Melon fruit color: More than just looks1
Y. Burger1*, Y. Tadmor1, E. Lewinsohn1, A. Meir1, U. Sa’ar1, N. Katzir1,
H.S. Paris1 and A.A. Schaffer2
1
Agricultural Research Organization, Newe Ya’ar Research Center, P. O. Box 1021, Ramat
Yishay 30-095, Israel
2
Agricultural Research Organization, Volcani Center, P. O. Box 6, Bet Dagan 50-250, Israel
*
Corresponding author e-mail: [email protected]
Keywords: Cucumis melo, chlorophyll, shelf life
Abstract
Muskmelons and cantaloupes are climacteric fruits that lose the green color of
their fruit rinds upon ripening. Their yellow or orange appearance is easily recognized
by consumers as a sign of ripeness. However, these melons have a short shelf life, as
this loss of chlorophyll is associated with ethylene synthesis. Observations and
comparisons of these melons with the non-climacteric, long-keeping, yellow-rinded
casaba melons suggest that through genetic recombination it should be possible to
develop cultivars of muskmelons and cantaloupes combining the consumer-driven
characteristic of non-green (yellow or orange) mature fruit color with long shelf life.
INTRODUCTION
One of the most conspicuous characteristics to consumers of melons is external
color. In climacteric melons, this color changes as the fruit ripens. In American
shipping-type and Galia-type melons, the fruit rinds change from dark green to
yellow-orange whilst rinds of Charentais-type melons change from off-white to
creamy yellow. Many non-climacteric melons retain their green rind color through
ripening whilst others change in rind color from green to yellow. Our objective was to
observe and consider the connection between external fruit color change and length of
shelf life, in order to determine if it would be possible, by conventional breeding, to
combine in muskmelons and cantaloupes the desired change of fruit color upon
ripening with a long shelf life.
MATERIALS AND METHODS
Ten cultivars grown in the field at Newe Ya’ar during the summer of 2004
were used for this study. Four of these, all climacteric, were ‘Noy Yizre’el’, an Israeli
cantaloupe, ‘Eshkolit Ha’Amaqim’, an Israeli cultivar derived from crossing a
cantaloupe with a muskmelon, ‘Krymka’ a muskmelon that originated in Crimea, and
‘Arava’, an Israeli hybrid derived from crossing a cantaloupe with a muskmelon. Two
other climacterics were ‘Védrantais’, a French cantaloupe, and ‘Dulce’, an American
shipping muskmelon. Three casabas and one honeydew (all non-climacterics) were
also grown: ‘Tendral Verde Tardio’ and ‘Rochet’ from Spain, ‘Noy ‘Amid’, a yellow
canary-type from Israel, and the American honeydew ‘Tam Dew’.
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Cucurbitaceae 2008, Proceedings of the IXth EUCARPIA meeting on genetics and breeding
of Cucurbitaceae (Pitrat M, ed), INRA, Avignon (France), May 21-24th, 2008
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Over the season, we sampled the fruit rinds of these ten cultivars for
chlorophyll content and, for four of these cultivars, beta-carotene content. Fresh
samples, 0.5 to 0.8 g, were taken from fruit rinds and frozen at -80oC. Techniques
using HPLC for carotenoid analysis were similar to those described by Tadmor et al.
(2005). Chlorophyll content was analyzed according to Arnon (1949).
RESULTS
The observed change in fruit color from green to orange-yellow in ‘Dulce’ can
be attributed to chlorophyll degradation (Fig. 1). Beta-carotene also decreased upon
ripening, although not as much as chlorophyll, leaving the fruit with an orange-yellow
external color. The light-colored non-climacteric ‘Tam Dew’ had low levels of
chlorophyll and beta-carotene throughout development, which approached zero as the
fruit matured.
Figure 1. Chlorophyll and beta-carotene content in the fruit rind of ‘Dulce’ (DUL)
and ‘Tam Dew’ (TAD).
‘Tendral Verde Tardio’ had a high chlorophyll content in the fruit rind from
approximately 20 days past anthesis through to the end of the experiment (Fig. 2). It
also had a high level of beta-carotene in the fruit rind, which tended to decrease from
around 40 days past anthesis. ‘Noy ‘Amid’, the yellow canary-type, had similar
amounts of chlorophyll and beta-carotene as did ‘Tendral Verde Tardio’ at 12 days
past anthesis, but levels of these pigments in ‘Noy ‘Amid’ gradually decreased toward
zero during the experiment.
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Figure 2. Chlorophyll and beta-carotene content in the fruit rind of the nonclimacteric ‘Tendral Verde Tardio’ (TVT) and ‘Noy ‘Amid’ (NA).
