In vitro screening of fungicides and antagonists against Sclerotium rolfsii

A study was conducted in the microbiology laboratory of Plant Pathology Department, Bangabandhu Sheikh Mujibur Rahman Agricultural University, Gazipur, during 2010 to 2011 to control Sclerotium rolfsii with  fungicides and Trichoderma harzianum. Six fungicides namely Provax-200, Bavistin, Ridomil, Dithane M-45, Rovral 50 WP and Tilt were screened at 100, 200 and 400 ppm concentration for their efficacy against the radial colony growth of S. rolfsii. The complete inhibition was obtained with Provax-200 at all the selected  concentrations. Complete inhibition also obtained at the highest concentration of Tilt. The highest  concentration of Rovral 50WP inhibits 93.88% radial growth and significantly superior to Dithane M-45 at the  highest concentration. Bavistin and Ridomil were found to be significantly lower when used against the test  pathogen. A total of 20 T. harzianum isolates collected from rhizosphere and rhizoplane of different crops were  screened against S. rolfsii following dual plate culture technique. The screened isolates of Trichoderma showed significantly variable antagonism ranging from 65.01 to 83.06% reduction of radial growth of S. rolfsii. Among the screened antagonists, the isolate TH-18 of T. harzianum showed the highest (83.06%) inhibition of radial growth of S. rolfsii.Key words: Sclerotium rolfsii, Trichoderma harzianum, fungicides, antagonist

Infection process of Stagonosporopsis tanaceti in pyrethrum seed and seedlings

Ray blight disease of pyrethrum (Tanacetum cinerariifolium) is caused by Stagonosporopsis tanaceti, with infected seed being a major means of transmission of this fungal pathogen. The infection process of S. tanaceti in pyrethrum seed and seedlings was determined. Infection hyphae only infected the outer and inner layers of the seed coat and not the embryo of naturally infected pyrethrum seed. During the process of germination of infected seed, S. tanaceti from the seed coat infected the developing embryo and cotyledon, resulting in preâ and postâ emergence death, depending on the level of infection in the seed coat. Preâ emergence death occurred due to disintegration of the infected embryo, which was replaced by hyphae and extracellular anthocyaninâ like material (EAM) at 7 days after incubation (dai). Postâ emergence death occurred after both epidermal and cortical tissues of infected cotyledons at the crown/hypocotyl region disintegrated due to colonization by hyphae. Moreover, most of the tissues of the vascular bundles and cortical tissues contained heavy depositions of EAM at 10â 14 dai. In 6â weekâ old infected seedlings, hyphae were confined to the epidermis and the cortical tissues at the crown/hypocotyl regions; the vascular bundles of both infected and uninfected regions, and cortical tissues of the uninfected regions of the seedlings were completely free from infection hyphae and EAM. These findings provide a better understanding of the early stages of the disease cycle of S. tanaceti and will lead to improved control measures for seedborne infection using seed treatments

TaqMan PCR assay for detection and quantification of Stagonosporopsis tanaceti in pyrethrum seed and seedlings

Pyrethrum seed has an important role in the transmission of Stagonosporopsis tanaceti, the cause of ray blight disease of pyrethrum. A TaqMan probe based polymerase chain reaction (PCR) assay was developed to quantify the level of S. tanaceti inocula in pyrethrum seed and seedlings. Primer pair (St_qF3, St_qR2) was designed based on the intergenic spacer (IGS) region of S. tanaceti, which produced a 125 bp amplicon specific to S. tanaceti. TaqMan PCR assay using St_qF3, St_qR2 and a probe St_qP was highly specific against the genomic DNA of S. tanaceti, but did not amplify DNA of 14 related Stagonosporopsis species or other foliar pathogens of pyrethrum. The sensitivity limit of this assay was measured using the cycle threshold (Ct) value which ranged from 17.59 for 10 nanograms (ng) to 36.34 for 100 femtograms (fg) genomic DNA of S. tanaceti. There was a significant negative correlation (r = −0.999, P < 0.001) between the Ct value and the percent of S. tanaceti infected seed. In addition, this TaqMan PCR assay detected latent infection within seedlings. This assay could be applied to test commercial seed and seedlings before deciding on the appropriate management practices