ISS N -0245-2528

~u- ().Q, tC1 9 t

PROCEEDINGS OF THE

INTERAMERICAN SOCIETY FOR TROPICAL HORTICULTURE

VOLUME 35 1991

XXXVII ANNUAL MEETING AND

MEMORIAS DE LA III SYMPOSIO DE MANEJO CALIDAD Y FISIOLOGIA POSTCOSECHA J)E FRUTAS

SPONSORED BY

INTERAMERICAN SOCIETY FOR SOCIEDAD CHILENA TROPICAL HORTICULTUH.E DE NEMATOLOGIA

CENTRO DE ESTUDIOS DE POSTCOSECHA SOCIEDAD AGRONOMICA UNIVERSIDAD DE CHILE DE CHILE

VINA DEL MAR, CHILE OCTOBER 7-12, 1991

Proc. Interamer. So c . Trap. Hor t . 35 : 133 -140

CALABAZA IMPROVEMENT AND CULTURAL PRACTICES TO ENHANCE THE POTENTIAL FOR INCREASED PRODUCTION

D. N. MAYNARD Gulf Coast Researc h and Edu c ati on Cen t e r

University o f Fl ori da

G. W. EU1STROM Ce n tral Florida ReseaL·ch and Educa ti on Cen ter

Un ive r si ty of Fl o r i d a 5336 University Avenu~

Leesbu r y, FL 34748

LINDA WESSEL-BEAVER Department o f Ag r onomy an d S o il s

Universit y o f Puer to Ri co Ma y a g ue z , PR 0 0 708

T. G. MCCOLLUM USD A/ ARS

2 120 Camden Roa d Or l ando , FL 32803

Abstract. Calabaza, Cucurbita moscllata (Duchesne) Poir, is a pumpkin-like fruit that is grown throughout the tropics and subtropics. In the Caribbean calabaza is used in soups and other traditional dishes. In Puerto Rico, the 1987-88 calabaza crop was worth $8 million and the value of the crop in Florida is estimated to exceed $5 million. Mainland United States production of tropical calabaza types of C. moscllata is limited largely to Florida. Despite the popularity and commercial significance of calabaza, little effort has been directed toward the study of cultural practices or varietal improvement. Only two improved cultivars, 'Borinquen ' introduced by the Puerto Rico Agricultural Experiment Station in the 1940s and ' La Primera' introduced by the Florida Agricultural Experiment station in 1979 are available. Tropical c. moschata is an extremely vigorous plant with fruit produced along trailing vines that spread up to 15 m from the base of the plant making it difficult to manage for the agricultural producer and plant breeder alike. Approaches to calabaza improvement including development of plants with shorter vines, incorporation of powdery mildew resistance, and production of uniform, symmetrical, hard-shelled, medium-sized fruit with enhanced nutritio11al quality in relationship to modified management systems are discussed.

Resumen. La calabaza, Cucurbita moschata (Duchesne), Pair, es un cultivo importante de areas tropicales y subtropicales del Caribe y Latinoamerica. En Puerto Rico el valor economico del cultivo fue $8 milliones en 1987-88 y su valor en Florida excede $5 milliones. A pesar de la popularidad y importancia comercial de la calabaza, se han realizado pecos esfuerzos para el mejoramiento de las practicas de campo o mejoramiento de variedades. Actualmente estan disponibles solamente des variedades mejorqades: 'La Primera,' introducida par la Estaci6n Experimental Agricola de Florida en 1979 y ' Borinquen, • introducida par la Estaci6n Experimental Agricola de Puerto Rico en los aiios 40. Tipos tropicales de C. moschata tieuden a se1- plantas grandes, produciendo frutas grandes en bejucos los cuales se extiend~11 hasta 15 m de la base de la planta, hacienda el manejo del cultivo dificil tanto para el agricultor como para el fitomejorador. Posibles enfoques en un programa de fitomejoramiento de calabaza incluyen el desarrollo de plantas compactas, incorporaci6n de resistencia de anublo polvoriento (Erysiphe cichoraceurum) y la producci6n de frutas simetricas y de tamaiio intermedio con una cascara ma dura y una alta calidad nutricional.

