Anatomical Study for Critical High Temperature on the Anthesis Day to Inhibit Passion Fruit Set

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(1)Trop. Agr. Develop. 64 （4）：171 － 177，2020. Anatomical Study for Critical High Temperature on the Anthesis Day to Inhibit Passion Fruit Set Hiroshi MATSUDA1, 2, Hirokazu HIGUCHI1, *, Masanori OKABE1, and Tatsushi OGATA3 Graduate School of Agriculture, Kyoto University, Kitashirakawa, Sakyo, Kyoto 606-8502, Japan. 1. Present affiliation: Tropical Agriculture Research Front, Japan International Research Center for Agricultural Sciences, Maezato. 2. Kawarabaru, Ishigaki, Okinawa 907-0002, Japan Tropical Agriculture Research Front, Japan International Research Center for Agricultural Sciences, Maezato Kawarabaru,. 3. Ishigaki, Okinawa 907-0002, Japan Abstract Passion fruit flowers were pollinated at various temperatures range from 28–42° C, and the fruit set and the number of seeds were recorded to determine the critical high temperature which negatively affected to the fruit set. Other flowers which were detached just before anthesis were incubated and pollinated also at various temperatures. The germination of the obtained pollen was tested on agar medium, and pollen-tube growth in pistil was observed anatomically to determine the thermal response of pistil receptivity. Fruit set was more than 90% when daytime temperatures were regulated at 28–34° C. Fruit set decreased at temperatures ≥38° C. Flowers did not set fruit at 42° C. The number of seeds reduced at temperatures ≥36° C. Pollen tubes reaching the embryo sac were observed within 24 h after pollination in all detached flowers which were incubated at 28–32° C. Whereas at incubation temperatures ≥34° C, pistil morphological disorder was observed in all detached flowers, and pollen tubes did not reach the embryo sac within 24 h. Pollen germinated on the stigma without elongation into the style, even 24 h after pollination at 40° C. Germination percentages of the pollen, which was obtained from detached flowers incubated at 28–40° C, did not vary on agar medium. Although pistils on a detached flower were damaged by high temperatures ≥34° C, those growing under orchard condition did not show any symptom of damages at 36° C. Key words: Fertilization, Heat stress, Passiflora, Pollen germination, Pollen tube growth, Thermal response. Introduction. ‘Summer Queen’ was reportedly high at temperatures below 30° C and decreased markedly at temperatures. Passion fruits are in the subtropical fruit species in-. above 35° C (Shimada et al., 2017). Pollen germination of. digenous to tropical highlands (Morton, 1987). The fruit. ‘Summer Queen’ decreased at higher temperatures than. set tends to decrease in hot summer when cultivating. 38° C (Matsuda and Ogata, 2020). However, thermal. in higher latitudes including subtropical and temperate. response of anther dehiscence and pistil receptivity is. zones. When flowers of ‘Summer Queen’, one of the. still unknown.. major cultivars in Japan, opened on a day of maximum. Thermal response of floral organs in tropical and. temperature exceeding 34° C, fruit set ratio was low even. subtropical fruit trees has been clarified by regulating. with hand-pollination (Matsuda and Higuchi, 2020).. sectional temperatures surrounding floral organs to. Fruit set of purple passion fruit, a related species, was. avoid the secondary effects by plant body responses.. also reported to decrease by higher temperatures than. Cherimoya pollen germinability decreased when pre-. 30° C (Utsunomiya, 1992). In subtropical to temperate. anthesis night temperatures ranged below 14° C and. zones, air temperatures often exceed 30° C during sum-. above 27° C (Matsuda et al., 2016); cherimoya pollen-. mer. In a greenhouse, temperatures in early summer. tube growth and fertilization was inhibited and the fruit. often get higher, especially around noon when passion. set decreased when post-pollination night temperatures. fruit pollination is generally performed.. were below 8° C (Matsuda et al., 2015); fruit set of. The direct damages by high temperatures to. ‘Monthong’ durian was inhibited by night temperatures. the floral organs and the secondary effects from. below 15° C (Kozai et al., 2014), while stable fruit set of. physiological responses of plant body can be considered. ‘Chanee’ was observed even at 15° C (Kozai et al., 2017).. as factors of decreasing fruit set. Photosynthesis of. In this study, first, sectional temperatures surrounding passion fruit flower on the plant were regu-. Communicated by M. Yamamoto Received Mar. 23, 2020 Accepted Jul. 7, 2020 * Corresponding author higuchi@kais.kyoto-u.ac.jp. lated within 28–42° C at 2° C increments to clarify the critical high temperature which causes fruit set failure. Flowers were pollinated under regulated temperature conditions, and fruit set percentage and the number of.

