In the period from 1960 to 1980 rootstocks were commonly used in greenhouse vegetable cultivation. After the introduction of the substrate cultivation the earthbound diseases vanished and rootstocks seemed unnecessary. But when it was discovered in the tomato cultivation that grafted plants had extra resistance to diseases like Verticilium and Pepino mosaic virus, the use of rootstocks increased again. Now around 90% of the area of tomatoes is on a rootstock. An added advantage is the increase in production of the grafted plants.
Good rootstocks are available for tomatoes, mainly crosses between the cultured tomato and wild tomato varieties. But to progress in the selection of new rootstocks it's necessary to understand how a rootstock influences the growth and production of the part above the ground.
Vigorous rootstocks
In the EU project ROOTOPOWER researchers are trying to explain how the roots influence the growth of the plants above the ground and which genes are responsible for this. For this, one variety is grafted onto a population of rootstocks, a mix between a wild tomato (Solanum pimpinellifolium) and a cultured tomato. It's determined from this graft how the growth above ground is influenced by the rootstocks.The growth of the graft is determined by cytokinins, a plant hormone which is produced in the roots. Through the sap stream (xylem) the cytokinins are transported to the parts above ground. At the end of the tests with rootstocks, the plants are cut above the grafting spot, and xylem sap is gathered. In this hormones are determined and to check which role these hormones play in the communication between the rootstock and the graft.
By combining this data with the hereditary characteristics of the rootstocks, the researchers expect it will be possible for breeders to select vigorous rootstocks early on.