Prior on-station research showed that sowing dates, sowing density and applications of fungicide and phosphorus (P) increased groundnut (Arachis hypogaea) pod yield by 60–80%. Farmer-managed trials were conducted in the Wa district of the Upper West Region of Ghana from 2004 to 2007 to test the yield response to sowing density, fungicide and P and to assess economic returns of these technologies to farmers. Treatments included: an early maturing groundnut cultivar, Chinese, sown at farmers' density (5–8 plant m−2) without fungicide and without P application (T1, control), with fungicide sprays alone (T2), or with fungicide and P application (T3), cultivar Chinese sown at recommended (higher) density (20 plant m−2) with fungicide and P application (T4), and a full season cultivar, Manipinter, with fungicide and P application (T5). Soil fertility, sowing density, days from sowing to first weeding, incidence and severity of leaf-spot disease and plant population at final harvest were recorded. Relative to farmers' practice, pod yield of cultivar Chinese was significantly increased by 80% with fungicide sprays alone, 108% with fungicide and P application, and 113% with fungicide and P application at higher sowing density. Cultivar Manipinter treated with fungicide and P gave 107% increase in pod yield relative to farmers' practice. Correlation and stepwise regression analyses suggested that major determinants of groundnut pod yield in farmers' fields were plant density, leaf-spot disease and P availability. The increase in yield with fungicide and P application translated into a 4–5-fold increase in gross margin for farmers in the region. Returns to labour and labour productivity were doubled with combined use of fungicide and P fertilizer.

Fonio millet (Digitaria exilis), a small-grained cereal, plays an important role in food security in West Africa. As part of efforts to increase its productivity, we studied the effects of moderate levels of nitrogen (0, 15.0 and 30.0 kg N ha−1), phosphorus (0, 6.6 and 13.2 kg P ha−1) and potash (0, 12.5 and 25.0 kg K ha−1) fertilizers under varying climatic conditions. The three experimental sites at Bareng and Bordo in Guinea, and Cinzana in Mali, are representative of the distribution of fonio millet in West Africa. The average recorded grain yields were 1.51 ± 0.229, 1.08 ± 0.141 and 0.47 ± 0.182 t ha−1 in Bareng, Bordo and Cinzana, respectively. We observed a marginal to significant impact of N fertilization coupled, in Bordo, with a significant interaction with the P and K response. This interaction was highlighted by the limited effect of N without P or K fertilization or with the application of only one of these two major elements. Overall, N application as low as 15 kg ha−1 led to a 12–22% increase in production if the P and K applications were not limited. For better control over the risks associated with poor soil fertility and limited rainfall, it appeared to be more effective to apply moderate levels of N, P and K fertilizers to the fonio millet crop than a large amount of one of these nutrients.

Nitrogen fixation by leguminous trees such as sesbania (Sesbania sesban) in acid soils is limited by aluminium (Al) toxicity and phosphorus (P) deficiency. We screened 214 East African sesbania accessions for Al toxicity tolerance, P use efficiency and sesbania–rhizobia symbiosis. Aluminium toxicity tolerance or sensitivity was measured by the relative root elongation index. Highly Al tolerant and sensitive accessions were screened for P use efficiency. Highly P use efficient and Al sensitive accessions were assessed for symbiotic effectiveness with acid tolerant rhizobia. Eighty-eight per cent of the accessions were Al toxicity tolerant. High Al levels reduced shoot P content by 88% and total dry matter (TDM) by 83%. P addition increased shoot P content and TDM. Rhizobia inoculation increased nodulation by 28–82%, shoot N content by 28–45% and TDM by 15–34% in the low rhizobia density acid soil of Bumala, Kenya. P use efficient accessions had higher nodulation, shoot N content and TDM in the ranges 32–70, 20–52 and 22–36%, respectively, compared to sensitive genotypes. The combination of sesbania accession (SSUG10) and rhizobia strain ASs48 was superior in shoot N accumulation. Inoculation of P use efficient germplasm with acid tolerant rhizobia can improve N-rich biomass accumulation suitable for N replenishment in acid soils.

The objective of this study was to elucidate the physiological basis of the significant yield decline that occurs during the fourth year of the pruning cycle of tea. Biomass partitioning, which was hypothesized to be a major factor in causing this yield decline, was measured by destructive harvests of entire tea bushes, in two contrasting, mature, field-grown tea cultivars (TRI 2025 and DT1) at the end of different years of the pruning cycle. In both cultivars, yield showed continuous increases from year 1 to 3, followed by reductions of 44% and 35% in TRI2025 and DT1 respectively in the fourth year. Patterns of biomass partitioning to roots, stems or branches did not correlate with the above yield variation whereas harvest index, canopy leaf area index and mature leaf dry weight showed variations which paralleled the yield variation. The fourth-year decline in harvest index was brought about by reductions in both shoot number per m2 and mean individual shoot weight, which indicate a reduction in sink strength. Both cultivars showed reductions in light-saturated photosynthetic rate of maintenance foliage during the second half of the pruning cycle, indicating reduced source capacity. Hence, a combined reduction of both sink strength and source capacity during the fourth year could have brought about the significant yield reduction in tea. A significant increase of root starch in the fourth year indicated a down-regulation of physiological activities of the bush towards the end of the pruning cycle. Mechanisms responsible for this down-regulation need to be elucidated by further research.

