Assessing tomato germplasm for potentially toxic elements tolerance using physiological and genomic markers

The scarcity of freshwater resources compels farmers to utilize wastewater for irrigation. The current study aimed to assess the performance of tomato (Solanum lycopersicum L.) genotypes for potentially toxic elements (PTEs), i.e., Ni, Pb, Mn, Zn, and Cr genetic tolerance. For this purpose, 44 tomato genotypes were grown in the field conditions under sewage water (T1) and canal water (T2) irrigation to screen tolerant and sensitive genotypes based on PTEs accumulation in reproductive and vegetative parts of both treatments. Selected genotypes were validated under hydroponic conditions with the same PTEs concentrations. Gene expression of metallothionein (MT) and heat shock protein (HSP) was assessed using ubiquitin (UBQ) as reference gene. The PB-017906 genotype was selected as the best metal-tolerant, and the 10592 was identified as high-yielding, and thus recommended for commercial production. At 200 μM Pb concentration, target genes, i.e., HSP and MT transcribed profusely 63.27 and 38.81 times, respectively in leaf tissue of "Riograndi" as compared to other genotypes. While in low metal accumulator PB-017906 genotype MT transcription in leaf tissue at 200 and 400 μM Pb concentrations was insignificantly upregulated (1.28 and 1.86 times than control), followed by CLN-2418A. RT-PCR clearly revealed Cr stress induced higher HSP and MT transcription in leaves at 200 µM (2.55 and 4.05 times), and same trend was observed in roots. The upregulation of MT and HSP genes may be attributed to PTEs tolerance mechanism and tolerance capacity largely depends upon the genetic variability of the plant. Current findings highlighted tomato germplasm genetic variability as a basis for PTE tolerance, and selected tolerant genotypes capable of sustainable agriculture under PTE stress. Hence, these genotypes could also be used for breeding tomatoes with low PTEs bioavailability and better yields. This would help to improve food security and environmental protection by allowing more crop production in contaminated regions.