Effects of rootstock and nitrogen fertiliser on postharvest anthracnose development in Hass avocado

These rootstock and nitrogen fertiliser studies confirmed that rootstock race can significantly affect the development of postharvest disease and mineral nutrient accumulation in Hass avocado fruit. When Hass (Guatemalan race) was grafted to seedling Velvick (West Indian race) rootstock, the severity and incidence of anthracnose in fruit were significantly reduced by up to 64 and 37%, respectively, compared with seedling Duke 6 (Mexican race) rootstock. Stem-end rot was also influenced by rootstock in some seasons, and significant reductions (up to 87%) in the severity and incidence of stem-end rot were recorded in Hass fruit from Velvick compared with Duke 6 rootstock trees. These improvements in postharvest diseases were associated with significantly lower concentrations of nitrogen and potassium, higher concentrations of calcium and magnesium, lower ratios of nitrogen:calcium and higher ratios of calcium + magnesium:potassium in Hass leaves and fruit from Velvick compared with Duke 6 rootstock trees. Altering the rate of nitrogen fertiliser had minimal impact on postharvest disease development. However, in one season, reducing the rate of nitrogen fertiliser to nil significantly reduced the concentration of nitrogen in the fruit skin, decreased the nitrogen:calcium ratio and significantly reduced the severity and incidence of anthracnose in Hass fruit from both Velvick and Duke 6 rootstock trees. The form of nitrogen fertiliser (ammonium compared with nitrate) applied to the trees did not significantly affect the postharvest disease susceptibility of Hass avocado fruit on either Velvick or Duke 6 rootstock. The Guatemalan race rootstocks, Anderson 8 and Anderson 10, were also found to be superior to the Mexican race rootstock, Parida 1, for reducing anthracnose severity. This again, was associated with a better balance of mineral nutrients (significantly lower nitrogen:calcium and higher calcium + magnesium:potassium ratios) in the fruit. This rootstock effect, however, was only observed in the first season of a 3-year experiment, possibly because of a better balance between vegetative growth and fruit production in Parida 1 in the latter two seasons. Significant positive correlations between anthracnose severity and fruit skin nitrogen:calcium ratios were evident across all experiments.

Relative host plant species use by the lantana biological control agent Aconophora compressa (Membracidae) across its native and introduced ranges

Aconophora compressa Walker (Hemiptera: Membracidae) was released in 1995 against the weed lantana in Australia, and is now found on multiple host plant species. The intensity and regularity at which A. compressa uses different host species was quantified in its introduced Australian range and also its native Mexican range. In Australia, host plants fell into three statistically defined categories, as indicated by the relative rates and intensities at which they were used in the field. Fiddlewood (Citharexylum spinosum L.: Verbenaceae) was used much more regularly and at higher densities than any other host sampled, and alone made up the first group. The second group, lantana (Lantana camara L.: Verbenaceae; pink variety) and geisha girl (Duranta erecta L.: Verbenaceae), were used less regularly and at much lower densities than fiddlewood. The third group, Sheena’s gold (another variety of D. erecta), jacaranda (Jacaranda mimosifolia D. Don: Bignoniaceae) and myoporum (Myoporum acuminatum R. Br.: Myoporaceae), were used infrequently and at even lower densities. In Mexico, the insect was found at relatively low densities on all hosts relative to those in Australia. Densities were highest on L. urticifolia, D. erecta and Tecoma stans (L.) Juss. ex Kunth (Bignoniaceae), which were used at similar rates to one another. It was found also on a few other verbenaceous and non-verbenaceous host species but at even lower densities. The relative rate at which Citharexylum spp. and L. urticifolia were used could not be assessed in Mexico because A. compressa was found on only one plant of each species in areas where these host species co-occurred. The low rate at which A. compressa occurred on fiddlewood in Mexico is likely to be an artefact of the short-term nature of the surveys or differences in the suites of Citharexylum and Lantana species available there. These results provide further incentive to insist on structured and quantified surveys of non-target host use in the native range of potential biological control agents prior to host testing studies in quarantine.

