Cytokinin activity in southern pines inoculated with Cronartium quercuum f.sp. fusiforme

Abstract

Cytokinin activity in tissue extracts from southern pine seedlings susceptible, moderately resistant, and resistant to the fusiform rust fungus was determined six months after inoculation. Qualitative and quantitative differences in cytokinin activity were detected among all rust-reaction groups and between inoculated and uninoculated trees within each pine species. Cytokinin activity in slash pines was detected at relatively low levels in 2 of 10 Rf zones bioassayed. After inoculation, cytokinin activity increased significantly within these zones, as well as in additional zones where activity had not appeared before inoculation with the rust fungus. Extracts from uninoculated resistant tissues were positive for cytokinin activity in all 10 Rf zones, whereas in extracts from inoculated tissues, activity was not detected in 3 zones and was diminished in the remaining 7 zones. Fresh weights of cocklebur cotyledons incubated in extracts from inoculated susceptible and moderately resistant seedlings were significantly higher than those incubated in extracts from uninoculated controls. The reverse occurred in resistant tissues. Less growth occurred in cotyledons incubated in extracts from inoculated seedlings than uninoculated.