Dependence of Pumpkin Yield on Plant Density and Variety

doi:10.4236/ajps.2011.25075

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American Journal of Plant Sciences, 2011, 2, 636-643

doi:10.4236/ajps.2011.25075 Published Online November 2011 (http://www.SciRP.org/journal/ajps)

Dependence of Pumpkin Yield on Plant Density

and Variety

Khalid El-Sayed Abd El-Hamed, Mohammed Wasfy Mohammed Elwan

Department of Horticulture, Faculty of Agriculture, Suez Canal University, Ismailia, Egypt.

Email: [email protected]

Received July 5th, 2011; revised August 29th, 2011; accepted October 4th, 2011.

ABSTRACT

Pumpkins (Cucurbita spp.) are an important specialty vegetable. Field studies were conducted on three pumpkin culti-

vars characterized with different growth habits to determine the effects of plant population and genotypes on market-

able yield. Increasing plant populations from 4780 to 9560 plant per hectare resulted in significantly greater fruit

number and yield in both growing seasons and for all tested genotypes. Average fruit weight declined at the higher

populations. The resp onse of pumpkin genotypes to different planting d ensities was genotype (growth habit) dependent

since the response was pronou nced in large vine types co mpared to bush type. Th e phenotypic variation existed among

pumpkin genotypes for yield seems to be under genetic control. Foliar application of potassium improved growth and

yield of pumpkin plants althou gh the non-significan t effect. These results demonstrate that growers may increase pump-

kin yield by increasin g pla nt p op ulat io ns.

Keywords: Cucurbita Pepo, Cucurbita Moschat a, Pumpkin, Planting Density, Plant Population, Competition,

Potassium, Cultivar by Environment Interaction

1. Introduction

The relationship between crop yield and planting density

(number of plant unit area) is of considerable agronomic

interest [1-3]. It is clear that the density-dependent ef-

fects on the yield are due to the competition between

adjacent plants for the necessary natural resources. There

is a basic assumption that a plant located at a given site is

constrained to draw nutrients only from its immediate

vicinity and this zone may be larger than the size of the

actual plant both on the surface and into the ground [4,5].

If a crop is grown at a range of plant densities, and all the

plants are harvested at one time, it is generally supposed

that the total dry matter yield per unit area will increase

with increasing density until a level of yield is reached

which is barely exceeded as density increase further. This

constant yield over a wide range of high density is

thought of as representing the maximum fixation of en-

ergy that crop can achieve in the time between sowing

and harvest [6]. Yield eventually reaches a plateau as

plant density increases to the point when crop yield be-

come unmarketable. Since competition between plants

greatly affect yield [3,7] it is therefore possible to adjust

size of the harvested crop to meet the requirements of the

market by manipulating density [8]. Plant population can

influence crop by pest interactions. For instance, closer

plant spacing may give crops competitive advantage over

weeds or provide ecological weed control. A key com-

ponent of alternative approaches to weed management

(other than chemical control) is the enhancement of crop

competitiveness against weeds [9]. Manipulation agro-

nomic factors such as row and plant spacing may provide

a non-chemical means of reducing the impact of weeds

interference on crop yields [10]. Leaf area increases and

light transmittance to the soil decreases as plant popula-

tion increases [11]. Decreased light transmittance through

the leaf canopy of crops planted in narrow rows or at

high populations could suppress growth and development

of weeds [12].

Increased plant density may discourage colonization

by certain insects or reduce percentage of insect-dam-

aged plants. While, in terms of disease pressure high-

density plantings may cause more rapid dissemination of

certain pathogens [12]. Also, closer rows and higher

plant populations reduced evaporation, increased effi-

ciency of water use and gave higher growth and yields by

increasing the energy available to the crop [13].

Pumpkin is commonly refers to cultivars of any one of

the species Cucurbita pepo, Cucurbita mixta, Cucurbita

Dependence of Pumpkin Yield on Plant Density and Variety637

maxima, Cucurbita moschata [14]. Pumpkin is popular

vegetable with high productivity, high nutritive value and

good storability. Pumpkin has good nutritive benefits

with balanced colories and is believed to be a good

source of carotenoids [15-17].

Plant density affects the growth and productivity of

numerous vegetable crops including cucurbits such as

squash [18,19], watermelon [20-23], muskmelon [24-29],

cucumber [30-35].

