Philippe Monneveux

Drought tolerance in potato (S. tuberosum L.): Can we learn from drought tolerance research in cereals?

Drought tolerance is a complex trait of increasing importance in potato. Our knowledge is summarized concerning drought tolerance and water use efficiency in this crop. We describe the effects of water restriction on physiological characteristics, examine the main traits involved, report the attempts to improve drought tolerance through in vitro screening and marker assisted selection, list the main genes involved and analyze the potential interest of native and wild potatoes to improve drought tolerance. Drought tolerance has received more attention in cereals than in potato. The review compares these crops for indirect selection methods available for assessment of drought tolerance related traits, use of genetic resources, progress in genomics, application of water saving techniques and availability of models to anticipate the effects of climate change on yield. It is concluded that drought tolerance improvement in potato could greatly benefit from the transfer of research achievements in cereals. Several promising research directions are presented, such as the use of fluorescence, reflectance, color and thermal imaging and stable isotope techniques to assess drought tolerance related traits, the application of the partial root-zone drying technique to improve efficiency of water supply and the exploitation of stressful memory to enhance hardiness.

Large-Scale Evaluation of Potato Improved Varieties, Genetic Stocks and Landraces for Drought Tolerance

Potato production worldwide is strongly affected by water stress, either because of insufficient rainfall or due to inadequate irrigation. Improving drought tolerance is consequently becoming a priority for potato breeders, particularly in the perspective of climate change. In the present study, a set of 918 accessions from CIP world potato collection was evaluated under field conditions with full irrigation and deficit irrigation, on the desertic coast of Peru. The set included improved varieties, genetic stocks and landraces. The subset of landraces comprised accessions from the species Solanum ajanhuiri Juz. & Bukasov, Solanum curtilobum Juz. & Bukasov, Solanum juzepczukii Bukasov and Solanum tuberosum L. S. tuberosum L. included non Andean accessions of the ssp. Chilotanum as well as accessions belonging to the Andean cultivar groups Andigenum, Chaucha, Goniocalyx, Phureja and Stenotomum. Under both drought and irrigated treatments, significant differences were found for tuber yield, tuber number and tuber weight among subsets, cultivar groups and accessions. On average, improved varieties and advanced bred lines yielded more under both deficit and well-irrigated conditions than did landraces, while variation for drought susceptibility was greater in landraces and genetic stocks than in improved varieties. Within the subset of landraces, the species Solanum juzepczukii Bukasov exhibited the lowest average values and highest variation for drought susceptibility. A high proportion of accessions combining low drought susceptibility and high irrigated yield were found in Andean landraces, and particularly in the species Solanum curtilobum Juz. & Bukasov in the S. tuberosum L. cultivar groups Stenotomum, Andigenum and Chaucha. The differences observed among species and cultivar groups were not directly related to their eco-geographic distribution. The polyploid species and cultivars groups appeared more drought tolerant than the diploid ones. The study evidenced the interest of Andean landraces as potential sources of drought tolerance in potato breeding programs.ResumenLa producción de papa en el mundo es fuertemente afectada por el estrés hídrico debido a la falta de precipitación o a irrigación inadecuada. Mejorar la tolerancia a sequía es, por lo tanto, una meta prioritaria para los mejoradores de papa, particularmente en la perspectiva del cambio climático. En el presente estudio, un total de 918 accesiones de papa del Banco de Germoplasma del CIP fue evaluado bajo riego completo y riego limitado, en las condiciones desérticas de la costa del Perú. La colección incluyó variedades mejoradas, genotipos de pre-mejoramiento y cultivares locales. El subconjunto de cultivares locales comprendió accesiones de las especies Solanum ajanhuiri Juz. & Bukasov, Solanum curtilobum Juz. & Bukasov, Solanum juzepczukii Bukasov and Solanum tuberosum L. S. tuberosum L. incluyo accessiones no andinas de la ssp. chilotanum y accessiones de los grupos de cultivares andinos andigenum, chaucha, goniocalyx, phureja y stenotomum. En condiciones de riego y de sequia se encontraron diferencias significativas para rendimiento, número y peso de tubérculos entre subconjuntos, grupos de cultivares y accesiones. En general, las variedades mejoradas tuvieron mayor rendimiento bajo condiciones de sequía y de riego, mientras la variación para susceptibilidad a sequía fue más amplia en cultivares locales que en genotipos de pre-mejoramiento y variedades mejoradas. En el grupo de cultivares locales, la especie Solanum juzepczukii Bukasov presentó mas amplia variación y menores valores medias para susceptibilidad a sequía. Una alta proporción de accesiones combinando bajo índice de susceptibilidad a sequía y alto rendimiento bajo riego fue encontrada en cultivares locales andinos, particularmente en la especie Solanum curtilobum Juz. & Bukasov y en los grupos de cultivares de S. tuberosumstenotomum, andigenum y chaucha. Las diferencias observadas entre especies y grupos de cultivares no dependieron de su distribución geográfica. Las especies y los grupos de cultivares poliploides monstraron mejor tolerancia a sequia que los diploides. El estudio puso en evidencia el interés de los cultivares locales andinos como fuentes potenciales de tolerancia a sequia en los programas de mejoramiento de papa.

