Jpn. J. Trop. Agr. 48(2): 88-93, 2004

Critical Temperature Leading to Frost Damage in Young of White ( edulis Llave & Lex.) cv. Florida

Yoshimi YONEMOTO1,Hirotsugu INOUE2, Mayumi MAJIKINA3and Hitoshi OKUDA1

1Department of Research, National Institute of Tree Science, Kuchinotsu, Nagasaki 859-2501, Japan 2Nago Branch , Okinawa Agricultural Experiment Station, Nago, Okinawa 905-0012, Japan 3Faculty of Law and Latters, University of the Ryukyus, Nishihara,Okinawa 903-0213, Japan

Abstract Frost damage in young fruits of white sapote (Casimiroa edulis Llave & Lex.) cv. •eFlorida•f was investigated under Japanese field conditions and in artificial growth chambers to identify the relationship between frost damage in young fruits and the low yield which occurs under the open-field culture of this sub-tropical fruit crop. In the crops grown in the field under Japanese climatic conditions, no fruits were produced in years when the minimum temperature dropped below -2.5•Ž . Severe frost damage was observed in young fruits at -3•Ž in an artificial growth chamber, and no frost damage was observed at -2•Ž after four consecutive days of exposure to five hour/day treatments. We recommend that commercial cultivation of white sapote take place at locations where minimum winter temperatures do not exceed -2.0•Ž. Key Words: Cultural condition, Minimum temperature, Sub-tropical fruit tree, Yield

シ ロサ ポ テ(Casimiroa edulis Llave & Lex.)品 種 フ ロ リダ の幼 果 に 寒害 を引 き起 こ す低 温 米 本 仁 巳1・ 井 上 裕 嗣2・ 真 境 名 真弓3・ 奥 田 均1 1農 業 ・生物 系特 定 産 業技 術 研 究機 構果 樹 研 究 所 カ ン キ ツ部 口之 津 〒859-2501長 崎 県 南 高来 郡 口之津 町2沖 縄 県農 業試 験場 名護 支場 〒905-0012沖 縄 県名護 市名 護3琉 球 大学 法文学 部 〒903-0213沖 縄 県西 原町

要 約 亜 熱 帯 性 果 樹 で あ る シ ロ サ ポ テ(Casimiroa edulis Llave & Lex.)を わ が 国 で露 地 栽 培 した 場 合 にみ られ る結 実 不 良 と幼 果 の 寒 害 と の 関 係 を明 らか にす る 目的 で,人 工 気 象 室 と圃 場 の 両 方 で シ ロ サ ポ テ‘ フ ロ リ ダ’ の幼 果 に 寒 害 を生 じる気 温 を 調 査 した.人 工 気 象 室 実験 で は,-3℃ に5時 間 遭 遇 し た場 合 幼 果 に 重 度 の 寒 害 が み られ た.し か し,4日 間連 続 して-2℃ に遭 遇 して も寒 害 は み られ な か っ た.圃 場 で の 栽 培 試 験 で は,最 低 気 温 が-2.5℃ 以 下 に な った 年 の 収 量 は皆 無 で あ っ た.シ ロ サ ポ テ の 露 地 栽 培 は冬 季 の 最 低 気 温 が-2.0℃ 以 下 に な らな い 場 所 が望 ま しい. キ ー ワ ー ド 亜 熱 帯 性 果 樹,最 低 気 温,栽 培 条 件,収 量

branches (YONEMOTO et al. 1996). However, the Introduction critical temperature that causes frost damage in

White sapote is an evergreen sub-tropical young fruits of these trees is unknown. Since tree that produces thin-skinned medium to large the major flowering season of C. edulis occurs in fruits with a fine-textured sweet flesh. This tree winter (NERD et al., 1992; YONEMOTO et al., 2001), is native to the highlands of and Central it is important to determine the critical temperature America (MORTON, 1987). Despite its high and duration at which young fruits become affected productivity, commercial cultivation remains limited by frost in order to increase commercial yields. (CAMBERS, 1984). White sapote grows well in warm In this study, the•eFlorida•fcultivar of white sapote, climates, and attempts have been made to introduce the most productive cultivar in Japan, was used this species as a novel orchard crop in New under artificial and Japanese field conditions to Zealand, Australia, Israel and Japan (DAWES and investigate the critical temperature at which young MARTIN, 1988; GEORGE et al., 1988; NERD et al., fruits become damaged by frost. 1992; YoNEMOTO et al., 2001). Materials and Methods White sapote is highly sensitive to tempera- tures below -4•Ž (SCHROEDER, 1951; THOMSON, Field trials 1973). In previous field-based studies of C. edulis Six two-year-old grafts of•eFlorida•fand two in Japan it was reported that die-back occurred trees of•eVernon•f(the pollinating cultivar) on at temperatures below -4•Ž in three year-old •e Florida•frootstock were planted in 1990 in a coastal branches and below -3•Ž in one or two year-old orchard near Cape Shionomisaki, Wakayama