(2) 172. Trop. Agr. Develop. 64 （4）2020. seed set were then recorded. Second, detached flowers. was self-pollinated using a paint brush, and closed. were incubated under various temperature conditions. again. In passion fruit, pollen tubes reached embryo. and pollinated as well to determine thermal response. sac and fertilization was observed within 18 h after pol-. of pistil receptivity, followed by pollen germination test.. lination (Ishihata et al., 1987). To avoid the effect of the. Pollen-tube elongation in the pistil was then observed. lower nighttime temperature during tube elongation,. anatomically to examine inhibition mechanisms of pol-. temperatures inside box were regulated constantly at. lination by high temperature.. 28° C during 1800–0900 h (i.e., until the next-day morn-. Materials and Methods. ing). Immediately after these temperature regulations, the box was removed and the pollinated flowers were. Twenty-four, 1-year-old ‘Summer Queen’ hybrid. replaced to grow at the atmospheric temperatures in. passion fruit plants (Passiflora edulis Sims × P. edulis. the greenhouse. Fifteen–twenty flowers were regulated. f. flavicarpa Deg.) grown in a greenhouse at Kyoto. in each daytime-temperature condition. The daily maxi-. University, Japan (35.0° N, 135.8° E) were used for this. mum and minimum temperatures in the greenhouse. study. Air ventilation fans were automatically operated. (Fig. 1) were recorded during the experiment, using a. when temperatures in the greenhouse exceed 30° C. The. hand-made forced ventilation thermometer installed at a. plants had been propagated by cutting in September. height of 1.5 m above the ground in the same manner as. 2016 and transplanted to 7-L pots with a mixture of 50%. described by Matsuda and Higuchi (2020).. bark compost and 50% weathered granite soil (v/v) in. Swollen ovaries of larger diameter than 2 cm were. April 2017. Plants were trimmed to a single stem each,. observed at 1 week after pollination and were regarded. trained vertically to a height of 1.8 m, and then trained. as set fruits, and fruit set percentage was calculated for. horizontally. After allowing the horizontally trained vine. each temperature treatment. Every young fruit was then. to elongate along a horizontal circle of which diameter. immediately removed. The removed fruits were then. was the same as the pot diameter, terminal buds were. vertically cut in tri-section along sutures using a scalpel,. pinched. Two newly emerged young axillary vines per. and the number of seeds per fruit was recorded.. plant were then grown as fruit-bearing vines spirally downward along the cylindrical outer circumference. Experiment 2: Effect of high temperatures on. thereof. Fruit-bearing vines reached to the ground, and. pollen. terminal buds were pinched. Plants were fertilized three. receptivity. germinability. and. pistil. times a week from April–May with a 0.5-L nutrient solu-. Flowers with the bearing stem were detached from. tion containing 6.0 mM NH4NO3, 6.0 mM (NH4)2SO4, 2.0. each vine just before anthesis at 0900 h during June–July. mM KNO3, 1.0 mM Ca(NO3)2, 1.5 mM K2HPO4, 3.0 mM. 2017. Detached flowers were then inserted into a glass. CaCl2, 2.0 mM MgSO4, and 1.0 mM K2SO4 (Niwayama. vial which contained liquid culture medium comprising. and Higuchi, 2019), and one time per every sunny