The effect of the time of taking side shoots on the regulation of fruit size in glasshouse-grown tomato crops

Young tomato plants were transferred to heated glasshouse compartments on 9 December at a density of 2.04 plants m(-2) and grown as a conventional long-season tomato crop. Beginning in either the third, fifth, seventh or ninth week of the year, every other plant was allowed to retain one side shoot so as to increase the effective plant density to 3.06 plants m(-2). Control crops were grown throughout at both the initial and the final densities. Two different patterns of taking the side shoots were tested in two sub-treatments: taking the required number of side shoots in four tranches over a period of six weeks was neither significantly better nor worse than taking them in two equal tranches, four weeks apart. The main effect of adding side shoots was to increase the number of fruit harvested per m(2), as compared with a control crop grown throughout at the initial density of 2.04 plants m(-2). However, these additional fruit were not harvested until at least 80 d after the first side shoots had been allowed to grow. When side shoots were taken as early as week 3, a high proportion of the marketable fruit were in the preferred size (viz. 47 to 57 mm in diameter, 50 to 90 g in weight, UK grade D) in all harvest periods. Thus, the additional side shoots enabled the crop to bear extra fruit and when the side shoots were taken early, the production of additional fruit coincided with the time when both the quantity of solar radiation incident per day and the concomitant assimilate production were increasing rapidly. Consequently, the supply of assimilates and the numbers of fruit available per m(2) were better matched for the purpose of continually producing fruit of one size. However, the presence of side shoots tended to reduce the number of marketable fruit carried on each truss. The addition of side shoots increased leaf area index and also significantly increased total fruit yield. The increased area of foliage served to shade more fruit from the heating effects of incident solar radiation and a smaller proportion of marketable fruit was downgraded to Class II in all side-shoot treatments. In general, the means of the four successive side-shoot treatments provided a graded series between those of the fixed low-density and the fixed high-density control treatments.