This study was designed to quantify the responses of leaf expansion, stomatal conductance, and transpiration of four genotypes of vegetable amaranth [Amaranthus tricolor L. (Hin Choi), A. tricolor L. (Co. 2), A. blitum L. (WS80-192), and A. cruentus L. (RRC 1027)] to soil drying. Two greenhouse experiments were conducted during 1999 and 2000. Soil water status was expressed as the fraction of transpirable soil water (FTSW). Leaf expansion rates, stomatal conductances, and transpiration rates of the stressed plants were determined relative to those of nonstressed plants, and expressed as relative leaf expansion (RLE), relative stomatal conductance (RSC), and relative transpiration (RT), respectively. The rate of soil water extraction differed among genotypes, with RRC 1027 depleting soil water fastest and Hin Choi slowest. Whereas in 1999 all genotypes were equally efficient in soil water use, RRC 1027 extracted a greater volume of transpirable soil water than the other genotypes in 2000. The responses of RLE, RSC, and RT to FTSW were well described by linear-plateau models which allowed calculation of soil-water thresholds for leaf expansion (CL), stomatal conductance (CS), and transpiration (CT). Values for CL were higher than for CS and CT. CL was similar for the four genotypes in each year, whereas, CS and CT differed among genotypes. CS and CT was lowest for Hin Choi and highest for WS80-192. Differences of CL, CS, and CT between the two experiments might have been due to the different soils used in the experiments and the different evaporative demands during the drought cycles. Under drought stress, the reduction of transpiration of vegetable amaranth was due mainly to reduction of stomatal conductance, not to reduction of leaf expansion. The relative reduction of dry weight caused by drought stress was positively correlated with CS or CT across the four genotypes. Variation in CS and CT among amaranth genotypes revealed different responses to drought stress, which could make them suitable for different drought situations.
A shoot-tip necrosis in actively-growing shoot cultures of various species has been observed. Using 3 cultivars of Solatium tuberosum grown on media differing in Ca concentration (0.3, 3.0, and 30 mm Ca), typical necrosis was induced or suppressed. Potatoes at 0.3 mm contained about 0.1% Ca g1 dry weight of shoot and also showed the highest incidence of shoot-tip necrosis, ranging from 48% to 72%, depending on the cultivar. Potatoes grown at 3 or 30 mm Ca contained 0.5% or 3% Ca g−1 dry weight of shoot, respectively, and showed only 0% to 9% necrotic shoots, depending on cultivar. In addition to medium Ca content, Parafilm used as the vessel closure promoted shoot-tip necrosis, but increased levels of Ca in the medium tended to overcome the effect. Although cultivar differences in tissue content of other minerals were apparent, these were not associated with the shoot-tip necrosis problem. We conclude that shoot-tip necrosis is associated with a Ca deficiency in actively-growing shoot cultures.
Seed germination was 90–95% for Kentucky coffeetree [Gymnocladus dioicus (L.) C. Koch] after concentrated sulfuric acid treatment for 120 to 150 minutes; 97–98% for honeylocust (Gleditsia triacanthos va. inermis L.) following 60, 90, or 120 minutes concentrated sulfuric acid scarification; and was 67–72% for redbud (Cercis canadensis L.) after 30, 60, or 90 minutes of concentrated sulfuric acid scarification followed by a 60-day stratification period. Scanning electron micrographs of acid-scarified Kentucky coffeetree, honeylocust, and redbud seed indicated that lumens of the macrosclereid cells on the seed surface were exposed after acid treatment, permitting imbibition of water. Boiling water treatment ruptured the macrosclerid layer, while seed treated with liquid N2 had fissures that did not appear to penetrate the macrosclereid layer.
Pectin is a class of complex polysaccharides that function as hydrating agents and cementing materials for the cellulose network. Pectin has various health benefits, such as decreasing serum cholesterol levels, alleviating diabetes mellitus, and preventing cancer. It has been reported that the cancer prevention effect is closely related to the structure of pectin (galactose-rich, molecular weight <10,000, and methylation degree 50% to 70%). This study was conducted to investigate the variation of grapefruit pectin content due to harvest time. `Rio Red' grapefruit on sour orange rootstock grown at Texas A&M Univ.-Kingsville Citrus Center were harvested every 2 months and analyzed for pectin content, galacturonic acid concentration, methylation degree, and neutral sugar composition. Results showed that lamella contains more pectin than flavedo and albedo. In the lamella, the edible section, the uronic acid content ranged from 85% to 90% from August to April the following year. Methylation degree increased from August (31.89%) to April (46.99%). Total neutral sugar content of lamella pectin decreased from 110.54 to 61.77% mg·g -1. Galactose, arabinose, and rhamnose are the major sugar contents of pectin (85%), and glucose content increased with the season from 3.14 to 13.34 mg·g-1. Molecular weight of pectin was also determined.
