Soil salinization is a widespread problem severely impacting crop production. Understanding how salt stress affects growth-controlling photosynthetic performance is essential for improving crop salt tolerance and alleviating the salt impact. Lima bean (Phaseolus lunatus) is an important crop, but little information is available on its growth and leaf gas exchange in relation to a wide range of salinity. In this study, the responses of leaf gas exchange and whole plant growth of lima bean (cv. Fordhook 242) to six salinities with electrical conductivity (EC) of 2.9 (control), 5.7, 7.8, 10.0, 13.0, and 15.5 dS·m−1 in irrigation waters were assessed. Significant linear reduction by increasing salinity was observed on plant biomass, bean yield, and leaf net carbon assimilation rate (A). As EC increased from the control to 15.5 dS·m−1, plant biomass and A decreased by 87% and 69%, respectively, at the vegetative growth stage, and by 96% and 83%, respectively, at the pod growth stage, and bean yield decreased by 98%. Judged by the linear relations, the reduction in A accounted for a large portion of the growth reduction and bean yield loss. Salinity also had a significantly negative and linear effect on leaf stomatal conductance (g S). Leaf intercellular CO2 concentration (Ci) and leaf C13 isotope discrimination (Δ13) declined in parallel significantly with increasing salinity. The A-Ci curve analysis revealed that stomatal limitation [L g (percent)] to A increased significantly and linearly, from 18% to 78% and from 22% to 87% at the vegetative and pod-filling stages, respectively, as EC increased from the control to the highest level. Thus, relatively nonstomatal or biochemical limitation [L m (percent), L m = 100 − L g] to A responded negatively to increasing salinity. This result is coincident with the observed Δ13 salt-response trend. Furthermore, leaf carboxylation efficiency and CO2-saturated photosynthetic capacity [maximum A (Amax)] were unaffected by increasing salinity. Our results strongly indicate that the reduction in lima bean A by salt stress was mainly due to stomatal limitation and biochemical properties for photosynthesis might not be impaired. Because stomatal limitation reduces A exactly from lowering CO2 availability to leaves, increasing CO2 supply with an elevated CO2 concentration may raise A of the salt-stressed lima bean leaves and alleviate the salt impact. This is supported by our finding that the external CO2 concentration for 50% of Amax increased significantly and linearly with increasing salinity at the both growth stages. Leaf water use efficiency showed an increasing trend and no evident decline in leaf chlorophyll soil plant analysis development (SPAD) readings was observed as salinity increased.
Nick E. Christians and Dianna L. Liu
It has previously been reported that a byproduct of the corn (Zea mays L.) wet-milling process, corn gluten meal, has potential as a natural preemergence herbicide for use in turf and certain horticultural crops. In 1993, two additional patents were issued on the technology. The first is on the use of hydrolyzed proteins from corn and other grains that were shown to have higher levels of herbicidal activity than the corn gluten meal. These materials are water soluble and can be sprayed on the soils surface. The second patent was on 5 dipeptides extracted from the hydrolyzed corn gluten meal. These dipeptides were shown to have the same type of biological activity observed when the corn gluten meal and the hydrolyzed meal are applied to the soil. The possible use of the hydrolyzed grains and the dipeptides as natural preemergence herbicides in horticultural crops will be discussed.
Dianna L. Liu and Nick E. Christians
Corn gluten hydrolysate (CGH) was evaluated in the greenhouse for its herbicidal activity on 19 selected monocotyledonous and dicotyledonous species. Treatments included CGH at 0, 1, 2, 4, and 8 g·dm-2. Plant susceptibility was based on plant survival, shoot length, and root length. The germination and growth of all species were inhibited by the application of CGH at all rates. Black medic (Medicago lupulina L.), buckhorn plaintain (Plantago lanceolata L.), creeping bentgrass (Agrostis palustris Huds.), purslane (Portulaca oleracea L.), and redroot pigweed (Amaranthus retroflexus L.) were the most susceptible species, exhibiting more than 70% reduction in root length, 60% reduction in plant survival, and 52% reduction in shoot length with CGH at 1 g·dm-2. Common lambsquarters (Chenopodium album L.), curly dock (Rumex crispus L.), dandelion (Taraxacum officinale Weber), giant foxtail (Setaria faberi Herrm.), large crabgrass [Digitaria sanguinalis (L.) Scop.], and yellow foxtail [Setaria lutescens (Weigel) Hubb.] exhibited more than 50% reduction in root length and plant survival at 1 g·dm-2. Annual bluegrass (Poa annua L.), barnyardgrass [Echinochloa crusgali (L.) Beauv.], green foxtail [Setaria viridis (L.) Beauv.], orchardgrass (Dactylis glomerata L.), perennial ryegrass (Lolium perenne L.), quackgrass [Agropyron repens (L.) Beauv.], and velvetleaf (Abutilon theophrasti Medic.) survivial was reduced by 60% at 2 g·dm-2. Annual ryegrass (Lolium multiflorum Lam.) was the least susceptible species.
