wild

African rice• Family Poaceae, order

Cyperales• Close relative of the cultured

Asian rice, Oryza sativa• Natural habitat: tropical Africa• Noxious weed in the US (see

USDA web site for the list of states), occurrence not reported

Upper image: O. longistaminata plants grown for the rhizome project, below: occurrence of red rice in Africa (source: www.gene.affrc.go.jp)

Phylogeny of rice• Plants of the genus Oryza exhibit dihaploidy• There are also species with tetraploid genome • The different genomes are identified by cytogenetic, DNA hybridization and

sequencing data• Red rice possesses an AA genome, just as cultivated rice does• Phylogeny of the A-genome complex studied, but results are often contradictory

[discussion in 1]• O. longistaminata has distinct morphological features, e.g. very long, pointed ligule,

facilitating botanical identification • Analysis of chloroplast, mitochondrial and nuclear DNA sequences indicates closer

relationship between the African species (O. longistaminata, O. barthii and cultivated African rice O. glaberrima) in comparison to Asian species like O. sativa [2]. The 3 African species are also likely to be close relatives of O. glumaepatula, a Central and South American species [3]. At the same time, RAPD and SSR analyses imply red rice to differ significantly from all other AA-genome species [4]

• Besides, the sequence of twin microsatellites RM20A and RM20B differs in red rice from all other species in the AA-genome complex [5]. Putatively, this is the ancestral form

• There are four rhizomatous species in the genus Oryza [6] • Red rice is the only perennial, i.e. rhizomatous species with AA

genome

[1] Zhu & Ge 2005 [2] Duan et al. 2007 [3] Ge et al. 1999 [4] Ren et al. 2003 [5] Akagi et al. 1998 [6] Hu et al. 2003

Desirable features - perenniality• O. longistaminata is partly self-incompatible and

allogamous [1]• Generating a perennial form of cultivated rice would

reduce soil erosion, a common problem of regional concern in Southeast Asia

• The first attempt to generate a perennial introgression line was in part successful [2]

• Origins of rhizomatousness studied [3]• Two complementary-dominant genes, designated Rhz2

and Rhz3 • These genes influence multiple features of rhizomes• They are closely related to the corresponding QTLs in

Sorghum halepense

[1] Ghesquiere 1985 [2] Sacks et al. 2006 [3] Hu et al. 2003

Desirable features - resistance

• Xanthomonas oryzae (pv. oryzae) blight: O. longistaminata Xa21gene encoding a putative receptor-like kinase [1] has been successfully transformed into O. sativa, leading to the breeding of resistant progeny [2,3].

• Physical mapping by in-situ hybridization revealed the Xa21 locus to be on chromosome 11 [4].

• The durability of resistance has to be studied yet. Molecular markers have been developed to enable selection [5,6]

• The grain yields of homozygous transgenic strain were comparable to those of non-transgenic control, as demonstrated by field tests [7] Bacterial blight infected rice leaves (above) and

field-screening for resistant progeny. Images from the International Rice Research Institute web site (www.knowledgebase.irri.org)

[1] Song et al. 1995 [2] Khush et al. 1990 [3] Wang et al. 1996 [4] Ronald 1997 and citations therein [5] Kameswara Rao et al. 2002 [6] Williams et al. 1996 [7] Tu et al. 2000

Desirable features - resistance

• Red rice accessions resistant to root-knot nematode Meloidogyne graminicola have been identified (also among O. glaberrima) [1]

• Red rice is less sensible to drought than several other species (O. latifolia and O. rufipogon). This is not only due to its rhizome system, but to superior membrane stability, stomatal conductance and leaf elongation behavior under water deficit [2]

• Generally, introgression of useful genes from wild rice species into O. sativa is a popular and much worked-on research area. The genetic pool is not restricted to species with AA-genome [3,4]

[1] Soriano et al. 1999 [2] Liu et al. 2004 [3] Brar & Khush 1997 [4] Ashikari & Matsuoka 2006

In-vitro culture

• Protocol for callus initiation and regeneration [1]

• Cultivated rice can be both transformed using Agrobacteria [2] or biolistics [3] and regenerated [2,4]

• The purpose of in-vitro experiments is gene transfer via somatic hybridization and protoplast fusion. It helps to overcome the cross-breeding boundaries and to obtain improved strains of cultivated rice O. longistaminata callus and

plantlets regenerated after two subcultures on differentiation medium, bar = 1 mm [1]

[1] Boissot et al. 1990 [2] Hiei et al. 1994 [3] Fauquet et al. 1996 [4] Jubair et al. 2008

Human use• O. longistaminata is mainly made use of in Africa,

where it is indigenous [1]– Red rice grain is sometimes sold at local markets in

Africa. However, the seed yields from this species are rather low

– It has been used as famine food in Ethiopia and Sudan

– Dense stands serve well for cattle grazing– Straw is used for thatching

[1] M. Brink, G. Belay “Cereals and Pulses” PROTA, 2006