Response of squash (
Cucurbita spp
.) as rootstock
for melon (
Cucumis melo
L.)
Ekaterini Traka-Mavrona
a,*, Metaxia Koutsika-Sotiriou
b,
Theodora Pritsa
aa
National Agricultural Research Foundation (N.AG.RE.F.), Agricultural Research Center of Macedonia-Thrace, 570 01 Thermi, Thessaloniki, Greece
b
Aristotelian University of Thessaloniki, Department of Agriculture, Laboratory of Genetics and Plant Breeding, 540 06 Thessaloniki, Greece
Accepted 7 July 1999
Abstract
The effects of different Cucurbita spp. rootstocks on melon cultivars belonging to different horticultural groups were studied by comparing grafted plants with non-grafted ones under greenhouse and open ®eld growing conditions. Winter melons (Cucumis meloL.) of the Inodorus group, cvs. `Thraki', `Peplo' and `Lefko Amynteou', and a summer melon of the Cantalupensis group, cv. `Kokkini Banana', were used as scions. The commercial hybrids ofCucurbita spp. `TZ-148' and `Mamouth' and the landrace of winter squash (C. moschataL.) `Kalkabaki' were used as rootstocks. The commercial rootstocks were compatible with all scion cultivars tested, while the landrace was compatible with the three cultivars but with lower survival ratios. Generally, differences in stem diameter betweenCucurbitaandCucumisreduced the survival ratio of grafts. Fruit yield was not affected by any rootstock. Descriptive and qualitative characteristics of the fruit of the grafted plants were similar to those of the intact ones, except for taste and texture, which showed a remarkable deterioration in some of the stock/scion combinations tried. The deterioration was more severe under protection. However, allCucurbita spp. rootstocks were found acceptable for honeydew melons (cv. `Lefko Amynteou'), withC. moschata(cv. `Kalkabaki') being the best. The landrace ofC. moschatais recommended as a source of breeding material for rootstocks of honeydew melons.#2000 Elsevier Science B.V. All rights reserved.
Keywords: Cucumis melo;Cucurbita moschata;Cucurbita spp.; Melon; Grafting; Rootstock; Scion
*
Corresponding author. Tel.:30-31-473433; fax:30-31-471209.
E-mail address: tpritsa@agro.auth.gr (E. Traka-Mavrona).
1. Introduction
The wide cultivation of unimproved local populations of melons, combined with injury by soil-borne diseases (Fusarium wilt., etc.) because of continuous cropping, resulted in a 20% decrease of the cultivated area in Greece in the last 10 years. Combined breeding programs could be applied to prevent the occurrence of soil-borne diseases (McCreight et al., 1993). However, breeding new cultivars, resistant to diseases, is time consuming and enhances the danger of the resistant cultivars becoming susceptible to new races of pathogens. On the other hand, grafting onto resistant rootstocks may enable the control of soil-borne diseases (Lee, 1994; Oda, 1995).
According to Lee (1994) and Oda (1995), grafting is an important technique for the sustainable production of fruit-bearing vegetables in Korea, Japan, and some Asian and European countries, where land use is very intensive and continuous cropping is common. In Greece, grafting is highly popular, especially in southern areas, where early cropping of watermelons and melons under low tunnels is practiced. The ratio of the production area using grafted plants to the total production area, amounts to almost 90±100% for watermelons and 40±50% for melons in the southern part of Greece. Cucumbers are grafted at a ratio of 5±10%, while eggplants and tomatoes at 2±3%. In northern Greece, growing grafted fruit-bearing vegetables is a rare practice.
Melons of all kinds are grafted to control Fusariumwilt and to increase low temperature tolerance (Oda, 1995). For this purpose, melons are grafted onto the same species (Cucumis meloL.), but very rarely onto pumpkin (Cucurbita spp.,
Cucurbita moschataCucurbita maxima hybrids) and white gourd (Benincasa
hispida) rootstocks, since fruit shape and the taste of plants grafted onto pumpkin, show a remarkable deterioration. Thus, inter-generic grafting is mainly applied to oriental melon (Lee, 1994). Generally, the following problems are commonly associated with grafting and cultivating grafted plants (Lee, 1994; Papadopoulos, 1994; Oda, 1995): Grafting requires time, space, materials and high expertise. Depending on the combination of scions and rootstocks, graft incompatibility and a decrease in the quality of fruits may appear. Also, the grafted plants often require improved cultivation methods and intensive postgraft care. The effects of rootstocks on fruit quality are often detrimental, except for fruit size, and, therefore, most newly devised growing recommendations are aimed at minimizing these effects (Lee, 1994). However, the grafting of vegetables is extremely popular in many countries, and the demand for successfully grafted seedlings is growing rapidly in commercial vegetable culture.
