From NewCROP™, Center for New Crops & Plant Products, Purdue University
by Charles B. Heiser
The naranjilla (Solanum quitoense), the cocona (Solanum sessiliflorum) and their hybrid
Introduction
The
Solanaceae has been one of the more important families in providing
useful plants for humankind. By far the greatest number of these comes
from tropical America, white potatoes, tomatoes and chili peppers being
the best known. In recent years the fruits of two others, the tree
tomato (Cyphomandra betacea) and the pepino (Solanum muricatum)
have begun to appear in our markets, both imported from New Zealand
where they had been introduced from tropical America. To my thinking
two other members of the family, the naranjilla (S. quitoense) and the cocona (S. sessiliflorum),
are equal or superior to the last two, but they have yet to reach
markets outside of Latin America. These species, both placed in the
section Lasiocarpa of Solanum, are the subjects of this paper.
The
naranjilla, or lulo as it is often called in Colombia, is a shrubby
perennial, nearly 2 m tall, with large purple veined leaves and white
corollas. The rotund berries are covered with short, stiff hairs which
are fairly readily deciduous so that they are glabrous or nearly so
when they reach the market. At maturity the fruits, 4.5 to 5.5 cm in
diameter, are orange, which is responsible for the Spanish name meaning
"little orange." The flesh or pulp of the fruit, however, is green
(Whalen, Costich and Heiser, 1981). The juice is used most commonly for
drinks. The fragrance and flavor are unique, but some people have
claimed a resemblance to a mixture of pineapple and strawberries,
others to that of citrus fruits. The fruit is rich in vitamins A and C
(Romero-Castañeda, 1961).
In the sixteenth century Cobo (Patiño,
1962) described plants from the regions of Popayan and Quito that are
thought to represent the naranjilla. To this day Colombia and Ecuador,
where the plants are generally grown at altitudes of 1000 to 1500 m
remain the principal producers. It is also grown in Venezuela and at
one time in Peru. Less than a half century ago it was introduced to
Panama and Costa Rica, where it is now well established, and more
recently to Guatemala (Heiser, 1985). Attempts to establish it as a
crop in Florida were unsuccessful, although the early trials appeared
promising (Ledin, 1952). The plant was promoted in a recent publication
(National Research Council, 1975) and since that time I have had
requests for seeds from people in tropical Asia and Africa.
For
a domesticated plant, the naranjilla shows extremely little variability
(Heiser, 1972; Whalen et al., 1983). Plants grown in Ecuador are
unarmed whereas to the north of that country, they generally have small
prickles on the leaves and stems (Schultes and Romero-Castañeda, 1962).
In Ecuador five "varieties" are recognized: agria, Baeza, Baeza roja,
bola, and dulce, distinguished by very slight differences in the
fruits. Because little breeding work has been done with the naranjilla,
the plants grown today probably differ little from those found by the
Spanish when they arrived in the Americas. Although the naranjilla
occasionally escapes from cultivation to establish weedy populations,
no truly wild type is known.
The cocona, also known as topiro or
tupiru and in Brazil as cubiu, became known to Europeans some half a
century later than the naranjilla (Patiño, 1962) and today is widely
cultivated in the upper Amazon basin at altitudes up to 700 m or
slightly higher. It is a shorter plant than the naranjilla, and it has
even larger leaves, generally with little or no purple pigmentation,
and greenish-white corollas. The hairs on the berry are softer and more
readily deciduous than those of the naranjilla. The mature fruits are
orange to maroon and rather variable in shape and size from 4 to 9 cm
in diameter. The fruit flesh is nearly white to pale yellow. The aroma
and taste of the juice are less pronounced than that of the naranjilla.
In addition to being used for juice, the fruits are also used as a
vegetable. The fruit is rich in iron and contains vitamins A, C and
niacin (Salick, 1989).
A wild type of the cocona (S. sessiliflorum var. georgicum),
known from a few collections in Colombia, Ecuador and Peru, differs
from the domesticate by being prickly and having much smaller fruits.
In Ecuador, a weedy or wild unarmed type, has fruits about 3 cm in
diameter, and is known as naranjilla jíbara. Clement (1989) considers
the cocona one of the several fruits domesticated in western Amazonia.
My
involvement with these species began in 1962. On my early trips to
South America I found the naranjilla very abundant and inexpensive in
markets in Ecuador but over the years it became less numerous and more
expensive. The principal reason for this apparently is the large number
of diseases and pests to which the naranjilla is subject. One of the
most serious of these is root knot nematodes. Resistance to root knot
nematode was discovered in S. hirtum (Heiser, 1971), a species that crosses readily with S. quitoense;
and although some effort has been made to incorporate this trait in the
naranjilla, resistant varieties have yet to be grown commercially
unless it is in Colombia, a country from which I have no recent
information.
