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No abstract

sand to ammonium (NH.*) or nitrate (NOr-) N source was investigated in controlled environments at27"lll", l9olll" and. lgol'loC day/night temperatures. Ammoniumtreated plants developed leaf chlorosis and necrosis. The pH of leachate from the rooting medium dropped from an initial level of 6.0 to values of 3.5-3.9 for NHo*-treated plants, while the pH increased to about 6.5 for NOr--treated plants. The NOr--treated plants had much greater growth overall than NHo*-treated plants. Temperature had little or no effect on plant responses to N source. The NOr--treated plants contained higher NO.-and Ca but lower total N, NHn* and P than NHo*-treated plants.Key words: Temperature, ammonium, nitrate, white bean, navy bean, phytotoxicity [R6action du haricot blanc i I'ammonium ou au nitrate i trois temp6ratures.]

Gigantism is a key component of the domestication syndrome, a suite of traits that differentiates crops from their wild relatives. Allometric gigantism is strongly marked in horticultural crops, causing disproportionate increases in the size of edible parts such as stems, leaves or fruits. Tomato (Solanum lycopersicum) has attracted attention as a model for fruit gigantism, and many genes have been described controlling this trait. However, the genetic basis of a corresponding increase in size of vegetative organs contributing to isometric gigantism, has remained relatively unexplored. Here, we identified a 0.4 Mbp region on chromosome 7 in introgression lines (ILs) from the wild species Solanum pennellii in two different tomato genetic backgrounds (cv. M82 and cv. Micro-Tom) that controls vegetative and reproductive organ size in tomato. The locus, named ORGAN SIZE (ORG), was fine-mapped using genotype-by-sequencing. A survey of literature revealed that ORG overlaps with previously mapped QTLs controlling tomato fruit weight during domestication. Alleles from the wild species led to reduced cell number in different organs, which was partially compensated by greater cell expansion in leaves but not in fruits. The result was a proportional reduction in leaf, flower and fruit size in the ILs harbouring the wild alleles. These findings suggest that selection for large fruit during domestication also tends to select for increases in leaf size by influencing cell division. Since leaf size is relevant for both source-sink balance and crop adaptation to different environments, the discovery of ORG could allow fine-tuning of these parameters.