Abstract
Cassava (Manihot esculenta Crantz) is a staple food for millions of people in the tropics, providing high energy and nutritional value. Problems associated with cassava in the arid tropics are low yield, high cyanide concentration, and low mineral and vitamin A availability in leaves and roots. These factors hinder the utilization of cassava greatly and are highly influenced by the plant water status and potassium (K) availability in the growth environment. The productivity of cassava in such environments could be improved using irrigation strategies not based on full crop water requirements, such as deficit irrigation combined with K nutrition to ensure sustainable quantity and quality production. Additionally, employing systems that can allow non-destructive estimation of plant performance, such as the use of plant imaging techniques, could provide early information on plant performance, which would facilitate phenotyping, as well as assist in the mitigation of abiotic challenges in cassava production. This study investigated how irrigation water, K fertigation and their interactions affect the growth responses of biofortified cassava during the early growth phase. It was also investigated whether K fertigation could improve the nutritional and reduce the anti-nutritional qualities of biofortified cassava growing under typical conditions of water deficit. The ability to use red-green-blue (RGB) and multispectral sensors to detect the effects of water deficit and low K in cassava, and whether the crop quality changes due to low moisture and low K could be observed from the images, were also examined. Pot experiments were conducted at early developmental stages of cassava under controlled greenhouse conditions at the University of Helsinki. Young biofortified cassava plants were established using cuttings. The plants were subjected to three irrigation treatments (30%, 60%, 100% pot capacity) that were split into five K (0.01 mM, 1 mM, 4 mM, 16 mM, 32 mM) application rates beginning 30 days after planting (DAP) and ended at 90 DAP, when plants were harvested. Irrigation treatments and K application rates significantly affected leaf water potential, leaf osmotic potential, net photosynthesis, stomatal conductance, leaf temperature, leaf chlorophyll, water usage, plant leaf area, plant height, tuber number and whole-plant biomass. The interaction was also statistically significant for these properties. Irrigation treatments and K application rates also affected leaf turgor, but the interaction was not statistically significant. Irrigation at 30% together with 16 mM K lowered the leaf water potential by 69%, leaf osmotic potential by 41%, net photosynthesis by 35%, stomatal conductance by 41%, water usage by 50%, leaf area by 17%, and whole-plant dry mass by 41%, compared with fully irrigated plants. Lowering the K application rate below 16 mM reduced the values further. Most importantly, the growth was decreased least when irrigation was decreased to 60% together with 16 mM K, compared with optimal applications. The combined effect of irrigation treatments and K applications was statistically significant for starch, energy, minerals, total carotenoids, and cyanide, but the interaction was not statistically significant for dietary fibre and crude protein in the leaves and roots. In the leaves and roots, water deficit and lower K applications inhibited starch, carotenoids, crude protein, and fibre synthesis. Water deficit interrupted the uptake of minerals by the cassava roots from the soil and ultimately to the leaves. Improved uptake of calcium, phosphorous, magnesium, zinc, iron, sulphur, and chloride to the leaves was recorded with increased K application regardless of water deficit. K application also mitigated the effect of water deficit at 30% irrigation. Crude protein, carotenoids, and minerals were revealed to be more abundant in the leaves than in the roots, while the inverse was the case for starch content and iron. Cyanide was diminished in the leaves and roots of the cassava with increases in both irrigation and K application rates. Full irrigation (100%) with 16 mM K application produced the highest nutritional quality and the least cyanide concentration. Also, 16 mM K significantly improved the nutritional qualities and diminished the cyanide concentration irrespective of the irrigation treatment. High estimation accuracy (R2 = 0.90) for biomass, chlorophyll, and net photosynthesis were recorded. The estimated leaf area associated strongly (R = 0.98) with the measured leaf area. The estimated biomass also associated strongly with the measured biomass. Starch, energy, total carotenoids, and cyanide were estimated reasonably (R2 > 0.80) and showed strong correlations with the most of spectral indices. The estimation accuracy for all mineral elements was low, and weak relationships existed between the mineral elements and the spectral indices. The regression models identified normalized difference vegetation index, green area index, and simple ratio index as the best estimators of growth and key nutritional traits in cassava. Moreover, irrigation at 30% together with 0.01 mM K reduced all the index values but increased crop senescence index. Regardless of water deficit, increasing K application rate to 16 mM resulted in high values for all the spectral indices but low senescence index. In conclusion, adjusting K fertigation rates in combination with deficit irrigation may improve the growth and dietary quality of young cassava, and reduce cyanide concentration. Findings from this work can be utilized as a foundation to develop agronomic management practices involving K application for cassava growing in water-limited environments. The study also shows that RGB and multispectral sensors can be used to provide indirect measurements of growth and key nutritional traits in cassava, thus representing a tool that breeders may use to facilitate evaluation of cultivars, especially in the developing areas. Information from imaging data may also be used to facilitate corrective measures to avert stress, such as the decision to irrigate or apply fertilizers. Nonetheless, laboratory analysis of plant samples should support sensor estimates, especially under field conditions, when all possible factors affecting plant growth are difficult to forecast. Future studies could place emphasis on field conditions with multiple cassava cultivars and employ different imaging techniques.