In 1982 a conference on the naranjilla was held in
Quito (Anon., 1984). Before the conference Saúl Camacho took me to the
experiment station for the naranjilla at Chaco and there for the first
time I saw hybrids of the naranjilla and the cocona. Although more like
the cocona in general aspect, the hybrids had a number of intermediate
characters. The hybrid was of great interest to me, for I had tried to
make it for many years without success. Even more surprising was the
account of its origin, for it had been made by a campesino, Raul
Viteri. He had heard of plant hybridization being used to improve
plants so he had crossed the two species, using naranjilla jíbara as
the pollen donor. Months later under the naranjilla he found seedlings
whose leaf coloration was intermediate between that of the putative
parents. He transplanted some of the seedlings and found that the
fruits were not attacked by diseases or insects. The fruits although
smaller than naranjillas had a similar color and taste. The seeds were
not viable but vegetative propagation was successful (Torre and
Camacho, 1981). I made a brief visit to Ecuador in 1985. I didn't visit
markets in Quito but in those at Ambato the only fruits I saw were from
the hybrid which were called naranjilla or naranjilla chica (small).
They were readily recognizable as the hybrid for they were only half
the size of true naranjillas and contained very few or no seeds. On
this trip I also learned that the experiment station at Chaco had been
abandoned by the government because of a recent financial crisis.
On
my return to Indiana I renewed my efforts to produce the hybrid and
numerous attempts during the next five years were again unsuccessful.
No fruit ever developed on the naranjilla as a result of the cross, and
although the reciprocal cross yielded several fruits, not a single seed
was found.
My next trip to Ecuador was in 1988, and I did see a
number of what appeared to be normal naranjillas. On two occasions our
hostess in Quito purchased some and I was puzzled because I failed to
find a single seed in any of the fruits. The answer was provided when
Jorge Soria and I made a trip to the new station that had been
established for the naranjilla at Palora. Although Palora at an
altitude of 950 m is too low for the best growth of the naranjilla, the
hybrid thrives there. We learned that a few years earlier some weeds
near a field where the hybrids had been growing had been sprayed with
2-4,D. It was later noted that the hybrids downwind of the spray had
fruits about twice the size of the other plants. Since that time
hybrids in flower have deliberately been sprayed with a very dilute
solution of 2-4,D to produce larger fruits, such as those we had seen
in Quito. In 1990 it was estimated that two thirds or more of the crop
in Ecuador resulted from hybrids sprayed with 2-4,D (J. Soria, pers.
commun.).
Again following my return to Indiana I attempted to
make the hybrid, using some new accessions that I had acquired from
Victor Rodriguez as well as my older ones. In addition to my own desire
to obtain the hybrid, there were other reasons for producing it as
well. First, the hybrid being grown in Ecuador was very uniform,
possibly constituting a single genotype, and hence likely had great
genetic vulnerability. Secondly, I thought that it might be possible to
produce a larger fruited hybrid by using a large fruited cocona as a
parent eliminating the necessity of spraying with 2-4,D. Again a number
of fruits was formed when the cocona was used as the female parent. In
order to attempt embryo rescue, my colleague Martha Crouch examined a
very young fruit in search of embryos. None was found. The other fruits
were allowed to reach maturity and in one of them two partially
developed seeds were found. These were planted on a nutrient medium
(Miller, 1969) supplied by Carlos Miller. Both germinated and were
transplanted to soil six weeks later. The parents of this hybrid were a
domesticated cocona which I had collected at Yanzatza, Ecuador (8255)
and the variety Baeza roja of the naranjilla.
The hybrids (8919)
grown in the greenhouse were more vigorous than either parent and
morphologically similar to Viteri's hybrid except in two respects. The
fruits were much larger, slightly larger than naranjillas, and the
fruit flesh was orange instead of green. The increase in size was
expected, for the cocona parent had fruits over 7 cm in diameter, but
the orange color was not anticipated. Little is known of the genetics
of this group of Solanum, so
the reason for the different fruit colors remains speculative. One
explanation may involve the difference in the parentage of the two
hybrids. Viteri used a wild cocona with small fruits that externally
are yellow-orange whereas I used a domesticate with maroon fruits;
both, however, have a very light colored flesh. The variety of the
naranjilla used by Viteri is unknown, but considering the region where
he made the hybrid I would judge that it was dulce. The fruit of that
variety has a deep green flesh, whereas Baeza roja, the male parent of
my hybrid, has a fruit with much lighter green flesh. Another possible
explanation in view of the different female parentage of the two
hybrids is that a maternal effect may be operating. Viteri's hybrid has
a light green fruit flesh approaching that of the naranjilla. Mine is
nearer to that of the cocona, but not identical to it by any means.
