Molecular tools and quality improvement in vegetatively propagated crops

Breeding and use of biodiversity in vegetatively propagated crops is a particular challenge, with many cultivars of the plants grown worldwide ‘improved’ only in the sense of being selected from landraces. The crops often have narrow genetic bases. A combination of sterility and, where fertile relatives are found, the difficulty of restoring the basic domestication traits in any crosses means breeding programmes have had only limited success. This week, I am at the final meeting for a program on molecular tools for quality improvement of the world’s most important vegetatively propagated crops: banana (and plantain, Musa species) and cassava (manihot or tapioca, Manihot esculenta). Together, these crops provide a huge proportion of the calories eaten in Asia and Africa, with most grown by smallholders for their own consumption or as a local cash crop in low-income, food-deficient countries, particularly in sub-Saharan Africa and Asia. However, compared to other staple crops including cereals, the understanding of natural diversity, and strategies for  breeding improved varieties for food security and quality has been extremely limited in banana and cassava.

The meeting is part of a Coordinated Research Project (CRP) sponsored by The International Atomic Energy Agency, IAEA, in a Joint Programme with the Food and Agricultural Organization (FAO) of the UN. It is one of their ongoing series of important CRPs which aim to build and share capacity in the application of scientific results and technological approaches to genetics and plant breeding. Listing the origins of the project participants, including Indonesia, the Philippines, Mexico, China, Cuba, Bangladesh, India, Ghana, Kenya and Nigeria, as well as our host Brazil, and Europe, shows the global reach of the programme and wide interest in developing and using new approaches for improvement of banana and cassava. Asha Nair and Chikelu Mba reported on the previous meeting in India in Current Science (2007); Brad Till has recently taken over from Chike (who has moved to FAO) as the IAEA project coordinator, and Nicolas Roux is representing Bioversity International.

It is always interesting to compare the aims of the programme with its outcome: I was part of the meeting, hosted by Mirek Maluszynski, in 2004 where the objectives of the programme were set out with Perry Gustafson (Missouri) and Martin Fregene (CIAT, Columbia). In the last six years, understanding the genetic basis of characters associated with post-harvest traits has been recognized as being much more important: I blogged about food wastage on AoBBlog earlier in the year. We didn’t foresee how much the new cheaper DNA sequencing methods would impact work reported by almost all participants. Certainly, the aims of measuring diversity, finding traits of value to farmers and consumers, and the development of molecular and tissue culture strategies, including use of mutations, have been reached through the work of the participants. Here in Brasilia, we have seen a range of valuable results about measurement of genetic diversity using a range of molecular tools that are now applicable to ‘orphan’ crops with a restricted research base, and all the speakers have kept the application of their work to release of genetically improved crops to farmers in mind – with tissue culture approaches to propagation and distribution of improved materials featuring strongly. Both in banana and cassava, the audience has been treated to some remarkable results from mutation induction using gamma rays and EMS. Already, more than 3000 crop varieties have (IAEA Mutant Variety database) been released from induced mutations. Using radiation doses from 30 to 50 Gy and developing new tissue culture protocols for propagation within this project, Emma Sales previewed several lines based on Philippine banana varieties with alteration in cell-wall and pulp softening enzymes (polygalacturonidases and proteases) which increased shelf-life of ripe bananas by several days. Enny Sudarmonowati (Indonesia), Luiz Carvalho (Brazil) and Andrew James (Mexico) showed extensive results about the diversity of starches in cassava and banana, where changing the nature of the starches has major impacts of end uses (not least for biofuels and ethanol production) and value of the crop. Zaochang Liu (China) showed his results with impressive yield improvements from radiation mutants, although stability in the long term is still unclear. Several papers (including Peter Njau, Kenya and John Beeching, UK) have discussed the problem of cyanide production in cassava leaves which is transported to roots making them unsuitable for consumption – although John noted that this character may have been inadvertently selected because the cyanide is a nitrogen source for the root and may improve storage quality, as well as being unpalatable to rodents and other pests. Papers from Andrew James (Brazil), Robert Miller (Mexico), as well as my own report of work with Mohamad Azhar (now at Nuclear Malaysia) have discussed progress to understanding some of the disease-resistant genes available in the crops – work which will underpin release of new varieties in years to come. In bananas, Mamun (Bangladesh) discussed some of the tissue culture protocols and field plant performance while our collaborator Asha Nair (India) showed data about anther culture and haploid production in banana, with extensive molecular data about loss of allele variation in the cultures. My own talk focussed on banana, covering work on marker development in banana (see, for example, Domestication of bananas, 2007; and the fascinating proposal on origins of banana from a group including one of the participants, Jaroslav Dolezel, see AoBBlog for a discussion (including links to cassava) and more at The origins of hybrid edible Banana and more from Alun Salt), and moving to discuss the molecular basis of evolutionary differences within and between cultivars and species.

Several participants have discussed the relevance of our group´s work to the Millennium Development Goals. We are all committed to the need for advanced crop research and breeding to underpin poverty alleviation, and I will later be discussing the new breeding paradigm of ‘superdomestication’ (see my paper with Duncan Vaughan et al, 2007), where the partnership of end-users (farmers and consumers) and breeders consider the ideal requirements for a new variety, which is then delivered by exploiting knowledge of genetic diversity and breeding technologies.

As the presentations are coming to an end, we now think about coordinated publication of our results and the future plans for individual research and collaborations. The results of meetings like this have often been published in IAEA Technical Reports, a format that is very specialized and does not use 21^st century approaches to making high quality research fully available and citable, linked through high-quality web-publication (in this case through Oxford University Press and Highwire Press). Therefore, our intention is that the work discussed during the meeting which meets rigorous peer-review standards should be published as a group of papers in the open-access journal AoB Plants, thanks to the generosity of the Annals of Botany company in sponsoring the costs of the open access publication and Mike Jackson as Editor of the Journal. This will make all the papers fully available through Pubmed Central and all other citation databases and search platforms, and the open access means that IAEA can disseminate the papers as a collection. The work is generally specialist in nature, but will have potentially wide impact and will be useful for both specifics and general approaches to molecular breeding of vegetative crops, so I am delighted that there is the prospect of publication in this new format.

From the botanical point of view, it is always exciting to be in Brazil, both because it is perhaps the major biodiversity ‘hotspot’ in the world, and also because it is the lowest-cost producer in the world for many agricultural products. This is my first visit to Brasilia, a city built on the cerrado as a new capital starting in the 1960s. We have seen plenty of green space in the city (through a very British drizzle of rain most of the time so far, albeit 5C warmer than the best of our summer), but there is not much evidence of native flora so far growing on the bright red tropical lateritic soils. The ‘sensitive plant’ Mimosa pudica is flowering abundantly in some grassed areas, the first time I have seen this plant in the wild, and the diverse range of leguminous trees with flowers ranging from white through blues, reds and yellows, is most impressive. Later in the week we have a day in the field, so more will follow here.