Tropical Food Research Articles

Governance for quality management in tropical food chains

This paper provides a framework that focuses on the linkages between several key dimensions of supply chain organisation and performance of perishable tropical food products. The focus is on the relationship between governance regime and quality management, however, two other related variables are also taken into account because they impact this relationship: channel choice and value added distribution in the supply chain. Governance regimes focus on how to enhance coordination and trust amongst supply chain partners and how to reduce transaction costs. Quality management deals with how to manage food technology processes such that required quality levels can be improved and variability in quality of natural products can be exploited. Governance regimes in relation to quality management practices are discussed to the extent that supply chain partners are able, or are enabled, to invest in required quality improvements. Reduction of transaction costs, creation of trust-based networks and proper trade-offs between direct and future gains may offer substantial contributions to effective quality management and enforcement. This framework has been applied to nine case studies about food supply chains originating from developing countries (Ruben et al., 2007). Three of these case studies are summarised in this paper to illustrate what challenges can be derived from this study. These selected case studies concern fish caught in Kenya, mangoes grown in Costa Rica and vegetables produced in China.

Characterization of the photosynthetic pathway of some tropical food yams (Dioscorea spp.) using leaf natural <sup>13</sup>C abundance

A total of 23 genotypes belonging to seven tropical food yams and two wild relative species of different origin and coming from two sampling ecological zones (the Republic of Benin in Africa and Guadeloupe in the Caribbean) was analysed for their 13C content. The δ13C values for all yam samples (from -25.39 and -30.07 ‰) indicated that all species had a C3 photosynthetic type.

Effect of particle size and drying temperature on drying rate and oil extracted yields of Buccholzia coriacea (MVAN) and Butyrospermum parkii ENGL

SummaryThe effect of particle size and drying temperature on drying rate and oil extracted yields of Buccholzia coriacea (MVAN) and Butyrospermum parkii (ENGL) was investigated. Air drying studies carried out on B. coriacea and B. parkii, tropical food sources subject to high post‐harvest losses, have resulted in the establishment of a significant difference between oil yields extracted from samples of various particle size pretreatments (paste, 4 mm, 8 mm and whole kernels) dried at 45 and 60 °C with the highest oil yield given by the 4 mm thick slices dried at 45 °C. The influence of temperature and particle thickness on the drying rate has been evaluated. The drying constants were found to depend on both temperature and particle thickness. Analysis of the oil extracted from the 4 mm thick slices dried at 45 °C showed that apart from the acid value (52.4%), the saponification (181.2 mg g−1 KOH), peroxide (8.6 meq kg−1) and the unsaponifiable (7.43%) matter values of the extracted shea butter remain within the limits cited in the literature while a close analysis of the cake suggests that it could be a good mineral source.

PARALYTIC SHELLFISH TOXINS IN TROPICAL OCEANS

The tropics possess some of the world's richest marine environments, most notably coral reefs. Concealed within these ecosystems are a group of potent neurotoxins called the paralytic shellfish toxins (PSTs), the most famous of which is saxitoxin. Thirty years ago, PSTs were recognized as a major danger to seafood consumers in the tropics. The tropical dinoflagellate Pyrodinium bahamense biosynthesizes PSTs and its contamination of seafood has caused more illnesses and deaths than any other PST-producing microalga. Apart from this and other dinoflagellates, PSTs have been confirmed in tropical benthic algae, molluscs, echinoderms, crustacea, and other arthropods. Some of these organisms are unique in that, to date, they have only been found to be toxic in tropical oceans. For example, species of grazing and predatory gastropods, crabs, and more recently cephalopods have been discovered to contain PSTs in a number of intertidal tropical locations. These animals are thought to accumulate the toxins from benthic sources rather than toxic dinoflagellates as happens with filter-feeding bivalve molluscs such as clams and oysters. Here we evaluate the current understanding of PST transmission through tropical food webs. Finally, we consider the prevalence of PST intoxications in tropical regions and their social and economic costs.

An archaeobotanical perspective on Holocene plant-use practices in lowland northern New Guinea

Existing archaeobotanical and palynological records of plant use in the northern New Guinea lowlands are reviewed in light of recent work at Kuk and theoretical refocusing on plant use practice. A practice-based approach is supported as the most useful way of investigating the highly problematical area of tropical plant food production. The existing direct record of past plant use in lowland New Guinea is considered woefully inadequate to achieve this task, as is that in Near Oceania and Island Southeast Asia. Archaeobotanical methods exist to fill the void, but full implementation requires a change in general archaeological and palaeoecological practice.

