Celery, Apium graveolens L. is an important vegetable in the state of California, grown mostly in the coastal areas of Ventura, Monterey, San Luis Obispo and Santa Barbara counties. According to 1992 statistics, 25,000 acres of celery were harvested that year, with a value of approximately $182 million. California has 50 to 60% of the total production in the country, enough to supply its own demand, as well as export to the rest of the US. Recognizing the high value and importance of this crop, the California growers established the California Celery Research Advisory Board in October of 1976 to promote research on this vegetable. The board has supported the UC Davis research program since its inception.

The Department of Vegetable Crops, at the University of California Davis, is one of the few institutions in the US and abroad working on celery breeding and genetics. Our leading role in this area of research matches with the leadership of the California celery industry as the main producer of this commodity in the world. The main objective of our program at Davis is the development of disease and pest resistant lines. This includes resistance to Fusarium yellows, late blight and leafminers. In order to have an effective celery breeding program, able to handle the present and the future needs of the California industry, our main priorities have been to gather a comprehensive germplasm collection and to develop the genetic infrastructure of this crop. At Davis we have assembled an Apium germplasm working collection of approximately 300 accessions, creating a fairly diverse germplasm bank. These include commercial varieties and land races of all cultivated types, and a few wild species. Although there are at least 15 species in the genus, very few are represented in germplasm banks throughout the world. Therefore, little is know about their potential in celery breeding.

Breeding for Fusarium resistance:

Fusarium yellows is a vascular disease caused by the pathogen Fusarium oxysporum f.s. apii, race 2, resulting from the penetration of the fungus through the roots and invasion of the vascular tissue of the plants. These become yellow and stunted due to crown and root rot, and eventually die. There is no practical means of controlling the disease, which is spreading in the celery fields of California and other states. New stands of celery cannot be grown in infected fields. A feasible solution to this problem is the development of fusarium resistant varieties. For this purpose, in 1977, Thomas Orton founded a celery breeding and genetics program at UC Davis, as a result of finding celeriac accessions resistant to fusarium yellows. I took over the program in 1983, which produced its first fusarium resistant line, 'UC1', in 1984 (Orton et al 1984). The main source for resistance used for the development of 'UC1' was the celeriac PI169001, a land race from Turkey. Although the plants of this accession are not immune, they have a high level of resistance. 'UC1' has served as the foundation material for further selection and release of the first commercial fusarium resistant varieties developed by the seed industry. In an effort to improve 'UC1' for horticultural traits, a backcross program was implemented to introgress the resistance to three popular celery varieties, 'Tall Utah 52-70R', 'T.U. 52-70HK' and 'T.U. 52-75'. As a product of this project Vincent D'Antonio, a Staff Research Associate in our program and I, released eight advanced lines, including of which 'UC8', 'UC10' (Quiros et al. 1993, Quiros 1993) 'UC390S' and 'UC862' which have been the most popular for further improvement by seed companies. In 1994 our program produced the fusarium resistant celery variety 'Promise' derived from 'UC10' after backcrossing it to 'T.U 52-75'. Certified seed of 'Promise' will be commercially available in 1996.

Our next task is to produce celery lines with multiple disease and pest resistance. This includes the foliar disease late blight, which is caused by the pathogen Septoria apicola Sp eg., another important disease affecting celery in California. Although there are means to control late blight, the development of resistant varieties are expected to significantly reduce production costs and the environmental impact caused by the application of fungicides. We have found resistance to this disease in the wild species from South America A. chilense (Ochoa and Quiros 1989). A. chilense hybridizes readily to celery, but the F1 hybrids have poor fertility due to the presence of chromosomal rearrangements. It has been possible ,however, to obtain F2 and backcross seed for the development of resistant lines.

Leafminer (Lyrimiza trifolii Burgess) is a major pest of celery, requiring control by constant insecticide spraying. Development of leafminer resistant celery varieties will reduce the use of hazardous chemicals and environmental risks linked to their use. No resistance to this pest was observed in the cultivated collection, however we found an accession of A. prostratum from Australia to be practically immune in no-choice tests performed in the greenhouse. No feeding or oviposition was observed in this species (Trumble et al 1988). We have hybridized A. prostratum to celery and derived first back cross progeny in an attempt to develop leafminer resistant lines. Chemical analysis of the foliage indicates the resistance for this pest is not based on compounds noxious to humans (Trumble et al 1990).

Development of celery genetics:

Another important thrust of our program is to develop the genetics of celery to expedite breeding. We have been working on the creation of chromosome markers and a genetic map on the basis of isozymes, non-specific proteins, morphological traits (Quiros et al 1987, Huestis et al 1993, Yang and Quiros 1995) and DNA based markers. The latter include restriction fragment length polymorphism and amplied DNA sequences by the polymerase chain reaction (RAPD markers). The purpose of the genetic map is to tag useful genes such as those determining fusarium resistance and male sterility. Male-sterility is another trait that we are interested in applying to our program for the development of disease resistant F1 hybrid varieties (Quiros et al 1986). Finally, another research component is the adaptation of genetic engineering techniques that may be used as promising new tools by the breeders. This includes the development of transformation procedures for gene transfer. We accomplished this task using Agrobacterium tumefaciens as a vector (Catlin et al. 1988).

In summary, we are confident that the celery genetics program at Davis with its broad germplasm base and comprehensive genetic information will serve to adapt and solve present and future problems faced by the celery growers.

Literature Cited

Catlin, D., O. Ochoa, S. McCormick and C.F. Quiros. 1988. Celery transformation by Agrobacterium tumefaciens: cytological and genetical analysis of transformed plants. Plant Cell Reports 7:100-103.

Huestis, G., McGrath, J.M. and C.F. Quiros. 1993. Development of genetic markers in celery based on restriction fragments length polymorphisms. Theor. Appl. Genet. 85:889-896.

Ochoa, O. and C.F. Quiros. 1989. Apium wild species: novel sources for resistance to late blight in celery. Plant Breeding 102:317-321.

Orton, T.J., S.H. Hulbert, M.E. Durgan and C.F. Quiros. 1984. UC1, Fusarium yellows-resistant celery breeding line. HortSci. 19:594.

Quiros, C.F., A. Rugama, Y.Y. Dong, and T.J. Orton. 1986. Cytological and genetical studies of a male sterile celery. Euphytica 35:867-875.

Quiros, C.F., McGrath, J.M. and J.L. Stites. 1987. Use of stem proteins and isozymes for the identification of celery varieties. Plant Cell Reports 6:114-117.

Quiros, C.F. 1993. Celery Breeding Program at the Department of Vegetable Quiros, C.F., D'Antonio, V., Greathead, A.S. and R. Blendler. 1993. UC8-1, UC10-1 and UC26-1: Three celery lines resistant to fusarium yellows. HortSci 28:351-352

Trumble, J.T. and C.F. Quiros. 1988. Antixenotic and antibiotic resistance in Apium species to Liryomiza trifolii (Burgess). J. Econ. Entomol.81:602-607.

Trumble, J.T., W. Derks, C.F. Quiros and R.C. Beier. 1990. Host plant resistance and linear furanocoumarin content in Apium species. J. Econ. Entomol. 83:519-525.

Yang, X.F. and C.F. Quiros. 1995. Construction of a genetic linkage map in celery using DNA-based markers. Genome 38:36-44.