Abstract Tomato petiole sap from potassium (K) rate experiments conducted on prairie loam and river coarse sand soils from 1998 to 2002 was used to measure K concentration via the battery‐operated portable Cardy flat membrane electrode meter and inductive coupled plasma (ICP) laboratory instrumentation. In 1998, for undiluted sap levels less than 3000 mg kg−1 the linear Cardy–ICP correlation was r=0.94, but when K was more than 3000 mg kg−1, r was only 0.53. Diluting the sap with water (1∶1) improved the linear range to 6000 mg K L−1 (r=0.87, n=190). Petiole sap K, measured by either Cardy or ICP, was highly correlated to whole‐leaf K concentration all years, r=0.8 to 0.91. Even through the slope of the regression lines were similar for the years, the intercepts were significantly different (P<0.01). The Cardy electrode can be reliably used for tomato petiole K determination provided the sap is diluted and the usual handling precautions are taken to prevent petiole moisture loss and maintain stability in electrode readings. Keywords: Fertilizerleaf petiole sapreal‐time analysistissue analysis
Raw and processed tomatoes are the major dietary source of lycopene in the U.S.; serum lycopene concentrations are inversely related with risk of chronic disease. In greenhouse tomato plants, we investigated the effects of different levels of potassium application on: 1) fruit concentrations of lycopene and the colorless precursors, phytoene and phytofluene; and 2) expression of carotenoid biosynthetic genes. Plants were grown in silica sand with nutrient solution containing selected potassium concentrations from 0 to 10 meq/L. Fruit potassium concentration was linearly related to potassium application level (r = 0.81). Phytoene, phytofluene, and lycopene concentrations were highly correlated with potassium concentration in the fruit (r = 0.69, 0.68, 0.70, respectively). Lycopene concentration increased from 39.3 ± 9.09 μg/g (0 meq/L potassium) to 55.6 ± 6.71 μg/g (10 meq/L potassium) (P < 0.007). Phytoene and phytofluene concentrations increased from 3.79 ± 0.79 μg/g and 2.79 ± 0.59 μg/g, respectively, to 7.84 ± 1.86 μg/g and 5.25 ± 1.26 μg/g, respectively (P < 0.002). Expression of carotenoid biosynthetic genes was analyzed by RT-PCR and RNA dot hybridization. Preliminary results indicated an increase in potassium application from 0 meq/L to 10 meq/L resulted in up-regulation during ripening of genes for phytoene synthase, phytoene desaturase, and carotenoid isomerase. Future research will elucidate the relation between potassium nutrition of the tomato plant and carotenoid biosynthesis. Supported by USDA/CDFIN 2004-06096.
Two tomato (Lycopersicon esculentum Mill.) cultivars, Mtn. Spring and Jet Star, were grown on black polyethylene-mulched beds of a loam soil with an organic matter content of 2.4% for two seasons, 1996 and 1997, to evaluate preplant N rate effects on fruit yield and leaf blade total nitrogen (N) and petiole sap NO3-N concentration. Four rates of N fertilizer (0 to 136 kg ha−1), as urea, were rotovated into the bed prior to laying the plastic mulch. Samples of the most recently matured leaves were taken every two weeks for N and NO3-N content. Fruit yield and quality were associated with early season, 4 and 6 week, petiole sap NO3-N concentration. Mtn. Spring required 1050 ppm sap NO3-N compared with 900 ppm for the Jet Star cultivar. In 1996, Mtn. Spring achieved maximum yield at 31 kg N ha−1 whereas Jet Star required 67 kg N ha−1. Maximum yield occurred at 67 kg N ha−1 for both cultivars in 1997. Nitrogen rates above the optimum decreased early yields in 1996, but not in 1997. Soil N mineralization data showed > 112 kg N ha−1 by mid-July in the top 30 cm of the soil profile. On the prairie soils of the upper Midwest soil N management should be similar for both determinate and indeterminate fresh market tomatoes.
Abstract Horticultural species vary in growth response to root‐zone temperature (RZT) that exceed 30°C, but little is known about the effects of RZT on nutrient absorption. We determined the amount of phosphorus (P), zinc (Zn), and manganese (Mn) in plants of tomato (Lycopersicon esculentum Mill. ‘Jet Star'), muskmelon (Cucumis melo L. ‘Gold Star'), and thornless honey locust (Gleditsia triacanthos L. var. inermis Willd.) grown in an Hoagland No. 1 nutrient solution that was held at 24°, 27°, 30°, 33°, and 36°C RZT. Tomato dry mass and P and Mn contents were highest at 27°C RZT, but tomato Zn content did not show a response to RZT. Muskmelon dry mass and P, Zn, and Mn contents, however, were highest at 36°C. Honey locust dry mass and P and Zn contents did not vary with RZT, but honey locust Mn content decreased linearly with increasing RZT. Growth and P, Zn, and Mn absorption by muskmelon were increased by continuous exposure to RZT > 30°C, whereas honey locust growth and P, Zn, and Mn acquisition were not changed by exposure to RZT > 30°C. Growth and P, Zn, and Mn absorption by tomato, however, were decreased by continuous exposure to RZT > 30°C.
Abstract The 6-month student intern program offered by the Department of Horticulture at Iowa State University assists rural and urban Iowans in home food production through extension programs, mass media, and community projects. Advanced undergraduate horticulture students are granted internships at the county/area level and receive credits and a salary for their work. An extension horticulture associate based in the department provides the overall leadership and coordination. Intern training sessions concentrate on the type of questions to expect and problem diagnosis methods. More than 50% of homeowner concerns are related to home food production. The intern program has been received enthusiastically and has reduced the summer workload of county staff and state specialists.
