Crop Wild Relatives

By: Perin McNelis, BRN Native Plant Program Assistant Manager

This summer, BRN’s Native Plant Program team continued its collaboration with the USDA Forest Service with support from the USDA Agricultural Resource Service to document and collect crop wild relatives (CWR) in the Wild Chile Botanical Area of the Tumacacori Highlands and surrounding public lands for future research and safeguarding of genetic material that may play a role in food security in the face of hotter drier conditions.

Wild Chile Botanical Area

What is a crop wild relative, and why are they important, you may be asking. As defined by the United States Forest Service, a crop wild relative is “a plant species occurring in the ‘wild’ that is a species from which the crop was domesticated, or a closely related species in the same genus to a particular domesticated crop species. Crop wild relatives may contribute genetic material to the crop species, which may provide for increased disease resistance, fertility, crop yield or other desirable traits.

Almost every species of plant that we humans have domesticated and cultivate has one or more crop wild relatives. When humans find plant characteristics that may be useful to us in crop wild relative individuals, we breed those CWR plants with desirable traits until those traits are maintained in all offspring. During this process of domestication, we focus on bringing out parts of the phenotype, or how the plant appears on the outside, that we like through breeding which in turn slowly alters the genotype. We maintain these traits through continued cultivation. Once we have achieved our cultivar, often the crop wild relatives cease to be used, but usually continue to grow in the wild. 

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Wild Chiltepines

Why are CWRs important? As we face unprecedented climate catastrophe, future food security is more important than ever. Gary Nabhan and Colin Khoury, who have advocated for CWR protection and research in our region for decades, write that “to produce good, affordable food while reducing the environmental impacts of production, more diversity will be needed both in the variety of plants cultivated or foraged for the market, and in the genetic variation within domesticated crops. Crop wild relatives offer the world both of these gifts.” CWRs that have adaptations for surviving and thriving in hot and dry conditions seem especially pertinent for the future of food security in the face of global warming. 

In their paper “Trans Situ Conservation of Wild Crop Relatives,” Gary Nabhan and Erin Riordan advocate for integrating in situ and ex situ strategies for CWR conservation by ramping up protective measures for landscapes where CWR plants grow, and maintaining ex situ backup in gene banks, while also promoting education, research, and relationship with these plants. BRN's CWR work is just a starting point that stemmed from this “trans situ” approach. Our work with CWRs started in 2019 and has primarily been focused in the Wild Chile Botanical Area.

Wild Chile Botanical Area outlined in red.

The Wild Chile Botanical Area (WCBA) is a 2,836-acre area under management of CNF and was designated in 1999 to protect the northernmost natural population of the chiltepin pepper (Capsicum annuum), the wild ancestor of many cultivated peppers. The special area was also created to provide protection and research opportunities for both the wild chile and other plants of economic importance or conservation concern.

At least 45 species of crop wild relatives (CWR) occur in the watershed containing the WCBA within the east side of the Tumacacori Mountains on the Nogales Ranger District. Many of these CWR species have proven or potential uses as crop genetic resources for improvement of domesticated crops already being grown commercially in Arizona and the rest of the U.S. and the world. The WCBA is also one of the most botanically interesting areas in southern Arizona, providing a fantastic snapshot of the unique biotic community of the Tumacacori Highlands, and is home to numerous plant species that are at the northern extent of their range and grow in few other locations in the United States. For this reason in and of itself, the WCBA deserves protective measures. 

In 2019 BRN played a small role in a project that the USFS was working on with support from USDA ARS to conduct a thorough botanical inventory of the WCBA. We supported the survey work which was lead by biologists from the Forest Service Enterprise Program, we then used the geolocations from the surveys to collect voucher specimens and seed that was sent to national germ plasm banks for research focused on the specific crop and its relatives.

This year we are continuing and expanding the project with the primary objective to continue locating and inventorying CWR and to collect seeds and voucher specimens of priority species for conservation and research. This is being done primarily in the WCBA and Coronado National Forest land in the Tumacacori Highlands, Santa Rita Mountains and Patagonia Mountains, for species not observed in the WCBA. Results of plant inventories for CWR will be used to determine if further protective designation for the WCBA should be pursued as an Important Genetic Resource Reserve (IGRR) for plant species in addition to the wild chile. 

Manihot davisiae or AZ Manihot, a wild relative of cassava.

There are over 300 taxa of CWR present in the Tumacacori Highlands area of southeastern Arizona, so BRN has partnered with Erin Riordan, a plant ecologist and researcher, to narrow down such a large list in order to prioritize species that have more urgent research and conservation needs, and to have a more targeted strategy for survey and seed collection work with limited timeline and people power. 

Although the insufficient precipitation during the monsoon season this year has posed a challenge to voucher and seed collection, this project feels urgent and timely, and BRN is thrilled to spearhead this work. 

Further reading from Erin Riordan on CWR.
Watch the zoom presentation by Perin McNelis to the AZ Native Plant Society, Tucson Chapter about our WCR work.