Drought may gradually suck out life from any life form denied of moisture, but not some plants’ ability to fight for it.
Built-in mechanism to fight for life in times of drought has enabled some genotypes of cassava to survive. This is what researchers from the Philippines Root Crop Research and Training Center (PRCRTC), and Nagoya University Graduate School of Bioagricultural Sciences of Nagoya, Japan found.
Water shortage due to long absence of rain marginalizes some planting areas. Although cassava is known to tolerate drought, it nevertheless exhibits sensitivity to lack of water in its first three months, otherwise known as the ‘establishment period’.
Stunted growth of roots and shoots of moisture-starved cassava results to low yield during normal maturity time.
The researchers cited in their study that stabilizing the productivity of cassava would entail understanding its basic ability to withstand adverse conditions like drought. This ability, they said, is important since different cassava genotypes have different ways to deal with drought. The researchers identified five genotypes of cassava as test materials. These genotypes were: PSB Cv-19, PSB Cv-11, VC-4, Golden Yellow, and Rayong 5. Sixty-four samples for each genotype were planted within 100 cm of one another, half of which were subjected to drought condition. During the experiment, leaf water potential, stomatal resistance, and transpiration rate were measured. After 8.5 months, the root crop was harvested.
Drought and Plant Physiology
Across genotypes, the highest transpiration rate was during the third month of growth both for the plants subjected to drought and those under rainfed conditions. The researchers interpreted this as an adaptive plant mechanism to maintain adequate water level to avoid leaf dehydration.
Stomatal resistance also increased during the stages when soil moisture was scarce. Except for the genotype Golden Yellow, the midday leaf water potential of the samples decreased during the later period of drought condition.
Drought and Plant Morphology
All the genotypes’ leaf development was affected under the drought condition . The Golden Yellow genotype was least affected in the height parameter. It was observed that the storage roots of the plants under the drought condition were smaller and woody. This was explained in the study as a mechanism where root function shifts from storage of assimilates to serving as a main channel of water nutrients to the shoots as a response to water shortage.
Over-all observations showed decrease in total plant biomass, shoot biomass, root biomass, root-shoot ratio, total yield, harvest index, plant height, number of leaves, and total number of and lengths of adventitious leaves.
While stomatal resistance was increased by drought, leaf water potential and transpiration rate were reduced.
Genotypes Golden Yellow and Rayong 5 were found to be most tolerant to drought while Vc-4 was identified as susceptible. Genotypes that tolerate drought have longer and more adventitious roots as ways to adopt to water shortage.
For more information, contact:
Bureau of Agricultural Research
Department of Agriculture
3/F RDMIC Bldg., Visayas Ave.
cor. Elliptical Rd., Diliman Quezon City 1104
Trunklines: 928-8505 or 927-0226
Local Nos. 2043, 2042, 2044
E-mail: [email protected]
author: Maria Lizbeth Severa J. Barona of www.bar.gov.ph, photo from tt.bhpbilliton.com