Distribution of Three Verticillium dahliae Races in Coastal California and Evaluation of Resistance in Lettuce

Verticillium wilt, caused by Verticillium dahliae, is one of the most devastating soilborne diseases of lettuce (Lactuca sativa L.). There are three races of V. dahliae and each race has been characterized by markers representing race-specific effectors. Race 1 is differentiated by the presence of the functional secretory Ave1 effector. Similarly, races 2 and 3 are differentiated by effectors VdR2e and VdR3e, respectively. While the presence of race 1 in coastal California was well-established, the presence of effector-based races 2 and 3 was uncertain. This study therefore focused on characterizing 727 isolates collected from 142 ranches of symptomatic lettuce and other crops from coastal California. Based on this evaluation, 523 isolates were designated as race 1, 20 isolates as race 2, 23 isolates as race 3, and 17 as race undefined. Isolates representing other Verticillium species totaled 110, and 34 were non-Verticillium fungal species. Since the use of resistant cultivars is a key strategy to manage this disease, we evaluated 48 lettuce germplasm lines and one endive (Cichorium endivia L.) line, comprised of commercial cultivars (cv.) and breeding lines, including the race 1-resistant heirloom cv. La Brillante and the susceptible cv. Salinas as controls. Resistance against races 1, 2, and 3 along with VdLs17, a virulent isolate of V. dahliae from lettuce that is currently not assigned to a race was evaluated in replicated greenhouse experiments. Two crisphead lettuce lines, HL28 and HL29, exhibited resistance against race 1 and a partial resistance against race 2 while all other lines were highly susceptible to races 1 and 2 and VdLs17. The majority of lines exhibited higher resistance to race 3 relative to the other two races. This study documents the current distribution of the different races in coastal California. In addition, the sources of resistance currently being developed should be effective or partially effective against these races for targeted deployment as soon as they are available. Keywords: Lactuca sativa, avirulence, effectors, host resistance, disease severity.

First report of Globisporangium uncinulatum (syn. Pythium uncinulatum) causing Pythium wilt of lettuce in Arizona

In 2021 and 2022, wilt symptoms were observed in lettuce (Lactuca sativa L.) fields in Yuma County, Arizona (AZ). Incidence was < 1% at all locations. Symptoms included stunting, yellowing and wilting of outer leaves. As disease progressed, outer leaves wilted and turned necrotic. In advanced stages, tap roots turned brown-gray, with few feeder roots. The crown remained intact until the plant collapsed. Symptomatic romaine and iceberg plants were collected from two sites. Necrotic roots were washed and then plated on amended corn meal agar (PARP) (Kannwischer et al. 1978). After 2-3 days, slow growing, coenocytic, submerged mycelia grew from these pieces. In culture, profuse oogonia formed with diameters of 30-39 (avg. = 33.7) µm and spiny protuberances (5-8 [avg. = 6.4] µm long) with thickened bases. Oospores were spherical and aplerotic, with diameters of 25-32 (avg. = 27.8) µm. Lettuce with identical symptoms from the Salinas Valley, California (CA) were also tested and similar isolates were recovered. Pathogenicity was tested using six AZ and one CA isolates. Inoculum was grown on barley seeds moistened with sterile distilled water, autoclaved three times (at 24 h intervals), then inoculated with colonized agar plugs and incubated at 20°C. Inoculum was used after two weeks. For each isolate, 12 3-week-old iceberg (cv. Speedway) and romaine (cv. Del Sol) plants were inoculated by placing 3-4 colonized barley seed next to the roots of the potted plants. Plants were maintained in a greenhouse at 24-26°C (daytime high) with ambient light. After eight days, all inoculated plants exhibited chlorotic lower leaves that later wilted. Both feeder roots and taproots showed brown-gray discoloration and were necrotic. Microscopy showed the presence of spiny oogonia in inoculated roots. Symptoms caused by the AZ and CA isolates were indistinguishable from each other. Isolations from necrotic tissue resulted in colonies morphologically identical to the original isolates. Twelve control plants inoculated with uncolonized barley seed developed no symptoms. DNA was extracted from all seven AZ and CA isolates pre-inoculation, and AZ isolate 2 recovered from both lettuce types post-inoculation for molecular characterization. The internal transcribed spacer (ITS) and cytochrome C oxidase subunit 2 (COX II) were amplified for the above isolates using primer sets ITS1/ITS4 (White et al. 1990) and FM66/FM58 (Villa et al. 2006), then sequenced. ITS of pre- and post-inoculated isolates for AZ (OQ054806 and OQ054807) and CA (OQ564388) matched 1078/1078 bases of Globisporangium uncinulatum (syn. Pythium uncinulatum; AY598712.2) with 99.8% identity. There were two SNPs in COX II for AZ isolate 1 (OR069239); all other isolates pre- and post- inoculation for AZ (OR069240 and OR069242) and CA (OR069241) uniformly matched 533/535 bases of G. uncinulatum (KJ595385.1) with 99.4% identity. Based on these molecular and morphological data, the isolates were identified as G. uncinulatum (Blok and Van Der Plaats-Niterink 1978; Van Der Plaats-Niterink 1981). To our knowledge, this is the first report of G. uncinulatum on lettuce in AZ. Designated as Pythium wilt, this disease is reported on lettuce in The Netherlands (Blok and Van Der Plaats-Niterink 1978), Japan (Matsuura, et al. 2010), and CA (Davis, et al. 1995). Arizona is an important lettuce growing region; if this disease becomes more prevalent, lettuce production in this region could be negatively impacted.

