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The motive of the author to embark upon the research reported here was the need to develop new concepts to approach the problem of crop losses, and eventually the problem of their prevention by means of disease control and plant breeding. The introduction of ecophysiology as an approach, explained above, was the first result. An ecophysiological treatment of processes like growth and development of plants in health and disease necessitates adjustments of current thoughts on experimental techniques and on organization in research (Van der Wal and Cowan, 1974).In order to measure plant or aegricorpus responses concurrently with environmental factors in climate chamber and field experiments during periods Of months, a great variety of instruments had to be bought, modified, or devised. The climate chamber had to be adjusted to allow for high light intensities with a view to growing wheat under conditions approximating those of early summer in the Netherlands; the yield of the spring wheat 'Kolibri' was c. 0.5 kg.m -2, which is nearly equivalent to the average field production of the country. Regulations for the prevention and control of contamination by aphids and mildew without any use of chemicals were issued after detailed experimentation (Van der Wal, unpubl.). Several instruments have been developed, usually with the help of others; this has led to two publications (Schurer and Van der Wal, 1972; Tegelaar and Van der Wal, 1974). These efforts resulted in the experimental designs described in the appendix. Field experiments, conducted in the same period as the climate chamber experiments reported here, will be published later. It is felt that the techniques to record growth of pathogens are still inadequate.The results reported in the appendix show that the 'state' of the plant at the time of infection is a major determinant of the plant's future behaviour, which plant breeders and pathologists can express in terms of resistance and tolerance. The conceptual framew

Results obtained and hypotheses that have been put forward to integrate them, are summarized in this section.1. Studies of chromosome association in F 1 hybrids Triticum aestivum X Secale cereale with and without chromosome 5B and in the presence or in the absence of B-chromosomes of rye, showed, as expected. that in the absence of chromosome 5B a high degree of pairing was observed. The presence of B-chromosomes only slightly reduced chromosome association, whether chromosome 5B was present or not.2. In F 1T. aestivum X S. cereale hybrids, at 20°C, a significant increase in the mean chiasma frequency per cell in nulli 5D + B's hybrids was observed. This interaction of genes carried by B-chromosomes of rye with genes carried by A-chromosomes was only detected in the absence of chromosome 5D of wheat.3. A substantial rise in chromosome association was also observed in an inter-varietal T. aestivum hybrid Chinese spring X Lindström when chromosome 5D of wheat was absent and B-chromosomes of rye were present, both at 20°C and at 10°C. This was mainly due to a shift in the relative numbers of rod and ring. bivalents, since the number of univalents was very low and similar. No change in chromosome association due to B-chromosomes was detected when 5D was present.4. Bayliss and Riley (1972) found in nullisomic 5D plants of T. aestivum a higher frequency of ring bivalents (with more than two chiasmata) than in disomic 5D plants. being however, the values of mean chiasmata per cell very similar in both plants. Mello-Sampayo and Miller (1979) detected a reduction in the number of ring bivalents with an increasing dosage of the long arm of chromosome 5D. These data together with our results led us to suggest the existence of a desynaptic gene in chromosome 5D which directly interacts with gene(s) carried by B-chromosomes of rye.5. It was also found that in F 1 hybrids T. aestivum X S. cereate , in the absence of chromosome 5D, synchronization within PMC's was reduced, which w

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The data for this study have been gathered in Ivory Coast during the period 1977-1980.The first purpose of the study was a description of the traditional okra cultivation and, in particular, the evaluation of the local planting material in order to determine its potential for crop improvement.The second purpose of the programme was a study of the agronomic limitations in the case of intensive cultivation and in what ways such problems might be solved.The inventories of vegetables offered for sale in 18 important regional markets (cf. chapter 2) proved that okra is one of the most important fruit vegetables in Ivory Coast. The young fruits are sold either fresh or dried. Especially in the western part of the country okra is also an important leaf vegetable.The indigenous vegetables are traditionally grown in the fields of foodcrops. From the inventory of a large number of these fields in different parts of the country, it appeared that vegetable growing is particularly important in yam and groundnut fields. Yam and groundnut are usually grown at the beginning and at the end of the rotation respectively. In whatever region or type of field, okra is one of the most common plants in this mixed cropping.The popularity of this vegetable is even more clearly shown in the bibliographical data on vegetable consumption in Ivory Coast.Contrary to the ample bibliographical information on okra cultivation in the subtropics, much less is published on its cultivation in the tropics, especially in the (sub)equatorial zones. General recommendations for intensive cultivation in Ivory Coast have been embodied by SODEFEL ("Société de Développement de la Production des Fruits et Légumes").In our experimental programme, we have been able to study in detail the local planting material (chapter 4), the dry matter production and its distribution (chapter 5), ecological influences (chapter 6), the mineral nutrition (chapter 7), cultural practices (chapter 8), pests and diseases (chapter 9) a