In search of target gene(s) to quantify pea pathogenic Nectria haematococca in agricultural soils

Footrot disease due to N. haematococca (anamorph Fusarium solani f. sp. pisi) is a globally, economically important disease of peas. The disease has been linked to the presence of six pea pathogenicity (PEP) genes (PDA1, PEP1, PEP2, PEP3, PEP4 and PEP5) inherent in pathogenic forms of the causal fungus N. haematococca MPIV. The disease is prevented only through avoidance of fields with high disease potential. Identifying agricultural fields with a high disease potential prior to pea cultivation has been paramount in the implementation of preventive measures. Although molecular techniques have been successfully used to quantify pathogenic strains of N. haematococca in agricultural soils, targeting all six pathogenicity genes in these assays would not be cost effective. This study therefore attempts to review the functions and roles of the different genes linked with pea pathogenicity with the aim of identifying gene(s) that would serve as a logical target in a quantitative molecular assay. Findings suggest that, whilst the PDA gene may be targeted in a preliminary diagnostic measure, a conclusive assay, targeting the PEP3 gene may be required to affirm pea footrot disease potential of agricultural fields. Agricultural fields with the PEP3 gene copy numbers of up to 100 per g soil prior to cultivation may be deemed unsafe for peas.