Nick E. Christians and Dianna L. Liu
Field and greenhouse studies on the use of a byproduct of the corn (Zea mays L.) wet-milling process, corn gluten meal, have shown that this high-protein fraction of corn grain contains an organic compound that inhibits root formation of a variety of monocotyledonous and dicotyledonous species. Seeds that germinate in a soil media to which corn gluten meal has been added form normal shoots, but no roots. The seedling quickly dies as the media drys. This inhibition of root formation can be timed to prevent the establishment of weeds in turf areas and other plant systems. Corn gluten meal also contains approximately 10% nitrogen and can be used as a natural fertilizer material. Repeated field trials have shown no detrimental effect of the corn gluten meal on mature grass plants. This combination of a natural fertilizer with a natural weed inhibiting compound may result in a `weed and feed' product for those who do not wish to use synthetic fertilizers and pesticides. A patent on the use of corn gluten meal as a weed control was issued in 1991.
L. Xu, G.F. Liu, and M.Z. Bao
Plantlets were regenerated from in vitro-grown leaf explants of five genotypes of Liquidambar formosana on WPM basal medium supplemented with different concentrations of TDZ and NAA. With the addition of 0.27 μm NAA, regeneration efficiency was increased by 2- to 4-fold over that with TDZ alone. Lower concentrations of TDZ (0.45–2.27 μm) were beneficial for regenerating shoot clusters. Four genotypes (P2, P6, P9, and P11) showed high regeneration rates (up to 90%), whereas genotype P13 showed a low capability for shoot regeneration on all media tested (<35%). For all five genotypes, the optimum medium for inducing adventitious shoots was WPM supplemented with 1.14 μm TDZ and 0.27 μm NAA, on which regeneration rate ranged from 72.6% to 89.5% and adventitious shoot clusters per regenerating leaf explant ranged from 2.63 to 3.11 in four genotypes (P2, P6, P9, and P11), while for P13, the regeneration rate and number of shoot clusters per regenerating explant were 23% and 1.39, respectively. Transfer of shoot clusters to WPM basal medium containing 0.54 μm NAA, 2.22 μm BA, and 1.44 μm GA3, resulted in shoot elongation. All the elongated shoots were rooted on WPM supplemented with 9.84 μm IBA, and plantlets were transplanted to soil successfully.
Chemical names used: 6-benzyladenine (BA), gibberellic acid (GA3), indole-3-butyric acid (IBA), 1-naphthalene acetic acid (NAA), plant growth regulator (PGR), thidiazuron (TDZ), woody plant medium (WPM).
X. Liu, P. Robinson, M.L. Arpaia, and G.W. Witney
Monthly samples were taken from 9-year-old `Hass' avocado trees on Duke 7 rootstock grown at the UC Southcoast Research and Extension Center in Irvine, Calif. Changes in starch and total soluble sugars were monitored from fine and coarse roots, trunk (above the bud union), small diameter stems, leaves, and fruit. When possible, seasonal carbohydrate changes were compared to root and shoot flushing patterns. In all of the vegetative plant organs monitored, total soluble sugars accounted for most of the carbohydrate. Starch accounted for ≈10% of the sample dry weight, whereas the total soluble sugars accounted for ≈18%. D-mannoheptulose and perseitol, both C7 sugars, were the predominant soluble sugars throughout the year. Fructose, glucose, and sucrose accounted for <5% of the total soluble sugars. During fruit development, soluble sugar content of the exo- and mesocarp tissues >25% of the dry weight. The significance of these findings will be discussed in relationship to tree phenology and carbohydrate partitioning.
R.L. Jarret, N. Bowen, S. Kresovich, and Z. Liu
Simple sequence repeats (SSRs) were isolated from a size-fractionated genomic DNA library of sweetpotato [Ipomoea batatas (L.) Lam.]. Screening of the library with five oligonucleotide probes, including; (GT)11, (AT)11, (CT)11, (GC)11, and (TAA)8, detected the occurrence of 142 positive colonies among ≈12,000 recombinants. Automated DNA sequencing revealed the presence of simple, compound, perfect, and imperfect SSRs. Five homologous PCR primer pairs were synthesized commercially and used to screen 30 sweetpotato clones for the occurrence of SSR polymorphisms. All primer pairs produced an amplification product of the expected size and detected polymorphisms among the genotypes examined. The potential for the use of SSRs as genetic markers for sweetpotato germplasm characterization is discussed.