In pumpkin, Reiners and Riggs [36] reported a signi-

ficantly linear increase in the number of fruit per acre as

plant population increased from 1874 to 7495 plant/acre

in two different types of pumpkin cultivars (semi-vining

and large-sized vine). Increased plant population resulted

in a significantly linear decrease in average fruit size [36].

The same authors reported in a similar study a signifi-

cantly linear increase in yield of same cultivars as plant

population increased from 1210 to 3626 plants/acre [37].

Increased plant population resulted in increased number

of fruit per acre and decreased average fruit size. In-

creased number of fruit more than compensated for de-

creasing fruit weight and resulted in an overall increase

in yield [37]. Cushman et al. [8] reported that plant

population significantly affected pumpkin yield and yield

components associated with plant productivity (fruit

weight and size, number and weight of fruit per plant).

Plant spacing had no significant effect on color, handle

quality and shape of marketable pumpkins [38].

Pumpkin fruit is characterized by its large volume and

heavy weight which hinder the harvest and transportation

processes. The consumption of pumpkin is constrained

by the inappropriate size of the fruit to most of consu-

mers. Small-to medium-sized fruits may assist in spread-

ing of pumpkin between consumers. Pumpkin growers

are exploring ways to increase yield per unit area in order

to save on land and maximize profitability. Increasing the

number of plants per area with careful attention to nitro-

gen nutrition and variety may accomplish this goal.

Growers have two options when increasing plant popula-

tions per unit area, either within-row or between-row

spacing can be decreased.

Better understanding of genotype and environment in-

teraction will help to optimize yield and quality of crops.

Any individual organism is able to alter its morphology

and/or physiology in response to changes in environ-

mental conditions [39]. The higher the proportion of the

phenotypic variation attributed to the genotypic diffe-

rences, the greater the feasibility of genetic manipulation

to improve crop performance. Partitioning of phenotypic

variance requires evaluating performance of genotypes in

a range of environments (years and/or locations).

Since competition between plants for water and nutri-

ents such as potassium deeply affect yield [3], the heal-

thy nutritional status of the plants can reduce competition.

If potassium is deficient or not supplied in adequate

amounts, growth is stunted and yields are reduced [40].

Potassium is associated with movement of water, nutri-

ents and carbohydrates in plants. The relation between

potassium and fruity vegetables such as pumpkin is well

established long time ago [41]. There is increasing evi-

dence from the literature that optimizing the potassium

nutritional status of plants can reduce the detrimental

build up of reactive oxygen species (ROS) which result

from various environmental stress factors [40]. In addi-

tion, it is widely acceptable that in general, high potas-

sium status in crops decreases the incidence of diseases

and pests [42].

The objectives of this research were to determine the

effect of altering plant population by varying in row

spacing while holding between row spacing constant on

the yield of three pumpkin varieties of different growth

habit (bush-type vs. vine type).

2. Materials and Methods

2.1. Experimental Set up

Field experiment was conducted at the Experimental Re-

search Farm, Faculty of Agriculture, Suez Canal Univer-

sity, Ismailia, Egypt. The experiment was carried out in

spring-summer season of 2010 and was repeated in

spring-summer season of 2011. The soil of the experi-

mental site was sandy soil (82.21% sand, 11.5% silt and

3.29% clay) with pH 8.27 and EC 0.47 dsm–1. Before

each planting, the experimental location was prepared

three months before transplanting. During preparation, a

rate of 48 m3 of cattle manure plus 700 kg calcium super-

phosphate (15.5% P2O5) per ha was supplemented, then

the soil of the site was cleared, ploughed, harrowed and

divided into plots. Each genotype occupied three rows

per replicate, each row represents one of the spacing

treatments and each row was 10 m in length and 2 m

width containing 10, 15 and 20 plants. Three different

plants spacing of 1, 0.75 and 0.5 m were used for each

genotype in each replicate. Weeds were controlled using

cultivation and hand weeding. Insect and disease pres-

sure was monitored and protective treatments applied

when warranted. A one-time harvest was made when

fruits reached marketable ripening stage, counted and

weighted. Only fruit that were representative to the cul-

tivars, firm and free from major blemishers or rot were

considered marketable.

