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Agrociencia (Uruguay)

versión impresa ISSN 1510-0839versión On-line ISSN 2301-1548

Agrociencia Uruguay vol.21 no.2 Montevideo dic. 2017

 

Articles

Thermal Requirements and Productivity of Squash (Cucurbita moschataDuch.) in the Cerrado-Amazon Transition

Necesidades térmicas y productividad de calabacín (Cucurbita moschata Duch.) en la transición Cerrado-Amazónica

Adilson Pacheco de Souza1 

Andréa Carvalho da Silva1 

Mariana Pizzatto1 

ManoelEuzébio de Souza2 

1Federal University of Mato Grosso, Institute of Agricultural and Environmental Sciences, Sinop, Brazil. E-mail:pachecoufmt@gmail.com

2Federal University of Mato Grosso, Department of Agronomy, Nova Xavantina, Brazil

Summary:

The thermal requirements for the phenological stages of squash cv. ‘Menina Brasileira Precoce’ were evaluated. Theexperiment was conducted in a Red-Yellow Dystrophic Oxil soil and Tropical Climate (Aw), with six winter/spring planting dates(June 5, 15, 25 and July 5, 15 and 25, 2013). The determination of accumulated degree days (GDD) was given consideringthe minimum and maximum basal temperatures of 12 and 35 °C. The average duration of phenological stages were 6.4, 29.2,48.2, 60.9, 63.0 and 69.6 days, with demands for thermal time of 88.2; 401.9; 661.5; 832.5; 858.6 and 985.5 GDD for phasesto emergence, emission of first male button and first female button, first male flower and first female flower and early harvest. Theproportion of female/male flowers ranged from 1:8.4 to 1:18.1. The smaller proportions of female/male flower provided a lowernumber of fruits per plant and productivity. The timing of fruit harvest should be set when fruit development reaches 100 GDD(8.0 days after the female flower emission).

Keywords: Curcubita moschata; degree days; flowering; phenology

Resumen:

Se evaluaron las necesidades térmicas de las diferentes etapas de crecimiento del calabacín cv. «Menina Brasileira Precoce». El experimento se realizó en un suelo Oxisol Distrófico rojo-amarillo y en clima tropical, en los cultivos de invierno/primavera, con seis siembras (5, 15, 25 de junio y 5, 15 y 25 de julio de 2013). La determinación de los grados acumulados(GDD) se hizo considerando las temperaturas mínima y máxima basales de 12 y 35 °C. La duración promedio de las etapasfenológicas fue de 6,4; 29,2; 48,2; 60,9; 63,0 y 69,6 días, con demandas de tiempo térmico de 88,2; 401,9; 661,5; 832,5; 858,6y 985,5 GDD para las fases de emergencia, primeros capullos de las flores masculinas y femeninas, primeras floresmasculinas y femeninas y cosecha precoz. La proporción de flores femeninas/masculinas fue de 1:8,4 a 1:18,1. Lasproporciones más bajas de flores femeninas:masculinas generaron un menor número de frutos por planta y menor productividadde la planta. El momento de cosecha de la fruta debe fijarse cuando el desarrollo del fruto alcance 100 GDD (8,0 díasdespués de la emisión de flores femeninas).

Palabras clave: Cucurbita moschata; grados día; floración; fenología

Introduction

Pumpkins belong to theCucurbitaceae family, genus Cucurbita, are important crops in different Brazilian regions.Overall, the C. moschata (Duch.), C. moschata (Duch.), C.pepo (L.), C. mixta (Pangalo) and C. ficifolia (Bouche)species are cultivated in Brazil. The species C. moschatais considered to be the most important pumpkin species inTropical America due to the large areas cultivated with it andto its variability(Mascarenhas et al., 2007).

This pumpkin is an annual plant with indeterminate growth.Vegetative, flowering and fruiting parts present concomitantdevelopment (Filgueira, 2008; Côrrea and Cardoso, 2016).Its culture is characterized by monoecy, as well as by largeand showy flowers. Male flowers emerge above the leavescanopy, at the end of long petioles. The female flowers haveprominent inferior ovaries, and they anticipate the size of thefuture fruit (Carpes et al., 2008). The number of male andfemale flowers differ in C. moschata, as the number of femaleflowers is quite smaller in comparison to the number of themale ones (Salata, Bertolini and Cardoso, 2008).

