Authors: Kate Evans, Washington State University, and Michael Coe, Cedar Lakes Research Group, LLC
This blog is based on researched published in Crop Science Journal (https://acsess.onlinelibrary.wiley.com/doi/10.1002/csc2.20227)
What is the status of public plant breeding programs in the United States?
Most plant-based foods we eat today are a product of innovative plant breeding programs. Careful choice of plant parents is followed by a multitude of intentional, hand-pollinated blooms. These result in thousands of unique seeds. This is just the start of a long process to create better crops.
In a paper we published recently in Crop Science, we outline a very critical issue: U.S. public investment in plant breeding programs has fallen. The current funding model of short-term grants (1-, 2- or sometimes 5-year awards) is particularly challenging for breeding programs which require typically a 7- to 12-year process, or far longer.
Crop breeders are not just looking for characteristics like drought tolerance or disease resistance in their breeding programs. They also must create new crops with these characteristics that taste good!
- Breeders select plant parents based on desirable characteristics. These could be taste, size, cooking ability, yield, disease resistance and more.
- They then cross-pollinate, growing seeds that are hybrids of the parents. They are the “children.”
- These “child” seeds are germinated, nurtured, and then meticulously evaluated. Many inferior seedlings are ultimately discarded, with only a few of them advancing to a new round of parenting.
Crops go through many such cycles of newly-created diversity and intentional selection. Eventually, the plant breeder may become satisfied that an elite seedling has what it takes to become a successful new variety. This practice is a long-term endeavor. Some crops can be brought to market in a few years, but crops like apples can take well over a decade.
The benefits of public plant breeding programs
As a result of plant breeding, yields and quality have increased, resulting in remarkable improvements in agricultural production systems. Related species have been used as parents to give important crop plants tolerance to biological and physical stressors. New varieties are adapted to withstand harsh growing conditions or potentially devastating invasive pests or diseases. As climate conditions and ecosystems change, plant breeding is an essential tool to address our long-term food security.
Both private and public institutions have crop breeders working to improve our food supply. Public plant breeding programs often focus on crops that are important to society but may be less profitable than crops that drive the bottom line for large businesses. These crops may have long generation times or otherwise be challenging to breed. They may be the focus of regional cultural specialties or beloved niche markets. Private breeding programs usually must focus on large multinational commodity markets with a potential to generate large, near-term financial returns on private investment. Given these pressures, private companies may find it difficult or impossible to address smaller national or regional markets or longer-term needs.
Public plant breeding programs frequently target such longer-term goals, many of which address food security issues. For example, “pre-breeding” enriches our agricultural base with diverse plant characteristics from crop wild relatives or other related plants. This requires a lot of research, and significant risk that some efforts won't pan out. But these trials can create new, superior seedlings which make it possible for public breeding programs and private breeding companies to produce important new crop varieties.
Public plant breeding programs also play a key role in educating the next generation of plant breeders and plant scientists for both public and private programs.
Funding issues cause problems
Several studies over the past 30 years have looked at the status of breeding programs. Each showed that U.S. plant breeding capacity is at risk. Budgets and personnel availability continue to decline, despite the development of new plant breeding technologies.
Our most recent survey cited above, in 2018, updated this information. The data indicates a significant reduction in public breeding program personnel over the last 5 years, and aging program leaders. Many programs report that budget shortfalls and uncertainty endanger or constrain their ability to support key personnel, maintain core infrastructure and operations, and make use of current technology.
Many surveyed said that when funding is reduced or sporadic, they focus on sustaining the most basic core operations of the program. These are items like fixing the greenhouse roof and watering the fields. Applying new scientific advances or continuing graduate student and postgraduate training opportunities are typically the first losses. This impacts not only the public program's advanced goals but also development of a long-term social resource: the next generation of plant breeders.
The bottom line is that the struggle to maintain adequate funding hampers public breeding programs. The timeline to bring new crops to market exceeds the time period of most funding sources by years. This requires program leaders to devote much of their time to the constant search for more funding, rather than focusing on their actual work. One solution is to create longer-term grant programs. Otherwise, advances in important crops that are not global commodities could start to decline.
Our study shows public plant breeding programs are at risk of disappearing. They need reinvigorated, stable, long-term access to funding, technology, knowledge, and expertise.
U.S. plant breeding capacity as a whole (both public and private) and, more broadly, U.S. food security, natural resource resilience, and public health will erode if the trajectory of declining budgets and reduced staffing and expertise in public plant breeding programs is allowed to continue.
