Effects of temperature and humidity on disease caused by Phoma medicaginis, resistance in some Medicago cultivars and the incidence of seed-borne inoculum

Abstract

The effects of temperature and humidity on the development of Phoma blackstem disease (caused by Phoma medicagrnis) on Medicago spp. were investigated. Disease was greatest at 21/16° (12-h photoperiod), followed by 18/13°C, and least at 15/10°. Extending the period of post-inoculation high humidity increased disease severity and the rate of symptom development. Although no Medicago species or cultivars tested were highly resistant, there were large differences among both different species and cultivars of the same species, with several showing moderate resistance. Results show there is potential for control of Phoma blackstem through breeding and/or selecting resistant cultivars. Phoma medicaginis was associated with all but 1 of the 16 seed lines tested and the incidence of seed-borne contamination ranged from 0 to 38%.