Depletion of the weed seed bank by stimulating germination during winter months and subsequently exposing the seedlings to adverse air temperatures is a possible means of controlling weeds in small-scale horticultural operations. Johnsongrass [Sorghum halepense (L.) Pers.], hemp sesbania [Sesbania exaltata (Raf.) Rydb. ex A.W. Hill], and barnyardgrass [Echinochloa crus-galli (L.) Beauv.] were seeded in soil trays and maintained for 4 days at 4 or -12 °C, then heated to 32 °C for 4 days using electric heating pads. Germination percentages, after heating soils, were: 55% and 70% for hemp sesbania, 82% and 72% for barnyardgrass, and 45% and 55% for johnsongrass, respectively; for seeds kept at -12 and 4 °C, respectively. Subsequent exposure of seedlings to -12 °C for 7 days killed all seedlings, while exposure to 4 °C killed only 18% to 28%. The temperature regimes of -12 °C for 4 days, and 32 °C for 4 days followed by -12 °C killed 95%, 78%, and 68% of the johnsongrass, hemp sesbania, and barnyardgrass, respectively.
Rakesh S. Chandran and Megh Singh
Jun Yu*, Romeo Toledo, Rakesh Singh, Leonard Pike, and Bhimanagouda Patil
Grapefruit seeds were studied for the extraction of limonoids using supercritical CO2 extraction (SC-CO2) technique. Limonin aglycone was successfully extracted with SC-CO2 directly from grapefruit seeds; and the limonin glycoside was extracted using SC-CO2 and ethanol as co-solvent from the spent seeds after the extraction of limonin aglycone. In an effort to optimize the extraction conditions of limonin aglycone, pressure, temperature, time effects were investigated. Various times of extraction, CO2 flow rate and the feeding modes of CO2 were also employed to obtain the highest yield of limonin aglycone. Optimal conditions to achieve the highest limonin aglycone (0.63 mg/g seeds) were 48.3 MPa, 50°C and 60 min with CO2 bottom feeding, flow rate about 5 L/min. The extraction conditions for limonin glycoside to achieve highest yield were further optimized. The highest extraction yield (0.62 mg limonin glycoside/g seeds) were at 48.3 MPa, 50°C, 30% molar fraction of ethanol (XEth =0.30) and 40 min with CO2 top feeding, flow rate about 5 L/min. The results demonstrated that supercritical CO2 extraction of limonoids from grapefruit seeds, a citrus juice industry byproduct, has practical significance for commercial production.
Ashish K. Pathak, Sudhir P. Singh, and Rakesh Tuli
Amplified fragment length polymorphism (AFLP) was used to assess genetic relatedness among 23 popular commercial cultivars of lychee (Litchi chinensis) and identify the markers associated with small-seeded cultivars. A combination of three primer pairs with high discriminatory ability was selected for resolving the identity of lychee cultivars. The marker system resolved the instances of synonymies and homonymies. The two cultivars, Dehrarose and Dehradun, whose names are often used interchangeably, could be discriminated by AFLP. A cultivar, Calcuttia (H), grown in the Punjab region was found genetically very similar to China (M) of Bihar region in India, suggesting that both could be the same clone. A number of cultivars with contrasting seed size were included in the study. The cultivars Bedana, Seedless Late, and China were positioned in one group, unlike the grouping previously reported based on morphological traits. The AFLP fingerprinting revealed five marker fragments exclusive to the genotypes, which bear fruit with small seed and large pulp.