Plant reproduction: Sexual versus asexual Plants are either reproduced sexually by seed, or by some method of asexual propagation (cloning). In sexual reproduction, male and female gametes, the pollen and the egg cell, are produced separately with half the normal chromosome number. Their combination during fertilization gives rise to the development of a seed that carries a unique combination of the genes derived from both parents. It is this recombination that causes variability in a sexually propagated population, as expressed in characteristics such as plant height, vigour, seed size and nutritional composition. Seeds are physiologically robust, naturally primed for growth and adapted for field emergence. Sexual reproduction and genetic uniqueness appear to have provided most species with evolutionary advantages. In agriculture, however, it can be often regarded as undesirable, since it causes variation that can negatively effect production practices and the quality of the harvested and processed product.  Asexual reproduction, in contrast, provides the advantages of absolute crop uniformity. The genetic make-up of the parents is identical to the progeny, so a single desirable plant can become the basis of a new variety. The efforts essential for sexually propagated plants to ‘fix’ characteristics to ensure ‘true breeding’ are therefore unnecessary. Consequently, cloning makes the development of new varieties more time and cost effective. Many economically important fruiting plants, such as date palms and grapevines, have been propagated by vegetative means for hundreds, sometimes even thousands of years. Similarly, many root and bulb crops are cloned by natural means, such as cassava, potato and garlic. More recently, technologies such as tissue culture and cutting propagation have greatly expanded the number of species that can be cloned routinely. Despite these opportunities, however, cloning is currently only economic for plants that either use a convenient natural mechanism or that have a high unit value. Absent from this list are crops such as maize, rice, wheat, millet, sorghum, most pulse species, and the majority of economically important forage, fibre and timber species.

The potential benefits of apomixis
Six principle benefits of apomixis can be perceived:

• Rapid development of new hybrid varieties. Generally, a hybrid is the product of crossing genetically dissimilar parents. A hybrid breeding programme includes the establishment of a group of genetically uniform and distinct lines that are inbred by repeated self-pollination, and the identification of those combinations of pure lines that render increased vigour, or heterosis. With apomixis the desirable genetic make-up of any individual plant could be ‘fixed’ immediately without the creation of inbred lines, thereby significantly reducing the costs of a hybrid breeding programme. It is hoped that access to apomixis will therefore provide an incentive encouraging National Agricultural Research Institutes (NARIs), producer cooperatives and possibly even individual producers in resource poor regions to develop their own varieties. As it will be theoretically possible to cross existing landraces with apomictic varieties, new hybrid varieties could be formed which may potentially be specifically adapted to local environmental conditions and growing practices.
• Economic hybrid seed production. In hybrid seed production, the maintenance of inbred lines is a cost decisive activity. Furthermore, the production of seed by these inbred lines remains complicated by their decreased viability, and the laborious and expensive activities for preventing cross-pollination, such as detasselling. With apomixis, the cost of hybrid seed production could be drastically cut. Once a favourable variety is created by the combination of inbred lines, the hybrid plant and its identical offspring could produce seeds asexually at a higher rate than inbred lines.
• Propagation of hybrid seed. The F1 generation of hybrid crops does not render the same genotype or performance as the parent plants. By contrast, apomictic varieties do not change their genetic make-up and thus ‘breed true’. Therefore, instead of purchasing new hybrid seed each planting, farmers could save and sow seed of apomictic hybrid varieties without losing its hybrid vigour. In principle, a producer could maintain an apomictic seed variety indefinitely, in the same way as potato, cassava and sweet potato varieties are used today.
• Resistance against pathogens. Plants propagated by vegetative division (such as sweet potato) transfer viruses, viroids and other pathogens from one asexual generation to the next. The pathogen load of the clone increases with each successive generation as plants are subjected to new strains and species of pathogen. This ‘horizontal transfer’ of pathogens causes the progressive degeneration of a clone, which is cited as a possible reason for the rarity of exclusively asexual propagation in natural plant species. In agriculture, the removal of viruses and the maintenance of healthy nuclear stocks has profoundly improved the productivity of several asexually propagated crops, but this requires a relatively high technology base and is expensive to maintain. By contrast, very few pathogens are capable of transfer through seed.
• Handling of propagation material. Many asexual propagules, such as the tubers of potato are awkward to store, due to their size, weight and perishability. In contrast, seed is typically both small and robust. It has been estimated that the quantity of seed potatoes (tubers) stored in a typical 500 tonne, 1000 square metre controlled-atmosphere facility could be replaced by the amount of seed that would occupy the top shelf of a domestic refrigerator. Moreover, seed is often easier to transport and sow.
• Increased reproduction efficiency. Crop losses are often caused by limitations of the ‘mechanics’ of sexual reproduction itself, such as fertilization or pollination difficulties, caused by incompatible varieties, inadequate pollinator activity, or biotic/abiotic stress. However, these limitations would only be overcome by ‘autonomous’ apomictic species without a requirement for pollination.