Received Nov. 20, 2003 Prefecture in Japan. The cape is located in the Accepted Feb. 28, 2004 southernmost part of Honshu Island (latitude Yonemoto et al.: Critical temperature leading to frost damage in young fruits of white sapote 89

33•‹26' north, and longitude 135•‹44' east). Trees All the damaged fruits were removed at this time, started producing fruits in 1993 and the number and the number of removed fruits was counted for of fruits produced on the•eFlorida•ftrees was the following 10 days, allowing fruit retention rates recorded each year. Field temperatures, recorded to be calculated. The daily maximum/minimum from 1997-2002, were measured hourly with a temperature range in the growth chamber was Thermo recorder Ondotori Jr. TR 52 (T&D 20/10•Ž (Fig. 1) for 10 days after the treatment Corporation). The relationship between the number and then the trees were kept at 25/10•Ž until of harvested fruits per tree and the lowest May 9. Thereafter, the trees were transferred to temperature or cumulative hours below 0•Ž was the same glasshouse. The minimum temperature examined. in the glasshouse was remained higher than 2.5•Ž in winter months and the temperature in the Growth chamber and glasshouse trials glasshouse was maintained in the range of 35•Ž The experiment was conducted in growth and 17•Ž from May to September. Ten fruits from chambers (Koitotoron 35-135A, KOITO INDUS- the growth chamber treatment 3 (-2•Ž for five TRIES, Ltd.) and in a glasshouse at the Department hours over four consecutive days) and ten fruits of Citrus Research (Kuchinotsu), National Institute from the trees grown continuously in the glasshouse of Fruit Tree Science, Nagasaki Prefecture Japan. were harvested on September 23. Fruit weight Three-year-old•eFlorida•fand•eVernon•fcultivars was measured immediately after harvest. Seed grafted on•eFlorida•frootstock used in this experiment weight, and number of seeds with embryo per fruit were grown in 10 liter unglazed pots in 2003. were determined after ripening at room temperature. Twelve of•eFlorida•f(fruit producer) and Results and Discussion two plants of•eVernon•f(pollinizer), were grown in a glasshouse where the temperature ranged Effect of temperature on fruit yield under field from 22•Ž and 2.5•Ž in December and January. conditions Artificial pollination was undertaken from Decem- Field temperatures over the duration of this ber 4, 2002 to January 22, 2003, according to the study are listed in Table 1. During this period, no methods of YONEMOTO and HENAYAKE (2002). fruit was produced in the years where the minimum Fresh pollen of•eVernon•fwas manually placed on temperature dropped below -2.5•Ž. However, 325 the stigma of•eFlorida•fon a daily basis using a fruits per tree were produced in 2001 when the standard paint brush. Germination percentage of minimum temperature reached -0.9•Ž. These the pollen examined by the method of YONEMOTO results suggest that the critical temperature at which et al. (2000) was around 8%. Nine•eFlorida•ftrees frost affects young fruits ranges between -0.9 were separated into three groups and transferred and -2.5•Ž under natural temperature gradients in

to the growth chambers on January 22, 2003. Japan. The remaining three•eFlorida•ftrees were kept in the same glasshouse. The temperature in the growth chambers was controlled to reach a maximum diurnal temperature of 20•Ž, while the minimum night temperatures were manipulated using the follow- ing three temperature/duration regimes: (1) -3•Ž for five hours over one day; (2) -2•Ž for five hours over two consecutive days; (3) -2•Ž for five hours over four consecutive days (summarized in Fig. 1). Chamber temperatures were measured hourly with a Thermo recorder Ondotori Jr. TR 52