day. 10% sucrose, 0.1% chemical fertilizer (Garden Meister;. after June with a 0.5-L 500-fold (w/v) dilution of water-. nitrogen: phosphorus: potassium [N:P:K] = 6:10:5;. soluble fertilizer (Yoekidoko No. 3 N:P:K = 15:15:15;. HYPONeX Japan Co., Ltd., Osaka, Japan) as described. OAT Agrio, Tokyo, Japan) per plant (Matsuda and. by Kondo et al. (2010). Immediately after insertion of. Higuchi, 2020).. the flowers, they were incubated at 28, 30, 32, 34, 36, 38, or 40° C for 3 h to attain anthesis. After the anthesis,. Experiment 1: Effects of daytime high temperatures on fruit set. flowers were self-pollinated from 1200–1300 h using a paint brush, and then incubated again at the same tem-. Flowers on the anthesis day were tagged daily. peratures. Pistils were sampled from flowers at 24 h after. at 0800 h during June–July 2017. These flowers were. pollination, and fixed in Copenhagen mixture (ethanol:. enclosed in styrene foam boxes equipped with tempera-. glycerol: distilled water = 10: 1: 8, v/v/v; Bridson and. ture regulating units using Peltier effect (Matsuda et al.,. Forman, 1989).. 2015). One flower or less than three flowers only were. Fixed pistils from each flower were vertically cut in. enclosed in a styrene foam box. Daytime temperatures. trisection along sutures into three pieces, so that each. inside the box were then regulated during 0900–1800 h. piece includes one fragment of tri-sectioned ovary and. at 28, 30, 32, 34, 36, 38, 40, or 42° C. Temperature devia-. one style. After rinsing with distilled water overnight,. tion between the target and measurement was ±0.2° C.. these pieces were dehydrated in an alcohol series. The box was opened around noon, while flower inside. and embedded in paraffin wax in the same manner as.

(3) 173. Matsuda et al.: High temperature inhibition of passion fruit set. 40. were sectioned longitudinally at 16 μm. The sections. 35. were stained with a 0.1% aniline blue solution containing 0.1 M K2PO4, and pollen-tube elongation in the pistil was observed under fluorescence microscope (CyScope, Partec GmbH, Saarbrüchen, Germany). The position of the longest pollen-tube tip in each piece was recorded by dividing pistil portion into stigma, style, upper part of ovary, middle part of ovary, funicle and micropyle, and embryo sac (Fig. 2). These incubation and observation were conducted for 5 flower replications for each temperature treatment. In total, the position of the longest. Air temperature (° C). described by Matsuda et al. (2011). Embedded pistils. 30 25 20 15 Maximum Minimum. 10 5 0 01-Jun. 20-Jul 01-Jul 10-Jul 31-Jul Day-month Fig. 1. Daily maximum and minimum air temperatures in the greenhouse of Fig. 1.‘Summer DailyQueen’ maximum andplants minimum temperatures in passion fruit from Juneair to July, 2017. 10-Jun. 20-Jun. the greenhouse of ‘Summer Queen’ passion fruit plants from June to July, 2017.. pollen-tube tip was illustrated for 15 pistil pieces in each treatment.. temperatures 28–42° C, fruit set was high at 28–34° C. To testify the pollen germinability, pollen was. and fruit set percentage was higher than 90% (Fig. 3A).. collected from the detached flowers just before hand-. Although fruit set tended to decrease at 36° C, fruit set. pollination, which were incubated at 28–42° C above.. percentage at 36° C was ≈80% which did not significantly. Collected