Soybean rust (SBR; caused by Phakopsora pachyrhizi Syd. and P. Syd.) leads to premature leaf loss and yield reduction. The objectives of this study were to assess effects of SBR infection on soybean [Glycine max (L.) Merrill] yield and to identify causes for the yield reduction. Experiments were conducted in the 2005–2006 and 2006–2007 growing seasons at Londrina, Brazil. The five treatments were SBR infection beginning at either (i) the R2 or (ii) R5 growth stages; nondiseased defoliation treatments to mimic the leaf loss when SBR started at either (iii) the R2 or (iv) R5 growth stages; and (v) a disease‐free, nondefoliated control. The control and defoliation treatments were protected against SBR by fungicide applications. Disease severity, lesion area, and leaf area were monitored from R2 to R7. Biomass and seed yield were measured at maturity. Mean SBR‐induced yield reductions were 67% when infection started at R2 and 37% when infection started at R5. Leaf loss alone reduced yield significantly in only one year and only when defoliation treatments were begun at R2 (31% in 2005–2006). Soybean rust–induced yield loss was attributable to (i) premature leaf loss, (ii) reduction in canopy green leaf area due to SBR lesions, (iii) reduction in dry matter accumulation per unit absorbed radiation by the nonlesion green leaf area, and (iv) reduction in harvest index. The response of harvest index was attributable to reduced seed set and seed mass resulting likely from SBR‐induced reductions in rate of dry matter accumulation.

Understanding how defoliation affects soybean [Glycine max (L.) Merr.] yield during the seed‐filling period will aid in making management recommendations for control of stresses that reduce yield through defoliation. Because previous research has studied defoliation effects at only one or two specific stages of seed filling, our objective was to gain a greater understanding of the mechanisms for yield reduction with defoliation at weekly intervals across the seed‐filling period. Defoliations were conducted from the bottom of the canopy upward to mimic the progress of soybean rust. Two experiments, one in Kentucky (38° N lat) and the other in Louisiana (30° N lat), were conducted in randomized complete block designs in split‐split plot arrangements with four replications. Main plots were two cultivars, split plots were defoliation timings at weekly intervals during seed filling, and split‐split plots were defoliation levels of 0, 33, 66, and 100% leaf removal. Data were obtained on yield and several growth dynamic and yield component factors. Defoliation‐induced yield losses corresponded more closely with percentage of light interception reductions than percentage of leaf area reductions. During the R5 to R6 period, defoliation levels sufficient to reduce light interception by 18 to 23% were required to cause yield loss. Yield losses from total defoliation were greatest at early seed filling (78%) but gradually diminished as seed filling progressed. Each 0.1 delay in developmental stage resulted in a 5% decline in yield loss.

Production of winter wheat (Triticum aestivum L.) under no-till (NT) can have economic and edaphic benefi ts over conventional tillage (CT) systems, although in some years it can result in lower yields. Analysis of yield-formation processes of wheat grown under NT and CT systems may elucidate why yields are sometimes lower under NT. Th e objective of this study was to determine the eff ects of tillage systems on yield-formation processes of soft red winter wheat. Two experiments were conducted at two locations in Kentucky using randomized complete block split-plot designs. Main plots in both experiments were two tillage systems (NT and CT). In Exp. 1, which was conducted in 2004, split plots were four cultivars with diff erent heading dates. In Exp. 2, which was conducted in 2005 and 2006, the split and split-split plots were two cultivars and three seeding rates, respectively. Total plant biomass, grain yield, yield components, and harvest index (HI) were measured at maturity. Grain yield was lower under NT than under CT in two of the fi ve location/years. Neither cultivar diff erences in days to heading nor seeding rates altered the impact of NT on grain yield. Th e dominant response of soft red winter wheat to NT in this study was to increase tillering and reduce HI. Th e increased tillering growth habit due to NT could increase internal competition for assimilates, thereby diverting assimilates away from grain production to vegetative growth and reducing HI. Th e reduction in HI led in some years to a reduction in yield.

