Toward pollen sterility in German chamomile ( Matricaria chamomilla )–Conventional breeding approaches of cytoplasmic/genic male sterility and chemical emasculation

Pollen sterility (PS) in mother lines is crucial for hybrid crossings in plant breeding. 21 di‐ (2 x ) and tetraploid (4 x ) accessions of the hermaphroditic chamomile were screened for spontaneous, thermic or gametocide induced PS. Two crossing trials with the diploid accessions ' Bona ' (BON) and ' Hungary 2 ' (HUN2) should specify maternally inherited cytoplasmic male sterility (CMS). Progeny thereof showed increased PS. BON as mother (BH) entailed means of 30 and 22% PS, versus 8% and 20% after reciprocal crossings. Backcrosses of BH with HUN2 in paternal and maternal direction revealed increasing mean PS (24% and 32%), without verification of CMS. A split plot design of 100 individuals treated with four chemical gametocides analyzed PS, seed set, germination rate and whole plant damage. Tri‐iodobenzoic acid caused the highest PS (43%). Progeny of two plants (2 x , 4 x ) with degenerated anthers without pollen, showed 100% PS either in tetraploid F 1 and F 2 (4% and 11%) or in diploid F 2 and F 3 (26% and 23%). High temperature (30/28°C day/night) decreased the male fertility to some extent.