What is Jojo CV?

Jojo cv. refers to a plum cultivar (Prunus domestica) developed through breeding programs at Hohenheim University in Germany. The term “cv.” stands for cultivar, meaning “cultivated variety”—a plant variety created through selective breeding for specific desired traits. Jojo was specifically bred to resist Plum pox virus, the most destructive viral disease affecting stone fruit trees worldwide.

Understanding the Term “cv.” in Plant Naming

The abbreviation “cv.” represents cultivar, a botanical term coined in 1923 by Liberty Hyde Bailey to describe plants selected and cultivated for particular characteristics. A cultivar differs from a naturally occurring variety in that it results from deliberate human intervention through breeding, selection, or hybridization.

In botanical nomenclature, cultivars follow specific naming conventions. Prior to 1996, the abbreviation “cv.” was commonly used before the cultivar name, as in Prunus domestica cv. Jojo. Modern naming standards prefer single quotation marks: Prunus domestica ‘Jojo’. However, scientific literature still frequently uses the “cv.” format, particularly in research papers and academic publications.

Cultivars must meet three criteria to qualify for official recognition. They must be distinct from existing varieties, display uniform characteristics across all plants, and maintain those characteristics when propagated. This ensures growers and researchers can reliably identify and reproduce the cultivar’s desired traits.

The International Code of Nomenclature for Cultivated Plants governs cultivar naming worldwide. This standardization helps prevent confusion in global trade and scientific research, where precise plant identification is critical for agriculture and horticulture.

Jojo: A Disease-Resistant Plum Cultivar

Jojo emerged from a critical need in European stone fruit production. Plum pox virus causes sharka, recognized as the most serious viral disease for the stone fruit industry, affecting plums, peaches, apricots, and other Prunus species. The disease was first detected in Bulgaria around 1917 and has since spread throughout most of continental Europe, causing devastating economic losses.

Economic losses from sharka disease have been estimated at over €2.4 billion for the 28-year period preceding 2024. The virus reduces fruit quality, causes premature fruit drop, and severely weakens affected trees. No cure exists for infected trees, which must be removed entirely to prevent further spread through aphid vectors.

Traditional plum cultivars developed for disease resistance in Yugoslavia during the 1970s and 1980s showed tolerance to Plum pox virus, but their fruit quality fell short of commercial standards. Growers faced an impossible choice: accept lower-quality fruit from resistant varieties or risk devastating losses with superior but susceptible cultivars.

This dilemma drove Professor W. Hartmann and his team at Hohenheim University to pursue a breeding program combining both disease resistance and high fruit quality. Their goal was ambitious—to create a plum variety that could thrive in virus-endemic regions while meeting market expectations for taste, size, and appearance.

The Breeding History of Jojo

The Hohenheim breeding program during the 1990s aimed to develop sharka-resistant cultivars with better fruit quality using hypersensitivity-based resistance. The result was a hybrid derived from crossing ‘Ortenauer’ × ‘Stanley 13’, which was registered and patented as plum cv. ‘Jojo’ in 1998. The cultivar was officially introduced to commercial production in 1999.

The choice of Stanley as a parent variety was notable. Stanley plums are highly susceptible to Plum pox virus, making them an unexpected choice for resistance breeding. However, Professor Hartmann achieved very good results on the PPV resistance line by using the Stanley variety as a parent, demonstrating that resistance traits can emerge from crossing susceptible varieties when specific genetic combinations are achieved.

The Ortenauer parent contributed the critical resistance mechanism. This variety exhibited hypersensitive reactions to viral infection, a defensive response where infected plant tissue dies rapidly to prevent virus spread throughout the tree. By combining this trait with Stanley’s favorable fruit characteristics, the breeding program successfully created a commercially viable resistant cultivar.

In extensive field tests with numerous cultivars, only the hypersensitive hybrids remained free of virus. Jojo stood out among these resistant hybrids for its combination of high yield, good fruit quality, and consistent resistance performance in field conditions. These attributes made it suitable for commercial release rather than remaining merely an experimental line.

The cultivar’s development represented nearly a decade of research, testing, and selection. Field trials in sharka-endemic regions confirmed Jojo’s ability to grow healthily for over 10 years in orchards severely infected with the virus, a performance unmatched by previously available resistant varieties.

