Guava Breeding in Israel

Transcription

1 Guava Breeding in Israel I. Zipori, S. Shuker, A. Dag and E. Tomer Agricultural Research Organization, Institute of Horticulture Gilat Research Center, Mobile Post Negev 4, 8528 Israel Keywords: Fruit section cycle, grading, emasculation efficiency Abstract Guava has been known in Israel for the last 12 years. The only commercial variety Ben-dov, was selected during the 195s. The fruit is pear-shaped, whitefleshed with a small seed cavity containing a relatively small number of seeds, and a sweet and good taste accompanied by very strong and dominant flavour that is not always favoured by the consumers. The fruit has a very short shelf life. In recent years there has been increasing interest in the fruit, in both the domestic and the export markets. However, the strong flavour and the short shelf life are two factors limiting the development of these markets. Propagation of this variety is from seeds, and the resulting plants resemble the parents phenotypically so it is assumed that the variety is also genotypically rather homogenous. Therefore, in order to obtain wide genetic variation, external genetic material had to be introduced into the breeding program, and hand pollination had to be employed. The imported genetic material included clones of Brazilian, Mexican and Thai origin, differing substantially from each other. Some combinations showed improvements of some desired properties compared to the parents whereas others caused deterioration in these properties. Five promising clones have been found so far, all having good taste combined with weaker flavour. The work is continuing: more hybrids await testing, and additional properties need to be improved. INTRODUCTION Guava (Psidium guajava L.) has been known in Israel for the last 12 years. The species was probably brought into the country from Egypt and became a popular tree in domestic gardens. There are also commercial plantations of about 1 ha from which the fruit is sold in the local market. The climate in Israel is typically Mediterranean, i.e., relatively mild, wet winters and hot, dry summers. Under these conditions the guava, although considered an evergreen, sheds most of its leaves during the winter and flowers in June; the fruit ripens from September to December. The major commercial variety is Ben-Dov, which was selected during the 195s (Gur et al., 1961; Kovetz, 2). This is a highly productive variety, yielding 3-5 t/ha. The fruit is white fleshed with a relatively small seed cavity, small seeds and a good taste, but it has very strong flavour, not always favored by the consumers. Although propagation is from seeds, there is little phenotypic variation and the resulting plants resemble the parents and it is assumed that the Ben-Dov is genetically homogenous, although this has not been tested directly (Kovetz, 2). The lack of phenotypic variation is probably the result of repeated spontaneous selfpollination during many years. Preliminary observations (Zipori, unpublished) showed that in many guava clones grown under Israeli conditions, the anthers open and spontaneous self-pollination occurs before anthesis. If there is no self-incompatibility, which sometimes occurs in guava (Chezhiyan, 1988; Rachna-Singla and Dahliwal, 23), fruit-setting can take place before anthesis, as the stigma is already receptive (Chezhiyan, 1988; Nalini et al., 1973; Pereira and Sao-Jose, 1987). An additional difficulty in guava breeding is the variation in fruit characteristics from one year to another, caused by environmental factors (Chezhiyan, 1988). There is evidence that there is variation in some properties, even between fruits on the same tree Proc. I st IS on Guava Eds. G. Singh et al. Acta Hort. 735, ISHS 27 39

