Survival, transmission and control of Phoma koolunga in field pea seed and reaction of field pea genotypes to the pathogen

Abstract

Little is known about the epidemiology of Phoma koolunga, a component of the ascochyta blight complex of field pea in southern Australia. The aims of this research were to investigate seed infection, efficacy of fungicides as seed dressings and the reaction of current field pea genotypes to this fungus. The frequency of isolation of P. koolunga from individual seed samples from South Australia, Victoria and Western Australia ranged from 0 to 6 %. Disease was transmitted to 98 % of seedlings that emerged from artificially inoculated seeds (AIS) in growth room conditions. The necrotic index on seedlings that emerged from AIS at 8 °C was greater than that for seedlings at 12, 16 and 20 °C. P-Pickel T® and Jockey Stayer® were the most effective fungicides for reducing disease incidence and severity on seedlings emerged from AIS sown in soil and on germination paper, respectively. The response of 12 field pea genotypes to one isolate of P. koolunga was assessed by spraying plants with pycnidiospore suspension in controlled conditions and examining symptoms from 3 to 21 days post-inoculation (dpi). Genotypes Sturt, Morgan and Parafield showed more severe disease on the lowest three leaves than the other genotypes at 21 dpi. In another experiment, four genotypes of short, semi-leafless type field peas were inoculated with three isolates of P. koolunga which differed in virulence and assessed as described above. Kaspa showed significantly less disease than Morgan or WAPEA2211 at 21 dpi when inoculated with two of the three isolates tested. Isolates of P. koolunga differed in aggressiveness based on % leaf area diseased until 14 dpi, but differences were not significant at 21 dpi.