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  • Author or Editor: J. Creighton Miller Jr. x
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Antioxidants have been widely reported to play an important role in disease prevention. In addition to preventing cancer, stroke, heart diseases, and inflammation, they are also involved in immune surveillance. Since the per capita consumption of potatoes in the U.S. is about 137 lb, even moderate levels of antioxidants in this most important vegetable crop probably have an important human health benefit. About 75% to 80% of antioxidant activity in specialty potatoes is due to phenolics and carotenoids. The objectives of this investigation were to evaluate antioxidant activity and total phenolic and carotenoid content of specialty potato selections from the Texas Potato Variety Development Program, and to identify candidate compounds for cancer cell culture investigations. Potato tubers were also used to identify and quantify individual phenolics and carotenoids. Some 320 specialty selections were screened for antioxidant activity (AA), total phenolic content (TP) and carotenoid content (CC) using DPPH (2,2-Diphenyl-1-picrylhydrazyl), FCR (Folin-Ciocalteu Reagent) and colorimetric assays, respectively. After the initial screening, the top 10% were used for analysis of individual phenolics and carotenoids using HPLC. Wide variability for antioxidant activity, phenolic content, and carotenoid content was found among specialty potato selections, providing evidence for genetic control of theses traits. The specialty selection CO112F2-2P/P (purple flesh, purple skin) had the highest AA (832 μg trolox equivalents/g fw), TP (1553 μg chlorogenic acid equivalents/g fw) and CC (590 μg lutein equivalents/100 g fw). Chlorogenic acid (55% to 60%), caffeic acid (≈5%), gallic acid (18% to 20%), and catechin (18% to 20%) were found to be the most prevalent phenolic acids, and lutein and zeaxanthin were the most prominent carotenoids contributing to antioxidant activity. Gallic acid was identified as the candidate compound for use in cancer cell culture investigations.

Free access

Abstract

A hydroponic experiment was conducted to determine the relationship between mycorrhizal dependency (MD) of cowpea [Vigna unguiculata (L.) Walp.] cultivars and their root morphology. Seeds of 19 cowpea cultivars with known MD levels were inoculated with Glomus fasciculatum and Bradyrhizobium in seedling trays. Twelve-day-old seedlings were transferred to a hydroponic culture system, where they were grown for 5 weeks. Leaf area, length of taproot, total root length, root weight, root abundance, average length of fine roots, number of nodules formed on lateral roots, and total nodule weight differed among cultivars. Less than 5% of the root length was colonized by mycorrhizal fungus in all cultivars. Average length of fine roots was negatively correlated with MD of cowpea cultivars; however, only 27% of the variability in MD was explained by this variable. Therefore, root morphology did not appear to determine MD in cowpea.

Open Access

Abstract

Two greenhouse studies were conducted to investigate the relationship between water stress and N2 fixation among drought-resistant and susceptible cowpea [Vigna unguiculata (L.) Walp.] genotypes. In both experiments, seeds were planted in 7.6-liter black polyethylene pots containing composted sawdust medium and were inoculated with Rhizobium. Throughout the experiments, flowers were removed to maintain vegetative growth. Water stress treatments were imposed by withholding water, while the control plants were watered as needed. The treatments were applied 58 and 56 days after planting (DAP) in the first and 2nd experiments, respectively. In both experiments, leaf water potential (LWP), shoot fresh weight (SFW), shoot dry weight (SDW), root fresh weight (RFW), nodule fresh weight (NW), nodule number (NN), and plant specific activity (PSA) by both in situ and destructive acetylene reduction methods were measured. Repeated observations of in situ acetylene reduction were made 58, 63, and 71 DAP in the first experiment. All other variables were measured 77 to 78 DAP in the first experiment. Single observations of all variables, including in situ and destructive acetylene reduction were made 56, 67, and 81 DAP in the 2nd experiment. Results suggested that resistant genotypes are capable of maintaining LWP and biomass production (as measured by SDW and SFW) during water stress. In addition, the effect of water stress on N2 fixation was far greater than the influence of genotype when genotypes were selected for relative drought resistance. Path analysis revealed that LWP is correlated to N2 fixation in water-stressed plants, and improvement of plant water status via drought resistance should increase N2 fixation potential under drought conditions. Therefore, breeding for drought resistance in conjunction with N2 fixation may be more beneficial than breeding strictly for N2 fixation potential without regard for environmental adaptation. The in situ method of acetylene reduction was found to be useful for detecting physiological changes due to water stress and estimating its genotypic N2 fixation potential.

Open Access

Abstract

Cuticular resistance to water loss was estimated for drought resistant and susceptible cowpea [vigna unguiculata (L.) Walp.] genotypes in a series of field and greenhouse experiments. The procedure consisted of harvesting the youngest, fully-expanded middle trifoliate leaf of a well-watered plant. The detached leaf was weighed immediately and then allowed to dry in an air-conditioned laboratory (about 25°C). Leaves again were weighed 24 and 48 hr after detachment and then oven dried at 70° for 24 hr. Oven dry weight was used to determine leaf water content (LWC) at each sampling time. Specific drought resistant and susceptible genotypes consistently expressed increased or reduced LWC, respectively, 48 hr after detachment. Interestingly, named cultivars generally had even higher LWC values after drying than did the selected resistant genotypes. Intraspecific variability for the trait appears to exist and may be related to drought adaptation in cowpea.