Today, a large number ofCucurbita spp.cultivars have been bred and released as rootstocks for practical use in melon production. In the present study, we investigated the response of `TZ-148' and `Mamouth', commercial hybrids of
`Kalkabaki', as rootstocks for Greek melon cultivars of C. melo L. group Inodorus andC. melo L. group Cantalupensis. It is the ®rst time that local, well adapted, cultivars of melons are tried as scions ofCucurbita spp. rootstocks, the last including an experimental rootstock of a traditional winter squash landrace.
2. Materials and methods
2.1. Plant material
The experiments were conducted in a plastic greenhouse during 1996 (Experiment 1) and in the open ®eld during 1998 (Experiment 2), at the Agricultural Research Center of Macedonia and Thrace farm, Thessaloniki. The cultivars used as scions, were `Thraki' and `Kokkini Banana' in Experiment 1 and `Thraki', `Kokkini Banana', `Peplo' and `Lefko Amynteou' in Experiment 2. `TZ-148' and `Mamouth' (Geoponiko Spiti, Greece), commercial hybrids of
Cucurbita spp., were used as rootstocks. In Experiment 2, an experimental rootstock, the winter squash (C. moschata L.) cv. `Kalkabaki', was added. `Kalkabaki' is a traditional cultivar grown to maturity for use as a sweet pie ingredient. The fruit has a deep orange ®ne-textured ¯esh, with high sweetness and taste. It was the ®rst time that it was tried as a rootstock.
The cultivars `Thraki', `Peplo' and `Lefko Amynteou' belong to theC. meloL. Inodorus group, the winter melons. They are late maturing, with ®rm ¯esh, usually white or green, sweet, with a cucumber like aroma and are long-keeping. Traditionally, they are grown in the open ®eld for local consumption or long-distance transport to markets in autumn±winter months. The cultivar `Kokkini Banana' belongs to the C. melo L. Cantalupensis group, the muskmelon or cantaloupe. It is adapted to grow early, but has relatively poor shipping and storage characteristics. The fruit is spherical, deeply ridged, with soft ¯esh texture, usually white to green, and with a strong aroma.
2.2. Evaluation tests
open ®eld, distances of 150 cm within rows and 200 cm between rows were applied. Normal cultural practices for each experiment were followed for irrigation, fertilizer and pesticide application. A randomized complete block design was adopted with three replications, each consisting of 10 plants. In detail, the treatments applied with each cultivar were: grafting onto `Kalkabaki', `TZ-148' and `Mamouth', and an ungrafted control. Experiments were terminated on 15 September 1996 and 22 September 1998.
The following measurements were recorded: (a) number of plants which survived until the transplanting date (in Experiment 2); (b) stem diameter at hypocotyl and ®rst internode of both grafted and non-grafted plants, 25 days after transplantation (Experiment 1); (c) fruit yield (kg/plant); (d) fruit size (kg/fruit); (e) fruit shape (Dequatorial/Dpolar); (f) thickness of mesocarp (cm); (g) total soluble solids (%); (h) ¯esh taste following a 1±5 scale (where 1very bad,
2bad, 3medium, 4good, 5very good) and (i) ¯esh texture following a
1±5 scale (where 1very spongy, 2spongy, 3medium, 4®ne, 5very
®ne). Yield measurements were recorded on ripe fruits which were gently hand-harvested and transported to the laboratory, where they were counted and weighed. Reported data on descriptive and qualitative characteristics were taken from 10 fruits of each replication. Calipers were used to measure the polar (Dp)
and the equatorial (De) diameter of each fruit. Shape index was calculated by De/ Dp. Each fruit was cut in half along the polar plane, and the thickness of the mesocarp was measured. Flesh taste and texture were measured in two sections of the edible tissue, cut from opposite equatorial zones of the halved fruit, and 3±5 tests per section were recorded. The soluble solids were determined with the use of an Atago PR-100 hand refractometer on the juice taken from the two pieces of mesocarp tissue, which was cut from opposite equatorial zones of the halved fruit.
