Farming system effects on root rot pathogen complex and yield of faba bean (vicia faba) in Germany

Abstract

A survey across Germany was undertaken from 2016-2019 to evaluate effects of management system (organic vs conventional), pedo-climatic conditions and crop rotation history on faba bean root health status, diversity of major root rot pathogens and yield. Root rot incidence was generally low and there was no effect of the management system on the spectrum of pathogens isolated. Among the most common fungal species identified, frequencies of Fusarium redolens and Didymella pinodella were significantly higher in roots from organic fields compared with conventional and lower was observed for F. avenaceum, F. tricinctum and F. culmorum. Faba bean roots were colonized at similar rates by F. equiseti and the members of the F. oxysporum (FOSC) and F. solani (FSSC) species complexes in both management systems. Almost no legumes had been grown in the 5-11 years preceding the conventional faba beans surveyed while legumes had almost always been present during this period in the organic fields. This difference in rotational histories between the farming systems led to apparent cropping systems effects on the isolation frequencies of several species. For example, D. pinodella was ubiquitous in organic fields with a high frequency of legumes in the rotations but much rarer and often absent in conventional fields. Pedo-climatic conditions, particularly cool conditions at sowing and plant emergence and/or during the vegetative season favored most of the most prevalent Fusarium species identified in this study. In organic systems, yields correlated negatively with D. pinodella and F. redolens frequencies whereas higher levels of F. tricintum in faba bean roots had a positive correlation with yield. In conventional systems, faba bean yields depended more on the total precipitation before sowing and during the main growing season but were also negatively correlated with the frequencies of FOSC and F. culmorum. Phylogenetic analysis based on the TEF1 alpha locus indicated that the FSSC isolates mainly belonged to the F. pisi lineage. In contrast, the FOSC isolates were placed in 9 different lineages, with a conspicuous dominance of F. libertatis that has until now not been associated with any leguminous host.

Didymella pinodella: An Important Pea Root Rot Pathogen in France to Watch Out For?

“…Furthermore, in their study only 1 out of 22 sampled fields had a legume crop (i.e., common beans) in rotation 5 years prior to green pea sampling. Recent research has indicated, however, that an increase in D. pinodella abundance in the roots of pea and faba bean (Vicia faba) is linked to a greater frequency of these two [11,15,53] and likely other legume crops in rotation. The continued monitoring of this potentially important pea pathogen under field conditions is recommended.…”

“…A subset of six pea and six wheat plants from each plot were used for fungal isolation and morphological identification following the methods described in Šišić et al [11]. Briefly, roots were surface sterilised for 10 s with 3% sodium hypochlorite, rinsed in distilled water and placed on filter paper under a laminar flow hood to dry.…”

“…The crown was regarded as the point of seed attachment up to approximately 0.5 cm below the soil surface, and the transition zone included the next ca. 1.5 cm up towards the stem [11]. Plates were incubated for 2 weeks at 20 • C under 12 h cycles of blacklight blue fluorescent light and dark.…”

“…Among the most common shared pathogens are Rhizoctonia, Pythium, and Fusarium species, including F. avenaceum, F. culmorum, F. tricinctum, F. oxysporum, and F. graminearum [2,3,[6][7][8]. The populations of pathogens, i.e., the presence or absence and relative abundance of individual species, involved in the disease complex vary with geographical region and climatic conditions [6,7,[9][10][11][12][13]. In addition to generalist pathogens, there are several specialist pathogens, such as Aphanomyces euteiches in pea and other legumes [7,14] and Gaeumannomyces graminis var.…”

“…Previous reports have highlighted the aggressive nature of D. pinodella in pea [17,[21][22][23] and demonstrated its capacity to asymptomatically colonise wheat roots, resulting in biomass reduction [22]. This fungal pathogen causes diseases in various other legume crops, including lentils, chickpeas, and faba beans [11,24]; however, to date, D. pinodella has not been reported in France as a root rot pathogen, where it has mostly been implicated as a minor part of the pea-Ascochyta blight complex, which affects the leaves, stems, and pods [25].…”