Characterization and control of Ophiosphaerella spp. Causing spring dead spot of bermudagrass in South Carolina, USA and Buenos Aires, Argentina.

摘要

Spring dead spot (SDS) disease is an important root disease of bermudagrass (Cynodon spp.) in transition zone habitats around the world. Causal agents have been identified in the U.S. as Ophiosphaerella korrae (OK), O. herpotricha (OH), and O. narmari, but they have not been identified in Argentina (ARG).;Pure cultures were obtained from symptomatic roots from six different bermudagrass cultivars from 24 different golf courses in SC (a total of 274 samples). In ARG, a total of 188 samples were collected from 17 different locations in the Buenos Aires province (BA), including golf courses, polo fields and a sod farm. 50 more samples were collected from three golf courses outside BA and one golf course in Uruguay. SDS pathogens were isolated from 78.5% of all soil cores collected in SC and 60.9% in ARG. The ITS region of genomic ribosomal DNA extracted from mycelia was amplified using the primers specific for OK: OKITS1/OKITS2, OH: OHITS1/OHITS2, and ON: ONITS1/ONITS2 to identify the causal agents of SDS of bermudagrass in SC and ARG. In SC, OKITS primers amplified a 454-bp fragment from 203 cultures out of 212. The amplification produced with OKITS primer set confirmed O. korrae as the causal agent of SDS in SC. 131 PCR products were successfully sequenced for phylogenetic analysis and 10 polymorphic sites were identified when they were compared with each other. Analysis of molecular variance (AMOVA) was used to compare variation by location or origin of isolates or by bermudagrass cultivar as the isolate source. Results of AMOVA showed that grouping populations by geographical regions better explained genetic diversity among O. korrae isolates: 43.27% of the genetic variation was due to geographical regions, while percentage of genetic diversity due to bermudagrass cultivar isolate source was 21.33%.;In ARG, OHITS primers amplified a 454-bp fragment from all 145 cultures. This is the first report of O. herpotricha as the causal agent of SDS in ARG. 85 consensus sequences were obtained and 23 polymorphic sites identified. AMOVA analysis showed that 49.75% of the genetic variation was due to geographical regions. Grouped by cultivars, percentage of genetic variability due to bermudagrass cultivar isolate source was 24.17%. Pairwise FST showed no significant differences between BA and outside BA isolates but significant differences when compared them to isolates from the Midwest USA (Missouri and Oklahoma).;Using another approach to compare SDS fungi, amplified fragment length polymorphism (AFLP) was performed with 2 samples from each location where isolates where collected, both in SC and ARG. Isolates from Oklahoma, Missouri, North Carolina, and California were also included in this study. 53 genotypes corresponding to O. korrae and 59 to O. herpotricha were successfully amplified. A total of 256 fragments ranging in size from 50 to 500 bp were scored using two primer combination sets.;Results of both molecular approaches support the conclusion that genetic variability of Ophiosphaerella spp. is due to geographical regions and it is not dependent on the host bermudagrass cultivar.;Some management practices influential in reducing SDS in the USA were examined in Argentina. A split-split plot randomized complete block design, 4 block experiment was conducted with nitrogen source as the whole plot, with aerification or no aerification (subplot), and no fungicide or fungicides as sub subplots. The experiment was placed on a 'Tifway' practice tee at Pilara Golf Club, Pilar, BA (Argentina) in 2012, 2013, and 2014.;Ammonium sulfate reduced soil pH at root zone depths. There were no differences between ammonium sulfate vs. calcium nitrate on DS ant TQ in 2012 and 2014 while calcium nitrate reduced DS and improved TQ in 2013. Aerification did not reduce DS or improve TQ. DS was best reduced by two fall applications of tebuconazole at 0.0875 gr/m2. Two applications of fenarimol at 0.144 gr/m2 also suppressed SDS in 2013. Both fungicides reduced SDS but did not differ in 2014. Ammonium sulfate best reduced Din in 2012, calcium nitrate was best in 2013 while no significant differences were found in 2014. Ammonium sulfate was the best source of nitrogen to reduce DIt both in 2013 and 2014. Hollow tine aerification reduced DIt in 2013 but no significant differences were found in 2014. DIn was reduced by the use of every fungicide applied when compared with the untreated control during the three years of the study, but no significant differences were found among fungicides. DIt was best reduced by two applications of tebuconazole at 0.175 gr/m2 followed by two applications of fenarimol at 0.144 gr/m2 and two applications of tebuconazole at 0.0875 gr/m2. Based on this experiment, acceptable reduction of SDS requires fungicide treatment. (Abstract shortened by ProQuest.).