VEGETATIVE INCOMPATIBILITY IN NEUROSPORA - ITS EFFECT ON HORIZONTAL TRANSFER OF MITOCHONDRIAL PLASMIDS AND SENESCENCE IN NATURAL-POPULATIONS

We have investigated the horizontal transfer of two mitochondrial plas mids and the Kalilo senescence phenotype in the fungus Neurospora with out the use of heterokaryon-forcing markers. The Kalilo senescent stat e was only transferred between fully-compatible N. crassa strains, but not between strains differing at any of the loci het-c het-d, het-e o r mating-type. However, the linear plasmid ka1DNA and the circular pla smid Han-2 were transferred following incompatible vegetative interact ions. Our data suggest that vegetative incompatibility due to allelic differences at het-e is more effective in preventing transfer than tha t due to het-d, het-e or mating-type. Based on these observations we h ave developed a novel test for assessing vegetative incompatibility be tween Kalilo and non-Kalilo field isolates of N. intermedia. In this p rocedure combinations of Kalilo and non-Kalilo field isolates of N. in termedia were grown together and tested for senescence. Compatibility is inferred if the young non-Kalilo strain dies along with the senesce nt Kalilo strain, whereas incompatibility is inferred when the Kalilo strain dies without imposing its senescent state onto the non-Kalilo s train. Our results suggest that each of the nine Kalilo strains tested is incompatible with each of 20 non-Kalilo isolates from the same N. intermedia population of the Hawaiian island of Kauai. However, the ob served incompatibility did not completely prevent cytoplasmic exchange , and in several cases plasmid transfer could be detected.