GENETIC INCOMPATIBILITY AND OFFSPRING QUALITY IN THE TRISTYLOUS PLANTLYTHRUM-SALICARIA (LYTHRACEAE)

The purpose of this study was to determine the incompatibility relatio nships among the three different morphs of the tristylous plant Lythru m salicaria, and to assess whether there are fitness consequences to b reakdown in incompatibility. Twenty-four different types of pollinatio ns were performed using all possible combinations of anthers and stigm as. These can be grouped as legitimate pollinations (pollinations from the appropriate anther level of a compatible morph), illegitimate int ermorph pollinations (pollinations from the inappropriate anther level of a compatible morph), intramorph pollinations (pollinations between individuals of the same morph), and self pollinations. Legitimate pol linations produced significantly more seed than illegitimate intermorp h pollinations, intramorph pollinations, and self pollinations. The di fference between legitimate and illegitimate intermorph pollination su ccess is particularly interesting because pollen for these crosses cam e from the same genetic individual. Pollination types also differed in offspring quality. In the rare examples where progeny were produced b y illegitimate intermorph pollinations, the progeny did not have signi ficantly lower values for seedling growth traits compared to legitimat e progeny. Seedlings produced by self pollinations had significantly l ower values for four out of six seedling growth traits measured. Compa risons of legitimate and self progeny traits indicate that inbreeding depression for most traits is close to or above 0.5. The finding that some seed were produced from illegitimate pollinations suggests that t here is variation among individuals in incompatibility. There was a si gnificant effect of parental morph type on the probability of breakdow n in incompatibility with the midstyled maternal parents setting more seed from illegitimate pollinations.