Cucurbit Genetics and BreedingAn Historical Perspective and a Look into the Future

Richard L. Lower

North Central Association of Agricultural Experiment Station Directors and
Department of Horticulture, University of Wisconsin, Madison, WI 53706-1562

Additional index words. cucumber, melon, squash, watermelon, Citrullus, Cucumis, Cucurbita, minor crops

Abstract. Cucurbit breeders, geneticists, biotechnologists, and seedsmen have made great strides in the improvement of cucurbits crops for food, fiber and industrial products. Progress from the application of molecular biology has been somewhat constrained due to the relatively small potential monetary return to industry, concerns for health and food safety, and the need to assure the quality of the environment. Future gains will be impeded by changes in public funding and reduction of private funding for public research programs, reduced numbers of public and private scientists devoted to cucurbits, constraints on international germplasm exchange. Initiatives at the national level promise to provide additional resources for plant germplasm preservation and minor crop breeding.

An historic overview requires the identi-fication of leaders in the world of cucurbit breeding and genetics. Initially, my thoughts were to highlight the research leaders in the major cucurbit crops and to review the types of breeding programs and procedures they conducted. However, the multitude and maze of literature available is so immense that it makes more sense to recognize the significant contributions of previous authors who have spent considerable time and effort in organizing literature reviews. Thus, it is more appropriate to cite earlier research and review publications than to simply reconstruct these multiple efforts into a reworked set of citations. While being identified as a leader may be viewed as positive in terms of a research contribution, being left off of such a list is neither derogatory or negative.

Genes and genetics

Numerous treatises on genes and genetics of cucurbits are found in the literature. The first major review and compilation of genes of the cucurbits was conducted by Robinson et al. (1976) in 1976. Their effort was very complete and it also cited models for gene nomenclature that serve as guidelines for scientists as they developed future gene lists. Since 1976, other major research contri

butions that update gene lists and identify linkage groups include the efforts of Pierce and Wehner (1990) on cucumber in 1990 and the annual contributions of the cucurbit gene list committee of the Cucurbit Genetics Cooperative (CGC) in Reports 6 through 21 from 1983 to 1998.


Cucurbit breeding has frequently been featured in vegetable breeding text books and professional society journals and proceedings. One of the earliest reviews is the U.S. Department of Agriculture Year Book of Agriculture in 1937 (USDA, 1937). More recently, Breeding Vegetable Crops by Bassett (1986) in 1986 has chapters on watermelon, cucumber and squash breeding. References in these publications highlight progress made in breeding for pest resistance and improved yield and quality, interspecific hybridization, polyploidy, heterosis and hybrid vigor, systematics and breeding techniques. Other publications that are dedicated entirely to cucurbits include those of Whitaker and Davis (1962) and Robinson and Decker-Walters, 1997. The proceedings from previous Cucurbitaceae and Eucarpia meetings are rich sources of scientific information for all researchers (Bates et al., 1990; Gómez-Guillamón et al., 1996; Lester and Dunlap, 1995) as is work of Rubatzky and Yamaguchi (1997). The annual report of the CGC

Cucurbitaceae '98

provides breeders with current research findings resulting from traditional breeding as well as biotechnological aspects related to breeding.

Human resources

Cucurbit breeders are fortunate to have numerous venues for interaction. In addition to professional society meetings involving scientists that conduct research on cucurbits, there are numerous formal and informal working groups for cucurbit breeders. For example, at this symposium there are separate meetings of four research groupsmuskmelon, watermelon, squash, and cucumber, the Cucurbit Crop Germplasm Committee (CCGC) of the USDA, ARS, National Plant Germplasm System (NPGS), and the Cucurbit Genetics Cooperative (CGC). The CCGC provides expert advice on acquisition, management, and use of cucurbit germplasm to NPGS. The CGC serves to develop and advance the genetics of economically important cucurbits. The membership of the CGC is now in excess of 220 scientists from 37 countries.

The European Association for Research on Plant Breeding, an international organization, sponsors the Eucarpia meetings that provide excellent opportunities for exchanging information. Attendance at the most recent Eucarpia meeting on Cucurbit Genetics and Breeding was over 144 scientists representing 25 countries.

The Cucurbit Network promotes conservation and understanding of cucurbits through education and research. Established in 1994, TCN links 300 research scientists, breeders, enthusiasts, educators, growers/resellers worldwide interested in virtually every aspect of cucurbits including botany, ethnobotany, archeology, and use.

The intensity and industriousness of cucurbit breeders over the last two decades have helped established cucurbit scientists as among the most talented and dedicated to ever work on what are generally referred to as minor crops. Perhaps the most significant event(s) for enhancing interactions among cucurbit scientists has been the development of the Internet and related electronic interfaces.