This pumpkin is a tropical plant, and its growth and developmentare favored by mean temperatures ranging from 18to 24 °C, although the species also tolerates higher temperatures(Maynard, 2007). The species of the genus Cucurbitaare monoecious and they depend on biotic vectors toensure pollination. Flowering is the most sensitive period toenvironmental effects during the phenological phases of speciesbelonging to this genus (Zehtab-Salmasi, 2006). Accordingto Maynard (2007), high temperatures promote maleflowers and delay female flower development. The exposureto daytime temperatures of 32 °C and to night temperaturesof 21 °C causes the death of female flower buds (Maynard,2007; Carpes et al., 2008).

Cucurbita moschata Duch.is one of the most consumedpumpkins worldwide; it represents an important foodsource in many countries. This species has great socialand economic importance in Brazil since it is the basic foodfor many low-income families. The Northeastern region presentsthe highest variability of this species, which is easilyaccepted by the market and is widely produced (Ramos etal., 2010).Cucurbita moschata Duch. is significantly importantto the Brazilian agriculture, mainly to traditional and/orfamily agriculture farms, since it has different regional usesand its applications depend on nutritional, cultural and socialvalues (Ramos et al., 2010; Carvalho, Peixoto and Ferreira,2011).

In Brazil, the species C. moschata can be consumed inits immature stage squash or when it is fully mature. Somefeatures such as rusticity, precocity, yield potential, yield stability,fruit size and color uniformity, excellent sensory qualities(texture, flavor and reduced cooking time) and goodpost-harvest conservation, make the different cultivars and/or squash hybrids greatly accepted for consumption (Resende,Borges and Gonçalves, 2013; Pôrto et al., 2014).

Although C. moschata is a widespread culture in theBrazilian scenario, it is necessary to know the possibleeffects of production technique changes (fertilization and/ormulching planting, irrigation, fruit thinning and phytosanitarytreatments), definition the growing seasons, crop planning ofproduction cycles, the storage and disposal, among othersdepending on the genetic diversity, as well as the soil typeand climatic requirements (Blank et al., 2013).

Mato Grosso State presents socio-economic dynamicsand complex spatial configuration based on the agriculturalactivity, despite its growing urbanization and great naturalresources (water, forests, etc.). Therefore, supplying certainvegetables is a huge problem due to the high transportationcosts and to the loss of in natura product quality, mainlywhen the cargo goes to regions located in the North of theState. Besides the distance from the production sites, thereis few scientific research related to physiologic responsesand/or the production yield of horticultural crops in this region.

The Northern region of Mato Grosso State presents twowell-defined seasons: the rainy season (from October toApril) and the dry season (from May to September). Thereis a narrow annual temperature amplitude (monthly averagesranging from 22 to 26 °C) and a greater temperaturerange in winter (Souza et al., 2013; Santos et al., 2013). Theregional water conditions favor the cultivation of this vegetable.Irrigation in the dry season is demanding due to thereduction in foliar diseases; however, air temperature variationscan lead to changes in the phenology and productiveperformance of the plant. The aim of the current study is toassess the phenological stage thermal requirements (accumulateddegree days) of squash cv. ‘Menina Brasileira Precoce’,in six winter crops sowing dates (with ten-day intervals)under Sinop climatic conditions, in Mato Grosso State,Brazil.

Materials and Methods

The experiment was conducted from June to December2013 in the experimental area of Plant Production Sector atFederal University of Mato Grosso, Sinop Campus, whichis located 11º85 ‘S and 55º38’57' W, at 345 m altitude. Thesoil is classified as Yellow Dystrophic Oxisol and presentsthe following chemical characteristics in the 0 to 0.20 mdepth: pH (H2O) = 5.11; OM, sand, silt and clay = 45.07;383; 146 and 471 g dm-3; P and K = 2.48 and 65.0 mg dm-3;Ca, Mg, H+Al = 1.02; 0.27 and 5.2 cmolc dm-3; SB = 1.46cmolc dm-3; Base saturation (%) = 21.9. According to theKoppen classification, the climate is Aw (Tropical climate),with two well-defined water seasons: the dry (May to September)and rainy (October to April) seasons. The meanmonthly temperature ranges from 22.96 to 25.76 °C. Theannual rainfall and evapotranspiration are approximately 1974and 1327 mm year-1, respectively (Souza et al., 2013).