2.2. Plant Materials

Pumpkin genotypes were “Frosty F1” (Cucurbita pepo),

“Dicknson F1” (Cucurbita moschata) and “Pro-gold F1”

(Cucurbita pepo). Seeds of pumpkin genotypes were

Dependence of Pumpkin Yield on Plant Density and Variety

638

sown in 84-cell styrophom trays under greenhouse con-

ditions. The trays were filled with soil mixture (Peat

moss and vermiculite mixes in 1:1 v/v, enriched with

different nutrients). After emerging, seeds were watered

with a commercial nutrient solution (19-19-19 N-P-K)

with micronutrient at a dilution of 1:200. The seedlings

were maintained in the greenhouse under high humidity

and with day/night temperature of 30/20˚C for four

weeks. Pumpkin seedlings, four weeks old were trans-

planted from the mid of February to the end of May in

both seasons.

2.3. Potassium Foliar Application

In the second experiment the plants of genotypes “Frosty”

and “Dickinson” were sprayed with KNO3 at a concen-

tration of 10 mM/l. Potassium nitrate was applied three

times during flowering and fruiting stages with one week

interval. The volume of sprayed solution ranged from 50

to 100 ml per plant each time, depending on plant size or

development. The same amount of water was pulverized

to the control plants. The pH was measured for water and

KNO3 solutions and adjusted to 7.0. All theses sprays

were applied in the morning (8.00 - 9.00 a.m.).

2.4. Statistical Analysis

The experiment was laid-out in a Randomized Complete

Block Design (RCBD) with three replications. Data were

statistically analyzed using ANOVA/MANOVA of Sta-

tistica 6 software (Statsoft, [43], Tulsa, Ok, USA) with

mean values compared using Duncanś multiple range

with a significance level of at least p ≤ 0.05.

3. Results

3.1. The Effect of Planting Density

The effects of planting population on fruit weight and fruit

yield in three different genotypes of pumpkin in both

growing seasons are presented on Table 1. Increasing the

plant population from 4780 to 9560 plant/ha by decreas-

ing the in row spacing from 1.0 m to 0.5 m significantly

decreased the fruit weight in genotype “Pro-gold” (large

vine type) while it did not show any effect on the other

two genotypes in the first season. In the second season

the performance of genotype “Frosty” (push type) was

not changed comparing with the first season while the

other two large vine type genotypes showed slightly dif-

ferent performance than first season.

The high density population showed significantly dif-

ferent fruit weight in genotype “Dickinson” (large vine

type) while genotype “Pro-gold” showed less pronounced

differences than the first season. In accordance with pre-

vious research, the fruit weight reduction associated with

increasing population density was compensated by the

increasing in the number of fruits due to the increasing in

number of plants which resulted in overall increase in

yield.

The fruit yield expressed in ton/ha significantly in-

creased with the increase of plant population in all three

pumpkin genotypes of different growth habit in the first

season. In the second season the genotypes almost showed

the same trend and this was clear in the genotype “Frosty”

and also in genotype “Pro-gold” but with less pronounced

effects. While the bush-type genotype “Frosty” did not

show any significance difference between different plant

populations in the second season.

The growth performance and yield of all genotypes

showed a consistent decline in the second season com-

pared with the first season. The performance of the geno-

types concerning fruit weight were reduced in the second

season by 33.4%, 35.2%, and 32.7% for the three geno-

types “Frosty”, “Dickinson” and “Pro-gold”, respectively.

Regarding fruit yield, the reduction was somewhat simi-

lar since the yield of three genotypes reduced by 32.1%,

37.4%, and 33.5% respectively compared with the first

season.

The response of pumpkin genotypes to different plant

densities was genotype (growth habit) dependent. The

response was pronounced (high) in large vine type geno-

type (Dickinson and Pro-gold) compared to bush type

with compact growth (Frosty). Generally, the large vine

type genotypes gave higher yield compared to the bush

type and this may be due to the large size of its fruits.

Dickinson tends to give higher yield compared to pro-

gold (Figure 1).

3.2. The Effect of Potassium Foliar Application

To add more information regarding the interaction be-

tween different planting density and the nutrition status

of the plants, a small scale experiment was conducted by

foliar application of KNO3 to pumpkin plants grown in

different densities only in two genotypes, “frosty” (bush-

type) and “Dickinson” (large vine type) for only one year

which was the second growing season and the results are

showed in Table 2. Generally, the foliar application of

KNO3 to pumpkin genotypes did not show significant

effect on yield. However the KNO3 sprayed plants tended

to give slightly higher yield in the different planting den-

sities in both genotypes, the data also did not give clear

trend of interaction between growth habit or plant densi-

ties on pumpkin fruit weight or yield.

