Abstract
Leguminous cover crop and living mulch species show not only great potential for providing multiple beneficial services to agro-ecosystems, but may also present pathological risks for other crops in rotations through shared pathogens, especially those of the genus Fusarium. Disease severity on roots of subterranean clover, white clover, winter and summer vetch grown as cover crop and living mulch species across five European sites as well as the frequency, distribution and aggressiveness to pea of Fusarium spp. recovered from the roots were assessed in 2013 and 2014. Disease symptoms were very low at all sites. Nevertheless, out of 1480 asymptomatic roots, 670 isolates of 14 Fusarium spp. were recovered. The most frequently isolated species in both years from all hosts were F. oxysporum and F. avenaceum accounting for 69% of total isolation percentage. They were common at the Swiss, Italian and German sites, whereas at the Swedish site F. oxysporum dominated and F. avenaceum occurred only rarely. The agressiveness and effect on pea biomass were tested in greenhouse assays for 72 isolates of six Fusarium species. Isolates of F. avenaceum caused severe root rot symptoms with mean severity index (DI) of 82 and 74% mean biomass reduction compared to the non-inoculated control. Fusarium oxysporum and F. solani isolates were higly variable in agressiveness and their impact on pea biomass. DI varied between 15 and 50 and biomass changes relative to the non-inoculated control -40% to +10%. Isolates of F. tricinctum, F. acuminatum and F. equiseti were non to weakly agressive often enhancing pea biomass. This study shows that some of the major pea pathogens are characterized by high ecological plasticity and have the ability to endophytically colonize the hosts studied that thus may serve as inoculum reservoir for susceptible main legume grain crops such as pea.
Highlights
In the past 10 to 15 years, there has been a tendency in Europe to switch from cereal based cropping systems, with winter and summer fallow, to cropping systems which combine greater crop diversity with maximum soil cover [1,2]
Plant samples were collected in a W pattern across the field plots at each site, washed under running tap water and individual plants were evaluated for root rot disease severity using a 0–5 rating scale modified from Aldoud et al [29] and Flett et al [30] as follows: 0 = healthy, 1 = lateral root discoloration, 2 = less than 1/3 of tap root discolored, 3 = 1/3 to 2/3 of tap root discolored, 3.5 = tap root rotted away but new lateral roots are growing, 4 = more than 2/3 of tap root discolored and no new lateral roots are growing, 4.5 = tap root rotted away, 5 = plant dead
The lowest symptom severities were observed on both clover species with mean disease severity ratings of 0.7 and 0.5 for subterranean and white clover, respectively
Summary
In the past 10 to 15 years, there has been a tendency in Europe to switch from cereal based cropping systems, with winter and summer fallow, to cropping systems which combine greater crop diversity with maximum soil cover [1,2]. When planned properly in terms of adequate diversity and appropriate density, legume based species mixtures and crop rotations may contribute to mobilization and remineralization of nutrients [8], improved soil structure [9], increased water infiltration and prevention of soil erosion [10,11] as well as weed suppression [12]. Under European conditions these are mainly pea (Pisum sativum) and faba bean (Vicia faba) that are comonly grown in rotation with cereals [13,14]. Despite their agronomic value, legume production in Europe, in particular pea, has been declining mainly due to problems with soil-borne pathogens and weeds [15,16,17]
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