Occurrence of drought under rainfed conditions is the foremost factor responsible for yield reduction in soybean. Developing soybean cultivars with an inherent ability to withstand drought would immensely benefit the soybean production in rainfed areas. In the present study, F2 derived mapping populations were developed by crossing drought tolerant (PK 1180, SL 46) and susceptible (UPSL 298, PK 1169) genotypes to investigate the inheritance of seedling survival drought mechanisms and to identify simple-sequence repeat (SSR) markers associated with them, using bulked segregant analysis. Parents as well as a F2 derived mapping population were screened for drought tolerance based on seedling survivability under controlled conditions. Segregation analysis of F2 population derived from a cross between PK 1180 × UPSL 298 was previously shown to have a 3:1 tolerant to susceptible ratio and a probability of 0.61 at a χ2(3:1) value of 0.258. This was confirmed in another F2 population derived from a cross between PK 1169 × SL 46 with a χ2(3:1) value of 0.145 obtained at a probability of 0.70. One SSR marker Satt277 showed polymorphism between contracting bulks (tolerant and susceptible) out of 50 polymorphic markers identified during parental polymorphism. Single marker analysis suggested that the marker, Satt277 is linked to seedling survival drought tolerance and is located on chromosome linkage group C2 (chr 6) with a map distance of 3.40 cM. The tolerant genotypes identified could be used as a donor in soybean improvement programs. The marker identified can be used in marker-assisted selection while screening large collection of germplasm.

Velvetleaf, eastern black nightshade, wild mustard, common cocklebur, green foxtail, and yellow foxtail, grown for 4 weeks in nonaerated nutrient solution, developed satisfactorily compared to plants grown in soil. For experiments involving certain weed species grown in nutrient solution, aeration may be unnecessary.

Experimental objectives were to assess metribuzin tolerance of predominately privately developed soybean cultivars and to evaluate a greenhouse screening procedure. In field results in 1982, ‘Vinton 81’, ‘Northrup King 1884’ and ‘L77-1863’ soybean cultivars were extremely sensitive to metribuzin at 0.56 kg/ha, averaging 34% injury. The other 45 cultivars showed no significant injury at the 0.56 kg/ha rate, from 9 to 46% injury at 1.4 kg/ha, and 18 to 72% injury at 2.2 kg/ha. In greenhouse hydroponic studies, these same three soybean cultivars were killed, while the other 45 cultivars were injured from 15 to 82%. A good agreement of greenhouse and field data was determined, with a correlation coefficient of r = 0.82.

Field studies have shown primisulfuron to be more injurious to sugarbeet than nicosulfuron 1 and 2 yr after herbicide application. Experiments were initiated to determine if primisulfuron is more injurious to sugarbeet grown in a nutrient culture and if the difference in sugarbeet response is a result of greater uptake, translocation, or acetolactate synthase (ALS) site sensitivity with primisulfuron. Concentrations of primisulfuron and nicosulfuron that reduced sugarbeet growth by 50% were 1.9 and 8.9 μg ai L−1, respectively, at pH 6.5. The pH of the nutrient solution did not influence sugarbeet response to either herbicide. Uptake of primisulfuron was greater (3%) than that of nicosulfuron (1%). Translocation (expressed as a percent of uptake) of nicosulfuron was more rapid than primisulfuron. Fifty-seven percent of the absorbed nicosulfuron translocated out of the root during the 12-h pulse period, while an equal concentration of primisulfuron was not translocated out of the root until 48 h after pulsing. The total nicosulfuron translocated after 144 h was half that of primisulfuron. The nutrient solution taken up by sugarbeet in the 12-h pulse period was reduced by 41% in the presence of either herbicide compared to the untreated control. The ALS enzyme was a minimum of 15 times more sensitive to primisulfuron compared to nicosulfuron which may account for greater sugarbeet response to primisulfuron.

