Self- and cross-fertility relationships in Lotus corniculatus L. and Lotus tenuis Wald. et Kit

1. Cytological and morphological studies have demonstrated that the two varieties of birdsfoot trefoil called broad and narrow leaf are probably two different species. The narrow leaf type, designated as L. tenuis by Dawson has six pairs of chromosomes and the broad leaf type, designated as L. corniculatus has 12 pairs. 2. Self sterility within the two types was measured by means of controlled self-pollination. In both types high sterility was obtained as measured by percentage pod set and number of seeds per pod. 3. A high percentage pod set and large number of seeds per pod were obtained from crosses between plants within each of the two types. 4. Failure in cross fertility was obtained for five plants of L. tenuis, but sufficient data are not available to conclude that failure was due to similarity in sterility alleles. 5. Complete failure of seed set was obtained in crosses between the two types. Stimulation resulting in pod formation was found in crosses when L. tenuis was used as the female parent but not in the reciprocal. These results were explained on the basis of chromosome balance of the two parents. 6. Differences in morphological characters observed in the two species were in general accord with those of diploid and artificially produced autotetraploid plants. 7. To test the possible phylogenetic relationship between the species, the chromosome number of L. tenuis was doubled with colchicine. The autotetraploid L. tenuis did not resemble L. corniculatus in leaf or stipule shape. Similarities of flowers and pollen grains are undoubtedly present. Crosses between the autotetraploid L. tenuis, L. tenuis and L. corniculatus showed a high percentage of pod set in crosses between L. corniculatus X autotetraploid L. tenuis but in no case was viable seed obtained. 8. Failure to obtain seed set may not be final evidence that L. corniculatus could not have arisen as an autotetraploid of L. tenuis. Chromosome differentiation after the natural autotetraploid was formed may have sufficiently separated this species from an experimentally produced autotetraploid to render them cross-sterile.