The drought stress tolerance of two Solanum tuberosum subsp. andigena landraces, one hybrid (adg×tbr) and Atlantic (S. tuberosum subsp. tuberosum) has been evaluated. Photosynthesis in the Andigena landraces during prolonged drought was maintained significantly longer than in the Tuberosum (Atlantic) line. Among the Andigena landraces, ‘Sullu’ (SUL) was more drought resistant than ‘Negra Ojosa’ (NOJ). Microarray analysis and metabolite data from leaf samples taken at the point of maximum stress suggested higher mitochondrial metabolic activity in SUL than in NOJ. A greater induction of chloroplast-localized antioxidant and chaperone genes in SUL compared with NOJ was evident. ABA-responsive TFs were more induced in NOJ compared with SUL, including WRKY1, mediating a response in SA signalling that may give rise to increased ROS. NOJ may be experiencing higher ROS levels than SUL. Metabolite profiles of NOJ were characterized by compounds indicative of stress, for example, proline, trehalose, and GABA, which accumulated to a higher degree than in SUL. The differences between the Andigena lines were not explained by protective roles of compatible solutes; hexoses and complex sugars were similar in both landraces. Instead, lower levels of ROS accumulation, greater mitochondrial activity and active chloroplast defences contributed to a lower stress load in SUL than in NOJ during drought.

The increasing amount of available expressed gene sequence data makes whole-transcriptome analysis of certain crop species possible. Potato currently has the second largest number of publicly available expressed sequence tag (EST) sequences among the Solanaceae. Most of these ESTs, plus other proprietary sequences, were combined and used to generate a unigene assembly. The set of 246,182 sequences produced 46,345 unigenes, which were used to design a 44K 60-mer oligo array (Potato Oligo Chip Initiative: POCI). In this study, we attempt to identify genes controlling and driving the process of tuber initiation and growth by implementing large-scale transcriptional changes using the newly developed POCI array. Major gene expression profiles could be identified exhibiting differential expression at key developmental stages. These profiles were associated with functional roles in cell division and growth. A subset of genes involved in the regulation of the cell cycle, based on their Gene Ontology classification, exhibit a clear transient upregulation at tuber onset indicating increased cell division during these stages. The POCI array allows the study of potato gene expression on a much broader level than previously possible and will greatly enhance analysis of transcriptional control mechanisms in a wide range of potato research areas. POCI sequence and annotation data are publicly available through the POCI database ( http://pgrc.ipk-gatersleben.de/poci ).

Significance: Guinea yam is an important staple tuber crop in West Africa, where it contributes to the sustenance and sociocultural lives of millions of people. Understanding the genetic diversity of Guinea yam and its relationships with wild relatives is important for improving this important crop using genomic information. A recent genomics study proposed that Guinea yam originated from a wild relative, the rainforest species Dioscorea praehensilis . Our results based on sequencing of 336 Guinea yam accessions do not support this notion; rather, our results indicate a hybrid origin of Dioscorea rotundata from crosses between the savannah species Dioscorea abyssinica and D. praehensilis.

Potato genotypes from a breeding population adapted to tropical highlands were analyzed for the stability of late blight resistance and also for marker-phenotype association. We harmonized the historical evaluation data, consisting of observations spanning 6 years from two field sites utilizing a resistance scale constructed by comparing the area under the disease progress curve (AUDPC) values of 172 genotypes with that of susceptible control ‘Yungay’. In total, 70 potato genotypes had a coefficient of variability <0.5 and were considered stable across the environments tested. A principal component analysis demonstrated that the ensemble of experiments formed two distinct groups that reflect the stability of genotype resistance to late blight. Phytophthora infestans isolates present in the experimental fields belonged to the EC-1 clonal lineage and showed variation in virulence beyond the concept of the avirulence determined by the conventionally used R1-R11 differential set. A single-nucleotide polymorphism (SNP) marker on chromosome 9 was associated with late blight resistance and linked to instability. Genotypes with either AACC or AAAC combinations for this SNP were highly resistant only in some environments, while the genotypes with the AAAA combination had more moderate levels of resistance but were stable across environments.