With the impact of climate change on agriculture becoming ever-more apparent, food producers and researchers need to be able to adapt quickly to environmental pressures. A greater reliance on nut crops could play an important role in this adaptation. Nuts are nutritionally dense and one of the most climate efficient food sources of protein. For example, producing 100 grams of beef protein generates almost 50 Kg of greenhouse gases, which is more than 150 times the greenhouse gas emissions produced for the same amount of nut protein 1.
Nuts have several appealing characteristics that make them a suitable crop for climate change. Pistachio is drought resistant and salt tolerant2,3 and both pistachio and walnut are wind pollinated, decoupling nut production from reliance on insect pollinators. As the effects of climate change progress insect pollinator populations are expected to decline4, so having nuts that aren’t reliant on insect pollinators could be an important consideration. While nuts are encouraging as sources of sustainable protein, there are challenges to the adoption of nut crops as well.
My work at the University of California, Davis is addressing some of the major challenges in cultivating pistachio and walnut production so that these crops can play a larger role as a sustainable food source. My projects specifically focus on three challenges hampering the pistachio and walnut industry to help make these nut crops increasingly viable.
One of the largest challenges facing the pistachio industry is what is known as chilling requirement. Chilling requirement is the minimum amount of time a plant needs under a certain temperature for flowering. Pistachio needs around 750 – 1400 chill hours depending on the cultivar5. The effects of climate change have led to a general reduction in the number of these chill hours. If the plants don’t receive enough chill hours, they will not flower and therefore will not produce nuts. This problem can be addressed by lowering the chill hours needed by our pistachio cultivars. To address this challenge, I am working with a large group of diverse pistachio species. With this large population, we hope to identify trees with lower chilling requirement and other traits that may be beneficial to the pistachio industry. These trees can then be used in the breeding program to introduce desirable traits and create new and better adapted cultivars.
Another challenge I am helping address is the time that it takes to identify new cultivars of nut crops through the generation of new reference genomes. A reference genome is like a map of the plants DNA. They tell breeders what genes are present and where they are located, so that the breeders can make better informed decisions. Cereal crops, like wheat, can go through multiple generations in a year6, but unfortunately the time it takes to breed nut crops is drastically longer. In pistachio and walnut, trees don’t begin to flower until they are several years old, decreasing the speed with which we can breed better varieties of these crops. This challenge requires us to create state-of-the-art tools and techniques to ensure that we can make the breeding process as fast and efficient as possible. Gene editing is a promising technology to help address this issue of slow breeding time, but we need high quality reference genomes order to employ this tool.
A third challenge facing pistachio and walnut production involves their propagation, or how we make new plants. Unlike crops that are grown from seed, like fast-growing corn or barley, we propagate tree crops like pistachio and walnut clonally through cuttings. This means that we take a piece of a tree with desirable properties like high yield and disease resistance and plant it out in the field. The plant that grows is genetically identical to the plant that we took this cutting from. This is mostly a good thing, as it allows growers to be confident in the genetics of their crop, but also presents its fair share of challenges. This system can provide an opportunity for diseases and pests to infest entire orchards, as all the trees are identical. If a plant is susceptible to a disease, all the other plants will be as well. This is a major concern in the context of climate change, as disease and pest pressures are increasing. Another problem that can occur when propagating plants clonally is due to mutation. While the plants are mostly genetically identical, very rarely a mutation can arise, and even more rarely that mutation may change something about the plant. It could make what is normally a high yielding variety produce less nuts. While rare, higher mutation rates have been observed in higher temperatures7. To understand the scope of this issue, I am investigating mutation in these plants so we can have a better idea about how frequently mutations are occurring.
With these projects, I hope to help in the effort to maintain sustainable nut crops into the future. While pistachio and walnut are good candidate nut crops for climate change, the solution won’t be putting all our nuts in one basket. We should be working to prepare as many nut crops as possible for the future, and while pistachio is a prime candidate nut crop, more work is needed to prepare it for climate change.
Support from the FFAR Fellows Program and the California Pistachio Research Board is providing me with an incredible opportunity to address critical challenges in agriculture and to develop professionally. With their support I am able to explore interesting questions in genomics, help contribute new resources to assist breeders, and cultivate professional relationships while preparing for my career.
Citations:
1Poore, J., & Nemecek, T. (2018). Reducing food’s environmental impacts through producers and consumers. Science, 360(6392), 987-992.
2Bagheri, V., Shamshiri, M. H., Shirani, H., & Roosta, H. R. (2011). Effect of mycorrhizal inoculation on ecophysiological responses of pistachio plants grown under different water regimes. Photosynthetica, 49, 531-538.
3Tajabadi Pour, A., Sepaskhah, A. R., & Maftoun, M. (2005). Plant water relations and seedling growth of three pistachio cultivars as influenced by irrigation frequency and applied potassium. Journal of Plant Nutrition, 28(8), 1413-1425.
4Potts, S. G., Biesmeijer, J. C., Kremen, C., Neumann, P., Schweiger, O., & Kunin, W. E. (2010). Global pollinator declines: trends, impacts and drivers. Trends in ecology & evolution, 25(6), 345-353.
5Rahemi, M., & Pakkish, Z. (2009). Determination of chilling and heat requirements of pistachio (Pistacia vera L.) cultivars. Agricultural Sciences in China, 8(7), 803-807.
6Watson, A., Ghosh, S., Williams, M. J., Cuddy, W. S., Simmonds, J., Rey, M. D., … & Hickey, L. T. (2018). Speed breeding is a powerful tool to accelerate crop research and breeding. Nature plants, 4(1), 23-29.
7Lynch, M. (2010). Evolution of the mutation rate. TRENDS in Genetics, 26(8), 345-352.