Cultivated einkorn wheat (Triticum monococcum L. subsp. monococcum): the long life of a founder crop of agriculture

The first cultivated wheat, cultivated einkorn (Triticum monococcum L. subsp. monococcum), was domesticated in South-East Turkey during the Pre-Pottery Neolithic period. It then spread to the Middle-East, the Balkans and Caucasus, Turkmenistan, Central and Mediterranean Europe, North-Africa, and finally to Western and Northern Europe. In all these regions, it played an important role in the development of agriculture and was cultivated for several centuries before being replaced by free-threshing wheats. Today, cultivated einkorn is only present in isolated, mountainous areas of a few countries. However, there is renewed interest for this crop due to the nutritional qualities of its grain, its adaptation to low-input agriculture and high level of resistance to pests and diseases that represent advantages for organic farming. Cultivated einkorn is also a valuable reservoir of genes for wheat improvement. Its utilization, limited by its hulledness, low yield and especially by a poor knowledge of its diversity and its low crossability with bread and durum wheat, is expected to increase in the future, particularly with the need for wheat breeding to face newly emerging diseases through the use of genetic resistances. Considering these perspectives, the present review attempts to analyse the current and historical importance of einkorn cultivation and utilization in wheat breeding, tracing back to its origin and diffusion. The main traits of resistance to pest and diseases, and the nutritional qualities and technological characteristics of the grain are described. Einkorn genetic resources diversity exploration is reviewed and successful examples of introgression of useful einkorn traits into cultivated wheat are reported. Lastly, perspectives of einkorn cultivation development in low-input agriculture and use for wheat enhancement are discussed.

Comparison of yield based drought tolerance indices in improved varieties, genetic stocks and landraces of potato (Solanum tuberosum L.)

Drought strongly influences potato (Solanum tuberosum) production and quality. Potato being a drought susceptible crop, the development of varieties with enhanced tolerance to water stress could highly improve productivity in drought prone areas. The objective of this study was to evaluate the ability of several yield based indices to be used in large scale screening for drought tolerance. The experiment included improved varieties, genetic stocks and landraces potatoes grown under drought and irrigated conditions. A group of accessions with high yield under both conditions was identified. Mean productivity (MP), geometric mean productivity (GMP), tolerance (TOL), drought tolerance index (DTI), drought susceptible index (DSI) and yield stability index (YSI) were calculated from tuber yield under drought and irrigated conditions. The relationships between these indices and yield were analyzed. The Fleiss’ Kappa concordance test was used to analyze the correspondence between accessions previously identified as highly productive under both drought and irrigated conditions and accessions with optimal values for the different indices. MP, GMP and DTI allowed identifying genotypes combining high yield potential and high yield under drought within the three subsets of genotypes. Conversely, DSI, YSI and TOL showed low and variable concordance values across subsets, suggesting that their efficiency in screening genotypes highly depends on the nature of the tested genetic material.