Genomic signatures of heterokaryosis in the oomycete pathogen Bremia lactucae

Lettuce downy mildew caused by Bremia lactucae is the most important disease of lettuce globally. This oomycete is highly variable and rapidly overcomes resistance genes and fungicides. The use of multiple read types results in a high-quality, near-chromosome-scale, consensus assembly. Flow cytometry plus resequencing of 30 field isolates, 37 sexual offspring, and 19 asexual derivatives from single multinucleate sporangia demonstrates a high incidence of heterokaryosis in B. lactucae. Heterokaryosis has phenotypic consequences on fitness that may include an increased sporulation rate and qualitative differences in virulence. Therefore, selection should be considered as acting on a population of nuclei within coenocytic mycelia. This provides evolutionary flexibility to the pathogen enabling rapid adaptation to different repertoires of host resistance genes and other challenges. The advantages of asexual persistence of heterokaryons may have been one of the drivers of selection that resulted in the loss of uninucleate zoospores in multiple downy mildews.

Detection and Quantification of Bremia lactucae by Spore Trapping and Quantitative PCR

Bremia lactucae is an obligate, oomycete pathogen of lettuce that causes leaf chlorosis and necrosis and adversely affects marketability. The disease has been managed with a combination of host resistance and fungicide applications with success over the years. Fungicide applications are routinely made under the assumption that inoculum is always present during favorable environmental conditions. This approach often leads to fungicide resistance in B. lactucae populations. Detection and quantification of airborne B. lactucae near lettuce crops provides an estimation of the inoculum load, enabling more judicious timing of fungicide applications. We developed a quantitative polymerase chain reaction (qPCR)-based assay using a target sequence in mitochondrial DNA for specific detection of B. lactucae. Validation using amplicon sequencing of DNA from 83 geographically diverse isolates, representing 14 Bremia spp., confirmed that the primers developed for the TaqMan assays are species specific and only amplify templates from B. lactucae. DNA from a single sporangium could be detected at a quantification cycle (Cq) value of 32, and Cq values >35 were considered to be nonspecific. The coefficient of determination (R2) for regression between sporangial density derived from flow cytometry and Cq values derived from the qPCR was 0.86. The assay was deployed using spore traps in the Salinas Valley, where nearly half of U.S. lettuce is produced. The deployment of this sensitive B. lactucae-specific assay resulted in the detection of the pathogen during the 2-week lettuce-free period as well as during the cropping season. These results demonstrate that this assay will be useful for quantifying inoculum load in and around the lettuce fields for the purpose of timing fungicide applications based on inoculum load.

MR Imaging of Monostotic Fibrous Dysplasia of the Clivus

We describe the MR appearance of a case of monostotic fibrous dysplasia confined to the clivus. The lesion showed intermediate signal intensity on T2-weighted images which is uncommon among clival diseases.

