Root Collar Rot Research Articles

Ayçiçeğinde Sclerotinia sclerotiorum (Lib.) De Bary’ye Karşı Bazı Bakteriyel Antagonistlerin In vitro ve In vivo Etkinliklerinin Belirlenmesi

This study was carried out in 2017-2018 to determine the in vitro and in vivo activities of some bacterial bioagents against Sclerotinia sclerotiorum, which causes root and root-collar rot in sunflower cultivation areas of Konya and Aksaray provinces. Against the two most virulent S. sclerotiorum (Hırkatol and Eskil) isolates selected as a result of pathogenicity tests after being isolated and diagnosed from diseased plants which were collected from sunflower cultivation areas in Konya and Aksaray provinces, the antifungal effects of 16 bacterial isolates from the soil in the rhizosphere region of the healthy sunflower plants from the same areas were evaluated. Primarily, the most effective bacterial bioagents were determined by dual culture tests. As a result of the in vitro tests, a total of 5 bacterial isolates constituting the largest zone diameter were molecularly identified according to 16S rRNA and were used in pot experiments. The bacteria were identified as Bacillus cereus, Bacillus simplex, Brevibacterium frigoritolerans, Bacillus toyonensis (2 isolates) and were coded using the BLAST program of the GenBank database (NCBI). As per in vitro, the highest effect in both isolates of S. sclerotiorum was observed in Bacillus cereus and Bacillus simplex with an inhibition rate of 49.19-57.95%. Except for Bacillus toyonensis (B1), one of the bacterial species which were tested in vivo, all the bacteria reduced or stopped lesion development compared to the control. As a result of the application, the biological control agent completely prevented the growth of both the isolates of Bacillus cereus and Bacillus simplex S. sclerotiorum in in vivo conditions (100%). Efficacy studies have shown that bacterial isolates both cause healthy growth of sunflower plants and significantly prevent disease formation in treated plants when compared to control plants. These results emphasize the importance of such studies as a tool for the development of sustainable agricultural practices that can be easily applied in our region, and also show that B. cereus and B. simplex in sunflowers can be potential bacterial bioagents that can be used in biological control against S.sclerotiorum. In addition, it will be useful to carry out studies on the development of commercial preparations of the bacterial isolates found in the study.

Determination of Disease Severity and Anastomosis Groups of Rhizoctonia solani Isolates from Chickpea Plant in Konya Province

This study was carried out to determine the anastomosis groups and disease severity of Rhizoctonia solani, which causes root and root collar rot in chickpea production areas in Konya. A total of eleven isolates of Rhizoctonia spp. were obtained in the isolations made from the root and root collar of the plants in the surveys. Rhizoctonia isolates examined microscopically were grouped as multinucleate, binucleate according to the number of nuclei. Ten isolates were multinucleate and identified R. solani, while one isolate was binucleate Rhizoctonia sp. In pathogenicity tests, five multinucleate isolates were found to be pathogenic. Disease severity was determined as 100% for 1.2 A and 1.2 B coded isolates, 86% for 1.1 A coded isolate, 75% for 1.1 B coded isolate, and 44% for 1.2 C coded isolate. It was observed that the other multinucleate five isolates caused only a shortening in plant heights. No disease symptoms were observed in the plants inoculated by the binucleate isolate. All isolates were characterized using the internal transcribed spacer (ITS) region of ribosomal DNA, and two different anastomosis groups were defined accordingly. It was determined that 5 virulence multinucleate R. solani isolates belonged to AG-4 HGII and 5 other multinucleate isolates to AG BI anastomosis group.

Root collar rot, a new lethal disease on Tectona grandis caused by Kretzschmaria zonata in Brazil.

