Content of carotenoids at different ripening stages in processing tomato in relation to soil water availability

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 beta-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 b-carotene content when expressed, respectively, on a fresh and dry weight basis. Both experimental factors influenced the beta-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 'beta-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.