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- Author or Editor: S. Naeimi x
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Fusarium wilt of tomato is one of the most prevalent and economically important diseases of tomato worldwide especially in tropical regions. The aims of the present study were to isolate and characterize Bacillus bacteria from tomato rhizospheric soil of various regions in Iran and determine the isolates that exhibit high levels of antagonistic efficiency against tomato Fusarium wilt pathogen, Fusarium oxysporum f. sp. lycopersici (Fol) and growth promotion activity. In this study, 303 Bacillus isolates were obtained from tomato rhizospheric soil. Dual culture and volatile metabolite tests were used to screen for antagonism of Bacillus isolates against Fol. Among them, 20 isolates were found to inhibit pathogen growth by 67.77% and 33.33% in dual culture and volatile metabolite tests, respectively. Based on the results of physiological tests and 16S rRNA and gyrA gene sequence analysis of 20 effective isolates, 11, seven and two isolates were identified as B. subtilis, B. velezensis and B. cereus, respectively. The results of greenhouse assessment showed that KR1-2, KR2-7 and A2-9 isolates which were characterized as Bacillus subtilis, reduced the disease index to 16.67% and promoted the plant growth by 80%. These isolates may serve as potential promising biocontrol agents against Fusarium wilt of tomato.
As a first step of a project aimed at the identification of potential biocontrol agents of Rhizoctonia solani, the rice sheath blight fungus, we surveyed the biodiversity of the genus Trichoderma based on sequence of the internal transcribed spacer (ITS) 1 and 2 of the ribosomal RNA gene cluster in paddy fields in Mazandaran province, Northern Iran. Amongst the six obtained species of Trichoderma, T. harzianum and T. virens proved to be the most frequent species in this habitat. Sequence alignment and phylogenetic analysis revealed that the T. harzianum isolates can be divided into 14 different ITS genotypes clustering in four groups. Our results are in agreement with previous molecular studies, which also revealed that T. harzianum is a complex species comprising more or less different ITS genotypes. T. virens was not as diverse as T. harzianum and three different genotypes were distinguished which constituted only one cluster. All T. atroviride and T. hamatum strains had identical ITS sequences.
In order to identify a specific marker for T. harzianum AS12-2, a strain capable of controlling rice sheath blight caused by Rhizoctonia solani, UP-PCR was performed using five universal primers (UP) both separately and in pairwise combinations. The application of two UP primers resulted in the amplification of unique fragments from the genomic DNA of T. harzianum AS12-2, clearly distinguishing it from other Trichoderma strains. The unique fragments had no significant sequence homology with any other known sequence available in databases. Based on the sequences of the unique fragments, 14 oligonucleotide primers were designed. Two primer sets amplified a fragment of expected size from the DNA of strain T. harzianum AS12-2 but not from any other examined strains belonging to T. harzianum, to other Trichoderma species assayed, or to other common fungi present in paddy fields of Mazandaran province, Iran. In conclusion, SCAR (sequence characterized amplified regions) markers were successfully identified and rapid, reliable tools were provided for the detection of an effective biocontrol Trichoderma strain, which can facilitate studies of its population dynamics and establishment after release into the natural environment.