133

Cucurbita moschata (Duchesne) Pair. , known as calabaza in Florida and Puert o Rico , is a pumpkin-like fruit tl1a t is grown through out the tropics and subtropics. This species is also known a s auyama in the Dominican Republic, calabash or pumpkin in the English - speaking islands, ayote in Central America, and zapall o in South America. Plants are monoec ious, and insects, mostly honey bees and bumble bees , are required f or transfer of pollen from staminate to pistillate fl owers . Fruit are produced along trailing vines that may spread up to 15 m fr om the base of the plant . Each plant commonly produces two to five fruit, h owever , some selections may produce as many as nine fruits per plant. Av erage fruit we ight varies fr o m 2.5 to 20 kg. Fruit shape is variable in unimproved types ; globe, r ou nd, oval, obovate, pear, oblate, gourd, and elliptic­shaped frui t are f o und in production fields and in the marketplace. Likewise, there is much variation in rind colo r from green immature fruit to light orange in mature f ruit and in rind pattern fr om piebald to mottled. The rind may be smooth or warterl . The frui t wal l va ries through several shades of yellow to orange in color a11d is 2 . 5 to 8 em thick .

Ec o n om.ic importance. Al though wide ly grown in tropical America, calabaza plan tings are generally sma ll and most do not exceed a few hectares in size. Nonethel ess , calabaza is a major crop in certain areas. For example, in 1987-88 Puerto Rico produced 20,136 MT o f calabaza va lued at $8 million which accounted for 29' o f t l1e income from vegetab les, exceeded only by that of tomatoes (Alamo, 199 0 ). It is estimated t hat 500 to 600 ha of ca labaza are grown in Puerto Rico. Many o f these plantings are less tha n 2 ha, howe ver, about one-half of the total area is made up of large plantings . Calabaza production in South Florida has increased f rom 500 ha in 1977 with a farm value o f $624 thousand (McGuire and Champagne 1977) to ove r 1000 ha with a f arm va lue exceeding $5 million. Considerable area is devoted to calabaza production in Central America, particularly Costa Rica , f or export t o the United States.

Consumpti on and cu linary usage . Calabaza is the most important traditional no n-root veg£?t-a!Jle crop in Puet·to Ri co. Per capita a nnual consumption is more than 7 kg of calabaza i11 Puet·to Rico com pared to 6 kg annual per capita consumption of tom<tto , tl1e second 111ost co nsumed vegetabl e (Alamo, 1990).

Puerto Ricans Pilt. t·ir::e and bea11s almost daily , with calabaza being added to the bean !'l.11 1ce to improve its flav or , colo r, and consistency. Calabaza also is us ed in soups , stews , custards , cakes and puddings. Calabaza is used in similar ways throughout the Caribbean . In Mexico, a ver y sweet candy is made by infusion o f fll lgCir into peeled and sli ced calabaza . For non-hispanic consumers, calabaza can l>e 11sed as a pie filling or as a main-course vegetable. Its quality compares f avorab l y with that of bu tternut squash.

Desirable fruit characteristics. In Florida, f ruit characteristics deemed to be important in high quality calabaza by researche rs, market personnel, and growers were: fre eclO III from cracks ; comparatively large, round fruit with a smooth , light-gt·ee JJ 1·incl; deep-yellow i 11terna l color; thick internal flesh; and high soluble sol ids (Volin et al. 19 76) .

