Strawberries are an important crop throughout the world. Due to genetic heterozygosity, adaptability, and plasticity of the plant, this species can grow in varied environments throughout the world, from Alaska to South Africa (Martinelli, A. [1992] xe2x80x9cMicropropagation of strawberry (Fragaria spp.)xe2x80x9d Biotechnology in Agriculture and Forestry 18:354-370, Springer Verlag, Berlin, W. Germany). The high value of the fruit allows for intensive production methods in many regions.
An estimated 1.8 billion strawberry plants are vegetatively propagated throughout the world each year (Boxus, P. [1989] xe2x80x9cReview of in vitro strawberry mass productionxe2x80x9d Acta Horticulture. Inter. Strawberry Symp., Cesena, Italy 265:309-320). Greater than 700 million of these plants are propagated in the United States. Commercial strawberry cultivars must be propagated vegetatively because seeds are not true to type. Strawberry transplants are produced conventionally by planting a field nursery in early summer, the nursery plants produce daughter plants on stolons in response to long day lengths and high temperatures. In late summer and early fall the daughter plants from the nursery field are dug, soil is removed from the roots, and then the plants may be cold stored for several months before planting, or planted immediately. These plants may become extremely stressed during this process. Additionally, inconsistency in strawberry transplant production and handling, coupled with post transplant conditions can contribute to delayed flowering and subsequent fruiting irregularity, and disease and spider mite epidemics due to pathogen infestation and plant stress. The percentage of marketable fruit may therefore be reduced. Mechanical digging and shaking (to remove soil from roots) often damages roots and breaks petioles, reducing the number of ftmctional leaves for use by the transplant during establishment and creating possible sites for pathogen infection. Bare-root transplants often require large quantities of water at planting, especially in warm climates. This further exacerbates plant pest problems and can leach nutrients.
One of the greatest challenges facing the current strawberry plant propagation system may be the elimination, by the year 2001, of the fumigant methyl bromide (Courter, J. W. [1993] xe2x80x9cAccord reached on production cuts from methyl bromidexe2x80x9d N. Amer. Strawberry Growers Assoc. Newsletter 18:6). Methyl bromide has been used on the majority of commercial acreage for disease control and effective alternatives have not been developed. Additionally, there have been years when nurseries have had difficulty digging plants because of adverse weather conditions during the digging period. Varying weather conditions during the transplant production season can cause variability in transplant performance from year to year.
Through micropropagation, large quantities of uniform, vigorous, pathogen-free plants can be produced (Boxus, P., C. Damiano, and E. Brasseur [1984] xe2x80x9cStrawberryxe2x80x9d In: Handbook of Plant Cell Culture, Vol. 3, p. 453-486, Macmillan Publishing Co., New York, N.Y.). Micropropagated plants are more expensive than standard plants, but the increased runner production of micropropagated plants (Swartz, H. H., C. J. Galletta, and R. H. Zimmerman [1981] xe2x80x9cField Performance and Phenotypic Stability of Tissue Culture-propagated Strawberriesxe2x80x9d J. Am. Soc. Hortic. Sci. 106:667-673) has justified the increased expense for some nursery growers. Micropropagated plants often produce smaller fruit and therefore have not been directly used for fruit production. In some cultivars, bare-root daughter plants of micropropagated mother plants had increased fruit production compared to conventional bare-root plants which were not micropropagated. The daughter plants from micropropagation, however, are produced in field nurseries and therefore can develop the same inconsistencies as conventional plants due to temperature fluctuations and exposure to pathogens.
The above problems of transplant variability could be avoided by the use of micropropagation derived plug transplants which can be mechanically transplanted into the field similar to other vegetable transplants. Plug (tray) transplants have been used successfully in Europe since the late 1980""s (Hennion, B., J. Schupp, and J. Longuesserre [1996] Fraisimotte: a strawberry-plug plant developed by CIREF. p. 87 Abstract; 3rd Inter. Strawberry Symp., Veldhoven, The Netherlands) and have been the subject of research in North America. In North Carolina, plugs have been reported to have several distinct advantages over bare-root transplants: plugs required only 10% of the water needed for bare-root establishment in spring production systems; a mechanical multiple-row plug transplanter could be used for planting; minimal root damage during transplanting which provided for quick root establishment; and plant survival was greater (Poling, E. S. and K. Parker [1990] xe2x80x9cPlug production of strawberry transplantsxe2x80x9d Adv. in Strawberry Prod. 9:37-39). xe2x80x98Chandlerxe2x80x99 plug transplants grown in New Jersey had three times the fruit production of dormant crowns, but primary fruit size was lower with the plug transplant (Fiola, J. and R. Lengyen [1995] xe2x80x9cPlug transplants are superior to dormant transplants for productivity in strawberry plasticulturexe2x80x9d pg. 289-291, In: Proc. of the IV N. Amer. Strawberry Conf., University of Florida Horticultural Sciences Department, Gainesville, Fla.).
The subject invention provides inexpensive materials and methods for growing strawberry plants. In a preferred embodiment the methods use tissue cultured mother plants in elevated troughs 12 to produce strawberry daughter plant tips. The daughter plant tips hang from the troughs 12 and continue to grow down towards the ground. The same mother plants can be used for extended periods and continue to produce large amounts of high quality daughter plant tips. The runners are harvested as long chains of daughter plant tips. When this system is used in a protective structure such as a greenhouse, the plants remain dry. This reduces pathogen dissemination and infection.
In a preferred embodiment, the subject invention further provides a system 14 for rooting the daughter plants 16. In a specific embodiment, this system 14 uses hanging trays 18. As the daughter plants grow they are placed in these hanging trays for immediate rooting. The trays 18 can either be watered from above by a mist or from below with a mist or capillary mat. In a specific embodiment, Rock wool or OASIS trays are used because they have preformed holes for placing daughter plants 16 and have high water holding capacity. There is no need for fertilizer for the daughter plant trays 18 because the daughter plants receive nutrients from the mother plant.