System design and production practices of aquaponic stakeholders.

Aquaponics is an agricultural practice incorporating aquaculture and hydroponic principles. This study assesses the current system design and production practices of the aquaponic industry, compares these metrics by stakeholder group, identifies trends, and provides recommendations for future development. An electronic survey of aquaponic stakeholders was conducted from December 2019 to June 2020 targeting hobbyists, producers, and educators from various aquaponic-focused professional associations, email and social media groups. Of 378 total responses, 84% came from the United States and were clustered in plant hardiness zones five to nine. Aquaponic systems were commonly homemade/do-it-yourself (DIY), many of which incorporated commercially available (turn-key) technology. Most growers used coupled systems that integrated recirculating aquaculture systems and either deep-water culture (DWC) or media bed hydroponic units. Common plant lighting sources were sunlight and light emitting diode (LED). Water sources were typically municipal or wells. Personal labor input was typically less than 20 hrs/wk. Funding sources were primarily personal funds, followed by government grants, and private investor funds. System sizes varied greatly, but the median area was 50 to 500 ft2 for hobbyists and educators and 500 to 3,000 ft2 for producers. Respondents commonly sold vegetable produce, training and education, food fish, and microgreens. Tilapia and ornamental fish were commonly grown, with 16 other species reported. Common crops were lettuce, leafy greens, basil, tomatoes, peppers, and herbs with many additional lesser-grown crops reported, including cannabis. Overall, the industry still growing, with a large portion of stakeholders having less than two years of experience. However, veteran growers have remained in operation, particularly in the producer and educator groups. The survey results suggest a shift away from outdoor systems, media beds, tomatoes, ornamental fish, and perch production, and a shift toward decoupled systems, DWC, drip irrigation, and wicking beds, larger system area, leafy greens, and trout/salmon production compared to previous industry surveys. The reduced diversity of plant species grown suggest some level of crop standardization. Commercial producers tended to sell more types of products than other stakeholders, suggesting that diversification of offerings may be key to profitability. The combined production area specified by respondents indicates the industry has grown substantially in recent years. Finally, the presence of bank loan-funded operations suggests increased knowledge and comfort with aquaponics among lenders.

Isolated hepatic perfusion for lapine liver metastases: impact of hyperthermia on permeability of tumor neovasculature.

BACKGROUND: Hyperthermic isolated hepatic perfusion (IHP) has been shown to cause significant regression of advanced unresectable liver metastases in patients. Although there are different agents and treatment modalities used in IHP, the contribution of perfusion hyperthermia is unknown. PURPOSE: A large animal model of unresectable liver metastases and a technical standard for IHP in this model were established. This model was used to assess the effects of hyperthermia on vascular permeability of tumors and normal liver tissue during IHP. METHODS: Sixty-five New Zealand White rabbits were used in a series of experiments. Disseminated liver tumors were established by direct injection of 1 x 10(6) VX-2 cells into the portal vein by laparotomy in anesthetized animals. Several surgical perfusion techniques were explored to determine a reliable and reproducible IHP model. Vascular permeability in tumor versus liver was then assessed with Evan's Blue labeled bovine albumin under normothermic (tissue temperature 36.5 degrees C +/- 0.5 degree C), moderate hyperthermic (39 degrees C +/- 0.5 degree C), or severe hyperthermic (41 degrees C +/- 0.5 degree C) conditions. RESULTS: Tumor model and perfusion techniques were successfully established with inflow through the portal vein and outflow through an isolated segment of the inferior vena cava. A gravity driven perfusion circuit with stable perfusion parameters and complete vascular isolation was used. Vascular permeability was higher in tumor than in normal tissues (P = .03) at all time points during IHP. Hyperthermia resulted in a significant (up to 5-fold) increase in permeability of neovasculature; when severe hyperthermia was used, tumor vascular permeability was increased even more than normal liver permeability (P = .01). CONCLUSIONS: The VX-2/New Zealand White rabbit system can be used as a reproducible large-animal model for IHP of unresectable liver metastases. It can be used to characterize the contribution and mechanism of action of different treatment parameters used in IHP. Hyperthermia preferentially increases vascular permeability in tumors compared with liver tissue in a dose-dependent fashion, thus providing a mechanism for its presumed benefit during isolated organ perfusion.

Tumor-specific gene delivery using recombinant vaccinia virus in a rabbit model of liver metastases.