Hypersensitive Resistance to Plum Pox Virus

Jojo’s resistance operates through hypersensitivity, a plant defense mechanism distinct from true immunity. When Plum pox virus infects hypersensitive tissue, the plant responds with localized cell death at the infection site. This extreme reaction prevents the virus from establishing systemic infection throughout the tree.

Hartmann initially declared Jojo as absolutely resistant to PPV, presenting it as the first plum variety with complete field resistance. This distinction was significant because earlier resistant varieties showed only partial or quantitative resistance, which could fail under certain environmental conditions or with heavy disease pressure.

However, subsequent research revealed more complex interactions. Czech researchers found that Jojo trees behaved differently when infected with three PPV strains. A strong hypersensitive reaction appeared one year after inoculation with PPV-M and PPV-Rec strains, though not all inoculated trees died. The virus was present in Jojo tissue and transferred to the rootstock St. Julien.

The rootstock findings were particularly important. Plants of the rootstock became systemically infected with PPV-M and PPV-Rec strains, showing severe symptoms. The presence of PPV was proved in leaves of rootstock St. Julien, but not in leaves of cv. Jojo. This indicated that while Jojo’s own tissue remained largely virus-free through hypersensitivity, the virus could move through its vascular system to infect susceptible rootstocks.

The strain-dependent response was most evident with PPV-D, the most common and widespread strain. Inoculation with strain PPV-D resulted in partial hypersensitive reaction of Jojo plants, with initial stunting and partial death of shoots, but subsequent recovery of plants was observed. This variability meant Jojo’s resistance, while strong, was not absolute across all virus strains and infection conditions.

Research from 2011 confirmed these limitations. Trees of Jojo infected with PPV-D began to die seven years after virus inoculation, demonstrating that the cultivar’s hypersensitivity could be disrupted by mildly pathogenic strains. This finding challenged the initial claims of absolute resistance and prompted more nuanced understanding of hypersensitivity as a resistance mechanism.

Performance and Limitations

Jojo demonstrates good horticultural characteristics beyond disease resistance. Following observations during 2020-2022, Jojo was noted for higher production than control cultivars Stanley and Centenar, very large fruits averaging over 50 grams, and resistance to Plum Pox Virus. These traits made it attractive for commercial orchards in PPV-endemic regions.

The fruit quality represented a significant improvement over earlier resistant varieties. Where previous sharka-resistant cultivars like those developed in Yugoslavia produced smaller fruits with less desirable taste profiles, Jojo achieved fruit characteristics competitive with traditional commercial varieties. This advancement made it economically viable for growers to adopt resistant planting material.

Field performance across multiple regions validated Jojo’s practical value. In 2003, the Plum pox resistant cultivar Jojo was introduced into the Central Balkan Mountains region of Troyan as an alternative to the tolerant cultivar Stanley, which was being used on a large scale. Its adoption in high disease pressure areas demonstrated confidence in its resistance characteristics.

However, the cultivar’s limitations became apparent through long-term field studies. The strain-specific nature of its resistance means effectiveness varies depending on which PPV strains are prevalent in a given region. In areas where PPV-D predominates, Jojo’s performance may not meet the “absolute resistance” initially claimed.

The rootstock transmission issue poses additional challenges. Even when Jojo tissue remains healthy, susceptible rootstocks can become infected, potentially serving as virus reservoirs. This complicates orchard management and suggests that combining Jojo with hypersensitive rootstocks may be necessary for optimal disease control.

These findings don’t diminish Jojo’s importance but rather refine understanding of how to deploy it effectively. The cultivar remains valuable as a resistance source, particularly when used appropriately with consideration for local virus strain prevalence and rootstock selection.

Jojo’s Role in Modern Plum Breeding

Beyond its direct commercial use, Jojo serves as an important parent in ongoing breeding programs. Research from 2007-2012 assessed 435 Prunus domestica seedlings from eleven F1 hybrid families obtained by crossing Jojo with other plum varieties. Results showed that Jojo, used either as maternal or paternal parent, can be a valuable parental form in plum breeding programs aimed at obtaining varieties resistant to sharka disease.

The Hohenheim breeding program obtained many hypersensitive clones after introducing Jojo. Crosses of Jojo with Haganta resulted in two PPV-resistant clones with fruits larger than 50 grams, while crosses with Hauszwetschge produced clones varying in ripening times. This demonstrates that Jojo reliably transmits resistance traits to its offspring while allowing combination with diverse fruit quality characteristics.