Public plant breeding programs are easy to overlook, but their loss would be a devastating blow to our food system./span>/h1>
Floyd Zaiger a world famous fruit breeder has just passed. Luther Burbank created such creations as the Russet Burbank Potato, the Shasta daisy and the ‘Santa Rosa” plum. This was all done through traditional breeding practices. Floyd Zaiger carried the breeding process to a more intense level for fruit trees, crossing plums and apricots to get ‘Pluots' and ‘Apriums' and a range of other crosses between species – interspecifics. He worked to create low-chill cherries, such as ‘Minnie Roya', ‘Royal Lee' an ‘Riyal Crimson' that are more adapted to Southern California growing conditions than traditional cherries. He and his company Zaiger Genetics were able to create new varieties by the sheer number of crosses that are done every year, thousands. Part of the success has been the use of moveable containers that allow them to create environments that are more conducive to crosses that would not normally occur because of different flowering times. The Zaiger family continues with the family business and we can expect to see many more new Zaiger fruits, nuts and rootstocks in the future.
New selections currently under development include:
- varieties with low winter chilling requirements,
- dwarf and semi-dwarf varieties,
- dwarfing rootstocks and extremely vigorous semi-dwarfing rootstocks,
- nematode and disease-resistant rootstocks,
- extra-early and extra-late-ripening varieties,
- low acid/high flavor white-fleshed peaches and nectarines,
- low acid/high flavor experimental varieties,
- Asian and European pear hybrids,
- apples, red pears, canning clingstone peaches,
You can read Floyd Zaiger's obituary below:
And we do have UC breeders of all manner of fruits – strawberries, walnuts, pistachios, citrus amongst many other crops. A couple of avocado breeders are Mary Lu Arpaia and Patty Manoslava
Floyd Zaiger, pioneer of modern fruit crosses, gives out samples. The Sacramento Bee
Every year growers get together to learn what is being done in the citrus research world that could affect their operations. This June, University of California and the Citrus Research Board are bringing some good talks to three different growing areas. All growers are invited, but RSVPs are appreciated.
'Pixie' mandarin is a very vigorous, upright tree. Although the fruit is small, hence its name, it can produce fruit on the ends of long branches which deform the canopy structure, making it hard to pick. The sweet, seedless fruit is worth picking, though. The rootstock standards for this small industry are ‘Citrumelo' and ‘C-35' citrange. The industry is looking for alternatives to these choices, especially those that reduce the vigor of the trees.
There is no one ideal rootstock at this point and growers have the option of a wide range of choices. The search includes those that are resistant to Citrus Tristeza Virus (CTV), Phytophthora, calcareous soils and ideally one that is resistant to the bacteria that causes Huanglongbing.
In many California coastal growing areas, land is expensive, water scarce and costly and prone to calcareous soils that are derived from marine sediments which can bring on iron chlorosis. Growers are also looking for smaller trees that will give early economic returns, are easier to prune and pick, and may be more compatible with the economics driven by Huanglongbing.
‘Citrumelo' citrange yields a large tree with good quality and quantity of fruit. It is tolerant of CTV (Citrus tristeza virus) and Phytophthora spp, but is susceptible to iron chlorosis in high pH soils. ‘C-35' citrange is a smaller tree than Citrumelo, also has resistance to Phytophthora spp and CTV, and is more tolerant of high pH soils.
The USDA had a breeding program in California which was taken over by the University of California. Out of this breeding project, the university selected three rootstocks for release in 2009 because of their horticultural characteristics, such as dwarfing, although not as much as ‘Flying Dragon' trifoliate, resistance to CTV and tolerance of calcareous soils. These three rootstocks also show good tolerance to Phytophthora parasitica and nematodes.
Pixie growers have been looking for a more compact tree, easier to handle and not need so much pruning. They funded a long-term project to see how these newer selections of rootstock performed in their area which has a hot summer/cool winter. A 2014 planting of ‘Pixie' has been evaluating the size reducing effects of the relatively new rootstocks ‘Bitters' citrange, ‘Carpenter' citrange and ‘Furr' citrange. After two years, ‘Pixie' on ‘Citrumelo' is the largest tree. Of the new rootstocks, ‘Furr' is the largest and ‘Bitters' the smallest. The trial was replicated at two sites with two different pH soils. At one site with the highest soil pH, ‘Bitters' showed iron chlorosis.
