Influence of High Temperatures at Blooming Time on Pollen Production and Fruit Set of Peach 'Maciel' and 'Granada'. M. Couto, M.C.B. Raseira and F.G. Herter.
Influence of High Temperatures at Blooming Time on Pollen Production and Fruit Set of Peach ‘Maciel’ and ‘Granada’ M. Couto, M.C.B. Raseira and F.G. Herter Embrapa Clima Temperado Caixa Posta, 403 - Pelotas, RS, 96001-970 Brazil
J.B. Silva Universidade Federal de Pelotas Pelotas Brazil
Keywords: Prunus persica, heat tolerance, adaptation, pollen viability Abstract Regions under subtropical conditions commonly have temperature fluctuations and at late winter time the occurrence of temperatures above 25°C followed by less than 10°C is not rare. This is probably one of the causes for production inconsistency over the years. Several field and laboratory tests were conducted using two peach cultivars, ‘Granada’ and ‘Maciel’, aiming to study the effect of high temperature (≥25°C) at blooming period. In vitro pollen viability at different temperatures was tested using a culture medium prepared with 1% agar plus 10% sugar in distilled water. Pollen production per anther was also evaluated. In field experiments, branches of these two cultivars were submitted to temperatures 2 to 8°C above field temperatures, using plastic bags or transparent bottles (pet) or covering a whole plant with a portable greenhouse. The observed parameters were: in vitro pollen viability, pollen production per anther (total and normal pollen grains), length of pistils and fruit set. In laboratory tests, pollen germination was lower at 32°C, than at 24 or 28°C for both cultivars. Higher temperatures did not significantly influence length of pistils, probably because the field temperatures at the tested years were already high. Total pollen production did not differ among tested temperatures, however percentage of normal pollen grains was significantly lower in ‘Granada’ at higher temperatures and did not differ for ‘Maciel’. The same was true for fruit set. The conclusion is that the negative effect of high temperatures at blooming time is larger for ‘Granada’ than for ‘Maciel’. INTRODUCTION In fruit production, especially in subtropical areas, inconsistency of yields is one of the major problems (Tromp, 1986). Under these conditions, the occurrence of high temperatures it is common which influence the flower development reducing fruit set and consequently the crop (Kozai et al., 2002). Several attempts have been done to evaluate the temperature effects, during pre-blooming on fruit set. These studies mainly used potted plants but the results are not always clear (Rodrigo and Herrero, 2002) and there is no certainty that they well represent plants in the field. Besides, there is not much information and the results are not consistent for Prunus species. High temperatures during pre-blooming reduced fruit set in potted cherries (Beppu et al., 1997), whereas the temperature increase, in bagged branches of almonds, did not affect fruit-set (Egea and Burgos, 1995). In regions with mild winters, temperature fluctuations are not rare and can cause problems during the fertilization process and consequently, in fruit set. In Southern Brazil, in the state of Rio Grande do Sul, the occurrence of temperatures above 25°C, during the winter months, followed by periods of temperature below 10°C is common. This fact can be one of the reasons for crop failure in some years (Couto and Raseira, 2004). Papers about the receptivity period pointed out that high temperatures can increase the rate of pollen tube growth whereas low temperatures decrease it (Furukawa and Bukovac, 1989; Burgos et al., 1991; Egea and Burgos, 1992; Sanzol and Herrero, 2001). As a consequence, the fruit set should be higher under warmer temperatures than cold ones. However, this is not always true in nature. High temperatures during blooming Proc. 8th IS on Temperate Zone Fruits in the Tropics and Subtropics Eds.: F.G. Herter et al. Acta Hort. 872, ISHS 2010
