Root promotion activity in avocado leaf extracts was determined by the mung bean bioassay. Ten different clones representing a wide range of rooting abilities were compared. Following chromatography of methanol extracts in 8 isoprapanol : 2 water (v/v), a positive correlation was found between rooting ability of avocado cuttings and a mung bean rooting promoter at Rf 0.9–1.0 of the chromatograms. The same zone inhibited the straight growth of wheat coleoptile.
The wheat coleoptile straight-growth test was used to determine the effects of (2-chloroethyl)phosphonic acid (ethephon) on endogenous auxins and inhibitors in seeds of ‘Late Santa Rosa’ plum. Seeds of both developing and abscissing ethephon-treated fruits attained higher levels of auxin activity than did their respective controls suggesting an ethylene-induced inhibition of auxin transport. The level of growth inhibitors remained similar throughout.
Dramatic increases have recently occurred in the productivity of the major food crops (rice, wheat, corn, grain sorghum, potatoes). These advancements have characterized a worldwide “green revolution” and received much publicity (2). An equally remarkable and parallel record of production efficiency, accompanied by an enhancement of quality, has also occurred with most fruits and vegetables (7). Many of these remarkable changes have transpired where as an increasingly greater percentage of the commodity is being utilized in the processed form.
Sweet onions (Allium cepa L.) are typically grown on bare soil and irrigated with high-pressure systems such as sprinklers or center-pivots. The objective of this study was to determine the effects of irrigation system and mulch on bolting, bulb yield and bulb quality over 3 years. The experimental design was a split plot, where the main plot was irrigation system (drip or sprinkler) and the subplot was the type of mulch (bare soil, black plastic film or wheat straw). The results showed that individual bulb weight and bulb yields under drip irrigation were similar to those under sprinkler irrigation. Plants grown on bare soil had the highest total yield during the three seasons and among the highest marketable yield. There were no consistent differences in the bulb number or yield of plants on plastic film mulch compared to those of plants on wheat straw mulch. Plants on wheat straw mulch had reduced foliar nitrogen content. Variability in yields among mulches and seasons was partly explained by changes in seasonal root zone temperature and soil water potential. Total and marketable yields and weight of individual bulbs increased with increasing root zone temperatures up to an optimum at 15.8 °C, followed by reductions in yields and individual bulb weight at >15.8 °C. Onion bolting increased with decreasing foliage nitrogen content, with plants on wheat straw having the highest bolting incidence. Bolting also increased with decreasing root zone temperatures for the season. Total and marketable yields increased with decreasing mean seasonal soil water potential down to -30 kPa. Irrigation system and mulches had no consistent effect on the soluble solids content or pungency of onion bulbs.
Field pennycress (Thlaspi arvense L.) seedmeal was found to suppress seedling germination/emergence and biomass accumulation when added to a sandy loam soil containing wheat (Triticum aestivum L.), arugula [Eruca vesicaria (L.) Cav. subsp. sativa (Mill.) Thell.] and sicklepod (Senna obtusifolia (L.) H.S. Irwin & Barneby) seeds. Covering the pots with petri dishes containing the soil-seedmeal mixture increased phytotoxicity at the lowest application rate, suggesting that the some of the phytotoxins were volatile. Dichloromethane, methanol and water extracts of the wetted seedmeal were bioassayed against wheat and sicklepod radicle elongation. Only the dichloromethane extract was found to be strongly inhibitory to both species. Fractionation of the dichloromethane extract identified two major phytotoxins, identified by GC-MS and NMR analyses as 2-propen-1-yl (allyl) isothiocyanate (AITC) and allyl thiocyanate (ATC), which constituted 80.9 and 18.8%, respectively, of the active fraction. When seeds of wheat, arugula and sicklepod were exposed to volatilized AITC and ATC, the germination of all three species were completely inhibited by both compounds at concentrations of 5 ppm or less.
