D. Ban, M. Oplanic and
A.S. Ilak Persuric
Institute of Agriculture and Tourism, Porec,
Croatia
B. Novak and I. Zutic
Vegetable Crops
Department, Faculty of
Agriculture University of Zagreb, Zagreb,
Croatia
S. Goreta
Institute for Adriatic
Crops and Karst
Reclamation, Split,
Croatia
Keywords: plant height, number of leaves per plant, stem diameter, fresh above ground mass, fresh root mass
Abstract
Modern technology of watermelon production is based on watermelon cultivation transplants. Watermelon transplants are cultivated exclusively with root ball. The aim of this research was to determine optimal plug size, cultivation period and influence of mycorrhiza on the quality of watermelon transplants. The research was conducted during spring 2003 and 2004 in a heated plastic greenhouse. A three factorial trial was set up in randomized complete-block design with three replications. Factor ”plug size” had three levels: 100 ml cells (plug tray with 40 cells), 80 ml cells (plug tray with 60 cells) and 60 ml cells (plug tray with 84 cells).
Second factor, “mycorrhiza” had two levels: substrate inoculated with endomicorrhizal fungi Glomus mossae and substrate without endomicorrhizal fungi.
Third factor, “age of transplants” also had two levels: 30 and 45 days old transplants in 2003, respectively 40 and 55 days in 2004. In both research years in average, the best developed watermelon transplants were the ones planted in 100 ml cells (highest stem, largest number of leaves, largest plant diameter, highest mass of plant and root). Differences between transplants in cells of 60 and 80 ml were not significant. In the second year inoculated transplants were better in all attributes comparing to uninoculated ones. In both years more mature transplants (45 and 55 days after sawing) had more leaves, larger plant diameter, higher plant mass and root comparing to younger ones (30 and 45 days after sawing).
INTRODUCTION
Watermelon is a warm-loving culture not bearing low temperature stresses as vegetation starts because it consequences in weak vegetative growth and lower yields
(Korkmaz and Dufault, 2001).
Therefore a modern technology of watermelon production should be based on transplants cultivation by which it is possible to achieve earlier maturation and setting production areas in marginal territories with a shorter period of warm weather (Lešić, 2002).
Watermelon transplants can be cultivated exclusively with root ball because they don’t tolerate transplanting with bare root. The most popular cultivation of transplants with root ball is cultivation in plug trays. Plug trays with different plug size and forms of cells can be purchased on the market (Styer and Koranski, 1997). Plug size, uniform provision of plant nutrients per each cell and age of transplants are major factors of

transplants quality. The transplants quality is a major feature which determines the future crop quality and yields (Schultheis and Dufault, 1994; Borošić, 2002).
Research of Novak et al (1999), on cucumbers showed that inoculated transplants had significantly bigger vegetative mass and height than uninoculated. On the other side, different cultivation periods of zucchini transplants had no significant influence on the set of female flowers (Toth et al, 1999).
Therefore, the aim of this research was to determine the optimal plug size, cultivation periods and influence of mycorrhiza on the quality of watermelon transplants.
MATERIALS AND METHODS
The research was conducted in springtime of 2003 and 2004 in a heated plastic greenhouse on the experimental grounds (at Vegetable Crops Department, Faculty of
Agriculture in Zagreb, Croatia).
A three factorial trial was set up in randomized complete-block design with three replications. Factor ”plug size (V)” had three levels: 100 ml cells (plug tray with 40 cells),
80 ml cells (plug tray with 60 cells) and 60 ml cells (plug tray with 84 cells). Second factor, “mycorrhiza (M)” had two levels: substrate inoculated with endomicorrhizal fungi
Glomus mossae and substrate without endomicorrhizal fungi. Third factor, “age of transplants (S)” also had two levels: 30 and 45 days old transplants in 2003, respectively
40 and 55 days in 2004 .
“Klasmann potground H” substrate was used for transplants production. Each polystyrene plug tray was divided in two equal parts: one half was filled with pure substrate while the other half was filled with the mixture of substrate and mycelia of endomycorrhizal fungi. Half of the plug tray represented basic plot for factor mycorrhiza.
Inside basic plot 15 middle plants were used for calculations.
On 26 March 2003 and 14 April 2004, two seeds were hand-sown per cell of watermelon variety Fantasy F
1
(Known – you seed co. Ltd). After germination (2 April
2003 and 23April 2004), one plant was left per cell. Plug trays prepared in this way were randomly arranged in blocks on cultivation table.
During vegetation, basic cultivation measures were performed: irrigation (manual overhead irrigation, daily), topdressing (foliar with Proferta mara - weekly), pest and disease control every ten days.
The greenhouse was regularly heated and ventilated in order to achieve undisturbed development of transplants. After 30 and 45 days in 2003 respectively 40 and
55 days in 2004 we measured several features. We choose 15 plants per each plot and calculated, plant height, number of leaves per plant, stem diameter and mass of aboveground part and root.
Statistical analysis of all three factors and interaction of investigated traits was performed by analysis of variance (F-test) while the average values of factor “plug size” was tested by the Duncan’s Multiple Range Test (p