Fast FIR Algorithms for the Continuous Wavelet Transform From Constrained Least Squares

New algorithms for the continuous wavelet transform are developed that are easy to apply, each consisting of a single-pass finite impulse response (FIR) filter, and several times faster than the fastest existing algorithms. The single-pass filter, named WT-FIR-1, is made possible by applying constraint equations to least-squares estimation of filter coefficients, which removes the need for separate low-pass and high-pass filters. Non-dyadic two-scale relations are developed and it is shown that filters based on them can work more efficiently than dyadic ones. Example applications to the Mexican hat wavelet are presented.

Interference and management of parthenium: The world's most important invasive weed

Parthenium (Parthenium hysterophorus L.) is one of the most aggressive herbaceous weeds of the Asteraceae family. It is widely distributed, almost across the world and has become the most important invasive weed. Comprehensive information on interference and control of this devastating species is required to facilitate better management decisions. A broad review on the interference and management of this weed is presented here. Inspite of its non-tropical origin, parthenium grows quite successfully under a wide range of environmental conditions. It is spreading rapidly in Australia, Western Africa, Asia, and Caribbean countries, and has become a serious weed of pastures, wastelands, roadsides, railwaysides, water courses, and agricultural crops. The infestations of parthenium have been reported to reduce grain and forage yields by 40–90%. The spread of parthenium has been attributed to its allelopathic activity, strong competitiveness for soil moisture and nutrients, and its capability to exploit natural biodiversity. Allelochemicals released from parthenium has been reported to decrease germination and growth of agronomic crops, vegetables, trees, and many other weed species. Growth promoting effects of parthenium extracts at low concentrations have also been reported in certain crops. Many pre- and post-emergence herbicides have been evaluated for the control of parthenium in cropped and non-cropped areas. The most effective herbicides are clomazone, metribuzin, atrazine, glyphosate, metsulfuron methyl, butachlor, bentazone, dicamba, and metsulfuron methyl. Extracts, residues, and essential oils of many allelopathic herbs (Cassia, Amaranthus, and Xanthium species), grasses (Imperata and Desmostachya species), and trees (Eucalyptus, Azadirachta, Mangifera species, etc.) have demonstrated inhibitory activities on seed germination and seedling growth of parthenium. Metabolites of several fungi, e.g., Fusarium oxysporun and Fusarium monilifonne, exhibit bioherbicidal activity against seeds and seedlings of this weed. Intercropping, displacement by competitive plant species like Cassia species, bisset bluegrass, florgen blugress, buffelgrass, along with the use of biological control agents like Mexican beetle, seed-feeding and stem-boring weevils, stem-galling and leaf-mining moth, and sap-feeding plant hopper, have been reported as possible strategies for the management of parthenium. An appropriate integration of these approaches could help minimize spread of parthenium and provide sustainable weed management with reduced environmental concerns.

The host range of three biotypes of Dactylopius tomentosus (Lamarck) (Hemiptera: Dactylopiidae) and their potential as biological control agents of Cylindropuntia spp. (Cactaceae) in Australia

The host range of two newly imported biotypes of Dactylopius tomentosus and their potential as biological control agents of Cylindropuntia spp. were investigated. A third biotype (imbricata) of D. tomentosus previously released in Australia to control C. imbricata was also screened to determine if it will feed on other species of Cylindropuntia occurring in Australia. Efficacy trials were conducted to evaluate the ability of the biotypes to retard the growth or kill those plant species supporting development of four or more individuals in the host test trials. The host range of the three biotypes of D. tomentosus was restricted to the genus Cylindropuntia. However, the biotypes showed varying degrees of specificity within this genus. The imbricata biotype was the only biotype to develop on Australian C. rosea provenances, albeit with a range of developmental success on all C. rosea provenances tested. The Spanish provenance supported the highest development success followed by Grawin (NSW), Lorne Station (NSW) while the least preferred was the Mexican provenance. The rosea and cholla biotypes were unsuitable candidates to control C. rosea in Australia. However, the efficacy trials showed that the cholla biotype had a high impact on four of the eight naturalised Cylindropuntia species in Australia. This biotype established rapidly and the sustained feeding of one fecund female and her progeny killed potted plants of C. imbricata and C. fulgida at week 18. This biotype has the potential to be an effective agent against C. fulgida, C. imbricata, C. kleiniae and C. tunicata and, as a consequence, an application seeking its release in Australia has been lodged.