Increasing the level of protein in soybean seeds has been a major target for soybean [Glycine max (L.) Merr.] breeders. The objective of this study was to examine the potential of predicting soybean seed protein based on oil values as determined by NMR. Seed protein and oil concentrations were determined in an F 2 population generated from the cross between a G. max (NK S08-80) and a G. soja (PI 458536) cultivar. The protein concentration in the population ranged from 40.4 to 52.6%. Protein-oil regression analysis was used to generate an equation for predicting seed protein concentration based on oil readings. The regression equation Protein = 62.3 − 1.3[Oil] (R 2 = 0.46) was developed, with a corresponding correlation of -0.69 between the traits. With this equation, the mean protein concentration of the selected 25% of the population (a simulated breeding pressure) was greater than the mean of the unselected population (46.1%, SE = 0.13) by about 1.9%. Individual F 2 plants that exceeded the mean protein value of the population constituted 86.4% of the selected samples. Selection based on oil concentration, however, failed to include 27.1% of the plants that were among the top 25% for protein concentration. Selection of highprotein plants based on NMR oil measurement was reasonably effective in the test population and might offer a new and rapid method of selecting high-protein individuals in soybean populations derived from the wild soybean progenitor, G. soja. If further tested on other populations and samples, it might be used as an analytical alternative for an indirect measurement of protein concentration based on NMR measurements of the oil.Paper no. J10884 in JAOCS 82, 87-91 (February 2005). FIG. 3. Linear protein-oil regression for a Glycine soja-derived F 2 soybean population (n = 235) from the cross NK S08-80 × PI 458536. The linear regression equation predicted Protein = 62.3 (SE = 1.12) − 1.3[Oil] (SE = 0.09) (R 2 = 0.46). Protein and oil are expressed as percent of total seed on a dry-seed basis.

Abbreviations: CER, carbon exchange rate; DAI, days after inoculation; LED, light emitting diode; PPFD, photosynthetic photon fl ux density; RB, reddish-brown lesions; RIL, recombinant inbred line; SBR, soybean rust.

Yield loss in soybean [Glycine max (L.) Merr.] due to soybean rust (SBR) (caused by Phakospora pachyrhizi Syd. & P. Syd.) has been associated with reduced radiation interception and reduced radiation use efficiency by green leaf area. The objective of this study was to determine the mechanisms involved in the SBR‐induced reductions in radiation use efficiency by quantifying the effect of SBR on (i) absorption of photosynthetic photon flux density (PPFD) and (ii) carbon exchange rate (CER) per unit absorbed PPFD of soybean leaves. A controlled‐environment study was conducted using a split‐plot design with three replications over time, with two disease levels as main plots and two soybean cultivars as subplots. The two disease levels were a disease‐free control and inoculation with P. pachyrhizi. Measurements included leaf CER, PPFD absorptance, and chlorophyll fluorescence. As disease severity increased, there was a small linear decline in leaf absorptance and a negative exponential decline in leaf CER. At 50% disease severity, absorptance was reduced by 10% and CER was reduced by 68% compared with the disease‐free control. The relative decline in CER was similar at low and saturating PPFD levels. Soybean rust–induced reductions in CER were mainly associated with lower efficiency of photosystem II (PSII) photochemistry and damage to PSII reaction centers. Therefore, visual indicators such as light absorptance and disease severity do not reflect the degree of impact of SBR on leaf photosynthesis.

Field studies were used to examine the management strategies of mowing, herbicide, fertility, and all possible combinations on tall ironweed populations, weed biomass, and pasture yield at three Kentucky locations. Mowing was performed in July 2008 and 2009, herbicide was applied in August 2008, and fertilizer was applied in September 2008 and 2009 at all locations. Weed populations were measured in 2008, 2009, and 2010, and forage grass, clover, and weed biomass was collected in May or early June of 2009 and 2010. All treatments with herbicide reduced tall ironweed stems by 64% or greater in 2009 at all locations. Mowing alone, fertilizer alone, and mowing plus fertilizer did not reduce tall ironweed populations, except at one location where mowing alone reduced tall ironweed stems by 64% in 2009. Tall ironweed stems were not reduced in 2010 with any treatment at two locations, but herbicide combined with mowing or fertilizer reduced tall ironweed stems by 78% at the other location. Tall goldenrod population was reduced up to 100% by all treatments with herbicide or mowing alone, and mowing with fertilizer reduced tall goldenrod from 59 to 89%. Treatments did not reduce horsenettle populations. Herbicide-containing treatments reduced weed biomass at all locations. Weed biomass did not differ when comparing all treatments with and without mowing or treatments with or without fertilizer. Forage grass biomass was greatest with herbicide plus fertilizer and with the combination of mowing plus herbicide plus fertilizer at all locations in both years.

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