Salick (1989) has postulated a maternal effect to account for the size
and shape of fruits in hybrids involving varieties of cocona with
different fruit types.
My hybrids gave pollen stainabilities of
28 and 38%. No seed was set on selfing, in sib crosses or in
backcrosses made to either parent in both directions. A few seeds,
however, were found in some of the fruits in a greenhouse open to
pollinators in which several accessions of both of the parental species
as well as other species of the section were growing. The low fertility
of the hybrids can probably be explained as the result of meiotic
irregularities. At diakinesis in one hybrid the following pairing
configurations were observed: 12II (3 cells), 11II2I (3). 10II1III1II
(8), 10II1IV (13), 10II4I (7), 9II1III,3I (7), 9II1IV2I (6) and 9II6I
(1).
The aroma and the flavor of the fruit of the new hybrid are excellent.
They are very similar to that of the naranjilla but not identical to
it. This opinion is based on my own evaluation and that of three
others. I do not yet have reports on it from the people who are growing
it in Florida and Ecuador. Possibly the different color of the juice
may hinder its acceptance in areas where people expect it to be green;
on the other hand, it may make it more acceptable in new areas.
Although I hesitate to make predictions, I feel that the juice of both
the naranjilla and the hybrid could become popular in the United States
and Europe. As for the cocona, it may become more widely grown in the
tropics, but I do not believe that either as a juice or as a vegetable,
it can compete with the many other juices and vegetables now available
in the northern temperate zone.
The enthusiasm for growing the
hybrid in Ecuador could mean that attempts to improve the naranjilla by
crossing will be abandoned. I hope that this does not prove true.
Although there is very little variability in this species, it is now
known to hybridize with five other species (Heiser, 1989) so that genes
for its improvement may be available. Through backcrossing it may be
possible to transfer desirable genes into the domesticated species.
Such a procedure can readily be accomplished by scientists in the Third
World who may lack the facilities to pursue newer more sophisticated
methods for gene transfer.
References
•
Anonymous, 1984, "Memorias de la primera conferencia
internacional de naranjilla," Instituto Nacional de Investigaciones
Agropecuarias, Quito, Ecuador.
• Clement, C., 1989, A center of crop diversity in western Amazonia, BioSciences 39:624-630.
• Heiser, C., 1971, Notes on some species of Solanum (sect. Leptostemonum) in Latin America, Baileya 18:59-65.
• Heiser, C., 1972, The relationship of the naranjilla, Solanum quitoense, Biotropica 4:77-84.
• Heiser, C., 1985, "Of Plants and People," University of Oklahoma Press, Norman.
• Heiser, C., 1989, Artificial hybrids in Solanum sect. Lasiocarpa, Syst. Bot. 14:3-6.
• Ledin, R., 1952, The naranjilla (Solanum quitoense Lam.), Proc. Florida Statc Hort. Soc. 65: 187-190.
•
Miller, C., 1969, Cytokinin production by mycorrhizal
fungi, in: "Proceedings of the first North American Conference on
Mycorrhizae," Misc. Publ. 1189, U.S. Dept. Agric., Washington, D.C.
•
National Research Council, 1975, "Underexploited tropical
plants with promising economic value," National Academy of Sciences,
Washington, D.C
• Patiño, V., 1962, Edible fruits of Solanum in South American historic and geographic references, Bot. Mus. Leaf., Harvard Univ. 19:215-234.
• Romero-Castañeda, R., 1961, El lulo: una fructa de imponancia economica. Agricultural Tropical 17:214-218.
• Salick, J., 1989, Cocona (Solanum sessiliflorum)
production and breeding potentials of the peach-tomato, in: "New Crops
for Food and Industry," Wickens, G. and Day, P., eds., Chapman and
Hall, London.
• Schultes, R. and Romero-Castañeda, R.,
1962, Edible fruits of Solanum in Colombia, Bot. Mus. Leaf., Harvard
Univ. 19:235-286.
• Torre, R. and Camacho, S., 1981,
Campesino fitomejorador de naranjilla, Carta de Frutales no. 14,
Instituto Nacional de Investigaciones Agropecuarias, Quito, Ecuador.
• Whalen, M. and Caruso, E., 1983, Phylogeny of Solanum sect. Lasiocarpa (Solanaceae): Confluence of morphological and molecular data, Syst. Bot. 8:369-380.
• Whalen, M., Costich, D. and Heiser, C. 1981, Taxonomy of Solanum section Lasiocarpa, GentesHerb. 12:41-129.
Last update Monday, February 23, 1998 by aw
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