A survey of consumer prefere11Ces f or desirab le calabaza characteristics included 527 l' espondents in Puerto fH co (Carbonell et al. 1990). Preferences were not affected c;p ·eat ly by geogr<tphica l region , age, sex, or frequency of consumption . Consumers preferred an orange-yellow to dark-orange fruit wall (pulp) compared to lighter-col o red fle sh. Unander and Varela-Ramirez (1988) descr ibed procedures f or selection o f flesh colo r and thickness in calabaza. Gl obe , fl at , and round regularly-shaped fruit were preferred over oval or irregularly-shaped fruit. The preferred rind color was piebald or dark piebald (pinta). Most consume rs preferred medium-siz e fruit weighing between 3.6 and 6.8 kg. However , most of those surveyed indicated a preference for cut, rather than whole frui t. The survey resu l ts did not indicate a preference for rind thickness or hardness , but there was a clear preference f o r a smooth versus a rough rind. Fruit characteristics , in o rder o f importance , deemed most important by Puerto Rican consumer s were internal color , rind color , fruit size, rind type, and fruit shape. Results o f tl1is survey are being used to guide the breeding program in Puert o Rico and Florida .

Compositi o n . Analyses were made o f ' La Primera' and 'La Segunda' fruit compared to ' Waltham Butternut' and 'Seminole' pumpkin fruit from a summer 1991 planting at Leesburg, Fl orida. Dry we ight was determined by weighing, freeze drying, and rewe ighing . A 200 mg sample of fre eze-dried tissue was prepared for

134

total soluble sugar analyses by grinding with a pestle in a mortar. The resulting powder was extracted in ethanol: chloroform (3:1 v/v), the insoluble residue was reextracted in 80 't. ethanol at 80°C. The soluble extracts were combined and evaporated to dryness. The extracts were redisolved in water and the total soluble sugars were determined using eh phenol-sulfuric assay. The insoluble material was oven dried and starch was determined by the method of Dekker and Richards (1971). Hunter L, a, and b values were determined with a Minolta CR-200 colorimeter. Firmness (resistance to puncture) of rind and flesh tissue was determined with the Instron universal testing machine.

The composition of two tropical ('La Primera' and 'La Segunda'), one subtropical ('Seminole Pumpkin'), and one temperate ('Waltham Butternut') C. moschata varieties is presented in Table 1. 'Waltham Butternut' had the highest percent dry weight and starch content whereas the tropical and subtropical varieties had higher soluble sugars. Hunter L, a , and b values differed among the four varieties. The deep orange color of 'Waltham Butternut' is reflected in the high 'a' (redness) value. Rind firmness (resistance to puncture) was highest in 'Waltham Butternut.' A firm rind may be important to resistance to mechanical injury and invasion by pathogens. Inner flesh firmness was also highest in 'Waltham Butternut.' Flesh firmness may affect consumer acceptability.

Table 1. Composition of tropical ('La Primera' and 'La Segunda' ), subtropical ( 'SPminn lP' 1 , .;nrl tPmnPrntP I 'Wa lth ;'lm Butternut') C. moschata.

C. moschata variety Canst i tuent/ . Waltham ~haracteristic L~ ~r]rm~ri L~ S~gynd~ Seminole Butternut

Dry wt (%) 7.3± 1.3 z 9.5±0.6 6.9±0.8 18.6±1.2 Starch (% Dry wt) 28.1±15.1 50 .1±3. 0 26.3±7.8 70.8±3.3 Sugar (% Dry wt) 8.8± 0.7 7.7±0.4 11. 4±0. 5 4.8±0.6

Hunter Values L 74.3±0.7 77 .5±0. 5 71. 6±0 .8 74.0±0.2 a 6 .4±1. 7 3.4±0.7 7.7±0.9 14.3±0.6 b 71.9±1.3 66.8±1. 2 62.3±2.1 70.5±0.6

Firmness (N) Rind 11.0±0.3 14.8+0.8 12.3±0.6 20.7±0.6

Outer F1 esh 31.9±1.2 36.5±1.0 30.5±2.1 31.0±0. 5 Inner Flesh 5.5±0.2 7 .1±0. 2 5.9±0.2 13.4±0.5

zstandard error of the mean. Incorporation of temperate C. moschata germplasm into calabaza may have the

beneficial effect of increasing color and rind firmness; however, there may also be a decrease in soluble sugar content and an increase in starch. The possibility of . s~ch changes must be considered in the development of new calabaza varieties.

