The role of biotechnology for agricultural sustainability in Africa

Sub-Saharan Africa could have a shortfall of nearly 90Mt of cereals by the year 2025 if current agricultural practices are maintained. Biotechnology is one of the ways to improve agricultural production. Insect-resistant varieties of maize and cotton suitable for the subcontinent have been identified as already having a significant impact. Virus-resistant crops are under development. These include maize resistant to the African endemic maize streak virus and cassava resistant to African cassava mosaic virus. Parasitic weeds such as Striga attack the roots of crops such as maize, millet, sorghum and upland rice. Field trials in Kenya using a variety of maize resistant to a herbicide have proven very successful. Drought-tolerant crops are also under development as are improved varieties of local African crops such as bananas, cassava, sorghum and sweet potatoes.     

Different Seed Selection and Conservation Practices for Fresh Market and Dried Chile Farmers in Aguascalientes,Mexico

Different Seed Selection and Conservation Practices for Fresh Market and Dried Chile Farmers in Aguascalientes, Mexico. The process of selecting and saving seed is the most basic and oldest of agricultural practices. In today’s modern and highly capital-intensive agriculture, seeds are often treated like another chemical input. This study sought to examine seed selection and saving practices among chile farmers in Aguascalientes, Mexico, where both industrial and traditional agriculture are practiced. We observed a clear division among farmers who plant chile peppers commercially. Sixty-eight chile pepper farmers were surveyed in order to document seed selection and saving practices. Fifteen respondents (22%) planted chile peppers destined for the fresh market and all utilized purchased commercial seed of F1 hybrid varieties. Fifty-three farmers (78%) planted chiles to be dried and either saved their own or purchased seeds that others had saved and selected. Farmers who saved their own seed sought to maintain an ideotype, rather than directionally select for certain traits, much like Cleveland et al. (2000) chronicled in central Mexican maize farmers. Farmers would benefit from a participatory plant-breeding program in order to maintain productive seed stock for the continued cultivation of dried chile pepper in the state.     

Indigenous diversity of Cassava: Generation, maintenance, use and loss among the Amuesha, Peruvian upper Amazon

For cassava (Manihot esculenta Euphorbiaceae), results from field collection, semistructured interviews, phenetic and cluster analyses, and Global Information Systems (G1S) indicate that cassava phenotypes vary with elevation and topography, but less with soils or pests and diseases. Amuesha women with a sense of tradition maintain many cassava varieties along with associated myths, songs, names and indigenous production. The shaman plays a key role in breeding new and maintaining traditional cassava germplasm, while the rest of the tribe nurtures cassava germplasm dynamics through collecting, trading, stealing, maintaining favored cassava varieties, and purging the less desirable. The future of cassava diversity is of concern to some Amuesha as production and market interests surmount more traditional attention to variety.     

Informal "seed" systems and the management of gene flow in traditional agroecosystems: the case of cassava in Cauca, Colombia

Our ability to manage gene flow within traditional agroecosystems and their repercussions requires understanding the biology of crops, including farming practices' role in crop ecology. That these practices' effects on crop population genetics have not been quantified bespeaks lack of an appropriate analytical framework. We use a model that construes seed-management practices as part of a crop's demography to describe the dynamics of cassava (Manihot esculenta Crantz) in Cauca, Colombia. We quantify several management practices for cassava--the first estimates of their kind for a vegetatively-propagated crop--describe their demographic repercussions, and compare them to those of maize, a sexually-reproduced grain crop. We discuss the implications for gene flow, the conservation of cassava diversity, and the biosafety of vegetatively-propagated crops in centers of diversity. Cassava populations are surprisingly open and dynamic: farmers exchange germplasm across localities, particularly improved varieties, and distribute it among neighbors at extremely high rates vis-à-vis maize. This implies that a large portion of cassava populations consists of non-local germplasm, often grown in mixed stands with local varieties. Gene flow from this germplasm into local seed banks and gene pools via pollen has been documented, but its extent remains uncertain. In sum, cassava's biology and vegetative propagation might facilitate pre-release confinement of genetically-modified varieties, as expected, but simultaneously contribute to their diffusion across traditional agroecosystems if released. Genetically-modified cassava is unlikely to displace landraces or compromise their diversity; but rapid diffusion of improved germplasm and subsequent incorporation into cassava landraces, seed banks or wild populations could obstruct the tracking and eradication of deleterious transgenes. Attempts to regulate traditional farming practices to reduce the risks could compromise cassava populations' adaptive potential and ultimately prove ineffectual.     

