Identifying Efficient Nitrogen-Uptake Genotypes from Tomato Germplasm Banks.

Florida is one of the leading states producing fresh market tomatoes (Solanum lycopersicum L.). There are more than 50 tomato varieties grown in Florida. Nitrogen (N) fertilization is the main part responsible for fertilization costs for tomato production. Increasing N uptake efficiency can improve N-use efficiency. Nitrogen use efficiency of tomato grown in Florida ranged from 146 to 388 kg/kg. The difference can be attributed to the significantly genotypic difference in N uptake efficiency. Thus, tomato seedling screening was hydroponically conducted in summer 2017 to identify the varieties with the greatest N uptake efficiency. Twenty-five commonly used varieties were employed in this experiment. Seeds were planted in rockwool in a complete randomized design with three single-plant replications until Day 5 (D5) and then transplanted without rockwool into an aeroponics system with 10% strength Hoagland solution. On D25, three uniform seedlings of each of the tested genotypes were selected as three replications and individually re-transplanted into a 5-cm diameter mesh cup hung on the 4.5-cm mouth of a brown plastic bottle with a 1000 ml containing 200 µM CaCl₂ and 529 µM H₂O₂ for nitrogen starvation for three days. Then, the seedlings were individually moved into a 1000 ml measuring solution with 2 ppm N as NH₄NO₃ with 200 µM CaCl₂ and 529 µM H₂O₂. Eight hours after the seedling uptake, a 20 ml solution sample was collected from each replication to measure ammonium N and nitrate N concentration by using a discrete analyzer, AQ2. The genotypic differences in N uptake of either ammonium or nitrate will be presented at the meeting.