Will biological control of Lantana camara ever succeed? Patterns, processes & prospects

Despite biocontrol research spanning over 100 years, the hybrid weed, commonly referred to as Lantana camara, is not under adequate control. Host specificity and varietal preference of released agents, climatic suitability of a region for released agents, number of agents introduced and range or area of infestation appear to play a role in limiting biocontrol success. At least one of 41 species of mainly leaf- or flower-feeding insects has been introduced, or spread, to 41 of the 70 countries or regions where lantana occurs. Over half (26) of these species have established, achieving varying levels of herbivory and presumably some degree of control. Accurate taxonomy of the plant and adaptation of potential agents to the host plant are some of the better predictors of at least establishment success. Retrospective analysis of the hosts of introduced biocontrol agents for L. camara show that a greater proportion of agents that were collected from L. camara or Lantana urticifolia established, than agents that were collected from other species of Lantana. Of the introduced agents that had established and were oligophagous, 18 out of 22 established. The proportion of species establishing, declined with the number of species introduced. However, there was no trend when oceanic islands were treated separately from mainland areas and the result is likely an artefact of how introductions have changed over time. A calculated index of the degree of herbivory due to agents known to have caused some damage per country, was not related to land area infested with lantana for mainlands nor for oceanic islands. However, the degree of herbivory is much higher on islands than mainlands. This difference between island and mainland situations may reflect population dynamics in patchy or metapopulation landscapes. Basic systematic studies of the host remain crucial to successful biocontrol, especially of hybrid weeds like L. camara. Potential biocontrol agents should be monophages collected from the most closely related species to the target weed or be phytophages that attack several species of lantana. Suitable agents should be released in the most ideal ecoclimatic area. Since collection of biocontrol agents has been limited to a fraction of the known number of phytophagous species available, biocontrol may be improved by targeting insects that feed on stems and roots, as well as the agents that feed on leaves and flowers.

Past, current and future approaches to mango genetic improvement in Australia

Improving the genetic base of cultivars that underpin commercial mango production is generally recognized as necessary for long term industry stability. Genetic improvement can take many approaches to improve cultivars, each with their own advantages and disadvantages. This paper will discuss several approaches used in the genetic improvement of mangoes in Australia, including varietal introductions, selection of monoembryonic progeny, selection within polyembryonic populations, assisted open pollination and controlled closed pollination. The current activities of the Australian National Mango Breeding Program will be outlined, and the analysis and use of hybrid phenotype data from the project for selection of next generation parents will be discussed. Some of the important traits that will enhance the competitiveness of future cultivars will be introduced and the challenges in achieving them discussed. The use of a genomics approach and its impact on future mango breeding is examined.

Eriophyid mites on spotted gums: population and histological damage studies of an emerging pest

A suite of co-occurring eriophyid mite species are significant pests in subtropical Australia, causing severe discolouration, blistering, necrosis and leaf loss to one of the region's most important hardwood species, Corymbia citriodora subsp. variegata (F. Muell.) K. D. Hill & L. A. S. Johnson (Myrtaceae). In this study, we examined mite population dynamics and leaf damage over a 1-year period in a commercial plantation of C. citriodora subsp. variegata. Our aims were to link the incidence and severity of mite damage, and mite numbers, to leaf physical traits (moisture content and specific leaf weight (SLW)); to identify any seasonal changes in leaf surface occupancy (upper vs. lower lamina); and host tree canopy strata (upper, mid or lower canopy). We compared population trends with site rainfall, temperature and humidity. We also examined physical and anatomical changes in leaf tissue in response to mite infestation to characterize the plants' physiological reaction to feeding, and how this might affect photosynthesis. Our main findings included positive correlations with leaf moisture content and mite numbers and with mite numbers and damage severity. Wet and dry leaf mass and SLW were greater for damaged tissue than undamaged tissue. Mites were distributed equally throughout the canopy and on both leaf surfaces. No relationships with climatic factors were found. Damage symptoms occurred equally and were exactly mirrored on both leaf surfaces. Mite infestation increased the overall epidermal thickness and the number and size of epidermal cells and was also associated with a rapid loss of chloroplasts from mesophyll cells beneath damage sites. The integrity of the stomatal complex was severely compromised in damaged tissues. These histological changes suggest that damage by these mites will negatively impact the photosynthetic efficiency of susceptible plantation species.

Identification of intersectional Corymbia hybrids based on seedling morphology improves with parental divergence

Differences in morphology have provided a basis for detecting natural interspecific hybridisation in forest trees for decades but have come to prominence again more recently as a means for directly measuring gene flow from planted forests. Here we examined the utility of seedling morphology for hybrid discrimination in three hybrid groups relevant to the monitoring of gene flow from plantings of Corymbia (L.D. Pryor & L.A.S. Johnson ex Brooker) taxa in subtropical Australia. Thirty leaf and stem characters were assessed on 907 8-month old seedlings from four parental and six hybrid taxa grown in a common garden. Outbred F1 hybrids between spotted gums (Corymbia citriodora subspecies variegata, C. citriodora subspecies citriodora and Corymbia henryi) tended to more closely resemble their maternal Corymbia torelliana parent and the most discriminating characters were the ratio of blade length to maximum perpendicular width, the presence or absence of a lignotuber, and specific leaf weight. Assignment of individuals into genealogical classes based on a multivariate model limited to a set of the more discriminating and independent characters was highest in the hybrid group, where parental taxa were genetically most divergent. Overall power to resolve among outbred F1 hybrids from both parental taxa was low to moderate, but this may not be a limitation to its likely major application of identifying hybrids in seedlots from native spotted gum stands. Advanced generation hybrids (outbred F2 and outbred backcrosses) were more difficult to resolve reliably due to the higher variances of hybrid taxa and the tendency of backcrosses to resemble their recurrent parents. Visual assessments of seedling morphology may provide a filter allowing screening of the large numbers needed to monitor gene flow, but will need to be combined with other hybrid detection methods to ensure hybrids are detected.