Germplasm resources

Cucurbit scientists have been leaders in the utilization of some of the world's most interesting

germplasmthe cucurbits. The availability and use of cucurbit collections held in gene banks around the world have been instrumental in the development of breeding methodologies, new and improved pest resistance, increases in fruit quality, yield and numerous other measurable characteristics. Both the freedom and frequency of exchange of information and germplasm have led to the sharing of raw materials that have resulted in cucurbit improvement. Wessel-Beaver (1995) discussed the level of genetic diversity existing in the cucurbits collection in the U.S. National Plant Germplasm System. Numerous authors in Bates et al. (1990) discuss evolution, systematics and variability of the Cucurbitaceae. For those who are reluctant to deal with larger collections of germplasm, concepts of core collections are discussed by Staub (1994a, 1994b). Robinson (1994) reported that the genetic resources of the Cucurbitaceae were surveyed in 1987 and 1988. He found that seed of many cucurbit species were not readily available.

The present state of affairs

Today, cucurbit scientists, as well as other plant researchers, are the beneficiaries of two great revolutions that have taken place over the last two decades. The electronic revolution, which has given us tremendous communication, analytical and automation technologies, and the biotechnology revolution, which has given plant breeders and geneticists a seemingly unending assortment of new research tools. In concert, these technologies provide scientists with a well-equipped tool box that will help to develop 1) timely pest resistances, 2) enhanced nutritional qualities, 3) increased yields, 4) an improved understanding of cucurbits at the molecular, cellular, and whole plant levels, 5) technologies that nurture and foster information exchanges and improved breeding methodology, and 6) a boundless horizon that is limited only by our dreams and legal barriers. These outputs will lead to a series of critical outcomes such as improved food supply, improved nutrition, increased sustainability, and a cleaner environment. All of which contribute to an improved quality of life.

Checks and balances

The technologies of the 1980s and 1990s, although positive contributors to genetics and plant

Cucurbitaceae '98

breeding as noted above, have been countered by a series of forces. In the 1980s, breeders were constantly reminded that new biotech innovations must be carefully checked and monitored to assure that all risks associated with the new technologies were eliminated. Risk management became a research agenda and the topic of numerous seminars on biotechnology. The scares and nuances of new technologies were mediated and moderated in the major crops. As vine crop scientists, we were somewhat fortunate since our so-called minor crops were usually not in the headlines. We were able to concentrate on science, and although we gave attention to safety and commercial acceptability of genetically engineered or modified plants, we were spared the time and effort necessary to assure that new technologies and the use of characters, such as Bt for insect resistance, were safe in the broadest senses of the word. The role of federal and state regulatory agencies in assuring the public of the safety of the new technologies was increased greatly as scientists hurdled headlong into utilization of new genetic constructs. Although there were many legitimate concerns such for health and food safety, and assuring the quality of the environment, it is doubtful that safety was compromised in the use of the new technologies. Plant scientists have responded to the mandates and charges put forth by regulatory agencies and have shown great resilience and resolve in continuing their efforts to utilize new technologies in combination with traditional breeding methods, to continue to improve cucurbits at nearly every opportunity.

Future constraints

Although we have more tools to assist us than has any scientist in history, we continue to face a series of very serious threats to our level of productivity.

A limited and/or declining number of scientists, i.e., scientific years (SYs), devoted to breeding cucurbits

A recent survey by Frey (1996) of the human and financial resources devoted to plant breeding research and development in the United States shows the following number of SYs at State Agricultural Experiment Stations (SAESs) devoted to breeding of

cucumber, 4.6; muskmelon, 0.8; pumpkin, 10; squash, 0.4; and watermelon, 3.6. The contributions (SYs) from the USDA­ARS were cucumber, 1.35; muskmelon, 1.55; pumpkin, 0; squash, 0; and watermelon, 0. Thus, the total number of public scientists involved in breeding vine crops in the United States is <14. In private industry, the SYs were as follows: cucumber, 8.3; muskmelon, 20.5; pumpkin, 4.3; squash, 9.85; and watermelon, 7.2.

A further breakdown of the SYs attributed to breeding vine crops at SAESs shows that the bulk of the effort in cucumber, muskmelon, squash and watermelon is in cultivar development with the remaining fractions in plant breeding research and gene enhancement. The other public breeder contributions to vine crops from the USDA are more heavily directed to plant breeding research and gene enhancement than to cultivar development. As expected, the SYs devoted to vine crops by industry are distributed predominately in the area of cultivar development with minor efforts in plant breeding research and gene enhancement.

The merger and conglomeration of the seed industry in developed countries has led to a decrease in the number of cucurbit breeders in private industry. A continuing trend of vertical integration of biotech interests with seed and food production and processing companies is likely to have a similar effect on the remaining number of cucurbit breeders.