The herein used squash cultivar Menina Brasileira Precoce(Cucurbita moschata, Duch.) has cylindrical neckshape, light green color with dark green streaks and its harvesttakes place between 60-70 days, a fact that highlights itsprecocity. The planting holes were 0.40 x 0.40 x 0.40 m(length, width and depth) and 2.0 x 2.0 m spacing (betweenplants and lines). Three (3) seeds, originated from the companyFeltrin Seeds, were sown per hole at the depth of 0.04 m.Thereafter, fifteen (15) days after sowing (DAS), thinningswere performed in order to keep one plant per hole. Limingand fertilization were done in the pit using 4.2 t ha-1Filler limestone and 150 kg ha-1 P2O5, 60 kg ha-1 K2Oand 60 kg ha-1 N, as it is recommended by Mascarenhas etal. (2007) for squash cv. Menina Brasileira. The P2O5 wasapplied all at once, whereas K2O and N were applied in 40and 30 % fractions in the base, and the remaining 60 and70 % were divided into two fertilization covers (30 and 55days after emergence (DAE), respectively. Soybean mulchwas applied (30 t ha-1) at 10 DAE to minimize the effect ofspontaneous vegetation. Whenever necessary, the phytosanitarytreatments against pests and diseases were appliedusing recommended products and doses. The water supplementationof 4.0 mm day-1 was adopted as a reference(Souza et al., 2013).

Plants were daily inspected in the morning shift to identifyphenological phases (emergence, first male flower bud, firstfemale flower bud, first male flower, first female flower, fructification,and harvest) and the number of fully expandedleaves. The number of male and female opened flowers perplant was quantified 30 days after flowering. Twenty-five (25)flowers (after opening) were selected and identified by sowingepochs to determine fruit growth rates; the performed measurementswere flower length, and open flower ovarian longitudinaland equatorial diameters. This is a fruit cultivar whichis prolonged after fertilization. The length and diameter of thesquash neck (1.0 cm apart from the stalk) and bulge (holewith seeds) were measured at two-day intervals, until harvesting.Harvest was manually done at the time the fruits hada length between 0.22-0.27 m, were still green (immature)and sensitive to pressure.

During the experimental period, the meteorological datawere collected by an automatic station through CR 1000 dataacquisition system and global solar radiation (pyranometerCS300), wind speed and direction (anemometer, 03002-LRM YOUNG) sensors, as well as through a psychrometerwith thermometer shelter (CS 215) and a rain sensor (TE525). The meteorological measurements were collected at5 minutes intervals and stored according to hourly and dailyscales. The minimum (Tb) and maximum (TB) basal temperaturesof 12 and 35 °C respectively (Mota et al., 1977),were used to find the thermal sums (accumulated degreedays, GDD) for squash. The proposal by Ometto (1981)was adopted due to cases that were seen as possible, dependingon the local weather conditions, as it was recommendedby Souza et al. (2011).

Case 1: Tm > Tb; TB >TM

GDD = [(TM - TB)²]/2 + (Tm - Tb) (eq. 1)

Case 2: Tm d» Tb <TM ; TB > TM

GDD = [(TM - TB)²]/[2(TM-Tm)] (eq. 2)

Case 3: Tb < Tm; TB <TM

GDD = 2[(TM Tm) (Tm - Tb)] + [(TM - Tm)²]-[(TM -

TB)²] / (2[TM - Tm)] (eq. 3)

Case 4: Tb > Tm; TB <TM

GDD = 0.5 [(TM - Tb)²]-[(TM - TB)²)] / (TM - Tm) (eq. 4)

where: TM and Tm = maximum and minimum are dailytemperatures (°C). Tb and TB = minimum and maximumbasal temperature.

The experiment was conducted in randomized blockswith six treatments (sowing epochs with ten-days intervals inwinter, on June 05, 15th, 25th, and July 05, 15th, 25th of 2013)and four repetitions of five plants each. The variables assessedin the present experiment were subjected to varianceanalysis (ANOVA) through F-test, which considered theseeding epochs as variation source. The means were comparedthrough Tukey test (p ≤0.05).

Results and Discussion

Minimal air temperatures of 10.13, 11.01 and 11.35 °Cwere observed in July 24th and 25th, as well as on November8th, 2013, respectively. The Tm was higher than Tb inthe other periods and TB was lower than TM in August andSeptember 2013 (23 days). Figure 1 shows daily temperaturerange reduction and global radiation caused by the rainfallperiod which goes from March 10 to December 21,2013, with rainfall accumulations of 34.4; 224.4; 219.8and 364.8 mm from September to December.

Figure 1 (A) Air temperature variations, (B) air relative humidity, (C) global solar radiation and (D) precipitation and referenceevapotranspiration from June.05 to December.23, 2013, in Sinop, Mato Grosso State, Brazil. 

Such climatic behavior allowed obtaining optimal conditionsto assess the floral biology of this culture. Accordingto Pacini et al. (1997), for C. pepo, the male flowersare prevalent and have short lifetime during high-temperatureperiods. These flowers open before dawn and closein mid-morning.

