Publication Date
1993
Description
Phoma black stem disease, caused by Phoma medicaginis, is the most important fungal disease of annual Medicago spp. (medic) pastures in Western Australia. It is readily seed-borne and this provides an important inoculum source for spreading the disease into new sowings in areas free of leguminous crop residues. The disease produces dark brown to black lesions on cotyledons, leaves, petioles and stems and can cause leaf drop and petiole and stem collapse, Reductions in herbage production of up to 169!, and seed yield of up to 209!, have been recorded in grazed swards, while in ungrued swards, losses in herbage and seed yield of up to 32 and 53% respectively have been measured, Even mild disease can reduce regenerating stand density by 18% in the following season. Severe disease in ungrazed swards frequently stimulates production of the phyto-oestrogenic coumestan, coumestrol, to levels between 300 and 550 ppm In stems and/or pods, and levels in excess of 1000 ppm have been recorded for M. tomaIa cv. Swani. A high degree of resistance to phoma black stem has been identified In screening programmes, and lhe incorporation of this resistance in commercial varieties offers the only promising long-term control measure for this disease in annual medics.
Citation
Barbetti, M J., "Rhoma Black Stem Disease- A Threat to Susceptible Annual Medic Pastures" (2024). IGC Proceedings (1993-2023). 21.
https://uknowledge.uky.edu/igc/1993/session22/21
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Rhoma Black Stem Disease- A Threat to Susceptible Annual Medic Pastures
Phoma black stem disease, caused by Phoma medicaginis, is the most important fungal disease of annual Medicago spp. (medic) pastures in Western Australia. It is readily seed-borne and this provides an important inoculum source for spreading the disease into new sowings in areas free of leguminous crop residues. The disease produces dark brown to black lesions on cotyledons, leaves, petioles and stems and can cause leaf drop and petiole and stem collapse, Reductions in herbage production of up to 169!, and seed yield of up to 209!, have been recorded in grazed swards, while in ungrued swards, losses in herbage and seed yield of up to 32 and 53% respectively have been measured, Even mild disease can reduce regenerating stand density by 18% in the following season. Severe disease in ungrazed swards frequently stimulates production of the phyto-oestrogenic coumestan, coumestrol, to levels between 300 and 550 ppm In stems and/or pods, and levels in excess of 1000 ppm have been recorded for M. tomaIa cv. Swani. A high degree of resistance to phoma black stem has been identified In screening programmes, and lhe incorporation of this resistance in commercial varieties offers the only promising long-term control measure for this disease in annual medics.