Resistance to Downy Mildew in Lettuce 'La Brillante' is Conferred by Dm50 Gene and Multiple QTL

Many cultivars of lettuce (Lactuca sativa L.) are susceptible to downy mildew, a nearly globally ubiquitous disease caused by Bremia lactucae. We previously determined that Batavia type cultivar 'La Brillante' has a high level of field resistance to the disease in California. Testing of a mapping population developed from a cross between 'Salinas 88' and La Brillante in multiple field and laboratory experiments revealed that at least five loci conferred resistance in La Brillante. The presence of a new dominant resistance gene (designated Dm50) that confers complete resistance to specific isolates was detected in laboratory tests of seedlings inoculated with multiple diverse isolates. Dm50 is located in the major resistance cluster on linkage group 2 that contains at least eight major, dominant Dm genes conferring resistance to downy mildew. However, this Dm gene is ineffective against the isolates of B. lactucae prevalent in the field in California and the Netherlands. A quantitative trait locus (QTL) located at the Dm50 chromosomal region (qDM2.2) was detected, though, when the amount of disease was evaluated a month before plants reached harvest maturity. Four additional QTL for resistance to B. lactucae were identified on linkage groups 4 (qDM4.1 and qDM4.2), 7 (qDM7.1), and 9 (qDM9.2). The largest effect was associated with qDM7.1 (up to 32.9% of the total phenotypic variance) that determined resistance in multiple field experiments. Markers identified in the present study will facilitate introduction of these resistance loci into commercial cultivars of lettuce.

Evaluation of brain metabolism in steno-occlusive carotid artery disease by proton MR spectroscopy: a correlative study with oxygen metabolism by PET

Carotid occlusive diseases may cause ischemic changes in both the gray matter and the white matter as a result of hemodynamic compromise. To validate the use of proton magnetic resonance spectroscopy (MRS) in evaluating the carotid occlusive diseases, we compared changes in peaks of choline, in the sum of creatine and phosphocreatine, and in N-acetyl-aspartate (NAA) of the white matter with cortical oxygen metabolism measured by PET.

METHODS

Eleven patients with unilateral steno-occlusive carotid artery disease underwent PET and MRS. Ten age-matched healthy volunteers underwent MRS. No subjects had cortical infarction. MRS was performed bilaterally in the centrum semiovale. Regional blood flow, regional metabolic rate of oxygen (rCMRO2), and regional oxygen extraction fraction (rOEF) of the cerebral cortex were measured by the steady-state method with 15O gas.

RESULTS

The asymmetry index of the ratio of NAA to the sum of creatine and phosphocreatine (NAA/Cr) correlated positively with the asymmetry index of rCMRO2 (r = 0.77; P < 0.01). Because rCMRO2 is a marker of tissue viability, the NAA/Cr of the centrum semiovale may reflect viable neuronal cells. The asymmetry index of the ratio of choline to the sum of creatine and phosphocreatine (Cho/Cr) showed a significant positive correlation with the asymmetry index of rOEF (r = 0.65; P < 0.05). All but 1 patient with an increased Cho/Cr (>1.03) showed an increase in rOEF of the ipsilateral cortex (>0.56). This finding may indicate membrane damage caused by ischemia, because the centrum semiovale is the deep watershed zone.

CONCLUSION

The metabolic changes in the centrum semiovale detected by proton MRS reflect a hemodynamically compromised state and are useful in evaluating tissue viability.

"Ivy sign" on fluid-attenuated inversion-recovery images in childhood moyamoya disease

We report on MR studies of a 15-year-old girl with moyamoya disease in whom diffuse leptomeningeal enhancement ("ivy sign") was revealed by fluid-attenuated inversion-recovery (FLAIR) and contrast-enhanced imaging. We speculate that the mechanism behind this enhancement is caused by a retrograde slow flow of engorged pial vasculature via leptomeningeal anastomosis. Nevertheless, it remains unknown whether the precise source of a high signal on FLAIR images is attributable to pial vessels themselves or congested thickening of the leptomeninges or both.

