Tomatoes

image via image via Diagnosis Diet - Nightshades

The Black Sheep of the Deadly Nightshade Family

The tomato (Solanum lycopersicum) is a unique species of plants belonging to the Nightshade family, Solanacae, native to the general high Andean region of western South America (Bai and Lindhout, 2007; Razdan et al., 2006), which, in the common day, stretches over the geographical regions of Peru, Ecuador, Columbia and Chile.

The ethnobotany of this unique plant has long been a subject of debate among ethnobotanists, historians and geneticists, but the timeline of domestication and cultivation stretches back to at least the 15th century AD when the Spanish made first contact with the Aztecs occupying the region, before taking the fruit back to Europe for further study and cultivation. Even before first contact with the Spanish, the Aztec Domestication of the tomato plant already reached a relatively advanced level, the extent of which, however, is obscured by the mists of time. More extensive cultivation ensued in 18th and 19th century Europe (Sims, 1980), and as soon as the plant hit the European market it was greeted with hostility and fear, an interesting and rather predictable response, seeing as the plant belongs to the same family as Belladonna and Datura, the Deadly Nightshades, which had an already deeply rooted ethnobotanical history within the Old World.

Image via Grosvenor Market


Wild tomatoes are considered herbaceous perennials with a wide spectrum of genetic variation in its natural habitat, the bulk of which has been subjected to extensive investigation for specific trait exploitation in commercial breeding (e.g. Walter, 1967; Rick and Chetelat, 1995; Larry and Joanne, 2007). The tomato cultivars used in commercial propagation, however, lacks the large spectrum of genetic variation compared to their wild relatives (Miller and Tanksley, 1990), which can be attributed to the genetic drift it experienced after squeezing through the genetic bottleneck during its migration from the homeland to Europe (Bai and Lindhout, 2007).


Image via Food Museum


The tomato subsequently underwent a morphological and physiological boom under the guidance of selective cultivation, clearly distinguishing it from its wild relatives, these characteristic changes are collectively called domestication syndrome (Frary and Doganlar, 2003). The most obvious of these characteristics would be the rapid expansion of fruit size, compared to small and inconspicuous fruits of its ancestors - suited purely for the propagation of future offspring, and not for feeding other animals such as the incisively curious Homo sapien.

Seed size also underwent alteration under the spade of cultivation, with domesticated cultivars having larger and more prominent seeds in relation to their wild relatives (Bai and Lindhout, 2007). This increase in size opened new possibilities for cultivators and breeders alike, and since tomatoes generally don’t undergo out-crossing, sexual propagation via seeds yield progeny that resemble the parental generation quite reliably (Bai and Lindhout, 2007).

The cultivation of tomatoes underwent radical changes in the 20th century, with four successive breeding stages unfolding.
Breeding for:
1)      An increase in yield in the 1970s,
2)      Improvement of shelf-life in the 1980s,
3)      Expansion of taste and textural qualities in the 1990s,
4)      And an increase in nutritional quality in following decades until current times, with a continuous line of investigation into general pest and pathogen control/resistance.
(Bai and Lindhout, 2007).

Tomatoes host at least 200 distinct species of pests and pathogens, luckily a wide range of resistances can be found in the wild relatives, which opens new avenues for breeders since most of these follow simple genetic inheritance (Bai and Lindhout, 2007).

Image via Grassroots Gardening

Where we come in:

Depending on the method of cultivation, tomatoes can have either a tap- or fibrous root system. Sexual propagation via seeds generally yields a tap root, while asexual reproduction via cuttings generally form a fibrous root system. Using seeds decreases the chances of pest or pathogen contamination from any nursery stock. Hydroponically seed-grown tomatoes will show an intermediate root morphology, as we will be starting our seeds in 35mm rockwool starter cubes that have been soaked in a nutrient solution with a pH of 4.5, before undergoing the subsequent steps to eventually fully integrate them into the hydroponic circuit.

Our Circuit:

After placing the seeds into the starter cubes they will be moved to a heated propagator, keeping them sufficiently moist and at a constant temperature, in darkness, until germination has taken place. After about 3-8 days the first cotyledons will appear, after which the seedling should be placed underneath grow lights with a general 18/6 light cycle (18 hours of light, 6 hours of darkness). Following approximately 3 weeks under the grow lights the seedlings should be ready for their first transplant into 75mm rockwool cubes, which have a handy pre-cut hole in the centre for easy direct transplant of the starter cubes.

The 75mm cubes will be soaked in a nutrient solution before insertion of the starter cubes containing the by-now eager seedlings. These will continue to grow under artificial lights until they reach a certain size before moving to the next step in the hydroponic circuit. Upon reaching the desired size, the plants are ready for transplantation into the rockwool slabs residing in troughs in the hydroponic circuit. Nutrients will be fed through restriction drippers directly into the Rockwool growing medium, any rundown will be caught within the nutrient reservoir tank that will recirculate the unused nutrients throughout the circuit.

Image via Hydroponics for Beginners

 A Drip/Trickle Irrigation system will be used for the ease of nutrient and water delivery regulation via active pumping, this not only improves water efficiency, but also offers complete control over nutrient delivery intervals. This variation of micro irrigation is the preferential method for commercial propagation.

A network of restriction drippers will run from plant to plant, with at least one drip emitter per plant. This is ideal for precision and accuracy purposes, since each emitter can be configured to the exact needs of each individual plant, or various plants grown in the same circuit or area. Rockwool is a slow draining medium that requires time to breathe between nutrient flushes, which can be easily regulated with a pump-incorporated drip system, designating specific (and precise) dripping cycles for each phase of growth, allowing for a high degree of automation.

The nutrient solution gets pumped from the reservoir through a network of tubes, before being secreted from the drip emitters, where it saturates the growing medium (coating the roots) before eventually soaking all the way through and dripping into the catch tray, flowing back into the reservoir, ready for another cycle. Tomatoes also prefer a general pH of 6.0-6.8 for optimum growth, so this will be closely monitored by sensors integrated into the circuit.



Image via Aquaponics Made Easy 101

As the tomatoes grow taller, they will be supported by what is known as a String-Tomahook system, vertically integrated and evenly spaced out plant support strings attached to hooks running along a horizontal tension wire. This provides support against gravity as the weight of the plant, and most importantly the yield, increases.

Image via Hydro-Industries


Image via Backyard Gardening Fun

Image via Chef, Bike, Ski


Watch this video about another hydroponic tomato nursery for more information: 
 


- Leo.
18199658



Citations: 
  • Bai Y, Lindhout P. Domestication and Breeding of Tomatoes: What have We Gained and What Can We Gain in the Future? Annals of Botany. 2007;100(5):1085-1094. doi:10.1093/aob/mcm150.
  • Frary A, Doganlar S. Comparative genetics of crop plant domestication and evolution. Turkish Journal of Agricultural Forestry. 2003;27:59–69.
  • Larry R, Joanne L. Genetic resources of tomato. In: Razdan MK, Mattoo AK, editors. Genetic improvement of solanaceous crops. Vol. 2. Enfield, NH: Science Publishers; 2007. Tomato.
  • Razdan MK, Mattoo MK. (2006) Genetic Improvement of Solanaceous Crops, Volume 2: Tomato. Florida: Taylor & Francis Group, LLC.
  • Rick CM, Chetelat RT. Utilization of related wild species for tomato improvement. Acta Horticulturae. 1995;412:21–38.
  • Sims WL. History of tomato production for industry around the world. Acta Horticulturae. 1980;100:25–26.
  • Walter JM. Heredity resistance to disease in tomato. Annual Reviewers. 1967;5:131–160.

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