Two potato clones (Solanum tuberosum L.) of the Andean cultivar group, called Sullu and SS2613, with different drought-tolerance phenotypes were exposed to a continuously increasing drought stress in a field trial. At the physiological level, while relative leaf water contents were similar in both clones, osmotic potential was lower in Sullu and declined more strongly during drought compared with SS2613. In the drought-stressed plants, tuber yield was reduced by about 70% compared with control plants in both clones. Potato cDNA microarrays and target metabolite analysis were performed on leaves sampled at several time-points after the onset of drought. At the transcriptomic level, photosynthesis-related genes were already strongly repressed in Sullu after 28 d of withholding irrigation and even more strongly after a longer stress duration, whereas, in SS2613, repression occurred only after 49 d of soil drying; similarly, a strong perturbation of carbohydrate-related genes was observed in Sullu. At the metabolite level, differential accumulation of osmotically active solutes was observed between the two cultivars; indeed, in Sullu, contents of galactose, inositol, galactinol, proline, and proline analogues were higher upon drought stress compared with SS2613. These results point to different drought responses in the cultivars at the leaf level, with, however, similar tuber yield reductions. The previously shown tolerant clone Sullu lost part of its tolerance under the experimental conditions used here; it was, however, able to maintain an absolute yield three times higher than SS2613.

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Solanum tuberosum cultivars, Solanum tuberosum × Solanum tuberosum subsp. andigena hybrids and breeding clones with different time to maturity were screened for drought tolerance in field plots located in the coastal desert of Peru. Variation for drought tolerance was illustrated by clone-dependent differences in tuber yield and yield loss under drought conditions. Neither changes in stomatal conductance nor maximum quantum yield of chlorophyll fluorescence were quantitatively associated with yield or yield loss under drought. In contrast, relative vegetation index (reflectance at 800 nm / reflectance at 650 nm) and normalized difference vegetation index [(reflectance at 800 nm -reflectance at 650 nm) / (reflectance at 800 nm + reflectance at 650 nm)] on day 25 and day 40 after drought were correlated with yield. The vegetation indices are related to leaf area index and above ground biomass, which appeared to be major determinants for yield in the tested cultivars under drought. Nitrate reductase activity was significantly decreased in drought-exposed plants, but activity depletion was independent of yield or yield maintenance. Putative drought tolerance genes were differentially expressed in leaves of water stressed genotypes. Induction of the protein phosphatase 2C gene was positively associated with yield maintenance under drought. Furthermore, Potato Research (2007) 50:71-85

Six potato varieties belonging to four different sub-species were submitted to drought stress during tuberization under controlled field conditions, resulting in contrasting responses of the genotypes to water stress with yield losses varying between 27 and 75%. In all clones free proline accumulated under drought, however, proline levels increased earlier in drought-susceptible varieties than in more tolerant ones. The expression of two key genes in proline metabolism, D 1 -pyrroline-5-carboxylate synthase and proline dehydrogenase, was monitored in the leaves of the experimental plants by r2eal time PCR 23 and 42 days after drought onset. Expression of both enzymes did not correlate with the proline levels found in leaf tissue indicating that mechanisms other than transcription participate in the regulation of proline accumulation in potato leaves.

In potatoes and many other crops, drought is one of the most important environmental constraints leading to yield loss. Development of drought-tolerant cultivars is therefore required for maintaining yields under climate change conditions and for the extension of agriculture to sub-optimal cropping areas. Drought tolerance mechanisms have been well described for many crop plants including Native Andean potato. However, knowledge on tolerance traits suitable for commercial potato varieties is scarce. In order to describe drought tolerance mechanisms that sustain potato yield under water stress, we have designed a growth-chamber experiment with two Solanum tuberosum L. cultivars, the more drought tolerant accession 397077.16, and the sensitive variety Canchan. After 21 days of drought exposure, gene expression was studied in leaves using cDNA microarrays. The results showed that the tolerant clone presented more differentially expressed genes than the sensitive one, suggesting greater stress response and adaptation. Moreover, it exhibited a large pool of upregulated genes belonging to cell rescue and detoxication such as LEAs, dehydrins, HSPs, and metallothioneins. Transcription factors related to abiotic stresses and genes belonging to raffinose family oligosaccharide synthesis, involved in desiccation tolerance, were upregulated to a greater extent in the tolerant clone. This latter result was corroborated by biochemical analyses performed at 32 and 49 days after drought that showed an increase in galactinol and raffinose especially in clone 397077.16. The results depict key components for the drought tolerance of this advanced potato clone.