2 and, to a lesser extent, among trees of the same genotype (Thaipong and Boonprakob, 25). This forces the breeder to test the same cultivars during a few years before final characterization. Unlike many other fruit trees in Israel, the guava has never become a large-scale crop whose marketing relies, to a large extent, on exports to the European market, as for avocado, mango, litchi and some other tropical species, although there is a demand for this fruit in Europe (Kahal, 2). The search for additional crops with an export potential as well as the limitations of water supply and the expanding use of saline water led to re-consideration of the guava as a potential export crop. The guava can adapt to a wide range of soils and water qualities and, therefore, could be attractive for marginal regions (Kovetz, 2). However, the strong flavour of the Israeli variety, Ben-Dov does not appeal to the European taste. In addition, the short shelf life of the fruit and its sensitivity to mechanical damage reduce its export potential. The aim of the present, ongoing study is to obtain a widely varied population of guava clones from which a selection can be carried out, according to pre-determined criteria. Criteria that seem to match the export demands were defined, in order to aim the selection towards this goal. MATERIAL AND METHODS Selection Procedure Guava seeds were germinated in 2-inch plug trays filled with peat. They were transplanted into 1-L plastic bags filled with tuff 3-4 months later, when the seedlings were about 15 cm tall. When they were about 1 year old, during the summer, these seedlings were planted in high-density (2 m 4 m) field plots at the Besor Experimental Farm in southern Israel, for mass selection (Canizares, 1981). The first fruits of most plants were obtained a year after planting and were evaluated during two or three successive seasons. Most seedlings were disqualified in the field, usually because of their small fruits; the remaining ones were fully evaluated in the laboratory. Between 1993 and 25 there were three selection cycles: 1. First Selection Cycle. The first cycle ( ) was based on plants obtained from seeds of open-pollinated Brazilian clones. There was no information as to the properties of any of the parents. In this selection cycle 17 seedlings were fully evaluated and 28 were disqualified in the field. 2. Second Selection Cycle. For the second selection cycle, started in 1994, flowers of Mexican genotype were emasculated and pollinated with pollen obtained from flowers of Thai genotype, and flowers of Brazilian genotype were pollinated with pollen obtained from Mexican ones. One hundred and thirty hybrids were prepared and evaluated during , and the promising ones were propagated vegetatively from cuttings. Twenty plants from each hybrid were planted in an experimental plot for further evaluation: five plants per hybrid in four replicates; they were planted at a spacing of 4 m 5 m. 3. Third Selection Cycle. For the third selection cycle, started in 1999, flowers of Thai types were emasculated and pollinated with pollen taken from the promising hybrids obtained in the second cycle. Four hundred and eighty hybrids were prepared and evaluated during 23-24, of these 39 were disqualified in the field and 9 were fully evaluated in the laboratory. Characterization of the fruits, in all cycles was done according to the following parameters: Fruit size: 1 = small (less than 15 g/fruit), 3 = medium (15 25 g/fruit), 5 = large (more than 25 g/fruit) Flesh color: 1 = mixed 2 = white 3 = pink Seed cavity size: 1 = large 2 = medium 3 = small Taste: 1 = bad 3 = good 5 = excellent Yield: 1 = low 2 = medium 3 = high 4

3 Fruit shape: 1 = distorted 3 = round 4 = oval, 5 = pear-shaped Skin shape: 1 = defective 2 = rough 4 = intermediate 5 = smooth Firmness: 1 = soft 3 = firm Flavour: 1 = strong 3 = medium 5 = no smell Juiciness: 1 = dry 3 = juicy Texture: 1 = jelly 2 = hollow 3 = uniform The final score of each tested clone was reached by adding all the scores of the different properties (maximum obtainable score: 43; minimum: 11). The underlined properties were essential for defining a certain accession as a promising one, i.e., even a fruit that was perfect in all other properties would not qualify as promising if it received a low grading in one of the underlined ones. Hand Pollination In preliminary observations (Zipori, unpublished) it was found that emasculation must be performed when the flower bud was one day before anthesis. This stage can be easily identified by the change in bud color from green to yellowish-green and swelling of the bud (balloon stage). At this stage buds were carefully emasculated, keeping the style and the stigma intact. The emasculated bud was enclosed in a paper bag, and 24 h later, pollen collected from open flowers of predetermined clones was applied to the stigma with a small brush and the bud was re-enclosed in a paper bag. In order to estimate the levels of spontaneous self-pollination in the various clones used, the buds were covered with paper bags before anthesis and the number of set fruits was counted about two weeks later. The efficiency of the emasculation method was determined by covering emasculated buds with paper bags without pollinating them and determining the fruit setting level two weeks later. RESULTS AND DISCUSSION First Selection Cycle Figure 1 presents the distribution pattern for the overall grading of the fully evaluated clones of the Brazilian cultivars in It is clear that there was quite a wide genetic variation within the tested population, and a normal distribution resulted. Figures 2 and 3 present the distributions of the gradings of the Brazilian cultivars in 1996 (as in Fig. 1) and 1995, respectively, for one grading property fruit taste. In 1995 no fruit received a taste grade above 3 (good), whereas in 1996, grades 4 (very good) and 5 (excellent) were found as well. When seed cavity size was assessed a substantial difference was observed between 1995 and 1996 (Figs. 4 and 5). In 1995 only 5% of the population had small seed cavities, whereas in 1996 over 25% of the population fell into this category. These differences between the properties of the same population in two successive years highlight the effects of the environment on the guava phenotype ((Thaipong and Boonprakob, 25). The selection carried out in the first cycle ( ) did not yield any cultivars that that showed sufficient promise for further study and improvement. Although the distribution of the overall grading of the fully evaluated clones shows a normal pattern (Fig. 1), and over 2% received high gradings, no cultivar could be selected as promising. The seeds used for the preparation of the Brazilian seedlings were all from openpollinated plants, and when the high rate of self-pollination in guava (Ojha et al., 1986; Rachna-Singla and Dhaliwal, 23) is taken into account, the probability of obtaining an extremely different cultivar is seen to be rather low. Therefore, in the next cycle, selection was based on hand pollination between extremely different clones. Second Selection Cycle Figure 6 presents the distribution of the fully evaluated clones obtained by hand pollination in the second (1994) cycle. All parents of the Mexican types were characterized by small (3-5g) fruits, sweet taste, white flesh, medium-size seed cavity 41

