The fungal genera Endothia and Cryphonectria include some of the most important pathogens of forest trees. Despite available new technology, no comprehensive comparative study based on DNA sequence data and morphology has been done on the available isolates representing these two genera.The main objectives of this study were to assess the phylogenetic relationships among species of Cryphonectria and Endothia, for which cultures are available, and to establish a taxonomic framework based on DNA sequence and morphological data, which will aid future studies and identification of species in these and related genera. Comparisons were based on sequence variation found in the ITS region of the ribosomal RNA operon and two regions of the -tubulin gene. In addition, the morphology of these species was examined. The phylogenetic data indicated that Endothia and Cryphonectria reside in two distinct phylogenetic clades. Cryphonectria parasitica, C. macrospora, C. nitschkei, C. eucalypti and C. radicalis represented the Cryphonectria clade. Endothia gyrosa and E. singularis were included in the Endothia clade. An isolate representing E. viridistroma grouped outside the Endothia clade and separately from other groups. Other clades outside the one encompassing Cryphonectria were those represented by the C. cubensis isolates and fungi isolated from Elaeocarpus dentatus originating from New Zealand. These clades could be distinguished from Endothia and Cryphonectria, based on anamorph morphology, stromatal structure and ascospore septation. Cr yphonectria and Endothia, therefore, appear to be paraphyletic and taxonomic relationships for these fungi need to be revised.
Peanut stem segments 8.5-cm long were inoculated at leaf nodes with mycelial plugs of Sclerotinia minor and incubated in moist chambers at 20 C. Water-soaked lesions were often visible after 24 hr. The rate of lesion elongation was used to quantitatively assess the physiological resistance of peanut genotypes to Sclerotinia blight, screen chemicals for fungicidal activity, and evaluate the pathogenicity of S. minor isolates. The age and/or developmental state of lateral limbs of plants had a marked effect on lesion development; 3 days after inoculation, mean lesion lengths were 58.8, 46.8, and 38.9 mm for terminal, median and basal parts of stems, respectively. The speed, simplicity and adaptability of this method make it a valuable tool for research on Sclerotinia blight of peanut. 16.Porter, D. M . , Beute, M. K., and Wynne, J. C. 1975. Resistance of peanut germplasm to Sclerotinia scfemciorum. Peanut Sci. 17. Porter, D. M., Powell, N. L., and Phipps, P. M. 1983. Disease detection and crop loss assessment in peanut fields with aerial infrared photography. (Abstr. 86).
Fluazinam provided effective control of Sclerotinia blight (Sclerotinia minor Jagger) of peanut in six field trials during a 4-yr period. Applications of fluazinam (0.56 kglha) at the onset of Sclerotinia blight and 4 wk later provided an average of 69% suppression of disease incidence and increased yields by 1598 kg! ha compared to untreated plots. Performance of fluazinam was significantly better than iprodione, the material currently used for control of Sclerotinia blight. Two applications of iprodione at 1.12 kglha provided only 31% suppression of disease incidence and increased yield by 718 kglha. Fungicides were also evaluated in 1990 as tank-mixes with chlorothalonil (1.26 kglha) that were applied in foliar sprays according to the Virginia peanut leafspot advisory program. Treatments consisted of no fungicide, chlorothalonil alone, and tank-mixes of chlorothalonil plus either dicloran at 2.10 kglha, fluazinam at 0.56 kglha, or iprodione at 0.84 kglha. Sclerotinia blight at harvest in untreated plots and plots treated with chlorothalonil alone averaged 27.8 and 35.8 disease foci per plot, whereas yields averaged 3624 and 2251 kglha, respectively. Compared to plots treated with chlorothalonil alone, Sclerotinia blight was suppressed by 92,25, and 25%, and yield was increased by 4020, 1925, and 1684 kglha in plots treated with chlorothalonil plus either fluazinam, iprodione, or dicloran, respectively. Applications of tank-mixes containing fluazinam plus chlorothalonil in 1991 provided additional evidence that this approach wasa highlyeffective means of controlling both Sclerotinia blight and early leafspot, a previously unattainable goal. Fluazinam did not control early leafspot (Cercospora arachidicola S. Hori) in field trials; however, the fungicide was fungitoxic in vitro to Sclerotium rolfsii Sacco and Rhizoctonia solani Kuhn.
Algorithms were evaluated for computing disease risk and improving the timing of fungicide applications for control of Sclerotinia blight of peanut. Disease risk was calculated by multiplying indices of moisture, soil temperature, vine growth, and canopy density each day, and summing values for the previous 5 days to obtain a 5-day risk index (FDI). After fungicide application, the FDI was reset to zero for 3 weeks. Fluazinam at 0.58 kg a.i./ha applied at FDI 24 or 32 in 1994 and 1995 suppressed disease and increased yield as much as or more than programs of weekly scouting and applying fungicide at the initial onset of disease with additional sprays at 3- to 4-week intervals. The FDI algorithm was also more efficient than calendar sprays at 60, 90, and 120 days after planting (DAP). Environmental and host parameters were expanded in 1996 and 1997 by adding new temperature and new vine growth indices. These parameters along with DAP-dependent thresholds consistently improved the timing of fungicide sprays and disease management when using the FDI algorithm in comparison to weekly scouting or calendar sprays at 60, 90, and 120 DAP.
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