pollen was placed on ≈1 mL of 2% w/v agar. differ from that at 28–34° C. Fruit set percentage signifi-. medium containing 30% w/v sucrose, 200 ppm w/v. cantly decreased (<60%) at temperatures ≥38° C. Flowers. boric acid, 1000 ppm w/v Ca(NO3)2·4H2O, 200 ppm. did not set fruit at 42° C even when hand-pollination was. w/v MgSO4·7H2O, and 100 ppm w/v KNO3 (Brewbaker. performed. The number of seeds was larger at 28–34° C. and Kwak, 1963; Ishihata, 1983). The agar medium. similarly to fruit set percentage, and the fruits contained. was prepared on a microscope glass slides, the pollen. ≈200 seeds per fruit (Fig. 3B). The number of seeds was. was placed on the agar medium, put into an airtight. largest at 32° C, and reduced at temperatures ≥36° C. The. plastic container with wet Kimwipes™ under the slide to. number of seeds was suppressed at temperatures ≥40° C.. maintain high humidity, and the medium was incubated at 28° C for 24 h. After incubation, pollen grains and pollen tubes were stained with 1% w/v cotton blue in a lactic. Experiment 2: Effect of high temperatures on pollen-tube elongation in the pistil. acid/phenol/glycerol/water (1:1:1:1, v/v/v/v) solution,. Results of anatomical observations of pollen-tube. covered with a cover-glass for overnight, and observed. elongation in the pistil from stigma to embryo sac are. under an optical microscope. Following the manner as. shown in Fig. 2. Germinated pollen grains were observed. described by Matsuda and Higuchi (2013), the number. on the stigma (Fig. 2.1), and many pollen tubes which. of germination (/1000 grains) and the lengths of six. elongated in a bundle were observed in the style (Fig.. pollen tubes were recorded per slide. These germination. 2.2). After elongating into the upper part of ovary (Fig.. tests were repeated five times, germination percentage. 2.3), pollen tubes elongated along the ovary wall surface. and the average pollen-tube length was calculated for. (Fig. 2.4). Pollen tubes then elongated as to coil around. each temperature treatment.. the funicle (Fig. 2.5a) and through the micropyle (Fig.. Results Experiment 1: Effects of daytime high temperatures on fruit set. 2.5b). Thereafter, pollen tubes penetrated into nucellus to reach the egg apparatus in the embryo sac (Fig. 2.6). When detached flowers on the anthesis day were incubated and pollinated at 28–40° C, every flower at 28–. Daily maximum temperatures were around 25° C. 32° C opened normally and the styles reclined towards. and daily minimum temperatures were around 15° C. anthers before the time of pollination (Fig. 4). Flowers. in the greenhouse, until mid-June (Fig. 1). Maximum. at 28–32° C, pollen tubes reaching embryo sac were. temperature in late June was similar to those in mid-. observed within 24 h after pollination for every piece of. June, while minimum temperatures increased and were. pistils tri-sectioned from each flower. In contrast, when. around 20° C. After July, maximum temperatures also. flowers opened at temperatures ≥34° C, styles of every. increased and were around 30° C and minimum tempera-. flower remained upright even at the time of pollination.. tures further increased and were 20–25° C.. At 34° C, although pollen tubes reaching funicle and. When flowers were pollinated at regulated daytime. micropyle were observed for ≈20% of pistil pieces, pollen.

