Detection of QTLs associated with shoot wilting and root ammonium uptake under chilling temperatures in an interspecific backcross population from Lycopersicon esculentum x L-hirsutum

The genetic basis for shoot wilting and root ammonium uptake under chilling temperatures was examined in an interspecific backcross (BC1) population d erived from Lycopersicon esculentum Mill. cv T5 and wild Lycopersicon hirsu tum f. typicum accession LA1778. The chilling sensitivity of shoot wilting and ammonium uptake was evaluated in four replicated cuttings from each of 196 BC1 plants. Wilting was evaluated at two different times: 2 hours (wilt ing 2 h) and 6 hours (wilting 6 h recovery) after root exposure to 4 degree sC. The BC1 plants were genotyped with 89 polymorphic RFLP markers, and com posite interval mapping was used to detect quantitative trait loci (QTLs). Three QTLs, one each on chromosomes 5, 6 and 9, were detected for wilting 2 h. The presence of a L. hirsutum (H) allele at the QTL on chromosomes 5 an d 9 decreased wilting, while the H allele at the QTL on chromosome 6 increa sed wilting. To analyze plant recovery from wilting at 6 h, subsets of the BC1 population were selected, based on phenotype and genotype, because not all plants wilted at 2 h. The phenotype subset (wilting 6 h-PS) included pl ants that wilted to a greater degree at 2 h, and the genotype subsets inclu ded plants carrying specific allelic compositions at the QTL for wilting 2 h on chromosomes 5 (wilting 6 h-GS-ch5), 6 (wilting 6 h-GS-ch6), and 9 (wil ting 6 h-GS-ch9). On chromosome 6, a QTL was located that was associated wi th three subsets (wilting 6 h-PS, wilting 6 h-GS-ch5 and wilting 6 h-GS-ch9 ), while on chromosome 7 a QTL was detected with two subsets (wilting 6 h-P S and wilting 6 h-GS-ch5). Three additional QTLs were detected within a sin gle subset: chromosome 1 (wilting 6 h-GS-ch6), chromosome II (wilting 6 h-G S-ch5) and chromosome 12 (wilting 6 h-GS-ch9). The presence of the H allele at the QTL on chromosomes 7 and 12 had a positive effect, enhancing recove ry from wilting, while the H allele at the other QTL had a negative effect. Three traits were used to evaluate the chilling sensitivity of root ammoni um uptake: ammonium uptake before a chilling episode, ammonium uptake after the chilling episode, and the relative inhibition of uptake (difference in uptake rates before and after chilling divided by the rate before chilling ). One QTL was detected on chromosome 3 for the rate before chilling and on e on chromosome 6 for the relative inhibition of ammonium uptake. Our resul ts demonstrate that shoot wilting and ammonium uptake under chilling are co ntrolled by multiple QTLs.