2.3. Data analysis
Analyses of variance and tests of signi®cance for all traits were performed to determine whether there were signi®cant differences among grafted and non-grafted plants of the same cultivar.
3. Results
Survival ratios of melon transplants grafted onto `TZ-148' and `Mamouth' commercial rootstocks were 42±91% (Fig. 2). The survival ratio of plants grafted onto `Kalkabaki' rootstock was zero in cv. `Thraki' and 8±52% in cvs. `Lefko Amynteou', `Kokkini Banana' and `Peplo'.
Stem diameter at the hypocotyl of the two commercial rootstocks was signi®cantly higher than that of the intact melon cultivars. Thus, it resulted in a proportional decrease in the quotient of the scion diameter at the ®rst internode to the rootstock diameter at the hypocotyl (Table 1). The corresponding quotient of the intact plants (controls) was equal to 1.
Fruit yield of all melon cultivars was not signi®cantly affected by grafting onto `TZ-148' or `Kalkabaki' rootstock (Tables 2 and 3). The use of `Mamouth' rootstock caused a signi®cant decrease in yield per plant of cv. `Thraki', grown under greenhouse conditions (Table 2). The mean fruit weight was also not signi®cantly affected by grafting onto any rootstock (Tables 2 and 3). Similarly, non-signi®cant differences in fruit shape were found (Tables 2 and 3). The effect of grafting on the thickness of the mesocarp of fruits, grown under protection, was not signi®cant (Table 4), while in the open ®eld, the cv. `Thraki' was favoured by grafting onto `Mamouth' rootstock (Table 5). In the case of soluble solids (%), a signi®cant difference in open ®eld growing conditions was noticed, with cv. `Peplo' being inferior after grafting onto `Mamouth' rootstock (Table 5). The consumer's perception of quality was signi®cantly affected by grafting in some applied combinations (Tables 4 and 5). Particularly, both fruit taste and
Table 1
Stem diameter at hypocotyl and ®rst internode of both grafted and non-grafted plants, 25 days after transplantation in the greenhouse (Experiment 1)
Treatment Hypocotyl (D1) (cm)a 1st internode (D2) (cm)a Quotient (D2/D1)a
Thraki/TZ-148 1.49 ab 1.16 a 0.78 b
Thraki/Mamouth 1.52 a 1.30 a 0.85 b
Thraki (control) 1.26 cd 1.26 a 1.00 a K. Banana/TZ-148 1.44 ab 1.13 a 0.78 b K. Banana/Mamouth 1.34 bc 1.08 a 0.81 b K. Banana (control) 1.17 d 1.17a 1.00 a
CV(%) 7 8 5
a
Same letter indicates the absence of signi®cant differences atp0.05 by Duncan's multiple range test.