(4) 174. Trop. Agr. Develop. 64（4）2020. A. 2. half-sectioned embryo sac embryo sac 5. 3. style ovary 1. 6 funicle. 4. micropyle egg apparatus. stigma. 5a. 1 stg pt. fn pg pt. 2. pt. stl. 5b es. fn. 3. mp. ovr pt pt. 6. ovl. ep. 4 pt. ovw pt. es nu. Fig. 2. Fluorescence microscopic observations of the pollen-tube elongation in the pistil of ‘Summer Queen’ passion fruit. A: left half of the ovary is a sectional view, pollen-tube (pt) attaining position was divided into 6 portions, and dashed lines indicate borders between the portions; 1: pollen grains (pg) germinating on the stigma (stg); 2: pollen tubes penetrating through the style (stl); 3: pollen tubes arriving at the upper part of ovary (ovr); 4: pollen tubes elongating along the wall at the middle part of ovary (ovw); 5a: pollen tubes elongating along the funicle (fn) toward ovule (ovl); 5b: through the micropyle (mp); 6: penetrating through the nucellus (nu) and attaining the egg apparatus (ep) in the embryo sac (es).. tubes barely reached ovary in most of the pistils. No. tures over 38° C, pollen grains merely germinated on the. pollen tube reaching embryo sac was observed within. stigma, and no pollen tubes reached ovary.. 24 h. At 36° C, pollen tubes did not reach funicle and. The pollen obtained at different temperature condi-. micropyle. Pollen tubes reached ovary for the half of. tions ranging 28–40° C showed similar germinations:. the pistil pieces, and the other half remained inside the. 20–30% on agar medium (Fig. 5A). Pollen tubes tended. style. When flowers were pollinated at higher tempera-. to elongate longer on agar medium when the pollen.

(5) Fig. 3 175. Matsuda et al.: High temperature inhibition of passion fruit set. 100. a. a. a. were obtained from anthers dehisced at higher tempera-. A. a. tures (Fig. 5B). Pollen-tube lengths became significantly. ab. longer after anther dehiscence at 40° C.. Fruit set (%). 80 bc. 60. Discussion. 40. c. 20. Number of seeds per fruit. 0 300 250. (20). (20). (20). ab. a. abc. (20). (20). (20). (20). In the present study, when detached flowers on the anthesis day were incubated and pollinated at tem-. d (15). peratures ≥34° C in the laboratory, pollen-tube growth in the pistil was inhibited and the elongation decreased at. B abc. 200. higher temperatures (Fig. 4). Because of heterotrophic elongation of pollen tubes in pistil among plant species. bc cd. (Cruzan, 1986; Herrero and Arbeloa, 1989), pollen-tube. 150. growth can be considered to be promoted when pistils d. 100. contained higher amount of nutrition at the time of pollination. Accordingly, inhibited pollen-tube growth of. 50. passion fruit at ≥34° C in our results can be attributed. 0 28. 30. 32. 34. 36. 38. 40. 42. to the pistil exhaustion caused by limited absorption. Daytime temperature conditions on the day of anthesis (° C). of water and nutrients and increased respiration under. Fig. 3. Effects of daytime temperature conditions on the anthesis day from. high temperature conditions.. Fig. 3. 0900–1800 Effects hofondaytime on(B)the fruit set (A)temperature and the number conditions of seeds per fruit of ‘Summer Queen’ fruit. Subsequent nighttime (1800–0900 h) anthesis day passion from 0900–1800 h on fruit set (A) and temperatures were regulated at 28° C for all treated flowers. Fruit set thethe number per fruit (B)1ofweek ‘Summer Queen’ and number of of seeds seeds were recorded after pollination. Values in parentheses indicate the number of treated flowers in each passion fruit. Subsequent nighttime (1800–0900 temperature treatment. Vertical bars indicate S.E. Different letters h) temperatures were regulated at 28° C for all indicate significant difference at P < 0.05 by Fisher’s exact test with treated Fruit set and the number of seeds FDR controlflowers. from the BH procedure (Benjamini and Hochberg, 1995) for fruit set percentage1 and by Tukey’s comparison test for were recorded week after multiple pollination. Values in the number of seeds. parentheses indicate the number of treated flowers in each temperature treatment. Vertical bars indicate S.E. Different letters indicate significant difference at P < 0.05 by Fisher’s exact test with FDR control from the BH procedure (Benjamini and Hochberg, 1995) for