Open Access

Abstract

A field study was conducted to determine the effects of rhizobial inoculation (cowpea ‘EL’ mixed strain) and N-fertilization with 100 kg/ha nitrate nitrogen (CaNO3 — 15.5% N) on seed and biomass yield in cowpea [Vigna unguiculata (L.) Walp.]. Four indeterminate cultivars, ‘Mississippi Silver’, ‘California Blackeye #5’, ‘Lady’, ‘Brown Crowder’, and one determinate, early maturing cultivar, ‘Bush Purple Hull’, were used. Seed yield in inoculated and N-fertilized plants was significantly greater than that of the unfertilized, uninoculated control treatment. Generally, yield of inoculated plants was equivalent to or greater than that obtained with 100 kg N. The indeterminate cultivars yielded more biomass than did ‘Bush Purple Hull’ in all 3 treatments. Seed yield was higher in the indeterminate cultivars with inoculation or N-fertilization than in ‘Bush Purple Hull’; however, there were no significant differences in seed yield among cultivars in the control treatment. Harvest index in the indeterminate cultivars was increased by inoculation but not by N-fertilization. Harvest index of ‘Bush Purple Hull’ was at least 3 times higher than the indeterminate cultivars. Among the major seed yield components, only pods/plant was influenced by all 3 treatments, whereas seeds/pod and seed weight were fairly stable and cultivar specific. Standardized regression analysis revealed that pods/plant was the major component which accounted for the variability in seed yield of inoculated plants within a cultivar, but not in ‘Bush Purple Hull’, where dry matter accumulation/plant/day was the major component. Factor analysis on the yield and N2 fixation components also indicated that cowpea cultivars behaved differently in the expression of traits which influenced seed yield. A measure of genetic divergence among these cultivars using Mahalanobis distances confirmed that the 5 cowpea cultivars differed significantly.

Open Access

Abstract

Plant growth aspects of field-grown cowpea [Vigna unguiculata (L.) Walp.] were investigated under four N regimes: No N, rhizobial inoculation (cowpea “EL” inoculum), 100 kg fertilizer N/ha (NO3-N) at planting, and inoculation + 50 kg fertilizer N/ha at flowering. Five indeterminate cultivars, Brown Crowder, California Blackeye No. 5, Mississippi Silver, Tennessee White Crowder, and Lady, and one determinate cultivar, Bush Purple Hull, were compared. Plant growth variables were measured biweekly starting at the 4th week. Dry matter and leaf area per plant reached maximum at 56 days after planting in all five indeterminate cultivars, and 1 week later in the determinate cultivar. Large-seeded cultivars, California Blackeye No. 5, Mississippi Silver, Brown Crowder, and Tennessee White Crowder, generally produced larger leaves throughout the season than did ‘Bush Purple Hull’ and ‘Lady’. The relative growth rate (RGR) declined linearly with harvest time, irrespective of N treatment. The RGR of ‘Bush Purple Hull’ was lower than that of the indeterminate cultivars throughout the growth period. The net assimilation rate (NAR) of the indeterminate cultivars declined slowly from maximum values at 4 weeks and became negative during pod development. However, ‘Bush Purple Hull’ NAR increased during pod development, but declined very rapidly during late pod development. The leaf area ratio (LAR) declined curvilinearly with time in all N treatments and cultivars. The LAR values were lowest for the determinate cultivar, and the differences among indeterminate cultivars were not significant. Total dry matter, leaf area per plant, and average leaf size of inoculated and N-fertilized plants were greater than the uninoculated and unfertilized control. Nitrogen treatments did not affect physiological components RGR, NAR, and LAR.

Open Access

Abstract

Rhizobial inoculation with commercial cowpea ‘EL’ mixed strain inoculant as compared to noninoculation, and effects of four levels (0, 14, 28, and 84 kg·ha−1) of fertilizer N (CaNO3–15.5% N) on yield and N2 fixation components in cowpea [Vigna unguiculata (L.) Walp.] were investigated in a field study. Plants were grown on a vertic albaqualf, fine, montmorillonitic, thermal soil with a pH of 6.7. Three high (H) and two low (L) N2-fixing, indeterminate cowpea cultivars, ‘H-California Blackeye No. 5’, ‘H-Brown Crowder’, ‘H-Tennessee White Crowder’, ‘L-Lady’, and ‘L-Mississippi Silver’, were used. In inoculated plants, N2 fixation was significantly reduced with increasing N levels. Although high-fixing cultivars produced more and larger nodules and expressed higher nitrogenase activity than the low fixers, no significant differences in top dry weight and total N/plant were observed between these groups at the time of flowering. Seed yield was greater in rhizobia-inoculated plants than in the noninoculated, fumigated controls. A significant linear increase in seed yield was observed with increasing N levels in the noninoculated, fumigated controls. The addition of fertilizer N to cowpeas inoculated at planting did not increase seed yield. In high-fixing cultivars, N2 fixation did not directly influence seed yield, but increased vegetative matter was produced. Seed and biomass yield were influenced by N2 fixation in low-fixing cultivars.

Open Access