Ability of an ELISA-Based Seed Health Test to Detect Erwinia stewartii in Maize Seed Treated with Fungicides and Insecticides.

Two sets of experiments were done to examine whether seed-treatment chemicals affected the ability of an enzyme-linked immunosorbent assay (ELISA)-based seed health test to detect Erwinia stewartii. The chemicals evaluated included Actellic, Apron, Captan, Cruiser, Gaucho, Maxim, Poncho, Thiram, and Vitavax in 11 seed-treatment combinations. In one experiment, seed-treatment chemicals were evaluated quantitatively in a critical region of ELISA absorbance values near 0.5 using maize seed that were spiked with uniform quantities of a liquid suspension of E. stewartii. The number of bacteria in each sample was estimated from ELISA absorbance values using standard curves. Log CFU of E. stewartii per sample were not significantly different among the untreated control and the 11 seed treatments compared with Tukey's Studentized Range Test (P = 0.05). Means of log CFU/ml for all treatments were tightly clustered around 5.70 which corresponded to an absorbance value of 0.440 and a bacterial population of about 500,000 CFU/ml. In a second set of experiments, seed treatment chemicals were evaluated based on qualitative decisions that resulted from the ELISA-based seed health test of seed lots of Jubilee and A632 infected with E. stewartii. The number of negative samples was not substantially greater than expected based on binomial probabilities except for samples of Captan/Vitavax-treated A632, which we considered to be a type I error. The mean absorbance values of positive samples ranged from 1.42 to 1.72 for A632 and from 1.51 to 1.91 for Jubilee and did not differ significantly among the seed treatments. There was no consistent evidence from these experiments that fungicide or insecticide seed treatments interfered with the sensitivity of the ELISA or altered low (e.g., 0.5) or high (e.g. 1.4 to 1.9) absorbance values. The ability of the ELISA-based seed health test to detect E. stewartii in maize seed was not affected by these seed treatments.

Relationship Between Late-Season Severity of Stewart's Bacterial Wilt and Seed Infection in Maize.

The relationship between the amount of foliar disease on maize plants and seed contamination by the causal bacterium, Pantoea stewartii, was studied by comparing disease severity on adult plants with results from laboratory seed tests. Seventy-seven naturally infected maize lines (25 in 1990 and 52 in 1992) were selected and assigned to one of six disease severity classes based on the percentage of ear leaf tissue killed by Stewart's wilt: trace to 2%, 6 to 14%, 25 to 34%, 35 to 49%, 50 to 74%, and 75 to 100%. Ears were harvested from 10 to 20 plants representative of the disease class for each maize line, and seeds were tested by enzyme-linked immunosorbent assay (ELISA) of bulk-seed samples. Seed infection percentages were estimated from the bulk-test results by using statistical equations for group testing. The accuracy of the bulk-seed method for estimating seed infection was validated by comparison with 300-kernel single-seed tests. Infected seed was detected only from seed of plants with ≥25% disease severity; however, 45 of 63 such seed lots had no infection. Three seed lots had >5% infected seeds, all from plants with >50% disease severity. The results suggest a possible threshold level between 15 and 25% disease severity for Stewart's wilt on leaves before bacteria are detected in seed. This study describes a relatively simple method for estimating the incidence of infected seeds in a seed lot and contributes additional evidence to indicate that the chance of spreading P. stewartii from U.S.-produced maize seeds is low.

Seed Transmission of Pantoea stewartii in Field and Sweet Corn.

Seed transmission of Pantoea stewartii was evaluated by assays of more than 76,000 plants in greenhouse and field grow-out trials. Fourteen P. stewartii-infected seed lots were obtained from two dent corn inbreds and two sweet corn cultivars that were inoculated with either a rifampicin and nalidixic acid-resistant strain (rif-9A) or a wild-type strain (SS104) of P. stewartii. Four additional seed lots were collected from naturally infected inbreds. Percentages of infected kernels ranged from 0.8 to 72%, as determined by agar plating or by individual-kernel enzyme-linked immunosorbent assay (ELISA). Plants grown from this seed were assayed by a stem-printing technique that consisted of cutting and pressing a cross-section of each stem onto agar media. Prints were examined for development of P. stewartii colonies after 24 and 48 h. The transmission rate from seed produced on the inoculated plants was 0.066% (28 of 42,206 plants), based on all seedlings assayed. Transmission was estimated to be 0.14% from infected kernels. The transmission rate from seed produced on naturally infected plants was 0.0029% (1 of 34,924 plants), based on all seedlings, and 0.022% from infected kernels. Seed transmission occurred significantly less often (P = 0.034) from seed produced on naturally infected plants than from seed produced on inoculated plants, probably due to greater kernel damage caused by ear shank inoculation. The rarity of seed transmission of P. stewartii from heavily infected seed lots that would ordinarily be rejected due to poor germination suggests that the likelihood of seed transmission from good quality commercial seed corn is virtually nonexistent.

Detection of Asymptomatic Fungal Infections of Soybean Seeds by Ultrasound Analysis.