Structure–texture relationships of fresh pastes prepared from different yam ( Dioscorea spp.) varieties

Yam ( Dioscorea spp.) presents an important tropical food crop rich in starch. In West Africa, yam is traditionally prepared by pounding of cooked yam to obtain a dough-like paste known as pounded yam or ‘foutou’. The present investigation deals with structure–texture relationships of yam pastes as influenced by yam varieties. In general, the firmness of yam pastes prepared from D. cayenensis-rotundata was higher than that from D. alata. Difference in firmness was found to be related to the extent of cell disintegration, which was more pronounced for D. alata as assessed by light microscopy. Pronounced textural changes were measured during ageing of yam pastes, which is a consequence of the reorganization (retrogradation) of the amylose fraction. Post-harvest storage of yam tubers resulted in increased firmness and decreased adhesion properties in the pastes, but no significant influence of the storage treatment with gibberellic acid, which reduces storage losses, was detected. It is concluded that the texture of yam pastes is largely determined by the integrity of cells and the properties of the continuous starch phase.

The control of hypertension by use of coconut water and mauby: two tropical food drinks

In this study, the authors investigated the effect of regular consumption of two tropical food drinks, coconut (Cocos nucifera) water and mauby (Colubrina arborescens), on the control of hypertension. Twenty-eight hypertensive subjects were assigned to four equal groups and their systolic and diastolic blood pressures recorded for two weeks before and then for another two weeks while receiving one of four interventions. One group (the control) received bottled drinking water, the second group received coconut water, the third received mauby and the fourth group, a mixture of coconut water and mauby. Significant decreases in the mean systolic blood pressure were observed for 71%, 40% and 43% respectively of the groups receiving the coconut water, mauby and the mixture (p < or = 0.05). For these groups, the respective proportions showing significant decreases in the mean diastolic pressure were 29%, 40% and 57%. For the group receiving the mixture, the largest decreases in mean systolic and mean diastolic pressure were 24 mmHg and 15 mmHg respectively; these were approximately double the largest values seen with the single interventions.

Novel Optical Biotest for Determination of Cyanide Traces in Marine Fish Using Microbial Cyanide Hydratase and Formate Dehydrogenase

A novel and simple enzymatic method for the determination of trace cyanide in marine fish is presented. This method is based on the conversion of metal-cyanide complexes by a fungal enzyme extract containing cyanide hydratase (E.C. 4.2.1.66; CyHT) and formamidase (E.C. 3.5.1.49) into formate and ammonia. The formate produced in the sample pretreated with the fungal enzymes was measured by adding formate dehydrogenase (E.C. 1.2.1.2; FDH) and excess NAD+. The NADH formed accordingly was monitored at 340 nm. The cyanide calibration curve was found to be linear in the range of 10–100 µM, and the detection limit was 1.1 µM (0.0286 ppm). The proposed biotest was successfully applied to the determination of trace cyanide in a tropical marine food fish species (Russell’s Snapper (Lutjamus russellii)) which had been exposed to cyanide.

Residue Decomposition and Nutrient Release Dynamics from Two Tropical Forage Legumes in a Kenyan Environment

Soil fertility decline is one of the factors limiting food production on the east coast of Africa. Increased awareness by smallholder farmers of the role of legumes as sources of food and fodder and for soil fertility improvement has stimulated research on the influence of herbaceous legumes in various cropping systems. Decomposition and nutrient release from foliage of legume species clitoria (Clitoria ternatea L.) and dolichos (Lablab purpureus L.) planted in monoculture and as an intercrop with tropical food crops cassava (Manihot esculenta Crantz) and maize (Zea mays L.) were evaluated under field conditions in fine‐loamy, kaolinitic, isohyperthermic, arenic Paleustalfs. The nylon mesh bag technique was used to obtain data to calculate the residue decomposition and nutrient release rates of the clitoria foliage cut every 6 or 10 wk and dolichos foliage cut at 2 or 4 mo. Asymptotic models provided the best fit for both dry matter decomposition and nutrient release. Legume residue decomposition rates (k) were unaffected by cropping system, with values of 0.2 and 0.5 wk−1 for clitoria and dolichos, respectively. Across cutting management strategies, the general order of nutrient release for clitoria at 6 or 10 wk was K &gt; P &gt; Mg &gt; N; while that of dolichos was K &gt; Mg &gt; P &gt; N and K &gt; P &gt; Mg &gt; N for cuts at 2 and 4 mo, respectively. Overall, the residue N, P, and Mg release curves became asymptotic shortly after 60% of the nutrients had been released. Clitoria and dolichos showed their potential to become sources of nutrients for associated crops while protecting the soil surface.

