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What the papers say March 2012 C&CI • Coffee & Cocoa Science• 43

offee leaf rust (caused by the fungus Hemileia vastatrix) famously destroyed the Ceylonese (Sri Lankan) coffee industry in the 19th century and subsequently spread to nearly every coffee country on earth, causing many billions of dollars of lost Arabica production and enduringly expensive spraying operations.


It also triggered the first major study of a tropical plant disease by Harry Marshall Ward, who elucidated the life-cycle of the disease in Ceylon in the 1880s. It is difficult to believe now, but at that time planters thought that the disease was caused by some deficiency in growing conditions that allowed the disease to take hold. They could not believe that a perfectly healthy plant could succumb to a tiny rusty spore. Ward described the life-cycle and conclud- ed that the disease propagates by asexual spores. This is significant because it is sex that introduces variation to help organisms quickly adapt to new conditions and therefore would mean that the disease takes the form of rather stable races that produce identical copies (clones) of themselves. These would vary only slowly through the occasional genetic mutation.

Hence it should be possible to develop resistant plants that have a long life (essential for a perennial) unlike rust-resistance in wheat that breaks down after a few years and so requires the continual introduction of new vari- eties. Such resistant coffee varieties have duly been developed through several breeding programmes around the world. Although this has been successful, the disease has been able to break down the resistance of many of these varieties. It must have done this entirely by genetic mutation – spontaneous changes in rust genes so that new races of the dis- ease evolve. Or so it had been thought.

Scientist vindicated

In the 1960s the Indian scientist R B Rajendren described the presence of sexual spores, but his work was largely ignored. Now, however, a new paper from the Universidade Federal de Viçosa (Carvalho C.R. et al. (2011). PLoS ONE 6:1-7) shows detailed and convincing evidence of sexual spore formation (meiosis).

The reason why this had not been spotted before (except by Rajendren) is that the process is hidden inside a spore that looks

Dr Peter Baker looks at academic publications recently appearing on the CABI Abstracts database (

have not invested much in plant breeding, and who now encounter wetter conditions due to climate change, may find themselves in a similar situation to Colombia but without a diverse supply of new planting material. As we have pointed out before in this column, much of the coffee industry rests on worrying- ly insubstantial research foundations, poten- tially limiting our scope to build sustainably intensive future harvests.

Complexities of Fairtrade

Coffee leaf rust continues to cause problems in coun- tries such as Colombia (photo: Neil Palmer, CIAT)

like the asexual form – a condition the authors describe as cryptosexuality.

Using quantitative DNA image cytometry, they were able to measure the amount of DNA present at the various stages of spore formation and clearly demonstrate the halving of the amount of DNA as meiosis takes place – that is, the formation of the sexual spore. The discovery means that we now have the possibility for the cross-fertilization of two genetically distinct spores when by chance they encounter each other within the leaf tis- sue. It also means that the present system of classifying genetically identical races of the disease (of which dozens are claimed to exist) is mistaken, and helps explain why resistance to the disease has not been as durable as hoped. Hence, an important underlying assumption upon which plant breeders develop new coffee varieties is also mistaken.

Colombian research

Leaf rust continues to be a great problem to the coffee industry, and the recent major decline in production in Colombia is at least partly due to the resurgence of rust. Fortunately, they had invested heavily in research to continually produce new resist- ant material, so the discovery of sexual spores suggests that their strategy of pro- ducing varieties with considerable genetic variation has been the right one. It also means that other countries, who

Lastly, another study on Fairtrade coffee (Weber J.G. (2011). Food Policy 36: 677–684.), this time from Mexico, con- cludes that there is a small but positive advantage to Fairtrade organic farmers, averaging US$103/household/year. The author acknowledges the major method- ological problems of trying to accurately account for all costs and benefits and admits that no account is taken of the costs of compliance with requirements, nor the 5 per cent social premium that Fairtrade pays to the co-operative.

Most interesting perhaps is how the premi- um compares with other farm income streams, which include nearly US$1,000/household in annual payments from government programmes, mostly from Oportunidades (a conditional cash transfer programme) or agricultural subsidies (Procampo).

Then there is US$163 from remittances of family members within Mexico and a remark- able US$2,900 in cases where there is a fami- ly member living in the US. Unfortunately, the author does not refer to Daniel Jaffee’s book on Fairtrade coffee in Mexico (Jaffee D., (2007). Brewing Justice, UC Press) that elaborated on the complexities of coffee farmers, emigration and remit- tances, concluding that families with migrants were mostly worse off.

What seems to be becoming clear is that quantifying the full social and economic costs and benefits of Fairtrade is a very difficult process, and one that will require consider- able further research. ■ C&CI

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