OCCURRENCE AND INHERITANCE OF RESISTANCE TO POWDERY MILDEW (OIDIUM-LYCOPERSICI) IN LYCOPERSICON SPECIES

Among 146 accessions of Lycopersicon pimpinellifolium, 132 of L. escul entum var. cerasiforme and 53 of L. peruvianum screened for resistance to powdery mildew, caused by Oidium lycopersici, a wide variation in reactions was found. Two plants of L. esculentum var, cerasiforme acce ssion LA-1230 were resistant. One resistant symptomless plant of acces sion LA-1230, designated LC-95, produced homozygous resistant progenie s. LC-95 was crossed with cv. Marmande (susceptible parent) and F-1, F -2 and backcrosses to the resistant and the susceptible parents were d erived. These genotypes were grown in glasshouses at 23 degrees C and 95-100% RH and inoculated with O. lycopersici. The F1 plants were susc eptible. F-2 and backcross segregations fitted the hypothesis of a sin gle recessive gene which is here designated ol-2.