In vitro micrografting and the histology of graft union formation of selected species of prickly pear cactus ( Opuntia spp.)

• Published in: Scientia horticulturae 2002-02, Vol.92 (3), p.317-327
• Main Authors: Estrada-Luna, A.A., López-Peralta, C., Cárdenas-Soriano, E.
• Format: Article
• Language: English
• Subjects: Cactus-pear; Graft union formation; Heterograft; Homograft; In vitro grafting; Micropropagation
• ISSN: 0304-4238; 1879-1018
• DOI: 10.1016/S0304-4238(01)00296-5

Horizontal and wedge grafts were utilized with micropropagated prickly pear cactus ( Opuntia spp.) to determine the best method for in vitro micrografts. By frequent sampling of the developmental stages of the micrografts we characterized the histological events during graft union formation. Five Opuntia species ( O. streptacantha Lemaire, O. robusta Wendland, O. cochinera Griffiths, O. leucotricha De Candolle, and O. ficus-indica Linné (Miller)) were used as rootstocks and combined with O. ficus-indica to produce homo- and heterografts. Total growth was recorded after 90 days of ex vitro culture to determine the effect of rootstock genotype on scion development. Our results indicate that the easiest and most successful method for micrografting prickly pear cactus was the horizontal graft. Within 28 days vascular connections occurred within the callus bridge between rootstocks and scions in all genetic combinations. Hence, the Opuntia species stock–scion combinations were compatible. Homografts (grafts between same species) grew significantly faster than the heterografts (grafts between different species) after 90 days of ex vitro transfer. Histological observations revealed five developmental stages of graft union formation: (1) development of a necrotic layer, (2) proliferation of callus bridge at the graft interface, (3) differentiation of new vascular cambium, (4) restoration of the new vascular tissue, and (5) restoration of the continuity of external epidermal tissue at the union zone. We conclude that the in vitro horizontal graft is a successful, easy and reliable method to graft micropropagated prickly pear cactus particularly since no contamination or tissue dehydration occurred and no special structures or adhesives were needed for successful graft union formation. This grafting technique has potential use in the commercial production of other cactus species.