Interaction Triticum durum/aestivum, Fusarium spp. et Trichoderma spp.

Abstract

Wheat (Triticum spp.) is one of the most important cereals in the world. Unfortunately, the wheat plant is the target of several species of the genus Fusarium. This genus causes two serious diseases: crown rot (FCR) and head blight (FHB). In this work a survey was conducted to study the most important species associated with this disease in Algeria, then two research axes were approached to try to solve this problem. One hundred and seventeen samples were collected (2019), sixty-three from the crown and fifty-four from wheat grains in several regions of northeast Algeria. Fusarium spp. were identified to the species level by sequencing the internal transcribed spacer (ITS1) regions of the rDNA. Also their life traits (growth rate and sporulation rate) were measured. Pathogenicity tests of the isolates were performed by two methods in vitro (tube test) and in vivo (pot test).A highly pathogenic strain of Fusarium culmorum (FC11) was used in three tolerance/susceptibility trials to evaluate the varietal resistance of eight cultivars (cv) of durum wheat and nine of bread wheat widely marketed in Algeria, several phenotypic parameters were measured. The biocontrol potential of 15 Trichoderma isolates (T1 to T15), isolated from different rhizosphere soils and Algerian ecosystems, was evaluated against 4 strains of F. culmorum (FC11, FC2, FC4, and FC20), in order to identify a new indigenous strain with a high biocontrol potential against FCR and FHB. This potential was evaluated by in vitro tests (direct and indirect confrontation) and confirmed by in vivo tests. In addition, tests in the greenhouse and in the field were carried out in order to select a better bio-control treatment method by using these indigenous strains. A total of 34 isolates representing 10 Fusarium species were obtained. The results showed the existence of five Fusarium species isolated from the crowns; Fusarium culmorum (16), F. cerealis (3), F. acuminatum (2), F. graminearum (1) and F. oxysporum (1); and seven species isolated from grains; F. culmorum (3), F. incarnatum (3), F. graminearum (1), F. equiseti (1), F. asiaticum (1), F. fujikuroi (1) and F. brachygibbosum (1). F. culmorum strains were dominant and more aggressive, as well as F. graminearum and F. cerealis which were aggressive in the in vitro test.However, the rest of the species were saprophytic rather than aggressive. A significant correlation was recorded between growth rate and sporulation rate (r =0.35 P=0.012<0.05). Also a strong correlation was recorded between the tube test and the pot test (r =0.62, P=0.007<0.01), this result demonstrates the effectiveness of a simple in vitro test to predict the aggressiveness of F. culmorum on wheat FCR. The cv. Sétifis and Akhamokh showed the most interesting tolerance levels among the tested durum and bread wheat cultivars, respectively. In this study, we concluded that a simple, easy and stable in vitro petri dish test can be used to predict the varietal resistance of different wheat cultivars against initial seed infection by F. culmorum. The results of the in vitro Trichoderma biocontrol showed significant inhibition of mycelial growth of F. culmorum species compared to the control. Isolate T14 was selected for biocontrol in in vivo tests. Tube and pot experiments against F. culmorum (FC2) showed that T14 decreased the severity of FCR with 50 and 63.63% reduction, respectively. FHB infection was significantly reduced by T14 in all tested durum wheat cultivars. The antagonist T14 was molecularly characterized using translation elongation factor 1-alpha (TEF1-α) and ITS1. Results identified T14 as Trichoderma afroharzianum with accession numbers assigned by NCBI GenBank as MW171248 and MW159753. This study highlights that F. culmorum is the dominant species associated with FCR and FHB in Algeria. Moreover, this is the first report concerning the identification of F. incarnatum, F. fujikuroi, F. cerealis, F. asiaticum, F. oxysporum, F. acuminatum and F. brachygibbosum of wheat in Algeria. Also this study highlighted the complexity of resistance testing against FCR and FHB, and demonstrated the need to use as many resistance screening protocols as possible. Trichoderma afroharzianum, evaluated for the first time in Algeria as a biocontrol agent, is a promising biocontrol approach against Fusarium. In addition, the biocontrol treatment with coated seeds before sowing showed a higher efficacy among the tested treatment methods.