The fine fescues are generally considered to be acid-tolerant compared to many other cool-season turfgrasses. However, there is a lack of documentation on aluminum tolerance of fine fescues at both the species and cultivar levels. A total of 58 genotypes belonging to five species or sub-species were screened under greenhouse conditions using solution culture, sand culture, and acid Tatum subsoil. This soil had 69% exchangeable Al and a pH of 4.4. An Al concentration of 640 μM and a pH 4.0 were used in solution screening and sand screening. Differences in Al tolerance were identified at both species and cultivar levels based on relative growth. The genotypes with endophyte infection generally exhibited greater Al tolerance than endophyte-free genotypes. The results indicate that fine fescues vary in Al tolerance and there is potential to improve Al tolerance with breeding and to refine management recommendations for fine fescues regarding soil pH.
Pruning methods 1.5 × 1.5 m (topping and hedging) and stumping to 0.70 m were used on coffee cultivars Guatemalan, Red Catuai, Yellow Caturra, and Mokka. In the hedged treatment, `Mokka' had the longest laterals, followed by `Guatemalan', with `Red Catuai', and `Yellow Caturra' having similar lengths. `Mokka' had the most nodes/lateral. `Guatemalan' showed the fastest growth (height), followed by `Mokka', with `Red Catuai' and `Yellow Caturra' having similar growth. For 0.70-m pruning, vertical lengths of `Guatemalan' were the longest. `Mokka' had the most vertical nodes. `Guatemalan' had the longest vertical internodes, followed by `Red Catuai' and `Yellow Caturra', with `Mokka' having the shortest. `Yellow Caturra' had the most laterals/vertical, followed by `Red Catuai' and `Guatemalan'. `Mokka' had the fewest. Lateral lengths, nodes/lateral, and internode length were similar for all cultivars. Two-meter pruning height may be best for `Red Catuai' and `Yellow Caturra' because of slow growth, shorter laterals, and fewer nodes/lateral. These two cultivars grew well after being stumped due to faster regrowth and more laterals remaining on new verticals. 1.5-m pruning appears optimum for `Guatemalan', but it grew very well after stumping. It may be better to prune `Mokka' to a 2-m height with a narrow canopy remaining because of its good multiple verticals, fast lateral growth from new verticals in canopy but not in full sun, and more vertical nodes but less laterals regrowing from new verticals on main trunks exposed to full sunlight.
Cuttings of sage (Salviaofficinalis `Tricolor'), currant (Ribesaureum), euonymus (Euonymus fortunei var. vegetus), and weigela (Weigela florida `Nana Variegata') were rooted under greenhouse conditions (40% shade) and mist in aerated hydroponic solutions consisting of deionized water, or mixtures of deionized water and nutrients with various levels of electrical conductivity (EC, 0.0625, 0.125, 0.25, and 0.5 dS·m-1) from each of three sources: compost tea from municipal solid waste; wastewater from anaerobic digestion of municipal solid waste; and Hoagland's (control) nutrient solution. Despite differences in species response, rooting tended to be similar with the three nutrient sources. Euonymus rooting percentage increased linearly with increasing EC and was similar with all three nutrient sources (common regression curve, 61% rooting at 0.5 dS·m-1), as did root length (1.4 cm at 0.5 dS·m-1), but root number was unresponsive. Currant rooting percent increased curvilinearly and similarly with nutrient sources (87% calculated maximum rooting at 0.25 dS·m-1), but root number and length were unresponsive. Sage rooting percentage and root number also increased curvilinearly and similarly with nutrient sources (common regression curve, 100% rooting at 0.34 dS·m-1, and 4.1 roots at 0.38 dS·m-1, respectively), as did also root length with the compost tea and Hoagland's (common curve for these two nutrient sources, 11.0 cm at 0.30 dS·m-1), but was unresponsive to wastewater. Weigela was unresponsive to EC or nutrient sources (mean percentage of rooting, 73; root number, 6.5; and root length, 1.9 cm).