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Claims 20
Claim · model-written summary
Irrigation, potassium and their interaction significantly affected water relations, photosynthesis and growth traits.
- Treatment
- Irrigation treatments and K application ratese0
- Outcome
- leaf water potential, leaf osmotic potential, net photosynthesise0
Not reportedTaxonComparatorDirection
Verbatim
e0“Irrigation treatments and K application rates significantly affected leaf water potential, leaf osmotic potential, net photosynthesis, stomatal conductance, leaf temperature, leaf chlorophyll, water usage, plant leaf area, plant height, tuber number and whole-plant biomass. The interaction was also statistically significant for these properties.”
Claim · model-written summary
Irrigation and potassium affected leaf turgor, without a significant interaction.
Not reportedTaxonComparatorDirection
Verbatim
e0“Irrigation treatments and K application rates also affected leaf turgor, but the interaction was not statistically significant.”
Claim · model-written summary
At 30% irrigation with 16 mM K, leaf water potential was 69% lower than under full irrigation.
- Treatment
- Irrigation at 30% together with 16 mM Ke0
- Outcome
- leaf water potentiale0
- Direction
- lowerede0
- Value
- 69%e0
- Comparator
- fully irrigated plantse0
Not reportedTaxon
Verbatim
e0“Irrigation at 30% together with 16 mM K lowered the leaf water potential by 69%, leaf osmotic potential by 41%, net photosynthesis by 35%, stomatal conductance by 41%, water usage by 50%, leaf area by 17%, and whole-plant dry mass by 41%, compared with fully irrigated plants.”
Claim · model-written summary
At 30% irrigation with 16 mM K, leaf osmotic potential was 41% lower than under full irrigation.
- Treatment
- Irrigation at 30% together with 16 mM Ke0
- Outcome
- leaf osmotic potentiale0
- Direction
- lowerede0
- Value
- 41%e0
- Comparator
- fully irrigated plantse0
Not reportedTaxon
Verbatim
e0“Irrigation at 30% together with 16 mM K lowered the leaf water potential by 69%, leaf osmotic potential by 41%, net photosynthesis by 35%, stomatal conductance by 41%, water usage by 50%, leaf area by 17%, and whole-plant dry mass by 41%, compared with fully irrigated plants.”
Claim · model-written summary
At 30% irrigation with 16 mM K, net photosynthesis was 35% lower than under full irrigation.
- Treatment
- Irrigation at 30% together with 16 mM Ke0
- Outcome
- net photosynthesise0
- Direction
- lowerede0
- Value
- 35%e0
- Comparator
- fully irrigated plantse0
Not reportedTaxon
Verbatim
e0“Irrigation at 30% together with 16 mM K lowered the leaf water potential by 69%, leaf osmotic potential by 41%, net photosynthesis by 35%, stomatal conductance by 41%, water usage by 50%, leaf area by 17%, and whole-plant dry mass by 41%, compared with fully irrigated plants.”
Claim · model-written summary
At 30% irrigation with 16 mM K, stomatal conductance was 41% lower than under full irrigation.
- Treatment
- Irrigation at 30% together with 16 mM Ke0
- Outcome
- stomatal conductancee0
- Direction
- lowerede0
- Value
- 41%e0
- Comparator
- fully irrigated plantse0
Not reportedTaxon
Verbatim
e0“Irrigation at 30% together with 16 mM K lowered the leaf water potential by 69%, leaf osmotic potential by 41%, net photosynthesis by 35%, stomatal conductance by 41%, water usage by 50%, leaf area by 17%, and whole-plant dry mass by 41%, compared with fully irrigated plants.”
Claim · model-written summary
At 30% irrigation with 16 mM K, water usage was 50% lower than under full irrigation.
- Treatment
- Irrigation at 30% together with 16 mM Ke0
- Outcome
- water usagee0
- Direction
- lowerede0
- Value
- 50%e0
- Comparator
- fully irrigated plantse0
Not reportedTaxon
Verbatim
e0“Irrigation at 30% together with 16 mM K lowered the leaf water potential by 69%, leaf osmotic potential by 41%, net photosynthesis by 35%, stomatal conductance by 41%, water usage by 50%, leaf area by 17%, and whole-plant dry mass by 41%, compared with fully irrigated plants.”
Claim · model-written summary
At 30% irrigation with 16 mM K, leaf area was 17% lower than under full irrigation.
