By Amanda Garris
Dr. Peter Cousins joined the USDA-Agricultural Research Service Grape Genetics Research Unit in Geneva, New York, in 1999 as a rootstock breeder and geneticist. As a USDA scientist and adjunct faculty in the Department of Horticulture, he breeds new rootstocks using wild species that are resistant to pests such as the root-knot nematode. His new and improved rootstocks are being tested across the country from the Lake Erie grape belt of New York, to the Rio Grande Valley of Texas and the San Joaquin Valley of central California. He is a frequent guest lecturer in Cornell undergraduate courses on variety identification, rootstocks, and grapevine evolution and ecology.
How did you end up here in New York, working with grapes?
I grew up on a tomato farm in the northern part of California's San Joaquin Valley. From an early age, I enjoyed plants both from an agricultural and a botanical perspective. As an undergraduate I studied biological sciences with a botany emphasis, and I thought that I would become a botanist. However, my interest in genetics and background in pedigreed show rabbits and sheep conspired with my love of plants to direct me into graduate study in plant breeding at the University of California, Davis. There I met professor Andy Walker, who showed me that grapes are not only one of the most important crops in the world—they are fascinating botanically. What a combination! Since then I've been hooked on grapes. I conducted my graduate studies at UC Davis with Dr. Walker and arrived in Geneva to work with the USDA Agricultural Research Service (USDA ARS) as the grape rootstock breeder in November 1999.
What are the major challenges in breeding rootstocks?
The major challenge in grape breeding is the time required to evaluate new selections. If we want to know how a potential rootstock will perform in the vineyard, we can complete the preliminary nematode resistance screening within nine months of the cross pollination being made. But it takes several years for the vine to grow large enough to provide dormant cuttings for propagation testing and grafting, then several more years for the grafted vines to be evaluated in vineyards. In other words, if you want to know what the average growth, yield, or other characteristics of vine performance are going to be over three years, the experiment is going to take at least three years. Patience is a virtue in all viticulture and enology, but perhaps even more so in breeding. Once a new variety is developed, however, it can be cultivated for many, many years.
What projects are going on in your program right now?
The USDA ARS rootstock program evaluates currently available rootstocks and releases new rootstocks for diverse growing conditions. Along the way we are developing the knowledge, methods, and germplasm to improve our ability to evaluate rootstock selections. Enhancing resistance to aggressive root-knot nematodes is the biggest component of the rootstock research program. In U.S. vineyards, root-knot nematodes are the most important soil pest. They affect more acres than any other soil pest—including grape phylloxera. I expect that our first new nematode-resistant rootstock varieties will be released to nurseries this year.
I'm also cooperating with USDA ARS researchers in the Rio Grande Valley of southern Texas to study the impact of rootstock variety on Pierce's disease (PD) symptoms in Chardonnay. PD is a bacterial disease of grapevines; the causal agent is spread by xylem-feeding insects. Chardonnay and other Vitis vinifera varieties are very susceptible to PD and the Rio Grande Valley is full of PD but otherwise amenable to viticulture.
To provide better tools for accelerating grape breeding and genetics, I am developing precocious and continuously flowering research grapevines, such as the 'Pixie' grape. Typically a grapevine seedling needs to grow at least three years in a vineyard before it flowers and fruits. Some of our vines have the ability to flower—and produce fruit—just a few months after the seed is planted in the greenhouse. Our goal is to make grape breeding and genetics faster and easier, bringing benefits to grape growers and wine makers more quickly.
In addition to hybridization and breeding projects, I am leading two projects in clonal selection; one in rootstocks (to develop lower vigor clones) and the other project to identify higher quality clones of Vignoles. Amanda Garris originally developed the Vignoles clonal selection project, the goal of which is to produce a 'loose clustered' Vignoles that will be less prone to botrytis and other fruit rots. This study is being conducted in cooperation with Cornell researchers at the Cornell Lake Erie Research and Extension Laboratory in Portland, New York. I have been responsible for that project since January 2010.
How will your research benefit the grape industry?
My research will result in improved varieties and clones that will help grape growers and wine makers produce more grapes and wine that meet or exceed composition targets while reducing their inputs of pesticides, energy, and water.
From your perspective as a grape breeder, what characteristics would the ideal grapevine have?
The domestic grapevines that we cultivate are not very different in form from wild grapevines, yet conditions in viticulture are quite different from those in nature. There are many opportunities to change grapevine growth habits through breeding to better match the needs of grape growers and wine makers. An ideal grapevine would have excellent light and air penetration into the canopy and fruiting zone, minimal growth of lateral shoots, no tendrils, and relatively few lateral buds at the distal ends (tips) of the canes. The canopy would have many small leaves with petioles longer than the leaf blade main vein and few non-count shoots (i.e., shoots that come from latent buds and are not 'counted' at pruning). The shoots would tend to grow upright. Clusters would be loose and amenable to mechanical harvest with little berry juicing.