Item

The effect of root confinement and calcium stress on the physiology, morphology and cation nutrition in tomatoes (Lycopersicon esculentum Mill.)

Al-Sahaf, F. H.
Date
1984
Type
Thesis
Fields of Research
ANZSRC::070601 Horticultural Crop Growth and Development
Abstract
Five pot experiments using nutrient solution culture were conducted in a glasshouse where the day and night temperatures were 25±5°C and l8±3°C respectively. Tomato (Lycopersicon esculentum Mill.) plants were trained as a single main stem except those in experiment IV where the lateral shoots were left to grow. For the purpose of this study different glasshouse tomato cu1tivars (Eurovite, Nemarex, Lincross and Angela) were used. To provide different degrees of confinement to the root system, plants were range of container sizes (0.025, 0.05, 0.1, 2.0 l) and compared with nonconfined plants (4.5 l). Other treatments involved releasing the roots after a period of confinement in experiment II, and calcium deficient treatments in combination with root confinement treatments in experiment V using radioactive calcium. The dry weights of roots, stems, leaves and fruits, total leaf surface area, leaf number, root length and root number were measured as well as uptake of potassium, calcium and magnesium. Growing plants under root confinement conditions retarded the growth of vegetative parts in all cultivars. The dry weight of leaves, stems and roots was reduced while that of fruits was not affected. Root confinement was also associated with an increase in the shoot:root and top:root ratios compared with the non confined plants. Releasing the roots after a period of confinement increased the dry weight of the vegetative parts with no effect on the dry weight of fruits. The shoot:root ratio in confined-released plants remained as high as the continuously confined plants although the roots were not under physical confinement particularly when they were released to 2.0 l container. It appears that the effect of root confinement is not a simple physical stress to the roots but also involves some physiological effects through the changes in pattern of the distribution of dry matter between the root and the shoot. During the vegetative stage of growth root confinement increased the proportion of dry weight of stems and reduced that of leaves compared with the non confined plants. After the transition to the reproductive phase, plants showed a new pattern of dry weight distribution mainly brought about by the growth of fruits. The increase in the proportion of dry weight allocated to the top of confined plants was not equally shared by all top components. The proportion of the stems and fruits increased while that of leaves decreased. Physical confinement of the roots reduced the dry weight of lateral shoots but had no effect on the relative partitioning of dry weight between the main stem and the lateral shoots. Root confinement changed the morphology of the leaves. The total and average leaf surface area of confined plants were smaller than those of non confined plants. The concentration of chlorophylls a and b in the leaves of confined plants, in particular Eurovite increased, and the leaves became thicker or denser. These changes in the leaf morphology may have increased the photosynthetic rate of the unit leaf surf ace area and ultimately increased its production of dry matter. Root morphology also changed in response to physical confinement of the root. Confined root systems were more branched, and when the confined roots were released to larger containers the number of lateral roots increased rapidly resulting in a greater ratio of root number:root length compared with those of continuously confined and non confined roots. Confined plants took up smaller amounts of K, Ca or Mg compared with the non confined plants. But when the mineral(s) uptake was expressed on the basis of the amount of mineral(s) absorbed by unit root length or root branch, confined plants showed a greater ability to absorb mineral(s) than non confined plants. The concentration of K in the leaves was not affected by root confinement treatments whereas the concentrations of Ca and Mg were lower in the leaves of confined plants than those whose roots were not confined. However, the lower concentrations of Ca and Mg in leaves of confined plants were higher than the optimum concentration suggested for tomato leaves by Ward (1963). The concentration of minerals in the fruits was the same in all treatments. Root confinement interfered with the translocation of Ca from the root to plant tops. Fractionation of root Ca showed that the majority of Ca was in the acid soluble form (Ca-oxalate, phosphate and carbonate). The possible mechanisms for this accumulation of Ca in the confined roots were suggested. Angela plants were more efficient in utilizing K while those of Eurovite were efficient in utilizing Ca. Root confinement increased the efficiency of utilization of K and Ca in both cultivars. It is concluded therefore that efficiency of mineral utilization is sensitive to environmental as well as to genetic factors. Both calcium treatments (+Ca and -Ca) resulted in a remobilization of radioactive calcium previously deposited in the plant tissues. However, the amounts of Ca remobilized were very small and could not prevent the development of calcium deficiency symptoms in different plant organs, particularly in the non confined plants. Confined plants under calcium deficiency conditions delayed the initiation and development of calcium deficiency symptoms on the leaves and fruits by at least five days compared with the corresponding plants with non confined roots. It is concluded that root confinement could be used as a technique to reduce the risk of sudden shortage of calcium supply in the growing medium. Blossom end rot (BER) in tomato fruits is directly related to the lower concentration of Ca in the fruits, and any factor(s) which may directly or indirectly affect the Ca uptake and/or translocation could enhance the development of this disorder. Angela plants under calcium deficiency conditions showed the symptoms of BER earlier and more severely than similar plants of Eurovite. These variations between the two cultivars were related to the ability of the cultivar to remobilize the previously deposited Ca from different plant tissues.
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