It should be noted that the compositional data presented here are from a single harvest of each variety. Carbohydrate composition (Culpepper and Moon, 1945) and color (Unander and Varela-Ramirez, 1988) of c. moschata fruit change considerably with fL-uit age. Tllerefoce, it will be important to determine how calabaza composition is affected by tt-uit age in order to compare different genotypes and also to develop appropri a te harvest indices.

Calabaza production practices. Specific production practices vary among regions. In general, however, ~he pcactices ou~lined below for Florida (Maynard and Elmstrom, 1991) should be appropriate for monoculture calabaza throughout its production area. In south Florida and in the Caribbean, calabaza can be grown

135

successfully throughout the year; elsewhere in Florida it is grown in the spring, summer, a nd f all .

crop establishment is generally by direct seeding although containerized transplants can be used. Product ion on raised beds on 3 to 4. 5 m centers provides drainage and space for extensive vine growth. In-row spacing of 1.2 to 3.0 m should provide adequate space f o r growth. In Puerto Rico, recommended spacing is 1.8 x 1.8 m. Using these spacings, plant population varies from about 1200 to 2700 plants/ha.

Second-crop plants on mulched beds with seepage irrigation following tomatoes or peppers provide some economies in production costs and are widely practiced in some Florida production areas . When seeded, additional fertilizer can be added before planting or soon thereafter using the fertilizer injector wheel. The total nitrogen (N) crop nutrient requirement (CNR) of 135 kg/ha can be injected in two or three applications. Potassium (K) application will be one­half to three-fourths of the CNR as determined by the soil test made before the first planting; the remainder coming fr om residual K. Residual phosphorus (P) and micronutrients in the bed should be sufficient for the calabaza crop.

For new plantings on mulched beds, 135 kg/ha N and P and K as determined from the soil test should be applied preplant. On unmulched beds, the P and micronutrients should be incorporated in the bed and the N and K applied in 45 kg increments at planting and in two sidedressings before the vines cover the beds.

Drip irrigation and fertigation can be used successfully for calabaza production in Florida and Puerto Rico. The P requirement as determined from soil test results should be incorporated in the bed with micronutrients, if needed. A portion, perhaps 25%, of the N, determined from CNR, and K, determined from soil test results, may also be incorporated in the bed. An alternative would be to apply all of the N and K through the drip-irrigation tube. In either circumstance, the remaining 75% or all of the N and K should be applied in a 14 to 16 week schedule.

Pest management practices should include preventive treatments for downy mildew ( Pseudoperonospora cubens is) and powdery mildew (PM) ( Erysiphe cichoracearum, Sphaerotheca fuliginea) in seasons or with weather conditions when the occurrence of these diseases is likely. Insecticidal control of pickleworm (Diaphania nitidalis), melonworm (diaphania l1yalinata), and of virus-vectoring aphids (Aphis spp.) and sweetpotato whiteflies (Bemisia tabaci) also is essential. Silverleaf of calabaza is caused by feeding of sweetpotato whitefly nymphs, however, the effects of this disorder on calabaza yields and quality is uncertain at this time.

Mature green fruit are ready for harvest 90 to 110 days after planting, and the initial harvest is made then for markets that accept fruit with green rinds. Subsequent harvests are made at about weekly intervals. Fully mature fruit with buff-colored ri nds are ready 100 to 120 days after planting. They may be harvested as they mature according to market demand or may be left in the field for once-over harvest. Be c ause of the possibi lity of damage to mature fruit in the field, most growers prefer to harvest fruit wh en they are market-acceptable.

Cala baza fruit are no t usually stored for extended periods because for the most part, tl1ey are sold and consumed close to the production area, and because storage fa cilities are not generally available in calabaza production areas. In Puerto Rico, L. Beaver found in preliminary studies that some calabaza varieties can be stored for up to 6 months at 25C and 70% relative humidity with god ventilation. These conditions are similar to those found in farmer's storage sheds. In the absence of definitive calabaza storage tests, it is likely that the 10°C and 50 % relative humidity found to be best for butternut squash (Francis and Thomps o n, 1965) would provide adequate storage conditions for calabaza.

