INCOMPATIBILITY IN ABUTILON ‘HYBRIDUM’

P andey , K. K. (John Innes Hort. Inst., Bayfordbury, Hertford, Herts, England.) Incompatibility in Abutilon ‘Hybridum.’ Amer. Jour. Bot. 47(10): 877–883. Illus. 1960.— Abutilon ‘Hybridum’ (2 n = 16) has a one‐locus multiallelic gametophytic ( Nicotiana‐type ) system of self‐incompatibility. Five S alleles were distinguished among the 4 plants studied. However, the incompatibility behavior in many crosses is obscured by the modifying effects of a number of other genes non‐allelic to the S locus. Since A . ‘Hybridum’ is a cultivar which has arisen through hybridization of 2 or more Abutilon species, it is suggested that the mixed polygenic background of the “species” is not adjusted to the proper functioning of the S gene system. Although most of the plants in the 6 groups studied were highly self‐incompatible in the early and mid season, many of them showed pseudo‐self‐compatibility late in the season. Seed‐set in illegitimate crosses also increased late in the season. Colchicine‐induced autopolyploidy brought about part or full self‐compatibility. After incompatible pollination, pollen germination appeared to be normal but a considerable proportion of the tubes were inhibited in the stigmatic region of the style; tubes which penetrated the style usually burst between ⅕ and ⅓ of the distance from the stigma to the base, a phenomenon not found in any of the other gametophytic‐type species yet studied.