Greenhouse studies were conducted to determine the influence of phosphorus (P) concentrations on the growth of lettuce, smooth pigweed, and common purslane in monocultures and in mixtures and to determine the P-absorption rate of each species over time. For the P-competition studies, lettuce–smooth pigweed and lettuce–common purslane mixtures were established in P-less hydroponic solutions. Each lettuce–weed mixture was established separately. Concentrations of P were 10, 20, 40, 80, and 160 mg L−1. Lettuce to weed planting proportions were 2:0, 0:2, and 1:1. In the mixtures, biomass of common purslane increased sharply between 10 and 20 mg P L−1, depressing lettuce growth. No biomass changes were observed in smooth pigweed as P concentration increased. However, both weeds increased their P content within this range, depriving lettuce of this nutrient. Common purslane competed for P for its own growth, whereas smooth pigweed absorbed P luxuriously. For the P-absorption studies, roots of lettuce, smooth pigweed, and common purslane plants were submersed in a 20 mg P L−1 solution for 1, 2.5, 5, 10, 20, 40, 60, 90, 180, 360, 720, and 1,440 min. Common purslane was shown to be the most aggressive species for the nutrient, absorbing 50% of the content in 295 min, whereas lettuce and smooth pigweed needed 766 and 825 min to absorb 10 mg P L−1.

It has been previously reported that POST-applied isoxaben can effectively control established hairy bittercress. Experiments were conducted to determine the relative importance of root vs. foliar entry of POST-applied isoxaben. At a common isoxaben rate of 0.56 kg/ha, foliar-only and foliar plus soil applications provided 10.5 and 23.3% control, respectively, as determined by fresh weight reduction. In contrast, soil-only application provided 47.0% control. Hairy bittercress foliar absorption of 14C–isoxaben did not exceed 15% of the amount applied after 72 h. Therefore, the comparatively less effectiveness of foliar-only applications may be attributed primarily to limited absorption. Minimal isoxaben concentration required to inhibit root growth of hydroponically grown hairy bittercress was 0.0025 mg/L. Higher concentrations were required to produce a response in the foliage. Sorption of isoxaben by pine bark rooting substrate, typical of what is used in container nursery production, exceeded 99% of amount applied after 36 h. Even with 99% sorption, the probable concentration within the aqueous phase remains sufficient to inhibit hairy bittercress root growth. Additional studies with 14C–isoxaben established that approximately 35% of the root-absorbed isoxaben was translocated into the foliage. Translocation from the roots into the foliage was reduced to 16% when the experiment was repeated during environmental conditions less favorable for vegetative growth (i.e., longer day length and higher temperature). Results indicate that the control of hairy bittercress with POST-applied isoxaben is likely the result of root absorption and root-growth inhibition. Expression of phytotoxicity within the foliage is also a component, but is dependent upon the root-absorbed isoxaben being translocated into the foliage. Extent of this translocation is dependent upon plant maturity and prevalent environmental conditions.

This study used a multidisciplinary approach to evaluate the potential for hydroponic production of vegetable amaranth (Amaranthus cruentus) in Kenya. Hydroponic systems have potential for increased efficiency in water and land use, but their potential has not been critically evaluated in many developing countries. To address this gap in knowledge, this study assessed the nutritional density and economic viability of hydroponic systems built from local materials. Specifically, vegetable amaranth was grown hydroponically and evaluated for increased nutritional density of key micronutrients. Manipulation of the nutrient solution used in hydroponic systems changed the bioaccumulation of zinc, iron and carotenoids, which are three of the most common micronutrients lacking in Kenyan diets. Economic viability was assessed with a benefit-cost analysis that compared three different hydroponic systems to soil-based production and purchasing vegetables from local markets. This analysis showed that none of the hydroponic systems were profitable under current conditions, but sensitivity analyses revealed certain scenarios where they could become so. Overall, hydroponic production has the potential to create nutrient-dense crops with high levels of zinc, iron, or carotenoids. However, hydroponic systems may be better suited to crops of higher value than amaranth, areas where soil-based production is not an option, or regions where vegetable markets are not available.