Pea seed-borne mosaic virus in Field Pea: Widespread Infection, Genetic Diversity, and Resistance Gene Effectiveness

From 2013 to 2015, incidences of Pea seed-borne mosaic virus (PSbMV) infection were determined in semi-leafless field pea (Pisum sativum) crops and trial plots growing in the Mediterranean-type environment of southwest Australia. PSbMV was found at incidences of 2 to 51% in 9 of 13 crops, 1 to 100% in 20 of 24 cultivar plots, and 1 to 57% in 14 of 21 breeding line plots. Crops and plots of 'PBA Gunyah', 'Kaspa', and 'PBA Twilight' were frequently PSbMV infected but none of PSbMV resistance gene sbm1-carrying 'PBA Wharton' plants were infected. In 2015, 14 new PSbMV isolates obtained from these various sources were sequenced and their partial coat protein (CP) nucleotide sequences analyzed. Sequence identities and phylogenetic comparison with 39 other PSbMV partial CP nucleotide sequences from GenBank demonstrated that at least three PSbMV introductions have occurred to the region, one of which was previously unknown. When plants of 'Greenfeast' and PBA Gunyah pea (which both carry resistance gene sbm2) and PBA Wharton and 'Yarrum' (which carry sbm1) were inoculated with PSbMV pathotype P-2 isolate W1, resistance was overcome in a small proportion of plants of each cultivar, showing that resistance-breaking variants were likely to be present. An improved management effort by pea breeders, advisors, and growers is required to diminish infection of seed stocks, avoid sbm gene resistance being overcome in the field, and mitigate the impact of PSbMV on seed yield and quality. A similar management effort is likely to be needed in field pea production elsewhere in the world.