Yoshiro Mano

Mapping quantitative trait loci for salt tolerance at germination and the seedling stage in barley (Hordeum vulgare L.)

Quantitative trait loci (QTLs) controlling salt tolerance at germination and the seedling stage in barley (Hordeum vulgare L.) were identified by interval mapping analysis using marker information from two doubled haploid (DH) populations derived from the crosses, Steptoe/Morex and Harrington/TR306.Interval mapping analysis revealed that the QTLs for salt tolerance at germination in the DH lines of Steptoe/Morex were located on chromosomes 4 (4H), 6(6H), and 7(5H), and in the DH lines of Harrington/TR306 on chromosomes 5(1H) and 7(5H). In both DH populations, the most effective QTLs were found at different loci on chromosome 7(5H). Genetic linkage between salt tolerance at germination and abscisic acid (ABA) response was found from QTL mapping. The QTLs for the most effective ABA response at germination were located very close to those for salt tolerance on chromosome 7 (5H) in both crosses.The QTLs for salt tolerance at the seedling stage were located on chromosomes 2(2H), 5(1H), 6(6H), and 7(5H) in the DH lines of Steptoe/Morex, and on chromosome 7(5H) in the DH lines of Harrington/TR 306. Their positions were different from those of QTLs controlling salt tolerance at germination, indicating that salt tolerance at germination and at the seedling stage were controlled by different loci.

Identification of QTL controlling adventitious root formation during flooding conditions in teosinte (Zea mays ssp. huehuetenangensis) seedlings

Adventitious root formation (ARF) at the soil surface is one of the most important adaptations to soil flooding or waterlogging. Quantitative trait loci (QTL) controlling ARF under flooding condition were identified in a 94 F2 individual population by crossing maize (Zea mays L., B64) × teosinte (Z. mays ssp. huehuetenangensis). A base-map was constructed using 66 SSR and 42 AFLP markers, covering 1,378 cM throughout all ten maize chromosomes. The ARF capacity for seedlings was determined by evaluating the degree of root formation at the soil surface following flooding for 2 weeks. ARF showed continuous variation in the F2 population. Interval mapping and composite interval mapping analyses revealed that the QTL for ARF was located on chromosome 8 (bin 8.05). Utilising a selective genotyping strategy with an additional 186 F2 population derived from the same cross combination and 32 AFLP primer combinations, regions on chromosomes 4 (bin 4.07) and 8 (bin 8.03) were found to be associated with ARF. Z. mays ssp. huehuetenangensis contributed all of the QTL detected in this study. Results of the study suggest a potential for transferring waterlogging tolerance to maize from Z. mays ssp. huehuetenangensis.

Genetic resources of salt tolerance in wild Hordeum species

Salt tolerance was evaluated in 340 accessions of Hordeum, consisting of 41 brittle-rachis forms of Hordeum vulgare L. subsp. vulgare (H. agriocrithon) accessions, 154 H. vulgare L. subsp. spontaneum (H. spontaneum) accessions, and 145 accessions of ten other species or subspecies of wild Hordeum. Germination was carried out at concentrations of 171, 257, and 342 mM NaCl. The levels of salt tolerance for seed germination in wild Hordeum species were generally lower than those found by Mano et al. (1996) in cultivated barley; the NaCl tolerance level of the different species were as follows: H. agriocrithon > H. spontaneum > other wild Hordeum species. In addition, leaf injury index was used to assess tolerance at the seedling stage after treatment with 500 mM NaCl solution for four weeks. The levels of salt tolerance at the seedling stage in wild Hordeum species were generally higher than those found by Mano & Takeda (1995) in cultivated barley. Most wild Hordeum species showed high NaCl tolerance at the seedling stage and are considered good sources of germplasm for salt tolerance breeding.

Relationship between constitutive root aerenchyma formation and flooding tolerance in Zea nicaraguensis

Background and aimsThe teosinte Zea nicaraguensis, which is adapted to frequently flooded lowlands, is considered a valuable germplasm resource for the development of flooding-tolerant maize. This species can form constitutive root aerenchyma under well-drained conditions. The objectives of this study were to screen Z. nicaraguensis accessions for the capacity to form constitutive aerenchyma, to obtain progeny with differing degrees of aerenchyma formation, and to compare the flooding tolerance of these progeny.MethodsWe evaluated constitutive aerenchyma formation in the root cortex of seedlings of eight accessions and several segregating populations of Z. nicaraguensis. We also evaluated flooding tolerance in lines selected for high or low degrees of constitutive aerenchyma formation.ResultsSeedlings of the eight accessions showed an extremely wide and continuous range of variation in aerenchyma formation. By phenotypic selection within two accessions, we obtained lines with either high or low degrees of constitutive aerenchyma formation. The lines selected for a higher degree of formation showed relatively high flooding tolerance evaluated by shoot dry weight ratio (flooded:control) than those with a lower degree of formation.ConclusionsA greater capacity to form constitutive aerenchyma can enhance flooding tolerance.

Identification of QTL controlling flooding tolerance in reducing soil conditions in maize (Zea mays L.) seedlings.

abstract We investigated the tolerance to flooding in reducing conditions of five maize inbred lines and identified a quantitative trait locus (QTL) for the trait. Flooding treatment with 0.1% to 0.4% starch solution for 14 d reduced soil redox potential to about – 200 mV, mimicking reducing conditions in soil. Treatment with 0.2% starch revealed wide varietal differences in dry matter production among the five maize inbred lines. We identified the QTL for flooding tolerance in reducing conditions in a population of 178 F2 plants derived from a cross of inbred lines F1649 (tolerant) and H84 (sensitive). Flooding tolerance, evaluated as the degree of leaf injury following treatment with 0.2% starch solution, revealed wide variation in the F2 population. Amplified fragment length polymorphism (AFLP) markers linked to flooding tolerance gene(s) were screened with 64 AFLP primer combinations using 15 of the 178 F2 plants from each extreme representing the ‘tolerant’ and ‘sensitive’ plants, and found 11 AFLP markers associated with flooding tolerance. Of these, 10 co-segregated and were assigned to chromosome 1. Six SSR primer pairs around these markers were used to construct a linkage map. Composite interval mapping analysis revealed that a single QTL for degree of leaf injury was located on chromosome 1 (bin 1.03-4). Another QTL for flooding tolerance, evaluated as dry matter production under flooding with 0.2% starch, was located at the same position. These results suggest the potential to increase productivity by transferring flooding tolerance genes from F1649 to elite maize inbred lines.

Accurate evaluation and verification of varietal ranking for flooding tolerance at the seedling stage in barley (Hordeum vulgare L.)

Soil flooding or waterlogging is a major abiotic stress in upland crops. In barley, there have been several reported studies of selection for flooding-tolerant genotypes, but it is difficult to obtain varietal rankings that are consistent among researchers. Our objectives were to establish experimental conditions that could be applied by other research groups and to verify the varietal ranking conducted in an earlier study. We conducted greenhouse experiments on 14 barley varieties. At the 2.5-leaf stage, they were flooded with 0% or 0.1% soluble starch solution (mimicking reducing conditions). At 13 to 15 days after the start of treatment, the degree of leaf injury and the shoot dry weight ratio (treatment:control) were recorded. Reliable and highly repeatable results were obtained for the criterion of leaf injury under reducing conditions, whereas shoot dry weight ratio was unstable. The varieties OUJ820 and OUA301 were highly tolerant, whereas OUA002 and OUJ247 were sensitive; these results matched those of the earlier study. The experimental conditions that we developed here may be useful for selection testing and genetic analysis of flooding tolerance in other laboratories.