Investigations of ophiognomonia clavigignenti-juglandacearum: inhibition by butternut bark extracts and viability of conidia

Abstract

Inhibition of Oc-j by Juglans species bark extracts. A reliable disease screening technique is needed for detecting Juglans cinerea with resistance to butternut canker. Both naphthoquinones and bark extracts of Juglans species inhibited germination of Oc-j conidia, depending on the selections of butternut. Juglone and plumbagin were found. Juglone levels correlated with the bark extract bioassay in some months. Influence of temperature and humidity on the viability of Oc-j conidia. Dispersal of Oc-j by vectors necessitates conidia to tolerate drying. Temperature and humidity influenced conidia germination and survival of air dried conidia. Conidia germinated on water agar over 4- 32oC and were viable after brief periods at 36oC when returned to lower temperatures. Viability of air dried conidia on nylon membranes varied from one day at 28oC, 90% RH to 16 days at 20oC, 80% RH. Conidia held at 100% RH remained viable for 168 days at all temperatures tested.