4 and strong scent; these fruits tended to ripen all at once, within about two weeks. Most parents of the Brazilian types were characterized by medium (15-25 g) fruits, good taste, pink flesh, medium-size seed cavity and medium level of scent. All parents of the Thai types were characterized by large (3-35 g) fruits, white flesh, strong scent and medium to poor taste; their fruits did not change color upon ripening, but remained green. The distribution pattern for the overall grading of the population of the second cycle (Fig. 6) was similar to that obtained for the previously evaluated clones of the first cycle (Fig. 1), obtained by open pollination. However, some clones from the second cycle population were selected as promising. A description of these clones is presented in Table 1. The clones of the second cycle were obtained by pollination of extremely different clones of guava, and the promising clones obtained from such crosses were very different from both parents, and certainly better. Third Selection Cycle Figures 7 and 8 present the distribution of taste grading and seed cavity size for the population produced by the third cycle (1999) of hand pollination. In this cycle, emasculated flowers of Thai guava were pollinated with pollen taken from the promising types obtained in the second cycle. It is clear that there was a regression in the taste of the clones obtained (Fig. 7) and an improvement regarding seed cavity size (Fig. 8), compared with the 1994 selection. Both properties seem to be strongly affected by the female parent the Thai guava in this case. The effect of the female parent was also visible in field observations: most clones obtained from the third cycle bore round fruits that resembled the Thai types. No clone from this selection cycle was selected as promising. Fruit Self-Setting The rate of fruit self-setting was tested in the Brazilian and the Mexican types: among the former 21% of self-pollinated flowers set fruit whereas, among the latter only.9% did so. The Mexican types are probably highly self-incompatible whereas the Brazilian types are self-compatible. It can be expected, therefore, that among Brazilian clones obtained by open pollination, a relatively high percentage of the progeny will be the result of self pollination, whereas among Mexican clones, most of the progeny will be hybrids. Emasculation Efficiency Fruit self-setting occurred in 5% of the non-pollinated emasculated buds, although they were covered with paper bags after emasculation. This could have been due to incomplete removal of anthers from some buds during emasculation. However, this means that emasculation efficiency was high and that the majority of fruit setting indeed resulted from manual pollination when that was applied. The objectives of the guava breeding program in Israel have been only partially achieved so far. The promising types that have been identified are being tested on semicommercial plots and preliminary export trials are to be carried out in 25. However, further improvement is needed as not all the goals have been achieved. An effort is being made to reduce seed-cavity size and seed size. The importance of the introduction of genetically different types into the breeding program has been demonstrated in this study, although sometimes the result obtained was no improvement, as is shown by comparing the 1994 and 1999 cycles. It is extremely important to evaluate the fruits over a number of years, as the environmental effects on important fruit quality parameters is substantial. An additional (fourth) cycle of hand pollination was done during June 25; it included both male and female sources of Egyptian origin. Literature Cited Canizares, Z.J Breeding guava, Psidium guajava, by mass selection. Ciencia y Tecnica en la Agricultura, Citricos y otros Frutales. 4(3/4):7-21 (Spanish, Eng. Abstr.) 42

