Regulation of growth and differential tissue dry mass accumulation by Citrus grandis, Poncirus trifoliata and their F1 under salinized and non-salinized environments

Salt stress responses of C. grandis L. (Osb.), P. trifoliata (L.) Raf. and their F 1 were investi-gated. Growth, growth rates, as well as leaf, stem, structural root (> 2 mm diameter), fine root (≤ 2mm diameter) and whole plant dry masses were determined for the three genotypes tested in 0, 40 and 80 mМ NaCl environments for 20 weeks. P. trifoliata and C. grandis were phenotypically distinct and their F1 had features that were a combination of both parents. The different growth habits resulted in significant differences between the net growth and growth ratios ([net growth / initial growth] × 100) of the three genotypes and between control and salinized plants within each genotype. The average growth and dry weights of nearly all tissues were reduced in salinized plants compared to those of control plants. The exceptions were the fine roots of P. trifoliata at both salinities and of the F1 plants at 40 mМ NaCl. The 40 mМ NaCl treatment stimulated fine root production in P. trifoliata plants, significantly increasing dry weight by 30% compared to control plants. Average shoot dry weight reduction was greatest in C. grandis and least in P. trifoliata in the 40 mМ NaCl treatment. While leaf tissues of P. trifoliata were the most sensitive to salinity, root tissues were the most sensitive in C. grandis. To avoid salt accumulation, P trifoliata plants increased root dry mass production while C. grandis plants increased leaf mass production. These traits appeared to be heritable, since the F1 plants displayed responses intermediate to its parents leading to increased salinity tolerance. We suggest that not only ion content of leaf tissues, but ion content and mass production of all tissues should be considered when the salinity tolerance of Citrus and related genera is characterized.