BACKGROUND: Several approaches to gene therapy for cancer have yielded promising results in rodent models. The translation of these results to the clinical realm has been delayed by the lack of tumor models in large animals. We investigated the pattern of transgene (i. e., foreign or introduced gene) expression and virus vector elimination after systemic gene delivery using a thymidine kinase-negative vaccinia virus in a rabbit model of disseminated liver metastases. METHODS: VX-2 rabbit carcinoma cells were maintained by serial transplantation in the thigh muscles of New Zealand White rabbits, and disseminated liver metastases were established by direct injection of tumor cells into the portal vein of the animals. Different doses of a recombinant thymidine kinase-negative vaccinia virus vector encoding the firefly luciferase reporter gene (i.e., transgene) were injected into tumor-bearing rabbits. Transgene activity in tumors and other organs was measured at multiple time points thereafter. The pattern of development of antibodies against the vaccinia virus vector was also examined. Two-tailed Student's paired t test was used for comparisons of transgene activity. RESULTS: Transgene expression was increased in tumors by at least 16-fold in comparison with expression in other tissues by day 4 after vector injection (all P<. 001) and was maintained for approximately 1 week, providing evidence of tumor-specific gene delivery in this model. Rapid elimination of the circulating vector by the host immune system was observed. Anti-vector antibodies were detectable in serum as early as day 6 and were maintained for more than 3 months. CONCLUSIONS: Tumor-specific gene delivery is possible after systemic injection of a thymidine kinase-negative vaccinia virus vector in a model of rabbit liver metastases. Although the period of transgene expression appears limited because of a rapid immune response, the therapeutic window might be sufficient for an enzyme/prodrug gene therapy approach in clinical application.

Chemisorption and chemical reaction effects on the resistivity of ultrathin gold films at the liquid-solid interface.

Ultrathin gold films, with thicknesses between the onset of conductivity (d ∼ 5 nm) and the electron mean free path (d ∼ 80 nm), display surface-sensitive resistivities, which have been exploited to follow the adsorption and desorption of molecular monolayers at the metal-solution interface with high precision. For nominal Au film thicknesses (d ∼ 40 nm), strongly chemisorbed thiolate monolayers increase the resistivity of the thin Au films by ∼4%, but weakly adsorbed species, such as pyridine or phenolate at open circuit, induce no observable change in the Au film resistance. Resistivity measurements implemented with a high-stability current source and high-precision digital voltmeter sampling at 1 Hz resulted in 3σ uncertainties in alkanethiolate coverage of 1.4 × 10(-)(4) monolayer. Surface plasmon resonance measurements, performed simultaneously with resistivity measurements, indicate that changes in resistivity vary monotonically with coverage with three distinct regions: a low-coverage region of heightened adsorbate mobility, an intermediate-coverage region with generally linear behavior, and a chain length-dependent saturation region at high coverages. Resistivity measurements were also capable of reproducibly following the chemical state of the Au surface through a complex set of redox manipulations, demonstrating the versatility of this simple measurement.

Clinical toxicity of peripheral nerve to intraoperative radiotherapy in a canine model.

PURPOSE: The clinical late effects of intraoperative radiotherapy (IORT) on peripheral nerve were investigated in a foxhound model. METHODS AND MATERIALS: Between 1982 and 1987, 40 animals underwent laparotomy with intraoperative radiotherapy of doses from 0-75 Gy administered to the right lumbosacral plexus. Subsequently, all animals were monitored closely and sacrificed to assess clinical effects to peripheral nerve. This analysis reports final clinical results of all animals, with follow-up to 5 years. RESULTS: All animals treated with > or = 25 Gy developed ipsilateral neuropathy. An inverse relationship was noted between intraoperative radiotherapy dose and time to neuropathy, with an effective dose for 50% paralysis (ED50) of 17.2 Gy. One of the animals treated with 15 Gy IORT developed paralysis, after a much longer latency than the other animals. CONCLUSIONS: Doses of 15 Gy delivered intraoperatively may be accompanied by peripheral neuropathy with long-term follow-up. This threshold is less than that reported with shorter follow-up. The value of ED50 determined here is in keeping with data from other animal trials, and from clinical trials in humans.

Use of arthroscopy in the evaluation and treatment of chronic wrist pain.

Chronic wrist pain can be frustrating for the hand surgeon. The most critical portion of the evaluation is the history and physical examination, which will lead to the various diagnostic modalities available. Table 2 is a summary of some of the more common tests and their uses. Wrist arthroscopy is one of the more useful tools available to the hand surgeon, being both diagnostic and therapeutic. The algorithms developed in this paper are by no means exhaustive or all encompassing. Rather they should be viewed as a guide to assist the hand surgeon in the treatment of these difficult problems.