0.05).
RESULTS AND DISCUSSION
Plant height
In conditions of less substrate volume per plant and higher transplants density in plug trays, unwanted elongation of stems can appear, especially in conditions of less light intensity and uncontrollably higher air temperature (Borošić, 2002). Therefore, higher plants are not necessarily better in quality. We confirmed this thesis in our research: in

the first year of research transplants were grown in shorter time period (30 and 45 days) respectively in the second year it was 40 and 55 days. Namely, plant height for plants in
100 and 60 ml cells did not significantly differ while the transplants in 80 ml cells were
17 % and 16 % (respectively) shorter than transplants from previously mentioned plug sizes in 2003 (see table 1).
In 2004. the transplants grown in cells with more substrate
(100 ml) were 14 respectively 10 % higher then transplants in cells of 80 and 60 ml.
Between the last two there were no significant differences considering plant height (see table 2.).
Transplants grown in pure substrate without mycelia of endomycorrhizal fungi were 9 % taller than plants grown in a mixture of substrate and mycelia of endomycorrhizal fungi in the first year. We noted an opposite situation in the second year: inoculated transplants were 28 % higher then uninoculated. We found out that this difference occurred because of later measuring (10 days difference) The transplants were therefore older and the effect of mycorrhiza stronger (plants and mycorrhiza were struggling for substrate nutrients.
Older transplants were in general higher, but the growth in height was determined by the production system and nutrients in substrate (the transplants could grow until the reserves of nutrients were spent - Borošić, 2002). In our case this was not the issue; the nutrients were totally consumed and the forty five days old watermelon plants were 31 % taller than those thirty days old in the first research year, while in the second year this difference was less. Transplants fifty five days old were 28% higher than transplants of 40 days.
From this findings we noticed that transplants were growing further in height even after fifty five days. Statistically significant interaction between plug size and age of transplants showed that the transplants were taller with bigger cell size (100 ml) or they were more elongated in smaller cell size (60 ml) as the production period in cell trays increases. Furthermore in the second year we found out that transplants achieved higher stems as they were inoculated with mycorrhiza and in 100 ml cells.
Number of leaves per plant
Leaves present the plant assimilation system necessary for photosynthesis upon which a plant can develop its vegetation mass above the land surface. In both research years we measured the highest number of leaves by transplants grown in 100 ml cells
(table 1 and 2). In the first year transplants in 100 ml cells had 18 % and 12 % more leaves than those in 60 ml and 80 ml cells, respectively, in the second year plants in the biggest cells had 12% more leaves than the ones in 80 ml cells, while there was no difference between the biggest and smallest cells.
There was no difference in number of leaves between inoculated and uninoculated plants in the first year, while in the second year inoculated plants had 17% more leaves than the uninoculated.
Older transplants in average had 24 % and 41 % more leaves than younger watermelon transplants (first and second year), what proves that transplants could develop without disturbance even after a longer period of growth in blocks.
Interaction between factors for this trait was not determined during the first year.
However, results in the second year showed significant differences in interaction of plug volume and mycorrhiza. Also an interaction was found between the plug volume and the transplants age: transplants inoculated in biggest cells had the most leaves as well the oldest transplants had the highest number of leaves.

