Articles
PUSHING THE LIMITS IN PLASTIC TUNNELS IN THE TROPICS AND THE NEED FOR SHADE
Article number
618_48
Pages
407 – 414
Language
English
Abstract
Zimbabwe is found in the high-altitude tropics and enjoys many hours of full sunshine.
As a result, several world records have been recorded in field crop production.
However, in the greenhouse/tunnel ambience at 1500 meters above sea level, sunshine can quickly be too hot and sunny, demanding expensive ventilation.
Cassava, a tropical staple, when passed through a virus elimination cycle, can challenge any crop in the world for productivity and for conversion of sunlight and water into carbohydrate (starch). Sixty tons wet weight of tubers per hectare (20t/ha dry weight) is likely under irrigation.
However to transfer “disease-free” plantlets from in-flask to field (planted as rooted cuttings) requires multiplication and survival.
It is shown that plants multiplied in vitro grow well under normal (for tissue culture) or high light.
However, plants from high light in vitro (> 100µmol s-1 m-2 PPFD) survive acclimatisation ex vitro poorly in this very dry atmosphere.
In addition, it requires low light in the greenhouse (< 500µmol s-1 m-2 PPFD) for survival of acclimatised cassava to be >95%. In-flask multiplication is expensive even in Zimbabwe while rapid multiplication under plastic is here shown to be effective and economic.
However, there are special constraints associated with tunnel horticulture in the dry, high altitude tropics.
Temperatures can rise above 50°C each day.
While most field plants die, or shed all their leaves at these temperatures, we show that tender cassava, ex vitro plantlets that are acclimatised under plastic with shade, can survive.
Thus, tender plants can survive extreme temperature, both in-flask and under plastic, but in both they have an absolute requirement for lower than normal sunlight.
This leads to a simple way to implement many tissue culture cleaning and GMO-linked projects that do not currently function effectively due to low survival ex vitro in the sub-Saharan situation of Africa.
As a result, several world records have been recorded in field crop production.
However, in the greenhouse/tunnel ambience at 1500 meters above sea level, sunshine can quickly be too hot and sunny, demanding expensive ventilation.
Cassava, a tropical staple, when passed through a virus elimination cycle, can challenge any crop in the world for productivity and for conversion of sunlight and water into carbohydrate (starch). Sixty tons wet weight of tubers per hectare (20t/ha dry weight) is likely under irrigation.
However to transfer “disease-free” plantlets from in-flask to field (planted as rooted cuttings) requires multiplication and survival.
It is shown that plants multiplied in vitro grow well under normal (for tissue culture) or high light.
However, plants from high light in vitro (> 100µmol s-1 m-2 PPFD) survive acclimatisation ex vitro poorly in this very dry atmosphere.
In addition, it requires low light in the greenhouse (< 500µmol s-1 m-2 PPFD) for survival of acclimatised cassava to be >95%. In-flask multiplication is expensive even in Zimbabwe while rapid multiplication under plastic is here shown to be effective and economic.
However, there are special constraints associated with tunnel horticulture in the dry, high altitude tropics.
Temperatures can rise above 50°C each day.
While most field plants die, or shed all their leaves at these temperatures, we show that tender cassava, ex vitro plantlets that are acclimatised under plastic with shade, can survive.
Thus, tender plants can survive extreme temperature, both in-flask and under plastic, but in both they have an absolute requirement for lower than normal sunlight.
This leads to a simple way to implement many tissue culture cleaning and GMO-linked projects that do not currently function effectively due to low survival ex vitro in the sub-Saharan situation of Africa.
Authors
A.I. Robertson, M.A.B. Jorge
Keywords
Acclimatization, Cassava, Temperature, Tissue Culture, Photosynthetic Photon Flux Density
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