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increase the pollen tube elongation rate but also speed up the stigma maturation and degeneration (Burgos et al., 1991; Egea et al., 1991) and ovule development (Stösser and Anvari, 1982; Postweiler et al., 1985; Cerovic and Ruzic, 1992). Several laboratory and field tests were conducted from 2003 to 2005, in order to better evaluate the influence of high temperatures on flower development, pollen viability and fruit set of two peach cultivars: ‘Granada’ and ‘Maciel’. MATERIALS AND METHODS Laboratory Experiments The temperature effect on pollen viability was studied in laboratory, by in vitro germination at different temperatures. Three experiments were carried out, using a completely randomized design, with the following cultivars and temperatures. 1. Laboratory Experiment 1. Cultivars ‘Granada’ and ‘Maciel’ – temperatures tested: 24, 28 and 32°C (±1°C). 2. Laboratory Experiment 2. Cultivars ‘Esmeralda’, ‘Granada’, ‘Jade’ and ‘Maciel’ – temperatures tested: 24, 28, 32 and 36°C (±1°C). 3. Laboratory Experiment 3. Cultivars ‘Esmeralda’, ‘Granada’, ‘Jade’ and ‘Maciel’ – temperatures: 20, 24, 28 and 32°C (±1°C). The pollen was obtained from anthers collected from flowers at balloon stage, dried at room temperature for 2 or 3 days and then stored in vials inside dessecators kept in a freezer, until used. Tests were done using slides adapted to this objective. The germination medium consisted of 10 g of sugar and 1 g of agar for 100 ml of distilled water. The mixture was warmed in a microwave until the agar was completely dissolved. After that, it was distributed on the slides while still warm and the pollen sprayed over the medium. The slides were then placed in petri dishes with a wet filter paper on the botton, making a humid chamber. The petri dishes were then left at the desired temperatures for three hours before germination percentages were counted. Any pollen grain which presented a pollen tube equal or greater than the pollen diameter was considered viable. Field Experiments Three experiments were conducted under field conditions using the same two, low chill, cultivars in all of them: ‘Granada’ and ‘Maciel’. 1. Field Experiment 1. It was carried out in the years 2003, 2004 and 2005. One-year-old shoots were bagged with plastic bags, transparent plastic bottles or were left under natural conditions and identified with colored ribbons. Temperatures under the three conditions were recorded. The experiment design was completely randomized. The parameters evaluated were pistil length (12 replications), fruit set (16 replications) and number of pollen grains. Each plot was constituted by one branch. Pollen viability was determined by the same method described for the laboratory tests. Pistil length was measured with a milimetric rule and fruit set was calculated by counting number of flowers and the final number of fruits on branches previously identified. Average number of pollen grains per anther was calculated by placing a sample of 50 anthers (collected from 10 different flowers) in a vial. Anthers were left until dry and deiscent. Then 1 ml of lactic acid was poured over them. After shaking the suspension it was placed on a Newbauer slide and the average number of pollen grain per anther was calculated as described by Tuite (1969). 2. Field Experiment 2. At beginning of blooming of peach ‘Granada’, 25 to 30-cm long one-year-old branches were covered with transparent plastic bottles at different phenological stages: bud swell, green tip, pink stage and compared to branches left uncovered (free). This experiment was carried out in the years 2004 and 2005 using a completely randomized design with four replications in 2004 and eight the following year. Pistil length, pistil fresh weight and fruit set were observed as well as the presence of abnormal flowers, time of leafing and flowering. 3. Field Experiment 3. It was carried out in the years 2004 and 2005. Close to the 226