The breeding strategy has expanded beyond simple resistance transfer. Modern programs aim to combine hypersensitive resistance with improved fruit size, extended ripening ranges, and enhanced quality attributes. After testing in different regions, several interesting resistant clones and cultivars were selected, covering more than six weeks of ripening time. This diversity allows growers to plant multiple varieties that maintain resistance while staggering harvest periods.

Some Jojo-derived clones address specific market needs. Several promising hybrids are very similar to Common Prune in shape, color, size, and taste, but with added resistance to fruit flesh damage from excessive heat during ripening. This addresses a growing concern as climate change increases temperature extremes during growing seasons.

The genetic resources Jojo provides extend beyond European plum improvement. Research into the mechanisms of its hypersensitive response contributes to broader understanding of plant-virus interactions, potentially informing resistance strategies in other crops and pathogens. The identification of specific genes and pathways involved in hypersensitivity may enable more targeted breeding approaches or biotechnological interventions.

Current breeding efforts also explore combining Jojo’s resistance with tolerance to other diseases and environmental stresses. Stone fruit production faces multiple challenges including fungal pathogens, drought stress, and late spring frosts. Developing cultivars that combine multiple resistance and tolerance traits remains a long-term goal, with Jojo serving as one component of more complex breeding strategies.

Frequently Asked Questions

Is Jojo cv. the same as JoJo the singer?

No, they are completely unrelated. Jojo cv. refers to a plum cultivar developed for agricultural use. The “cv.” indicates this is botanical terminology for a cultivated variety, not a person’s name.

Can home gardeners grow Jojo plums?

Jojo is available through some commercial nurseries, particularly in Europe. However, availability varies by region, and the variety is primarily marketed to commercial orchards in areas with Plum pox virus concerns. Home gardeners in affected regions may find it a worthwhile choice for disease resistance.

Does Jojo’s resistance mean orchards don’t need virus management?

No. While Jojo shows strong resistance, field research demonstrates its protection varies by virus strain and requires proper rootstock selection. Integrated disease management including aphid control, certified planting material, and regular monitoring remains important even with resistant varieties.

What does hypersensitive resistance mean for the tree?

Hypersensitive resistance causes localized cell death at viral infection sites, preventing virus spread through the tree. This differs from immunity, where infection never occurs. The tree may show some necrotic spots or stunted shoots where resistance responses occurred, but overall health and productivity are maintained in most cases.

Conclusion

Jojo cv. represents a significant advance in stone fruit disease resistance breeding. As a plum cultivar developed specifically to combat Plum pox virus through hypersensitive resistance mechanisms, it offered European growers their first viable option combining meaningful disease protection with acceptable fruit quality. While subsequent research revealed the resistance is strain-dependent rather than absolute, Jojo remains valuable both as a commercial variety and as breeding material for developing improved resistant cultivars. Its introduction in 1999 marked a turning point in how the industry approaches sharka disease management, shifting from purely susceptible varieties to resistance-based strategies that enable continued production in virus-endemic regions.

Data Sources

1. Polák J, Pívalová J, Svoboda J. Prune cv. Jojo resistance to different strains of Plum pox virus. Plant Protect. Sci. 2005;41(2):47-51. https://pps.agriculturejournals.cz/artkey/pps-200502-0001_prune-cv-jojo-resistance-to-different-strains-of-plum-pox-virus.php

2. Susceptibility of plum trees cv. ‘Jojo’ to a Czech isolate of Plum pox virus strain D. Canadian Journal of Plant Pathology. 2011. https://www.tandfonline.com/doi/full/10.1080/07060661.2011.640711

3. García JA, et al. Plum pox virus and sharka: a model potyvirus and a major disease. Molecular Plant Pathology. 2014. https://pubmed.ncbi.nlm.nih.gov/24102673/

4. Hartmann W, Petruschke M. Sharka-Resistant Plum Hybrids and Cultivars from the Plum Breeding Programme at Hohenheim. Proceedings of the Latvian Academy of Sciences. 2019. https://sciendo.com/article/10.2478/prolas-2019-0036

5. Plum Breeding. IntechOpen. 2020. https://www.intechopen.com/chapters/72301

6. Cultivar – Wikipedia. https://en.wikipedia.org/wiki/Cultivar

7. Plum pox – Wikipedia. https://en.wikipedia.org/wiki/Plum_pox

8. García JA, et al. Plum pox virus: An overview of the potyvirus behind sharka. Annals of Applied Biology. 2024. https://onlinelibrary.wiley.com/doi/10.1111/aab.12958