Walnut production research goes back several decades. But the initial research depended a lot on the University of California system and interest of researchers. It was in 1971 that walnut industry joined forces with UC Davis to formally launch an industry supported production research program. That year, one project received funding of about $ 25,000. From that small beginning, this partnership has grown leaps and bounds just as the industry has and now more than a dozen projects totaling some $ 1.6 million are underway. These cover orchard management, entomology, walnut breeding, pest management, and so on. The industry has benefitted from this partnership in a variety of ways, from having tools to address diseases and pests to better yielding varieties. Further, the California Walnut Board research endowment to ensure continued research into walnut breeding now stands at $ 2.9 million. Part of the ‘California Walnuts’ brand appeal has been consistent quality, and the production research program has certainly played a major role in that.
Over the years, production research has played an important part in providing practical tools to growers.
Orchard management is perhaps the most encompassing field of research as it deals with several aspects of production – rootstock, new varieties, cultural practices throughout the year, water management, tree and soil nutrition, and so on. Since partnering with UC Davis more than 4 decades ago, the ongoing research has resulted in several new varieties and rootstocks that are widely used today by walnut growers. Some of the varieties include Chandler, Howard, Vina and rootstocks include VX211, Paradox, and Vlach. Compared to older varieties and rootstocks, the newer ones can be planted more densely and are bred for disease resistance. This allows for more production while keeping the losses as low as possible. Further, improvement in orchard management practices has resulted in water conservation as flood irrigation has mostly given way to micro irrigation (drip, micro sprinklers) which can be programmed to operate in tandem with soil moisture sensors so trees are irrigated only when needed. In addition, better disease resistance has also resulted in lowering the use of chemicals. Given the current drought in California, some of the ongoing research is focused on improved water management strategies and managing soil nutrition to avoid leaching into ground water.
The field of plant pathology deals with studying plant diseases and identifying solutions to it. These diseases could be a result of pathogens (fungi, bacteria, viruses) or environmental factors. Some of the common diseases affecting California walnuts include Botryospheria and Walnut Blight. The California Walnut Board and Commission has partnered with UC Scientists on several projects aimed at finding solutions to various diseases through a combination of strategies – suitable chemicals, improved orchard management practices or more disease resistant rootstocks. This allows the growers the option to choose from a toolkit what’s best for their operation and unique scenarios.
Genetic improvement is perhaps the most exciting field as development in gene analysis technology leads to a better understanding of which genes control what aspects of production, harvest time, pellicle color, lateral branching, and so on. UC Davis recently announced that the walnut genome was completely mapped for the first time. What this means is that we now have a better understanding of how the tree functions and what triggers certain functions. Aside from the obvious implications of this for future breeding efforts, we can also identify the ‘culprit’ genes that may be responsible for controlling how and if the tree responds to pathogens and infections. This will vastly speed up improvement in disease resistance compared to conventional breeding techniques. This is the way of the future! Some of the interesting research aims to identify genes responsible for resistance to soil borne pathogens. This, in turn, would help the industry reduce or eliminate dependence on soil fumigants, which are becoming increasingly regulated. In the same vein, identifying disease resistance genes for other diseases like crown gall, Phytopthora, root lesion nematode or Armillaria root disease and expressing them in future rootstocks could help the industry save thousands of dollars in fumigants, fungicides and pesticide costs.
Just like any other commercial crop, walnuts are also susceptible to a variety of insect pests. The entomology research focuses on identifying potentially dangerous pests for the walnut tree and ways of mitigating this pest pressure. Some of the important walnut pests are Husk Fly, Coddling Moth and Navel Orange Worm. Besides the obvious commercial aspects of managing pests, identifying and dealing with them is especially important as majority of walnuts are exported and the importing countries have regulations to prevent sale of any commodity with a potential of spreading diseases for their own local crops. As such, it becomes important to manage these pests with both chemical and biological controls and better orchard management and post-harvest practices. Entomology research focuses on identifying the life stages of problem pests and various ways of controlling them so growers can have options should they need them. The variety of options in the grower toolkit also helps in preventing resistance buildup.
In sum, the walnut research program has been of invaluable help to growers by providing them with improved varieties with desirable traits, various options for dealing with disease and pests and better orchard management tips to maximize the production with optimum resource input.