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Fowler, J.L. and R. Tinguely. 1993. Growth of direct seeded and transplanted guayule seedlings. p. 352-353. In: J. Janick and J.E. Simon (eds.), New crops. Wiley, New York.

Growth of Direct Seeded and Transplanted Guayule Seedlings

James L. Fowler and Robert Tinguely

  1. METHODOLOGY
  2. RESULTS AND DISCUSSION
  3. CONCLUSIONS
  4. REFERENCES
  5. Fig. 1
  6. Fig. 2
  7. Fig. 3
  8. Fig. 4
  9. Fig. 5
  10. Fig. 6
Guayule (Parthenium argentatum Gray), a semi-desert shrub native to the Trans-Pecos Region of southwest Texas and northcentral Mexico, is a potential domestic source of rubber for the United States (National Academy of Sciences 1977). The feasibility of domestic rubber production from guayule is dependent on improved rubber yield, increased rubber prices, and the reduction of production costs (Foster and Moore 1987). One of the major production costs of guayule is stand establishment by transplanting nursery seedlings into the field which can cost $900 to $1,200/ha (Bucks et al. 1986). Recent advances in direct seeding techniques have resulted in a less costly option of stand establishment of guayule than transplanting (Bucks et al. 1986). Seedlings for transplanting are grown in a greenhouse or nursery in small, root restricting containers and generally have a two to four month growth advantage over direct seeded guayule. The objective of this study was to determine if transplants maintain this initial growth advantage over direct seeded guayule and whether the restricted root of the transplant limits shoot and root development.

METHODOLOGY

Seeds of guayule cultivar Cal-6 were planted in a greenhouse in a soil mixture in 5 x 5 cm peat pots on Feb. 8, 1989. Seedlings were thinned to one seedling per pot and maintained in the greenhouse until transplanted to containers (polyvinylchloride pipe, 15 cm in diameter x 76 cm high, filled with very fine sandy loam soil) in a shade house (30% shade) on June 30. Seeds were also planted in similar containers in the shade house on June 30. Transplant containers and direct seeded containers were arranged in a randomized complete block design with five replications. The direct seeded containers were thinned to one plant per container. Sufficient containers of transplanted and direct seeded plants were planted for four harvests [57, 87, 117, and 146 days after planting (DAP)] over a 146 day growth period. Two containers per treatment per replication per harvest were fractionated into leaves, stems, and roots. Leaf area, leaf dry weight, shoot dry weight, root length, root volume, and root dry weight were measured. Roots were removed from the containers by cutting the containers in two, lengthwise, and gently washing the roots from the soil. Fine roots were collected by straining the soil-water mixture through a fine mesh screen several times. Nonroot plant debris and other foreign particles were removed from the roots by hand. Roots were stored in glass jars in FAA solution (Sass 1958) until processed for root length, root volume, and dry weight. Root volume was determined by displacement and root length was measured using a Delta-T Area Meter (Delta-T Devices Ltd., Cambridge, England). The shoot was separated into leaves and stem. Leaf area was measured with a LiCor, Inc. Model 3000 Leaf Area Meter with Transparent Conveyor Belt Accessory (LiCor, Inc., Lincoln, Nebraska). Dry weights of leaves, stems, and roots were determined by drying in a forced draft oven for 48 h at 70°C and reported on a dry weight per plant basis. All data were subjected to analysis of variance (SAS 1985).

RESULTS AND DISCUSSION

The increase in leaf area of guayule transplants exceeded that of the direct seeded plants for the first two harvest dates (57 and 87 DAP), but leaf area of the transplants and the direct seeded plants tended to level out between 117 and 146 DAP (Fig. 1). Leaf weight of both the transplants and direct seeded plants increased throughout the experimental period but at a greater rate in the transplants (Fig. 2). The shoot dry weight advantage of the transplants increased over the direct seeded plants throughout the experimental period (Fig. 3). Leaves from transplants had higher specific leaf weights (leaf weight/leaf area) than leaves from direct seeded plants except for the second harvest (no significant difference) which may account for the high rate of dry matter accumulation of the transplants over the last growth period (between 117 and 146 DAP) when leaf area was leveling off. Root growth as measured by root length (Fig. 4), root volume (Fig. 5), and root dry weight (Fig. 6) followed a similar growth pattern as that of the shoot with the rate of transplant root development exceeding that of the direct seeded plants throughout the measurement period.

CONCLUSIONS

The initial growth advantage of the transplants over the direct seeded plants increased with time over the 146 day growth period for both shoots and roots. There was no indication that the initial restricted root growth of the transplants had any adverse effects on subsequent root or shoot development. If the growth advantage of the transplants over the direct seeded plants is maintained through the second year of growth, the initial cost advantage of direct seeding would be decreased. A field study comparing the growth of transplanted and direct seeded guayule plants is needed to determine if the initial growth advantage of the transplants is maintained through harvest and this would permit a detailed economic comparison.

REFERENCES


Fig. 1. Leaf area of direct seeded and transplanted guayule. Fig. 2. Leaf dry weight of direct seeded and transplanted guayule.

Fig. 3. Shoot dry weight of direct seeded and transplanted guayule. Fig. 4. Root length of direct seeded and transplanted guayule.

Fig. 5. Root volume of direct seeded and transplanted guayule. Fig. 6. Root dry weight of direct seeded and transplanted guayule.
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