Fusarium oxysporum f. sp. pisi (Fop) is an important pathogen of field pea (Pisum sativum) 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. Here, a detailed evaluation method coupling disease incidence, disease rating over time and its related area under the disease progression curve (AUDPC) was established and used to screen a Pisum spp. germplasm collection against one isolate of Fop race 2. A large variation in the disease response of specific pea accessions ranging from highly resistant to susceptible was observed within the collection, indicating the quantitative expression of the resistance. The repetition of the inoculation experiments on a subset of 19 accessions, including two susceptible accessions, indicated that the scoring method was robust and reproducible and confirmed the highly resistant phenotypes of 11 accessions. To initiate the characterization of resistance mechanisms within these accessions, the external and internal stem symptoms were compared between these selected pea accessions, together with the extent of fungal colonization within plants. All these tests indicated that, in all resistant accessions, the resistance mechanisms efficiently stopped pathogen progression at the crown. Incorporation of these sources of resistance to breeding programmes will contribute to improved Fop resistance in pea cultivars.
3Fusarium oxysporum f. sp. pisi (Fop) is a pathogen of field pea inducing severe vascular wilt 4 worldwide. Plant resistance to race 1, 5 and 6, producing wilt symptoms, is conferred by a single 5 dominant gene, while resistance to race 2, which gives near-wilt symptoms, have been recently 6 showed to be quantitative. Among the virulence factors reported to play a role in the infection 7 process, toxin production is one of the best studied. Thus, five race 2 isolates have been investigated 8 for toxins production in vitro and their relation to isolates pathogenicity. All the isolates produced 9 different amounts of fusaric and 9,10-dehydrofusaric acids. The content of the two toxins has been 10 quantitated and correlated with the pathogenicity and aggressiveness of isolates on field pea.
Fusarium wilt, caused by several formae speciales of Fusarium oxysporum, is an important disease of most crop and pasture legumes, including field pea (Pisum sativum), chickpea (Cicer arietinum), lucerne (alfalfa, Medicago sativa) and barrel medic (M. truncatula). Medicago truncatula is an important pasture legume and a model legume species. Hence, it can be used to increase our knowledge of resistance mechanisms efficient to block F. oxysporum infection if its response to the disease is characterised. We evaluated the physiological and susceptibility responses to the disease of two contrasting M. truncatula genotypes, and the effect of several cultural conditions known to affect the disease incidence, such as plant age at infection time, growth substrate and the method of inoculation. Our results indicated that the A17 accession harbours a moderate level of resistance to the disease. We also showed that the method of inoculation strongly affected development of fusarium wilt disease in this model species, whereas it was not significantly altered by plant age or the inorganic growth substrate tested. In addition, we describe a rapid change in leaf temperature after infection, which can be used as an indirect parameter to confirm fungal infection at a very early stage of the interaction.
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