Anatomical and karyotypic comparison of induced tetraploid of Oryza sativa var Latisail with the allotetraploid halophytic wild rice Oryza coarctata

The allotetraploid wild rice, Oryza coarctata grows in sea water and is the only halophyte which sets rice-like grains. It is a unique genetic resource for introducing salt tolerance into elite rice cultivars of Oryza sativa. Hybridization between these two remains unsuccessful. Our aim was to induce tetraploidization in the traditional Latisail cultivar of rice and compare its anatomical features to O. coarctata. Colchicine was used on the apical shoot tips of germinating seeds to produce the induced autotetraploid of Oryza sativa. Detailed anatomical comparisons of the leaves, stems, roots and chromosomes of the diploid and induced tetraploid of the Latisail variant of O. sativa and wild O. coarctata were carried out. Chromosomes of the induced tetraploid of O. sativa were shorter than diploid O. sativa, but longer than the 48 chromosomes in O. coarctata. The anatomical features of the induced tetraploid, like the number and size of bundle sheath cells, vascular bundle sizes and cuticle sizes were closer to that of the perennial allotetraploid, O. coarctata. It had more than twice the number of bulliform cells compared to the diploid and the number was similar to those found in O. coarctata. Crosses between the induced tetraploid and O. coarctata produced fertile offspring resembling O. sativa with evidence of small introgressions from O. coarctata pollens. The induced tetraploid of the Latisail variant of O. sativa and its progeny with O. coarctata are valuable plant genetic resources and may help introduce the vigorous halophytic traits of O. coarctata into commercial rice.