Effects of transgenic rootstocks on growth and development of non-transgenic scion cultivars in apple

Abstract

Although cultivation of genetic modified (GM) annual crops has been steadily increasing in the recent 10 years, the commercial cultivation of GM fruit tree is still very limited and reports of field trials on GM fruit trees are rare. This is probably because development and evaluation of GM fruit trees require a long period of time due to long life cycles of trees. In this study, we report results from a field trial on three rolB transgenic dwarfing apple rootstocks of M26 and M9 together with non-transgenic controls grafted with five non-transgenic scion cultivars. We intended to investigate the effects of transgenic rootstock on non-transgenic scion cultivars under natural conditions as well as to evaluate the potential value of using the rolB gene to modify difficult-to-root rootstocks of fruit trees. The results showed that all rolB transgenic rootstocks significantly reduced vegetative growth including tree height regardless of scion cultivar, compared with the non-transgenic rootstocks. Flowering and fruiting were also decreased for cultivars grown on the transgenic rootstocks in most cases, but the fruit quality was not clearly affected by the transgenic rootstocks. Cutting experiment and RT-PCR analysis showed that the rolB gene was stably expressed under field conditions. PCR and RT-PCR analyses displayed that the rolB gene or its mRNA were not detectable in the scion cultivars, indicating no translocation of the transgene or its mRNA from rootstock to scion. Our results suggest that rolB modified rootstocks should be used in combination with vigorous scion cultivars in order to obtain sufficient vegetative growth and good yield. Alternatively, the rolB gene could be used to dwarf vigorous rootstocks of fruit trees or produce bonzai plants as it can significantly reduce the vegetative growth of plants.

Silencing of Agrobacterium tumefaciens oncogenes ipt and iaaM induces resistance to crown gall disease in plum but not in apricot

“…Fruit trees are generally propagated by grafting a scion cultivar onto a rootstock, which is of significant value for fruit production because it can control tree vigour, producing higher yields and enhancing tolerance to biotic and abiotic stresses . The potential use of genetically engineered rootstocks that can be grafted with standard non‐transgenic commercial scion cultivars to produce non‐genetically modified fruits may be a more efficient strategy, addressing the public's concerns regarding genetically modified fruits …”

MdWRKY9 overexpression confers intensive dwarfing in the M26 rootstock of apple by directly inhibiting brassinosteroid synthetase MdDWF4 expression

“…Modern apple orchards cultivate grafted trees, in which apple scions are grafted onto dwarfing rootstock; this enables highdensity planting, a reduced juvenile period, better reproductive growth, increased flower density, higher yield per hectare and efficient mechanized management (Bulley et al, 2005;Smolka et al, 2010). The dwarfing rootstocks effectively limit tree size and influence the growth and development of the grafted cultivars (Tworkoski & Miller, 2007).…”

Molecular basis of angiosperm tree architecture

“…As a result of the relatively small number of naturally dwarfing rootstocks available and their variable effectiveness, transgenic dwarfing rootstocks are being developed. One example is the dwarfing ability of apple rootstock over-expressing the Rooting Locus B (RolB) gene from Agrobacterium rhizogenes that stimulates rooting (Smolka et al, 2010).…”