There were significant variations in the duration (numberof days) and thermal requirements (GDD) of the phenologicalphases linked to flowering depending on the different sowingdates (Table 1). Similar results were found by Paula et al.(2005) in a study conducted in a potato crop. Trentin et al.(2008) conducted a study in a watermelon crop and foundvariations in the duration of the development stages ratherthan in the GDD. According to these authors, such resultregards the mean air temperature throughout the cycle,which did not exceed the optimum temperature for culturedevelopment.

Table 1 Time duration and thermal requirements on phenological stages of squash cv. Menina Brasileira Precoce, in different planting dates in winter, Sinop, MT. 

This behavior is often expected since the degree-daysmethod assumes a linear link between temperature and plantdevelopment; however, such connotation is only true into thecardinal temperature range of the plant - minimum basetemperature Tb; optimum temperature - Topt; and maximumbase temperature TB (Fagundes et al., 2010; Cardoso,2011; Souza et al., 2011). The coefficient of variation(CV %) could be used to measure the duration variability(days or degree days) on the developmental phases of culturesgrown at different times (Cardoso, 2011). Regardingthe total squash cycle (sowing-harvest), the highest CV values(%) were found when the time was expressed in degreedays, rather than in the civil calendar. This result corroboratesthe one found by Paula et al. (2005) in their studyconducted in a potato crop. As for the duration of the developmentalsub-periods in GDD, the CV values (%) rangedfrom 9.3 to 14.2 %.

The greatest changes between sowing dates were seenin the emission of the first male and female flower buds andin the openings of male and female flowers. Such resultsuggests that the induction of reproductive stages presentsmore variation than the GDD definition. The proximitybetween the CV percentage found in the duration of the developmentalsub-periods (in days) and the thermal time maybe a good method to describe the biological time of the plant(Trentin et al., 2008; Paula et al., 2005).

The emergence of squash seedlings in different sowing timesdemanded from 75.1 to 91.4 degree-days (5.3 to 7.3 days).The cucurbit seeds depend on well-defined temperature limits inorder to germinate. Temperatures below 15 °C delay the germinationrate (Nascimento, 2005). The recorded maximumtemperatures increased from 35.9 °C (T1 - June.05) to 37.8 °C(T6 - July.25). It was noticed that the plant developmental cyclein the last planting season was prolonged when TM exceededTB (Cardoso, 2011) (Table 1).

According to Miranda and Campelo Junior (2010),higher temperatures can reduce the vegetative growth of thisplant, thus they delay the developmental stages. However,Bueno et al. (2012) studied the variability effects on the thermalrange in orange growth (Citrus sinensis L. Osb.) andfound that thermal range reduction negatively interfered in thevegetative growth. There was first male and female flowerbud emission delay (Carpes et al., 2008); therefore, theywere affected by the lower daily thermal conditions and bythe reduced daily accumulated GDD. Thus, they demandedlonger time to accumulate the same thermal sum and to,subsequently, change the reproductive stages in squashplants. The female sowing-flowering period demanded from763.4 to 993.1 GDD (56-76 DAS). There was an early maleflower opening trend in comparison to the female flowers.

According to Salata, Bertolini, and Cardoso (2008), maleflowers often appear before the female ones, in squash crops.According to Côrrea and Cardoso (2016), squash is a monoeciousplant, i.e., it has male and female flowers in differentplaces. Pollination problems may occur due to lack ofsynchronicity between the opening of the first male and femaleflowers in the same plant (Salata, Bertolini andCardoso, 2008). Overall, pollination failures may be due tothe absence of pollinating insects, continuous rains or lowtemperatures (Lattaro and Malerbo-Souza, 2006).

The number of squash female flowers opening daily isusually smaller than the number of male flowers, thus influencingthe intensity of pollination and fruit formation. Femaleand male flower proportions ranged from 1: 8.4 to 1: 18(Table 2), and only significant differences were observedbetween the sowing of June.05 and June.25.Lattaro and Malerbo-Souza (2006) found ratios betweenfemale:male flowers of 1: 3.2 in Cucurbitamixta (hillbillyzucchini), whereas Amaral and Mitidieri (1966), in theirstudy about the pollination of Cucurbitamoschata, found1: 17.7. Thus, their results corroborated those findings in thecurrent study. Fruit development starts after the squash floweris pollinated. The harvesting point can be the mature orgreen stages depending on the consumption rate. The fruitswould remain in the field during this period.

Table 2 Male and female flowers number per plant of squash cv. Menina Brasileira Precoce, in different planting dates in winter, Sinop-MT. 

