TBA Evolutionary Impacts of Plant Grafting

Assessment of the evolutionary significance of plant grafting involves two levels of considerations: Benefits for plant survival (a), and  potential role in the formation of new species (b).   

 (a) The plausible ecological benefits of root grafting have been discussed. Grafting also plays a critical role in the survival of thousands of man-selected plant genotypes which are only propagated by grafting and have not evolved in natural habitats.

(b) Addressing the significance of grafting as a potential evolutionary mechanism must take into account the ancient belief that grafting may give rise to new plant species. Some of the novel species records may be attributed to graft chimeras, which are not true hybrids, but are inheritable.

However, recent research has brought us much closer to real evolutionary impacts of grafting, mainly via research by Bock and his team (Germany). Exchange of plastid genome material between stock and scion cells has been demonstrated in interspecific graft junction zones; such changes can become heritable only via lateral shoot formation from the graft site.Subsequently it was shown that entire nuclear genomes are transferred between plant cells in the graft junction zone, leading to the formation of novel, alloploid plant cells. Plants recovered from these cells are real graft hybrids; a fertile, stable hybrid between herbaceous and woody Nicotiana species was thus obtained. Similar results have now been obtained with other plant species ( Unpubl. data). These findings raise the exciting option that natural grafting may have played an active evolutionary role in plant speciation. It is difficult to estimate the actual participation of this asexual path in plant evolution. Although seemingly dependent upon a rare sequence of events, Nature may have exploited this evolutionary niche as a survival bypass under extreme, catastroph selective pressure conditions.