Evaluation of the effects of thiamethoxam on three species of African termite (Isoptera: Termitidae) crop pests.

Thiamethoxam formulated as ACTARA 25 WG has been tested on three species of higher African termites: Trinervitermes trinervius Rambur, Odontotermes smeathmani Fuller, and Amitermes evuncifer Silvestri, which are pests of the principal tropical food crops (e.g., rice, maize, sorghum, sugarcane). The doses used ranged from 0.03 to 10 ppm. The effective dose for these termites was 0.3 ppm, which resulted in 100% mortality within 2-8 d, depending on the species studied. Excluding O. smeathmani, which consumed the product, thiamethoxam proved to be an anti-feedant but not repellent to T. trinervius and A. evuncifer. For all species studied, mortality was not dependent on consumption of the products, which acts principally by contact. In O. smeathmani, thiamethoxam could be transmitted in the colony from contaminated individuals to healthy individuals.

Prospects for using conventional techniques and molecular biological tools to enhance performance of 'orphan' crop plants on soils low in available phosphorus

Molecular biology, combined with Mendelian and quantitative genetics in quantitative trait locus (QTL) mapping and marker-assisted selection (MAS), provides powerful new tools to facilitate efficient genetic manipulation by plant breeders of complex traits such as drought tolerance and phosphorus (P) acquisition ability. This paper examines current opportunities for genetically manipulating the ability of crop plants to more efficiently acquire (i.e. access and take up) essential soil nutrients, using as examples P and several of the crops in the genetic improvement mandate of the International Crops Research Institute for the Semi-Arid Tropics (ICRISAT) – chickpea (Cicer arietinum L.), groundnut (Arachis hypogaea L.), pearl millet [Pennisetum glaucum (L.) R. Br.], pigeonpea [Cajanus cajan(L.) Millsp.], and sorghum [Sorghum bicolor (L.) Moench]. It is concluded that for at least some of these important, but often academically and economically orphaned tropical food, forage and feed-grain crops, the genetic variation and molecular tools that we will need already exist or can be expected to become available in the very near future. With appropriate, targeted research, these tools can permit empirical exploration of the potential for marker-facilitated mapping and manipulation of major genes that can contribute to enhanced ability of these crops to acquire P from sources with limited availability. With these tools, delivery of new versions of currently popular high-yielding, high quality, disease resistant crop cultivars, having genetically improved ability to acquire P currently in soils but unavailable for crop growth, could take as little as five to seven years. Sustainable use of such improved cultivars would require their utilization as components of integrated soil fertility management systems.

Reviving global poverty reduction: what role for genetically modified plants?

This lecture presents seven inter-related points. 1) The poor continue to depend on staples for income and progress, via consumption, prices, nutrition, employment, farm income, and overall rural income. 2) 1965-85 saw huge falls in poverty based on rising food yields, employment, and public agricultural research effort; all four have stalled since 1985-90. 3) Fertility transition opens a 'window of opportunity' to complete the task of eliminating food poverty. 4) The window is useful only if yield potential revives for tropical food staples. 5) Genetically modified (GM) plant research is a key tool for breeding to improve staples yield potential, stability, spread, sustainability and employment - but is not being used well. 6) Proper application of GM on plant research to help the world's poor requires radical institutional innovation in agricultural research. 7) Realigning the public debate about GMs.