Ethylene concentrations were monitored using gas chromatography (GC/PID) throughout growth and development of wheat, soybean, and lettuce stands grown hydroponically inside a large, closed growth chamber (20 m2 area, 113 m3 vol.). For wheat (cv. Yecora Rojo), ethylene concentration increased from < 10 ppb to about 120 ppb at about 28 days after planting (pre-anthesis) and then declined sharply over the next 4 weeks to a plateau of about 10 ppb during canopy maturation and senescence. A similar pattern of evolution was measured for soybean stands (cv. McCall), with peak concentrations of 40 to 70 ppb occurring near 50 days after planting. Unlike wheat, a slight increase in ethylene was noted in the latter stages of soybean stand senescence. For lettuce stands (cv. Waldmann's Green), ethylene increased slowly to 10 to 15 ppb by 24 days after planting, and then rose sharply to 40 ppb by 28 days, when plants were harvested. Data will be used to define ranges for phytotoxicity studies and to project atmospheric contaminant control needs for tightly closed plant growth systems.
Leaf stomatal conductance was monitored with a steady-state porometer throughout growth and development of soybean and potato plants grown at 500, 1000, 5000, and 10,000 (potato only) μmol mol-1 carbon dioxide (CO2). All plants were grown hydroponically with a 12-hr photoperiod and 300 μmol m-2 s-1 PPF. As expected, conductance at 1000 was < 500 μmol mol-1 for both species, but conductance at 5000 and 10,000 μmol mol-1 was ≥ that at 500 μmol mol-1. Subsequent short-term (24-hr) tests with potato and wheat plants grown at 1000 μmol mol-1 showed that raising CO2 to approx. 10,000 μmol mol-1 or lowering CO2 to 400 μmol mol-1 increased conductance compared to 1000 μmol mol-1 for potato, while only lowering CO2 to 400 μmol mol-1 increased conductance for wheat. Furthermore, raising the CO2 to 10,000 μmol mol-1 increased dark-period conductance in comparison to 1000 μmol mol-1 for potato, while dark-period conductance for wheat leaves was low regardless of the CO2 concentration. Results suggest that very high CO2 levels (e.g. 5000 to 10,000 μmol mol-1) may substantially increase water use of certain crops.
In 1991, a four year study was initiated in which staked tomatoes and snap beans are rotated annually and grown with three cover crop treatments (wheat, crimson clover, and bareground) and three N rates (0, 60, and 120 kg N/ha) in a RCB with four replications. Crop growth, yield, nutrient status, N cycling, and pest populations are being studied. The first year there was no response to cover crop. The next two years, crimson clover reduced bean yields due, in part, to high levels of disease. Mexican bean beetle populations were also highest with clover and increased with increasing N rate. In 1992, wheat increased tomato fruit crack, but there was no effect on yields. In 1993, wheat reduced early season tomato yields but had no effect on total season yields. Aphid populations were highest on tomatoes grown with crimson clover. The study reveals that cover crop systems are dynamic and long-term studies are required before dependable grower recommendations can be made. This study is part of the Tri-State Vegetable Project, a cooperative research project with N.C., S.C. and Ga.
fermented wheat bran, molasses, and naturally occurring microbes) to the biochar ( Sales et al., 2020 ). With or without bokashi, the biochar increased soil pH by 0.3 units or less, even when it was incorporated at a rate as high as 20% by volume.
The effects of elevated CO2 on stomatal density and index were investigated for five crop species currently being studied for NASA's Advanced Life Support program. Lettuce (cv. Waldmann's Green) and radish (cv. Giant White Globe) were grown at 400, 1000, 5000, or 10,000 μmol·mol–1 CO2, tomato (cvs. Red Robin and Reimann Philip 75/59) were grown at 400, 1200, 5000, or 10,000 μmol·mol–1 CO2, and wheat (cv. Yecora Rojo) and potato (cv. Denali) were grown at 400, 1000, or 10,000 μmol·mol–1 CO2 within controlled-environment growth chambers using nutrient film technique hydroponics. Leaf impressions were made by applying clear silicone-based RTV coating to the adaxial and abaxial leaf surfaces of three canopy leaves of each crop at each CO2 treatment. Impressions were examined using a light microscope, whereby the number of stomatal complexes and epidermal cells were counted to calculate stomatal density and stomatal index. Results indicate that stomatal density increased for lettuce and radish at 10,000 μmol·mol–1 CO2, whereas tomato density was highest at 1200 μmol·mol–1 CO2. Potato had the lowest density at 1000 μmol·mol–1 CO2, and there was no effect of CO2 on density for wheat. Stomatal index correlated with density for lettuce and tomato; however, stomatal index for radish, potato, and wheat was not influenced by CO2. This suggests that there may be a species-specific CO2 response to epidermal cell size that influences stomatal density and stomatal index.