fruit set percentage and by Tukey’s multiple comparison test for the number of seeds.. Pollen-tube attainment. Embryo sac. In contrast, when surrounding temperatures were only regulated in an orchard condition, fruit set decreased at temperatures ≥38° C (Fig. 3). This temperature regime was higher than 34° C at which pollen-tube growth was inhibited in detached flowers (Fig. 4).. Fig. 4. Detached flowers absorb water and nutrients from the liquid medium, whereas flowers on the plant are influenced by assimilates in the plant body. Photosynthesis of ‘Summer Queen’ passion fruit was reported to be highest at 30° C under common cultivation conditions and. ○○○○○ ○○○○○ ○○○○○ ○○○○○ ○○○○○ ○○○○○ ○○○○○ ○○○○○ ○○○○○. Funicle & micropyle. ●●●. Middle-ovary wall. ●●●●● ●. A piece of pistil with ○ Normal Style ● Upright Style ●●. Upper ovary. ●●●●● ●●●●● ● ●●. Style. ●●●●● ●●. ●●● ●●●●● ●●●●● ●●●●● ●●●●● ●● ●●●●●. Stigma No germination 28. 30. 32. 34. 36. 38. 40. Incubation temperatures (° C). Fig. 4. Fig. Effect of temperature conditions fromfrom 09000900 h onh the anthesis 4. Effect of temperature conditions on the anthesisday daytotothe thenext-day next-daynoon on noon elongation on pollen-tube elongation in pistils of passion ‘Summerfruit. Queen’ passionwas fruit. pollen-tube in pistils of ‘Summer Queen’ Pollination conducted Pollination h was 1200–1300 h on the day of aanthesis. circle from 1200–1300 onconducted the day ofwithin anthesis. Each circle indicates piece ofEach pistil comprising indicates a piece of pistil comprising one style and one fragment of tri-sectioned one style and one fragment of tri-sectioned ovary which were sampled from the same flower. ovary which were sampled from the same flower. Open circles represent a piece of Open circles represent piece of pistilstyles fromreclined a normal flower whichbefore stylespollination. reclined towards pistil from a normala flower which towards anthers anthers beforecircles pollination. Closed circles represent of pistil fromwhich a disordered Closed represent a piece of pistil from aa piece disordered flower styles flower whichremained styles remained time of pollination. data are presented according upright atupright the timeatofthe pollination. The data areThe presented according to the of of pollen tubes observed in each pistil.of pistil. to the deepest deepestpositions positions pollen tubes observed inpiece eachofpiece.

(6) Fig. 5. 176. Trop. Agr. Develop. 64 （4）2020. Germination (%). 50. occur under orchard conditions. Plant body conditions. A. during pollination are likely to influence largely the pistil. 40. receptivity and fruit set.. n.s.. Among detached flowers of passion fruit at tem-. 30. peratures ≥34° C, in addition to the inhibition of pollen-. 20. tube growth, flowering became disordered where the styles still remained upright after flower opening (Fig.. 10. Elongation (µm). 0 1000. 4). This disordered flowering was observed at ≥34° C, a. B. 800. ab. b. 600 b. b. b. b. 400. absorption of pistils which were affected by heat stress. On the other hand, occurrence of the upright style flowers was minor among flowers on plants in the field (data not shown). Ishihata (1981) noted relationships between such disordered flowering with upright styles in purple passion fruit and high temperatures. He (Ishihata, 1981). 200 0. can be attributed to inhibition of water and nutrient. reported that flowers with upright styles did not set fruit 28 30 32 34 36 38 40 Temperature conditions during anthesis (° C). Fig. 5. temperatures during anthesis on pollen Fig. 5. Effects Effectsofofdaytime daytime temperatures during anthesis on germination percentagepercentage (A) and pollen-tube elongation pollen germination (A) and pollen-tube (B) of ‘Summer Queen’ passion fruit. Temperatures elongation (B) of ‘Summer Queen’ passion fruit. during anthesis were regulated from 0900–1200 h on the Temperatures duringgermination anthesis was were anthesis day, and pollen thenregulated tested on frommedium 0900–1200 on anthesis and pollen agar at h28° C. the Vertical barsday, indicate S.E. germination testedsignificant on agar differences medium atat28° Different letterswas indicate P C. < Vertical bars indicate Different indicate 0.01 by Tukey’s