Quantitative analysis of cerebral microvascular hemodynamics with T2-weighted dynamic MR imaging

The purpose of this study was to quantify cerebral microvascular hemodynamics with T2-weighted dynamic susceptibility contrast-enhanced magnetic resonance imaging (DSC-MRI) using a half-Fourier acquisition single-shot turbo spin-echo (HASTE) sequence. We performed T2-weighted DSC-MRI with HASTE sequence in 19 normal subjects. After bolus injection of gadopentetate dimeglumine, HASTE images of two sections were acquired for the simultaneous creation of concentration-time curves in the internal carotid artery and in brain tissue. Absolute regional cerebral blood volume (rCBV), regional cerebral blood flow (rCBF), and mean transit time (MTT) values of brain tissue were calculated on a base of the indicator dilution theory, and all values were corrected on the assumption that rCBF of white matter is constant in 22 mL/100 g tissue/min without age-dependent alteration. A decrease in rCBV and rCBF of gray matter was age dependent, while rCBV of white matter did not show significant change with aging. The mean rCBF value in gray matter was 37.3 +/- 8.4 mL/100 g tissue/min. The mean rCBV value was 4.1 +/- 0.8 mL/100 g tissue in gray matter and 2.9 + 0.4 mL/100 g tissue in white matter. The rCBV and rCBF values of gray and white matter obtained from T2-weighted DSC-MRI with HASTE sequence were slightly lower than the published data calculated by gradient-echo sequence. We were able to perform absolute quantifications of the capillary blood volume and flow, using a HASTE sequence, which would not have been possible with a gradient-echo sequence. This technique provides a new method for estimating cerebral microvascular hemodynamics.

Crossed cerebellar diaschisis: assessment with dynamic susceptibility contrast MR imaging

The authors investigated the feasibility of using T2-weighted, half-Fourier rapid acquisition with relaxation enhancement, or RARE, dynamic susceptibility contrast magnetic resonance (MR) imaging to depict crossed cerebellar diaschisis. In 10 patients after unilateral supratentorial stroke, crossed cerebellar diaschisis was demonstrated in the relative regional cerebellar blood volume maps obtained with MR imaging. Cerebellar blood volume values for the nonaffected cerebellar hemisphere were significantly larger than those for the affected side (P = .0003).

[Dynamic susceptibility contrast MRI with echo planar imaging using 1.0T system: comparison of different EPI sequences]

Dynamic susceptibility contrast MRI has been performed using the gradient echo sequence on conventional MR imagers. On echo planar imaging (EPI) devices, not only gradient-echo EPI but also spin-echo EPI allow for the monitoring of contrast agent-induced changes in susceptibility. The purpose of this study was to evaluate the contribution of each EPI pulse sequence to susceptibility-induced delta R2(*) through the first pass of a bolus of Gd-DTPA. Thirty healthy volunteers were examined with a 1.0T superconducting MRI unit (IMPACT, Siemens) using EPI. For dynamic susceptibility contrast MRI, we used gradient echo EPI (TE = 60), spin echo EPI (TE = 60) and asymmetric spin echo EPI (TE = 88). Regional relative CBV (rrCBV) maps were generated. On the rrCBV map generated with gradient echo EPI, the high-intensity area of the brain surface was more conspicuous than that generated with spin echo EPI. The rrCBV map generated with asymmetric spin echo EPI represented the contrast between those generated with spin echo EPI and gradient echo EPI. The rrCBV rate between gray matter and white matter with gradient echo EPI was significantly higher than that with spin echo EPI. We suggest that the rrCBV map calculated with spin echo EPI tends to reflect capillary blood volume and the rrCBV map calculated with gradient echo EPI tends to reflect total blood volume.

Evaluation of peri-infarcted hypoperfusion with T2*-weighted dynamic MRI

The purpose of this study was to evaluate cerebral perfusion with T2*-weighted dynamic MRI in the area around the infarcted core. We examined seven patients with subacute cerebral infarction. After bolus injection a gadopentetate dimeglumine, a series of gradient-echo images were recorded in a selected slice. From these images, concentration-time curves were created on a region-of-interest (ROI) basis around infarction for calculating relative regional cerebral blood volume (rrCBV). Brain perfusion single photon emission computed tomography (SPECT) study also was performed with intravenous injection of 123I-labeled N-isopropyl-p-iodoamphetamine (123I-IMP). All patients showed prolonged signal decrease in the area around the infarcted core. ROI analysis showed significantly increased rrCBV compared to the normal side (P < .01, paired t test). The 123I-IMP SPECT study showed that these areas had decreased cerebral blood flow. Theses findings suggest compensatory vascular dilatation due to decreased perfusion pressure. T2*-weighted dynamic MRI is a useful method for detecting compensatory vasodilatation of ischemic insult in the peri-infarcted area.

