Effect of defoliation on leaf physiology of sugar beet cultivars subjected to water stress and re-watering

Abstract Water stress causes defoliation, which can reduce yield and root quality of sugar beets (Beta vulgaris L.) through altered gas exchange characteristics of the leaves. In a two-year experiment, three sugar beet cultivars (Europa, Rival and Corsica) were subjected to three defoliation levels (control-C, moderate-MD, severe-SD) and re-watering after their exposition to drought for a month. Leaf physiological traits including net photosynthesis (A), transpiration rate (E), stomatal conductance (g s ), intracellular CO 2 (C i ), water use efficiency (WUE L -A/E and WUE i -A/g s ), leaf N concentration, petiole NO 3 -N concentration, specific leaf area (SLA), leaf water potential (WP) and leaf water content (LWC), were determined before defoliation and 15, 30 and 40 days after defoliation (DAD). On contrary to previous reports, water-stressed cultivars differed significantly in their leaf physiology; the late-season cultivar Corsica had the lowest E and g s values without any significant reduction in A. Thus, Corsica was the most water-conservative cultivar. Re-watering rapidly restored leaf physiology but a gradual decline, with the progress of DAD, was evident for A, E, g s and C i . After re-growth, cultivars differed only in WP and LWC with Europa, the early-harvested cultivar, to have the highest values. Thus, the better response (higher yield increase and lower root quality degradation) of Corsica to re-watering and the subsequent re-growth, as reported b

Genotypic response to re-growth of defoliated sugar beets after re-watering in a water-limited environment: effects on yield and quality.

Abstract Defoliation produced by abiotic factors and the subsequent re-growth can reduce sugar beet (Beta vulgaris L.) sucrose content and final sugar yield. Field experiments were conducted during 2003 and 2004 growing seasons in the farm of Hellenic Sugar Industry SA, Larissa factory, central Greece. Three sugar beet cultivars (Rival, Europa and Corsica) were ordinary irrigated till the beginning of July and then left without irrigation for a month. Three defoliation levels (control-C, moderate-MD and severe-SD) were performed at early August and irrigation was simultaneously started to promote re-growth. Four samplings were conducted (before defoliation, 15, 30 and 40 days after defoliation) to determine the changes in physiological and productive traits. Yields were lower in 2003 compared to 2004 because sugar beets were grown under more stressful conditions due to the delayed sowing, the higher temperatures and the lower rainfall. Both defoliation level and cultivar had significant effects on physiological and productive traits after re-growth only in 2003. The late-season cultivar, Corsica, showed better LAI maintenance compared to Europa and Corsica and had the greatest performance after re-growth in regard to fresh root weight and sugar yield. Also, this cultivar showed the least decrease of sucrose percentage in fresh root weight and juice purity mainly due to the stable potassium (K) concentration and limited increase of sodium (Na) accumulation in roots. Corsica consumed the least root α-amino N for its re-growth. Quantitative and qualitative traits were negatively affected only by the SD treatment. Plants suffered from MD treatment gradually recovered during growing season. This study demonstrates that under Mediterranean conditions, the adverse effects of re-growth on sugar beet yield and quality depend on the growing conditions and they can be restricted by the selection of an appropriate cultivar