No abstract

Genetic analyses have suggested that the clonal reproduction of Arundo donax has resulted in low genetic diversity. However, an earlier common garden phenotyping experiment identified specimens of A. donax with contrasting biomass yields (ecotypes 6 and 20). We utilized the same well-established stands to investigate the photosynthetic and stress physiology of the A. donax ecotypes under irrigated and drought conditions. Ecotype 6 produced the largest yields in both treatments. The A. donax ecotypes exhibited identical high leaf-level rates of photosynthesis (P N ) and stomatal conductance (G s ) in the well-watered treatment. Soil drying induced reductions in P N and G s , decreased use of light energy for photochemistry, impaired function of photosystem II and increased heat dissipation similarly in the two ecotypes. Levels of biologically active free-abscisic acid (ABA) and fixed glycosylated-ABA increased earlier in response to the onset of water deficit in ecotype 6; however, as drought progressed, the ecotypes showed similar increases in both forms of ABA. This may suggest that because of the low genetic variability in A. donax the genes responding to drought might have been activated similarly in the two ecotypes, resulting in identical physiological responses to water deficit. Despite the lack of physiological ecotypic differences that could be associated with yield, A. donax retained a high degree of P N and biomass gain under water deficit stress conditions. This may enable utilization of A. donax as a fast growing biomass crop in rain-fed marginal lands in hot drought prone climates.

The influence of 2 water regimes (a fully irrigated treatment receiving 100% of evapotranspiration for the whole growing season and an unirrigated control watered up to plant establishment only) on lycopene and β-carotene accumulation during fruit ripening in a field-grown processing tomato was studied. Since a strong effect of irrigation treatments on fruit water content was expected, carotenoid content on both a fresh and dry matter basis was studied. Regardless of ripening stage and adopted parameter unit (fresh or dry matter), higher amounts of lycopene were measured in the well watered treatment. Positive and no effects of water stress were reported on β-carotene content when expressed, respectively, on a fresh and dry weight basis. Both experimental factors influenced the β-carotene/lycopene ratio mostly in the first 2 ripening stages and there is evidence to suggest that, under soil water deficit conditions, the carotenoid biosynthetic pathway is more ‘β-carotene accumulation’ oriented, especially at the beginning of the fruit ripening process. Appropriateness of adopting both a fresh and dry basis calculation, in order to better evaluate the role of water stress on carotenoid content, is emphasised. The possibility of reducing the irrigation water supply without drastically decreasing the studied fruit quality characteristics is suggested.