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W.A. Mulkey and J.H. Hernandez

Foundation sweetpotato [Ipomoea batatas (L.) Lam] seedstock has been produced annually at the Sweet Potato Research Station since 1949. Breeder seedstock is selected from superior hills and used for the following year's foundation seedstock. Fields are intensely monitored after planting until harvest to remove off-type plants, mutations, etc. Seedstock is harvested from August through October, stored, graded, and repacked beginning in late January, and then made available to the growers during the early spring.

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M.S. Hernandez, H.E. Arjona, O. MartÌnez, M.S. Hernandez, and J.P. Fernandez-Trujillo

Araza (Eugenia stipitata Mc Vaugh) is a plant from the Myrtaceae family originated from Amazonia. The postharvest behavior of its promissory fruit has been sparingly studied. Weight loss, softening, decay, and chilling injury (skin scald) at temperatures below 10-12 °C limits its shelf-life to less than 10 days. The application of calcium pretreatments slightly improved flesh firmness after 7 days at 20 °C and resulted in skin injury, particularly at concentrations higher than 4% (w/v). A warming treatment of 6, 12 or 18 h at 20 °C was applied to fruit after 6 d storage at 10 °C. Treated fruit had less scald, suppressed decay, and ripened normally after a total of 2 weeks of storage and a shelf life of 3 days.

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J.L. Garcia-Hernandez, E. Troyo-Dieguez, H. Nolasco, H.G. Jones, and A. Ortega-Rubio

The phytotoxic effects on the physiology of chili (Capsicum annum L. cv. Ancho San Luis) caused by four different insecticides were evaluated. Three commercial mixes (methyl azinfos, methyl parathion CE720, and metamidophos 600 LM), and an active ingredient alone (methamidophos) were assayed; water was used as the control. The main goal was to evaluate the insecticide effects on chili using four different doses; the mean dose, recommended on the label of the product (R), a half one (1/2R), 1.5 times (1.5R) and twice the recommended dose (2R). Three frequencies of application were applied; once a week, twice a week, and once every other week, for 6 weeks from the beginning of flowering. Phytotoxicity was evaluated measuring the response of some physiological traits, Chlorophyll Fluorescence (CF), Leaf Temperature (LT), Transpiration (Tr), and Stomatal Resistance (SR). CF was measured by means of a portable chorophyll fluorscence meter; LT, Tr, and SR were measured using a LI-Cor Porometer. The doses and frequencies used are all common in commercial chili fields in Mexico. Results showed that phytotoxicity caused by insecticides can be an important damage factor to the plants, something that can cause reduction of yields. CF was shown to be the most sensitive variable to evaluate the phytotoxicity caused by insecticides. Fruit malformation was observed in all treatments. Chlorophyll content was reduced up to 25%, on average. The phosphorate insecticides affected the physiological parameters more drastically than the others. Results evidence the irreversible crop damage caused by excessive insecticide applications.