The competitiveness of annual weeds in irrigated sweet Spanish onions (Allium cepaL.) was studied at North Platte, Nebraska, during 1969 and 1970. Weeds allowed to grow in the row for 2, 4, 6, and 8 weeks after onion emergence reduced onion yields 20, 20, 40, and 65%, respectively. When plots were kept weed-free until onion emergence and 2, 4, 6, 8, 10, and 12 weeks after emergence, onion yields were reduced 100, 99, 87, 75, 46, 25, and 5%, respectively. Redroot pigweed (Amaranthus retroflexusL.), kochia (Kochia scopariaL.), and grass weeds accounted for 54, 21, and 21%, respectively, of the total weed yield.

Additional index words. Phaseolus vulgaris, rust, common bacterial blight, halo blight, bacterial brown spot, white mold The release of 'Chase' fulfills a need in southwestern Nebraska for a Pinto dry bean cultivar (Phaseolus vulgaris L.) with resistance to rust [Uromyces appendiculatus (Pers.) Unger] and several bacterial diseases. Rust, common bacterial blight [Xanthomonas campestris pv. phaseoli (Smith) Dye], and bacterial brown spot (Pseudomonas syringae pv. syringae van Hall) diseases have recently reduced bean yields and seed quality of Pinto dry beans in that region and northeastern Colorado. 'Chase' is the first Pinto cultivar that combines resistance to rust(races of rust prevalent in recent years in Nebraska and Colorado), bacterial brown spot, halo blight [P. syringae pv. phaseolicola (Burkholder)], moderate resistance to common blight, and moderate avoidance of white mold [Sclerotinia sclerotiorum (Lib.) de Bary] due to a porous canopy. 'Chase' also has resistance to potato leafhopper "bum" injury caused by Empoasca fabae Harris. OriginWe deemed it important to develop an early maturing Pinto line with resistance to rust and common blight and with moderate avoidance to white mold. 'Chase' (evaluated as PWM 2 -89-5 from 1989 to 1992) was derived by pedigree selection (Fig. 1) from a cross of a Nebraska (NE) Great Northern (GN) breeding line GN WM 2 -84-17 (upright plant habit, moderately early, resistant to common bacterial blight and rust, and moderate avoidance of white mold) and a NE Pinto (P) breeding line PWM 2 -84-45 (prostrate habit, early maturity, good Pinto seed size and shape, rust-

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1998) Use of hydrogen release or a combination of hydrogen release and iron reduction for selecting iron-efficient dry bean and soybean cultivarsABSTRACT Iron (Fe) chlorosis continues to be a problem in the world where crops are grown in calcareous soils. Although it is possible to remedy this problem with fertilizer application, selection of cultivars resistant to Fe-deficiency chlorosis is a more economical and practical solution. In addition to field chlorosis rating studies, several methods have been developed to screen cultivars. One of the most promising is quantifying individual plant response mechanisms induced during Fe-deficiency stress, such as Fe reduction or hydrogen ion (H+) extrusion by the roots. Eight dry bean (Phaseolus vulgaris L.) and 11 soybean (Glycine max L.) cultivars of varying resistance to Fe-deficiency chlorosis were grown in solutions of low (0.05 mg L -1 ) and no (0 mg L -1 ) Fe, 2639 ELLSWORTH ET AL.respectively. Beginning at day 2 after imposition of low Fe treatments, plant roots were incubated for one hour in a solution to collect H + ions. This solution was then titrated with NaOH to the pH of the control solutions (no plants grown in solution, but air bubbled through it for one hr). The results of six consecutive days were summed and correlated with field chlorosis scores. In dry bean, there was a statistically significant positive relationship between H + release and field chlorosis scores, which is opposite of the theoretical relationship, i.e., dry bean cultivars with high chlorosis scores released the largest quantity of H + ion and vice versa. Soybean exhibited a statistically significant negative relationship between quantity of H + release and field chlorosis scores, but Fe reduction measurements provided better screening ability than H + ion release. Adjusting the measurements for fresh root weight did not alter these relationships; thus, eliminating the need to weigh roots in a breeding nursery. Combining the effects of H + release and Fe reduction using standardized scores did not improve the selection of Fe efficient cultivars over Fe reduction alone in either dry bean or soybean. Hydrogen ion quantification was time consuming, tedious, and gave conflicting results in the two species studied. Thus, it is not recommended as a screening technique in either dry bean or soybean.