LEAF AND FLOWER INITIATION IN POTATO (SOLANUM-TUBEROSUM) SPROUTS AND STEMS IN RELATION TO NUMBER OF NODES AND TUBER INITIATION

Experiments were conducted in controlled environment cabinets and in the field at Cambridge, UK, in 1987-90 and in Valencia, Spain 1989-90 with several varieties of potato. The initiation of leaf primordia and flowers was recorded in sprouts stored for long periods at 13-degrees-C with constant illumination and in sprouts exposed to different photoperiods and periods of cold storage. In field experiments, the effects of a wide range of planting dates, differences in physiological age, the time at which seed tubers were sprouted and of imposing an 8 h photoperiod were investigated. More than 40 leaf primordia were initiated in the sprouts of Home Guard and Arran Comet stored at 13-degrees-C, but, in other varieties, fewer leaves were initiated. Flowers were initiated in the sprouts of some varieties. In field-grown plants, the number of nodes to the first flower differed between varieties and was increased by ageing sprouts before planting. Stems from physiologically old seed of all varieties had more nodes below ground than young seed but the number of aerial leaves to the first flower increased only slightly with increasing physiological age. The number of aerial leaves to the first flower was lower and less variable in Estima than in Maris Piper. Initiation of flowers usually occurred before tuber initiation and within two weeks of emergence but was earlier in some varieties than others. There was little influence of photoperiod on the time to initiation of flowers and tubers in most experiments but, with low levels of radiation, flowering was completely inhibited in the variety Maris Piper.