Cucurbit Genetics Cooperative Report 7:14-16 (article 7) 1984

Effect of Length of Vegetative Phase on Total Dry Matter Production and Its Partitioning

D.R. Ramirez and T.C. Wehner

Department of Horticultural Science, North Carolina State University, Raleigh, NC 27695-7609

The onset of fruit development usually determines the extent of vegetative growth in crops. The length of both vegetative and reproductive phases in the growth of plants have been claimed to be important in determining yields in maize (Zea mays L.) (4) and cereals (1). Inhibition of vegetative growth by fruit development has been demonstrated in cucumbers (3). Assimilate supply from source leaves could also be limiting growth (2).

Dry matter production depends basically on the amount of photosynthetic leaf surface and the rate of carbon fixation (photosynthesis) per unit of leaf area. Most of the variation in yields of crop species was related to differences in rate of increase in leaf area rather than differences in net assimilation rate (5).

This experiment was aimed at determining the effect of an increase in the length of the vegetative phase on total dry weight production (a good estimate of net photosynthetic capacity). A second consideration was the effect on Partitioning of assimilates into source (leaves, stems) and sink (fruits) tissues.

Methods. Plants of the cultivar Calypso were grown in pots in the Horticultural Science greenhouses at the North Carolina State University in Raleigh, NC, from Jan. 27 through April 11, 1983. The experiment consisted of 4 flower removal treatments arranged in a randomized complete block design with 4 replications. Treatments consisted of the daily removal of female flowers for 0, 7, 14 and 21 days beginning when plants were 36 days old. The following parameters were measured at harvest: fresh and dry weights of leaves, stems and fruits; number of branches, leaves and fruits; stem length; and leaf area.

Results. Total fresh and dry weight production was not increased by increasing the length of the vegetative phase, but dry matter and fresh matter partitioning were greatly modified (Tables 1 and 3). Removal of flowers for 14 and 21 days significantly increased the percentage of dry and fresh weight that were devoted to leaf and stem growth and decreased the dry and fresh weight devoted to fruit growth. All flower removal treatments resulted in an increase in the number of branches and leaves, producing a larger plant (Table 2). Leaf area increased with increased flower removal but was only significant for the 21 day treatment. Flower removal for 7 days resulted in an increase in the number of fruits per plant, and fresh and dry weights of fruits (Tables 1 and 2), but the differences were not significant. This lack of significance could be due to the fact that fruit set was not uniform in the population of plants and treatment differences could have been masked by this variability. It seems that excessive vegetative development (as that obtained by the 14 and 21 day flower removal) is detrimental for fruit growth, as more assimilates are then diverted into unneeded leaf and stem growth.

Table 1. Fresh and dry weight production as affected by number of days of flower removal.z
Days of Flower Removaly	Fresh Weight Production (g)				Dry Weight Production (g)
	Leaves	Stems	Fruits	Total	Leaves	Stems	Fruits	Total
0	65.7	65.3	726.7	857.7	8.2	4.0	29.3	41.4
7	69.6	72.0	761.4	903.0	8.6	4.4	30.6	43.7
14	84.3	90.8	665.0	840.1	10.4	6.4	25.5	42.1
21	115.4	113.6	635.3	864.2	13.9	8.7	19.4	42.0
LSD (5%)	10.3	18.2	101.1	118.1	1.0	1.3	3.5	4.3
CV (%)	8	13	9	9	6	14	8	6
zData are means over four replications.
yTreatments begun 36 days after planting.

Table 2. Branch number, leaf number, fruit number, stem length and leaf area as affected by number of days of flower removal.z
Days of Flower Removaly	Branch number	Leaf number	Fruit number	Stem length (cm)	Leaf area (cm2)
0	0.0	16	2.5	110	3250
7	2.5	25	3.0	119	3473
14	4.0	26	2.3	134	4134
21	7.0	39	2.8	159	5190
LSD (5%)	2.0	4.6	0.7	36	897
CV (%)	37	11	17	18	14
zData are means over four replications
yTreatments begun 36 days after planting

Table 3. Distribution of fresh or dry matter in plant parts as affected by the number of days of flower removal.z
Days of Flower Removaly	Distribution of Fresh Weight (%)			Distribution of Dry Weight (%)
	Leaves	Stems	Fruits	Leaves	Stems	Fruits
0	19.8	9.5	70.7	7.7	7.6	84.7
7	19.7	10.2	70.1	7.7	8.0	84.3
14	24.7	14.9	60.5	10.1	10.9	79.1
21	33.2	20.8	46.0	13.4	13.1	73.4
LSD (5%)	1.9	3.0	4.5	0.9	1.6	2.0
CV (%)	5	14	5	6	10	2
zData are means over four replications.
yTreatments begun 36 days after planting.

Literature cited:

1. Bingham, J. 1969. The physiological determinants of grain yield in cereals. Agric. Prog. 44:30-42.
2. Clifford, P.E. 1979. Source limitation of sink yield in mung beans. Ann. Bot., N.S. 43:397-399.
3. Denna, D.W. 1973. Effects of genetic parthenocarpy and gynoecious flowering habits on fruit production and growth of cucumber, Cucumis sativus L. J. Amer. Soc. Hort. Sci. 98:602-604.
4. Hanway, J.J. and W.A. Russell. 1969. Dry matter accumulation in corn (Zea mays L.) plants: comparisons among single cross hybrids. Agron. J. 61:947-951.
5. Watson, D.J. 1952. The physiological basis of variation in yield. Adv. Agron. 4:101-145.