THE PROPORTION OF INDIVIDUAL LUCERNE PLANTS RESISTANT TO PHYTOPHTHORA-MEDICAGINIS AND COLLETOTRICHUM-TRIFOLII IN AUSTRALIAN CULTIVARS

Phytophthora root rot (Phytophthora medicaginis) and colletotrichum cr own rot (Colletotrichum trifoli) are the 2 most serious pathogens of l ucerne in eastern Australia. Work reported in this paper shows that in glasshouse tests of the 11 most commonly grown Australian lucerne cul tivars, the proportion of individual plants with resistance to both pa thogens ranges from 0 (Hunter River and Aurora) through to a maximum o f 19.8% (Sequel HR). Within 9 of the cultivars, the proportion of indi vidual plants resistant to the 2 pathogens was <7%. Since these 2 dise ases are known to cause serious losses in eastern Australia, the resul ts indicate further improvement in lucerne production can be obtained by increasing the proportion of individual plants in a cultivar resist ant to both pathogens. This would be best achieved by identifying domi nant sources of resistance and incorporating this into on-going lucern e breeding programs.