Relationship Between Fungicide Sensitivity and Control of Gummy Stem Blight of Watermelon Under Field Conditions.

Gummy stem blight (GSB), caused by the fungus Didymella bryoniae, is the most destructive disease of watermelon and is managed primarily with fungicides. D. bryoniae has developed resistance to many fungicides that were once very effective, including azoxystrobin, boscalid, and thiophanate-methyl. Field experiments were conducted in Tifton (TN) and Reidsville (RV), GA in 2009 and 2010 to establish a relationship between frequency of resistance to a fungicide based on in vitro assays and its efficacy in the management of GSB. Frequency of resistance to boscalid, thiophanate-methyl, and azoxystrobin was >0.80 in isolates collected from nontreated plots in both locations and years. All isolates collected after six applications of boscalid, thiophanate-methyl, or azoxystrobin were resistant to the respective fungicide. All isolates collected from treated and nontreated plots were sensitive to tebuconazole and difenoconazole. GSB severity was assessed on a weekly basis from 63 days after planting. GSB severity in plots treated with boscalid, thiophanate-methyl, or azoxystrobin was not significantly different from that in the nontreated plots (39%, TN-2009; 45%, TN-2010; and 16%, RV-2010). GSB severity in tebuconazole-treated plots (27%, TN-2009; 14%, TN-2010; and 4%, RV-2010) was significantly lower than all other treatments and the nontreated control. There was a consistent negative association between frequency of fungicide resistance and disease control in the field. Thus, knowledge of the frequency of fungicide resistance in the pathogen population will be helpful in selecting the most effective fungicides for the management of GSB in watermelon fields.

First Report of Colletotrichum gloeosporioides Causing 'Twister Disease' of Onion (Allium cepa) in Georgia.

In the fall of 2007, onion seedlings with twisted and distorted leaves were observed in seedbeds in multiple fields in the Vidalia onion region of Georgia. Tests for viruses and bacteria were negative and chemical injury was deemed improbable because of disease distribution in the fields. Upon further investigation, fungal fruiting bodies were observed on the outside sheath of a few of the seedlings. Symptomatic plants were cut into 1-cm segments and surface sterilized in 70% ethanol for 3 min. After rinsing in sterile water, the segments were placed onto potato dextrose agar amended with tetracycline. The fungus isolated from symptomatic plants fit the description of Colletotrichum gloeosporioides (Penz.) Penz. & Sacc. Conidia were aseptate, cylindrical, and hyaline. Sequencing of the internal transcribed spacer region and a BLAST search in GenBank (99% sequence similarity to C. gloeosporioides accessions) confirmed the identification. Ten onion seedlings were spray inoculated with a suspension of 1 × 107 spores/ml until runoff, and four seedlings were inoculated with water as negative controls. Plants were bagged for 12 h to maintain high relative humidity. Five plants were placed in the greenhouse and five plants placed in a growth chamber at 22°C. All plants inoculated with C. gloeosporioides developed distorted and twisted leaves 3 weeks after inoculation in the growth chamber and 5 weeks after inoculation in the greenhouse. Night time temperatures in the greenhouse (15°C) were lower than those in the growth chamber (22°C). Seedlings inoculated with water showed no symptoms. The fungus was reisolated from symptomatic plants. C. gloeosporioides has been reported to cause a disease called twister on onion in tropical regions (1). The fall of 2007 was unusually warm with maximum temperatures reaching 26°C during the day. The pathogen is present on many crops in the United States, but to our knowledge, this is the first report of C. gloeosporioides causing twister disease of onion in the United States. In Nigeria and Brazil, yield losses as much as 100% were observed in fields with infected onions (1). The impact of infection on the growth of the transplants and subsequent yield in Vidalia onions is currently unknown. References: (1) J. P. Hill. Compendium of Onion and Garlic Diseases. 2nd ed. The American Phytopathological Society, St. Paul, MN, 2008.

Cervical discectomy. A prospective analysis of three operative techniques.

BACKGROUND: Cervical disc herniation causing neurological compromise is a common affliction. Sophisticated surgical treatments have been developed throughout the twentieth century and are largely successful. Although each procedure has its supporters, it is still unclear if one surgical technique is superior. METHODS: A prospective trial was designed to evaluate the efficacy of three surgical procedures for the treatment of cervical radiculopathy caused by a unilateral acute herniated cervical disc. Patients were randomized to posterior cervical foraminotomy (FOR), and anterior cervical discectomy with (ACDF), and without (ACD) fusion. Perioperative data, office follow-up and long-term follow-up were used to compare the procedures. RESULTS: All of the procedures yielded excellent relief of symptoms and signs postoperatively and during follow-up. Operative time and hospital stay were slightly shorter for ACD compared with ACDF and FOR. Reoperations occurred in all groups but there was a trend for higher recurrence at the same level with FOR and recurrence at other levels with ACDF. CONCLUSION: All three of the procedures were successful for treatment of cervical radiculopathy caused by a herniated cervical disc. Although the numbers in this study were small, none of the procedures could be considered superior to the others. This study suggests that the selection of surgical procedure may reasonably be based on the preference of the surgeon and tailored to the individual patient.