Cryopreservation of sweetpotato (Ipomoea batatas) and its pathogen eradication by cryotherapy

Sweetpotato (Ipomoea batatas) ranks as the seventh most important staple crop in the world and the fifth in developing countries after rice, wheat, maize and cassava. Sweetpotato is mainly grown in developing countries, which account for more than 95% of total production of the whole world. Genetic resources, including cultivated varieties and wild species, are a prerequisite for novel sweetpotato breeding in both conventional and genetic engineering programs. Various cryopreservation protocols have been developed for shoot tips and embryogenic tissues. The former explants are preferred for long-term conservation of sweetpotato genetic resources, while the latter are valuable for sweetpotato genetic improvement. This review provides update comprehensive information on cryopreservation of sweetpotato shoot tips and embryogenic tissues.Plant pathogens such as viruses and phytoplasma severely hamper high yield and high quality production of sweetpotato. Thus, usage of pathogen-free planting materials is pivotal for sustainable sweetpotato production. Cryotherapy of shoot tips can efficiently eradicate sweetpotato pathogens such as viruses and phytoplasma. The mechanism behind pathogen eradication by cryotherapy of shoot tips has been elucidated. Pathogen eradication by cryotherapy provides an alternative, efficient strategy for production of pathogen-free plants. In addition, cryopreserved tissues may also be considered to be safer for exchange of germplasm between countries and regions.     

Keepers of maize in Chiapas,Mexico

This study concerns the knowledge and selection of biological diversity of maize (Zea mays) within its center of domestication in Mesoamerica. Maize farmers in central Chiapas of Southern México keep local varieties (landraces) belonging to six races and four race mixtures. Fifteen local varieties are recognized. In spite of widespread adoption of a modern, high yielding variety, maize farmers continue to select local varieties for specific soils and because of agronomic and use criteria. Farmers maintain maize varieties primarily through seed selection. Spatial and temporal separation do not seem sufficient to maintain varieties. The management of improved varieties can lead from a uniform population to a heterogeneous one as hybridization with local maize populations occurs.     

The Puzzle of Italian Rice Origin and Evolution: Determining Genetic Divergence and Affinity of Rice Germplasm from Italy and Asia

The characterization of genetic divergence and relationships of a set of germplasm is essential for its efficient applications in crop breeding and understanding of the origin/evolution of crop varieties from a given geographical region. As the largest rice producing country in Europe, Italy holds rice germplasm with abundant genetic diversity. Although Italian rice varieties and the traditional ones in particular have played important roles in rice production and breeding, knowledge concerning the origin and evolution of Italian traditional varieties is still limited. To solve the puzzle of Italian rice origin, we characterized genetic divergence and relationships of 348 rice varieties from Italy and Asia based on the polymorphisms of microsatellite fingerprints. We also included common wild rice O. rufipogon as a reference in the characterization. Results indicated relatively rich genetic diversity (H _e = 0.63-0.65) in Italian rice varieties. Further analyses revealed a close genetic relationship of the Italian traditional varieties with those from northern China, which provides strong genetic evidence for tracing the possible origin of early established rice varieties in Italy. These findings have significant implications for the rice breeding programs, in which appropriate germplasm can be selected from a given region and utilized for transferring unique genetic traits based on its genetic diversity and evolutionary relationships.     

Multi-trophic level interactions in a cassava-maize mixed cropping system in the humid tropics of West Africa

Multi-trophic level interactions in a mixed crop, involving cassava and maize, were studied in derived-savanna in Benin, West Africa. Two trials were planted, one during the short rainy season two months before onset of the dry season and one during the long rainy season in spring. Key pests under study on maize were the noctuid Sesamia calamistis Hampson and the pyralids Eldana saccharina Walker and Mussidia nigrivenella Ragonot, and on cassava, the exotic mealybug, Phenacoccus manihoti Matile-Ferrero and its encyrtid parasitoid Apoanagyrus lopezi De Santis. Both crops received insecticide treatments to assess the crop loss by a pest species. On maize, intercropping with cassava reduced egg and immature numbers of S. calamistis by 67 and 83%, respectively, as a result of reduced host finding by the ovipositing adult moth and of higher egg parasitism by Telenomus spp. Both trials showed similar effects on maize yields: on insecticide-treated maize, intercropping with cassava reduced maize yields by 9-16%, while on untreated maize the net effect of reduced pest density and increased plant competition resulted in zero yield differences; yield losses were lower in inter- compared to monocropped maize. For cassava, cropping system had no effect on parasitism by A. lopezi. Yield differences between mono- and intercropped cassava depended on time of harvest: they were large at the beginning and zero at final harvest. Land equivalent ratios were mostly > 1.5 indicating that a maize/cassava mixed crop, protected or unprotected, considerably increased the productivity per unit area of land.     