Photo: long whip growth on 'Pixie'
- Editor: Ben Faber
Vanessa Ashworth and Philippe Rolshausen, Department of Botany and Plant Sciences, University of California Riverside.
Have you ever wondered where your favorite avocado variety came from? Not the nursery where it was purchased but the long, tortuous path that led to its selection. How are different varieties related? Did the expert tell you that your avocado is a “Guatemalan x Mexican” but you were afraid to ask what that means? Has your carefully nurtured seedling raised from a ‘Hass' pit morphed into a tree bearing unconvincing fruit? If so, read on.
Avocado breeders refer to the different types of avocado as varieties or, more correctly, as cultivars. The ‘Hass' cultivar is by far the best known, but several hundreds of named avocado cultivars have been bred in the USA alone since avocado was first introduced here. None was developed by the big commercial seed companies; Instead, avocados were patiently selected, originally by indigenous cultures of Mesoamerica, much later by growers/enthusiasts, and fairly recently in avocado breeding programs. Almost never do we know the precise pedigree of a cultivar. We are sometimes told the maternal parent, but older cultivars (including ‘Hass') typically lack a record of parentage, and any thought of fitting today's cultivars into a concise family tree is hopelessly optimistic. In any case, prior to the mid-19th century very little is known about the plant material that was imported from abroad, with at best an indication of geographic provenance. And yet it would be far more efficient if we could arrange cultivars in a hierarchy or a series of related assemblages, instead of just looking at a random scatter.
In order to understand how today's cultivars are related we need to dig deeper. Going back in time, we know that indigenous civilizations in Mesoamerica recognized the value of the avocado's wild ancestor(s) and were actively selecting superior forms for thousands of years, which eventually led to a semi-domesticated avocado. Evidence of selection by human hand as far back as 8,000 years before present is preserved in archaeological sites in Puebla State, Mexico. At the time of European contact, written records indicate that there already existed three distinct types of avocado, each from a separate geographic center of origin. Today, we refer to them as botanical races, and they represent the “primeval soup” that gave rise to modern avocado cultivars.
Here is what we know about the three botanical races of avocado, respectively called (1) the West Indian (formerly known also as the South American), (2) the Guatemalan, and (3) the Mexican (also known as the “criollo”): Each exhibits a characteristic suite of traits that includes differences in leaf chemistry, peel texture and color, and sources of tolerance (diseases and salinity). The races were domesticated in separate geographic regions, the “West Indian” race in lowland coastal Mesoamerica (possibly Yucatán), the Guatemalan race in upland Guatemala, and the Mexican race in highland Mexico. The Guatemalan and Mexican races remained fairly local, so their names reflect their respective centers of domestication, but the “West Indian” race seems to have been spread far and wide by indigenous cultures in Meso- and South America and was, incorrectly, named for a much later destination. The explorations of the 15th and 16th centuries kicked off the worldwide distribution of (mostly West Indian race) avocados, reaching Spain in the early 17th century, Jamaica in the mid-17th century, and Indonesia by the mid-18th century. It wasn't until the mid- to late 19th century that the three races of avocado found their way to the United States, primarily Florida and California.
After the avocado was introduced to California and elsewhere, there followed countless rounds of selection, generally resulting in hybrids among the botanical races. The selection process consisted of growing out seedlings from the seeds of “good” cultivars and screening them for chance seedlings with promising characteristics. However, in the same way that children are not identical to their parents, seedlings grown from the pit of a fruit are not identical to the tree the fruit came from. Each seedling represents a reshuffled version of its parents' genomes. The only procedure that preserves an identical genome is clonal propagation. Budding and grafting techniques that, today, ensure clonal propagation and keep cultivars “true to type” were not used until the first half of the 20th century.
Contrary to many major crops, most avocado cultivars we have today are bursting with so much genetic diversity that breeding is actually rendered difficult. When we grow out seedlings we get a huge number that look (and taste) nothing like their parents and most are discarded. The poor selection efficiency (an estimated 0.2%) has to do with the large variability caused by multiple domestication centers and a long history of open-pollination. There is no immediate danger of a genetic bottleneck, but breeding is slow and outcomes are unpredictable.