Steam diameter
Stem diameter is an indicator of transplants’ hardness, so the thicker the stem, the better the quality of transplant (Borošić, 2002). In both research years, we measured biggest plant diameter by transplants in 100 ml cells. We presume it is a consequence of bigger vegetative space – bigger distance between cells. Watermelons grown in 100 ml cells had in average 14 % and 12 % bigger diameter compared with those grown in 60 ml and 80 ml cells, respectively (table 1).
In the second year transplants grown in 100 ml cells had 9 % bigger diameters comparing to smallest cells, while there was no significant difference between transplants in 100 ml and 80 ml cells (table 2).
Influence of mycorrhiza was not significant in the first research year. However, in the second year inoculated transplants had 12% bigger stem diameter than uninoculated ones. We presume that measuring period that was 15 days later in second year was a possible cause of this result differences. Therefore the mycorrhiza influence was more intense.
Older transplants in both years had thicker stem. This result was expected because there was no nutrient insufficiencies because transplants were regularly manured by topdressing (foliarly). Namely, older transplants had 12 % respectively 23 % bigger diameter than younger transplants.
Inoculated transplants in 100 ml cells had the biggest stem diameters. The stem diameter was decreasing with the cell volume. Also the inoculation effect was minor on smaller cells. Regarding both years the interaction of these two features were significant.
Between the cell size and the vegetation period the stem diameter in both years was bigger in the biggest cells. In the second year the plants inoculated with mycorrhiza had bigger diameters.
The transplant development was affected also by all three measured factors: most developed transplants were gained by mycorrhiza inoculation, by longer growing period and in bigger cells (because of more nutrients).
Fresh above-ground mass
In both research years watermelon transplants in 100 ml cells had the biggest above-ground mass (table 1 and 2). These results are a consequence of feautures mentioned in paragraph above (height, number of leaves and diameter per transplant) which were especially significant in 100 ml cells. Their mass above ground was 27 % bigger than the mass of transplants in 80 ml cells, respectively, 25 % bigger than those in
60 ml cells in the first research year. In the second year it had 28 % more above ground mass than the ones in 80 ml cells, respectively 34 % more than in 60 ml cells. In both years there were no differences in plant mass between plants in 80 ml and 60 ml cells.
Uninoculated watermelon transplants had 9 % bigger mass than inoculated ones during the first year, while this effect was opposite in the second year – inoculated transplants had 27 % more above ground mass. The reason lies in the fact that measuring was done with a ten days difference. Therefore the root was more developed, mycorrhiza more spread and the nutrient intake better (also confirmed by Novak et al in 1999 on cucumber transplants.
In both years, transplants grown for a longer period were more developed then shorter grown transplants what is logical to conclude as growth was not determined by other factors. Forty five days old watermelons had 25 % bigger above-ground mass than thirty days old transplants in the first year. In the second year fifty five days old transplants had 41 % more mass above ground than 15 days younger transplants.

In both research years the interaction between cell size and mycorrhiza indicated that the reduction of cell size decreases the influence of mycorrhiza and the increase of above-ground plant mass. With longer cultivation period the increase of above-ground plant mass is bigger in the cells with more substrate.
Fresh root mass
Well developed root system which completely wraped substrate is a prerequisite for good establishment of transplants in the field Borošić (2002). Transplants grown in
100 ml cells had 40 % bigger root mass compared with those in 60 ml cells and 27 % more root mass compared with those in 80 ml cells during the first year (table 1).
Similarly in the second year the transplants in 100 ml cells had 21 % more root mass then the 80 ml cell transplants and 27 % more mass than the ones in 60 ml cells (table 2).
Plants grown in 80 ml cells had 19 % bigger root mass than plants grown in 60 ml cells during the first year, while in the second this difference was not statistically significant.
Mycorrhiza in both years had no significant influence on root development, because it was limited by the cell volume. Therefore the root could develop only as much the cell size was.
Forty five days old transplants had 36% bigger root mass than thirty days old transplants during the first year. Transplants of fifty five days had 41 % more root mass then the fourty day ones.
Only the interaction between cell volume and days was significant in the second year, while other features weren’t correlated. This conclusion refers to root mass development which was the most in the largest cells and longest period of growth.
CONCLUSIONS
Watermelon transplants production in plug trays with 40 cells and 100 ml volume obtains higher plants, higher number of leaves and thicker stem. These features result in more vegetative mass above ground and more root mass than the transplants in plug size
60 cells per 80 ml.
Differences in measured features between transplants in 60 and 80 ml cells were not noticed.
Inoculation with endomycorrhiza on watermelon transplants has sense in protected spaces and production longer than 40 days. Otherwise mychorrhizza has no effects because the root is not enough developed and the spores are not sufficiently penetrated through the substrate. Inoculation along with longer growth periods gain better results through transplant development (higher transplants, more leaves per plant, thicker and firmer plant stem and more plant mass above ground).
In field circumstances 55 days after sawing the transplants are strong and firm. At this state they can handle the cold stress and they can grow faster then the younger ones.
Therefore, from the agricultural point of view, the best quality transplants were achieved by cultivation of watermelons in 100 ml cells, inoculated by some of endomycorrhizal fungus and growth period of 40-55 days.
However, having in mind production economy and minimal parameters of satisfactory transplants quality this can be achieved with production systems in 80 and 60 ml cells and at least 40 days growth along with inoculation by endomycorrhizal fungus.