<Emphasis Type="Italic">Brief Communication</Emphasis>: Does Integration to the Market Threaten Agricultural Diversity? Panel and Cross-Sectional Data From a Horticultural-Foraging Society in the Bolivian Amazon

Trade theory predicts that the expansion of markets induces households to specialize and intensify production. We use plot-level data (n = 64) from a panel study of 2 village and cross-sectional data from 511 households in 59 villages of Tsimane Amerindians (Bolivia) to test the predictions. Results of bivariate analyses using both data sets suggest that as households integrate into the market economy they: (1) deforest more, (2) expand the area under rice cultivation, the principal cash crop, (3) sell more rice, and (4) intensify production by replanting more and by replanting newly cleared plots with maize, another cash crop. Results mesh with predictions about production specialization and intensification of trade theory. The analysis also produced results running counter to predictions from trade theory. For example, households and villages more integrated into the market planted more cassava and rice varieties, intercropped more, and put more crops in new fields than more autarkic households. Although the expansion of markets induces specialization and intensification in selected cash crops, it does not erase completely agricultural diversity. We hypothesize that despite the expansion of markets, households retain agricultural diversity because the market does not yet provide modern forms of self-insurance or well-functioning labor, credit, and product markets that would allow households to protect food consumption when faced with shocks. Without better insurance mechanisms, some agricultural diversity might still allow households to smooth consumption.     

Allelic Diversity Among Basmati and Non-Basmati Long-grain Indica Rice Varieties using Microsatellite Markers

Microsatellite or simple sequence repeat (SSR) marker analysis was carried out to assess allelic diversity and prepare a DNA fingerprint database of 24 rice genotypes including three premium traditional Basmati, 9 cross-bred Basmati, a local scented selection, eight indica and three japonica rice varieties. A total of 229 alleles were detected at the 50 SSR loci and 49 alleles were in fact present in only one of the 24 varieties. The size difference between the smallest and largest allele varied from 1 (RM333) to as high as 82 (RM206). Multiple alleles were observed at 13 loci. Polymorphism information content (PIC) values ranged between 0.0 (RM167) to 0.78 (RM170), with an average of 0.62 per marker. At 15 of the SSR loci, traditional and cross-bred Basmati rice varieties amplified different alleles than those in the indica andlor japonica rice varieties. A number of SSRs have been identified, which can be used to differentiate among the traditional Basmati varieties and between traditional Basmati and other cross-bred Basmati or long grain, non-Basmati rice varieties. Genetic relationships among rice genotypes as determined by UPGMA cluster analysis and three-dimensional scaling basedon Principal Component Analysis showed that the three traditional Basmati rice varieties are closely related and have varying degree of similarity with other cross-bred Basmati rice varieties. Further implications of these results in genotype identification, monitoring purity and adulteration, and plant variety protection are discussed.     

Effects of Mn-Cd antagonistic interaction on Cd accumulation and major agronomic traits in rice genotypes by different Mn forms

Maize (Zea mays L.) is the largest food crops in China with the plangting area and total yield of 37.076 million hectares and 215.67 million tons respectively in 2014. The technology of cross breeding was the primary method to cultivate new maize varieties and promote the yield level. In recent years, more and more agriculturalists discovered the existence of endophyte in maize and their close relationship with soil environmental adaption which affect the production of maize. In this study, the seeds of six different maize varieties which were self-developed and cultivated from capital city of China “Beijing” and extensively planted in China were collected, this is the first time to acquire all of the “Beijing” hybrid maize to investigate their endopytes. We clarified eight species exists in all the varieties and the relative abundance of top three species including Pantoea agglomerans, Enterobacter cloacae and Aeribacillus pallidus taken about 60?% of the whole endophyte. Besides these, we also discovered the correlations between the endophytic bacteria which might affect the growth of maize. On the other hand, the distributions of E. cloacae and A. pallidus between maize varieties with different male parent were apparently different. So we deduced the endophyte affect the environmental adaptation of different maize varieties and the results showed the light on the future maize variety cultivation from the angle of endophyte.     