Tolerance of the bladder to intraoperative radiation in a canine model: a five-year follow-up.

PURPOSE: Late effects of intraoperative radiation therapy (IORT) on bladder were investigated in a canine model. METHODS AND MATERIALS: After laporatomy and cystotomy in adult female foxhounds weighing 25-35 kg, 12 MeV electrons were delivered intraoperatively to a 5 cm circular bladder field which included the trigone and both uretero-vesicle junctions. Each animal received doses of 0, 20, 25, 30, 35, or 40 Gy. All the dogs were followed 5 years postoperatively. An unoperated dog receiving no surgery or radiation treatment was followed as a control. Close clinical monitoring was performed with regular cystometrics and intravenous pyelography. Animals were killed as scheduled with complete necropsies, including histopathology, with special attention to genitourinary structures. RESULTS: There were no acute or late bladder complications detected clinically in any animal. The dog receiving 30 Gy IORT developed rhabdomyosarcoma in the treatment field at 58 months. On follow-up testing over 5 years, there was no loss of bladder contractility on cystometry, and mild changes in the ureters on intravenous pyleography when animals receiving IORT were compared with baseline pretreatment values or with control animals. Histologically, a difference was evident between irradiated and unirradiated animals, but the changes were not clearly dose-related. CONCLUSION: Intraoperative radiation therapy may by safely delivered to the canine bladder with few acute or chronic complications. It is an approach which has potential for clinical use and should continue to be explored in human clinical trials.

Effects of intraoperative radiotherapy on vascular grafts in a canine model.

PURPOSE: The effects of intraoperative radiotherapy +/- external beam radiotherapy on prosthetic vascular grafts were investigated in a canine model. METHODS AND MATERIALS: In 1986 and 1987, 30 adult beagles underwent laparotomy with transection and segmental resection of the infrarenal aorta followed by immediate reconstruction with a prosthetic graft. Intraoperative radiotherapy at varying doses from 0-30 Gy was then administered to all animals. Half of the dogs received 36 Gy external beam radiotherapy in 10 fractions postoperatively. Animals were sacrificed and necropsied at predetermined intervals and as clinically indicated to assess early (< or = 6 months) and late (> 6 months) effects to the vascular graft and surrounding normal tissue. RESULTS: Histopathologic analyses of irradiated vascular structures were performed and correlations were made with the clinical outcome. The most frequent early clinical toxicity was graft thrombosis, occurring in 7 of 10 animals followed for < or = 6 months. Early graft thrombus formation appeared unrelated to radiotherapy dose and probably represented a technical surgical complication. Anastomotic stenosis of varying severity occurred in most animals followed > 6 months. Late (> 6 months) graft stenosis was correlated with intraoperative radiotherapy dose. At < or = 20 Gy of intraoperative irradiation, 3 of 14 animals developed late graft occlusion; at > 25 Gy, five of six animals developed late occlusion. On histopathologic review, increasing intraoperative dose and increasing total radiotherapy dose (intraoperative+external beam) appeared to correspond with increasing severity of graft changes seen after 6 months of follow-up. CONCLUSIONS: Thrombus formation is a frequent early complication of vascular graft placement of the infrarenal aorta in our beagle dog model. Intraoperative doses up to 20 Gy appear to contribute minimally to late graft occlusion, while doses > or = 25 Gy contribute to late occlusion with high likelihood. Both intraoperative dose and total radiotherapy dose correlated with late graft occlusion, and with histopathologic changes in the graft and anastomoses.

Late effects of intraoperative radiation therapy on retroperitoneal tissues, intestine, and bile duct in a large animal model.