3.3. Analysis of Variance

Pooled analysis of variance was applied to investigate the

interaction between pumpkin genotypes and the growing

environments and the contribution of each of them to the

total variation of yield. In general, the data showed con-

Dependence of Pumpkin Yield on Plant Density and Variety

639

Table 1. Fruit weight and yield of three pumpkin genotypes grown for two seasons with three different planting populations.

Fruit weight (g) Fruit Yield (ton/ha)

Genotype Plant

population/ha Season of 2010 Season of 2011 Mean Season of 2010 Season of 2011 Mean

722.65e 461.19f 591.9 3.47g 2.20d 2.84

782.87e 476.52f 629.7 5.62f 3.42d 4.52

Frosty

4780

7170

9560 685.49e 521.29f 603.4 6.55f 4.99d 5.78

Mean 730.3c 486.3c 608.3 5.21c 3.54c 4.38

3866.7a 2860.8a 3363.8 18.47c 13.67b 16.08

3893.2a 2562.6a 3227.9 27.92b 18.38a 23.16

Dickinson

4780

7170

9560 3791.2a 2062.6bc 2926.9 36.26a 19.72a 27.99

Mean 3850.4a 2495.3a 3172.9 27.55a 13.26a 22.41

2500.0b 1712.5cd 2106.3 11.95e 8.20c 10.07

2266.7c 1527.7de 1897.2 16.25d 10.95bc 13.60

Pro-gold

4780

7170

9560 1750.0d 1143.6e 1446.8 16.73d 10.92bc 13.83

Mean 2172.2b 1461.3b 1816.8 14.98c 10.02b 12.50

Values are the means of three replicates. Values followed by the same letter within a column are not significantly different at the 0.05% level of probability

according to Duncan’s multiple range test.

Table 2. Fruit weight and yield of two pumpkin genotypes grown under three different planting populations and tested for

potassium spraying (−/+) effect.

Genotype Plant population/ha KNO3 (10 mM) Fruit weight (g/fruit) Fruit Yield (ton/ha)

− 461.19f 2.20f

4780 + 539.5f 2.58f

− 476.52f 3.42ef

7170 + 500.00f 3.56ef

− 521.29f 4.99e

Frosty

9560 + 356.96f 3.42ef

− 2860.8ab 13.67d

4780 + 2942.2a 14.05d

− 2562.6bc 13.38bc

7170 + 2394.9cd 17.16c

− 2062.6e 19.72ab

Dickinson

9560 + 2203.2de 21.06a

Values are the means of three replicates. Values followed by the same letter within a column are not significantly different at the 0.05% level of probability

according to Duncan’s multiple range test.

Figure 1. Fruit weight (a) and yield (b) of three pumpkin genotypes grown for two seasons with three different planting

populations.

Dependence of Pumpkin Yield on Plant Density and Variety

640

siderable environment and genotype variation (Table 1)

(Figure 1). The range in fruit weight of genotypes was

between 0.7 to 3.9 kg in the first season and between 0.5

to 2.5 kg in the second season. While the range for fruit

yield was from 3.5 to 36.26 t·ha–1 in the first season and

from 2.2 to 19.72 t·ha–1 in the second season (Table 1).

When the genotypes were ranked for fruit yield and fruit

weight, there were high agreement from environment to

environment indicating the importance of genotype in

determining the yield of pumpkin (Table 1) (Figure 1).

Dickinson and Frosty usually exhibited the highest and

lowest pumpkin fruit weight and yield respectively. The

pooled analysis of variance over seasons for three geno-

types is presented in Table 3. For fruit weight, genotypic

differences described the greatest percent of the variation.

Genotypic sum of squares accounted for almost 91% of

total sum of squares (Figure 2).

Although variation due to the environment and geno-

type by environment interaction were significant but they

contribute less to the total variation (5% and 4% respec-

tively) (Table 3, Figure 2). Similar trend was observed

for fruit yield since all the three components were statis-

tically significant and represented 88%, 6%, and 6% for

genotype, environment and genotype by environment

interaction respectively (Table 3, Figure 2).

4. Discussion

Pumpkin growers are seeking different approaches to

maximize yield per unit are in order to save on land and

increase profitability. Growers need to be cognizant of

the market demands and adjust their cultural practices

accordingly to meet market expectations. The current

pumpkin market is limited by the improper size of the

fruit to most consumers.

