Drought resistance of potato cultivars with contrasting canopy architecture

There has been little research in potatoes (Solanum tuberosum L.) to define the ideal canopy structure for obtaining high and stable tuber yields. Two field experiments were conducted on a loamy sand soil (Haplic Luvisol) near Braunschweig in the North German Plain. The eight medium late potato cultivars grown in the year 2000 under non-limiting conditions differed significantly (P < 0.05) for leaf and stem dry weight, leaf/stem mass ratio, leaf number, leaf area, and other canopy structure parameters. Genotypes characterised by a high leaf/stem ratio (leaf-types) produced a lower shoot biomass than those with a low leaf/stem ratio (stem-types). The cultivars Producent and Tomba, representing a leaf- and a stem-type, respectively, were chosen to study the relationship between shoot and tuber yield under rainfed and irrigated conditions during the years 2001–2003. Different seasonal rainfall together with varying levels of extra water from irrigation created a wide range of soil moisture levels. The detrimental effects of drought on light interception were much greater for the leaf-type than for the stem-type. Under rainfed conditions, the relative tuber dry weight of the stem-type as compared with the leaf-type amounted to 99% in the absence of drought (2002), 109% under moderate drought (2001), and 148% under severe drought (2003). Obviously, the ability of stem-types to form a greater aboveground biomass is especially advantageous under soil water deficit conditions. High availability of water under irrigation in the years 2002 and 2003 produced a canopy size in the stem-type in excess of that required for maximum light interception. Consequently, the tuber dry weight of the stem-type displayed an optimum relationship with the shoot dry weight whereas the tuber yield of the leaf-type increased linearly with the shoot yield.