ACKNOWLEDGEMENTS
This research was set in the frame of a scientific research project financed by the
Ministry of agriculture, forestry and water management, and the Ministry of scince, education and sports of Republic Croatia. We wish to confirm our gratitude for financial support.
LITERATURE CITED
Borošić, J. 2002. Uzgoj presadnica. p. 93-105. In: Lešić, R., Borošić, J., Buturac, I.,
Ćustić, M., Poljak, M. and Romić D., Povrćarstvo. Zrinski d.d., Čakovec.
Lešić R., 2002. Specijalno povrćarstvo. p. 107-627. In: Lešić, R., Borošić, J., Buturac, I.,
Ćustić, M., Poljak, M. and Romić D., Povrćarstvo. Zrinski d.d., Čakovec.
Korkmaz, A. and Dufault, R.J. 2001. Developmental consequences of cold temperature stress at transplanting on seedling and field growth and yield. J. Amer. Soc. Hort. Sci.
126:404-409
Schultheis, J.R. and Dufault, R.J. 1994. Watermelon seedling growth, fruit yield and quality following pretransplant nutritional conditioning. Hortscience 29:1264-1268
Novak, B., Žutić, I. and Toth N. 1999. Influence of vesicular arbuscular mycorrhiza on the growth and yield components of pickling cucumbers. XXXV Croatian Symposium on Agriculture with an Internacional Participation «Agricultural Science in Croatia at the Treshold of Third Millenium». Opatija, Croatia 22-25 February. p. 146
Styer, R.C. and Koranski, D.S. 1997. Plug & transplant production. Ball Publishing,
Batavia, Illinois
Toth, N., Žutić, I. and Novak, B. 1999. Effect of the age of seedlings on courgette flowering. XXXV Croatian Symposium on Agriculture with an Internacional
Participation «Agricultural Science in Croatia at the Treshold of Third Millenium».
Opatija, Croatia 22-25 February. p. 147

Table1. Influence of plug size, mycorrhiza and cultivation period on growth and development of watermelon transplants, 2003
Plug size-V
100 ml (40 cells)
80 ml (60 cells)
60 ml (84 cells)
Mycorrhiza-M
Without mycorrhiza
With mycorrhiza
Plant height, cm
8.78 A 1
7.25 B
8.67 A
8.63*
2
7.83
Number of leaves/plant
3.39 A
3.01 B
2.78 B
3.03
3.09 n.s.
Stem diameter, mm
5.00 A
4.41 B
4.29 B
4.62 n.s.
4.50
Fresh aboveground mass, g
2.30 A
1.68 B
1.73 B
1.99*
1.82
Fresh root mass, g
2.08 A
1.53 B
1.25 C
1.64 n.s.
1.59
Age of transplants -S
30 days
45 days
Interactions
V x M
V x S
M x S
6.76
9.71**
3
n.s.
* n.s.
4
2.64
3.48** n.s. n.s. n.s.
4.28
4.84**
*
* n.s.
1.64
2.17**
*
* n.s
1.27
1.96** n.s. n.s. n.s.
V x M x S n.s. n.s. n.s. n.s. n.s.
1 Duncan’s Multiple Range Test with p  0.0¸5 significance level for factor “plug size”
2 justified F-test with p

0.05 significance level for factor “mycorrhiza”, “age of
3 transplants” and interactions justified F-test with p
 0.01 significance level for factor “mycorrhiza”, “age of transplants” and interactions
4 not significant

Table 2.
Influence of plug size, mycorrhiza and cultivation period on growth and development of watermelon transplants, 2004
Plant Number of height, cm leaves/plant
Stem diameter, mm
Fresh aboveground mass, g
Fresh root mass, g
Plug size-V
100 ml (40 cells)
80 ml (60 cells)
60 ml (84 cells)
22.12 A
1
18.92 B
19.98 B
18.40
5.16 A
4.52 B
4.92 A
4.42
5.22 A
5.01 A
4.77 B
4.69.
8.95 A
6.48 B
5.95 B
6.03
2.01 A
1.59 B
1.47 B
1.63 n.s.
Mycorrhiza-M
Without mycorrhiza
With mycorrhiza
Age of transplants -S
40 days
55 days
Interactions
V x M
V x S
22.28**
17.03
23.65**
3
*
2
n.s.
4
5.31**
3.62
6.12**
*
**
5.31**
4.35
5.64**
*
**
8.22**
5.30
8.96**
**
**
1.74
1.25
2.12** n.s.
**
M x S n.s. n.s. * n.s n.s.
V x M x S n.s. n.s. * n.s. n.s.
1 Duncan’s Multiple Range Test with p  0.0¸5 significance level for factor “plug size”
2 justified F-test with p
 0.05 significance level for factor “mycorrhiza”, “age of
3 transplants” and interactions justified F-test with p
 0.01 significance level for factor “mycorrhiza”, “age of transplants” and interactions
4 not significant