In the absence of accurate breeding pedigrees, we have come to describe avocado cultivars in terms of their resemblance to one or several botanical races, based on their combination of traits. For example, ‘Hass' is considered to be a Guatemalan x Mexican (G x M) hybrid because it has the thick, rough skin of the Guatemalan race but the high oil content of the Mexican race. Cultivar ‘Gwen' is also called a G x M hybrid, but is possibly a little more Guatemalan than Mexican and certainly more Guatemalan than ‘Hass'. Cultivar ‘Fuerte' is often called a G x M hybrid or sometimes Mexican which makes it more Mexican than ‘Hass' and a lot more Mexican than ‘Gwen' but not as Mexican as ‘Mexicola'... What these examples show is that description of avocado cultivars in terms of botanical race composition has its limitations and we are most likely dealing with a continuum of blending among the three botanical races. Can we improve on this? ¡Sí, se puede!
Enter the modern tools of genomics: molecular markers and new analytical approaches are emerging that can peek inside ancestral genomes and discover hidden patterns within genetic information. The new approaches track the progress of tiny nuggets of genetic information (markers) by comparing their distribution across a large numbers of cultivars. Several studies have revealed that today's cultivars continue to harbor the genetic footprints of the three botanical races and a lot more besides. In this instance, having cultivars bursting with genetic diversity is a good thing. Eventually, given a large enough dataset (markers and cultivars), we will be able to place cultivars into assemblages that go beyond first-pass assignments to one or more botanical races.
A working framework of cultivar assemblages confers predictive information that helps guide cultivar choice and breeding decisions. In a slow-growing tree crop such as avocado where years elapse before many traits are available, a marker-guided, predictive framework represents huge savings in time and resources. A simple example illustrates this point: In the event of an epidemic there is no time to start breeding new cultivars from scratch. Instead, the first line of defense is to explore tolerance present in existing cultivars, and having access to a framework helps prioritize among hundreds of cultivars. Avocados of Mexican ancestry are known to exhibit better disease tolerance than Guatemalan and West Indian stock, so material that contains a Mexican-race footprint would be a good choice for early screenings for tolerance. Epidemics such as grape phylloxera or potato blight are well known examples where the mainstream cultivars shared too uniform a genetic base and where a cultivar monoculture permitted disease pressure to attain dangerous proportions. Consequently, today's dominance of ‘Hass' should be viewed with some trepidation.
In fact, it is possible that we are facing a new epidemic right now: Fusarium dieback (FD) has impacted many tree species, especially the avocado, in southern California since its introduction in 2013. The Fusarium fungus is transmitted by a beetle, the polyphagous shot hole borer (PSHB), and fungus and beetle act in partnership to breach the defenses of their plant host, leading to wilting, branch dieback, and fruit losses. Moreover, we know that ‘Hass' is highly susceptible to the disease. It is time to look for sources of tolerance and to revisit the cultivars that have lost ground to ‘Hass', such as ‘Bacon', ‘Fuerte', and ‘Reed', and to take advantage of germplasm collections that contain material of older vintage, often dating back to the start of the 20th century, if not before. A major germplasm collection is maintained at the University of California South Coast Research & Extension Center in Irvine, and additional material is grown at UC Riverside's Agricultural Operations. A good digital resource to study the diversity of cultivars available in California is the UC Riverside Avocado Information website http://ucavo.ucr.edu/avocadovarieties/VarietyFrame.html.
Is the consumer ready to embrace new cultivars? Preliminary evidence is promising. There are few opportunities today to come face-to-fruit with the more unusual cultivars because they have largely been banished to back yards or live sheltered lives in today's germplasm collections. A notable exception is the UC Riverside avocado breeding program. Headed by Dr. Mary Lu Arpaia, the program runs a monthly avocado tasting session where participants record their views on visual (external) fruit characteristics and on fruit sensory qualities (flavor). These tasting sessions have shown that participants are drawn to novel fruit shapes/sizes and value the taste of many cultivars, not just of ‘Hass'. There is also considerable interest in learning more about existing cultivars and about the history of avocado breeding and domestication.
Some of the avocado cultivars featured on the UC Riverside Avocado Information website
Clearly, to place avocado cultivars into a workable framework that reflects their interconnections as well as the footprint of the three botanical races will be a valuable addition to the tools available to breeders and will benefit our knowledge of avocado diversity. For now, however, we are unable to give concise answers to the questions of the introductory paragraph, but it is safe to say that your favorite cultivar is probably a hybrid between at least two botanical races of avocado, contains genetic footprints left by ancient Mesoamerican breeders, capriciously gives rise to highly promising seedlings, and has a murky pedigree yet to be laid bare.