(T&D Corporation). Frost damage in the newly developing shoots at the tip of the branches was observed and the percentage of fruits that had undergone browning (Figs. 2 and 3) as a result Fig. 1. Time course changes in air temperature of of frost was recorded at 11 am, six hours after three low temperature treatments. the end of each minimum temperature treatment. Treatments were started on January 22, 2003. 90 Jpn. J. Trop. Agr. 48 (2) 2004

Table 1. Effect of cumulative hours below 0•Ž and minimum temperatures in winter

on yield of white sapote•eFlorida•fat Kushimoto, wakayama Prefecture

Grafted 2 years old trees were planted in 1990. Number of harvested fruits per tree: average•}SD of three trees.

Effect of temperature on fruit yield under harvested fruit size and seed development artificial growth conditions between the fruits exposed to a temperature of Young fruits were prone to frost damage -2•Ž (Treatment 3) and the fruits that were not when held at -3•Ž for five hours (Treatment 1), exposed to sub-zero temperatures (Table 3). No while no frost damage was observed at -2•Ž frost damage occurred in the branch tips of

(Treatments 2 & 3), even after four consecutive newly developed shoots in any of the minimum days of exposure to five-hour treatments per day temperature treatments used in this study (Table

(Table 2, Fig. 2). There was no difference in the 2, Fig. 3). Fruits that showed no immediate damage

Table 2. Effect of low temperatures on frost damage in young fruits and trees of white

sapote•eFlorida•f

Observations were performed 6 hours after the end of each minimum temperature treatment. Values correspond to the average of 3 trees. Letters within a column represent separations of means by Tuckey's test at p=0.01.

Table 3. Effects of exposure to -2•Ž for 5 hours over 4 consecutive days on fruit and

seed development

10 fruits from each treatment, pollinated in early January and harvested in September, 2003 were compared. Numbers are average•}SD. Yonemoto et al.: Critical temperature leading to frost damage in young fruits of white sapote 91

Fig. 2. Fruit appearance and cross-section view after low temperature treatments.

A and B: 6 hours after -3•Ž•~5-hour treatment. C and D: 24 hours after -3•Ž•~5-hour treatment. E and F: 24 hours after -2•Ž•~5-hour•~4-day treatment. Arrow head indicates browning of seed. Distance between the bars is 1mm.

after being subjected to Treatment 1 (-3•Ž) began growth chambers indicated that the new shoots to drop four days after the end of the trial, but were resistant to the minimum temperature most of the remaining fruits had dropped after treatments in this study, while the critical seven days (Fig. 4). No fruits dropped after being temperature that caused frost damage in young subjected to Treatments 2 and 3 (-2•Ž). Moreover, fruits ranged between -2 and -3•Ž. Type-I cultivars the harvested fruits contained the same numbers (with large ovaries and stigmas and lacking pollen) of seeds with embryo. Results from artificial of white sapote, were similar to the•eFlorida•f 92 Jpn. J. Trop. Agr. 48 (2) 2004

the•eType-I•f cultivar were also likely to be more

prone to frost damage compared to the other fruit trees that bloomed in spring. Loquat is another fruit tree that blooms in winter, and young fruits are often damaged by frost when minimum temperatures reach -3•Ž

(SU(;AIRA, 1991). The embryo of a loquat is killed when a young fruit is exposed to temperatures of -3•Ž for three hours, but the fruit remains on the tree for a long period of time (NAKAI and MORIOKA, 1978). These frost-induced seedless

loquat fruits attain the same size as seeded fruits , provided that they are sprayed with an aqueous solution of gibberellic acid (TAKA(I et al., 1994). In the present study, approximately twenty percent Fig. 3. Flowers and young fruits with frost damage of the remaining fruits contained a discolored compared with a newly growing without seed after the -3•Ž treatment, and eighty percent damage (six hours after exposure to -3•Ž for of the fallen fruits contained a discolored seed 5-hour treatment). (Data not shown). This implies that the drop of the remaining•eFlorida•ffruits, after the -3•Ž cultivar, in that they also bloomed from winter to treatment, may be caused by damage to the spring (YONEMOTO et al., 2001). Peak of the bloom seed, even though the external surface of the in Type-I cultivars occurred from December fruit did not appear to have suffered (Fig. 2). through February when the temperature was Frost tolerance of young fruits and seeds of the the lowest. On the other hand, Type-II cultivars white sapote seem to be equivalent to that of the (with small ovaries and stigmas and producing loquat. pollen in large anther) of white sapote, were similar to the•eVernon•fcultivar, in that they Factors limiting the yield of white sapote continuously bloomed normally in winter and Under artificial growth conditions, no frost damage spring. Therefore, flowers and young fruits of was observed in young fruits after daily exposure

Fig. 4. Effect of low temperature treatments on fruit retention rates of white sapote•e

Florida•fafter the treatment.

