Development of cassava periclinal chimera may boost production

Abstract

ABSTRACT. Plant periclinal chimeras are genotypic mosaics arranged concentrically. Trials to produce them to combine different species have been done, but pratical results have not been achieved. We report for the second time the development of a very productive interspecific periclinal chimera in cassava. It has very large edible roots up to 14 kg per plant at one year old compared to 2-3 kg in common varieties. The epidermal tissue formed was from Manihot esculenta cultivar UnB 032, and the subepidermal and internal tissue from the wild species, Manihot fortalezensis. We determined the origin of tissues by meiotic and mitotic chromosome counts, plant anatomy and morphology. Epidermal features displayed useful traits to deduce tissue origin: cell shape and size, trichome density and stomatal length. Chimera roots had a wholly tuberous and edible constitution with smaller starch granule size and similar distribution compared to cassava. Root size enlargement might have been due to an epigenetic effect. These results suggest a new line of improved crop based on the development of interspecific chimeras composed of different combinations of wild and cultivated species. It promises boosting cassava production through 820

Research Article Periclinal chimera technique: new plant breeding approach

“…UnB 031) and characterized in this study. The four chimeras obtained so far at UnB are, therefore, chimera 1 induced in 2012 from M. fortalezensis x M. esculenta UnB 201 (Nassar and Bonfim, 2013), chimera 3 induced in 2012 (M. fortalezensis x M. esculenta UnB 032) (Bomfim and Nassar, 2014), and two others (chimera 2 and chimera 4) induced in August 2013 characterized in this investigation. Graft combination 1 had a chimera induction efficiency of 2.1%; one chimera was produced from 48 grafts that are lower than that the 5% obtained by Nassar and Bomfim (2013) (2 chimeras of 40 grafts) using the cassava cultivar UnB 201 as the rootstock and M. fortalezensis as the scion with hormones applied on the graft junction.…”

“…These heterotic phenomena let us call it 'graft hybrid' effects that arise from epigenetic interactions between the two species that coexist together in the same plant, although the specific mechanism remains unknown. Epigenetic interactions that caused complex heritable traits such as plant height have also been reported by Bomfim and Nassar (2014). It was found out that exchange of RNA and DNA to adjacent cells in grafts occurs (Hirata et al, 1999(Hirata et al, , 2000Stegemann and Bock, 2009;Nassar and Bomfim, 2013).…”

“…This chimera manifested high parent heterosis not only in root yield but also in plant height. Chimera 3 was also superior in yield to one of its parents, with a 7-fold increase (Bomfim and Nassar, 2014). This chimera was later released as cassava variety UnB 703.…”

“…Two interspecific chimeras of cassava have recently been produced from grafts of the wild triploid cassava species, M. fortalezensis, on rootstocks of two cassava cultivars at Universidade de Brasília (UnB), Brazil. By using hormones, they gave 3-to 7-fold increase in tuber production relative to donor plants (Nassar and Bomfim, 2013;Bomfim and Nassar, 2014).…”

Research Article Cassava cultivars selected or developed from interspecific hybrids and periclinal chimeras

“…It is a compact shrub 2m high (Figure 9), with dichomous branches, a glabrous stem, membranaceous leaves, and cylindrical and conical roots, without a peduncle that have a reddish-yellow pulp and are very soft when cooked. UnB 703 Nassar, 2014). The epidermis is from fortalezensis cuttings.…”