Table 2
Fruit yield (Kg/plant), fruit size (Kg/fruit) and fruit shape (Dequatorial/Dpolar) of grafted and non-grafted plants grown in the greenhouse (Experiment 1)
Treatment Fruit yield (Kg/plant)a Fruit size (Kg/fruit)a Fruit shape (De/Dp)a
Thraki/TZ-148 2.69 ab 1.92 a 0.92 b
Thraki/Mamouth 2.51 b 1.86 a 0.90 b
Thraki (control) 3.23 a 2.39 a 0.90 b K. Banana/TZ-148 2.41 b 1.83 a 0.96 ab K. Banana/Mamouth 2.48 b 2.11 a 1.08 a K. Banana (control) 2.02 b 1.69 a 0.98 ab
CV(%) 14 13 6
a
texture of the grafted melons were inferior compared to those of the plants grown on their own roots, especially under greenhouse conditions. In open ®eld conditions, ¯esh texture was signi®cantly affected by grafting in cvs. `Thraki'
Table 3
Fruit yield (Kg/plant), fruit size (Kg/fruit) and fruit shape (Dequatorial/Dpolar) of grafted and non-grafted plants grown in the open ®eld (Experiment 2)
Treatment Fruit yield (Kg/plant)a Fruit size (Kg/fruit)a Fruit shape (De/Dp)a
Thraki/Kalkabaki ± ± ±
Thraki/TZ-148 4.49 a 1.57 a 0.87 b
Thraki/Mamouth 6.26 a 1.82 a 0.91 b
Thraki (control) 5.95 a 1.35 a 0.84 b Peplo/Kalkabaki 2.40 a 0.80 a 0.60 c
Peplo/TZ-148 3.52 a 1.28 a 0.59 c
Peplo/Mamouth 2.61 a 1.07 a 0.58 c
Peplo (control) 3.91 a 1.14 a 0.59 c L. Amynteou/Kalkabaki 5.47 a 1.74 a 0.90 b L. Amynteou/TZ-148 3.39 a 1.48 a 0.88 b L. Amynteou/Mamouth 3.96 a 1.51 a 0.88 b L. Amynteou (control) 5.69 a 1.57 a 0.90 b K. Banana/Kalkabaki 2.47 a 0.71 a 1.01 a K. Banana/TZ-148 3.31 a 1.51 a 1.06 a K. Banana/Mamouth 3.00 a 1.62 a 1.03 a K. Banana (control) 4.13 a 1.52 a 1.01 a
CV(%) 29 17 5
a
Same letter indicates the absence of signi®cant differences atp0.05 by Duncan's multiple range test.
Table 4
Thickness (cm), total soluble solids (TSS%), taste and texture of ¯esh of grafted and non-grafted plants grown in the greenhouse (Experiment 1)
Treatment Thickness (cm)c TSS (%)c Tastea,c Textureb,c
Thraki/TZ-148 3.77 a 4.98 a 1.97 b 3.67 bc Thraki/Mamouth 3.48 a 4.89 a 2.42 ab 3.80 bc Thraki (control) 4.01 a 5.43 a 3.54 a 5.00 a K. Banana/TZ-148 3.78 a 6.11 a 2.20 ab 3.41 c K. Banana/Mamouth 3.92 a 5.53 a 1.72 b 3.69 bc K. Banana (control) 3.98 a 5.77 a 3.56 a 4.52 ab
grafted onto `TZ-148' and `Mamouth', `Lefko Amynteou' onto `Mamouth' and `Kokkini Banana' onto `Kalkabaki'. Flesh taste was affected in cvs. `Thraki' grafted onto `TZ-148' and `Mamouth', and `Peplo' onto `Kalkabaki' and `Mamouth'. `Kalkabaki' rootstock contributed to producing fruits of equal quality to those from intact plants of cv. `Lefko Amynteou'.
4. Discussion
From the results obtained on scion-rootstock compatibility, it was found that the landrace `Kalkabaki' (C. moschata L.) as rootstock gave a satisfactory survival ratio of grafts (52%) only in cv. `Lefko Amynteou'. `Thraki' was not compatible (100% mortality), while cvs. `Kokkini Banana' and `Peplo' survived at a ratio of 14% and 8%, respectively. Particularly, the leaves of the non-compatible unions turned yellow and cupped, and the plants died. This is a characteristic of graft-rootstock incompatibility, which contributes to poor vascular connections that possess connecting sieve tubes, cambium and xylem
Table 5
Thickness (cm), total soluble solids (TSS%), taste and texture of ¯esh of grafted and non-grafted plants grown in the open ®eld (Experiment 2)
Treatment Thickness (cm)c TSS (%)c Tastea,c Textureb,c
Thraki/Kalkabaki ± ± ± ±
Thraki/TZ-148 3.03 ab 8.66 cd 1.83 d 2.13 e Thraki/Mamouth 3.41 a 8.84 bcd 1.83 d 2.30 de Thraki (control) 2.57 bc 9.87 abc 3.83 a 4.17 a Peplo/Kalkabaki 2.27 c 8.89 bcd 2.06 d 2.22 e Peplo/TZ-148 2.45 bc 9.15 abcd 2.49 bcd 2.44 de Peplo/Mamouth 2.27 c 7.85 d 2.10 d 2.06 e Peplo (control) 2.47 bc 9.99 abc 3.40 abc 2.80 bcde L. Amynteou/Kalkabaki 2.40 bc 10.35 a 3.90 a 3.90 a L. Amynteou/TZ-148 2.56 bc 10.02 abc 3.51 abc 3.47 abc L. Amynteou/Mamouth 2.42 bc 10.11 ab 3.57 ab 2.86 bcde L. Amynteou (control) 2.42 bc 10.35 a 3.99 a 4.03 a K. Banana/Kalkabaki 2.77 bc 9.72 abc 2.36 cd 2.56 cde K. Banana/TZ-148 2.71 bc 9.67 abc 3.40 abc 3.63 ab K. Banana/Mamouth 2.55 bc 9.66 abc 2.96 abcd 3.27 abcd K. Banana (control) 2.61 bc 10.29 a 3.00 abcd 3.57 ab
CV(%) 14 7 21 17
a
Flesh taste, in a scale 1±5 (1very bad, 2bad, 3medium, 4good, 5very good).