The ethnoecology of maize variety management: A case study from Mexico

This paper presents a case study of the relationship between farmers' knowledge of maize varieties and their selection and management of these varieties under conditions of technological change. Research for this paper was done among Spanish-speaking small farmers in an ejidoof central Chiapas, Mexico. This ejido is well integrated into the market, and the use of modem technologies is widespread. This research demonstrates that farmers have an extensive and widely shared knowledge of their maize varieties. This knowledge reflects objective maize characteristics. Variation occurs in the farmers' selection and management of maize varieties, but on average the variation deviates from a random pattern in the direction predicted by the farmers' knowledge base. They have incorporated the technological changes brought about by development into their knowledge base. Farmers maintain maize varieties with contrasting traits, and their knowledge base provides important information about which traits and constraints are important to them.     

Neighbor Trees: Shade, Intercropping, and Cacao in Ecuador

Previous studies have shown that shade trees in cacao and coffee are important habitats for inter-American migratory birds. A survey of 21 cacao farmers along the northern, central, and southern Pacific Coast of Ecuador found that shade trees are associated with unirrigated, traditional cacao varieties and low levels of chemical inputs. Farmers stressed the importance of shade for managing soil moisture and soil fertility, and for managing some weeds and diseases. Most of the shade trees were not wild forest trees, but had been planted and protected by the farm families. Many other trees are intercropped with cacao for economic reasons, not related to shade. Chocolate manufacturers, consumers, and environmental activists can encourage farmers to maintain shade canopies by paying a premium for the traditional, shade-loving, high-quality aromatic cocoa varieties.     

Evaluation of the potential of cassava-based residues for biofuels production

Cassava is the third significant source of calories after rice and maize in tropical countries. The annual production of cassava crop is approximately 550 million metric tons (MMT) which generates about 350 MMT of cassava solid residues, including peel, bagasse, stem, rhizome, and leaves. Cassava peel, bagasse, stem, and rhizome can be exploited for solid, liquid and gaseous biofuels production. Biofuels production from cassava starch started in the 1970s and researchers are now extensively studying cassava residues like peel, bagasse, stem, rhizome, and leaves to unravel their applications in biofuels production. However, there are technical and economic challenges to overcome the problems existing in the production of biofuels from cassava-based residues. This review provides a comprehensive summary of the techniques used for biofuels production from various cassava-based residues.     

水稻模型ORYZA2000在湖南双季稻区的验证与适应性评价

校准与验证水稻生长模型ORYZA2000,为模型本地化、区域化研究应用提供依据。本文采用湖南双季稻区作物田间观测数据,结合栽培管理措施、土壤以及同期逐日气象数据等资料对ORYZA2000进行参数校正,调试确定了早稻、晚稻有代表性品种的作物参数;利用独立的数据资料,对双季稻生育期、叶面积指数、生物量、产量等指标的模拟结果进行了详细地验证与适应性评价。结果表明：模型对双季稻品种的生育期模拟较好,开花期和成熟期的相对模拟误差为1—2d;早稻和晚稻叶面积指数的归一化均方根误差（NRMSE）均为24%,地上部总生物量、绿叶生物量、茎生物量和穗生物量的NRMSE值分别为18%、22%、22%、24%和19%、24%、28%、28%,产量的NRMSE值分别为11%和16%。校验的作物参数反映了湖南早稻和晚稻品种的生物学特性,参数值合理、有效。通过校准作物参数,ORYZA2000可较为准确地模拟双季稻生长发育及其生物量的动态累积过程,适应性较强,能够应用于双季稻生产。     

Spatial and Temporal Spread of Cassava Mosaic Virus Disease in Cassava Grown Alone and when Intercropped with Maize and/or Cowpea