blooming period trees of ‘Maciel’ and ‘Granada’ were submitted to three different conditions. A small plastic house was built around and over one of the trees of each cultivar; a plant of each one was painted white and the third plant was maintained under natural conditions. Temperatures were recorded in branches under the three conditions. When flowers, in the previously identified branches, were recently opened they were evaluated for pistil length, pistil fresh weigh and number of pollen grains per anther. Samples of pollen under the three conditions were tested for pollen germination and number. Fruit set was also recorded. The pistil fresh weight was obtained by weighting a sample on a precision scale. The other parameters were determined as described for Field Experiment 1. RESULTS Laboratory Experiments 1. Laboratory Experiment 1. Results obtained in laboratory tests are summarized in Table 1. In the first experiment, pollen germination for both tested cultivars was significantly lower at 32°C, as compared to 24 or 28°C. 2. Laboratory Experiment 2. Cultivars ‘Esmeralda’ and ‘Jade’ were included in experiments 2 and 3. There was a significant interaction between cultivars and temperatures. 3. Laboratory Experiment 3. All tested cultivars had better pollen germination at an incubation temperature of 24°C. ‘Esmeralda’ had the lowest results. Results obtained with ‘Maciel’, showed that germination was still very good at high temperature in 2004, but in the following year, the germination percentage dropped to nearly half when the temperature of incubation was increased from 24 to 28°C. Field Experiments 1. Experiment 1. On the bagged branches and the ones covered by transparent plastic bottles maximum temperatures were respectively, 7,9 and 8,1°C higher than temperatures on the free branches. Average temperatures were 2°C higher than on the free branches whereas there was no difference for minimum temperatures. Thus, the use of these devices is a cheap and effective way of increasing temperatures and can be used in preliminary studies, since it is not possible to control the field temperature. The branches submitted to the heat treatments bloomed, on average, five to eight days before the free branches and blooming period was shortened by seven to ten days. No differences were found on the pistil length for any of the treatments. The same was true for number of pollen grains per anther. However, when only normal pollen grains were counted, the number did not differ for ‘Maciel’ but was significantly lower on bagged branches of ‘Granada’ as compared to flowers on the free branches of the same cultivar. There was a difference in fruit set ‘Granada’ being the one which had negative influence of the high temperatures on fruit set, whereas for ‘Maciel’ there were no statistic differences on fruit set among the different treatments. 2. Experiment 2. The obtained results are hard to explain based on the treatments. They were not clear probably because the maximum temperatures, under natural conditions, during the period were high, around 28°C, and thus even the free branches had high temperatures. However, it seems that the high temperature effect on pistil length and fruit set development stage had a tendency to be greater if the treatments were applied earlier, at flower development stage. 3. Experiment 3. When a portable, small plastic house was used, average maximum temperatures were around 5°C higher than on trees maintained under natural conditions or painted white. Average medium temperatures were around 1,3°C higher and no significant differences were observed in minimum temperatures. There were no differences in pistil length for ‘Maciel’ under the different treatments. The same was true for ‘Granada’ in the year of 2004. However, in 2005, 227
flowers of ‘Granada’ from the plant under the plastic portable house had longer style length than the ones from the plant under natural conditions or painted white. Pistil fresh weight did not differ in 2004, among the three plants for both cultivars. However, in 2005, pistil fresh weight of flowers of both ‘Granada’ and ‘Maciel’ was higher on the plants under plastic portable greenhouse. Differences in fruit set were not significant for ‘Maciel’, in any of the studied years. For ‘Granada’, however, the fruit set was significantly lower on the three under plastic greenhouse. In 2005, the fruit set was null for ‘Granada’, under the three treatments, probably because in this year, the maximum temperatures were higher and longer lasting than in 2004. This leads to the hypothesis that there must be differences among genotypes in relation to heat tolerance at blooming period and ‘Maciel’ is more tolerant than ‘Granada’. The percentage of pollen germination was greater in flowers from the three