When an aphidlike insect known as the grape phylloxera louse punctures grapevine roots to suck nutritious juices, it creates a handy hole that grape disease organisms can enter. The combined effects of phylloxera's feeding and the diseases caused by the microbes that sneak in through the punctures may eventually kill infested vines.
Known to scientists as Daktulosphaira vitifoliae, phylloxera is one of the world's most destructive vineyard pests. In greenhouse and outdoor tests, Agricultural Research Service research horticulturist David W. Ramming at Fresno, California, is scrutinizing the phylloxera resistance of popular grapevines. And he is investigating experimental grapevines that have already shown promise in tests of other critical traits, such as resistance to wormlike, soil-dwelling pests called nematodes. In addition, his team is raising seedlings from the parent grapevines of the best performing offspring, in an effort to unlock secrets about inheritance of phylloxera resistance.
On another front of the phylloxera battle, ARS-funded studies at the University of California at Davis have produced a convenient, practical test for estimating a plant's phylloxera susceptibility in only 8 weeks. Grape plantlets and the surface of phylloxera eggs are first sterilized to kill any fungi and bacteria that might skew test results, then are placed inside small, clear-plastic boxes equipped with a bed of nutrient-rich gel. Insects and plantlets then grow in tandem inside the boxes, which are housed in a temperature-controlled growth chamber--something like a walk-in refrigerator.
The technique is an improvement on earlier approaches in which egg surfaces were not sterilized. M. Andrew Walker and colleagues at UC Davis determined how to do it without killing the phylloxera embryos. The team has already produced new phylloxera-resistance estimates for some 40 different plantlets--most grown from samples from the ARS grape genebank at Davis.
Researchers can also snip off bits of plantlet roots, right after hungry phylloxera attack, to see if resistant grapevines form natural chemicals that repel the tiny pests. These compounds may be a key to phylloxera resistance. If so, scientists might be able to trace the chemicals back to the grapevine genes that control them and, after that, perhaps rebuild the genes to boost their effectiveness. Or the scientists might transfer the genes into phylloxera-susceptible vines.--By Marcia Wood, Agricultural Research Service Information Staff. .
"A Possible Preventive for Phylloxera" was published in the December 1998 issue of Agricultural Research magazine.