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Fibre formation in hemp (Cannabis sativa L.) is a dynamic process. In order to follow this process, the chemical composition of the hemp stem was studied during plant development using the acid and neutral detergent fibre and lignin methods. Additionally, near infra-red spectroscopy was carried out. To predict the chemical composition of the stem samples partial least square (PLS) analysis was carried out. The developed PLS models can predict the level of %ADF and %NDF in the hemp bast and core samples. For %ADL, the models are only suited for either core or bast tissues and can not be used for both tissues simultaneously.

In order to assess the potential of Crambe hispanica, either in breeding programmes of C . abyssinica or as an oilseed crop in itself, 36 accessions of C. hispanica (29 of var. hispanica and 7 of var. glabrata) were grown in a greenhouse and evaluated for morphological characteristics, earliness, plant habit, seed characteristics and fatty acid composition . Four lines of C. abyssinica were included for reference . The 29 accessions of var . hispanica showed significant variation for all observed characteristics . Besides morphological characteristics, large variation was found for earliness, number of primary branches, seed yield, 1000 seed weight and volume, and linoleic, linolenic and erucic acid content . Morphological characteristics, earliness and plant habit did not show any high correlations with seed characteristics or fatty acid composition, except for seed hull (pericarp) mottling, which was related to a high oil and erucic acid content . The seven accessions of var. glabrata showed little variation . The large genetic variation in combination with promising figures for several characteristics, found in C . hispanica, may be useful in breeding programmes of the oilseed crop C . abyssinica, for which the available genetic variation is limited : Prospects of selection for high-erucic acid genotypes are discussed . Compared to C. abyssinica, both botanical varieties of C. hispanica are characterized by a cordate shape of the basal leaves, lack of seed retention and a lower DNA content. Plants of var. glabrata differed from var. hispanica in a sparsely hispid upper leaf surface and round stems and branches covered with a waxy layer . These clear differences and lack of success in intercrossing both varieties of C. hispanica strongly suggest that their taxonomic classification should be reconsidered .

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Genotypic differences for growth stage dependent expression of partial resistance to barley powdery mildew have been identified on the basis of two components of resistance in the glasshouse and the pattern of epidemic development in the field.Differences for infection frequency and proportion of sporulating colonies were highly significant between the 16 genotypes investigated at four stages of plant development in the glasshouse. Both resistance components were significantly correlated mutually (r = 0.73 to 0.86) and with the infection level on leaves developed at comparable growth stages in the field (r = 0.52 to 0.73). The infection level of seedlings in the glasshouse was significantly correlated with the infection level of the leaves of the first until the third node in the field (r = 0.70 to 0.73). Adult plant resistance was predominantly expressed at the uppermost leaf. A clear genotype x growth stage interaction was apparent for infection level; some genotypes showed partial resistance predominantly at the seedling stage and others predominantly at the adult plant stage.

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