PURPOSE: The late histopathological effects of intraoperative radiotherapy (IORT) on retroperitoneal tissues, intestine, and bile duct were investigated in dogs. METHODS AND MATERIALS: Fourteen adult foxhounds were subjected to laparotomy and varying doses (0-45 Gy) of IORT (11 MeV electrons) delivered to retroperitoneal tissues including the great vessels and ureters, to a loop of defunctionalized small bowel, or to the extrahepatic bile duct. One control animal received an aortic transection and reanastomosis at the time of laparotomy; another control received laparotomy alone. This paper describes the late effects of single-fraction IORT occurring 3-5 years following treatment. RESULTS AND CONCLUSION: Dogs receiving IORT to the retroperitoneum through a 4 x 15 cm portal showed few gross or histologic abnormalities at 20 Gy. At doses ranging from 30-45 Gy, radiation changes in normal tissues were consistently observed. Retroperitoneal fibrosis with encasement of the ureters and great vessels developed at doses > or = 30 Gy. Radiation changes were present in the aorta and vena cava at doses > or = 40 Gy. A 30 Gy dog developed an in-field malignant osteosarcoma at 3 years which invaded the vertebral column and compressed the spinal cord. A 40 Gy animal developed obstruction of the right ureter with fatal septic hydronephrosis at 4 years. Animals receiving IORT through a 5 cm IORT portal to an upper abdominal field which included a defunctionalized loop of small bowel, showed a few gross or histologic abnormalities at a dose of 20 Gy. At 30 Gy, hyaline degeneration of the intestinal muscularis layer of the bowel occurred. At a dose of 45 Gy, internal intestinal fistulae developed. One 30 Gy animal developed right ureteral obstruction and hydronephrosis at 5 years. A dog receiving 30 Gy IORT through a 5 cm portal to the extrahepatic bile duct showed diffuse fibrosis through the gastroduodenal ligament. These canine studies contribute to the area of late tissue tolerance to IORT.

The locked metacarpophalangeal joint: report of four cases and review of the literature.

Four cases of locked finger metacarpophalangeal joints are reported. Two of these cases were caused by entrapment of the sesamoid behind an exostosis off the second metacarpal head. The third was from subluxation of the dorsal interosseous tendon over a dorsal osteophyte on the metacarpal. The fourth was from an exostosis tethering the accessory collateral ligament. Surgical exploration using a palmar approach was the treatment of choice. All patients regained full range of motion within two months. A review of the various causes and treatment options for this unusual condition is presented.

Isolated lung perfusion with tumor necrosis factor: a swine model in preparation of human trials.

Isolated lung perfusion with tumor necrosis factor (TNF) potentially could deliver high doses of drug and avoid systemic toxicity in patients with unresectable lung cancer or metastases. We investigated the feasibility of isolated lung perfusion with TNF in a pig model. Eleven animals had left-sided isolated lung perfusion with no TNF (n = 3), 40 micrograms/kg TNF (n = 2), 80 micrograms/kg TNF (n = 3), and 40 micrograms/kg TNF at moderate (39.5 degrees C) hyperthermia (n = 3). Hemodynamic monitoring and measurement of systemic and pulmonary circuit TNF levels were performed. Surviving animals were electively sacrificed a minimum of 6 months after isolated lung perfusion. All sham-perfused pigs survived. Isolated lung perfusion elevated pulmonary artery pressure, decreased cardiac output, and had minimal effects on mean pressure (15 +/- 0 versus 32 +/- 8 mm Hg, 4.5 +/- 1.1 versus 3.03 +/- 0.03 L/min, 67 +/- 11 versus 61 +/- 2 mm Hg; before versus after 90 minutes of isolated lung perfusion). Both 40 micrograms/kg animals and 2 of the 3 hyperthermic perfusion pigs survived, with 1 requiring pneumonectomy. Of the three 80 micrograms/kg animals, 1 survived, 1 died, and 1 required pneumonectomy. Survivors, compared with dying animals, had lower systemic/pulmonary TNF ratios and lower peak systemic TNF levels. All surviving pigs were electively sacrificed. These data justify phase I human protocols of isolated lung perfusion with TNF and hyperthermia; however, intraoperative leak rates must be monitored to ensure pulmonary isolation because systemic TNF levels may dictate treatment morbidity/mortality.

Intrathoracic photodynamic therapy: a canine normal tissue tolerance study and early clinical experience.

Surgery with intraoperative photodynamic therapy (PDT) has the potential to improve the treatment of pleural malignancies. Before embarking on such treatment in humans, however, thoracic tissue tolerance to PDT was studied. For each of three (1 week, 1 month, and 6 month) study end-points, one control (no Photofrin II [PII]) and four treated animals underwent thoracotomy 72 hours after I.V. injection (6 mg/kg) PII. Red light (630 nm) was delivered (5-40 J/cm2) to the pleural surface (1 cm diameter) of selected thoracic organs. No clinical differences were observed between PDT and control dogs. The control showed no histological changes; however, in the treated animals focal areas of coagulation necrosis were found at 1 week which progressed to fibrosis at 1 month. The extent and depth of injury was proportional to light dose. The lung was the most sensitive; the chest wall was the most resistant. Myocardium had superficial damage, whereas coronary arteries appeared normal. The results provide the basis for proceeding to phase I human trials in the evaluation of PDT as an intraoperative adjuvant treatment in the management of pleural malignancies.