5 Chezhiyan, N Stigma receptivity, flower shedding, flower abnormality and pollination studies in Psidium sp. Madras Agri. J. 75(1-2):29-32 Gur, A. Spiegel, P., Openheimer, C., Y. Pat and S. Stoller Fruit Growing. Hassadeh Library (Publ.) (In Hebrew). Kahal, Y. 2. Guavas in the markets of Europe (in Hebrew). Mkt. Res. Unit., Ministry of Agriculture, Israel. A collection of reports. Kovetz, J. 2. New fruit crops in Israel (in Hebrew). Fruit Board of Israel (publish). Nalini, A.S., Gubbaiah, Narayana-Reddy, M.A., Farooki, A.A. and Nalawadi, U.G Studies on the floral biology of guava (Psidium guajava L.) variety Lucknow-49 (Sardar). Mysore J. Agri. Sci. 7(1):24-37 Ojha, A.P., Tiwari, J.P. and Misra, K.K Studies of floral biology of guava (Psidium guajava L.) cultivars under Tarai conditions of Uttar Pradesh. Prog. Hort. 18(3-4): Pereira, F.M. and Sao Jose, A.R Study of different methods of pollen collection and pollination of guava (Psidium guajava L.) (Portuguese, English abs.). Cientifica 15(1/2): Rachna-Singla and Dhaliwal, G.S, 23. Pollen, pollination and fruit set studies in different genotypes of guava in winter and rainy seasons under Ludhiana conditions. Haryana J. Hort. Sci. 32(3/4) Thaipong, K. and Boonprakob, U. 25. Genetic and environmental variance components in guava fruit qualities. Sci. Hort. 14:37-47 Tables Table 1. Some properties of promising guava clones from the breeding program in Israel. male Parents female clone Fruit size (g) Flesh color Seedcavity size taste Thai Mexican 61/ white Medium 3 5 Mexican Brazilian 58/ white small 4 4 Mexican Brazilian 68/ pink medium 3 4 Mexican Brazilian 61/ pink small 5 3 Thai Mexican 11/ white small 4 4 Scent 43

6 Figures overall grading level (37=v. good; 22=v.bad) Fig. 1. Population distribution of fruits obtained from progenies of Brazilian cultivars, (bad) 2 (reasonable) 3 (good) 4 (v. good) 5 (excellent) Taste grade Fig. 2. Distribution of taste grading 1995 of seedlings obtained from Brazilian cultivars. 44

7 (bad) 2 (reasonable) 3 (good) 4 (v. good) 5 (excellent) Taste grade Fig. 3. Distribution of taste grading 1996 of seedlings obtained from Brazilian cultivars (large) 2 (medium) 3 (small) Seed cavity size Fig. 4. Distribution of seed-cavity size of seedlings obtained from Brazilian cultivars,

8 (large) 2 (medium) 3 (small) Seed cavity size Fig. 5. Distribution of seed-cavity size, of seedlings obtained from Brazilian cultivars, overall grading level (35=v. good) Fig. 6. Population distribution of cultivars of 1994 hand pollination. 46

9 (bad) 2 (reasonable) 3 (good) 4 (v. good) 5 (excellent) Taste grading Fig. 7. Distribution of taste grading of 1999 hand pollination (large) 2 (medium) 3 (small) Seed cavity size Fig. 8. Distribution of seed-cavity size of 1999 hand pollination. 47

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