Introduction of apomixis into crop plants
The potential value of apomixis for plant breeding has been recognized for many years. Attempts to introduce this trait into sexually propagated crops have taken two approaches.

• Introgression. Typically this involves wide hybridization between a crop species and an apomictic relative, followed by a backcrossing programme using the sexually propagated species as the recurrent parent. Examples of this approach include the attempted transfer of apomixis from Pennisetum squamulatum to the cultivated species P. glaucum (millet), from Elymus rectisetus to Triticum (wheat) and from Tripsacum dactyloides to Zea (maize) (see table 1). Two US patents have been issued in association with this approach (see table 2).
• Synthesis. Other researchers are trying to synthesize apomixis by crossing plants with mutations in key processes, which, in combination, are expected to create a form of apomixis. Examples of the types of mutations include those that produce an egg with an unreduced number of chromosomes (meiotic mutants), and those that develop an embryo without fertilization (parthenogenetic mutants). Significant progress has been made in potato using this approach, although a mutation that leads to apomixis has yet to be found.

Current research on apomixis
Apomictic species/approach	Organization	Location
wheat	Institute of Plant Genetics	Gatersleben, Germany
Hieracium	C&FR	Christchurch, New Zealand
evolution of apomicts	Utah State University	Logan, UT, USA
histology of apomixis	Jagellonian University	Krakóv, Poland
Taraxacum	NIOO	Heteren, the Netherlands
Pennisetum	USDA-ARS	Tifton, GA, USA
molecular tools for apomixis	CAMBIA	Canberra, Australia
Allium	Kyushu National Agricultural Experimental Station	Miyazaki, Japan
rice	Academia Sinica	Bejing, China
Hieracium	CSIRO	Adelaide, Australia
Pennisetum	University of Georgia	Tifton, GA, USA
Paspalum	IBONE	Corrientes, Argentina
Tripsaccum dactyloides	CIMMYT	Mexico, Mexico
Brachiaria	CIAT	Cali, Colombia
somatic embryogenesis	Wageningen Agricultural University	Wageningen, the Netherlands
cassava	University of Brasilia	Brasilia, Brazil
Arabidopsis mutagensis	CSIRO	Canberra, Australia
	University of California	Berkeley, CA, USA
	Cold Spring Harbor Laboratory	Cold Spring Harbour, NY, USA
	CPRO-DLO	Wageningen, the Netherlands
	Harvard University	Cambridge, MA, USA