Yield s . In Puerto Rico, average commercial yields are expected to be 26.7 MT/ha (Universidad de Puerto Rico, 1979), whereas average yields in Florida are estimated to be 16.8 MT/ha as compared to 6.7 MT/ha reported in 1977 (McGuire and Champagne, 1977).

Exper imental yields obtained in Florida for three entries are shown in Table 2. 'La Primera' plants produced an average of 58.2 MT/ha over two seasons, 'La Segunda' p1: o du c ed 33.7 MT/ha, and a short - vined 'La Primera' produced 32.7 MT/ha. Average fruit weight was 8.4, 4.4, and 2.8 kg for 'La Primera,• 'La Segunda,' and 'La Primera SV,' respective ly. In Puerto Rico, experimental plots

136

of 'Borinquen ' ha ve produced up to 60 MT/ha.

Table 2.

Year

1987 1990

calabaza yields and average fruit weight . Gulf Coast Research and Education Center, Bradenton , FL.

Average Entry Weight (MT/ha) Fruit Weight (kg)

La Primera 61.6 9.7 La Primera 54.7 7.0 La Segunda 33.7 4.4 La Primera sv 32.7 2.8

The distri bution of calaba za fruit into various weight c lasses is shown in Table 3. Fruit produced by 'La Primera' are quite variab le in weight , ranging from 2.3- 4.5 kg to > 13.6 kg. On the other hand, fruit of 'La Segunda' and 'La Primera SV' are smaller and more uni f ot·m . Uniformity could be a useful characteristic if whole fruit were to be mass merchandi zed. Small fruit are desirable for whole fruit sales.

Table 3.

Year

1987 1990

Calabaza fruit weight distribu t ion. Edu cation Center, Br adent on , F'L .

Gulf Coast Research and

Fry it Weight (kg) 2.3- 4.6- 6.9- 9.2- 11.4 -

Entry <2.3 4.5 6.8 9.1 11.3 13.§ >13.6 --------------- % of fruit ------------- ----

La Primera 0 3 18 29 23 14 13 La Primera 0 16 33 38 6 7 0 La Segunda 8 50 35 5 2 0 0 La Primera sv 41 51 9 0 0 0 0

Previ ous ca labaza improvement . For the most par t, growers must produce their own calabaza seed because co~nercial sources are lacking. As previously noted, calabaza fruit characteristics vary widely among and within populations. Some growers hav~ selected various fruit c l1aracteristics that they believe are important, and have develo ped rather uniform lines which are close ly guarded. On the other hand, other growers do r1ot use care in selection of fruit for seed which results in popul a t ions that produce fruit with variable characteristics . The practice of grower production o f seeds is manda ted by the low value of open­pollinated seed9, the absence o f exclusivity that they provide , and the almost total lack of recognized varieties .

In Puerto Rico, Wallace Bailey began a calabaza collection and breeding program in 1936 at the USDA station in Mayaguez and continued his work until the early 1940's. His co llection o f photographs and seed was apparently lost. E. Molinary-Sales, foll owed by Angel Acosta-Mat ienzo and Fausto Mar iota-Trias carried on a breeding project for the Puerto Rican Agricultural Experiment Station during t he 1940's . An island - wide collect i on made in 1942-43 was appare ntly the base material used in their programs . The collection also included at least some germplasm from Cuba , Costa Rica and the U.S. Sometime during this peri od, the varieties 'Bo rinquen' and 'Camaguey' (from Cuba) were released by the Ag ricultural Experiment Station . In 1951 , the Experiment Station

