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The effect of diurnal maximum/minimum (20/10 or 25/15 °C) temperatures on seed and fruit development of ‘Irwin’, ‘Kensington’ and ‘Nam Dok Mai’ mangoes ( Mangifera indica L.) was studied in a controlled-environment glasshouse. Exposure to low temperatures (20/10 °C day/night) 3 days after hand pollination significantly increased the percentage of stenospermocarpic fruit (nubbins), in which embryos were aborted at some stage during early fruit development. There were significant differences between cultivars in the percentage of nubbins produced out of the total fruit set following overnight exposure to 10 °C with 21% for ‘Nam Dok Mai’, 11% for ‘Kensington’ and 3% for ‘Irwin’. At 45 days after pollination, nubbin fruits were much smaller in size and weighed ca. 50% less than normal fruits. The lower percentage of nubbin fruits in ‘Irwin’ implies a greater adaptation to cool temperatures by this cultivar during fruit set and early embryo development.

Trees of two mono-embryonic (‘Irwin’ and ‘Sensation’) and two poly-embryonic (‘Nam Dok Mai’ and ‘Kensington’) mango cultivars were exposed to winter temperatures to induce flowering. They were subsequently transferred into controlled environment glasshouse rooms under day/night temperature regimes of 15/5, 20/10, 25/15 and 30/20°C for 20 weeks. Inflorescence development only occurred on trees that were maintained at 20/10, 25/15 and 30/20°C. Higher temperatures generally increased the inflorescence size while there was an inverse effect on the mean number of flowers per inflorescence with 619.6 at 20/10°C decreasing to 431.3 at 30/20°C. There was an inverse relationship between the length of the anthesis period and temperature. Low temperatures at 20/10°C decreased the percent hermaphrodite flowers in poly-embryonic cultivars but increased the percentages in mono-embryonic cultivars. Style length and stigma width was reduced when the trees were held at 20/10°C compared to those trees held at either 25/15 or 30/20°C. Trees of ‘Kensington’ grown at 20/10°C mainly produced flowers which had short styles (0.62 mm) and small stigmatic surfaces while ‘Nam Dok Mai’ and ‘Irwin’ trees produced some flowers which had deformed ovaries or fused ovaries. A decrease in percent hermaphrodite flowers and floral changes which occur in poly-embryonic cultivars when inflorescences develop under low temperatures (20/10°C), are likely factors contributing to their low fruit set when grown in subtropical climates.

SummaryThe effect of a constant (10, 15, 20 or 25°C) or a diurnal maximum/minimum (15/5, 20/10, 25/15 or 30/20°C) incubation temperature on in vitro pollen germination and pollen tube growth in the pistils of two poly-embryonic (‘Kensington’ and ‘Nam Dok Mai’), and two mono-embryonic (‘Irwin’ and ‘Sensation’) mango cultivars was studied. In in vitro experiments where pollen was incubated in a liquid germination medium for 24 h in darkness, little difference was found between pollen germination of mono- and poly-embryonic cultivars. Averaged over the four cultivars, 53.9% of pollen germinated at 10°C, this increased to 76.2% when the incubation temperature was increased to 15°C, thereafter up to 25°C the percentage germination remained stable but germination decreased slightly to 68.2% at 30°C. Similarly, there was no difference in percent germination between cultivars when pollen was incubated under diurnal temperature regimes. Mean pollen germination of all four cultivars was 52.3% at 15/5°C and pollen g...

