Quantifying lucerne (Medicago sativa L.) genotype by environment interactions in the cool temperate dairy regions of Australia

摘要

Lucerne (Medicago sativa L.) has a considerable amount of genetic diversity for many agronomic and physiological traits. This diversity is highlighted through the considerable genotype by environment interaction influences on yield observed in Europe, North America, and the subtropical regions of Australia. There is a need to quantify the influence of genotype by environment interactions on yield and key physiological processes in the cool temperate dairy regions of Australia. This information will ensure that appropriate cultivars can be selected and best management practices developed so that lucerne can become a greater component of the dairy feedbase. Field experiments indentified that genotype by environment interactions occur in cool temperate regions, with winter dormant genotypes adapted to low yield potential environments, and winter active genotypes adapted to high yield potential environments. Irrigation was identified as a major management input determining genotype by environment interactions. The relative influence of each yield component was not affected by a genotype by environment interaction, and mass per shoot consistently had the greatest impact on yield accounting for up to 80% of the variability in yield. Cultivar influenced taproot sugar and starch concentrations only with irrigation. SARDI 10 (a highly-winter active cultivar) had lower taproot sugar concentration and SARDI 7 (a winter active cultivar) had lower taproot starch concentrations than the other cultivars. When not irrigated over summer, taproot soluble protein concentrations of Grasslands Kaituna (a semi-winter dormant cultivar) were greater than SARDI 10. All cultivars had a greater abundance of vegetative storage proteins (VSPs) in taproots and enhanced phenotypic and genetic expression of winter dormancy under dryland conditions. ivudGlasshouse experiments revealed that increasing water deficits during regrowth decreased mass per shoot and shoots per plant. Water deficits of 75% or less of the replacement water requirement decreased total plant photosynthesis only through a reduction in leaf area and not by a decrease in either net carbon dioxide exchange rate or efficiency of photosystem II. Taproot starch concentration decreased and soluble sugar concentration increased with increasing water deficit. Plants receiving 25% of their water requirement accumulated soluble proteins seven days earlier than fully watered plants. Water deficits of 50% or less than the replacement water requirement also increased the abundance of VSPs, but VSP accumulation patterns and gene transcript levels were similar irrespective of drought treatment. With water deficit, the cold acclimation responsive gene CAR1 had a fivefold increase in expression in taproots of Grasslands Kaituna but not SARDI 10. These experiments have shown that in the cool temperate dairy regions of Australia, under dryland conditions, the more winter dormant cultivars should be grown, while if irrigation is available, winter active cultivars should be grown. In addition this study has highlighted that, for winter dormant cultivars, cold acclimation genes impart the ability to adapt to dry conditions.