Chronic progressive nephropathy is a spontaneous disease common among aging laboratory rats, often making it difficult to distinguish age-related from drug-related effects in chronic toxicity studies. Morphological changes of the kidney that occur with age include thickening of glomerular and proximal tubular basement membranes, mesangial proliferation, fusion of foot processes, and, ultimately, glomerular sclerosis. Proteinuria (specifically, albuminuria) is the most striking characteristic change in renal function of aging rats and, generally, correlates well with the severity of age-related glomerular pathology. Changes in tubular functions also may occur with aging but have not been investigated sufficiently. The pathogenesis of chronic progressive nephropathy is not known; however, hemodynamic adaptations after ad libitum consumption of protein-rich diets may be a contributing factor. High-protein diets increase glomerular pressures and flows, perhaps facilitating excretion of metabolic end products. These hemodynamic adaptations may impair the permselective properties of the glomerulus, leading to: enhanced accumulation of macromolecules in the mesangium, progressive mesangial expansion, and, ultimately, glomerular sclerosis. Indeed, decreasing total food or protein intake retards or prevents the progression of age-related nephropathy. Inasmuch as chronic toxicity studies are complicated by a high incidence of spontaneous nephropathy, implementation of a restricted dietary regimen may improve detection of drug-induced toxicity.

Peanuts (Arachis hypogaea L.) are often subjected to drought during some period in the growing season. A large root system may improve the plant's ability to continue growth during a drought. During greenhouse and field screening trials for resistance to the peanut root-knot nematode [Meloidogyne arenaria (Neal) Chitwood, race 1],16 peanut genotypes were observed to have very large root systems. Using these 16 genotypes plus cultivars Florunner, Southern Runner, and germplasm line Tifton 8 as checks, several studies were conducted to evaluatethese genotypesfordrought avoidance characteristics. In the first study, root and shoot development were observed at 15-d intervals on plants grown from seed in sand-filled pots. In a second 2-yr study, selections were grown in the field under portable rain-exclusionshelters that created controlled periods of stress. In addition, the genotypes were also planted and observed in unsheltered naturally drought stressed field plots. In the sand-filled pot study, plant inventory (PI) numbers 315628, 268885, 318740, 269106, and 314893 developed the largest root systems. In the field drought stress studies, lowvisualstress ratings were recorded for Southern Runner, Tifton 8, PI 295722, and PI 315628. Low canopy temperatures characterized PI 315628, Tifton 8, and PIs 295722,259637, and 268885. When averaged over three tests, sheltered (1991and 1992)and unsheltered (1991), Tifton 8, PI 318740, Florunner, PI 315622, and PI 315628 produced the highest yields. Two of these higher yielding genotypes (Tifton 8 and PI 315628) had low stress and temperature ratings and PI 315628also had the largest root system measured in this study.'Cooperative investigation between the Univ. of Georgia, College of Agric. and Environ. Sci. and USDNARS. Mention of a product name given for information and should not be considered an endorsement to the exclusion of like products.

Peanuts become contaminated with aflatoxins when subjected to prolonged periods of heat and drought stress. The effect of drought tolerance on aflatoxin contamination is not known. The objectives of this research were to evaluate preharvest aflatoxin contami nation in peanut genotypes known to have drought tolerance and to determine the correlation of drought tolerance characteristics with aflatoxin contamination. Twenty genotypes with different levels of drought toler ance were grown in Yuma, AZ«(a desert environment) and under rain-protected shelters in Tifton, GA. Two drought-tolerant genotypes (PI 145681 and Tifton 8) and an intolerant genotype (PI 196754) were selected for further examination in a second experiment with two planting dates in 1997 at Tifton. Drought and heat stress conditions were imposed for the 40 d preceding harvest. The drought-intolerant genotype had greater preharvest aflatoxin contamination than Florunner (the check cultivar) in the tests conducted in 1997. Both droughttolerant genotypes had less preharvest aflatoxin con tamination than Florunner in these tests. Significant positive correlations were observed between aflatoxin contamination and leaf temperature and between afla toxin contamination and visual stress ratings. Leaf tem perature and visual stress ratings are less variable and less expensive to measure than aflatoxin contamination. Leaf temperature and visual stress ratings maybe useful in indirectly selecting for reduced aflatoxin contamina tion in breeding populations.

Although subsurface drip (SSD) is used as a water‐efficient alternative to overhead irrigation in many crops, the effects of SSD on the distribution of bolls on cotton plants (Gossypium hirsutum L.) have not been thoroughly examined. The purpose of this study was to add to the current knowledge about the effects of SSD on cotton yield dynamics. Cultivar DP 488 BG/RR was grown in three studies during 2 yr with irrigation treatments consisting of overhead irrigation (Overhead), a nonirrigated control (Nonirrigated), SSD matched to overhead irrigation amounts and frequency (SSD Matched), and SSD based on soil moisture (SSD Fed) irrigated cotton. The cotton was grown in two locations in 2004 and one location in 2005 in Georgia. Crop height, maturity, and soil moisture status were monitored throughout the growing season in each location. At harvest, a subplot consisting of one harvest row measuring 3 m in length was removed from each plot and handpicked to determine cotton boll distribution in each plot. Irrigation method had a significant impact on boll distribution on the plants, with the overhead irrigation treatment consistently having less cotton near the bottom of the plant and more cotton near the top than either of the SSD methods. We conclude that SSD irrigation decreases early‐season fruit loss, resulting in heavier carbohydrate sinks and decreasing overall growth and upper boll filling on the crop.

Vegetation indices based solely on visible reflectance may simplify and decrease the cost of crop growth estimates compared to visible and near‐infrared (NIR) indices. Ground‐based and aerial visible and visible/NIR vegetation indices based on aerial images were compared for sensitivity to ground cover fraction (GCF) of cotton (Gossypium hirsutum L.) under four irrigation treatments in 2004 and five treatments in 2005 and 2006. In‐season cotton imagery was collected using an unmodified Nikon COOLPIX 4300 camera and a COOLPIX 4300 camera modified for NIR imaging attached to a tethered blimp. GCF imagery was collected at 45 to 60 m and compared with normalized difference vegetation index (NDVI) and green/red ratio values from imagery collected at 180 to 250 m. Ground‐based (1.5 m) spectrometer NDVI measurements using multiple spectral regions were also evaluated. Spectrometer (r2 = 0.40 to 0.80) and camera (r2 = 0.68 to 0.90) indices were highly correlated with season‐wide GCF between fractions of 0.20 and 0.80 and were sensitive to irrigation treatments. Camera green/red ratio was linearly correlated with GCF throughout the 3 yr. The pooled comparison for the 3 yr was strongly linear (r2 = 0.86). Our results suggest that the green/red ratio index might allow quick, simple, and accurate crop growth estimates for production.