A thermosensitivity index for Lupinus albus L.

Phenology and plant architecture of spring lupin Lupinus albus L. vary with early thermal environment, which dramatically affects seed maturation and production. This study was conducted to develop and evaluate an index to qu antify the relative differences among a selection of genotypes to "warm" an d "cold" temperatures during early development. Seedlings of 27 lupin acces sions and cultivars were incubated at 5 and 24 degrees C for 3 wk and then grown to maturity in the greenhouse. The number of mainstem vegetative node s at maturity were counted and used as the basis for developing an index of thermosensitivity. The simple difference between mainstem vegetative node numbers from seedlings incubated at 24 and 5 degrees C provided a means for quantifying thermosensitivity and identifying thermoneutral genotypes. Sig nificant simple difference values ranged from 4.69 to 20.33 and were not si gnificant for cv 'Start', An alternative standardized index was developed t hat allowed for comparisons within genotypes among gears.