Thifensulfuron susceptibility in tomatoes and possible linkage with blossom end rot

Jim Dick, Tomato Solutions, 23264 Mull Road, Chatham, Ontario, Canada N7M 5J4

jimdick@netrover.com

Thifensulfuron (brand name Pinnacle in Canada) is a broadleaf herbicide registered on processing tomatoes in Canada.  It is applied as an overall spray about 3-4 weeks after transplanting.  Some hybrids and inbred lines are quite susceptible to the herbicide.  An inbred line called N1069 was found to have about 10% susceptible plants.  Except for the susceptibility to thifensulfuron, the plants were identical to the resistant plants.  It was assumed therefore that a mutation had arisen spontaneously.  Seed was saved from both resistant and susceptible lines and grown out to confirm resistance and susceptibility.  The two lines bred true for either resistance or susceptibility with no segregation, and appeared exactly identical for all horticultural traits.  The F1 hybrid was made between the two lines, and F2 seed was produced and grown out.  The F2 population segregated for resistance and susceptibility in a 3:1 ratio indicating that there was a single recessive gene involved.  Crosses made with another thifensulfuron susceptible inbred line called CC390 also indicated that a single recessive gene was involved.   Hybrids using the susceptible N1069 crossed with resistant lines were all resistant.  Under extremely dry conditions, it was found that the susceptibility to thifensulfuron was associated with susceptibility to blossom end rot in the N1069 inbred lines.