Delayed flowering in pineapples (Ananas comosus (L.) Merr.) caused by co-suppression of the ACACS2 gene

Natural flower induction is a major pineapple industry problem. It usually occurs when shortening days and low temperatures give raise to increased ethylene production in the leaf tissue and plant stem apex which in turn stimulates flowering. Natural flowering fruit matures 4 to 6 weeks ahead of the normal summer harvest resulting in the need for extra harvest passes and considerable yield losses. Ethylene is produced through the sequential action of ACC synthase and ACC oxidase. Our team has cloned an ACC synthase gene from pineapple (ACACS2), which is expressed in meristems and activated under the environmental conditions that induce flowering in nature. Genetic constructs have been produced containing ACACS2 in sense orienta¬tion to induce silencing of the host gene in the plant by co-suppression mechanisms. Two independent lines of transgenic plants have been produced and field trials have been conducted in Queensland for four years in order to study the characteristics of the transgenic lines. We have identified a group of transgenic plants demonstrating inherited flowering delay and confirmed co-suppression of the ACACS2 gene due to methylation.

Adventitious root formation in cuttings of Backhousia citriodora F. Muell: 1. Plant genotype, juvenility and characteristics of cuttings

Backhousia citriodora is a commercially valuable Australian woody species that has a reputation for being recalcitrant in forming adventitious roots from cuttings. A study was carried out to determine whether maturation and plant genotype influenced rooting. It also tried to establish whether genotypic differences in rooting ability were related to characteristics of the cutting material. The rooting of cuttings in B. citriodora declines after maturation and is strongly influenced by genotype. The cutting characteristics of actively growing axillary buds, wide stems and mature leaves are associated with rooting and survival but not related to genotype. Furthermore, the 8-24 weeks required by B. citriodora to form roots from cuttings makes it difficult to distinguish between the characteristics that increase rooting and those characteristics that enhance survival. A subsequent disbudding experiment demonstrated that axillary buds per se have an inhibitory effect on rooting. This suggests that the presence of actively growing axillary buds are an indication of overall growth and condition of the stock plant unrelated to the formation of adventitious rooting. The effects of other cutting characteristics on rooting are also discussed. (C) 2004 Elsevier B.V. All rights reserved.

Identifying and discriminating among lucerne cultivars using plant morphological characters

The use of morphological data obtained from field (plot test) and glasshouse trials to identify and discriminate among four Iranian and two New Zealand lucerne (Medicago sativa L.) cultivars was investigated, following guidelines established by the International Union for the Protection of New Varieties of Plants (UPOV) for cultivar registration and the Organisation for Economic Co-operation and Development (OECD) for seed certification. Data were collected for terminal leaflet length, width and ratio, angle of stem growth, date of first flowering, stem height at first flowering, flower colour, cutting recovery height, and disease scores. None of these characters were sufficient to identify or discriminate among the six cultivars. The results indicate a need to find cost-effective and efficient laboratory techniques to enhance the assessment of distinctness of lucerne cultivars (UPOV) and for determining cultivar purity for lucerne seed certification (OECD).