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  • Author or Editor: Charles L. Guy x
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There is wide variation in Citrus and related genera in tolerance to cold and salt stress. While Poncirus trifoliata (L.) Raf. is an important rootstock for cold regions, it is salt sensitive. C. grandis (L.) Osb., on the other hand, is cold sensitive, but is relatively salt hardy. We are attempting to map genes (quantitative trait loci, QTLs) influencing salt and cold tolerance in Cirrus, using a BC1 population from [C. grandis × (C. grandis × P. trifoliata)]. As a first step, 2 year old containerized replicates of individual BC1 progeny plants have been salinized with 30 mM NaCl over a 9 month period under greenhouse conditions. Growth response under saline conditions, as evaluated by plant height and node number, varied significantly between individual progeny. Concentrations of 11 macro- and micro-elements, including Na and Cl, in leaf and root tissues were also determined. Ultimately, this data will be analyzed in conjunction with our current linkage map of this population, which consists of more than 200 marker genes, in order to map QTLs for salt tolerance.

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It has been previously established that cold acclimation increases freezing tolerance in Citrus. Because both salt and cold streeses are osmotic stresses, salt application may also increase freezing tolerance. Freezing tolerance of salt treated `Pineapple' orange (C. sinensis [L.] Osb.), large pink pummelo (C. grandis [L.] Osb.), and Pomeroy trifoliate orange (Poncirus trifoliata [L.] Raf.) seedlings is being examined. LT50s for each species under our freezing conditions were established by subjecting nonacclimated and cold acclimated plants to temperatures ranging from 0 to -19°. Seedlings were treated with various concentrations of NaCl (0, 40, 80, and 150 mM) under cold-acclimating and nonacclimating conditions for 2 months, then subjected to freeze stress and examined for ability to recover. In an initial trial, pummelo seedings treated with 40 and 80 mM salt under cold-acclimating conditions displayed an increase in freezing tolerance, while exposure to any level of salt decreased freezing tolerance of sweet orange and trifoliate orange seedlings.

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