Segregation distortion and linkage analysis of hand pollinated avocados

Various cultivars of avocado (Persea americana MIll.) were hand pollinated to produce 138 seedings in 29 families with from one to 19 progeny. Because the probability of premature fruit drop is normally very high (about 1000 to 1), some of the hand pollinated progeny that abscissed were rescued with embryo culture. Leaf samples of parents and seedlings were assayed for nine genes that specify seven polymorphic enzyme systems—glutamate oxaloacetate transaminase (GOT), leucine aminopeptidase (LAP), malate dehydrogenase (MDH), phosphoglucose Isomerase (PGI), phosphoglucose mutase (PGM), cathodal peroxidase (CPX) and those phosphate isomerase (TPI)—to document the parentage and for further analyses. Families with fewer than four progeny were eliminated from the data sets and several were combined for single-gene segregation and linkage analyses. Some single-gene segregation ratios among the 106 remaining progeny in 10 families were significantly distorted. A linkage analysis indicated that the genes Got1 and Got2 are very tightly linked but those specifying the LAP2, PGI1 and 2, MDH1, PGM1, CPX0 and TPI1 Isozyme sets assorted independently. Eight of the avocado's 12 chromosomes now have Isozyme gene markers.