Lantana (Lantana camara) Seed Bank Dynamics: Seedling Emergence and Seed Survival.

Seed persistence is poorly quantified for invasive plants of subtropical and tropical environments and Lantana camara, one of the world's worst weeds, is no exception. We investigated germination, seedling emergence, and seed survival of two lantana biotypes (Pink and pink-edged red [PER]) in southeastern Queensland, Australia. Controlled experiments were undertaken in 2002 and repeated in 2004, with treatments comprising two differing environmental regimes (irrigated and natural rainfall) and sowing depths (0 and 2 cm). Seed survival and seedling emergence were significantly affected by all factors (time, biotype, environment, sowing depth, and cohort) (P < 0.001). Seed dormancy varied with treatment (environment, sowing depth, biotype, and cohort) (P < 0.001), but declined rapidly after 6 mo. Significant differential responses by the two biotypes to sowing depth and environment were detected for both seed survival and seedling emergence (P < 0.001). Seed mass was consistently lower in the PER biotype at the population level (P < 0.001), but this variation did not adequately explain the differential responses. Moreover, under natural rainfall the magnitude of the biotype effect was unlikely to result in ecologically significant differences. Seed survival after 36 mo under natural rainfall ranged from 6.8 to 21.3%. Best fit regression analysis of the decline in seed survival over time yielded a five-parameter exponential decay model with a lower asymptote approaching −0.38 (% seed survival = [( 55 − (−0.38)) • e (k • t)] + −0.38; R2 = 88.5%; 9 df). Environmental conditions and burial affected the slope parameter or k value significantly (P < 0.01). Seed survival projections from the model were greatest for buried seeds under natural rainfall (11 yr) and least under irrigation (3 yr). Experimental data and model projections suggest that lantana has a persistent seed bank and this should be considered in management programs, particularly those aimed at eradication.

LC/MS/MS analysis of the daphnane orthoester simplexin in poisonous Pimelea species of Australian rangelands.

Liquid chromatography/mass spectrometry (MS)/MS was used to analyse toxins in P. trichostachia, P. simplex subsp. continua, P. simplex subsp. continua and P. elongata samples (flowers, seeds, branches, main stem, leaves and roots) collected from various locations in Queensland, Saskatchewan and New South Wales, Australia. Simplexin was the major analyte in all taxa, with varying minor levels of huratoxin. Simplexin levels in P. trichostachia and P. elongata were higher (580 and 540 mg/kg in flowering foliage, respectively) than in P. simplex (255 mg/kg). Levels of huratoxin were higher in P. simplex (relative to simplexin) than in P. trichostachia or P. elongata. P. simplex flower heads and roots contained similar simplexin levels, with very small amounts of toxins detected in branches, stems and leaves. In P. trichostachia, simplexin levels were high in flower heads but low in the the other plant parts. The simplexin levels in aerial parts were generally higher from the pre-flowering to the flowering stage, decreasing towards the post-flowering stage; similar trends were recorded for P.elongata samples collected from a site near Bollon and P. trichostachia samples collected from a site near Jericho (both sites in Queensland). The simplexin concentration in roots was much less variable. Flowers and seeds had much higher simplexin levels than the foliage. The breakdown of the toxin in litter was more rapid compared to seeds under the same weathering conditions. Unlike the results from the litter samples, no significant decrease occurred in seed samples after 18 months of exposure.

An outbreak of Potato spindle tuber viroid in tomato is linked to imported seed

In 2011, an outbreak of the quarantine-regulated pathogen Potato spindle tuber viroid (PSTVd) occurred in a commercial glasshouse-grown tomato crop in Queensland, Australia. Phylogenetic studies showed that the genotype of this isolate grouped in a cluster of PSTVd genotypes from tomato and Physalis peruviana, and exhibited an interesting mutation (U257→A) that has previously been linked to lethal symptom expression in tomato. Transmission studies showed that the viroid could be mechanically transmitted from crushed fruit sap, but not from undamaged fruits. A low rate of asymptomatic infection was determined for plants in the affected glasshouse, demonstrating the efficacy of using symptoms to detect PSTVd infections in tomato. No PSTVd infections were detected in solanaceous weeds located outside of the infected glasshouse, excluding them from playing a role in the viroid epidemiology. Monitoring and subsequent testing of new tomato crops grown in the facility demonstrated successful eradication of the pathogen. A trace-back analysis linked the outbreak of PSTVd to an infected imported tomato seed-lot, indicating that PSTVd is transmitted internationally through contaminated seed

Infection of mungbean seed by Macrophomina phaseolina is more likely to result from localized pod infection than from systemic plant infection

The ubiquitous fungal pathogen Macrophomina phaseolina is best known as causing charcoal rot and premature death when host plants are subject to post-flowering stress. Overseas reports of M.phaseolina causing a rapid rot during the sprouting of Australian mungbean seed resulted in an investigation of the possible modes of infection of seed. Isolations from serial portions of 10 mungbean plants naturally infected with the pathogen revealed that on most plants there were discrete portions of infected tissue separated by apparently healthy tissue. The results from these studies, together with molecular analysis of isolates collected from infected tissue on two of the plants, suggested that aerial infection of aboveground parts by different isolates is common. Inoculations of roots and aboveground parts of mungbean plants at nine temperaturexsoil moisture incubation combinations and of detached green pods strongly supported the concept that seed infection results from infection of pods by microsclerotia, rather than from hyphae growing systemically through the plant after root or stem infection. This proposal is reinforced by anecdotal evidence that high levels of seed infection are common when rainfall occurs during pod fill, and by the isolation of M.phaseolina from soil peds collected on pods of mungbean plants in the field. However, other experiments showed that when inoculum was placed within 130mm of a green developing pod and a herbicide containing paraquat and diquat was sprayed on the inoculated plants, M.phaseolina was capable of some systemic growth from vegetative tissue into the pods and seeds.