ARS | Publication request: Development of Phytophthora root rot-resistant avocado rootstocks for the Caribbean.

Submitted to: Florida State Horticulture Society and Citrus Industry
Publication Type: Proceedings/Symposium
Publication Acceptance Date: October 25, 2006
Publication Date: June 20, 2007
Citation: Violi, H.A., Borrone, J.W., Ploetz, R., Olano, C.T., Schnell Ii, R.J. 2007. Development of Phytophthora root rot-resistant avocado rootstocks for the Caribbean.. Florida State Horticulture Society and Citrus Industry. 119:41-44

Interpretive Summary: Avocado is indigenous to Central America where evidence of it's use by native people dates back nearly 10,000 ears. It is now a commercially important, nutritious and high calorie fruit crop. Three avocado varieties include commercial cultivars. These cultivars are adapted to different climates allowing for production on almost every continent. Global production exceeded 3.2 million metric tons (MMT) in 2004, much of which occurs in the Caribbean and surrounding areas. The most serious threat to the industry is a disease called Phytophthora root rot. Root rot greatly reduces avocado production and can kill trees. The pathogen that causes this disease, Phytophthora cinnamoni, is considered one of the world's worst invasive organisms. It has an enormous host range, can cause disease in avocado under a wide range of conditions and disperses easily. Consequently it causes economic loses to the avocado industry in every area of the world where avocado is commercially grown. There are no known eradication methods for this pathogen, and the efficacy of chemical control is very limited. Thus, the most effective method of fighting Phytophthora root rot is to breed avocado rootstocks that can tolerate this disease. Root rot tolerant avocado cultivars are badly needed for subtropical and tropical regions. The Subtropical Horticulture Research station in Miami, Florida holds one of the largest collections of subtropical and tropical avocados. The diverse germplasm housed in this collectin is being used to breed avocados for the Caribbean region. This is a collaborative effort between researchers at the USDA-ARS facility in Miami and the University of Florida. Researchers from these institutions are combining conventional and molecular breeding techniques to select superior avocado rootstocks. Large numbers of seedlings are being screened each year for tolerance to Phytophthora root rot. Concurrently, work is underway to identify genes involved in disease tolerance mechanisms. The expected outcome is to produce tolerant rootstocks that diminish crop losses due to Phytophthora root rot. Production of PRR tolerant rootstocks holds great promise for maximizing economic yield while minimizing the environmental impact of controlling for PRR in the subtropical and tropical regions including the Caribbean.

Technical Abstract: Phytophtora root rot (PRR), caused by Phytopthora cinnamoni Rands, poses the greatest limitation to avocado production worldwide. Through a collaborative effort between researchers at the USDA-ARS facility in Miami and the University of Florida in Homestead, PRR-resistant avocado rootstocks are being developed for the Caribbean. Avocado breeding presents several challenges. These include a long regeneration time (4-15 years) and the low efficiency of controlled pollinations. To overcome these challenges we will: i) increase the number of accessions from the Caribbean in breeding blocks; ii) screen large numbers of half-sib and full-sib seedling progeny in controlled greenhouse and field trials; iii) genetically characterize parents of PRR-tolerant and -susceptible progeny with molecular markers; and iv) with the identified markers, develop marker-assisted selection protocols for resistance.