Seed potato quality improvement through positive selection by smallholder farmers in Kenya

In Kenya, seed potato quality is often a major yield constraint in potato production as smallholder farmers use farm-saved seed without proper management of seed-borne pests and diseases. Farm-saved seed is therefore often highly degenerated. We carried out on-farm research to assess whether farmer-managed positive seed selection could improve yield. Positive selection gave an average yield increase in farmer-managed trials of 34%, corresponding to a 284-€ increase in profit per hectare at an additional production cost of only 6€/ha. Positive selection can be an important alternative and complementary technology to regular seed replacement, especially in the context of imperfect rural economies characterized by high risks of production and insecure markets. It does not require cash investments and is thus accessible for all potato producers. It can also be applied where access to highquality seed is not guaranteed. The technology is also suitable for landraces and not recognized cultivars that cannot be multiplied formally. Finally, the technology fits seamlessly within the seed systems of Sub-Saharan Africa, which are dominated by self-supply and neighbour supply of seed potatoes

Detection of latent infection by Ralstonia solanacearum in potato (Solanum tuberosum) using stems instead of tubers

The potential of using stems for the detection of latent infection caused by Ralstonia solanacearum (Rs) was studied. Forty plants each were collected from four farms with bacterial wilt incidence below 4% intwo growing seasons (season A and season B of 2005). The tubers of all the selected plants including 10 cm of the all lower stems were collected. Samples were taken to the laboratory for indexing againstR. solanacearu (Rs) using ELISA techniques. The Rs status of each of the composite samples of all the tubers and of stems was determined and then correlation coefficients computed. There was a notabledifference in the percentage number of samples per farm with particular categories of R. solanacearum status. When stems were compared to tubers for detection of Rs, an average r – value of 0.4 wasobtained when r-values for the four different farms were averaged. The lowest r-value recorded was 0.2 while the highest was 0.5. When individual farms were considered it was only in one farm out of the fourthat r was not significant (p = 0.2). Overall the r-value was significant (p < 0.05). These results indicate that there is scope for adoption of stems as an alternative sample to tubers for indexing against R.solanacearum in potato tuber seed certification schemes more so in screening for presence of R. solanacearum in seed potato fields. However, although significant, the low r-value calls for moreinvestigations to be done prior to final recommendation on use of stems from potato fields

Principles for enhancing virus capsid capacity and stability from a thermophilic virus capsid structure

The capsids of double-stranded DNA viruses protect the viral genome from the harsh extracellular environment, while maintaining stability against the high internal pressure of packaged DNA. To elucidate how capsids maintain stability in an extreme environment, we use cryoelectron microscopy to determine the capsid structure of thermostable phage P74-26 to 2.8-A resolution. We find P74-26 capsids exhibit an overall architecture very similar to those of other tailed bacteriophages, allowing us to directly compare structures to derive the structural basis for enhanced stability. Our structure reveals lasso-like interactions that appear to function like catch bonds. This architecture allows the capsid to expand during genome packaging, yet maintain structural stability. The P74-26 capsid has T = 7 geometry despite being twice as large as mesophilic homologs. Capsid capacity is increased with a larger, flatter major capsid protein. Given these results, we predict decreased icosahedral complexity (i.e. T \u3c /= 7) leads to a more stable capsid assembly

Principles for enhancing virus capsid capacity and stability from a thermophilic virus capsid structure [preprint]

The capsids of double-stranded DNA viruses protect the viral genome from the harsh extracellular environment, while maintaining stability against the high internal pressure of packaged DNA. To elucidate how capsids maintain stability in an extreme environment, we used cryoelectron microscopy to determine the capsid structure of the thermostable phage P74-26. We find the P74-26 capsid exhibits an overall architecture that is very similar to those of other tailed bacteriophages, allowing us to directly compare structures to derive the structural basis for enhanced stability. Our structure reveals lasso-like interactions that appear to function like catch bonds. This architecture allows the capsid to expand during genome packaging, yet maintain structural stability. The P74-26 capsid has T=7 geometry despite being twice as large as mesophilic homologs. Capsid capacity is increased through a novel mechanism with a larger, flatter major capsid protein. Our results suggest that decreased icosahedral complexity (i.e. lower T number) leads to a more stable capsid assembly