painted white for both cultivars and higher in ‘Maciel’ than ‘Granada’. Number of pollen grains per anther was greater in ‘Maciel’ and percentage of normal pollen grains was greater on trees under plastic house or painted white for ‘Maciel’ whereas for ‘Granada’, it was higher on trees under natural conditions but did not differ from the others. DISCUSSION The highest temperatures provided by the different treatments advanced the flower opening. For that reason, lack of synchrony between the style development and the other flower parts was expected, which would lead to morphologic abnormalities and consequently poor fruit set. However, in general there were no differences among treatments in length of the style. Flowers of ‘Maciel’, in general had longer style than flowers of ‘Granada’ and the variation among treatments and years was rather small. Abnormal flowers with short styles and ovaries poorly developed had been observed under high temperatures conditions in apricot (Rodrigo and Herrero, 2002; Suranyi, 1976; Viti and Monteleone,1991; Guerriero and Bartolini, 1995; Layene et al, 1996). It is interesting to point out that during the realization of the experiment, an elevation of the average maximum temperature occurred from June to August in the years 2004 and 2005 (1.2 and 2.4°C) as compared to 2003. The amount of rainfall was also reduced in these years, as compared to 2003, being even worse in 2005. Probably, the differences among treatments were not evident because the natural conditions were bad enough to cause stress on flowers. High temperatures in all the experiments, reduced fruit set in ‘Granada’. This cultivar has shown inconsistency in yields over the years, even in absence of frosts. The same does not happen with ‘Maciel’. Previous researchers showed the same influence for other peach cultivars (Kozai et al., 2002; Erez et al., 1998), apricot cultivars (Rodrigo and Herrero, 2002), cherry (Beppu et al., 1997) and persimmon (George et al., 1994). According to Kozai et al. (2002), fertilization and consequently, fruit set, can be influenced by pistil development, pollen germination, pollen tube growth and ovule development. In the present experiments, the lower fruit set of ‘Granada’ under warmer temperatures could not be explained by differences in pistil development, since there were no differences in pistil fresh weight or length of style, among treatments. Probably the effect was due to shorter period of stigma receptivity and/or ovule abortion (which was not tested). High temperatures during pre-blooming and blooming stage not only influence flower quality but also the embryo sac development of cherry flowers (Beppu et al., 2001), effective pollination period and stigma receptivity in apricot (Egea and Burgos, 1992) and ovule viability of cherry flowers (Strösser and Anvari, 1982). According to Beppu et al. (2001), the gibberellins content in the embryo sac is higher under high temperature which leads to a precocious degeneration, right after flower opening. The maintenance of lower temperatures using shade or the application of gibberellin inhibitors could improve fruit set in cherry trees cultivated in areas where high temperature can 228
occur at beginning of blooming stage. New experiments should be conducted with ‘Granada’ observing all the variables not checked in the present studies, such as stigma receptivity, ovule viability and so on. CONCLUSIONS Under laboratory conditions, the incubation temperature for viability tests should be from 24 to 28°C. Under the field tested conditions it can be concluded that the use of plastic bottles or plastic bags is an effective and cheap way to increase temperature. Higher temperatures in the pre-blooming stage advanced the flower opening in peach ‘Granada’ and ‘Maciel’. High temperatures negatively influenced the fruit set and percentage of normal pollen in peach ‘Granada’, and did not have the same effect on ‘Maciel’. Literature Cited Beppu, K., Suehara, T. and Kataoka, I. 2001. Embryo sac development and fruit set of ‘Satohnishiki’ sweet cherry affected by temperature, GA3 and paclobutrazol. Journal of Japanese Society for Horticultural Science, Tokyo-Japan 70(2):157-162. Beppu, K., Okamoto, S., Sugiyama, A. and Kataoka, I. 