Eriophyid mites on spotted gums: population and histological damage studies of an emerging pest

A suite of co-occurring eriophyid mite species are significant pests in subtropical Australia, causing severe discolouration, blistering, necrosis and leaf loss to one of the region's most important hardwood species, Corymbia citriodora subsp. variegata (F. Muell.) K. D. Hill & L. A. S. Johnson (Myrtaceae). In this study, we examined mite population dynamics and leaf damage over a 1-year period in a commercial plantation of C. citriodora subsp. variegata. Our aims were to link the incidence and severity of mite damage, and mite numbers, to leaf physical traits (moisture content and specific leaf weight (SLW)); to identify any seasonal changes in leaf surface occupancy (upper vs. lower lamina); and host tree canopy strata (upper, mid or lower canopy). We compared population trends with site rainfall, temperature and humidity. We also examined physical and anatomical changes in leaf tissue in response to mite infestation to characterize the plants' physiological reaction to feeding, and how this might affect photosynthesis. Our main findings included positive correlations with leaf moisture content and mite numbers and with mite numbers and damage severity. Wet and dry leaf mass and SLW were greater for damaged tissue than undamaged tissue. Mites were distributed equally throughout the canopy and on both leaf surfaces. No relationships with climatic factors were found. Damage symptoms occurred equally and were exactly mirrored on both leaf surfaces. Mite infestation increased the overall epidermal thickness and the number and size of epidermal cells and was also associated with a rapid loss of chloroplasts from mesophyll cells beneath damage sites. The integrity of the stomatal complex was severely compromised in damaged tissues. These histological changes suggest that damage by these mites will negatively impact the photosynthetic efficiency of susceptible plantation species.

Planet of the cavendish - understanding the domination

Those seeking to bring change to cultivars sold in the banana markets of the world have encountered major difficulties over the years. Change has been sought because of production difficulties caused by banana diseases such as Fusarium wilt or a desire to invigorate a stagnant market and obtain a competitive advantage by the introduction of diversity of product. Currently the world banana scene is dominated by cultivars from the Cavendish subgroup with their production in excess of 40% of total world production of banana and plantain combined, and in most western countries Cavendish is synonymous with banana. But Cavendish production usually necessitates very regular applications of pesticides, particularly fungicides for Mycosphaerella leaf spots control. So genetic resistance to these and other diseases would be very beneficial to minimizing costs of production, as well as reducing health risks to banana workers and the general population and minimizing impacts on the environment. In recent years, the overall market sales of some crops, such as tomatoes, have increased by providing diversity of cultivars to consumers. Can the same be done for banana? Perhaps a better understanding of how we have arrived at our current situation and the forces that have shaped our preference for Cavendish will allow us to plan more strategic crop improvement research which has enhanced chances of adoption by the banana industries of the world. A scoping study was recently undertaken in Australia to determine the current market opportunity for alternative cultivars and provide a roadmap for the industry to successfully develop this market. A multidisciplinary team reviewed the literature, surveyed the supply chain, analyzed gross margins and conducted consumer and sensory evaluations of 'new' cultivars. This has provided insight on why Cavendish dominates the market, which is the focus of this paper, and we believe will provide a solid foundation for future progress.

Description of vectors of arboviruses of livestock in Northern Australia

The project aimed to detect exotic C"11coides species recently established in northern Australia and to map the distribution of Cullcoid"' bi'e\, nth'sis and C. 1.1-, oddiill Western Australia and NT. Between February 1990 and June 1992, collections were Inade throughout Cape York Peninsula, Nortlierii Territory and northern and central Western Australia. Six previously unreported species were collected. These species an'e considered unlikely to be recent jininigrants and seein to pose little threat as potential arboviiT. Is vectors. C. woddi was restricted to coastal 1101tlierii Qld, the northernmost areas of NT and the northern Kiinberley region in WA. 111 NT C. bi'evitai'sis was collected as far soutli as Katlierine. In WA it was collected throughout the Kiinberley and in the Pilbara region ill all area bounded by Nullagine, KanTatha and 300km nortli of Carnalvon. C. bi'evilcii'sis reinains tlie only Guncoide. s species of known 11npoitance as a vector of livestock an'boviruses to extend into Inajor sheep-grazing areas. Generally, CUIicoides distributions in northern Australia between 1990 and 1992 were coinparable but not identical to those defined ill surveys conducted ill tlie 1970's and 1980's. Species distributions were not static and will continue to fluctuate witli variation ill rainfall. . .