multipleS.E. comparison test.letters n.s. stands for not significant. significant differences at P < 0.01 by Tukey’s multiple comparison test. n.s. stands for not significant.. as a result of inhibited pollen germination on the stigma, whereas pollen well germinated in our observations (Fig. 4). Anthers of ‘Summer Queen’ dehisced normally at 28–40° C and the germination percentage of obtained pollen did not vary on the same agar medium (Fig. 5). Similarly, pollen germinability reportedly did not vary after an exposure to higher temperatures than 40° C in lily (Vantuyl et al., 1982) and Brassica species (Rao et al., 1992). Although passion fruit pollen was not susceptible. decreased at higher temperatures of 35° C (Shimada et. to high temperatures during anthesis, the pistils were. al., 2017). Throughout the present experiments, air tem-. damaged by high temperatures ≥34° C (Fig. 4). In pas-. peratures inside the greenhouse generally maintained. sion fruit, the male organ can be considered to be more. below 35° C (Fig. 1). Accordingly, in the present study,. tolerant against high temperatures than the female. passion fruit plants were considered to suffer less from. organ. This is different from rice (Satake and Yoshida,. heat stress. In our results, flowers on the plant were able. 1978), sorghum (Djanaguiraman et al., 2018), chickpea. to set fruit well even in higher temperatures than those. (Devasirvatham et al., 2012), tomato (Iwahori and. where high temperature damages were observed in. Takahashi, 1964), and cherimoya (Higuchi et al., 1998;. detached flowers. This can be attributed to a supply of. Matsuda and Higuchi, 2012).. water and assimilates toward pistils from the plant body less exposed to heat stress.. In subtropical fruit trees, cherimoya and lychee, temperature on the anthesis day was reported to influ-. Similar in cherimoya, pollen-tube growth after pol-. ence the pollen germinability. Germination of cherimoya. lination was inhibited at higher temperatures than 32° C. pollen on agar medium decreased when flowers attained. in detached flowers (Matsuda et al., 2011), whereas flow-. anthesis at 30° C (Matsuda and Higuchi, 2015). Germi-. ers on the tree set fruit well even after a surrounding. nation of lychee pollen also decreased when flowers. temperature regulation at 32° C during a post-pollination. attained anthesis by temperatures higher than 25° C. night (Matsuda et al., 2015). Matsuda et al. (2015) noted,. (Matsuda and Higuchi, 2017). On the other hand, the. however, that the fruits from the 32° C treatment con-. pollen germinability of passion fruit was not affected. tained smaller number of seeds than those from cooler. by temperatures during anthesis, and the pollen-tube. temperature treatments. They (Matsuda et al., 2015). elongation rather increased after anthesis at higher tem-. reported to observe a decrease of cherimoya fruit set. peratures (Fig. 5). Effects of high temperatures during. after temperature treatments above 35° C. Considering. the anthesis day on the male organ are considered to be. the heat stress for detached flowers, emasculation of. negligible for passion fruit cultivations.. the heat stress for flowers on plant can be presumed to. Our results indicate that plant body of passion fruit.

(7) Matsuda et al.: High temperature inhibition of passion fruit set. on the anthesis day might be influenced to the fruit set; although pistils of detached flowers were damaged by high temperatures ≥34° C (Fig. 4), the pistils on plant growing under orchard conditions avoided the high temperature damages at 36° C (Fig. 3). Whereas, Matsuda and Higuchi (2020) reported that the fruit set of ‘Summer Queen’ decreased on the anthesis days of which maximum temperatures exceeded 34° C even when the flowers were hand-pollinated. Accordingly, in passion fruit on high temperature days, inhibited physiological responses including photosynthesis can be considered to cause low pistil receptivity and fruit set. Acknowledgements This study was supported by a Grants-in-Aid for Scientific Research (KAKENHI No. 15K07290) from the Japan Society for the Promotion of Science. References Benjamini, Y. and Y. Hochberg 1995. 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