In the dry areas of Nicaragua, white-grain sorghum is an important subsistence crop for resource-poor farmers. From 2002 to 2007, participatory varietal selection (PVS) was implemented in three regions with the aim of identifying new varieties matching small farmers' needs. This paper describes the general approach, the partnership and the methods used to identify farmers' selection criteria (FSC), as well as the evaluation of new germplasm using the scoring method. Data analysis involved relating farmers' evaluation data to agronomic data and farmers' selection decisions (FSD), using Spearman correlations and the chi-square test. In the three regions, higher grain yield and good grain quality for making tortillas were identified as the two main FSCs for both the ‘tortillero’ and ‘millón’ sorghum types; the ranking of the other important FSC differed between the sites and the sorghum types. Our data shows that farmers' scores for earliness were highly correlated with breeder's observations while farmers' assessments of grain yield were correlated with measured yield in half the cases, depending on their knowledge of the crop. The study shows that in evaluating grain quality the farmers used several specific traits which were not considered by breeders. Overall appreciation, grain yield and grain quality were the key farmers' criteria that contributed to FSD. The PVS work enabled breeders to obtain a better understanding of farmers' criteria as well as identifying new progenitors, which should be useful for the sorghum breeding schemes in Central America in the future. Furthermore, by exploring wide genetic diversity, it was possible to release several farmer-preferred and high-performing varieties within a fairly short period.

Greater yam (Dioscorea alata), a popular crop in India, is cultivated widely in Orissa state, India. In spite of the availability of several improved varieties, farmers preferred the local landraces. An investigation was carried out to identify whether the varietal preferences of yam farmers in two production systems, subsistence and commercial, were different. While the subsistence farmers demanded the yam varieties adaptable to a wide range of soils, the commercial farmers preferred the anthracnose-resistant cultivars. This study demonstrated that the farmers' varietal preferences were highly influenced by the production systems. Identifying the convergence/divergence of varietal preferences across production systems can help breeders to develop the high impact varieties.

Ecuadorean mashua (Tropaeolum tuberosum) germplasm has been found to be widely infected with the potyvirus Tropaeolum mosaic virus (TropMV). The objective of this research was to produce virus-tested (VT) germplasm to compare growth in vitro and in the field with virus-infected (V) germplasm. Twenty-three of 25 apical dome-derived clones tested free of virus based on bioassays using Nicotiana benthamiana and Chenopodium quinoa. In vitro-generated plant tissue was just as effective for determining VT status as greenhouse-generated plant tissue. Genotype rather than virus-infection status appeared to have a greater effect on in vitro proliferation. There were no differences in in vitro rooting among the genotypes or between the VT clones compared to the V clones, with at least 90% of the microcuttings rooting. However, rooted microcuttings of V clones were taller than rooted microcuttings of VT clones. Plants were readily re-established in a greenhouse at the USDA, Foreign Disease-Weed Science Research Unit at Fort Detrick, USA. In field experiment 1, ca. 75% of the plants survived field transplanting and VT plants of genotype 1147 had greater tuber weight (928 g) than V plants (235 g). In field experiment 2, plant mortality was high one month after field transplanting. Genotypes 1093 (59%) and 1141 (54%) had higher survival than genotype 1147 (44%); however, survival did not differ between the VT (46%) and V (59%) plants of all genotypes. No differences were noted in field performance for the three genotypes after 10 months of growth. Although overall tuber yield among the V, VT and VTR (reinfected-VT plants) did not differ, V plants produced big tubers that weighed more than those from VT plants. Thirty-three percent of the VT plants became reinfected and 42% of the V plants tested negative after 10 months in the field based on double-antibody-sandwich ELISA.

Artemisia herba-alba Asso has been successfully cultivated in the Tunisian arid zone. However, information regarding the effects of the harvest frequency on its biomass and essential oil yields is very limited. In this study, the effects of three different frequencies of harvesting the upper half of the A. herba-alba plant tuft were compared. The harvest treatments were: harvesting the same individual plants at the flowering stage annually; harvesting the same individual plants at the full vegetative growth stage annually and harvesting the same individual plants every six months. Statistical analyses indicated that all properties studied were affected by the harvest frequency. Essential oil yield, depended both on the dry biomass and its essential oil content, and was significantly higher from plants harvested annually at the flowering stage than the other two treatments. The composition of the β- and α-thujone-rich oils did not vary throughout the experimental period.