The effect of phosphite on meiosis and sexual reproduction

The fungicide phosphite was found to reduce pollen fertility in Australian and exotic species. In the perennial Dryandra sessilis the reduction was evident for a year after treatment with 2.5-10 gL-1 phosphite sprayed to run off. Pterochaeta paniculata, an annual, showed reduced pollen fertility in flowers that opened 16-30 days after spraying. The horticultural species Pelunia hybrida and Tradescantia virginiana also displayed reduced pollen fertility after phosphite treatment. Pollen mother cells of Tradescantia had a significant percentage of abnormal first and second divisions and micronuclei in the microspores for up to one month after spraying. There was evidence that phosphite induced premature tapetum breakdown in Pelunia but not Tradescantia. The percentage of abnormal meiotic cells and the frequency of premature tapetum breakdown appeared insufficient to account for the high levels of pollen infertility observed after phosphite treatment

The effect of the fungicide phosphite on pollen germination and fertility

The fungicide phosphite (previously known as phosphonate) is a cheap and effective means of controlling Phytophthora cinnamomi Rands (the fungus that causes jarrah dieback) (1,2). To date, studies have focused on the effect and mechanism of action of phosphite on P. cinnamomi and its effects on agricultural species and native Western Australian plants which are under threat from P. cinnamomi. The fungicide appears to have minimal phytotoxic effects on the vegetative parts of the plant (3). The phytotoxic effects of phosphite on flowers and reproduction has not been studied in detail

Low success of controlled pollination in Eucalytpus marginata (jarrah)

The success of controlled pollination techniques was investigated for clones and wild trees of Eucalyptus marginata. The number of pollen tubes in the style was used as a measure of pollination success. The stigma was receptive from 3-11 days after anthesis, but it appeared that stigmatic receptivity may be highest from 4-7 days after anthesis. Flowers were isolated using aluminium foil squares, and fresh pollen was found to be more effective for pollination success than processed pollen. Results were inconclusive comparing self- to cross-pollination success, and no difference was found comparing pollination success in clones and wild trees. However clones generally tended to flower earlier than the wild trees, whatever their origins, and very few mature fruits resulted from any controlled pollinations in jarrah clones. Clones also produced a lower proportion of mature capsules from the flowers produced (Wheeler 2004)

Pollination techniques, fruit loss and pollen viability in Eucalyptus marginata (Jarrah)

Techniques were evaluated to develop an effective controlled-pollination technique for jarrah (Eucalyptus marginata). Pollination success was scored by counting pollen tubes in squashed styles. The most effective method to isolate the flowers after emasculation was to wrap each in a twist of aluminium foil. Pollen application was best when several freshly-picked, newly-opened flowers were wiped across each receptive stigma. Stigmas were receptive from 3-6 days after anthesis and most pollen tubes were observed pollination in the middle of the flowering season. Very few mature fruits resulted from any controlled-pollution technique. Bud, flower and fruit-loss rates under natural conditions were recorded (in five clones and five wild trees) and 0-13% of buds remained on the trees to develop into fruits. The percentage of pollen germination from different trees was very variable. Pollen was most fertile in the middle of the flowering season, environmental conditions had little effect. Fresh pollen in anthers was more fertile than pollen separated using a fine sieve

Mitosis and meiosis in plants are affected by the fungicide phosphite

To investigate the effect of the fungicide phosphite on mitosis, Vicia faba and Petunia hybrida were sprayed with 0, 2.5, 5 and 10 g/L phosphite, and V. faba was also soil drenched using 5 g/L phosphite. In V. faba, phosphite increased the number of abnormal mitotic cells in root tips of both sprayed or soil drenched plants. The effect was evident 12 h after treatment and persisted for 14 days in young V. faba plants, 21 days in mature V. faba and 14 days in P. hybrida. Phosphite did not affect the proportion of cells undergoing mitosis in either species, or the karyotype of V. faba. Phosphite reduced pollen fertility in plants of P. hybrida and Tradescantia virginiana treated with 0 to 20 g/L phosphite, but the effect was most marked in P. hybrida where pollen fertility was zero for a period between 7 and 14 days after treatment. Pollen fertility was still reduced 21 days after treatment. Phosphite increased the number of abnormal meiotic cells at all stages in T. virginiana microspores but the numbers were insufficient to totally account for the observed drop in pollen fertility

