Establishment and life history characteristics of the southern South American mistletoe Misodendrum punctulatum (Misodendraceae)

Abstract

Taking advantage of host annual ring formation and synchronic embedding of the mistletoe haustorial system within the host xylem, we analyzed age-dependent life history traits and establishment conditions of Misodendrum punctulatum (Misodendraceae) infecting two deciduous species of Nothofagus in northern Patagonia, Argentina. Absolute determination of infection ages was performed by examining the number of host tree rings traversed by deepest haustoria in slices/cross-sections of parasitized branches/main trunks. Concomitantly, the number of branching events and basal stem diameters were taken from emerging aerial parts of the mistletoes. Host rings preceding the infection were used to determine branch trunk ages during infection. Relationships between haustorial and aerial age indices indicate that: (1) branching events are good non-destructive estimators of mistletoe age while basal diameters were poor estimators of age, (2) early development of M. punctulatum includes a multiyear holotrophic incubation period before producing aerial shoots, (3) the incubation period span is site and/or specie dependent being longer (4-6 yr) on the subalpine Nothofagus pumilio, and shorter (2 yr) on the lower altitude shrub N. antarctica, (4) Mistletoes infecting subalpine trees of Nothofagus pumilio in the harsher sites grew slower and were longer-lived than mistletoes infecting lower altitude shrubs of N. antarctica. M. punctulatum infected only young host branches (< 4 yr) suggesting strong limitations of mechanically penetrating thicker bark. When M. punctulatum shoots were present on Nothofagus trunks, absolute aging of haustorial systems in cross-sections revealed non-vegetative infections when trees were saplings. Multiple discrete events of renewal of the endophytic system spanning each about 24 yr are probably related to the maintenance of appropriate connections with functional host xylem.