Age, menopause, bone turnover markers and lumbar bone loss in healthy Japanese women

The change in lumbar vertebral bone mineral density (BMD) during a 2-year study period was examined in 167 healthy middle-aged and elderly Japanese women with reference to age, menopausal status and bone turnover markers at baseline. The perimenopausal and postmenopausal groups of the subjects showed a significant loss of BMD during the study period but the premenopausal women did not. The annual percent decrease of BMD (delta BMD) in the perimenopausal women (-2.40% in average) was significantly greater than that in either of the premenopausal (-0.01%) or over-all postmenopausal women (-0.85%). The subjects who had been postmenopausal for less than 10 years showed a significant bone loss. delta BMD in the postmenopausal women became less marked as the postmenopausal duration increased. The bone loss was accelerated for about 10 years after menopause. The pattern and magnitude of bone loss of Japanese women seemed to be similar to those of Caucasian women. The regression equation for delta BMD based on the bone turnover markers at baseline was shown to be significant in the postmenopausal women and the serum level of bone-specific alkaline phosphatase isoenzyme had a significant relation to delta BMD. However, this equation accounted for only 17.3% of the total variance of delta BMD and, hence, its validity was not sufficiently high for the prediction of bone loss in clinical settings.

Relative contributions of age and menopause to the vertebral bone density of healthy Japanese women

The relative contributions of age and menopause to vertebral bone mineral density were evaluated based on the estimated weights for age- and menopause-related bone loss components using a mathematical model in 177 healthy female volunteers ages 35-81 years, living in a community in Fukui, Japan. Bone mineral density was determined by dual X-ray absorptiometry. The model used was that which afforded the best fit among the eight possible models to the data observed. Each model was composed of a linear function for the age-related component and a different type of function for the menopausal component, without interaction between them. The weights for these components in each model were estimated by the least-squares method. The coefficient of determination and Akaike information criterion disclosed that among the eight models tested, the model affording the best fit was composed of a logarithmic decrease in bone density with an increase in years since menopause, up to 10 years postmenopausal, with no further decline thereafter. In this model, the weights for both components were statistically significant and the type III sum of squares of the menopausal component was greater than that of the age-related component. We suggest that both age and menopause made significant contributions to the decline in vertebral bone mineral density, with the contribution of menopause being greater than that of age.

Fluid attenuated inversion recovery (FLAIR) imaging in acute Wernicke encephalopathy

We report a case of Wernicke encephalopathy in which the FLAIR sequence could reveal involvement of the mammillary bodies. FLAIR imaging was useful in monitoring the lesions as well as in diagnosing Wernicke encephalopathy.

[Bone mineral density of the lumbar spine and its relation to biological and lifestyle factors in middle-aged and aged Japanese women (Part 3). Relationships of physical fitness and lifestyle factors to bone mineral density in premenopausal and postmenopausal women]

We recruited community-dwelling women for participation in a study to investigate the effects of risk factors in lifestyle on bone mineral density (BMD). The subjects were 177 women aged 35 years and over living in a rural area in Fukui Prefecture. Their BMD of the lumbar spine (L2-L4) was determined by dual energy X-ray absorptiometry (DXA). In addition to measurements of height, body weight and grip strength, the lifestyles of the women, including physical load in work, sporting activities, smoking habits, calcium intake, and history of bone fracture were interviewed in detail. Adjusted for age, the BMD significantly correlated to body weight (r = 0.337, p < 0.05 for premenopausal women and r = 0.289, p < 0.01 for postmenopausal women) and body mass index (kg/m2) (r = 0.291, p < 0.05 for premenopausal women and r = 0.190, p < 0.05 for postmenopausal women). These results indicated the lower body weight to be a risk factor for the osteoporotic process in middle-aged and aged women. With respect to the grip strength as a physical fitness indicator, a significant correlation coefficient (r = 0.267, p < 0.01) with BMD was obtained for postmenopausal women independent of age and body weight. In univariate analysis, BMD showed no significant correlations with sporting activities, smoking habits, lower back pain and history of bone fracture for either premenopausal women or postmenopausal women.(ABSTRACT TRUNCATED AT 250 WORDS)

MR imaging of monostotic fibrous dysplasia of the clivus. A case report

We describe the MR appearance of a case of monostotic fibrous dysplasia confined to the clivus. The lesion showed intermediate signal intensity on T2-weighted images which is uncommon among clival diseases.