All the visually damaged fruits were taken off the tree after the treatment . Vertical bars indicate SD (n=3). Yonemoto et al.: Critical temperature leading to frost damage in young fruits of white sapote 93 to five-hour periods of -2•Ž temperature over four degree of the damage under field conditions. Bulletin consecutive days, corresponding to a cumulative of the Chiba Horticultural Experiment Station 9:1-11.* exposure of more than 20 hours below 0•Ž. NERD,A., M. LAPIDOTand Y. MIZRAHI1992 White sapote Over six Japanese field seasons, the cumulative (Casimiroa edulis): performance under various culture hours below 0•Ž per year were less than the 20 salinities and environmental stress conditions in field studies. Scientia Horticulturae 51: 213-222. hours which were less than those used in the SCHROEDER,C. A. 1951 The white sapote. Texas artificial growth trials of this study. Shortly after Yearbook 60-65. pollination, the fruits of white sapote are small SUGIURA,A. 1991 Handbook of fruit tree culture. (SUGIURA, (YONEMOTO et al., 2001) and it is not surprising eds.) Yokendo (Tokyo) 584-585.** that only short periods of exposure to sub-zero TAKAGI,T, H. MUKAI,R. IKEDAand T. SUAUKI1994 Effect temperatures damage young fruits. Therefore, of application of gibberellic acid and N-(2-chloropyri- minimum winter temperatures are likely be a dyl)-N'-phenylurea on the enlargement of frost-induced factor limiting the yield of white sapote. Both seedless fruit of loquat (Eriobotrya japonica Lindl.). natural and artificial growth conditions used in J. Japan. Soc. Hort. Sci. 62: 733-738.* this study suggest that the critical temperature THOMSON,P. H. 1973 The white sapote. California Rare leading to frost damage in young fruits ranges Fruit Growers Yearbook 5: 6-20. between -2 and -2.5•Ž. We recommend that YONEMOTO,Y. and C. K. HENNAYAKE2002 Pollen tube commercial cultivation of white sapote take place growth in the pistil as affected by temperature and effective pollination period in white sapote (Casimiroa at locations where minimum winter temperatures edulis Llave and Lex.). Jpn. J. Trop. Agr. 46: 77-81. do not exceed -2.0•Ž. YONEMOTO,Y., H. HIGUCHI,K. ISHIHATA,M. IKEDAand E. References TOMITA2001 Analysis of varietal differences in floral and fruit morphology in white sapote (Casimiroa edulis CHAMBERS,R. R. 1984 White sapote varieties: progress Llav and Lex.). Jpn. J. Trop. Agr. 45: 38-44. report. California Rare Fruit Growers Yearbook, 16: YONEMOTO,Y., H. HIGUCHI,K. ISHIHATAand E. TOMITA2000 56-64. Effect of artificial medium conditions on in vitro DAWES,S. N. and P. J. MARTIN1988 The casimiroa is close germination and storage conditions of white sapote to commercial fruit crop status. Orchards New Zealand (Casimiroa edulis Llave and Lex.) pollen. Jpn. J. Trop. 61: 72-74. Agr. 44:171-177.* GEORGE,A. P., R. J. NISSENand D. J. WALLACE1988 The YONEMOTO,Y., M. OGAWAand K. ISHIHATA1996 Cold casimiroa. Queensland Agricultural Journal 114: 57-62. hardiness of young white sapote tree. Jpn. J. Trop. MORTON,J. F. 1987 White Sapote. In Fruits of Warm Agr. 40 (Suppl. 2): 59-60.** Climates. Media Incorporated (North Carolina) 191-196. (*: in Japanese with English summary, **: in Japanese) NAKAI,S. and S. MORIOKA1978 Studies on the cold injury in loquat fruit I. Influence of air temperature on the