137

released 'Fortuna' (Anon. 1950). These varieties had fairly small fruits that averaged about 4 kg each which could be purchased whole and stored for a period of time. All three varieties were maintained until the early 1970's. Since then, all seed of 'Fortuna' and 'Camaguey' appears to have been lost. Several sources of 'Borinquen,' all of which are slightly different are included in the Puerto Rican breeding program. Old reports fr om the Puerto Rican Agricultural Experiment Station are being investigated in order to find an original description of 'Borinquen' since we are not even sure of the original varietal phenotype. In 1970, Marcial Rico-Ballester and Marietta-Trias began a new breeding program, again starting with a collection made from across the island. In 1980, Abad Morales assumed leadership of this project followed by David Unander in 1984. During the 1980's, accessions from Colombia and Florida were added to the local collection. 'La Primera' was introduced by the Florida Agricultural Experiment Station in 1979 (Volin 1979). Although improved in many ways from its parental stock, internal flesh color is too light to be widely accepted. Furthermore, commercial seed has not been widely available for the reasons discussed previously.

Current breeding priori ties and strategies. Calabaza improvement is proceeding in three phases. The first phase conducted in Puer~o Rico focused on collection of material from Puerto Rico and the Dominican Republic and its evaluation for horticultural characteristics (Wessel-Seaver and Carbonell 1989). Two advanced breeding populations, 'Soler' and 'Linea C,' were derived from this material, and are currently being evaluated in the Latin American and Caribbean Winter Squash Variety Trials for possible var iety release.

A second project, also in Puerto Rico, focuses on incorporation of PM (Wessel-Seaver and Cienfuegos, 1990) tolerance in calabaza germplasm. A total of 1576 Cucurbita moschata genotypes from 46 populations have been evaluated for PM resistance in the greenhouse. Of those genotypes, 125 have shown some resistance in the greenhouse (no symptoms or 1 to 2 spots) and were transplanted to the field for further testing. Most of those genotypes were field-susceptible but 30 have been selfed and intermated for use in the breeding program. New materials continue to be planted and inoculated in the greenhouse about every 8 weeks during the cooler winter months.

In order to effectively use recurrent selection for developing polygenic resistance to PM, methods to quantify resistance are being studied. Seven inoculation methods were tested on each of two susceptible C. moschata varieties planted in pots and arranged in a randomized complete block design with five replications. The experiment was repeated two times. Single degree of freedom comparisons found no difference in number of lesions resulting from inoculation by rubbing the host with infected tissue vs. attaching infected tissue. Using no adherent resulted in as many lesions as using Triton. Egg white as an adherent resulted in fewer lesions than using Triton or no adherent. Spraying with a Triton spore suspension was not an effective method of inoculation. While rubbing leaves is a fast and easy way of PM inoculation, attaching pieces of infected tissue may afford more control of spore concentration. Rubbing or dusting host leaves with infected tissue can be recommended for a simple screening program where uniform spore concentration would not be essential (as is the case in the first phase of this project). A method with greater control of spore concentration would be recommended for quantifying polygenic resistance in a recurrent selection program. Currently greenhouse experiments are being conducted to dete r mine the effect of leaf age on lesion production. The use of spore suspensions as inoculation method is being further evaluated. Results of recent stud ies indicate that drops of spore suspension produce lesions that allow reliable quantification of PM resistance.

In order to improve the efficiency of the breeding program, we have carried out two small studies. The first compared pollinating and pruning techniques. Pollination o f the first female flower by hand, removal of other fruits or flowers, and pruning of the end of the vine resulted in improved fruit set when making hand po llinations. Pruning to one main branch may also help to better quantify PM resistan ce o f the plant since single calaba za plants left unpruned may cover as much as 300 m2 o f area , with different parts of the plant in different vegetative stages, making it difficult to evaluate resistance.

In the second study, germination o f seed obtained from fruits of different maturities (from 20 to 50 days after pol lination) was compared. Preliminary

138

results suggest that while fruit for commercial purposes take 45 days or more to develop good internal color, seed reaches physiological maturity as early as 30-34 days after pollination. Time between generations in a breeding program could be reduced by an early harvest of seed. A graduate student at the University of Puerto Rico is currently studying the effects of field maturity, time seed is left in the fruit, and storage time on seed germination.

