| An apetalous mutant of Ethiopian mustard (Brassica carinata A. Braun) was studied to determine both its floral development and the inheritance of the trait. It has been speculated that apetally will benefit the plant by eliminating dried petals which, when they stick to the plant, are infection sites for the pathogen Sclerotinia sclerotiorum (McClean, 1958; Kruger, 1974).; Scanning electron and light microscopy of developing flower buds of petalous and apetalous types indicated that the sequence of floral development was sepals, androecium and gynoecium simultaneously, and lastly the corolla. Until corolla initiation, the development of apetalous and petalous types was similar. Petal development appeared to be in delicate balance with the internal and external environment, manifested by apetalous flowers on petalous plants and petalous flowers on apetalous plants and also by the frequent presence of rudimentary petals in apetalous types.; Reciprocal crosses of two plants of each of the apetalous and petalous parents provided F(,1) plants that were all similar to the petalous parent, indicating the absence of cytoplasmic effects and the presence of dominant gene action. Studies of F(,2), F(,3) and F(,1) and F(,2) progeny of testcrosses indicated that two major genes governed the degree of petally. The presence of variable numbers of partially petaled plants in segregating populations complicated the studies and indicated the presence of an unidentified number of modifying genes. No true-breeding partially petaled type was found, possibly because such types are heterozygous but perhaps also because such types are very sensitive to the internal and external environments.; It is assumed that the ancestral species of B. carinata, B. nigra and B. oleracea each contributed a gene that governed petally. |
