Inheritance of resistance to systemic symptom expression of Melon necrotic spot virus (MNSV) in Cucumis melo L. `Doublon

In melon (Cucumis melo L.) a resistance mechanism to Melon necrotic spot virus (MNSV) controlled by a single recessive gene called nsv has been reported. We found that following mechanical inoculation of the virus C. melo cv. `Doublonʹ shows only local reaction, but it does not develop any systemic symptom and the virus only can be recovered from the local lesions. This reaction could be considered as a new source of resistance to MNSV. In this work, the genetic control of this behaviour in the progenies from the cross `Doublonʹ × `ANC-42ʹ (a susceptible line) is studied. We report two complete dominant genes, which we propose to call Melon necrotic resistance 1 (Mnr1) and Melon necrotic resistance 2 (Mnr2), controlling this character. The genetic linkage between one of these genes and nsv in the populations derived from the cross between `Doublonʹ and `PMR-5ʹ (a resistant line) is also reported. The map distance between these two loci was estimated to be 19 cm.