The spread of cassava mosaic disease (CMD) and populations of the whitefly vector (Bemisia tabaci) were recorded in cassava when grown alone and when intercropped with maize and/or cowpea. The trials were planted under conditions of high inoculum pressure in 1995 and 1996 at a site in the lowland rainforest zone of southern Cameroon. In the 1995 experiment, the maize and cowpea intercrops reduced the final incidence of CMD in the cassava cvs. Dschang White and Dschang Violet, but not in the more resistant cv. Improved. In the 1996 experiment with cv. Dschang Violet, the maize and cowpea intercrops grown alone or together decreased adult whitefly populations on cassava by 50% and CMD incidence by 20%. The monomolecular population growth model generally provided the best fit for disease progress. Areas under the disease progress curves (AUDPCs) and incidences expressed as multiple infection units were significantly (P<0.05) less for cassava intercropped with maize and/or cowpea than in cassava alone; times to 50% CMD incidence were significantly (P<0.05) longer in all intercrop systems. In 1995 the basic infection rates (r) were similarly low (0.010 per month) in the moderately resistant cv. Dschang Violet intercropped with maize and in all treatments in the more resistant cv. Improved. By contrast, rates were significantly higherfor cv. Dschang Violet alone or with cowpea and in all treatments for the less resistant cv. Dschang White (0.030–0.060). In 1996, r values in cassava grown alone (0.077) were significantly larger (P<0.05) than in the other cropping systems (0.042–0.052). There were no significant differences in the symptom severity in the different cropping systems. Disease foci were isodametric and more compact in plots containing cowpea than in other cropping systems.     

Thai elite cassava genetic diversity was fortuitously conserved through farming with different sets of varieties

Many in situ conservation programs have been developed to preserve plant landrace diversity and to promote its sustainable utilization, but little is known about the effectiveness of the developed programs in conserving plant genetic diversity. We investigated the effectiveness of an unregulated (i.e., unplanned or open) conservation system maintained by Thai farmers in conserving Thai elite cassava (Manihot esculenta Crantz) varieties. Specifically, we compared genetic diversity of 266 cassava clones that were collected from 80 farms in eight provinces with 16 cassava landraces and varieties released since the 1970s through genotyping with 35 informative simple sequence repeat (SSR) markers. The SSR analysis revealed a large regional heterogeneity in cassava diversity, with a strong genetic differentiation of the assayed clones among the 80 farms (19.8 %) and across the eight provinces (11.8 %). Significant associations were also found between SSR variation and farm agro-ecological factors or some farming practices. However, there was no significant genetic differentiation (0.9 %) between the 266 farm clones and 16 reference varieties. These findings suggest that the Thai elite cassava genetic diversity was fortuitously conserved by the farmers through farming with different sets of varieties. Implications of these findings are discussed with respect to on-farm conservation of plant genetic resources.     

What it will take to Feed 5.0 Billion Rice consumers in 2030

Major advances have occurred in rice production due to adoption of green revolution technology. Between 1966 and 2000, the population of densely populated low income countries grew by 90% but rice production increased by 130% from 257 million tons in 1966 to 600 million tons in 2000. However, the population of rice consuming countries continues to grow and it is estimated that we will have to produce 40 more rice in 2030. This increased demand will have to be met from less land, with less water, less labor and fewer chemicals. To meet the challenge of producing more rice from suitable lands we need rice varieties with higher yield potential and greater yield stability. Various strategies for increasing the rice yield potential being employed include: (1) conventional hybridization and selection procedures, (2) ideotype breeding, (3) hybrid breeding, (4) wide hybridization and (5) genetic engineering. Various conventional and biotechnology approach are being employed to develop durable resistance to diseases and insect and for tolerance to abiotic stresses. The availability of the rice genome sequence will now permit identification of the function of each of 60,000 rice genes through functional genomics. Once the function of a gene is identified, it will be possible to develop new rice varieties by introduction of the gene through traditional breeding in combination with marker aided selection or direct engineering of genes into rice varieties.     

Residual effects of natural bush,Cajanus cajan and Tephrosia candida on the productivity of an acid soil in southeastern Nigeria

An experiment was established in 1986 to examine the contribution of Tephrosia candida and Cajanus cajan shrubs to improving the productivity of an acid soil. The main treatments were N levels (0 and 60 kg ha^-1) with subplots of maize/natural bush, maize/Tephrosia candida, maize/Cajanus cajan, maize + cassava/natural bush, maize + cassava/Tephrosia candida, and maize + cassava/Cajanus cajan. In 1988, all plots were cleared and maize uniformly planted to study the residual effects of the treatments. No residual effects of N application were observed. Tephrosia candiada and Cajanus cajan increased surface soil organic carbon and total N levels over the natural bush. However, only Tephrosia candida plots produced improved maize grain and stover yield. Highly significant correlations were found between maize grain yield and earleaf N (r=0.73^**), grain N (r=0.51^**), and stover N (r=0.54^**) contents. These results suggest that Tephrosia candida increased N availability in the soil. Therefore, the shrub has potential for improving the productivity of acid soils under traditional systems, where N is limiting due to the absence of N₂-fixing legumes in the natural bush fallow.