Institute of Plant Nutrition Justus Liebig University Giessen Prof. Dr. S. Schubert Evaluation of two sugar beet cultivars (Beta vulgaris L.) for growth and yield under drought and heat conditions A thesis submitted in partial fulfillment of the requirements for the degree of Doctor in Agriculture Submitted by Fathi Mohamed Fathi Abd-El-Motagally Assiut / Egypt 2004 Approved by the examination commission Dean: Professor Dr. Dr. h.c. W. Friedt 1- Advisor: Professor Dr. S. Schubert 2- Advisor: Professor Dr. K-H. Kogel 1- Examiner: Professor Dr. B. Honermeier 2- Examiner: Professor Dr. D. Steffens To my father in spirit whom I always remember and to my mother and dear sisters for their love and to my wife Mervat who helped me to finish this work and last to my daughter Rana that I wish her a good future. 1 Introduction..............................................................................................................................................................1 2 Objectives...................................................................................................................................................................6 3 Material and Methods ......................................................................................................................................7 3.1 Soil experiments.........................................................................................................7 3.1.1 Evaluation of the effects of K+ and Na+ fertilization on growth of two sugar beet cultivars grown under natural conditions (Experiment 1)...................................7 3.1.2 Effects of water stress and substitution of K+ by Na+ related to the growth and water use efficiency of two sugar beet cultivars grown under natural conditions (Experiment 2)................................................................................................8 3.1.3 Effect of drought and heat on the growth and sugar storage of two sugar beet cultivars grown in growt h chambers (Experiment 3)...................................................9 3.2 Nutrient solution experiments................................................................................11 3.2.1 Effects of K+ substitution by Na+ on the growth of two sugar beet cultivars grown under natural conditions (Experiment 4) .........................................................11 3.2.2 Effect of Ca2+ deficiency on the growth of sugar beet plants grown in growth chamber (Experiment 5).................................................................................................12 3.3 Analyses...................................................................................................................13 3.3.1 Water relations....................................................................................................13 3.3.2 Leaf area...............................................................................................................14 3.3.3 Plant fresh and dry weight .................................................................................14 3.3.4 Inorganic cations concentration.........................................................................14 3.3.5 Inorganic anions concentration..........................................................................15 3.3.6 a-Amino-N concentration..................................................................................15 3.3.7 Sugars concentration...........................................................................................16 3.4 Statistical analysis....................................................................................................16 4 Results........................................................................................................................................................................17 4.1 Soil culture experiments .........................................................................................17 4.1.1 Evaluation of the effects of K+ and Na+ fertilization on the growth of two sugar beet cultivars grown under natural conditions ..................................................17 4.1.2 Effects of water stress and substitution of K+ by Na+ related to the growth and water use efficiency of two sugar beet cultivars grown under natural conditions .........................................................................................................................33 4.1.3 Effect of drought and heat on the growth and sugar storage of two sugar beet cultivars grown in growth chambers.............................................................................58 4.2 Nutrient solution experiments................................................................................73 4.2.1 Effects of K+ substitution by Na+ on the growth of two sugar beet cultivars grown under natural conditions.....................................................................................73 4.2.2 Effect of Ca2+ deficiency on the growth of sugar beet plants grown in growth chamber ............................................................................................................................89 5 Discussion................................................................................................................................................................98 5. 1 Plant growth............................................................................................................98 5. 2 Water relations ......................................................................................................106 5. 3 Leaf area..................................................................................................................110 5. 4 Ion concentrations..................................................................................................112 5. 5 a-amino-N concentrations ....................................................................................116 5. 6 Sugar yield..............................................................................................................118 6 Summary...............................................................................................................................................................123 7 Zusammenfassung .........................................................................................................................................125 8 References............................................................................................................................................................132 Introduction 1 1 Introduction Sugar beet is a specialized type of Beta vulgaris cultivated for sugar production. It was developed in Europe at the end of the eighteenth century from white fodder beet, which was found to be the most suitable alternative source of sugar to tropical sugar cane. It is a biennial plant which stores up reserves in the root during the first growing season so that it is able to over-winter and produce flowering stems and seeds in the following summer. Sugar beet is a short-term crop of about 6 months grown in temperate regions of mainly the northern hemisphere for sugar production. Fresh root yields range from 50-60 tonnes/hectare, sugar concentrations of the roots average 18.7% and sugar yields are 9-11 tonnes/hectare. Estimated world sugar production is 124.4 million metric tonnes for 2000-01 of which about 30% (37.3 million tonnes) is from sugar beet (USDA, 2000). The sugar beet plant is commercially and physiologically interesting because of its ability to store sucrose at high concentrations within its root. Although the developmental physiology of the plant has been studied, little is known of the factors that govern the sugar content of the root or the physiological changes that cause it to vary (Milford and Thorne, 1973). In recent years, improvements in sugar concentration of sugar beet and development of more heat-tolerant varieties has created interest in growing sugar beet in areas currently growing sugar cane for sugar production. Potassium is an important univalent cation generally recognized to be indispensable for growth of all plants. It is characterized by high mobility in plants at all levels within individual cells, within tissues, and in long-distance transport via xylem and phloem (Marschner, 1995). Potassium, one of the major plants nutrients, is required by plants in amounts similar to or greater than N. In plants with only a moderate or even inadequate potassium supply the concentrations are highest in the younger, actively growing parts, owing to the higher metabolic activity. Potassium has various functions in turgor-related processes, such as cell extension. It is a highly mobile carrier of positive charge and it is important for enzyme activation, photosynthesis, and respiration (Huber, 1985). According to Mengel and Haeder (1977) potassium plays an important role in the transport of metabolites in the phloem, particularly with respect to transport into storage tissues. Potassium ions increase the Introduction 2 synthesis of carbohydrates with high molecular weights, also in storage tissues. Plants that accumulate large reserves of protein, carbohydrate and fats in their storage tissue therefore have high potassium requirements (Evans and Wildes, 1971; Mengel, 1999). The rate of photosynthesis is high in plants receiving adequate amounts of potassium, probably due to the positive effect of K+ ions on the transport of the products of photosynthesis, because