Tectona grandis L.f., known as teak, is one of the most valuable tropical hardwood species that has been extensively planted in tropical zones, covering about 6,8 million hectares (Kollert and Kleine 2017). Recent advances in silvicultural management and use of improved clones have enhanced productivity and wood quality of teak plantations in Brazil. However, the incidence of diseases has increased over time being a threat to sustainability of commercial teak plantations. Therefore, forest pathology studies have been conducted in Brazil to minimize the risks of losses caused by the diseases on teak, ensuring the expected economic profitability. In a recent disease survey conducted in Midwest of Brazil, almost one thousand teak trees showing typical die-back symptoms with root collar rot were found. The diseased trees showed undersize leaves displaying yellowish to pale brown color, followed by wilt, defoliation and death. At the base of the trunk, root collar rot was observed, with sloughing and deterioration of the bark exhibiting flattened and encrusted fungi fruiting bodies of gray to bright white color. Over the time, the wood of infected trees develops black zone lines and soft tissue due to both lignin and cellulose decay. The disease begins in the root and spreads to the collar of the tree, causing a collapse in sap flow leading to mortality. To discover the disease cause, samples of infected trees were collected to perform an accurate pathogen identification by polyphasic approach, as well as pathogenicity test. From isolation in Malt Extract Agar (MEA), one fungus showing white progressing to gray mycelial growth was consistently isolated. Two isolates named as GFP131 and GFP132 were characterized. Microscopic examination showed conidia aseptate, hyaline, ovoid to fusiform-ellipsoid shaped, measuring 6-8 x 2-4 μm; stromata with surface brown to dark brown; perithecia with variable shapes and ostioles papillate; and ascospores aseptate, dark brown, fusiform to ellipsoid, measuring 20-37 × 8-15 μm, displaying a straight germinal line slightly less than ascospore length. These morphological characteristics were similar to descriptions for genus Kretzschmaria (Rogers and Ju 1998; Stadler et al. 2013). Genomic DNA was extracted from mycelium, and the internal transcribed spacer (ITS) region of rDNA with primer pair ITS1/ITS4 was sequenced and then deposited under Genbank codes MH481853 and MH481854. A BLASTn search showed >99% identity with K. zonata sequence (KY660541). Phylogenetic inference by Maximum Likelihood method using Kimura 2-parameter model confirms that the isolates belong to Kretzschmaria zonata (Lév.) P.M.D. Martin. A pathogenicity test was established in a greenhouse with controlled conditions of temperature (28-30 °C) and humidity (80-90 %). Five plants were inoculated with GFP132 at the collar region with one mycelium disk of approximately 5 mm in diameter each, and the inoculated area was wrapped in plastic film. Disks of MEA culture media were placed on five additional plants as controls. Forty days after inoculation, all of the previously mentioned symptoms were observed for all inoculated plants, while control plants showed only scars at the inoculation point. The pathogen was reisolated from all five of the inoculated plants. Kretschmaria zonata has been reported on teak in Nigeria (West 1938) and in Mexico (Cibrian Tovar et al. 2014). However, this is the first report of K. zonata on T. grandis for Brazil and the first report anywhere to include Koch's postulates, proving the etiology of the disease.

Bioecology of the fungus Sphaeropsis sapinea dyko & Sutton - agents of pinus species decline

Sphaeropsis sapinea is a cosmopolitan fungus, identified in more than 50 countries of the world, on all continents, but it is primarily the species of warm lands. It is also a polyphagous fungus recorded from 11 coniferous genera. The most endangered and the most frequent host plants are Pinus species - it occurs on 48 pine species, among which the most susceptible are Pinus Radiata, P. nigra, P. sylvestris, P. ponderosa, P. resinosa, P. mugo, P. pinaster and P. elliotti. The greatest damage is caused on the introduced Pinus species and on those cultivated in artificial plantations, shelterbelts and in urban environments. In Yugoslavia S. sapinea is widely distributed both in the continental and in the Mediterranean parts. It was identified from ten pine species and six hosts from other coniferous genera. By the study in our country, the new hosts of this fungus were detected - Pinus jeffrey, P. peuce and P. heldreichii. The most endangered species in our country is Austrian pine, both in urban environments, and in plantations The symptoms of the disease are bud wilt, curling, stunting and necrosis of current year shoots and needles, dieback of top shoots, parts of crown or tree tops, branch and stem bark canker, root collar rot on the young plants in nurseries and their dying. This fungus also prevents seed germination of Pinus species and causes blue sap stain of the freshly cut wood, although sap stain was also observed on standing trees. More rarely it causes root rot and crown wilt of Pinus species. The main symptoms of infection, both of young plants and older trees, are the dieback of current year shoots S. sapinea can penetrate through buds, bark of young shoots and needles. The critical time of infection is the period from mid April to mid May. Then infection mainly penetrates through the bark of young shoots, which results in their dying. Infection through the needles occurs mainly at the time of their sudden growth or during summer months. The first visible symptoms of infection of the young shoots are in the form of brown necroses, resin bleeding and several short pairs of needles at the place. S. sapinea can infect male and female flowers, current year and second-year cones. The pycnidia with mature conidia can form on the shoots, needles, first-year and second-year cones during the year of infection. The first mature fructifications are mostly formed in the bark of young shoots, in the zone of infection, and they were recorded in late June at the earliest. They were recorded on the cones at the beginning of the third decade of July. Pycnidia are formed in the bark, on the needles and on the second-year and older cones, on male and female flowers, as well as on the cones in the first year of development. The size of S. sapinea conidia on different Pinus species is very variable throughout the world and ranges widely from 16.8-55.0?7.0-21.0 ?m. Our study shows that the size of pycnospores in our country is also variable and it ranges 14.8-51.4?9.7-20.2 ?m The optimal temperature for spore germination and germ tube growth is 27?C, and the optimal temperature for mycelial growth on the media PDA and MEA is 28?C. The formation of fruiting bodies in the culture is affected by light and the presence of sterilised needles on the mycelium The correct and timely control measures can contribute to reduce the consequences of this serious disease, by the combined application of silvicultural and chemical measures. Chemical control is recommended in the nurseries, severely infected plantations and in urban environments. The fungicides which showed the greatest efficiency are the preparations based on copper and Benomil.