The relationship between powdrey mildew (Sphaerotheca fuliginea) resistance and leaf chlorosis sensitivity in cucumber (Cucumis sativus) studied in single seed descent lines

The genetic relation between powdery mildew resistance and sensitivity for leaf chlorosis of glasshouse cucumber was investigated. The powdery mildew resistant, leaf chlorosis sensitive hybrid variety 'Profito' was crossed with the powdery mildew susceptible, non chlorosis sensitive hybrid variety 'Corona'. Forty four F6 inbred lines of this cross, produced by single seed descent, were tested for powdery mildew resistance (PMR) and leaf chlorosis sensitivity (LCS). PMR and LCS were positively correlated (r = 0.59). One or more of the PMR genes probably causes LCS as a pleiotropic effect or is closely linked to LCS, but also other factors, not genetically linked to PMR can cause LCS. Five F6 lines combined a significantly higher level of PMR than 'Corona' with a significantly lower LCS than 'Profito'. Three of these lines could hardly be distinguished from 'Corona' for the level of LCS.