Although Frey's data (1996) are quite inclusive when compared to previous less complete studies (Brooks and Vest, 1985; Collins and Phillips, 1991), it is not sound or rational to make SY comparisons or forecast trends in the number of SYs assigned to cucurbits. It is likely that tight budgets and downsizing at public institutions and the SAESs has led to a decline in the member of cucurbit breeders in the public research arena.

Reduced exchange of germplasm

Public-to-public exchange. Traditional plant breeding research and funding to support it is in jeopardy in many SAESs due to declining resources. Because of this, universities are exerting more control over germplasm to capture intellectual property rights and subsequent returns in order to support research programs. However, many colleges of agriculture/SAESs are losing

Cucurbitaceae '98

control over the distribution of royalties and returns from plant breeding achievements. Thus, minor crop support is not likely to increase without major shifts in research priorities. Also, the level(s) of germplasm exchange between SAESs is likely to decline if competition for IPR and subsequent royalties increases between SAESs.

Public-to-private exchanges and vice versa. The exchange of germplasm and information between public and private sector scientists has been greatly reduced in recent years and it is unlikely that this trend will reverse.

Private-to-private exchanges. Although data in the private sector is not easily accessible, it is highly unlikely that exchanges between companies are common and less likely that they would increase. Exceptions include the merger or "stacking" of traits resulting from genetic engineering.

Reduced availability of germplasm

In 1971, the Consultative Group on International Agricultural Research (CGIAR) was initiated. This led to development of 16 International Agricultural Research Centers (IARCs). These centers developed significant germplasm collections. The Food and Agricultural Organization (FAO) of the United Nations was responsible for the development of these entities. The USDA, through its Agricultural Research Service (ARS) and joint cooperation with SAESs, developed a series of national and regional gene banks for germplasm collections. Until recently, germplasm held at the IARCs and in U.S. gene banks was freely available. Also, germplasm found in the wild was assumed to be a common heritage of mankind, i.e., available throughout the world. More recently, germplasm in the wild is now an item of national sovereignty and thus in many countries is unavailable for exchange except through some form of multilateral or bilateral agreement. Presently, an international debate is ongoing regarding the availability of germplasm, both in situ and ex situ. The Convention on Biological Diversity (1993) affirms national sovereignty over plant genetic resources for food and agriculture. The international community continues to attempt to resolve and/or develop guidelines that will ensure the availability of germplasm throughout the

world. However, the caveats to availability are likely to involve significant legal costs and monetary returns to the donor country. A growing list of world staple crops, which includes some vine crops (melon, squash, pumpkin, watermelon) is likely to be exempt from national sovereignty concepts and available when negotiated through multilateral agreements. The agreements between the recipients and the donor will vary in complexity, particularly if a model for exchange is not standardized. It is likely that the longer the time it takes to resolve these germplasm access questions, the more likely we are to lose germplasm to natural forces. A thorough discussion of the factors affecting global access to plant genetic resources and the effects of IPR on exchange of plant germplasm can be found in IPR III, Global Genetic Resources: Access and Property Rights (Eberhardt et al., 1998).

Unavailability of biotechnology innovations for minor crops

Biotech innovations, such as the Bt gene, have been nearly inaccessible to cucurbit breeders in the public sector because they are effectively tied up by the private sector and thus unavailable. The private sector priorities for the various new biotechnologies are usually for major rather than minor crops. Frey (1998) points out that IPR protection could result in limited public access to protected genes and sequences.

The future and its promises

The future for cucurbit breeders is bright, in spite of many of the negatives noted above. Demographers talk of burgeoning populations and reduced farmlands in the next 2 decades. There will be an increased demand for cucurbits and your research, as a cucurbit scientist, will be greatly needed and appreciated as you play a role in meeting this demand. The National Plant Breeding Study II (7) A National Plan for Promoting Breeding Programs for Minor Crops in the United States has been developed as a result of the findings from the survey in NPBS I. The plan of action develops a set of guidelines for improvement and use of minor crops. Although the plan today is only a plan, it will be given serious consideration

Cucurbitaceae '98

by the SAES Committee on Genetic Resources and subsequent consideration by USDA. The National Plant Breeding Study III (8) A National Plan for Genepool Enrichment of U.S. Crops calls for establishing an organization to implement a crop genepool enrichment program. It will provide for the timely and orderly enrichment of genepools of U.S. crops and secure sustained funding for crop genepool enrichment. Concomitantly, it is important to promote an awareness of the significance of crop genepool enrichment to the future viability of U.S. agriculture. It should be the job and task of everyone here, but particularly those from the United States, to become familiar with the National Plant Breeding Studies I, II, and III and to discuss them with your leaders and administrators and encourage their development. Encouraging and assisting private industry and other stakeholder organizations in supporting and being strong advocates for these national plans for enhancement of genetic resources to the U.S. Congress should be a worthy goal for all of us.

