The objective of this study was to determine if the growth of sweet orange (Citrus sinensis (L.) Osbeck cv. 'Valencia') nonembryogenic callus could be regulated and controlled via the mineral nutrient components of the medium. The 14 salts comprising Murashige and Skoog (MS) basal medium were subdivided into five component groups. These five groups constituted the independent factors in the design. A five-dimensional hypervolume constituted the experimental design space. Design points were selected algorithmically by D-optimality criteria to sample of the design space. Growth of the callus at each design point was measured as % increase of fresh weight at 14 d. An analysis of variance was conducted and a response surface polynomial model generated. Model validation was conducted by mining the polynomial for design points to two regions-"MS-like" growth and MS+25% growth and comparing callus growth to predicted growth. Five of the eight selected MS-like points and three of the six MS+25% growth points validated, indicating regions within the design space where growth was equivalent to MS, but the salt combinations were substantially different from MS, and a smaller region where growth exceeded MS by greater than 25%. NH 4 NO 3 and Fe were identified as important factors affecting callus growth. A second experiment was conducted where NH 4 NO 3 and Fe were varied, thus creating a two-dimensional slice through the region of greatest callus growth and provided increased resolution of the response.
The western corn rootworm (WCR), Diabrotica virgifera virgifera LeConte, is the most serious insect pest of corn (Zea mays L.) in the United States and parts of Europe, and arguably one of the world’s most expensive pests to control. Several diet formulations are currently used by industry and public researchers to evaluate WCR larvae in diet-toxicity bioassays. However, a publicly available diet that produces normative insects that are physiologically similar to WCR larvae reared on corn roots will accelerate development of management technologies. We report a new diet formulation that supports improved weight gain, larval development and survival compared with the only public diet for WCR that is currently available in the refereed literature. The formulation was created by using response surface methods combined with n-dimensional mixture designs to identify and improve the formulation of key ingredients. Weight gain increased two-fold, and survival and molting rates increased from 93% and 90%, respectively when reared on the public diet, to approximately 99% for both survival and molting at 11 days when reared on our new formulation. This new formulation provides a standardized growth medium for WCR larvae that will facilitate comparison of research results from various working groups and compliance with regulatory requirements.
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