Yield and quality evaluations on a pair of processing tomato lines nearly isogenic for the Tm2^a gene for resistance to the tobacco mosaic virus

A pair of processing tomato (Lycopersicon esculentum Mill.) lines, nearly isogenic for the Tm-2^a gene for resistance to tobacco mosaic virus, were grown in replicated trials under commercial production conditions in five locations worldwide. The lines were evaluated for 17 processing traits including fruit yield, size, soluble solids concentration, color, firmness, and viscosity. Eight of those traits differed significantly among the nearly-isogenic lines (NILs). Most notably, the NIL heterozygous for Tm-2^a yielded, on average, 16% more than the NIL homozygous for the susceptible allele and 33% more than the NIL homozygous for Tm-2^a. Viscosity was lower in the heterozygous NIL and the homozygous and heterozygous resistant NILs had softer fruit with larger stem scars compared to the homozygous susceptible NIL. These results indicate the presence of the Tm-2^a locus affects many traits of importance for processing tomatoes and may be used, in the heterozygous state, to significantly increase yield. Whether the observed effects are due to the Tm-2^a gene itself or genes associated via linkage drag could not be determined.