There are at least two other major U.S. initiatives that will support further development of plant germplasm collections, plant genomics and other genetic resource activities. First, the development of the program for increasing support to our national and regional gene banks. The Plant Genetic Resource Consumer Focus Group (PGRCFG) has recently enlisted industry support for development of an initiative seeking $20 million for the National Seed Storage Lab (NSSL) at Fort Collins, Colorado. Second, the USDA is currently developing a national Agricultural Genome Initiative (AGI). This initiative is an interagency program, involving the USDA, NSF, DOE, NIH and other federal agencies. Although the program will support all life forms, plants will receive priority in the early years. The Agricultural Research, Extension and Education Reform Act of 1998 (AREERA) (a.k.a. The 1998 Farm Bill) is the likely source of support for the AGI. It will be critical to assure Congress that these many initiatives are all part of a well-coordinated genetic resources plan of great national interest and nonduplicative with ongoing research.

Finally, cucurbit breeders have been productive and innovative scientists and there is every reason to believe that you will willingly accept the challenges demanded by the next millennium.


Literature cited

Bassett, M.J. 1986. Breeding vegetable crops. AVI Publishing Co., Westport, Conn.

Bates, D.M , R.W. Robinson, and C. Jeffrey (eds.). 1990. Biology and utilization of the Cucurbitaceae. Cornell Univ. Press, Ithaca, N.Y.

Brooks, H. J. and G. Vest. 1985. Public programs on genetics and breeding of horticultural crops in the United States. HortScience 20:826­830.

Collins, W.W. and R.L. Phillips. 1991. Plant breeding training in public institutions in the United States. Rpt. 591 (Rev.) National Plant Genet. Resources Board, Office of the Undersecretary for Science and Education, USDA, Washington, D.C.

Eberhardt, S., H.L. Shands, W. Collins, and R.L. Lower. 1998. IPR III. Global genetic resources: Access and property rights. CSSA, Madison, Wis.

Frey, K.J. 1996. National plant breeding Study I. Spec. Rpt. 98, Iowa State Univ., Ames.

Frey, K.J. 1997. National plant breeding Study II. Spec. Rpt. 100. Iowa State Univ., Ames.

Frey, K.J. 1998. National plant breeding Study III. Spec. Rpt. 101. Iowa State Univ., Ames.

Gómez-Guillamón, M.L., C. Soria, J. Cuartero, J.A. Torés, and R. Fernández-Muñoz (eds.). 1996. Cucurbits towards 2000. Proc. VIth Eucarpia Meeting on Cucurbit Genetics and Breeding 28­30 May 1996, Malaga, Spain.

Lester, G.E. and J.R. Dunlap (eds.). 1995. Cucurbitaceae '94: Evaluation and enhancement of cucurbit germplasm, 1­4 Nov. 1994, South Padre Island, Texas. Gateway Printing, Edinburg, Texas.

Pierce, L.K. and T.C. Wehner. 1990. Review of Genes and Linkage Groups in Cucumber. HortScience 25:605­615.

Rubatzky, V.E. and M. Yamaguchi. 1997. World Vegetables. Chapman and Hall, N.Y.

Robinson, R.W. 1995. Genetic Resources of the Cucurbitaceae, p. 92. In: G.E. Lester and J.R. Dunlap (eds.). Cucurbitaceae '94: Evaluation and enhancement of cucurbit germplasm, 1­4 Nov. 1994, South Padre Island, Texas. Gateway Printing, Edinburg, Texas (abstr.).

Robinson, R.W. and D.S. Decker-Walters. 1997. Cucurbits. CAB Intl., New York.

Robinson, R.W., H.M. Munger, T.W. Whitaker, and G.W. Bohn. 1976. Genes of the Cucurbitaceae. HortScience 11:554­568.

Staub, J.E. 1994a. A core collection for cucumber: To be or not to be. Cucurbit Genet. Coop. 17:1­5.

Staub, J.E. 1994b. A core collection for cucumber: A starting point. Cucurbit Genet. Coop. 17:6­11.

United States Government Printing Office. 1937. USDA Yearbook. U.S. Govt. Printing Office, Wash., D.C.

Wessel-Beaver, L. 1995. Broadening the genetic base of cucurbit spp.: Strategies for evaluation and incorporation of germplasm, p. 69­94. In: G.E. Lester and J.R. Dunlap (eds.). Cucurbitaceae '94: Evaluation and enhancement of cucurbit germplasm, 1­4 Nov. 1994, South Padre Island, Texas. Gateway Printing, Edinburg, Texas.

Whitaker, T.W. and G.N. Davis. 1962. Cucurbits, botany, cultivation and utilization. Interscience Publ., Inc., New York.

Cucurbitaceae '98