Sowing time does not influence the fruit growing rates. Itwas found that 15.7 % of the assessed fruits were harvestedsix days (70.7 GDA) after flower opening (DAF). Thesefruits’ fresh mass was 0.4343 kg (Table 3), on average;approximately 100 and 127.3 GDD (8 and 10 DAF). Harvestingpercentages were higher than 66.7 % and 87.6 %.However, it was observed that fruits required 179 GDD toreach the harvesting point; they showed no massive increasein comparison to fruits harvested in earlier GDDstages.

Table 3 Productive compounds of squash cv. Menina Brasileira Precoce, in different planting dates in winter,Sinop-MT. 

The fast growth of immature squash fruits is justified bythe localized distribution of flowers and fruits in the reproductivephase of cucurbits (Floss, 2006). Braga et al. (2011)found that the higher dry matter accumulation in the aerialpart of watermelon plants occurs at fruit onset and that thefruits are responsible for 63 % of the accumulated mass.

Harvest time duration did not significantly differ betweendifferent sowing times (Table 3). Harvest times lasted from72 to 83-day intervals and from 1.5 to 2.4 fruits per harvest,on average. Table 4 shows the physical characteristics offruits harvested at different sowing times.

Table 4 Lenght, diameter, and fruits fresh mass of squash cv. Menina Brasileira Precoce, in different planting dates inwinter, Sinop-MT. 

The mean fruit length varied from 242.8 to 277.5 mm,whereas the apex diameters (near the peduncle) rangedfrom 48.2 to 58.6 mm, and the bulge diameter from 66.8 to76.3 mm. As for the relationship between the bulge and apexdiameters, it was observed that the planting dates influencedfruit shape and length. Longer length fruits had greater apexand bulge diameters; however, the diametric relations werelower (more elongated and thinner fruits). The mean of freshmass of each fruit ranged from 0.5288 to 0.7155 kg. Thesowing in July.25 led to greater dimension and fresh massfruits, as well as to smaller harvest number (10). With sowingat August.02.2013, Côrrea and Cardoso (2016) found meanvalues of 73.0 mm; 51.0 mm and 310 mm for bulge diameter,apex diameter, and length of squash fruit cv. MeninaBrasileira, in hot humid temperate climate (mesothermal) inBrazil.

In general, with increases of the fruit numbers per harvest,occurs reduction of the size and fresh mass of the fruit,because the plant directs the new photo-assimilates producedfor the formation of new fruits (source-sink dynamics).The sowing performed in June.05 showed significant differencesin production per plant and productivity; it led to lowerproduction rates per plant and productivity (10.10 kg plant-1and 25.26 ton ha-1). Overall, the mean production valuesranged from 15.92 to 19.22 kg plant-1, whereas the meanyield ranged from 39.79 to 48.06 ton ha-1. Côrrea and Cardoso(2016) found mean values of 627.0 g (fresh mass offruit), 7,3 fruits per plant and 4.54 kg of fresh mass per plant,in mesothermal climate.

According to Mascarenhas et al. (2007), squash hybridscan produce approximately 20-24 ton ha -1 of fruit. However,regardless the planting season, the current study foundbetter yields, a fact that suggests the great potential of thiscrop under Sinop- MT soil and weather conditions. An increasingproduction per plant (kg plant-1) and productivity(ton ha-1) trend are associated to later sowing dates. Such atrend may be due to the beginning of the rainy season in theregion (September/October) at the time of fruit production.

The rainfall reduces the solid particle concentrations (aerosols,burned waste, dust, and others) in the air, and providesincreased incidence of direct radiation on these plants,consequently, generating more radiation availability in thephotosynthetic processes. However, according to Lattaroand Malerbo-Souza (2006), the rains also reduce the insectpollinators, indicating that plantations in the rainy season inthe Sinop-MT region may not always indicate higher productivityfor squash. According to Larcher (2004), the plantproductivity increases due to the intercepted and absorbedradiation. The assimilation period and the type of assimilativecapacity of cucurbit crops sowed between the third and tenthday of June showed greater yield.

Conclusions

The highest productivity levels of squash in the Sinop-MT region, for winter planting, are obtained with sowing datesin July. Later sowing dates do not influence the thermalrequirements of fruit growth but increase the size and freshmass of squash fruit. Squash developmental stages were48 and 69.6 days, on average, and the accumulated thermalsums were 661.5 and 985.5 GDD for the first femalebutton emission and the early harvest, respectively.

The proportion of male and female flowers influenced theharvest number, the fruits per plant and productivity. Greatermale and female flower proportions resulted in smaller agronomicperformance. The fruit of squash cv. Menina BrasileiraPrecoce should be harvested at 100 GDD (8 days)after the female flower opening.

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Received: July 21, 2016; Accepted: July 21, 2017

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