Résumé:
Early blight is one of the most important diseases of tomato in eastern Algeria. Tomato samples exploration (leaves, stems and fruits) with symptoms of early blight, grown under
glass in Hamma Bouziane locality (Constantine), allowed obtaining a filamentous fungal
isolate (Alt 1). The morphological and molecular identification (DNA-ITS analysis) of this
isolate revealed that it is Alternaria alternata (HQ846574.1). Pathogenicity testing of
seedlings by isolate resulted in the challenge of the typical early blight disease with a severity
of ≥ 76%. Samples exploration from various environments in the Algerian Sahara (Biskra and
Tougourt) resulted in the obtaining of 45 microbial isolates capable of developing an effect on
early blight agent. The selection test showed that; E1B3, S5 (isolated from Biskra) and E2X1,
S1.1 (isolated from Tougourt) possess a considerable antifungal effect against A. alternata
(inhibition rates vary between 60% and 75%), however, the E1B3 isolate developed the best
effect. The morphological and molecular identification of the selected isolates by analysis of
the 16S DNA and the "gyrase-A" gene showed that the bacterial isolates; E1B3, S5, and S1.1,
are identified as Bacillus mojavensis (KC977492), Bacillus amyloliquefaciens (KC977493),
and Bacillus Subtilis (KP699114.1) respectively, whereas the bacterial isolate E2X1 is
identified as Providencia vermicola (KP059130.1). To the best of our knowledge, the
isolation of P. vermicola from the palmerais rhizospheric soil and the demonstration of its
antifungal potential are established for the first time in this work.
The in vivo tests that carried out in pots and field conditions on tomato showed different
effects according to the bacterial species, and B. mojavensis developed the best effect
considering the most studied parameters (disease severity, Seedling size, leaves number and
flowers number per seedling). The P. vermicola strain showed the greatest result on the
severity reduction of early blight disease, indicating that the present work is the first one
which revealed this effect. In contrast, B. mojavensis developed the best protective effect,
considering the majority of the parameters studied in vitro and in vivo. This impact is due to
the ability of this strain to produce antifungal substances in this case; the enzymes (lipase and
protease) and the three families of lipopeptides (iturin, surfactins, and fengycins). The
evaluation of the antagonistic effect developed by B. mojavenssvis versus A. alternata through
flow cytometer (FCM) showed a considerable decrease in the rate of A. Alternata living cells,
confirming the inhibitory effect of B. mojavensis against the pathogenic agent of early blight.
