Application of Preplant Fumigants via Drip Irrigation Systems for the Management of Root Rot of Melons Caused by Monosporascus cannonballus.

Root rot and vine decline, caused by Monosporascus cannonballus, is a destructive disease of melons in the desert production regions of southern California. In 1998, we initiated studies on the use of preplant fumigation to reduce resident pathogen populations in soil. Preplant fumigation with methyl iodide injected as a hot gas at 448.4 kg/ha through drip irrigation tape in preformed, tarped beds consistently provided significant (P < 0.05) reductions in the percentage of roots infected compared with the nonfumigated controls; these reductions were equal to or better than those achieved with an equivalent rate (448.4 kg/ha) of methyl bromide. Chloropicrin applied in water at 249.0 kg/ha through buried drip irrigation tape to either tarped or nontarped beds significantly (P < 0.05) reduced the percentages of both roots infected and roots on which perithecia were produced compared with nonfumigated controls.

The accuracy of pulse oximetry in the emergency department.

The objective of this retrospective study was to identify factors affecting the accuracy of pulse oximetry in the ED. Over a 3-year period, 664 consecutive emergency department (ED) patients had simultaneous arterial blood gas (ABG) and pulse oximeter readings taken. Pulse oximeter saturations (SpO2) were compared with ABG CO-oximeter saturations (SaO2) for accuracy. Multiple variables including age, sex, hemoglobin, bicarbonate, pH, and carboxyhemoglobin (COHb) were analyzed to see if they affected SpO2 accuracy. ROC curves were used to determine the best pulse oximeter threshold for detecting hypoxia. Using multivariate analysis, COHb was the only statistically significant factor affecting the accuracy of pulse oximetry. In patients with COHb <2%, SpO2 overestimated SaO2 by more than 4% in 8.4% of cases. In patients with COHb > or = 2%, SpO2 overestimated SaO2 by more than 4% in 35% of cases. The best pulse oximetry threshold for detecting hypoxia is 92%. At this threshold, if COHb is <2%, pulse oximetry has a sensitivity of 0.92 and specificity of 0.90. If COHb is > or =2%, sensitivity is 0.74 and specificity is 0.84. For patients likely to have a COHb < 2, pulse oximetry is an effective screening tool for detecting hypoxia. However, more caution must be exercised when using pulse oximetry in patients likely to have a COHb > or = 2%.

A New Bipartite Geminivirus (Begomovirus) Causing Leaf Curl and Crumpling in Cucurbits in the Imperial Valley of California.

During fall 1998, volunteer watermelons (Citrullus lunatus L. (Thunb.) Matsum. & Nakai) showing leaf curl, crumpling, and yellowing symptoms were found in a commercial honeydew melon (Cucumis melo L. subsp. melo Inodorus group) field in the Imperial Valley of California. The plants were infected with a begomovirus (family Geminiviridae, genus Begomovirus) based on (i) a positive response in squash blots probed with a general begomovirus DNA probe (1) and (ii) amplification of DNA-A (≈1.2 kb) and DNA-B (≈1.4 kb) fragments by polymerase chain reaction (PCR) with degenerate DNA-A (PAL1v1978/PAR1c496) and DNA-B (PBL1v2040/PBR1c970) primers, respectively (3). The DNA-A and -B fragments were cloned and sequenced (GenBank accession nos. AF224760 [DNA-A] and AF224761 [DNA-B]). The DNA-A and -B fragments had a nearly identical (99.5%) common region (CR) of 186 (DNA-A) and 187 (DNA-B) nucleotides, indicating they were from the same begomovirus. Database searches conducted with these sequences revealed no high degree of sequence identity (i.e., >90%) with other begomoviruses, including Squash leaf curl virus (SqLCV [2]) from southern California. The partial AC1 sequence (669 nt) was most identical to Tomato severe leaf curl virus (ToSLCV) from Guatemala (83%) and SqLCV (81%), the partial AV1 sequence (135 nt) was most identical to Tomato golden mosaic virus from Brazil (84%) and SqLCV (81%), and the CR was most identical to Squash yellow mottle virus from Costa Rica (81%), ToSLCV (81%), and SqLCV (77%). The partial BV1 sequence (465 nt) was most identical to Bean calico mosaic virus and SqLCV (72%), and the partial BC1 sequence (158 nt) was most identical to SqLCV (75%). Watermelon seedlings bombarded with a DNA extract from infected watermelon volunteers developed crumpling and distortion symptoms, whereas seedlings bombarded with gold particles alone developed no symptoms. Geminivirus infection in symptomatic seedlings was confirmed by PCR. These results suggest a new begomovirus caused the disease symptoms in the watermelon volunteers. Leaf crumpling and curling symptoms were not observed in spring melons in the Imperial Valley in 1999, but on 2 July and 17 August 1999, cantaloupe (C. melo L. subsp. melo Cantalupensis group), muskmelon (C. melo L. subsp. melo Cantalupensis group), and watermelon plants with leaf crumpling and yellowing were found. These plants were infected with the new begomovirus based on sequence analysis of PCR-amplified DNA-A fragments (97 to 98% identity for CR and partial AC1 sequence). A survey of fall melons, conducted 23 to 24 September 1999, revealed widespread symptoms of leaf curl and crumpling on new growth of muskmelon plants in all seven commercial fields examined (estimated incidence 25 to 50%) and on watermelon volunteers. No such symptoms were observed on leaves of honeydew melons. Symptomatic muskmelon and watermelon leaves, collected from eight locations throughout the Imperial Valley, were infected with the new begomovirus based on sequence analysis of PCR-amplified DNA-A fragments. Thus, a new begomovirus has emerged in the Imperial Valley; the name Cucurbit leaf crumple virus (CuLCrV) is proposed. References: (1) R. L. Gilbertson et al. Plant Dis. 75: 336, 1991. (2) S. G. Lazarowitz and I. B. Lazdins. Virology 180:58, 1991. (3) M. R. Rojas et al. Plant Dis. 77:340, 1993.