‘‘Beet-ing’’ the Mountain: A Review of the Physiological and Performance Effects of Dietary Nitrate Supplementation at Simulated and Terrestrial Altitude

Exposure to altitude results in multiple physiological consequences. These include, but are not limited to, a reduced maximal oxygen consumption, drop in arterial oxygen saturation, and increase in muscle metabolic perturbations at a fixed sub-maximal work rate. Exercise capacity during fixed work rate or incremental exercise and time-trial performance are also impaired at altitude relative to sea-level. Recently, dietary nitrate (NO3-) supplementation has attracted considerable interest as a nutritional aid during altitude exposure. In this review, we summarise and critically evaluate the physiological and performance effects of dietary NO3- supplementation during exposure to simulated and terrestrial altitude. Previous investigations at simulated altitude indicate that NO3- supplementation may reduce the oxygen cost of exercise, elevate arterial and tissue oxygen saturation, improve muscle metabolic function, and enhance exercise capacity/ performance. Conversely, current evidence suggests that NO3- supplementation does not augment the training response at simulated altitude. Few studies have evaluated the effects of NO3- at terrestrial altitude. Current evidence indicates potential improvements in endothelial function at terrestrial altitude following NO3- supplementation. No effects of NO3- supplementation have been observed on oxygen consumption or arterial oxygen saturation at terrestrial altitude, although further research is warranted. Limitations of the present body of literature are discussed, and directions for future research are provided

Microplot research supports the existence of virulence phenotypes in populations of reniform nematode endemic in Louisiana

Microplot studies were conducted to assess virulence phenotypes of populations of reniform nematode (Rotylenchulus reniformis) endemic in Louisiana. Reniform nematode populations were derived from single egg mass collected from West Carrol, Rapides, Morehouse, and Tensas parishes in Louisiana. Trials were conducted using the upland cotton cultivars (Gossypium hirsutum) Phytogen 499 WRF, Deltapine 1133 B2RF, and Phytogen 333 WRF that are recommended for use in Louisiana. Experiments were established as a 3 X 4 X 5 design (cotton cultivars X isolates of reniform nematode X replications) with inoculum level of 50,000 vermiform life stages of nematodes. After 165 days, nematodes were extracted and enumerated from a 250 cc subsample of soil from each microplot. Plant data collected include number of bolls, seed cotton weight, lint weight, and plant dry weight. A significant difference in reproduction among the reniform nematode isolates was observed. Of the four isolates and across all varieties, the Morehouse isolate displayed the greatest level of reproduction; Tensas and West Carroll were intermediate; and Rapides had the least. Reproduction of Morehouse isolate was 31% greater than that of Rapides isolate. A significant reduction in plant dry weight, numbers of bolls, seed cotton weight, and lint percentage were observed for the nematode inoculated plants when compared with uninoculated controls. Plant dry weight losses caused by West Carrol, Rapides, Morehouse, and Tensas isolate was 26%, 9%, 55%, and 21%, respectively. Number of bolls, seed cotton weight, lint weight, and lint percentage reduction by the most damaging Morehouse isolate were 66%, 59%, 65%, and 14%, respectively. Similarly, number of bolls, seed cotton weight, lint weight, and lint percentage reduction by the least damaging Rapides isolate were 14%, 15%, 19%, and 4%, respectively. Results suggest that endemic populations of reniform nematode behave differently on cotton indicating virulence phenotypes. Cotton varieties, across all isolates, did not differ significantly in terms of reproduction of reniform nematodes. Nematode reproduction in DP1133 was approximately 3% higher than in PHY333, and PHY499. Data obtained from this research supports previous reports of the existence of virulence phenotypes of reniform nematode

Evaluating the resistance of some soybean cultivars on reniform isolates from Louisiana

Nematodes pathogenic to soybeans include soybean cyst, root-knot, lesion, lance and reniform. In 2014, loss from these nematodes was estimated at about 3% in the southern soybean producing states. In the resent years, Rotylenchulus reniformis has become a predominant species damaging to both cotton and soybeans. The use of resistant soybean varieties is the most economical and environmentally friendly management tac-tic. In research reported herein, we evaluated the resistance of known soybean cultivars to two isolates of reniform nematode from Louisiana. A single greenhouse and a single field trial were conducted. In the 60-day-duration greenhouse study, ten-day-old seedlings of each of 14 cultivars were inoculated with 10,000 mixed life stages of the nematode. At 60 days, the numbers of nematodes per 500g of soil was determined for each cultivar. Nematode population densities ranged from 953 to 101,120 vermiform life stages. Culti-vars supporting the highest population levels were MPG 4714N and R04-1268. Cultivars on which final pop-ulation density was lower than the infestation level were Dyna Grow 5575, Delta Grow 4940 and S11-20354. The field study was conducted at the LSU AgCenter, North East research station in Tensas parish, Louisiana. In this trial, fumigated (1,3-dichloropropene) and non-fumigated treatments representing 9 cultivars were employed. Nematode population data were collected at-planting, midseason and at-harvest. Application of the nematicide significantly reduced nematode population levels at all three sampling intervals. Similar to the data from the greenhouse trial, at midseason and at harvest, Delta Grow 4940 and S11-20354 had the lowest reniform nematode populations without fumigation. The cultivar R04-1268 produced the highest nematode populations in the absence of fumigation at both midseason and at-harvest. Application of the nematicide reduced nematode population significantly when compared to those without fumigation. In both the presence and absence of the fumigant, lowest yields were observed with R04-1268, MPG 4714N, and Asgrow 4534. Further studies evaluating the host status of these cultivars should be conducted using reniform isolates from multiple geographical locations