The genetic engineering of Lettuce (Lactuca sativa L.) requires a reliable and efficient tissue culture method. Callus induction and
direct shoot regeneration of lettuce using cotyledon explants was investigated by studying the effects of genotype, explant age and
different combinations of plant growth regulators. The landrace genotypes were collected from central (Yazd) and southwest (Ahvaz)
of Iran. Cotyledon explants of Lettuce with different explant age and genotypes were cultured on MS medium supplemented with
different concentrations of NAA and BA. The highest frequency of callus induction was obtained on 2.7 µM NAA and 4.4 µM BA
from 3-day-old explants of Yazd genotype. In addition, the effect of explant age for callus induction was a genotype-dependent
characteristic. The highest number of direct shoot regenerations was obtained at low BA concentrations (