Variation over time and environments in resistance to Erysiphe graminis hordei in samples from a barley germplasm collection

Summary Twenty carnation genotypes of diverse origin were planted in September and were kept under an 8h day and a light intensity of 15 W/m² visible radiation in a phytotron from 30 November to 24 February. Long photoperiods (24 h; LD) were applied in December-January for 25 days. In addition to flowering dates of individual shoots, records wer kept on shoot development (number of visible leaf pairs) on four dates: (1) six weeks after pinching, (2) at the beginning of the LD treatment in December, (3) when plants were transferred from the phytotron to the glasshouse in February and (4) at the time of flowering of individual shoots.The genetic variation in number of visible leaf pairs on each of these dates, in relation to shoot position and rate of unfolding of leaf pairs, was analysed.On the basis of these analyses, the between and within-genotype variation in time of flowering, yield distribution and LD response could be, at least partly, related to variation in the above-mentioned parameters. It was established that relevant genetic variation exists in (1) the initial development of the axillary bud from which a primary shoot is produced after pinching; (2) the rate of leaf unfolding; (3) the minimum number of leaf pairs required for flower initiation and (4) the within-plant variation in the above three characters in relation to shoot position.