Scientists with the Agricultural Research Service are a step closer to improving the cold hardiness of grape varieties grown in the northern United States.

Grapes, like many other woody plants, drop their leaves and go dormant in late fall.

If scientists can identify the gene or genes that control this process, they could help develop more cold-tolerant varieties, according to a news release.

The wild grape species Vitis riparia is unusual abecause it stops growing when the day length drops to less than 13 hours. Most other grape varieties are not sensitive to day length, says Amanda Garris, a geneticist at the ARS Grape Genetics Research Unit in Geneva, N.Y.

Garris and her colleagues identify genes for day length sensitivity in V. riparia.

The researchers crossed V. riparia with Seyval, a hybrid grape insensitive to day length.

They raised some of the offspring in fields and others in greenhouses, where they could control environmental variables.

As part of their work, they mapped differences among 120 DNA markers and six genes.

The work is considered a preliminary step toward identifying specific genes responsible for day length, Garris says.