Breeding tomato for fruit production with urban sewage water

Abstract

Wastewater is often used for irrigation, especially in farming near urban areas, causing heavy metal accumulation and pathogenic infection in soils and crops grown there. A socio- economic survey conducted in a peri-urban area in Faisalabad called “Uchkara” revealed that in spite of being aware of the potential harmful effects of waste water, farmers preferred to use it due to its low cost and lack of alternatives. Comparison of irrigation water from different sources showed that in wastewater the concentrations of Cr, Mn, Zn, Ni, and Pb were many folds higher than their recommended safe limit, rendering affected water sources unfit for use in irrigation. Crops irrigated with this waste water also had very high concentrations of heavy metals. Higher concentrations were found in leafy vegetables than in other crops. Screening was carried out to identify high yielding and heavy metal tolerant tomato genotypes when irrigated with waste water. Diverse tolerance to heavy metals and yield- related traits were observed among tomato accessions. Higher concentrations of metals were found in vegetative parts than in fruits. The concentrations of Cr (0.35-50 ug/g), Mn (3.75- 16.25 ug/g), Ni (0.75-3.25 ug/g), Pb (0-3.75 ug/g) and Zn (13.74-69.5 ug/g) varied in fruit tissues of different tomato accessions. The tomato accessions PB-017906 and 10592 had better fruit yield and appeared relatively tolerant to heavy metals accumulation. With maternal effects and additive type of gene action was involved in the inheritance of number of flowers and number of fruits, while a dominance type of gene action was involved in the inheritance of heavy metals tolerance. Transcriptome analysis of heavy metal tolerance genes i.e., HSP and M. Thio showed that tomatoes respond to high concentrations of heavy metals through increased transcription of the HSP and M. Thio genes. It was observed under Pb and Cr stress that HSP and M. Thio protein transcripts accumulated to levels many times higher than in the in roots and leaves of control plants, reducing protein damage from heavy metals and sustaining cellular homeostasis. PCR-based diagnostics showed that the waste water had S. enterica bacterium. In contrast, tomato fruits were free of S. enterica contamination in 14 out of 16 (87.5%) tomato accessions, showing that most of the time S. enterica was physiologically blocked from gaining access to the tomato fruit. Although waste water application is the need of time the resulting information from this research will be helpful in the development of low metal-accumulators as well as S. enterica tolerant tomato genotypes suitable for heavy metals and bacterial problems by the use of wastewater.