From Neglected crops: 1492 from a different perspective
by the Food and Agriculture Organization of the United Nations
Tomatillo, husk-tomato
(Physalis philadelphica)
Common
Names: Physalis philadelphica Lam.
Family: Solanaceae
Common
Names: English:
tomatillo, husktomato, jamberry, ground cherry; Spanish: tomate de
cáscara, tomate de fresadilla, tomate milpero, tomate verde, tomatillo
(Mexico), miltomate (Mexico, Guatemala)
The tomatillo or husk-tomato (Physalis philadelphica)
is a solanaceous plant cultivated in Mexico and Guatemala and
originating from Mesoamerica. Various archaeological findings show that
its use in the diet of the Mexican population dates back to
pre-Columbian times. Indeed, vestiges of Physalis
sp. used as food have been found in excavations in the valley of
Tehuacán (900 BC-AD 1540). In pre-Hispanic times in Mexico, it was
preferred far more than the tomato (Lycopersicon
sp.). However, this preference has not been maintained, except in the
rural environment where, in addition to the persistence of old eating
habits, the tomato's greater resistance to rot is still valued.
Possibly because of the fruit's colourful appearance and because there
are ways of eating it which are independent of the chili (Capsicum sp.), the tomato achieved greater acceptance outside Mesoarnerica and Physalis
sp. was marginalized, or its cultivation was discontinued, as happened
in Spain. It is relevant to note that only in central Mexico is the
fruit of Lycopersicon sp. known chiefly as "jitotomate", since in other parts of the country and in Central and South America it is called "tomate".
P. philadelphica
was domesticated in Mexico from where it was taken to Europe and other
parts of the world; its introduction into Spain has been well
documented. Indeed, it is believed that this species originated in
central Mexico where, at present, both wild and domesticated
populations may be found.
The name "tomato" derives from the Nahuatl
"tomatl"; this word is a generic one for globose fruits or berries
which have many seeds, watery flesh and which are sometimes enclosed in
a membrane.
Of the great number of species of the genus Physalis, very few are used for their fruit. P. peruviana L. has been grown in Peru since pre-Columbian times. The fruit of P. chenopodifolia is picked in the state of Tlaxcala, Mexico. In Europe, P. alkekengi
is grown as an ornamental plant because of the colourful calyx of its
fruit, and its fruit also is used in central and southern Europe. The
tomatillo has been a constant component of the Mexican and Guatemalan
diet up to the present day, chiefly in the form of sauces prepared with
its fruit and ground chilies to improve the flavour of meals and
stimulate the appetite.
The tomatillo is also used in sauces with green chili, mainly to lessen
its hot flavour. The fruit of the tomatillo is used cooked, or even
raw, to prepare purees or minced meat dishes which are used as a base
for chili sauces known generically as salsa verde (green sauce); they
can be used to accompany prepared dishes or else be used as ingredients
in various stews. An infusion of the husks (calyces) is added to tamale
dough to improve its spongy- consistency, as well as to that of
fritters; it is also used to impart flavour to white rice and to
tenderize red meats.
About ten years ago the crop began to be
industrialized in Mexico and agro-industries are currently estimated to
process 600 tonnes per year, 80 percent of which is exported to the
United States as whole tomatillos, without a calyx and canned, while
the remainder is used in the preparation of packaged sauces for the
domestic market.
P. philadelphica
is acquiring importance as an introduced crop in California as a result
of the growing popularity of Mexican food in the United States.
Furthermore, numerous medicinal properties are attributed to it.
Official statistics show that, in 1984, 15 248 ha were sown in Mexico,
with a total production value of 5 797 million pesos and an average per
capita consumption of 2.32 kg. Both in Mexico and Guatemala, wild
tomato fruit from cultivated fields has a predominant place in the
diet, hence in some regions it is an important product among those
gathered in rural areas for immediate consumption and for sale.
Botanical description
P. philadelphica is an
annual of 15 to 60 cm; it is subglabrous, sometimes with sparse hairs
on the stem. The leaf lamina is 9 to 13 x 6 to 10 mm; its apices are
acute to slightly acuminate, with irregularly dentate margins and two
to six teeth on each side of the main tooth, of 3 to 8 mm. The pedicels
are 5 to 10 mm, the calyx has ovate and hirsute lobules measuring 7-13
mm. The corolla is 8 to 32 mm in diameter, yellow and sometimes has
faint greenish blue or purple spots. The anthers are blue or greenish
blue. The calyx is accrescent, reaching 18 to 53 x 11 to 60 mm in the
fruit, and has ten ribs. The fruit is 12 to 60 x 10 to 48 mm in size
and sometimes tears the calyx.
Figure 11. Tomatillo, husk-tomato (Physalis philadelphica): details of the flower and fruit with an accrescent calyx, and a cross-section of the fruit
Ecology and phytogeography
The P. philadelphica plant grows from southern Baja California to Guatemala, from 10 m in Tres Valles, Veracruz, to 2 600 m in the valley of Mexico.
Genetic diversity
There are many local or indigenous varieties of P. philadelphica
which producers recognize by fruit colour and size as well as by the
plant's growth habit although, within these varieties, there is wide
variation, possibly because of their self-incompatibility. The
wild forms are very often found growing in cultivated fields in
traditional agricultural systems, mainly in combination with maize,
beans and gourd. In Mexico, another type of tomato is found which is
sold on the markets as wild from cultivated fields. In actual fact, it
is a cultivated tomato with a small fruit; the reason for this
fraudulence lies in the fact that the price of wild tomatoes growing in
cultivated fields is double that of the cultivated tomatoes.