bFlesh texture, in a scale 1±5 (1very spongy, 2spongy, 3medium, 4®ne, 5very
®ne).
cSame letter indicates the absence of signi®cant differences at
in the heterografts Cucumis/Cucurbita(Tiedermann, 1989). Even in the case of `TZ-148' and `Mamouth' commercial rootstocks, the survival ratio of grafts was high only in cv. `Thraki' (92%). Other cultivars survived at a ratio of 42±83%. This could be possibly attributed to the differences in stem diameter between
Cucurbita and Cucumis, which reduced the chance of scion vascular bundles meeting stock bundles, thus resulting in less sites with vascular and phloem connections. Tiedermann (1989) found different numbers of connecting sieve tubes betweenCucumis/CucurbitaandCucumis/Cucumisconnections because of differences in stem anatomy,Cucurbitahaving a large pith cavity.
The results of the effect of the three rootstocks on the agronomic and qualitative characteristics of the four melon cultivars, allow a series of considerations on the feasibility of this technique in the cultivars tested. Contrary to Leoni et al. (1990); Lee (1994) and Oda (1995), there was no clear interaction between rootstocks and varieties, resulting in a fruit yield enhancement. This indicates the importance of the rapid development of phloem and xylem connections, resulting in growth promotion and yield increases.
In agreement with Leoni et al. (1990), fruit descriptive and qualitative characteristics were not signi®cantly affected by grafting in most combinations applied. Even the fruit size was not affected, after grafting onto rootstocks with a vigorous root system. However, in some combinations, deterioration of the consumer's perception of quality was noticed, mainly with respect to ¯esh taste and texture. This was more severe under greenhouse conditions, where fertigation was more ef®cient. Both, `TZ-148' and `Mamouth'Cucurbita spp. commercial rootstocks caused poor taste and texture in cv. `Thraki' (casaba melons, ovoid shaped). `Mamouth' and `Kalkabaki' (C. moschata L.) caused a signi®cant deterioration in taste of cv. `Peplo' (casaba melons, elongated ovoid shaped). All
Cucurbita spp. rootstocks were found suitable for cv. `Lefko Amynteou' (honeydew melons, spherical shaped), producing fruits of equal taste and texture to those of the intact plants, with cv. `Kalkabaki' being the best. Both commercial rootstocks were suitable for `Kokkini Banana' (muskmelons), grown in the open ®eld, but not for the same cultivar under protection. The landrace ofC. moschata
caused a remarkable deterioration of texture.
These results, compared with previous information ± which shows that
are synthesized in the root and are translocated to the scion through the xylem (Biles et al., 1989). Sex expression in cucurbitaceous crops may be in¯uenced by the rootstock (Friedlander et al., 1977; Takahashi et al., 1981). Fruit quality characteristics, such as fruit shape, skin colour, skin or rind smoothness, ¯esh texture and color, rind thickness, soluble solids concentration, etc. are in¯uenced by the rootstock (Lee, 1994). However, honeydew melons (cv. `Lefko Amynteou') were very well adapted to Cucurbita spp. rootstocks. Additionally, this cultivar showed the highest survival ratio of grafts onto the landrace of
Cucurbita moschata rootstock, producing fruits of equal quality to that of the intact plants. The landrace is recommended as a source of breeding material for rootstocks of honeydew melons.
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