Chlorophyll contents of the immature (10 days past anthesis) fruit rinds
differed greatly amount the climacterics (Fig. 3). However, chlorophyll contents of
the mature (40 days past anthesis) fruit rinds of all of these cultivars were nearly zero.
Figure 3. Chlorophyll content in the fruit rind of the climacteric ‘Dulce’ (DUL),
‘Eshkolit Ha’Amaqim’ (ES), ‘Védrantais’ (VED), ‘Noy Yizre’el’ (NY), ‘Krymka’
(KRY) and ‘Arava’.
Among the non-climacterics, high chlorophyll contents were measured in the
mature fruit rinds of the ‘Tendral Verde Tardio’ and ‘Rochet’ (Fig. 4). In contrast,
‘Noy ‘Amid’ and ‘Tam Dew’ had almost no chlorophyll by 32 days past anthesis,
well prior to their maturity.
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Figure 4. Chlorophyll content in fruit rind of the non-climacteric ‘Tendral Verde
Tardio’ (TVT), ‘Noy ‘Amid’ (NA), ‘Tam Dew’ (TAD) and ‘Rochet’.
DISCUSSION
Fruit rind and flesh color have importance not only for consumer acceptability
but also in association with aroma, flavor, and health benefits (Burger et al. 2006).
Understanding the genetic and physiological mechanisms determining developmental
fruit color has important implications for attempting to improve melon fruit quality.
All of the climacteric melon cultivars tested lost the green color of the fruit rind
at maturity, suggesting that this loss is connected with ethylene synthesis. Some of the
non-climacteric melon cultivars retained high amounts of chlorophyll while others did
not. Notably, ‘Noy ‘Amid’ was non-climacteric, having a long shelf life, even though
it lost all of its chlorophyll and became intense yellow at maturity. Obviously,
retention of green color through fruit maturity is not a pre-requisite for long shelf life.
Besides the variation in external fruit color, in melon there is also variation in
flesh (mesocarp) color that includes green, white, cream, and orange, with the
intensity of the orange color being in accordance with beta-carotene content (Burger
et al. 2006). While chlorophyll degradation, fruit softening, and activation of the
abscission zones are clearly ethylene-dependent, the accumulation of soluble sugars
and beta-carotene in the flesh of ripening fruits is ethylene-independent (Ayub et al.
1996; Guis et al., 1997; Hadfield et al. 2000; Nishiyama et al. 2007).
Preliminary results (Y. Tadmor, unpublished) suggest that the development of
the intense yellow color of the mature fruits of ‘Noy ‘Amid’ is conferred by flavonoid
synthesis. The color change from green to yellow in this cultivar is of a different
mechanism than that exhibited by the climacteric melons. These observations suggest
that, through genetic recombination, it should be possible to develop cultivars of
muskmelons and cantaloupes having the consumer-driven characteristic of non-green
(yellow or orange) mature fruit color, as a sign of ripeness, together with long shelf
life.
Literature Cited
532
Arnon DI (1949) Copper enzymes in isolated chloroplasts. Polyphenoloxidase in Beta
vulgaris. Plant Physiol 24: 1-15
Ayub R, Guis M, Ben Amor M,. Gillot L, Roustan J P, Latche A, Bouzayen M, Pech JC
(1996) Expression of ACC oxidase antisense gene inhibits ripening of cantaloupe melon
fruits. Nature Biotech 14: 862-866
Burger Y, Sa’ar U, Paris HS, Lewinsohn E, Katzir N, Tadmor Y, Schaffer AA (2006) Genetic
variability as a source of new valuable fruit quality traits in Cucumis melo. Israel J Plant
Sci 54: 233-242
Guis M, Botondi R, Ben-Amor M, Ayub R, Bouzayen M, Pech JC, Latche A (1997)
Ripening-associated biochemical traits of cantaloupe Charantais melons expressing an
antisense ACC oxidase transgene. J Amer Soc Hort Sci 122: 748-751
Hadfield KA, Dang T, Guis M, Pech JC, Bouzayen M, Bennet AB (2000) Characterization of
ripening-regulated cDNAs and their expression in ethylene-suppressed Charentais melon
fruit. Plant Physiol. 122: 977-983
Nishiyama K, Guis M, Rose JKC, Kubo Y, Bennet KA, Wangjin K, Kato K, Ushijima K,
Nakano R, Inaba A, Bouzayen M, Latché A, Pech JC, Benet AB (2007) Ethylene
regulation of fruit softening and cell wall disassembly in Charentais melon. J Exp Bot 58:
1281-1290
Tadmor Y, King S, Levi A, Davis A, Meir A, Wasserman B., Hirschberg J, Lewinsohn E
(2005) Comparative fruit colouration in watermelon and tomato. Food Res Intl 38: 837841
533
534