J. agric. Sci., Camb. (1980), 95, 25-27 With 2 plates Printed in Great Britain The use of radiography in studies of pod growth in oil-seed rape (Brassica napus L.) BY P. M. PECHAN*, J. A. BASHFORDt AND D. G. MORGAN* Department of Applied Biology* and Department of Anatomy^, University of Cambridge (Received 10 December 1979) SUMMARY The technique of radiography has been used successfully to provide permanent records of mature and developing pods in oil-seed rape. X-ray films and photographs of the pods show clearly the shape and size of the pods as well as the numbera, positions and to some extent the size of the seeds within them. 25 INTRODUCTION The numbers of pods and the numbers and sizes of the seeds they contain are the components which determine seed yield in oil-seed rape. In order to interpret variations in seed yield it is therefore necessary to study the factors which regulate pod development and to examine inter- and intra- inflorescence variations at different stages after anthesis (Allen & Morgan, 1972, 1975; Tayo & Morgan, 1975, 1979). In a study to compare the growth, development and yield of Maris Haplona and Bronowski the technique of radiography has been applied to provide a permanent record of pods in the terminal and axillary inflorescences. Soft X-rays (long wave X-radiation) gave sharper definitions of the pods and their contents but the exposure times required were much longer than those with hard X-rays (short wave X-radiation) which were therefore used for the large numbers of ripe pods at final harvest. The soft X-ray technique was employed on the unripe pods. The procedures followed in both instances and the results obtained are described and discussed. MATERIALS AND METHODS The plants of both Maris Haplona and Bronow- ski from which pods were taken were sown on 7 March 1978 and transplanted 21 days later into John Innes Compost No. 2 in 12-5 cm diameter pots standing on trays of moist sand in a glass- house. At harvest the plants were separated into the component parts of the roots, stems and pods with their pedicels and placed into separate cello- phane bags and labelled. The procedures then followed for radiation with hard and soft X-rays were as follows. Radiation with hard X-rays. After drying in the cellophane bags at 120 °C selected pods, every fifth from the terminal inflorescence, every fourth from axillaries 1-4 inclusive and every third from other axillaries, were chosen for radiography and taken in their bags to the building housing the X- ray machine. In a room adjacent to this, for each plant in turn, the pods from the different inflor- escences were laid out and arranged separately and systematically on an envelope containing a non-screen X-ray film (Kodak Industrex C) (Plate 1). The envelope was labelled with the variety, plant and inflorescence number from which the pods were taken. Restricted bench space dictated that only six plants could be so arranged before proceeding with the radiography itself. At this stage one envelope with its pods was trans- ferred to the adjacent room with the X-ray machine (General Radiological Electronic Mark 2 with Mullard MRA 150 tube). Lead markers were placed over the labelling and the envelope centred under the X-ray beam using a plumb-bomb, care being taken not to displace any of the pods in so doing. So as to reduce any heel-effect the envelope was orientated so that one of its long sides was next to the cathode and the other to the anode. Exposure to the X-rays was carried out at 40 kV, 200 mA for 0-2 sec at focus film distance of 102 cm as pre- viously determined using similarly dried pods. The above procedure was repeated for the five remain- ing envelopes, and, when all had been exposed and returned to the ante-room, the pods were replaced into the labelled cellophane bags and returned to the laboratory. The time taken from the removal and the return of the pods to the respective 0021-8596/80/2828-3650 $01.00 © 1980 Cambridge University Press