Regulation of growth and differential tissue dry mass accumulation by Citrus grandis, Poncirus trifoliata, and their F-1 under salinized and non-salinized environments

Salt stress responses of C. grandis L. (Osb.), P. trifoliata (L.) Raf. and their F-1 were investigated. Growth, growth rates, as well as leaf, stem, s tructural root (> 2 mm diameter), fine root (less than or equal to 2mm diam eter) and whole plant dry masses were determined for the three genotypes te sted in 0, 40 and 80 mM NaCl environments for 20 weeks. P. trifoliata and C . grandis were phenotypically distinct and their F-1 had features that were a combination of both parents. The different growth habits resulted in sig nificant differences between the net growth and growth ratios ([ net growth / initial growth] x 100) of the three genotypes and between control and sa linized plants within each genotype. The average growth and dry weights of nearly all tissues were reduced in salinized plants compared to those of co ntrol plants. The exceptions were the fine roots of P. trifoliata at both s alinities and of the F-1 plants at 40 mM NaCl. The 40 mM NaCl treatment sti mulated fine root production in P. trifoliata plants, significantly increas ing 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 m M NaCl treatment. While leaf tissues of P. trifoliata were the most sensiti ve to salinity, root tissues were the most sensitive in C. grandis. To avoi d salt accumulation, P trifoliata plants increased root dry mass production while C. grandis plants increased leaf mass production. These traits appea red to be heritable, since the F-1 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 a ll tissues should be considered when the salinity tolerance of Citrus and r elated genera is characterized.