The third phase of calabaza improvement is being initiated in Florida and Puerto Rico. A preliminary assessment of tropical and temperate parents and crosses has been made (Wessel-Seaver and Varela, 1991). The goal of this work is to produce a short-vined calabaza plant with PM tolerance that will produce high-quality fruit with a hard rind, superior internal flesh color, good culinary ad nutritional qualities. A secondary objective is to develop production practices for the short-vined type.

Development of hybrids should be included in future variety improvement. With hybrids, the seed industry will have exclusivity which should provide the incentive ad profit necessary for commercial seed production. Seed costs to the grower will be increased and the practice of farm-saved seed will be eliminated if hybrids are adopted. Nonetheless, the grower should benefit from the availability of high quality commercial seed and improved varieties.

Acknowledgements

Florida Agricultural Experiment Station Journal Series No. R-01930. This research was supported in part by the U.S. Department of Agriculture under CSRS Special Grant Nos. 89-34135-4661, 91-34135-6172, and 91-34135-6165, managed by the Caribbean Advisory Group (CBAG).

Literature Cited

Alamo, C. I. 1990. Ho rtalizas. p. 4-13 Ln M. Antoni, M. Cortes, G. M. Gonzales, and s. Velez (eds.) Situaci6n y perspectivas: Empresas agricolas de Puert o Rico en 1987-88. Estaci6n Experimental Agricola, Univ. of Puerto Ri co , Mayaguez.

Anonymous. 1950. 'fortuna.' Proc. Amer. Soc . Hort. Sci. 63: 514.

Carbonell, M. E., L. Wessel-Seaver, F. Varela, and B. Luciano. 1990. Pumpkin (Cucurbita moschata) breeding priorities based on a survey among Puerto Rican consumers. J. Agr. Univ. Puerto Rico 74: 229-236.

Culpepper, C. W. and Moon, H. H. 1945. Differences in the composition of the fruits of Cucurbita varieties at different ages in relation to culinary use. J. Agr. Res. 71: 111-136.

Dekker, R. F. H. and G. N. Richards. 1971. Determination of starch in plant material. J. Sci. Food Agt·. 22: 441-444.

Francis, F. J. and c. butternut squash.

L. Thompson. 1965. Optimum storage conditions Proc. Amer. Soc. Hart. Sci. 86: 451-456.

for

Maynard, D. N. and G. W. Elms~rom. 1991. Pumpkins and calabaza -opportunities for Flori?a growers. Cttrus and Vegetable Magazine 54(10): 10-11.

McGuire, J. F. and R. J. Champagne. 1977. The subtropical vegetable industry in Dade County. Proc. Fla. State Hart. Soc. 90: 363-365.

Universidad de Puerto Rico. 1979. Conjunto technologico para la producci6n de hortilizas. Estaci6n Experimental Agricola Publicaci6n 102 (2nd edition).

Unander, D. W. and F. Varela-Ramirez. 1988. Selection of pulp color and thickness in calabaza . HortSc ience 23: 755-757.

Volin, R. B. 1979. La Primera. A ca labaza for Florida and the tropics. Fla.

139

Agr. Expt. Sta. Circ. S-261.

Volin, R. B., W. M. Stall, and R. F. Mathews. 1976. Selection and evaluation of impr o ved plant lines in calabaza, Cucurbita moschata. Proc. Amer. Soc. Ha rt. Sc i., Trap. Reg. 24: 402-409.

Wessel-Seaver, L. and M. W. Carbo nell. 1989. Cucurbita moschata half-sib families co llec ted in Puerto Ri co and the Dominican Republic. Cucurbit Genet. Coo p. 12: 68-69.

Wessel-Seaver, L . and R. Cienfuegos. 1990. Screening for resistance in Caribbean germplasm of Cucurbita moschata. Intl. Hart. Congr., Firenze, Italy. . . .

powdery mildew Abstracts XXIII

Wessel-Seaver, L. and F. Varela. 19 91. Perf o rmance of parents and progenies in Caribbean x temperate crosses of Cu c urbita moschata. HortScience 26: 124 (Abstr.).

14 0