1997. Effects of temperature on flower development and fruit set of ‘Satohnishiki’ sweet cherry. Journal of the American Society for Horticultural Science, Mount Vernon-VA 122(4):707-712. Burgos, L., Egea, J. and Dicenta, F. 1991. Effective pollination period in apricot (Prunus armeniaca L.) cultivars. Annals Applied Biology, Cambridge-England 119:533-539. Cerovic, R. and Ruzic, R. 1992. Senescence of ovules at different temperatures and their effect on the behavior of pollen tubes in sour cherry. Scientia Horticulturae, Amsterdam-Holland 51:321-327. Couto, M. and Raseira, M.C.B. 2004. Efeito de altas temperaturas na pré-floração, floração e frutificação efetiva nas cultivares de pessegueiro Granada e Maciel. In: XVIII Congresso Brasileiro de Fruticultura, 2004, Florianópolis. CDROM do. Florianópolis: SBF. Egea, J. and Burgos, L. 1995. Double kernelled fruits in almond (Prunus dulcis Mill.) as related to pre-blossom temperatures. Annals Applied Biology, Cambridge-England 126:163-168. Egea, J. and Burgos, L. 1992. Effective pollination period as related to stigma receptivity in apricot. Scientia Horticulturae, Amsterdam-Holland 52:77-83. Erez, A., Yablowitz, Z. and Korcinski, R. 1998. Greenhouse peach growing. Acta Hort. 465:593-600. Furukawa, Y. and Bukovac, M.J. 1989. Embryo sac development in sour cherry during the pollination period as related to fruit set. HortScience, Alexandria-VA 24:10051008. Guerriero, R. and Bartolini, S. 1995. Flower biology in apricot: main aspects and problems. Acta Hort. 384:261-272. Kozai, N., Beppu, K. and Kataoka, I. 2002. Adverse effects of high temperature on the development of reproductive organs in ‘Hakuho’ peach trees. In: Reports of the First International Workshop on Production Technologies for Low-Chill Temperate Fruits, 1. 2002, Chiang Mai. Reports, Chiang Mai: TRFRPF. p.212-220. Layene, R.E.C., Bailey, C.H. and Hough, L.F. 1996. Apricots. In: J. Janick and J.N. Moore (eds.), Fruit Breeding Vol. I, Tree and Tropical Fruits. Yeley, New York, p.79111. Postweiler, K., Stösser, R. and Anvari, S.F. 1985. The effect of different temperatures on the viability of ovules in cherries. Scientia Horticulturae, Amsterdam-Holland 25:235239. Rodrigo, J. and Herrero, M. 2002. Effects pre-blossom temperatures on flower development and fruit set in apricot. Scientia Horticulturae, Amsterdam-Holland 92:193-197. 229
Sanzol, J. and Herrero, M. 2001. The “effective pollination period” in fruit trees. Scientia Horticulturae, Amsterdam-Holland 90:1-17. Stösser, R. and Anvari, S.F. 1982. On the senescence of ovules in cherries. Scientia Horticulturae, Amsterdam-Holland 59:207-214. Suranyi, D. 1976. Differentiation of self-fertility and self-sterility in Prunus by stamen number/pistil length ratio. HortScience, Alexandria-VA 11:406-407. Tromp, J. 1986. The effect of four early spring temperature regimes on apple fruit set, tree growth K end Ca level in fruits. Scientia Horticulturae, Amsterdam-Holland 30:109116. Tuite, J. 1969. Use the spencer hemacytometer. p.182-185. In: J. Tuit (ed.), J. Plant pathological methods fungi and bacteria. Printed Burgess: Publishing Company, USA. Viti, R. and Monteleone, P. 1991. Observation on flower bud growth in some low yield varieties of apricot. Acta Hort. 293:319-326.
Tables
Table 1. Germination percentage of in vitro pollen (%) of peach cultivars ‘Granada’, ‘Maciel’, ‘Esmeralda’ and ‘Jade’, under different temperatures (°C). Embrapa Clima Temperado, Pelotas, RS, 2006. Experiments and cultivars Granada Maciel Average Granada Maciel Experiment 2* Esmeralda Jade Granada Maciel Experiment 3* Esmeralda Jade Experiment 1
20°C 18,7 bcA 17,5 bA 6,5 bB 21,7 bA
24°C 84,5 a 81,0 aA 83,0 aA 64,0 aB 66,3 aB 35,3 aA 41,2 aA 21 aB 33,8 aA
Pollen germination (%) 28°C 32°C 81,1 a 71,2 b 75,0 bB 73,0 bA 82,8 aA 77,0 bA 55,7 bC 44,0 cB 57,5 bC 46,8 cB 26,2 bA 16,3 cA 14,5 bB 12,5 bA 11,8 bB 11,5 bA 13,8 cB 12 cA
36°C 56,0 cB 67,8 cA 44,5 dD 36,0 cC -
Average 83,7 a 72,2 b -
Averages followed by the same capital letters on the columns and small letters on the lines, do not differ by Duncan test at 5% of probability; * There was significant interaction between cultivars and temperatures in the experiments 2 and 3.
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