Influence of Soil Moisture and Fertilizer Potassium on the Vegetative Growth of Mungbean (Vigna radiata L. Wilczek) and Cowpea (Vigna unguiculata L. Walp)

Tropical food legumes are grown in a wide range of environments, and water stress is considered the principal environmental factor limiting growth and yield. Potassium fertilizer mitigates the impact of water stress in plants. However, the benefits of potassium in overcoming stress in tropical food legumes have not been investigated in comparative studies. The purpose of this study was to determine the benefits of potassium in overcoming water stress in mungbean and cowpea, two important tropical food legumes with different adaptabilities to soil moisture regimes. The experiment carried out under controlled conditions placed emphasis on vegetative growth and selected physiological parameters. The impact of potassium was different in the two legumes grown at optimal and suboptimal soil moisture. Potassium increased shoot growth of mungbean to a greater extent than in cowpea under suboptimal moisture conditions. The roots of cowpea showed a greater response to potassium fertilizer than in mungbean under suboptimal soil moisture. The plant water relations and photosynthetic rates of mungbean were improved to a greater extent by potassium under suboptimal soil moisture than those of cowpea. Although differences were observed in the responses of the vegetative growth of these species to moisture and potassium, in overall terms potassium promoted growth of both species when subject to suboptimal soil moisture. While field studies are required to validate the results, the application of potassium fertilizer can be considered a significant factor in overcoming soil moisture stress in these legumes commonly grown in tropical cropping systems.

Influence of Forest Clearing Methods on Nutrient Uptake of Some Tropical Food Crops

The adverse effects of forest clearing on crop yield have often been directly ascribed to decline in soil fertility. However, the effect of various forest clearing methods on crop nutrient uptake as reflected by the content in the leaf tissues has been the subject of few scientific investigations. A study to determine the effect of forest clearing on nutrient content of some arable crops was, therefore, carried out in the tropical rainforest of south-western Nigeria. Three forest clearing methods—mechanical, semi-mechanical and manual clearing—were used, while maize, cowpea, and cassava were the test crops. Nutrient content in the tissues of these crops was assessed by sampling maize ear leaves at silking, youngest mature leaves (YML) of cowpea at flowering and YML of 3-month-old cassava for analysis. Correlation analysis was carried out to establish the relationship between nutrient content and crop yield. The method of forest clearing had no significant effect on the nutrient content of maize and cowpea during the first cropping cycle. However, nutrient content of maize in the manually cleared plots was higher than those in the semi- and mechanically cleared plots for all elements analyzed except Mg. Nitrogen content of cowpea was much higher than that of maize. Except for P and K, the nutrient content of cassava was not markedly different among the forest clearing methods. Calcium and P content in the leaves of maize and cassava varied inversely with their levels in the soil, implying that crop uptake could have accounted for the differences in their availability within the soil. Nitrogen, P and K had significant positive correlations with maize yield (r = 0.77, 0.89, and 0.71). Potassium content also had significant positive correlation with cassava root yield (r = 0.69). This is not surprising because compared with other crops, cassava requires large amounts of K for starch formation and root development. It is concluded that differences observed in crop yields under different forest clearing methods are a function of nutrient uptake and availability within the soil. However, the uptake of some nutrients does not seem to be determined by the level of soil availability alone.

Effect of Soil Moisture and Potassium Fertilizer on Shoot Water Potential, Photosynthesis and Partitioning of Carbon in Mungbean and Cowpea

The effect of different rates of potassium (K+) on shoot water potential, photosynthesis and carbon movement (using 14C) at the V3/4 growth stages was studied in mungbean (Vigna radiata L. Wilczek), a drought‐susceptible legume, and cowpea (Vigna unguiculata L. Walp), a drought‐tolerant legume, grown under low‐ and high‐irrigation regimes under controlled conditions. Soil moisture and K+ affected all measured parameters in the two species. The rate of photosynthesis was higher at reduced water stress when K+ was applied. The impact was greater in cowpea, which had an inherently high rate of carbon assimilation. Mungbean and to a lesser extent cowpea allocated greater quantities of carbon to roots under dry conditions, especially with added K+. The distribution of 14C into other plant parts was also increased at higher rates of K+ application under both soil moisture regimes. Thus, application of K+ seems to have a beneficial effect in overcoming soil moisture stress and increasing physiological parameters and carbon partitioning in these two important tropical food legumes.