Correction of the severe nonrheumatoid chronic boutonnière deformity with a modified Matev procedure.

Twenty consecutive patients with severe chronic nonrheumatoid deformities were treated with a modification of the Matev procedure. Fourteen of the 20 had normal passive range of motion preoperatively, with the proximal interphalangeal joints lacking 59 degrees of active extension and the distal interphalangeal joints hyperextended 17 degrees. In the other six patients with PIP contracture at the time of reconstruction, PIP joints lacked 68 degrees of active extension and the DIP joints were hyperextended 13 degrees. Follow-up averaged 8 months, and at that time the patients with no contracture had an average of 14 degrees/96 degrees of active motion at the PIP joint and 9 degrees/59 degrees of motion at the DIP joint. The group with contracture had an average of 21 degrees/80 degrees of active motion at the PIP and 13 degrees/41 degrees of motion at the DIP joint. There were 85% good or satisfactory outcomes in the group without contracture and 67% good or satisfactory outcomes in the group with contracture.

Arthroscopic treatment of TFCC lesions.

The TFCC bears axially applied load and stabilizes the distal radioulnar joint. Palmer's classification of TFCC lesions into traumatic and degenerative injuries allows a rational approach to treatment. Wrist arthroscopy provides both diagnostic and therapeutic capabilities in the treatment of these lesions.

Threshold dose for peripheral neuropathy following intraoperative radiotherapy (IORT) in a large animal model.

Radiation injury to peripheral nerve is a dose-limiting toxicity in the clinical application of intraoperative radiotherapy, particularly for pelvic and retroperitoneal tumors. Intraoperative radiotherapy-related peripheral neuropathy in humans receiving doses of 20-25 Gy is manifested as a mixed motor-sensory deficit beginning 6-9 months following treatment. In a previous experimental study of intraoperative radiotherapy-related neuropathy of the lumbro-sacral plexus, an approximate inverse linear relationship was reported between the intraoperative dose (20-75 Gy range) and the time to onset of hind limb paresis (1-12 mos following intraoperative radiotherapy). The principal histological lesion in irradiated nerve was loss of large nerve fibers and perineural fibrosis without significant vascular injury. Similar histological changes in irradiated nerves were found in humans. To assess peripheral nerve injury to lower doses of intraoperative radiotherapy in this same large animal model, groups of four adult American Foxhounds (wt 20-25 kg) received doses of 10, 15, or 20 Gy to the right lumbro-sacral plexus and sciatic nerve using 9 MeV electrons. The left lumbro-sacral plexus and sciatic nerve were excluded from the intraoperative field to allow each animal to serve as its own control. Following treatment, a complete neurological exam, electromyogram, and nerve conduction studies were performed monthly for 1 year. Monthly neurological exams were performed in years 2 and 3 whereas electromyogram and nerve conduction studies were performed every 3 months during this follow-up period. With follow-up of greater than or equal to 42 months, no dog receiving 10 or 15 Gy IORT shows any clinical or laboratory evidence of peripheral nerve injury. However, all four dogs receiving 20 Gy developed right hind limb paresis at 8, 9, 9, and 12 mos following intraoperative radiotherapy. These experimental data suggest that intraoperative doses of less than 20 Gy may not result in clinically significant peripheral nerve injury with follow-up of 3.5 years. Longer (5 yrs) follow-up with planned sacrifice of the remaining dogs is scheduled to assess any late peripheral nerve damage.

Response of canine esophagus to intraoperative electron beam radiotherapy.

