Short communication
Effect of the male parent on pericarp and seed
weights in several Floridian mango cultivars
A. Dag
a,*, S. Gazit
a, D. Eisenstein
a, R. El-Batsri
b, C. Degani
ba
The Kennedy±Leigh Centre for Horticultural Research, The Hebrew University of Jerusalem, Rehovot, 76100, Israel
b
Institute of Horticulture, Agricultural Research Organization, The Volcani Center, Bet Dagan, Israel
Accepted 30 March 1999
Abstract
Self- and cross-pollination effects on mango pericarp and seed weights were studied. Fruit was collected from cultivar `6±6' trees caged with, and without, `Tommy Atkins' (`Tommy') as he pollenizer, and from plots consisting of adjacent blocks of `Maya' and `Tommy' or `Maya' and `Kent' cultivars. Selfed and outcrossed offspring were identified using the triosephosphate isomerase (TPI) isozyme system. Selfed `Keitt' progeny showed no significant relationship between TPI isozyme genotypes and pericarp and seed weights. No significant differences in pericarp or seed weights were found between outcrossed and selfed fruit for `Maya', `Tommy' or `Kent'. In contrast, pericarp and seed weights from fruit of `6±6' originating from cross-pollination were >50% heavier than self-pollinated fruit.#1999 Elsevier Science B.V. All rights reserved.
Keywords: Isozyme analysis;Mangifera indica; Pollen-parent effect; Pollenizer
1. Introduction
Most of the world's modern commercial mango (Mangifera indicaL.) cultivars were selected in Florida, or are descendants of Floridian cultivars (Campbell,
* Corresponding author. Tel.: +972-8-9481090; fax: +972-8-9468263
E-mail address:dagarnon@agri.huji.ac.il (A. Dag)
1992; Knight, 1997). `Keitt', `Tommy Atkins' (`Tommy'), `Kent' and `Maya' are the main commercial mango cultivars in Israel (Homsky, 1997). The first three were selected in Florida and `Maya' is probably an offspring of the Floridian `Haden'.
In mango, the effect of the male parent on pericarp and seed weights cannot be explored by hand-pollination studies because of the very low fruit set of pollinated flowers (Davenport and Nunez-Elisea, 1997). However, in studies carried out in mango orchards, this effect could be determined by identification of the pollen parent, using isozymes as genetic markers (Dag et al., 1997, 1998).
In avocado (Degani et al., 1990b), litchi (Degani et al., 1995) and highbush blueberry (MacKenzie, 1997), outcrossed fruits are heavier than selfed ones, and the outcrossed fruit of avocado, litchi and almond (Torre Grossa et al., 1994) contain heavier seeds than their selfed counterparts. The reduced fruit and seed weight of selfed progeny has been suggested to be due to inbreeding depression (Sedgley and Griffin, 1989).
Pericarp and seed weights are economically important traits. The consumer prefers a medium-sized fruit with a small seed. The potential for positive or negative pollenizer effects should be determined and taken into account in orchard planting design.
In the present work, isozyme analysis was used to study the possible relationship between embryo triosephosphate isomerase (TPI) isozyme genotypes in `Keitt' progeny and the weights of the pericarp and seed, and the effect of the pollen parent on pericarp and seed weight in fruit progeny of several Floridian mango cultivars.
2. Materials and methods
Studies were carried out in adjacent `Tommy' and `Maya' blocks at Merom Golan and Neve Ur in 1994, and in adjacent `Kent' and `Maya' blocks at Ramat Magshimim in 1996. In February 1994, before flowering, six `6±6' trees in a mango plot at the Faculty of Agriculture Farm in Rehovot were enclosed in 15-mesh screen cages and a small beehive was placed inside each. Small flowering `Tommy' pollenizer plants (two-to-three per caged tree) were introduced into three of the cages. In February 1995, 10 `Keitt' trees were enclosed in five cages (two per cage), without pollenizer, at The Volcani Center in Bet Dagan.
2.1. Isozyme analysis
3. Results
3.1. Relationship between fruit TPI isozyme genotypes and pericarp or seed weights
`Keitt' is heterozygous (ab) in the TPI isozyme system (Table 1). Isozyme analysis of 137 selfed `Keitt' offspring obtained from caged trees showed the following genotype distribution: 31 aa, 76 ab and 27 bb. No significant relationship was found between the three TPI isozyme genotypes and the fruit's pericarp or seed weights. Hence, differences between differentTpi genotypes in the following studies were attributed to the effect of the pollen parent.
3.2. Effect of the pollen parent on pericarp and seed weights
TPI analysis enabled us to unequivocally identify selfed and crossed offspring of four mango cultivars (`Tommy', `Maya', `Kent' and `6±6') exposed to a specific pollenizer (Table 1). For the first three cultivars, no significant difference in pericarp or seed weight was found between selfed and outcrossed progeny (Table 2). In contrast, a highly significant difference was found between `6±6' selfed and outcrossed progeny: outcrossed pericarp and seeds were ca. 1.5 times heavier.
4. Discussion
There was no noticeable difference in pericarp weight between selfed and crossed fruit of the four commercial mango cultivars (`Tommy', `Lily', `Kent' and `Maya') studied in the present (Table 2) and prior (Dag et al., 1997, 1998) works. In the prior studies, seed weight was affected: it was significantly greater in crossed fruit by 15% in `Tommy' and 17% in `Lily'. For `Tommy' no such effect was found in the present study (Table 2). This inconsistency may result from different fruit-setting periods, which might counteract the advantage of
Table 1
Tpiisozyme genotypes of five mango cultivars used as mother trees and their pollenizers
Cultivar Tpi Pollenizer Tpi
`Keitt' ab Ð Ð
`Kent' bb `Maya' aa
`Tommy' bb `Maya' aa
`Maya' aa `Tommy' bb
hybrid seeds. Although `Tommy' tends to start flowering two-to-three weeks before `Maya', the early bloom does not usually set fruit in Israel. However, early warm weather allows early fruit set of selfed fruitlets only, giving them the advantage over the later-setting, crossed fruitlets. In contrast, when fruit set is delayed, both selfed and crossed fruitlets are of the same age: the advantage of the latter can then be realized.
In contrast to the above findings, a pronounced and significant increase, of over 50%, in pericarp and seed weights was found in `6±6' crossed fruit (Table 2). Other mango cultivars may show a similar response to a suitable pollenizer. `Irwin', the parent of `6±6' (Slor and Gazit, 1982), may be such a cultivar.
Different pollenizers have been found to differ in their effect on seed and pericarp weight in avocado (Degani et al., 1990b) and apple (Keulemans et al., 1996). That such a phenomenon may also occur in mango is worth taking into account.
Table 2
Effect of the pollen parent on pericarp and seed weights in mature mango fruits from progenies of caged (`6±6') and open-pollinated (`Tommy', `Maya' and `Kent') trees
Fruit
Selfed `6±6' 18 258 10.9
Outcrossed `Tommy' 26 392 16.6
Significancea **c ***d
`Tommy'
Selfed `Tommy' 68 256 17.5
Outcrossed `Maya' 185 242 16.8
Significancea NSb NSb
`Maya'
Selfed `Maya' 86 274 16.0
Outcrossed `Tommy' 63 259 16.8
Significancea NSb NSb
`Kent'
Selfed `Kent' 137 333 16.6
Outcrossed `Maya' 32 341 16.7
Significancea NSb NSb
a
t-Test with equal variances. b
NS, nonsignificant,p> 0.05. c
Significant,p< 0.05. d
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