SUMMARYMethods of adjustment for two-dimensional spatial heterogeneity of grain yield were investigated for 224 UK cereal trials. The methods used row and column ‘block’ analysis of plot yields and neighbour analysis based on first differences of plot yields. In 36% of trial analyses for block models and 30% for neighbour models the average variance of variety differences was reduced by more than 10% compared with the better of the one-dimensional row or column models. Compared with complete blocks, 2-D block analysis had a mean efficiency of 153% whereas the conventional 1-D block analysis (by rows) had a mean efficiency of 127%. Similarly, 2-D neighbour analysis had a mean efficiency of 159% whereas the 1-D analysis had a mean efficiency of 137%. Recently, general statistical methods have been developed for two-dimensional design and analysis; their wider use should lead to major gains in the precision of variety trials.

The total glycoalkaloid concentration of dormant (non-sprouted) and sprouted potato tubers cv Pentland Hawk was measured following 13 days continuous illumination (250 pmol m -' s-photosynthetically active radiation) using high-performance liquid chromatography. Comparisons were made of the influence of three sources of illumination : high-pressure mercury, high-pressure sodium and fluorescent tube type warm white. Glycoalkaloid concentrations in both dormant and sprouted tubers increased over 13 days illumination regardless of the form of illumination used. Glycoalkaloid concentrations accumulated with time in dormant and sprouted tubers exposed to sodium and fluorescent light but fluctuated in those exposed to mercury light. Dormant tubers were more sensitive to illumination than sprouted tubers regardless of light souce. Fluorescent light was associated with maximum glycoalkaloid synthesis in dormant tubers; while sodium light enhanced glycoalkaloid synthesis in sprouted tubers to the greatest extent. Mercury light weakly elicited glycoalkaloid synthesis in both sets of tubers. Exposure of dormant tubers to continuous light altered the ratio of a-chaconine to a-solanine irrespective of illumination source.

Seven different types of starch based fat substitutes were used for the production of set-style yogurt from reconstituted skimmed milk powder. The yogurt milks contained 14. 0-15.8% total solids, 7.3-9.1% carbohydrates, 5.3-5.6% protein and 1.0-1.2% ash. The fat content of all the batches was 0.1% except the control (1.5%), which was made with anhydrous milk fat. Yogurts made with P-Fibre 150 C and 285 F contained 0.5 and 1.1% fibre respectively. Decrease in whey syneresis and increase in firmness in all the yogurts were observed during 20 days' storage at 5°C. Yogurt made with P-Fibre 150 C had the least amount of whey syneresis. Scanning electron microscopy and transmission electron microscopy revealed subtle differences in the microstructure of set-style yogurts due to the different starch based fat substitute used. 'Spikes' and 'hair' like structures were evident around the casein micelles in the milk base. They were lightly stained when compared with the caseins. Their detection in the yogurt was very difficult and only P-150 C and P-285 F substitutes were visualized whereas the others could not be detected even when their concentration was increased to 5%. Yogurt made with Lycadex' 100 was more porous and had slightly larger void spaces filled with milk serum. The use of a higher concentration (5%) of.fat substitutes increased the firmness, but impaired the flavour and mouth feel of the yogurts.

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