Tolerance of esophagus to intraoperative radiotherapy (IORT) was investigated in dogs. Thirteen adult foxhounds were subjected to right thoractomy, mobilization of the intrathoracic esophagus, and IORT to a 6 cm full-thickness esophageal segment using 9 MeV electrons at doses of 0, 2,000, or 3,000 cGy. Dogs were followed clinically and were evaluated at regular intervals after treatment with fiberoptic esophagoscopy, barium swallows, and postmortem histologic evaluations. One sham-irradiated control dog showed no abnormalities during follow-up of 24 months. Seven dogs receiving 2,000 cGy IORT showed transient mild dysphagia and mild esophagitis, but no clinically or pathologically significant complications. Five dogs receiving 3,000 cGy demonstrated severe ulcerative esophagitis within 6 weeks of treatment which progressed to chronic ulcerative esophagitis with stricture formation by 9 months following IORT. One 3,000 cGy dog died at 13 months from an esophageal perforation. On the basis of a pilot experience using 13 experimental animals, it was concluded that intact canine esophagus tolerates IORT well to doses of 2,000 cGy, but doses of 3,000 cGy pose serious and potentially lethal risks. The clinical application of IORT to the treatment of human intrathoracic neoplasms requiring esophageal irradiation should be approached with caution, particularly at doses exceeding 2,000 cGy.

Two cases of chondroid syringoma of the hand.

Two cases of benign chondroid syringoma of the hand are described. Both patients did not have this tumor in the differential diagnosis at the time of operation. The importance of this tumor lies in its recognition. Eighty-two percent of the malignant chondroid syringomas occur in the extremities, and the differences in benign versus malignant presentation are discussed.

Response of the mediastinal and thoracic viscera of the dog to intraoperative radiation therapy (IORT).

IORT may be a potentially useful adjunctive treatment combined with surgery and/or external beam irradiation in treating locally advanced lung and esophageal tumors. To begin investigation of this modality, the tolerance of intact mediastinal structures to IORT was studied using adult American Foxhounds (wt. 25-30 kg). Groups of six animals received IORT to doses of 20, 30, or 40 Gy to two separate intrathoracic ports, using 9 MeV electrons to treat a portion of the collapsed right upper lobe, and 12 MeV electrons to treat the mediastinal structures. A group of three dogs received thoracotomy with sham irradiation. Two dogs from each treatment dose group, as well as one sham-irradiated control, were sacrificed electively at 1, 3, and 12 months following IORT. There were no acute nor late IORT related mortalities. Post-operative weight loss was minimal (average 4.5% of pre-operative weight) for all dogs. Serial esophagrams showed no inflammation or ulceration. No cardiac nor pulmonary changes were noted clinically. At autopsy, the irradiated lung showed evidence of acute pneumonitis at 1 month with progressive fibrosis at 3 months and 1 year. Esophageal reactions were minimal, with only two dogs (one 30 Gy and one 40 Gy) demonstrating histologically confirmed esophagitis at 1 month. Tracheal changes were minimal. Cardiac damage was evident in the right atrial tissues. In several dogs, this cardiac damage ranged from myocardial vascular changes to frank ischemic necrosis noted at 1 and 3 months, and dense fibrosis at 1 year. The phrenic nerves showed normal function, but had evidence of perineural fibrosis. The large vessels demonstrated only mild histologic evidence of irradiation. The results of this large animal study suggest that intact mediastinal structures will tolerate small volume IORT to doses of 20 Gy without significant clinical sequellae. Although the histologic changes in the right atrium and contralateral lung are worrisome, no cardiac nor pulmonary problems arose over the 1 year follow-up. Irradiation of the contralateral lung and other sensitive structures can be reduced by careful selection of electron beam energy and use of custom lead shielding.

Effects of Continuous Cropping of Resistant and Susceptible Cultivars on Reproduction Potentials of Heterodera glycines and Globodera tabacum solanacearum.

The reproductive potentials of Heterodera glycines (mixture of races 3 and 4 and unidentified races) and a tobacco cyst nematode Globodera tabacum solanacearum were studied in the field. The experiments involved four cultivars of soybean Glycine max and four cultivars of Nicotiana tabacum. The reproductive potential of the H. glycines population was high on Essex and Lee 74 soybean but low on Forrest and Bedford over the 3 years (1982-84) of continuous cropping. The reproductive potential of H. glycines was 12% on Forrest and 6% on Bedford in 1982 but increased to 37 and 35% in 1983 and to 71 and 41% in 1984, respectively, on these two cultivars. The reproductive potential of G. tabacum solanacearum was high on McNair 944 and Coker 319 tobacco cultivars and low on VA 81 and PD 4 over the 3 years of cropping. The reproductive potential of G. tabacum solanacearum on VA 81 and PD 4 was 18 and 17% in 1982, 7 and 16% in 1983, and 5 and 5% in 1984, respectively. The changes in reproductive potentials of H. glycines and G. tabacum solanacearum may be related to inherent genetic variability in the systems that control reproduction of the two cyst nematodes and nature of resistance incorporated in the soybean and tobacco cultivars.