Since competition between plants for natural resources

greatly affect yield [3] consequently it is feasible to mo-

dify size of the harvest crop to meet the requirements of

the different markets by manipulating plant density [8].

The effect of plant population on fruit weight and

yield in pumpkin genotypes were investigated in this

study. The increase of plant population from 4780 to

9560 plant/ha significantly decreased the fruit weight in

particular in large vine type genotypes which was asso-

ciated with increase in overall yield due to the increase in

number of plant per unit area. These results are in ac-

cordance with previous research in pumpkin [8,36-38,

44-46].

Potassium is the most abundant inorganic cation in

plant tissues and involved in many biochemical and

physiological functions in plant such as osmoregulation

and cell extension, stomatal movement, activation of

enzymes, protein synthesis, photosynthesis and many

Table 3. Analysis of variance for yield weight (g/fruit) and

fruit yield (ton/ha) in three pumpkin genotypes grown over

two environments.

EffectSS df MS F P

Season

(S) 20116218 1 20116218 155.4050.0000***

Genotype

(g) 378322805 2 189161402 1461.3370.0000***

Fruit

Weight

(g/fruit)

S*G 159316692 7965835 61.5390.0000***

Season

(S) 228.326 1 228.326 64.9470.0000***

Genotype

(g) 3281.5662 1640.783 466.7150.0000***

Fruit

Yield

(ton/ha.)

S*G 225.34 2 112.670 32.0490.0000***

***Significant at 0.001% level.

Figure 2. Percentages of total phenotypic variation of fruit

weight (a) and yield (b) associated with genotype, environ-

ment, and genotype by environment interaction for three

pumpkin genotypes grown over two seasons.

more [40]. Although the foliar application of potassium

to pumpkin cultivars did not reveal any significant effect

on yield, the sprayed plants tended to show slightly

higher yield in both tested genotypes overall planting

densities. The failure of potassium application to show

any significance may be due to either the low concentra-

tion of potassium foliar fertilizers or the low number of

applications. The pumpkin plants are characterized by

the huge volume of vegetative growth particularly in the

large vining types which require high inputs of foliar

application of fertilizers to be effective. Also, pumpkin

plants are known to have stiff hairs on leaf surface which

may also explain the reason of the non-significant effect

of foliar application. The slight increase in yield as a

result of potassium foliar application may be due to the

known effect of potassium in plant tolerance of biotic

and a biotic stresses [47]. In addition, this can be ex-

plained by the process of biomass allocation [48]. Ac-

cording to this process the group of non-sprayed plants

allocates a greater proportion of their biomass to the root

system compared to the sprayed plants which accumu-

lated more in their shoot system that resulted in slightly

higher fruit yield [48].

Dependence of Pumpkin Yield on Plant Density and Variety641

Development of pumpkin germplasm with enhanced

yield will potentially promote pumpkin cultivation and

production. This investigation found that the phenotypic

variation existing among pumpkin genotypes for yield is

primarily under genetic control. The ANOVA revealed

that the mean squares for genotypes were significant for

fruit yield. This indicates the existence of a high degree

of genetic variability in the tested plant materials that can

be exploited in a breeding programme which was also

reflected in the broad ranges observed between geno-

types for fruit yield (Table 1). The differences between

pumpkin genotypes for yield were recorded also in pre-

vious studies [49]. Plant size and growth habit differen-

ces can profoundly affect response to plant density varia-

tion [6]. Differential response of pumpkin cultivars to

increased plant density can be explained by differences

in their plant size and growth habits.

The results of this study concerning the genetic control

of pumpkin yield are supported by the moderate herita-

bility (43%) with moderately high genetic gain (44%)

that was recorded for yield by Mohanty and Mishra [50].

In addition, additive gene action has been suggested to

control the expression of yield and its components in

pumpkin [51]. These results support the feasibility of ge-

netic manipulation of yield in pumpkin. Further research

is required to investigate the influence of between rows

spacing on pumpkin yield and to confirm same results

from experiments conducted over one year (potassium

foliar application) or one location (genotype by envi-

ronment interaction).

Higher plant densities may maximize pumpkin num-

bers per unit area, but growers must realize that greater

fruit number will result in a smaller average fruit size.

Growers who choose higher population need to ensure

that all inputs are optimized to reduce potential plant-to-

plant competition. These data provide a basis for new

closer spacing recommendations for pumpkin in Egypt as

long as water and nutrients are limiting.

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