Effects of seasonality and fish movement on tropical river food webs

Effects of seasonality and fish movement on tropical river food webs

THE BIOTECHNOLOGY CASE HISTORY FOR MUSA

Banana and plantain (Musa spp. L.) is a major tropical food crop and world commodity. Being a polyploid and vegetatively-propagated crop, its genetic improvement by conventional hybridisation is complex and difficult, yet not impossible. Simple tissue culture techniques, such as shoot-tip and embryo culture, are well developed and have greatly enhanced Musa germplasm handling and breeding. Plant regeneration by somatic embryogenesis is used to recover transgenic plants from single cells transformed by Agrobacterium or biolistic techniques for fungal and viral disease resistance. The potential of somaclonal variation as a source of novel and useful variability is limited, but it may be used as a secondary tool in Musa improvement. Molecular genetic techniques are being applied for improving the efficiency of Musa breeding. RFLPs appear to have limited application due to the low frequency of detected polymorphisms. The RAPD technique holds great promise for genome analysis. It detects high levels of polymorphism, yet still suffers from a number of practical drawbacks. Microsatellites are used to study genetic behaviour and structure in Musa, for fingerprinting hybrids, and to develop marker-assisted breeding systems. Candidate markers for such complex and important characters as parthenocarpy, earliness and regulated suckering are being tested. PCR primers have also been developed for virus diagnostics, already providing a specific and sensitive method to detect banana streak virus among in vitro plants. Reliable diagnostic protocols are increasingly needed for safe international movement of germplasm. Musa improvement requires a holistic approach to produce better cultivars. Hence, it is advocated that multidisciplinary public Musa breeding programmes should be central to any improvement effort. Such programmes will benefit from three biotechnologies that are clearly valuable in Musa breeding - tissue culture, diagnostics and molecular markers. Realistic, well defined targets for genetic engineering are occasionally warranted for inclusion within innovative breeding programmes.

Application of Intercropping in Organic Agriculture

ABSTRACT Intercropping is growing two or more crops in the same field. There are various reasons for the application of intercropping in both tropical and temperate food production. So far, intercropping in European intensive agriculture has not been applied because of possible yield loss due to competition between the main crop and intercrop, the availability of cheap pesticides and growers' reluctance to use more complicated cropping systems. In addition, there was no consumers demand for pesticide-free crops and no legislation from governments limiting pesticides. During the last decade, intercropping research in field vegetables demonstrated significant pest suppression effects, enabling cropping of cabbages and leek of good commercial quality without using pesticides. Presently, research efforts focus on the clarification of underlying mechanisms and the solutions of constraints, competition effects and acceptable weed management. Progress has been made in this direction. For sustainable food production methods, both ecological and economic conditions must be fulfilled. While satisfying ecological demands, attention must be given to the economic viability of intercropping-based crop production methods. Yield quality and quantity are important, but so also is the balance of inputs and savings. A consumer market demand for products which are produced in an ecologically acceptable way is also crucial.

Response of Root Branching and Shoot Water Potentials of French Beans (Phaseolus vulgaris L.) to Soil Moisture and Fertilizer Potassium

AbstractExtensive branching patterns of roots and the maintenance of adequate water within shoots enables plants to overcome water stress. However, information on the relationship between fertilizer potassium, root branching patterns and shoot water potentials of food legumes grown under different soil moisture regimes is scarce. Thus, an experiment was conducted in a phytotron to ascertain the effect of fertilizer potassium on root branching patterns and shoot water potentials of a popular tropical food legumes (Frenchbeans Phaseolus vulgaris L). The plants were grown in a sand medium with 0.1, 0.8 or 3.0 mM of potassium under a suboptimal and optima) soil moisture regime.Root lengths and dry weights were enhanced by potassium, especially under a suboptimal soil moisture regime. The branching patterns changed due to potassium, where the numbers of second and third order roots increased under both soil moisture regimes, although the impact was greater in plants grown with low soil moisture. Plant water contents measured in terms of shoot water potential, relative water contents, rurgid weight: dry weight ratio and water uptake capacity were also increased by potassium. A positive relationship was observed between root branching patterns and water potentials with increasing potassium levels especially in plants grown under suboptimal soil moisture conditions. Shoot growth and nodulation was also promoted by potassium. The ability of plants to develop a more extensive branching pattern of roots by inducing a greater number of second and third order roots and changing the root branching habit from a herringbone to a dichotomous type to maintain a greater shoot water potential especially under low soil moisture regimes is presented.

The Ecology of Tropical Food Crops, 2nd edn.

The Ecology of Tropical Food Crops, 2nd edn.