Identification and characterization of new resistant accessions to Fusarium oxysporum f.sp. pisi within a Pisum spp. germplasm collection

Abstract

Fusarium oxysporum f. sp. pisi (Fop) is an important pathogen of field pea (Pisum sativum). At present four races of Fop have been described, races 1, 2, 5 and 6. Among them, Races 1 and 2 occur worldwide. The constant evolution of the pathogen drives the necessity to broaden the genetic basis of resistance to Fop. To achieve this, it is important to have a large germplasm collection available and an accurate and efficient method for disease assessment. In this study we searched for new sources of resistance to Fop races 1 and 2 in a Pisum spp. germplam collection. Different methods of disease assessment coupling disease incidence, disease rating over time and its related area under the disease progression curve (AUDPC) were assessed to accurately evaluate Fusarium wilt disease in a controlled environment. The results of this screening revealed large variability in the response of the different accessions to Fop race 2 ranging from resistance to susceptible, indicating the quantitative nature of the resistance to Fop race 2 in this Pisum spp. collection. On the other hand, the response to Fop race 1 revealed a qualitative distribution, confirming the monogenic resistance of our genotypes to Fop race 1. Two independent repetitions of the inoculation experiments indicated that the scoring method was robust and reproducible and confirmed the highly resistant phenotypes of nine accessions to both races of Fop. The incorporation of these sources of resistance to breeding programmes will contribute to improved Fop resistance in pea cultivars. The characterization of resistance mechanisms acting within selected resistant accessions by histological methods indicated that, in all resistant characterized accessions, the progression of the pathogen is blocked in the basal part of plant suggesting that the main resistance mechanisms act at the root and crown level.