Resistance in annual Medicago species to Phoma medicaginis under controlled environment and field conditions

Abstract

Seven Medicago species, comprising 11 cultivars and 9 seed lines, were screened for resistance to Phoma black stem disease (caused by Phoma medicaginis) at 3 temperature regimes (day/night) of 15/10, 17.5/12.5 and 20/15¦C and at 3 plant ages under controlled environment conditions. The same cultivars and lines were screened in the field over 2 seasons. There were large differences among species, and between cultivars and lines of any 1 species, in the severity of Phoma black stem disease on plants 1,4 and 10 weeks of age and at the 3 temperature regimes under controlled environment conditions, and in field screenings. Under controlled environmental conditions the cultivar and line resistance rankings were influenced by plant age, in particular, and also by the temperature regime. Cultivar and line resistance to P. medicaginis on 10-week-old plants under controlled environment conditions was correlated with some field results but resistance to this disease on 1- and 4-week-old plants was not correlated with field data.