Improving potato drought tolerance through the induction of long-term water stress memory

Knowledge of drought tolerance in potato is limited and very little is known about stress memory in this crop. In the present study, long-term stress memory was tested on tuber yield and drought tolerance related traits in three potato varieties (Unica, Désirée and Sarnav) with contrasted yields under water restriction. Seed tubers produced by plants grown under non-restricted (non-primed tubers) and restricted (primed tubers) water conditions were sown and exposed to similar watering treatments. Tuber yield and leaf greenness of plants from primed and non-primed seeds as well as tuber carbon isotope discrimination (Δ(13)C) and antioxidant activity (AA) responses to watering treatments were compared. Higher tuber yield, both under non-restricted and restricted water regimes, was produced by primed Sarnav plants. The decrease of tuber yield and Δ(13)C with water restriction was lower in primed Unica plants. Long-term stress memory consequently appears to be highly genotype-dependent in potato. Its expression in plants originated from primed tubers and facing water restriction seems to be positively associated to the degree of inherent capability of the cultivar to yield under water restriction. However, other effects of priming appear to be genotype-independent as priming enhanced the tuber AA in response to water restriction in the three varieties.

Drought and Heat Tolerance Evaluation in Potato (Solanum tuberosum L.)

The impacts of water restriction and high temperatures on potato production will increase over the next decades, due to climate change and the extension of cultivation in drought and heat prone areas. We review recent achievements and describe new avenues in the evaluation of tolerance to these abiotic stresses in potato, focusing on the definition of target populations of environments, choice and characterization of the managed stress environment, stress monitoring, and secondary traits measurement.

Breeding Strategies to Enhance Drought Tolerance in Crops

Global climate change is expected to increase the occurrence and severity of drought episodes due to increasing temperatures and evapotranspiration. Therefore, food security in the twenty-first century will increasingly depend on the release of new cultivars with improved adaptation to drought conditions. However, selection for drought tolerance is difficult due to a complex genotype and by environment interactions. Recent progress in genomics makes possible a more efficient assessment and enhanced diversity in germplasm collections, introgression of valuable traits from new sources and identification of the genes that control key traits. Marker-assisted selection helps to reduce the environmental impact of breeder selection. Significant advances have been made in the development of in vitro selection methods. The broader use of traits from alien species and the manipulation of heterosis and polyploidy create new perspectives for improving yield potential and adaptation to abiotic stresses. The use of the knowledge generated by these approaches should clarify the functional basis of drought adaptation traits. The integration of these new methods and tools into breeding programs and their potential impact in the development of drought-tolerant germplasm are discussed.

Heritability of Yield Components Under Irrigated and Drought Conditions in Andigenum Potatoes

Drought is one of the major abiotic factors that affect potato production in the tropics and sub-tropics. Molecular plant breeding offers promising opportunities for developing drought tolerant cultivars, but genetic gains to be achieved through breeding depends strongly on the genetic variance and heritability of traits used in the selection process. In the present study, genetic variance and heritability of tuber yield and its components were estimated in the native potato cultivar group Andigenum, expected to include promising drought tolerant progenitors. Twenty-seven full sib families obtained from crossing 18 parents arranged in 3 mating sets were grown under irrigated and terminal drought conditions. Heritability for tuber yield, estimated from female to male variance components was 0.68 and 0.41, respectively, in the irrigated treatment, and only 0.18 and 0.06 under drought conditions. Tuber number was highly significantly correlated to tuber yield but the heritability of this trait (estimated both from female to male variance) was lower than yield heritability and its non-additive genetic variance was higher than its additive genetic variance, particularly when estimated from the female variance component. Heritability of average weight per tuber estimated for male variance component was very high under both irrigated and drought conditions. Its additive genetic variance was much higher than its non-additive genetic variance. However, average weight per tuber correlated to tuber yield within parents but not within families. These results indicate that selection for increased tuber yield under drought conditions in the Andigenum cultivar group may be slow due to its low heritability and high value of non-additive genetic variance. They also suggest that yield components may not be useful as indirect selection criterion for yield, because of their low heritability and/or poor association with yield. The identification of drought tolerance related traits with high heritability and closely associated to tuber yield under drought is consequently required to improve adaptation of potato to drought-prone conditions and efficient utilization of Andigenum potatoes for this purpose.ResumenLa sequía es uno de los factores abióticos principales que afectan la producción de papa en los trópicos y subtrópicos. El mejoramiento molecular de plantas ofrece oportunidades prometedoras para desarrollar variedades tolerantes a la sequía, pero las ganancias genéticas a lograr a través del mejoramiento, dependen fuertemente de la varianza genética y de la heredabilidad de los caracteres usados en el proceso de selección. En el presente estudio, se estimaron la varianza genética y la heredabilidad del rendimiento de tubérculo y sus componentes en variedades nativas de papa del grupo Andigenum, esperando que se incluyeran progenitores prometedores tolerantes a la sequía. A 27 familias completas obtenidas del cruzamiento de 18 progenitores arreglados en tres juegos de apareamiento, se les cultivó bajo condiciones de riego y de sequía terminal. La heredabilidad para rendimiento de tubérculo, estimada de los componentes de varianza de machos y hembras, fue de 0.68 y 0.41, respectivamente, en el tratamiento con riego, y solo de 0.18 y 0.06 bajo condiciones de agobio hídrico. El número de tubérculos estuvo alta y significativamente correlacionado al rendimiento, pero la heredabilidad de este carácter (estimada de la varianza, tanto de hembras como de machos) fue más baja que la heredabilidad de rendimiento, y su varianza genética no aditiva fue más alta que su varianza genética aditiva, particularmente cuando se estimó del componente de varianza femenino. La heredabilidad del promedio del peso por tubérculo, estimada para el componente de varianza masculino, fue muy alta bajo ambas condiciones, de riego y de sequía. Su varianza genética aditiva fue mucho más alta que la no aditiva. No obstante, el promedio de peso por tubérculo se correlacionó con rendimiento de tubérculo entre progenitores pero no dentro de las familias. Estos resultados indican que la selección para aumento del rendimiento de tubérculo bajo condiciones de sequía en las variedades del grupo Andigenum pudiera ser lenta debido a su baja heredabilidad y al alto valor de la varianza genética no aditiva. También sugieren que los componentes de rendimiento pudieran no ser de utilidad como criterio indirecto de selección para rendimiento, debido a su baja heredabilidad y/o su pobre asociación con rendimiento. Se requiere, consecuentemente, la identificación de caracteres relacionados a la tolerancia a la sequía con alta heredabilidad y estrechamente asociados al rendimiento de tubérculo bajo agobio hídrico, para mejorar la adaptación de la papa a condiciones propicias a la falta de agua y utilización eficiente de las papas Andigenum para este propósito.

