Cucurbit Genetics Cooperative Report 7:17-18 (article 8) 1984
D.R. Ramirez and T.C. Wehner
Department of Horticultural Science, North Carolina State University, Raleigh, NC 27695-7609
It is known that the activity of a developing fruit in a cucumber plant inhibits the development of fruit that set later (1), as well as the development of other plant parts (2). This inhibitory effect ceases when the growing fruits are removed from the plant, allowing the production of several fruit per plant under multiple harvest conditions. The prevention of simultaneous development of several fruit per plant greatly reduces yield of fruit, especially in once-over harvest systems.
One explanation for this inhibitory effect could be that fruits of the commercial cultivars of Cucumis sativus L. constitute strong sinks for assimilates, drawing heavily on plant supplies and inhibiting in this way the development of other fruit. Inhibition or cessation of vegetative growth could indirectly limit the ability of a plant to support the growth of more fruit. This study was run to advance our understanding of the partitioning of assimilates in cucumber plants. The objective of this experiment was to determine relationships between vegetative and reproductive plant parts throughout the entire cycle of development of 3 lines that differ in growth habit and yield.
Methods. Growth analysis studies of 3 lines differing in growth habit and yield were conducted in the Horticultural Science greenhouses in Raleigh, NC during the Fall, 1982. The 3 lines studied were LJ 90430, an accession of Cucumis sativus var. hardwickii; ‘Calypso’, a widely-used indeterminate cultivar; and M 21, a dwarf, determinate breeding line for NCSU. After germination, plants of LJ 90430 were subjected to a 9.5 hour daylength for 17 days in order to induce fruit set.
The experiment design was a split plot in a randomized complete block with 4 replications. Whole plots were the 9 harvests and subplots were the 3 lines. Harvests were made 32, 39, 46, 53, 60, 67, 74, 81 and 88 days after planting beginning November 2 and ending December 28. At each harvest, one whole plot in each replication was removed and the following measurements made: fresh and dry weights of leaves, stems fruits, and roots; number of leaves, fruits and branches; stem length, and leaf area. Leaf area was determined with an electronic leaf area meter. After each harvest, the border plants were moved in to fill the space left.
Results. At the end of the growing period (88 days), both LJ 90430 and ‘Calypso’ produced the same amount of total dry weight and fruit dry weight. However, M 21 produced significantly less total dry weight. LJ 90430 incorporated a higher amount of dry weight into leaves, stems and roots than the other 2 lines (Table 1).
Table 1. Partition of dry weight production into leaves, stems, fruits and roots in three lines at final harvest (88 days)z.
|
Line |
Dry Weight (g) | ||||
|---|---|---|---|---|---|
| Leaves | Stems | Fruits | Roots | Total | |
| LJ 90430 | 10.2 | 9.9 | 40.9 | 2.6 | 63.1 |
| Calypso | 8.1 | 5.3 | 43.7 | 1.7 | 53.2 |
| M 21 | 7.0 | 3.0 | 24.3 | 0.7 | 35.3 |
| LSD (5%) | 1.3 | 0.8 | 12.6 | 0.9 | 15.1 |
| CV (%) | 9 | 8 | 20 | 31 | 17 |
| zData are means over four replications on a per plant basis. | |||||
‘Calypso’ produced a significantly higher total fresh weight and fruit fresh weight than LJ 90430 and M 21 (Table 2). When dry and fresh weights were compared, it was evident that ‘Calypso’ fruits and stems had a higher water content. The number of fruits per plant were significantly higher in LJ 90430 than in the other 2 lines.
Table 2. Fruit number,and fresh weight of leaves, stems and fruits in three lines at final harvest (88 days)z.
|
Line |
Fresh Weight (g) | ||||
|---|---|---|---|---|---|
| Leaves | Stems | Fruits | Roots | Total | |
| LJ 90430 | 26 | 79 | 120 | 504 | 703 |
| Calypso | 3 | 76 | 86 | 769 | 930 |
| M 21 | 2 | 73 | 43 | 468 | 585 |
| LSD (5%) | 4 | 16 | 13 | 108 | 123 |
| CV (%) | 24 | 12 | 9 | 11 | 10 |
| zData are means over four replications on a per plant basis. | |||||
Leaf photosynthetic area was higher in ‘Calypso’ in the first 2 harvests (32 and 39 days), but LJ 90430 had a significantly higher leaf area than ‘Calypso’ and M 21 thereafter. This early advantage of ‘Calypso’ and to a lesser extent M 21 was related to earliness. Fruits started developing when plants were 39 days old in ‘Calypso’ and M 21, and when plants were 53 days in LJ 90430. At this time their leaf area had developed 63, 59 and 93%, respectively, of their total mean leaf area for the remainder of the period when it was fully developed (Table 3).
Table 3. Leaf area per plant for nine weekly harvests in three linesz.
|
Line |
Leaf area per plant (cm) | ||||||||
|---|---|---|---|---|---|---|---|---|---|
| Days from planting to harvest | |||||||||
| 32 | 39 | 46 | 53 | 60 | 67 | 74 | 81 | 88 | |
| LJ 90430 | 74 | 1928 | 3734 | 5153 | 5715 | 5744 | 5601 | 5583 | 5395 |
| Calypso | 123 | 2489 | 3604 | 4025 | 3770 | 3832 | 3980 | 4082 | 4086 |
| M 21 | 105 | 1928 | 3106 | 3547 | 3473 | 3254 | 2958 | 3151 | 3252 |
| LSD (5%) | 15 | 560 | 806 | 717 | 885 | 906 | 759 | 995 | 1075 |
| CV (%) | 9 | 15 | 13 | 10 | 12 | 12 | 11 | 13 | 15 |
| zData are means over four replications. Analysis were performed separately for each of the nine harvests. | |||||||||
These results indicate that ‘Calypso’ was capable of producing the same amount of total dry weight and a significantly higher total fresh weight and fruit fresh weight with a lower leaf photosynthetic area. However, the inhibitory effect of fruits in ‘Calypso’ and in M 21 was very high. It could be that early fruit set at the time when leaf area has not developed fully could enhance this inhibitory effect.
Literature Cited
- Denna, D.W. 1973. Effect of genetic parthenocarpy and gynoecious flowering habit on fruit production and growth of cucumber, Cucumis sativus L. J. Amer. Soc. Hort. Sci. 98:602-604.
- McCollum, J.P. 1934. Vegetative and reproductive responses associated with fruit development of the cucumber. Cornell Agric. Exp. Sta. Memoir 163:1-27.