Different levels of asymptomatic, seed-borne infection by storage fungi (Aspergillus and Penicillium spp.) or Phomopsis seed decay (PSD) (Phomopsis longicolla, Diaporthe phaseolorum var. sojae, and D. phaseolorum var. caulivora) were induced in sub-lots of separate soybean seed lots by incubation of seeds or pods, respectively, for different times at 25°C and at a relative humidity >95%. Seeds were then air-dried to a constant moisture content in the laboratory atmosphere, and each sub-lot was tested for incidence of infection, germination, and moisture content. Individual seeds in each sub-lot also were dropped 10 cm onto a transducer in an ultrasound analyzer. The average peak value of the ultrasound signals for each sub-lot, which indicates the weight of seeds, decreased linearly as the incidence of seed infection by storage fungi (r2 = 0.85) or PSD (r2 =0.82) increased. The slope and width of the signal, which indicates seed softness, increased as seed infection increased for both groups of fungi, although coefficients of determination were lower (r2 ranged from 0.42 to 0.59). Germination values, which decreased as seed infection for both pathogens increased, showed similar but inverse relationships to ultrasound parameters. Peak values of ultrasound signals decreased, and slope and width increased, as seed moisture content increased for sub-lots of soybeans at three levels of infection by Phomopsis seed decay. The potential for ultrasound technology to identify soybean seeds with asymptomatic infections of seed-borne pathogens was thus established.

Importance of Different Pathways for Maize Kernel Infection by Fusarium moniliforme.

ABSTRACT The relative importance of several infection pathways (silks, stalks, and seed) leading to kernel infection of maize hybrids by Fusarium moniliforme was investigated in field experiments in 1993 and 1994. Systemic movement of specific fungal strains within plants was detected by using vegetative compatibility as a marker. Transmission of F. moniliforme from inoculated seed to stalks and developing kernels was detected in two of three field experiments; the seed-inoculated strain was detected in kernels on approximately 10% of ears. The percentage of kernels infected with the seed-inoculated strain ranged from 0 to 70%, with a mean of 0 to 2.5% (0 to 8.3% of F. moniliforme-infected kernels). Other pathways to kernel infection were more effective than seed transmission and systemic infection. F. moniliforme strains inoculated into the crowns and stalks of plants were found throughout the stalks and in up to 95% of the kernels in individual plants. Infection through the silks was clearly the most effective pathway to kernel infection. This was the only inoculation method that significantly increased overall incidence of F. moniliforme infection in kernels; the silk-inoculated strain infected up to 100% of the kernels in individual ears, with a treatment mean as high as 83.7% of kernels. When plants were silk-inoculated, the percentage of kernels infected by other F. moniliforme strains from the seed or stalk was reduced, apparently due to competition among strains. This study provides evidence that systemic development of F. moniliforme from maize seed and stalk infections can contribute to kernel infection, but silk infection is a more important pathway for this fungus to reach the kernels.

Waste Corn as a Point Source of Inoculum for Aspergillus flavus in the Corn Agroecosystem.

Sporulation of Aspergillus flavus was detected on kernels in deposits of waste corn close to corn storage cribs and bins at 18 locations throughout Iowa in 1991 and 1992. A. flavus was detected in spore traps located 3 m from the deposits and was isolated from nitidulid beetles within the deposits or in insect traps within 3 m of the deposits. A. flavus also was isolated from asymptomatic corn kernels in the deposits and from soil beneath the deposits. Linear dispersal gradients of airborne conidia of A. flavus, sampled at distances of 2, 6, 10, and 14 m from waste corn deposits into adjacent cornfields, were detected at three sampling times between 28 July and 1 September 1992 at Cedar Rapids and Williamsburg, Iowa. Linear dispersal gradients from the deposits also were detected for A. flavus-infested nitidulid beetle species Carpophilus lugubris and Glischrochilus quadrisignatus. The incidence of A. flavus infection on corn leaves, silks, and kernels in the fields adjacent to the deposits were correlated to numbers of airborne conidia at each sampling time at both locations. In a field experiment in Ames in which waste corn was placed in the center of individual corn plots, linear dispersal of conidia of A. flavus and plant infection gradients similar to those found from natural deposits were detected at distances of 1.7 to 8.5 m from the deposits at four sampling times from 6 August to 26 September 1992. Few airborne conidia of A. flavus were detected, and no infection of leaves, silks, and kernels by A. flavus occurred in the corresponding noninfested control plots. This study showed that deposits of waste corn infested with A. flavus found in the vicinity of corn storage cribs and bins are point sources of inoculum for A. flavus in the corn agroecosystem.

The perinatal nurse practitioner: an innovative model of advanced practice.

When a major urban hospital received notice it would no longer have resident physicians to serve its perinatal population, nurses and physicians joined forces with a private university to develop a curriculum for advanced level caregivers. This willingness to rise to a challenge helped to create the Perinatal Nurse Practitioner Program and has paved the way for other needed inpatient nurse practitioner roles.

Results of surgical treatment for hyperparathyroidism associated with renal disease.

Recently, the role and timing of surgery for treating secondary and tertiary hyperparathyroidism (HPT) have been questioned. In order to delineate the indications for surgery in these patients, a retrospective analysis of 53 consecutive patients treated with parathyroidectomy was conducted. Subtotal thyroidectomy was done in 37 of 45 patients undergoing their initial operations for HPT. Eight additional patients were referred after failed operations. Of 33 patients with preoperative bone pain, 70% improved. Joint pain improved in 87% of 30 patients, pruritus improved in 81% of 27 patients, and preoperative malaise improved in 73% of 33 patients after parathyroidectomy. Abdominal pain and irritated eyes were unlikely to improve. The best predictors of a successful outcome were a markedly elevated preoperative immunoreactive parathyroid hormone (mid-region) level and an elevated alkaline phosphatase level. There were no perioperative deaths. One patient (1.6%) had a recurrent laryngeal nerve injury, and one patient required reoperation for a neck hematoma. No patient had permanent hypoparathyroidism, but transient hypocalcemia (less than 7 mg/dL) occurred in 22%. Postoperative hypocalcemia correlated with elevated preoperative alkaline phosphatase levels (r2 = 0.247).