There are various clubroot pathogen (Plasmodiophora brassicae) resistance genes within Brassica species with european turnip (B. rapa ssp. rapifera) being identified as potentially the best source of resistance for the development of clubroot-resistant cultivars in chinese cabbage (B. rapa ssp. pekinensis). To use clubroot resistance genes effectively, it is necessary to map these genes so that molecular markers inside or closely linked to these resistance genes can be developed. Using molecular marker-assisted selection, the clubroot resistance genes can be effectively transferred from cultivar to cultivar and from species to species. In this report, one clubroot resistance locus was mapped on linkage group A3 using five segregating populations developed from five chinese cabbage cultivars, suggesting that all the five cultivars shared the same clubroot resistance locus. Furthermore, one of these five chinese cabbage cultivars was used to develop a large segregating population to fine-map this clubroot resistance locus to a 187-kilobp chromosomal region. Molecular markers that are closely linked to the mapped clubroot resistance locus have been developed that can be used for marker-assisted selection in chinese cabbage and canola/rapeseed (B. rapa and B. napus) breeding programs.
Lettuce (Lactuca sativa L.) is the most common leafy vegetable produced hydroponically in the United States. Although hydroponic systems are advantageous due to lower pest and disease pressure, and reduced water and nutrient requirements, the increasing prices of fertilizers, including phosphorus (P), still influences the profitability of hydroponic production of lettuce. Characterizing lettuce germplasm capable of producing high yield using less P inputs may help reduce fertilizer use, production costs, and P loads in wastewater. In this study, 12 lettuce accessions were grown in four experiments in a nutrient film technique system. In the first two experiments, the treatments consisted of two P concentrations (3.1 and 31 mg·L−1). Lettuce cultivated with 3.1 mg·L−1 of P had variable shoot and root biomass, root–shoot ratio, P uptake efficiency, and P utilization efficiency, indicating the existence of genetic variation. Five accessions (‘Little Gem’, 60183, ‘Valmaine’, BG19-0539, and ‘Green Lightning’) were considered efficient to P because produced similar shoot biomass with the low and high P treatments. In the third and fourth experiments, the treatments consisted of two P sources (monosodium phosphate (NaH2PO4) and tricalcium phosphate [TCP; Ca3(PO4)2]. Initially, extra 5 mM of calcium (Ca) was added to the TCP solution to reduce the TCP solubility and, hence, P bioavailability to plants. All accessions produced similar shoot and root weight with both treatments, indicating that the TCP treatment did not cause low-P stress to the plants. After, the extra Ca concentration added to TCP was increased to 10 mM, resulting in low-P stress and a significant reduction in shoot weight of all accessions. Despite the severe P stress, ‘Little Gem’ and 60183 were among the accessions with the least shoot weight reduction in the TCP treatment. Variability was observed in root biomass root–shoot ratio among accessions under the TCP treatment, suggesting that lettuce accessions responded differently to P stress conditions. The genetic variation for P use efficiency (PUE) and PUE-related traits in lettuce grown hydroponically suggests the feasibility of breeding new lettuce cultivars from elite lettuce germplasm adapted to low P availability in hydroponics.
Leaf water potentials did not limit stomatal opening of Vitis labruscana Bailey cv. Concord during the summers of 1972 and 1973 in a New York vineyard. Midday leaf-water potentials ranged from −8 to −16 bars and were closely related to individual leaf irradiance. The diurnal variation of leaf, stem, and fruit cluster water potentials on a typical clear day were about 5, 11, and 6 bars, respectively. Water potential gradients at midday across the root, shoot, and petiole-leaf systems averaged about 10, 1 and 3 bars, respectively. The gradient across the root consistently increased throughout the day relative to plant transpiration rate. Minimum stomatal resistance on days after cold nights (less than 10°C) was 2.7 ± 1.1 s cm-1, while the mean resistance on all other days was 1.0 ± 0.5 s cm-1. Cool night temperatures inhibited stomatal opening and closing independently of leaf water potential.