Possible impact of apomixis on agricultural biodiversity
As apomixis results in the formation of large clonal populations, it represents a form of monoculture. It therefore poses a possible risk of widespread infestation, leading to varietal collapses and thereby losses in production. Although apomictic varieties can be vulnerable to collapse, they do have some advantages over current inbreds and F1 hybrid varieties, and could reduce the impact and frequency of such events. As resistance genes no longer need to be genetically fixed through homozygosity, many of the generations normally required to breed resistance could be skipped. Apomixis therefore permits the rapid development of new, resistant replacements for a collapsed variety.
Moreover, it facilitates the incorporation of several resistance genes in a new variety, reducing the possibility of future collapse, as multiple susceptibilities need to occur simultaneously. Currently, the main cost factor of a collapse is the use of a single variety, or a cohort of varieties with similar ancestry, over large areas of land. This is an indirect effect of the high cost of breeding. By reducing the cost and increasing the speed of varietal development, apomixis is expected to encourage the use of a broader range of varieties, each chosen either because they are uniquely suited to a particular micro-environment, farming practice or end use.
Furthermore, the simplicity of apomictic breeding may encourage the wider use of ‘synthetic’ varieties where several similar clones are deliberately mixed to provide field variation for characteristics such as disease resistance, yet still ensure sufficient uniformity for critical yield characteristics. Such synthetics may prove to be particularly suitable in developing countries, where yield security may be considered more important than absolute yield quantity.
In any crop at any one time, only a fraction of the original species diversity is utilized in production varieties. This would not change significantly with apomixis. By encouraging local breeding efforts, germplasm could be valued and become more dispersed, providing some extra security against its loss.

Patents related to apomixis
Publication number  (Filing date)	Title	Abstract of claims	Applicant(s)
WO9743427 (13 May 1996)	production of apomictic seed	expression of a gene which renders the embryogenetic production of embryo sac tissue	Novartis
US5710367 (22 Sept 1995)	apomictic maize	maize/Tripsacum hybrids used to introgress apomixis into a maize background. DNA primers are listed to facilitate this process.	USDA
US5811636 (22 Sept 1995) WO9710704 (23 Sept 1996)	apomixis for producing true-breeding plant progenies	gene(s) transferred from Pennisetum squamulatum into cultivated plants resulting in apomictic progeny	USDA
WO8900810 (9 Feb 1989) EP329736, AU629796, CN1040123, AU2255288	asexual induction of heritable male sterility and apomixis in plants	induction of male sterility and apomixis through the introduction of transmissible male sterility factors present in extracts of male sterile alfalfa plants.	Maxell Hybrids Inc.
WO9836090 (17 Feb 1998) AU6405498	means for identifying nucleotide sequences involved in apomixis	genes in sexual species of Gramineae known to be orthologous to equences associated with apomixis in related species. Isolation and modification of those sequences.	CIMMYT-ABC
WO9833374 (5 Feb 1998)	methods for producing apomictic plants	construction of apomictic varieties by combining plants lines with asynchronous female developmental programmes.	Utah State University
CN1124564 (19 June 1996)	hybrid vigor fixing breeding process for rice apomixis	breeding and selection strategies for isolating apomixis in rice and for developing apomictic rice varieties.	Chen Jiansen
WO9828431 (24 dec 1997)	transcriptional regulation in plants	meiosis specific promoter that will direct gene activity to tissues associated with gamete formation in plants.	John Innes Centre Innovations Ltd
WO9837184 (28 Oct 1998)	leafy cotyledon1 genes and their uses	embryo specific genes and their promoters that will be valuable for targeting gene expression to embryos.	University of California
WO9808961 (5 March 1998)	endosperm and nucellus specific genes, promoters and uses thereof	endosperm specific and a nucellus specific promoter.	C. Linnestad, O.A. Olsen, D.N.P. Doan
Sources: http://patent.womplex.ibm.com/patquery; http://ep.espacenet.com/