To study the effect of low temperature on inflorescence and floral development of mango (Mangifera indica L.), 'Nam Dok Mai', 'Kensington', 'Irwin' and 'Sensation' trees were exposed to natural winter temperatures to induce flowering, and then transferred to controlled-environment glasshouse rooms where day/night temperature regimes of 15/5 degrees, 20/10 degrees, 25/15 degrees and 30/20 degrees C were maintained for 20 weeks. Day/night temperatures of 15/5 degrees C severely inhibited the emergence and elongation of inflorescences of all cultivars with inflorescence development only occurring on trees that were maintained at the warmer temperatures (20/10 degrees, 25/15 degrees and 30/20 degrees C). The time taken for inflorescences to reach maximum length was 15-20 days on trees held at 25/15 degrees or 30/20 degrees C but extended to 54 days on trees kept at 20/10 degrees C. Warmer temperatures generally increased the inflorescence size of all cultivars, At 20/10 degrees C, pollen viability of 'Sensation' was significantly lower than the other cultivars, but there was no significant difference between cultivars held at 25/15 degrees and 30/20 degrees C, Low temperatures caused morphological changes in styles, stigmas, ovaries and anther size in all cultivars, and changes were especially pronounced in 'Kensington'. Style length and stigma width of all cultivars were reduced when trees were held at 20/10 degrees C compared to trees field at either 25/15 degrees or 30/20 degrees C. Trees of 'Kensington' grown at 20/10 degrees C mainly produced flowers that had short styles (0.62 mm) and small stigmas (0.09 mm) while 'Nam Dok Mai' and 'Irwin' trees produced some flowers with deformed or fused ovaries. Scanning electron microscopic studies indicated that normal 'Kensington' flowers had non-symmetrical stigmas that were covered with undeveloped papillae cells. The short-styled 'Kensington' flowers (produced at 20/10 degrees C) had a much smaller receptive stigmatic area compared to normal flowers produced at 30/20 degrees C. Low temperature-induced (20/10 degrees C) changes in ovary size in 'Nam Dolt Mai' and style length in 'Kensington' flowers may contribute to low fruit set in these two cultivars when grown in subtropical climates. (C) 1999 Elsevier Science B.V. All rights reserved.

SummaryThe effect of temperature on inflorescence development and sex expression in two mono-embryonic (`Irwin' and `Sensation'), and two poly-embryonic (`Nam Dok Mai' and `Kensington') mango cultivars was studied. Trees were subjected to natural winter temperatures to induce flowering prior to transfer into controlled environment glasshouse rooms under day/night temperature regimes of 15/5, 20/10, 25/15 and 30/208C for 20 weeks. Inflorescence development did not progress when trees were held at 15/58C. Cooler temperatures (20/108C) delayed the start of anthesis (42.4.d) compared with trees grown at 25/158C (23.d) and 30/208C (16.1.d). At 20/108C, the delay in the start of anthesis was greatest for `Sensation' (55.5.d) and least for `Nam Dok Mai' (25.5.d) while at other temperatures there was little difference between cultivars. The distribution of hermaphrodite flowers within the inflorescence was independent of temperature with the highest percentage found in the apical half of the inflorescence. There ...

The viability of kangaroo paw pollen (Anigozanthos manglesii) was estimated by germination in vitro and by fluorescence and the more reliable method was then used to assess the effect of storage conditions on pollen longevity. Pollen germination was more accurate than staining for pollen of low and intermediate viability levels. Effective storage could be achieved in a number of ways depending on the duration required. Dehydrated pollen retained viability longer in storage than did hydrated pollen. Pollen from intact anthers could be stored for up to 5 weeks at room temperature with 50% or better germination provided it was stored on silica gel. Pollen isolated from anthers and stored at 2°C had reduced viability in comparison with that stored at room temperature or at ‐80°C. Pollen stored at ‐196°C lost only 5% viability after 20 weeks and presumably this would be the most suitable method for long term storage for breeding or conservation purposes.

Cold-induced photoinhibition of photosynthesis and recovery from photoinhibition in mono- and poly-embryonic mango cultivars were investigated under field and controlled temperature and light conditions. Photoinhibition, measured as a decrease in the ratio of variable to maximum chlorophyll fluorescence emission (Fv/Fm), occurred in trees growing in the field in winter and early spring. Fv/Fm ratios of all cultivars began to decrease from about 0.49 in May, reaching minimum values of about 0.33 in mid July, and then gradually increased to around 0.68 and exceeded pre-winter values by early November. A seasonal change of leaf chlorophyll content in all cultivars followed a similar pattern to the changes in Fv/Fm ratios during winter. Susceptibility to cold-induced photoinhibition and a reduction in leaf chlorophyll content were greater in poly-embryonic cultivars than in mono-embryonic cultivars. There was a positive linear relationship between the minimum air temperature the night before the measurement and the leaf Fv/Fm ratio (r(2) = 0.62-0.70). In controlled environmental experiments, poly-embryonic cultivars were also more susceptible to photoinhibition than mono-embryonic cultivars. When held at 10 degrees C and irradiated with a photosynthetic photon flux (PPF) of 450 mu mol/m(2).s, photoinhibition in detached leaves increased linearly with time. The extent of the reduction in Fv/Fm ratios induced by 6 h irradiation was 43% and 56%, respectively, in mono- and poly-embryonic cultivars. Recovery from photoinhibition in detached leaves was promoted by exposure to a PPF of 20 mu mol/m(2).s for 24 h at 20 degrees C. Negligible recovery occurred in photoinhibited leaves maintained at 10 degrees C.