Effect of the fungicide phosphite on pollen fertility of perennial species of the Eucalyptus marginata forest and northern sandplains of Western Australia

The fungicide phosphite was shown to affect pollen fertility in a range of perennial species from the south-west of Western Australia. Phosphite was applied to perennial species of the jarrah (Eucalyptus marginata) forest by spraying to run-off with 2.5, 5 and 10 g L–1 phosphite in either autumn or spring. Pollen fertility of Dryandra sessilis was reduced by phosphite for up to 35 and 60 weeks after spraying in spring or autumn, respectively. Trymalium ledifolium pollen fertility was reduced by phosphite 38 and 61 weeks after spraying in spring or autumn, respectively. Lasiopetalum floribundum was less affected with a reduction in pollen fertility being observed for up to 3 weeks after spraying in spring. Other perennial understorey species of the jarrah forest, Adenanthos barbiger, Boronia cymosa, Hovea elliptica and Phyllanthus calycinus were also shown to have reduced pollen fertility after treatment in autumn or spring, as did Comesperma calymega, Eremaea astrocarpa and Hibbertia hypericoides, species of the northern sandplains when sprayed in summer

The effect of phosphite on the sexual reproduction of some annual species of the jarrah (Eucalyptus marginata) forest of southwest Western Australia

Phosphite is a cost-effective fungicide used to control the pathogen Phytophthora cinnamomi which is damaging the diverse flora of the southwest of Western Australia. Three annual species of the southwest jarrah (Eucalyptus marginata) forest of Western Australia (Pterocheata paniculata, Podotheca gnaphalioides and Hyalosperma cotula), were studied to determine the effect of the fungicide phosphite on the species' reproduction. Phosphite at concentrations of 2.5, 5 and 10 g L-1 reduced pollen fertility of Pt. paniculata when plants were sprayed at the vegetative stage. Pollen fertility of all three species was reduced when plants were sprayed at anthesis with 10 g L-1 phosphite. Seed germination was reduced by phosphite in Pt. paniculata and H. cotula when plants were sprayed in the vegetative stage. Phosphite when sprayed at anthesis at a concentration of 5 g L-1 reduced seed germination of H. cotula. Phosphite at concentrations of 5 and 10 g L-1 killed a proportion of plants from all three species and up to 90% of Po. gnaphalioides plants. The frequent application of phosphite, therefore, may reduce the abundance of annual plants in this ecosystem

Comparisons of phosphite concentrations in Corymbia (Eucalyptus) calophylla tissues after spray, mist or soil drench applications with the fungicide phosphite

The fungicide phosphite was applied to 4- and 8-month-old Corymbia (Eucalyptus) calophylla (marri) seedlings, by spraying to run-off with 0.25, 0.5 and 1% phosphite (2.5, 5 and 10 g/L a.i., respectively), misting with 10, 20, and 40% phosphite (100, 200 and 400 g/L a.i., respectively) or applying a 1% phosphite (10 g/L a.i.) soil drench. The phosphite concentrations in plant tissues were determined by High Performance Ion Chromatography analysis, 7 days after treatment. Phosphite concentrations found in the plant tissues were higher than previous published results. Phosphite concentrations were generally higher in the root tips than in mature roots, and in shoot tips compared to stems and leaves. Highest concentrations were recorded in root tips of soil drenched plants. When phosphite concentrations in shoot apices were compared, spray to run-off at 0.5% gave a comparable concentration to a 10% mist treatment and the soil drench, while a 1% spray was comparable to the 20% and 40% mist treatment. When phosphite concentrations i n root apices were compared, spray to run-off at 0.5% and 1% gave comparable concentrations to a 10 or 20% mist treatment. All treatments except 0.25%, 0.5% spray and soil drench caused some phytotoxicity on the foliage