Kampala — Digital camera images can be used to detect stresses hindering the growth of tall crops such as banana, scientists have discovered.
According to a study published in PLoS One last month (28 December), using digital photography to measure leaf cover could provide a rapid method of assessing the impact that adverse weather such as drought or parasites have on such crops.
Digital images of tall crops' canopies have been used to detect yield-cutting parasitic stress
The technique enables the health of such crops to be rapidly assessed
But restrictions on planting patterns and the systems' expense are likely to limit its use in Africa
In the field trial, conducted in Uganda, a digital camera fitted with a semicircular lens was used to measure the area of canopy leaves for two crops whose roots are vulnerable to nematodes - a plantain, Gonja manjaya, and an East African Highland banana called Mbwazirume - and a banana, Km5, that is resistant to the parasite.
Nematodes - microscopic parasitic worms - were added to the soil around half the crops prior to field planting. After 106 days, photos of the canopy were taken from the ground and used to generate a leaf area index (LAI). This process was repeated fortnightly for two cropping cycles.
The plantain and Mbwazirume that were infected with nematodes had lower LAI values than those that were not, according to the study, and these were linked to the biotic stress caused by the parasite by assessing the number of nematodes in the roots and the necrosis they caused.
Yield losses in the infected plants, including a component due to toppling, was more than half for the plantain and Mbwazirume at the second harvest, the study found.
According to Elvis Mbiru, one of the authors and a researcher at the International Institute of Tropical Agriculture in Uganda,the study shows that LAI correlates with leaf and root development and yields.
"We assume that if the roots are damaged and the leaves are healthy, the yields may be unstable, but this technology helps us understand this better," he says.
The technology could make it easier for scientists to assess the health of tall crops, as camera images can be rapidly turned into LAI estimates using computer software. For example, the traditional method of assessing nematode damage involves uprooting the crop, getting the roots and analysing the parasites, which is destructive to the crop
"The technology is not about control, it eases assessment of damage," Mbiru says.
But Andrew Kiggundu, head of banana biotechnology research at the Uganda's National Agricultural Research Laboratories Institute (NARL) in Kawanda, says it would be difficult to use the camera technology on farms because planting has to be done in a precise way including proper spacing, straight rows and with canopy cover to allow LAI to be accurately measured.
"It therefore remains a research tool, but it can be used to generate data much faster," he says.
Mbiru agreed, saying the method is currently only of use for research stations because it would be too expensive for farmers.