Fusarium foot rot: Monitoring and characterization of soil-rhizosphere populations in durum wheat

Abstract

A complex of Fusarium species is commonly isolated from soil rhizosphere of durum wheat plants affected by Fusarium foot rot (FFR), but information on their distribution and relative abundance as well as their role in the pathogenic process has yet to be clarified. To this end, two aspects were analyzed in our investigation. On the one hand we examined Fusarium populations from soil rhizosphere of affected durum wheat plants harvested at tillering growth phase (29 BBCH - scale) in 8 cereal farms (sites A-H) in the most representative areas of durum wheat production in Sicily. Regarding this first aspect, 17 Fusarium species were identified based on their morphological characteristics and molecular traits. F. acuminatum, F. compactum, F. equiseti, F. oxysporum, and F. solani were isolated from soil rhizosphere samples of all sites and their inoculum densities averaged 483, 864, 649, 1629 and 1543 colony forming units per gram of soil (CFU/g-1), respectively. F. culmorum (1158 CFUs) was found in 7 of the 8 sites. The other Fusarium species were isolated from 5 (F. lateritium and F. semitectumi), 4 (F. merismoides), 2 (F. avenaceum and F. sporotrichioides) and 1 (F. crookwellense, F. dimerum, F. graminearum, F. verticillioides, F. subglutinans and Microdochium nivale) of the 8 cereal sites respectively. On the other hand, 30 pure cultures of the most frequent Fusarium spp. (Fusarium acuminatum, F. compactum, F. equiseti and F. culmorum), chosen to represent all four species of each of the sites, were assayed in vitro to evaluate their effect on seed germination and seedling development. In comparison to the (uninoculated) control, F. acuminatum significantly decreased seed germination, shoot height, root length and vegetative vigour by 80.2, 79.6, 90.8 and 97.4 % respectively. F. culmorum showed the greatest inhibition of all vegetative parameters. F. compactum and F. equiseti resulted in increased, albeit not statistically significant, seed germination. Moreover, F. compactum significantly increased root length (+ 39.0 %) and vegetative vigour (+ 17.0 %), while F. equiseti improved both coleoptile growth (+ 34.0 %) and vegetative vigour (+ 18.0 %). These results corroborate the pathogenicity of F. acuminatum and F. culmorum identified in this study, in terms of reduced seed germination and seedling growth of durum wheat. On the contrary, F. compactum and F. equiseti seem uninfluential on seed germination. In particular, F. equiseti increased shoot growth while both species (F. compactum and F. equiseti) increased root development and vegetative vigour, prompting speculation as to actual role of these two species in the soil rhizosphere of durum wheat plants affected by FFR complex.