ALBERT

Notes: Narrow-leaved bird's-foot-trefoil (Lotus tenuis) is a perennial forage legume adapted to waterlogged and heavy and infertile soils and can replace alfalfa (Medicago sativa) in areas with these soils in Argentina. Its seeds are hard and water-impermeable but the effects of environmental factors on seed dormancy and germination are not known. The objective was to evaluate the hypothesis that water availability during seed development and maturation affects the degree of hardseededness in L. tenuis by changing seed coat properties, conditioning water uptake through the seed coat; and subsequently affecting dormancy, germination and speed of germination. Seeds were harvested in December/January and in February in both 1993/1994 and 1994/1995 from a permanent pasture of L. tenuis growing in a Hapludol soil in San Miguel del Monte province of Buenos Aires. Environmental conditions of each anthesis-harvest period were determined. Seeds of each harvest were subjected to chilling, washing and mechanical scarification. After 12 months seeds from each harvest were observed in a scanning electron microscope. The water deficit of the soil and relative humidity were greater in the second than the first anthesis-harvest period in both seasons. In 1993/1994 the control treatment in December had a higher germination rate than the February control seeds (0·40 vs. 0·20) and a faster germination rate. Mechanical scarification and chilling significantly enhanced the germination rate (0·95) and its speed in seeds of both harvests. Low temperatures significantly enhanced germination rate, starting after 60 d for the seeds harvested in December, and 90 d for the seeds harvested in February. In 1994/1995 the results were similar but both the January and February control treatments had higher germination rates (0·60 vs. 0·40) than in the previous year. Seeds harvested in February were more dormant in both years. These differences could be explained by the conditions in February anthesis-harvest period in both years that could have hastened the natural dehydration process of seed, changing integument structure and enhancing its impermeability.

Notes: In hexaploid bread wheat, Triticum aestivum (2n = 6x = 42), little work has been carried out to study the genetic control of the synthesis of reduced, non-reduced and total non-structural carbohydrates and soluble proteins in aerial and rooting structures. The aim of this paper was to determine the chromosomal location of genes determining carbohydrate and protein synthesis that could be used for diagnostic selection in segregating breeding populations. A set of wheat intervarietal chromosome substitution lines [‘Chinese Spring’ (CS) × synthetic wheat (Triticum diccocoides×Aegilops squarrosa) (Syn)], was used. Plants were cultivated in hydroponic solutions to the fully expanded third leaf stage. Carbohydrate and protein contents and dry matter were determined for aerial and root parts. The root dry weight did not show significant differences between the parental varieties and the substitution lines, except for 5A, 2B and 6B, which had significantly lower dry weights. The aerial dry weight was significantly higher for Syn and the 2A substitution line. The ratio aerial dry weight/root dry weight was significantly higher in Syn, 1A, 2A and 4B. The protein content of the plant showed highly significant differences between both parental lines but 6A and 1D of the substitution lines showed highly significant differences, with contents as high as that for Syn. Syn produced significantly lower total aerial carbohydrates. The substitution lines 2A, 5A, 6A, 7A, 2B, 3D, 5D and 6D showed highly significant total carbohydrate content increases in the aerial parts compared with both parental lines. The non-reduced carbohydrate contents showed a pattern similar to that of the total carbohydrates. Syn had a lower reduced carbohydrate content than CS. Only the 5A, 2B, and 1D substitution lines had a highly significantly different content of reduced carbohydrates than CS. In roots, Syn produced the lowest values for every type of sugar. The highest significant values for total carbohydrates were found in substitution lines 2B, 4B, 5B, 6B, 1D and 6D. The non-reduced carbohydrate levels were significantly higher than CS in 2B, 5B, 6B and 6D substitution lines. Only the substitution lines 3B and 1D showed a significantly higher reduced carbohydrate content in roots compared with CS. The photoassimilate partitioning in Syn, 1 A, 2A and 4B favoured the aerial parts but, in contrast, higher partitioning to the roots was found in the 7B, 1D and 3D substitution lines. Both groups appear to carry interesting patterns worth incorporating in wheat cultivars.

Notes: A collection of 26 cultivars of wheat Triticum aestivum were screened for resistance against the two main aphid pests of cereals, the greenbug Schizaphis graminum Rond. and the Russian wheat aphid (RWA) Diuraphis noxia Mordvilko. Since genetic variability has been found in Argentinean populations of both aphid species, this work was aimed at determining the response of different types of resistance in wheat cultivars when infested with aphids. Antixenosis, antibiosis and tolerance were evaluated with traditional tests in controlled environmental conditions using a clone of greenbug biotype C and a clone of RWA collected on wheat. Genetic resistance was found against one or both aphid species in several wheats. Most of the highest levels of antixenosis, antibiosis and tolerance against the two aphids occurred in different cultivars; as a consequence the resistance mechanisms for both pests appear to be partly independent. Antibiosis against greenbug or RWA appears to be determined by two different sets of genes, one affecting development time and the other reducing fecundity and longevity. The antibiosis against both aphid species in terms of their development time and the intrinsic rate of population increase resulted in a partial cross effect of these aphid traits against the alternative insect species. Nonetheless, the same cultivars affected the total fertility and the longevity of both aphids. Since the highest plant performance levels and the least plant damage were recorded in different wheats, different patterns of tolerance were displayed against the greenbug and the RWA. Consequently, different genes appear to be involved in several traits of the resistance mechanisms against the two aphids. The genes that independently conferred resistance to aphids could be combined in new cultivars of wheat to broaden their genetic base of resistance against the greenbug and the RWA.