The
diameter of the 'fruit is bigger in the Mexican tomato (1.08 to 4.9 cm)
than in the Guatemalan tomato (1.04 to 2.89 cm). However, these
measurements correspond mainly to the cultivated tomatoes. In
Guatemala, purplish green, yellowish green and purple tomatoes are
preferred; in Mexico, on the other hand, the variation in colour is
greater, as there are yellow, various shades of green and purple fruits.
The
characteristics showing the greatest variation are fruit size, colour
and average weight; the number and weight of fruit per plant; the
consistency and colour of the flesh; the colour and length of the
calyx; flower size; the number and size of the nodes on the first
bifurcation of the plant; stem colour; the size and number of teeth per
leaf; branching; earliness and pubescence.
The tomatillo or husk-tomato
is a vegetable which is used widely and continuously throughout the
year its current situation is as follows:
· wild fruit found growing in
cultivated fields is picked and sold;
· small-fruited varieties, similar
to those found growing wild in cultivated fields, are specifically
grown for the market;
· there are numerous local indigenous selections
with a large fruit;
· the Mexican varieties Rendidora and Rendidora
mejorada, produced by INIFAP's plant improvers, are rarely used.
In
several regions of Mexico the species P. chenopoclifolia Lam. grows wild in cultivated fields: its use as a potential resource has been recorded.
The species of Physalis
in Mexico and Guatemala are not in any immediate danger of genetic
erosion. However, extensive explorations must be carried out to collect
both cultivated material and wild plants found in cultivated fields so
as to consolidate the gene banks and contribute material and
information towards the genetic improvement programme for this crop. At
present, INIFAP's gene bank in Mexico has approximately 190 collections
of Physalis species, obtained
from four of the country's states while, in the gene bank at the
University of San Carlos, there are 41 accessions from several regions
of Guatemala.
Cultivation practices
Cultivation
practices are cotnmon to the majority of the solanaceous plants.
Transplanting of the tomato is widespread, principally in the areas
where frosts make it essential. Its advantages include saving on seed,
reduced weeding and the possibility of starting the cycle while there
is still another crop on the ground as well as shortening the growing
cycle. Generally speaking, weeding is done by hand or using mechanical
implements. Most growers use chemical fertilizers (nitrogen and
phosphorus): the doses range from 120 to 240 kg of nitrogen and from 60
to 150 kg of phosphorus per hectare. Given the resources, growers are
confident they can control pests and diseases affecting the crop.
However, they would need to know more about the doses, appropriateness,
products and cost-effectiveness ratios of these control practices.
The
tomatillo or husk-tomato is grown mainly on irrigated land. Because of
this, sowing dates vary within each producing area, which explains why
this tomato is found on the market throughout the year. In some areas
it is grown on dry land, both using residual humidity and during the
heavy rainstorms. Sowing density ranges from 17 000 to 25 000 plants
per hectare. The fruit is harvested when it reaches its normal size,
when it has a firm consistency and generally when the apex of the calyx
has begun to break. Small-fruited varieties, selected for this purpose,
undergo cultivation practices similar to those used for the large
tomato.
The greater percentage of dormancy occurs in the seed
recently extracted from the fruit. In less than a year it reaches its
maximum germination potential, losing it drastically as from the third
year under commercial storage conditions. For marketing purposes, the
small fruit must not fill the calycinal envelope. On the other hand,
the large tomato must fill it completely and should preferably break it
to reveal part of the fruit (this is visually attractive to the
purchaser). The wild tomatillo found in cultivated fields adapts to
various environments but it appears mainly on cultivated ground and
sometimes care is taken to prevent its removal during weeding and
earthing up. It appears most commonly on parts of land where vegetable
waste is concentrated and burned after clearance. This tendency may be
due to enrichment of the soil with the ash, the effect of which is to
stimulate high temperatures in the seeds. Its apparent resistance to
the herbicide 2,4-D amine, which is widely used on maize, may help its
survival and even its spread (through the reduction of competifion in
the treated fields) in some agricultural regions.
The only two
Mexican improved varieties, Rendidora and Rendidora mejorada, have the
following characteristics: a smaller and more uniform habit; few or no
hollow fruits; and firmer fruit of a lime-green colour.
Prospects for improvement
The
variety Rendidora was formed from the best collections selected in the
state of Morelos, where improvement work was carried out. Rendidora
mejorada was derived from this variety. In Guatemala, in spite of the
wide genetic variation recognized, genetic improvement of this crop is
still in its early stages. The characteristics most affected by the
environment are leaf size and shape, growth habit and the growing cycle
of the plant. Soil fertility stands out as an environmental factor in
expression of the phenotype.
Genetic improvement work in Mexico
should aim at: plants with large and firm, deep green (not yellow)
fruit; high yield, wide adaptation and resistance to viral diseases and
powdery mildew (Oidium spp.).
Improvement aims in Guatemala should be the same, except regarding
fruit colour, since purplish green and yellowish green tomatoes are
preferred in that country.
P. chenopodifolia
is in the initial stage of domestication and shows a favourable
response to agricultural practices; accordingly, it must be collected
and evaluated so that the potential for better utilization in the
future may be established.
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