Determination of drought tolerance related traits in Helianthus argophyllus, Helianthus annuus, and their hybrids

Drought is a major constraint for sunflower (Helianthus annuus) production worldwide. Drought tolerance traits have been identified in the related wild species Helianthus argophyllus. This study was initiated to develop sunflower drought-tolerant genotypes by crossing cultivated sunflower with this species and analyze drought tolerance traits in the H. annuus and H. argophyllus populations, H. annuus intraspecific hybrids, and H. annuus × H. argophyllus interspecific hybrids along with the commercial hybrid Hysun-33 under three stress regimes: exogenous application of ABA, both by foliar spray and irrigation, and 5% PEG-induced osmotic stress. H. argophyllus populations had a significantly lower leaf area and higher water-use efficiency and leaf cuticular wax content under all treatments, and maintained a higher net photosynthetic rate and stomatal conductance under osmotic stress. Small leaf area and high cuticular waxes content of the wild species were, however, not inherited in interspecific hybrids which suggested for selection in F2 for these traits. Therefore, transgressive plants were selected in the F2 population to establish F3 plant progenies with silver-leafed canopy of H. argophyllus which showed higher achene yield under stress condition. These results are discussed with a view to using H. argophyllus to improve drought tolerance in cultivated sunflower.

Genetic analysis of proline concentration under osmotic stress in sunflower (Helianthus annuus L.)

Proline concentration has been often suggested as an indicator of osmotic stress. A better understanding of the genetics of this trait is however needed. In the present study, proline concentration has been assessed, together with root and stem growth, potassium, calcium and total soluble sugars concentration and stress injury symptoms, in seedlings of sunflower hybrids and their parents grown under control and osmotic conditions. Proline strongly accumulated with osmotic stress. Its concentration exhibited a large variation among genotypes and was higher in hybrids than in parental lines. A positive association was noted between proline concentration and osmotic adjustment that was reflected in a reduction of osmotic stress induced injury, as showed by the reduced number of calli in the hybrids with higher proline concentration. Broad and narrow sense heritability was higher under osmotic stress suggesting applying the selection in osmotic stress condition. In the control treatment, dominance effects explained most of the genetic variation for proline concentration while under osmotic stress both dominance and additive variance were high. The importance of dominance and additive effects suggested that several genomic regions are controlling this trait. Good general combiners, presumably carrying positive additive alleles affecting proline concentration, were identified.