W.T. Liu, C.L. Chu, and T. Zhou
Fumigation with 1 mg·L-1 of thymol vapor retarded mycelial growth of Monilinia fructicola (G. Wint.) Honey. Mean colony diameter was reduced from 49 mm in the control to 13 mm when the conidia were cultured on potato dextrose agar. Fumigation of apricots (Prunus armeniaca L.) with 2 mg·L-1 of thymol vapor reduced the germination of M. fructicola conidia to 2% compared with 98% on untreated fruit. Microscopic observations showed that the spores fumigated with thymol were shrunken and had collapsed protoplasts. In in vivo experiments, surface-sterilized apricots and plums (Prunus salicina L.) were inoculated with conidia of M. fructicola by applying 20 μL of a spore suspension to wounds on the fruit, and then were fumigated with thymol or acetic acid. The incidence of brown rot was reduced to 3% and 32% when `Manch' apricots were fumigated with thymol or acetic acid at 5 mg·L-1, respectively, compared with 64% incidence in untreated fruit. Fumigation of `Violette' plums with thymol or acetic acid at 8 mg·L-1 reduced brown rot from 88% in the control to 24% and 25%, respectively. Fumigation of `Veeblue' plums with thymol at 4 mg·L-1 reduced brown rot from 56% in the control to 14%. Fumigation of apricots with thymol resulted in firmer fruit and higher surface browning, but total soluble solids and titratable acidity were not affected. Fumigation of plum with thymol resulted in higher total soluble solids, but firmness and titratable acidity were not affected. Thymol fumigation caused phytotoxicity on apricots but not on plums.
Clyde Wilson, Xuan Liu, Scott M. Lesch, and Donald L. Suarez
Over the last several years, there has been increasing interest in amending the soil using cover crops, especially in desert agriculture. One cover crop of interest in the desert Coachella Valley of California is cowpea [Vigna unguiculata (L.) Walp.]. Cowpea is particularly useful in that as an excellent cover crop, fixing abundant amounts of nitrogen which can reduce fertilizer costs. However, soil salinity problems are of increasing concern in the Coachella Valley of California where the Colorado River water is a major source of irrigation water. Unfortunately, little information is available on the response of cowpea growth to salt stress. Thus, we investigated the growth response of 12 major cowpea cultivars (`CB5', `CB27', `CB46', `IT89KD-288', `IT93K-503-1', `Iron Clay', `Speckled Purple Hall', `UCR 134', `UCR 671', `UCR 730', `8517', and `7964') to increasing salinity levels. The experiment was set up as a standard Split Plot design. Seven salinity levels ranging from 2.6 to 20.1 dS·m–1 were constructed, based on Colorado River water salt composition, to have NaCl, CaCl2 and MgSO4 as the salinization salts. The osmotic potential ranged from –0.075 to –0.82 MPa. Salt stress began 7 days after planting by adding the salts into irrigating nutrient solution and ended after 5 consecutive days. The plants were harvested during flowering period for biomass measurement (53 days after planting). Data analysis using SAS analysis of variance indicated that the salinity in the range between 2.6 and 20.1 dS·m–1 significantly reduced leaf area, leaf dry weight, stem dry weight and root dry weight (P ≤ 0.05). We applied the data to a salt-tolerance model, log(Y) = a1 + a2X + a3X2, where Y represents biomass, a1, a2 and a3 are empirical constants, and X represents salinity, and found that the model accounted for 99%, 97%, 96%, 99%, and 96% of salt effect for cowpea shoot, leaf area, leaf dry weight, stem dry weight and root dry weight, respectively. We also found significant differences (P ≤ 0.05) of each biomass parameter among the 12 cultivars and obtained different sets of the empirical constants to quantitatively describe the response of each biomass parameter to salinity for individual cowpea cultivars. Since a significant salt × cultivar interaction effect (P ≤ 0.05) was found on leaf area and leaf dry weight, we concluded that salt tolerance differences exist among the tested cultivars.
C.M. Baldwin, H. Liu, L.B. McCarty, W.L. Bauerle, and J.E. Toler
A 2-year greenhouse study was conducted at Clemson University, Clemson, S.C., in 2003 and 2004 to determine drought responses of six bermudagrass (Cynodon spp.) cultivars at four irrigation intervals. Cultivars selected from the 2002 National Turfgrass Evaluation Program Bermudagrass Trial were `SWI-1012', `Arizona Common', `Tift No.3', `Tifsport', `Aussie Green', and `Celebration'. Treatments included 5-, 10-, and 15-day irrigation intervals plus a control (irrigated daily). Volumetric soil water content (VSWC) and evapotranspiration (ET) rates were recorded every 3 days. Turfgrass quality (TQ) was observed weekly and root weight was measured at the end of a 6-week study. `Aussie Green' and `Celebration' produced the highest TQ rating (>7) at week 4 when watered daily. After 4 weeks of the 5-day irrigation interval, all cultivars showed unacceptable quality ratings (<7). However, `Aussie Green' and `Celebration' were able to maintain an acceptable TQ rating (7), compared to `Arizona Common' (5.1) and `Tift No.3' (5.8) at week 2 (5-day treatment). `Celebration' produced 114% and 97% greater root weight than `Tifsport' and `Aussie Green', respectively, when pooled across all irrigation treatments. At the 15-day irrigation interval treatment, six bermudagrass cultivars pooled together produced 78%, 22%, and 11% greater root weight vs. control, 5-day, and 10-day treatments, respectively. When pooled for all treatments, `Aussie Green' and `Celebration' VSWC was 5% and 7% lower than `Tift No.3', and ET rates were 26% and 30% greater than `Arizona Common'. Based on these results, irrigating bermudagrass in 5-day intervals should be carefully monitored.