Distributing the benefits of apomixis
Apomixis is a technology with the potential to influence almost every farming system around the world. The distribution of rewards, however, will depend on the controlling parties and how they use this technology.
If apomixis were widely available to all parties, including breeders, seed merchants and producers throughout the world, its likely primary impacts would be to accelerate the rate of hybrid variety advance and to stimulate ‘boutique breeding’ towards specific product uses, production regions and farming practices. Apomixis technology could provide advantages to large and small producers in both the developed and developing worlds. Apomixis could also bring specific advantages to resource-poor farmers in developing nations. Currently, for many crops, the elite varieties available are bred for resource-intensive agriculture in the major production areas of the industrialized world. Furthermore, as they are controlled by international seed suppliers, the availability of seed is subject to variations in the global seed market. Apomixis would encourage local hybrid breeding programmes, which, if the agronomic characteristics are selected in a participatory manner, could ensure hybrid seed supply appropriate to farmers’ needs. Farmers could save and re-sow this seed without losing its vigour. However, the benefit for farmers would strongly depend on their ability to manage and control the use of apomixis themselves, and the possibilities for crossbreeding with locally adapted landraces. Furthermore, farmers, including peasants, producing for market or processing purposes could benefit from increased uniformity of yield.
The potential value of apomixis for the development and production of hybrids has been recognized for many years and it can be expected that seed companies will try to develop it as part of their technology portfolios. According to Michiel van Lookeren Campagne, head of the Department of Developmental Biology at the Centre for Plant Breeding and Reproduction Research (CPRO-DLO) in the Netherlands, all large ‘life science’ companies have an interest in apomixis research. At present, however, their research activity is rather limited to joint ventures, such as the contribution of Novartis (Switzerland) to the apomixis research of the European Plant Embryogenesis Network (EPEN). Novartis has already gained a patent through an earlier cooperation with CPRO-DLO (see table 2). However, Van Lookeren Campagne states that most life science companies seem mainly to be interested in keeping up to date with recent developments rather than having apomixis as a priority in their own research programmes. As apomixis undermines the proprietary protection currently provided by hybrid seed, commercial actors will only be able to reap the full benefits of apomixis if they can prevent farmers from seed saving. Therefore, recent technological developments in the control of seed germination, and the production crops that deliver non-viable seed, are of potential interest for these companies. According to Van Lookeren Campagne, however, it remains to be seen if the combination of these two approaches is technically feasible in the near future.
Apomixis technology could become a tool to cut costs in modern variety development. However, if apomixis technology were controlled by only one or a very small number of commercial entities, and protected by strict technical and/or legal means, then the wider benefits of this technology would hardly reach other actors in agriculture.
In May 1998, leading researchers in apomixis launched a declaration stating that apomixis technology needs to remain available to parties in, and/or working for developing countries. The Bellagio Apomixis Declaration expressed concern that the concentration of legal rights into a small number of hands will delay the utilization of this technology to address the needs of resource poor farmers. It was acknowledged that, realistically, the private sector will have an important role in developing apomixis technology and its commercial needs cannot be ignored. The challenge ahead will be to retain access for all parties while ensuring a reasonable return on investment for commercial agents. To this end, novel approaches to technology generation, patenting and licensing will need to be developed, because current practices promote monopolization. One possibility could be that key apomixis patents generated by public sector institutions are placed collectively under the trusteeship of a foundation. The licensing policy of this legal entity should be, while economically sound, sufficiently permissive to make the technology widely available to all interested parties.
Ross A. Bicknell¹ and Katie B. Bicknell²

1. Crop & Food Research Ltd, Private Bag 4704, Christchurch, New Zealand.
Phone (+64) 3 325 64 00; Fax (+64) 3 325 20 74; E-mail bicknellr@crop.cri.nz
2. Economics and Marketing Department, Lincoln University, Canterbury, New Zealand.

Sources
Jefferson, R.A. (1995), "Apomixis: A social revolution for agriculture?" Biotechnology and Development Monitor, 19, 14-16.

Koltunow, A.M., Bicknell, R.A. et al. (1995), "Apomixis: Molecular strategies for the generation of genetically identical seeds without pollination." Plant Physiology, 108, 1345-1352.

Bellagio Apomixis Declaration: http://billie.harvard.edu/apomixis/