Genetic and physiological evidence for the role of gibberellic acid in the germination of dormant Avena fatua seeds

Abstract

germinating soon after they fall to the soil (Naylor, 1983; Cavers et al., 1992). The combination of dormancy and Genetic and physiological data indicate that gibberellic seed longevity allows viable wild oat seeds to infest acid does not have a primary role in the regulation of agricultural soils for several years (Naylor, 1983). Better seed dormancy in wild oat (Avena fatua L.). The gibberel- understanding of seed dormancy may enhance integrated lic acid sensitivity threshold of dormant caryopses weed management strategies, allow the development of imbibed for 7 d was 1 mM. Intact dormant seeds were predictive seed germination models, and provide insights after-ripened for 0, 2, 4, 8, 12, 16, and 20 weeks at into developmental arrest in plants. 40°C and imbibed in H 2 0, 100 nM or 1 mM gibberellic A dormant wild oat seed fails to germinate under acid. The length of the after-ripening interval was conditions which normally favour germination, but afterinversely related to the mean base gibberellic acid con- ripening in warm and dry conditions releases the seed centration (the concentration resulting in 50% germina- from dormancy. Germination of dormant wild oats can tion). Thus, after-ripening, not gibberellic acid, is the be stimulated by treatment with exogenous gibberellic principal factor that regulates the release of seed dorm- acid (GA) (Adkins et al., 1986). Thus, GA may play a ancy in wild oat. F 2 caryopses (dormant◊non-dormant) role in releasing dormancy. However, there is no generally classified by germination response to progressively accepted hypothesis to explain the role of after-ripening higher gibberellic acid concentrations, were pooled or GA in the breaking of seed dormancy (Simpson, 1990). according to their gibberellic acid requirement: low, Our hypothesis is that after-ripening regulates genes or medium and high. Germination responses of the F 3 pro- gene products that control the germination response of geny from the low, medium, and high gibberellic acid dormant wild oat seeds and the activities of these factors requirement pools were regressed on to the F 2 parent are largely independent of GA. The overall objective was values, and a heritability for germination response to to characterize the role of GA in the dormancy of wild gibberellic acid, h2=0.24, was calculated. Random amp- oat seed. Specific objectives were to (1) establish the lified polymorphic DNA analysis of DNA samples from mean GA base concentrations for dormant and partially F 2 pools requiring low and high gibberellic acid concen- after-ripened caryopses, (2) determine if there is genetic trations were screened with 200 decamer primers and evidence for the role of GA in releasing dormancy, and no polymorphisms were found. The findings of this (3) screen for polymorphic DNA markers between F