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Jeffrey C. Stark, Joseph J. Pavek, and Ian R. McCann

Field studies were conducted in 1986 and 1987 to evaluate the potential of using canopy temperature measurements to evaluate the relative drought tolerance of potato genotypes. In both years, 14 potato genotypes representing a relatively wide range of Solarium tuberosum L. germplasm were grown under well-watered [irrigation ≈100% potential evapotranspiration (ET) and stressed (irrigation ≈40% to 50% potential ET) coditions. Irrigation differences were imposed with a line source irrigation system. Canopy temperatures of the 14 genotypes were measured between 0900 and 1430 hr on 7 clear days during tuber bulking. A general linear relationship between canopy minus air temperature (ΔT) and air vapor pressure deficit (VPD) was determined for each year by regressing all ΔT data onto corresponding VPD values. The relative sensitivity of each genotype to changes in VPD was determined by regressing observed ΔT values onto the estimated ΔT from the general equation for that year. Genotypes with higher than average temperatures under well-watered conditions were generally less sensitive to changes in VPD than those with lower than average temperatures. Warmer genotypes under well-watered conditions were also generally less susceptible to drought than cooler genotypes. Thus, ΔT measurements from well-watered plots can be effectively used to assess the relative drought tolerance of potato genotypes.

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Esmaeil Fallahi, Bahman Shafii, Jeffrey C. Stark, Bahar Fallahi, and Saad L. Hafez

Cane growth, leaf blade area, blade and petiole fresh and dry weights and mineral nutrients of six grape (Vitis vinifera) cultivars were evaluated in 2000 and 2001 under climatic conditions of southwestern Idaho. The cultivars were: `Barbera 02', `Cabernet Sauvignon 02', `Cabernet Sauvignon 04', `Chardonnay 29', `Merlot 01', and `Sangiovese 04'. No differences were found in cane growth of different cultivars. `Sangiovese 04' and `Merlot 01' had larger leaf area and heavier leaves (both blades and petioles) and higher concentrations of blade nitrogen (N), while `Merlot 01' and `Chardonnay 29' had higher petiole nitrate-N than all other cultivars. `Merlot 01' had relatively the highest potassium (K) concentrations in both blade and petiole tissues. `Chardonnay 29' had lower concentration of calcium (Ca) and `Sangiovese 04' had lower concentrations of magnesium (Mg) in both blade and petiole tissues than other cultivars although differences were not always significant. `Barbera 02' had higher blade iron (Fe) and tended to have higher blade copper (Cu) than other cultivars. However, `Chardonnay 29' had higher petiole Fe than `Barbera 02', `Cabernet Sauvignon 04', and `Sangiovese 04'. `Merlot 01' had higher blade manganese (Mn) than `Sangiovese 04'.