Genetic variation for drought stress in sugarbeet.

Fluctuation in sugarbeet (Beta vulgaris L.) yield in semi-arid regions often can be attributed to duration and intensity of drought stress. In this study, 49 diverse breeding lines were evaluated for root yield, sugar content, sugar yield, and white sugar yield, with adequate water and under two levels of drought stress at Karadj and Mashhad in 1996, 1997, and 1998. All lines were not evaluated each year; however, some lines were grown in all environments. Water stress was initiated at about the six-leaf stage. In Karadj, the stress was continuous throughout the growing season. In Mashhad, the stress period was limited to 50 days. The five indexes used to identify high-yielding genotypes in both the stressed and non-stressed environments were: stress susceptibility index (SSI), stress tolerance (TOL), stress tolerance index (STI), yield stability index (YSI), and mean productivity (MP). Root yield and sugar yield exhibited large differential genotypic responses to drought stress. Some high yielding genotypes were productive in stress and non-stress environments. Stress applied either for a limited period (Mashhad) or throughout the growing season (Karadj) gave similar results, with effects of the long-term stress being more pronounced. Under severe drought stress, root yield, sugar yield, and white sugar yield decreased to 59%, 59%, and 60%, respectively, of the values obtained with adequate water; whereas, sugar content increased 6%. Root yield, sugar yield, white sugar yield, and sugar content decreased under drought condition at Mashhad to 72%, 67%, 64%, and 95% of the well-watered sugarbeet, respectively. The stress tolerance index (STI) effectively distinguished genotypes with high yield in both stressed and non-stressed environments. Selection based primarily on root yield in diverse environments is suggested as a breeding strategy for developing productive sugarbeet genotypes with broad adaptation.