ABSTRACT
Evaluation of the Resistance of Transgenic C5 Plum (Prunus domestica L.) against Four Chilean Plum Pox Viurs Isolates through Micro-Grafting

Wendy Wong1, Paola Barba2, Catalina Álvarez2, Álvaro Castro3, Manuel Acuña2, Pablo Zamora3, Marlene Rosales2, Paola Dell´Orto4, Michael R. Moynihan4, Ralph Scorza5, and Humberto Prieto2*
 

The transgenic plum (Prunus domestica L.) C5, in which the coat protein (CP) gene of the Plum pox virus (PPV) is inserted, represents a unique example of the use of genetic engineering for fruit crop improvement in Prunus spp. Field trials in Poland, Romania, and Spain have demonstrated resistance of C5 to several D and M strain PPV isolates. In Chile, the quarantine regulations for PPV and for genetically modified (GM) plants require that the testing of C5 for resistance to Chilean PPV isolates be done under controlled isolated conditions. To carry out these tests C5 shoots were multiplied in vitro and micro-grafted onto four Adesoto101 (Prunus insititia L.) rootstock populations that had been previously infected each with one of four Chilean PPV-Ds. Tests were carried out under controlled conditions in a biosafety greenhouse. Symptoms appearance, virus detection, and viral mRNA levels for the cylindrical inclusion (CI) and CP genes were determined during three consecutive growing seasons. Complete resistance to all PPV isolates was demonstrated during the first 2 yr in all of the C5 plants. In the third season, four of 10 C5 plants showed mild symptoms on leaves close to the graft union and low but detectable CI mRNA levels in the C5 scions. These results support the effectiveness of using of micro-grafting on P. insititia for PPV resistance studies, especially in the limited space of a quarantine facility; whereas resistance levels in C5 after 3 yr indicate the importance of long term and field scale evaluations.

Keywords: C5, Plum pox virus, Chilean isolates, Prunus domestica, Prunus insititia, micro-grafting.
1Universidad de Chile, Facultad de Ciencias Agronómicas, PO Box 1004, Santiago, Chile.
2Instituto de Investigaciones Agropecuarias INIA, PO Box 549, Santiago, Chile. *Corresponding author (hprieto@inia.cl). 3Universidad de Santiago de Chile, Facultad de Química y Biología, PO Box 10233, Santiago, Chile.
4Fundación Chile, PO Box 6671199, Santiago, Chile. 5USDA Agricultural Research Service (ARS), Appalachian Fruit Research Station, Kearneysville, PO Box 45, West Virginia, USA.