M. Paula Watt

The status of temporary immersion system (TIS) technology for plant micropropagation

The development of temporary immersion systems (TIS) for in vitro culture, in the late 1990s heralded new and semi-automated means of micropropagation of plants for agricultural and conservation purposes. By 2005, various systems had been developed and tested and their benefits were proven with a variety of commercially-important crops such as sugar-cane, coffee, banana, and yam. Progress in the field and the adoption of these systems in subsequent years has been reviewed. Improvements on previously-developed TIS protocols for economically-important species have been reported, and this continues to attest to their benefits when compared with protocols that employ semi-solid or liquid media. Though TIS protocols have recently been developed for other species, this list is limited. On the other hand, there appears to be an increasingly great interest in TIS technology for the production of secondary metabolites and for physiological studies.

Agronomic evaluation and molecular characterisation of the acetolactate synthase gene in imazapyr tolerant sugarcane ( Saccharum hybrid) genotypes

Key messageMutagenesis had no effect on number of stalks/plot, stalk height, fibre and sucrose content of mutants. Imazapyr tolerance is likely due to a S622N mutation in the acetolactate synthase gene.AbstractThe herbicidal compound imazapyr is effective against weeds such as Cynodon and Rottboellia species that constrain sugarcane production. This study aimed to compare agronomic characteristics of three imazapyr tolerant mutants (Mut 1, Mut 6 and Mut 7) with the non-mutated N12 control after 18 months of growth, and to sequence the acetolactate synthase (ALS) gene to identify any point mutations conferring imazapyr tolerance. There were no significant differences in the number of stalks/plot, stalk height, fibre and sucrose contents of the mutants compared with the N12 control. However, Mut 1 genotype was more susceptible to the Lepidopteran stalk borer, Eldana saccharina when compared with the non-mutated N12 (11.14 ± 1.37 and 3.89 ± 0.52% internodes bored, respectively), making Mut 1 less desirable for commercial cultivation. Molecular characterisation of the ALS gene revealed non-synonymous mutations in Mut 6. An A to G change at nucleotide position 1857 resulted in a N513D mutation, while a G to A change at nucleotide position 2184 imposed a S622N mutation. Molecular dynamics simulations revealed that the S622N mutation renders an asparagine side chain clash with imazapyr, hence this mutation is effective in conferring imazapyr tolerance.

The effect of form and level of inorganic N on nitrogen use efficiency of sugarcane grown in pots

ABSTRACT To-date, assessments of nitrogen use efficiency (NUE) of sugarcane have not included the contribution of its components, nitrogen uptake efficiency (NUpE) and nitrogen utilization efficiency (NUtE). This study determined these values, based on biomass and plant nitrogen (N) content, in two four-month-old pot-grown genotypes. The treatments included six N regimes, with nitrate (NO3—N) or ammonium (NH4+-N) supplied alone, or as NO3−-N for the first 6 weeks and then NH4+-N until harvest, each as 4 or 20 mM. Regardless of the N form, NUE was higher at four than at 20 mM due to significantly higher NUpE at low N supply. The results indicated that there was luxury N uptake and preference for NH4+-N nutrition, which resulted in the highest determined NUE. There were significant differences between genotypes in biomass, morphological growth parameters, N uptake, total plant N and NUE, the latter matching previously established sucrose yield-based NUE field rankings.