Developing container protocol for screening sugarcane (Sacchurum officinarum L) varieties for tolerance to water-deficit stress
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Date
2021
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University of Zululand
Abstract
In Zimbabwe, sugarcane (Sacchurum officinarum L) is an important crop grown for sucrose, ethanol and other by-products such as molasses, bagasse and filter cake. Drought due to climate change is projected to negatively reduce the production of sugarcane. The effects of water-deficit stress due to climate change can be mitigated by growing water-deficit stress tolerant sugarcane varieties. There is limited information on drought tolerant genotypes among the 14 released sugarcane varieties in the Zimbabwe Sugarcane Industry. Screening of these varieties can be effectively done in containers as it is rapid and economic. It has been noted that plants grown in containers under natural environmental conditions show symptoms of stress. Consequently, it was prudent to first develop a protocol that minimises the stress inherently associated with growing plants in a container. Sources of stress for container-grown sugarcane plants include the rate and frequency of applying irrigation water, growth medium, fertiliser rates and size of the container used. After obtaining the protocol that minimised stresses associated with these sources, the varieties were screened on their tolerance to water-deficit stress.
Five experiments were done at the Zimbabwe Sugar Association Experiment Station (ZSAES) located in Chiredzi. The first experiment tested seven rates of applying irrigation water for sugarcane plants grown in container (35 cm top diameter, 23 cm bottom diameter and 27.5 cm height). The water application rates tested were 0.25, 0.5, 1.0, 1.5, 2.0, 2.5 and 3.0 litres per container per day. The growth media used in this experiment were pine bark (6-8mm) + vermiculite (1:1 v/v) and ZSAES soil medium comprised of a mixture of top soil: composted cattle manure: sand (5:2:2 v/v). The study showed that water application rates greater than 2.5 L per container per day increased stem height, number of tillers anddry matter of sugarcane plants in the ZSAES soil medium over pine bark + vermiculite. However, reduced germination of cane setts and root dry matter was observed in plants grown in the ZSAES soil medium.
The second experiment assessed the suitability of four media for growing sugarcane plants in containers. The media tested were filter cake only, filter cake + pine bark, pig manure + pine bark, and the ZSAES soil medium. Growing plants in pig manure + pine bark produced more
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tillers, shoot and root dry mass, green leaf area and number of leaves and leaf nutrient adequacy than the other media tested although stem height was suppressed.
The third experiment assessed the suitability of five blend fertiliser rates for growing sugarcane plants in containers. The rates tested were 312.5mg/l, 937.5mg/l, 1562.5mg/l, and 2187.5mg/l of Triple 16 blend fertilizer (16% N, 16% P2O5 and 16% K2O) and Hoagland nutrient solution per container (control). The study revealed that the application of 937.5mg/l Triple 16 blend fertiliser fortnightly until 56 days after planting (DAP) resulted in more tillering but, also reduced stem height in all the four media tested. This was deemed adequate nutrition for sugarcane plants.
The fourth experiment tested the interactions of pot sizes and three growth media for suitability for growing sugarcane plants in containers. The three sizes of containers tested in the experiment were respectively small (25.5 cm deep x 31.3 cm diameter), medium (45 cm deep x 54 cm diameter) and large (90 cm deep x 54 cm diameter). The three media used were filter cake, filter cake+ pine bark and the ZSAES soil medium. Filter cake + pine bark in large containers produced sugarcane plants with thicker and taller stems and heavier total plant dry matter than the other treatments.
The fifth experiment tested all 14 commercial sugarcane varieties in Zimbabwe for their tolerance to water-deficit stress by growing the varieties in two levels of irrigation viz well-watered (100%) and water stress (30% of daily water volume applications). The varieties tested were ZN1, ZN2, ZN3, ZN4, ZN5, ZN6, ZN7, ZN8, ZN9, ZN10, CP72-1312, NCo376, N14 and CP 72-2086. All things considered, sugarcane varieties that can be grown by cane famers when faced with drought instigated by climate change are NCo376, ZN1, ZN8, ZN10 and N14.
Description
A thesis submitted the Department of Science, Agriculture and Engineering in fulfilment of the requirement for the degree of Doctor of Philosophy in the Faculty of Science, Agriculture and Engineering at the University of Zululand,2021.
Keywords
Sugarcane, Water application rate, Blend fertiliser, water-deficit stress