What the papers say May 2012 C&CI • Coffee & Cocoa Science• 33
problem will get worse. Hence a new review of the science of water relations and irrigation requirements for cocoa is particularly wel- come (Carr and Lockwood (2011) Experimental Agriculture 47: 653-676). The authors stress that cocoa is a
W
drought-sensitive crop with much of the world’s production concentrated in zones with distinct wet and dry seasons. The threat of climate change is leading to less or more erratic rainfall in these areas, whilst higher temperatures cause higher evaporation rates and faster drying soils. This detailed review leaves the authors
puzzled; they are surprised at the limited number of field studies on mature crops, compared to those on immature plants in controlled conditions. This issue was also raised by da Matta and Ramalho for coffee in 2006 (Braz. J. Plant Physiol. 18: 55-81), where they found much research conducted with potted seedlings under semi-controlled conditions, whose results cannot always be extrapolated to the field. Hence, say Carr and Lockwood, there is a
scarcity of information of practical value for cocoa farmers; the lack of data on crop water use and water productivity means it is impossible to quantify yield losses due to drought or yield benefits from irrigation. In view of cocoa’s international impor-
tance, the authors find it difficult to under- stand why cocoa production at a field level is so under-resourced. The answer they feel, must be in part due to the structure and nature of the industry, and the way research is organised and funded. Regular readers of this column may not
be surprised by these conclusions – every- where we see mounting systemic problems for both coffee and cocoa production, which are not being met by an organised and coherent response.
West Africa’s growing cocoa virus problem
The cocoa swollen shoot virus disease situa- tion in Ghana is succinctly reviewed by Domfeh et al. (2011, Afr. J. of Agric. Res. 6: 5033-5039). The virus continues to spread in Ghana despite control efforts based on
Midges play a key role in pollinating cocoa flowers
localised eradication of infected trees and their neighbours. Between 2006 and 2010 a staggering
28.5 million trees were removed, two-thirds in the Western North region which, they con- sider, is now the epicentre of this disease. The recent detection of disease symptoms at Goaso is also a major concern, where a huge backlog of diseased trees awaits treat- ment. The authors urge that the disease must
be tackled from several fronts since focal eradication alone has not checked the dis- ease’s spread. They suggest a rigid imple- mentation of recommendations such as bar- rier cropping, use of recommended planting materials and elimination of all of the virus’s alternative host plants. They also urge that demonstration farms incorporating the new innovations should be established in farm- ers’ farms and to intensify farmer education on the dangers of ineffective treatment or complete neglect of this dangerous disease. Results of a small sample of farms from
the Bazre’ locality in west-central Côte d’Ivoire (Kouakou et al. J. Appl. Biosci. 2011 43: 2947 – 2957) also gives much cause for concern. A tree mortality rate of 23 per cent caused by Group B of the virus was found and related to a significant decrease (up to 50 per cent) in pod number and weight reduction of beans on diseased trees com- pared to controls. The authors conclude that it is imperative to develop a strategy for effi- cient control of swollen shoot disease in Côte d'Ivoire.
ater is a growing problem in farm- ing: sometimes there is too much – often not enough. Most believe this
Dr Peter Baker looks at academic publications recently appearing on the CABI Abstracts database (
www.cabdirect.org)
Enhancing flowering
A previous column in this series looked at the poor state of knowledge about how the cocoa flower is pollinated. A new study (Frimpong et al. (2011) J. Pollination Ecology, 5: 74-80) based on trapping the midges that are the principal pollinator of cocoa, provides some interesting new field data on flowering patterns. As expected, they found that in fields
where more midges were trapped, percent- age pod set was higher. Most interesting though was that in fields with clusters of plan- tain or bananas, at around 10 clumps/hectare, midge numbers were signifi- cantly higher and pod set as well. Nearness of a farm to natural forest offered no addition- al pollination advantage however.
Nutrient status of cocoa and those growing it
Cocoa is the primary cash crop in most coastal areas of Papua New Guinea, support- ing an estimated 150,000 households, mostly smallholders. Yields are low; about 10 per cent of the maximum. This being the case, the authors of a
recent report (Nelson et al. (2010) 19th World Congress of Soil Science, p. 71-74) surveyed soil nutrients as a potential cause of this prob- lem. Based on leaf analyses, nitrogen and iron deficiencies were very widespread, with 95 per cent of sampled blocks falling below the critical level for nitrogen and 89 per cent for iron. On the other hand, in Ondo and Kwara
states of Nigeria, Oluyole et al. (World J. Agric. Sci. (2011) 7: 617-623) looked instead at the nutrition levels of the farmers growing cocoa. They found that 56 per cent of the house-
holds were food insecure, subsisting on less than the recommended daily calorie require- ment of 2,450 kilocalories. Families on the smallest farms, or with a female head, or not belonging to an association, were all more likely to be short of food. C&CI
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