- Treatment
- Irrigation at 30% together with 16 mM Ke0
- Outcome
- leaf areae0
- Direction
- lowerede0
- Value
- 17%e0
- Comparator
- fully irrigated plantse0
Not reportedTaxon
Verbatim
e0“Irrigation at 30% together with 16 mM K lowered the leaf water potential by 69%, leaf osmotic potential by 41%, net photosynthesis by 35%, stomatal conductance by 41%, water usage by 50%, leaf area by 17%, and whole-plant dry mass by 41%, compared with fully irrigated plants.”
Claim · model-written summary
At 30% irrigation with 16 mM K, whole-plant dry mass was 41% lower than under full irrigation.
- Treatment
- Irrigation at 30% together with 16 mM Ke0
- Outcome
- whole-plant dry masse0
- Direction
- lowerede0
- Value
- 41%e0
- Comparator
- fully irrigated plantse0
Not reportedTaxon
Verbatim
e0“Irrigation at 30% together with 16 mM K lowered the leaf water potential by 69%, leaf osmotic potential by 41%, net photosynthesis by 35%, stomatal conductance by 41%, water usage by 50%, leaf area by 17%, and whole-plant dry mass by 41%, compared with fully irrigated plants.”
Claim · model-written summary
Lower K rates further reduced the listed growth and physiological measures.
Not reportedTaxon
Verbatim
e0“Lowering the K application rate below 16 mM reduced the values further.”
Claim · model-written summary
Growth decreased least with 60% irrigation and 16 mM K relative to optimal applications.
- Treatment
- 60% together with 16 mM Ke0
- Outcome
- growthe0
- Direction
- decreased leaste0
- Comparator
- optimal applicationse0
Not reportedTaxon
Verbatim
e0“the growth was decreased least when irrigation was decreased to 60% together with 16 mM K, compared with optimal applications.”
Claim · model-written summary
The irrigation and K interaction significantly affected starch, energy, minerals, carotenoids and cyanide.
Not reportedTaxonComparatorDirection
Verbatim
e0“The combined effect of irrigation treatments and K applications was statistically significant for starch, energy, minerals, total carotenoids, and cyanide”
Claim · model-written summary
The irrigation and K interaction was not significant for fibre and crude protein.
- Outcome
- dietary fibre and crude proteine0
Not reportedTaxonTreatmentComparatorDirection
Verbatim
e0“the interaction was not statistically significant for dietary fibre and crude protein in the leaves and roots.”
Claim · model-written summary
Water deficit and low K inhibited starch, carotenoid and protein synthesis in leaves and roots.
- Organ / stage
- leaves and rootse0
- Treatment
- water deficit and lower K applicationse0
- Outcome
- starch, carotenoids, crude proteine0
- Direction
- inhibitede0
Not reportedTaxonComparator
Verbatim
e0“In the leaves and roots, water deficit and lower K applications inhibited starch, carotenoids, crude protein, and fibre synthesis.”
Claim · model-written summary
Water deficit interrupted mineral uptake from soil into roots and leaves.
- Taxon
- cassava
Manihot esculentae0 - Treatment
- Water deficite0
- Outcome
- uptake of mineralse0
- Direction
- interruptede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Water deficit interrupted the uptake of minerals by the cassava roots from the soil and ultimately to the leaves.”
Claim · model-written summary
Higher K improved uptake of calcium, phosphorus and magnesium into leaves despite water deficit.
- Organ / stage
- leavese0
- Treatment
- increased K applicatione0
- Outcome
- uptake of calcium, phosphorous, magnesiume0
- Direction
- Improvede0
Not reportedTaxonComparator
Verbatim
e0“Improved uptake of calcium, phosphorous, magnesium, zinc, iron, sulphur, and chloride to the leaves was recorded with increased K application regardless of water deficit.”
Claim · model-written summary
Increasing irrigation and K diminished cyanide in leaves and roots.
- Taxon
- cassavaManihot esculentae0
- Organ / stage
- leaves and rootse0
- Treatment
- increases in both irrigation and K application ratese0
- Outcome
- Cyanidee0
- Direction
- diminishede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Cyanide was diminished in the leaves and roots of the cassava with increases in both irrigation and K application rates.”
Claim · model-written summary
Full irrigation with 16 mM K gave the highest nutritional quality and least cyanide.
- Treatment
- Full irrigation (100%) with 16 mM K applicatione0
- Outcome
- nutritional quality and the least cyanide concentratione0
- Direction
- higheste0
Not reportedTaxonComparator
Verbatim
e0“Full irrigation (100%) with 16 mM K application produced the highest nutritional quality and the least cyanide concentration.”
Claim · model-written summary
Imaging estimated biomass, chlorophyll and photosynthesis with R2 of 0.90.
Not reportedTaxon
Verbatim
e0“High estimation accuracy (R2 = 0.90) for biomass, chlorophyll, and net photosynthesis were recorded.”
Claim · model-written summary
Mineral element estimation from spectral indices had low accuracy and weak relationships.
Not reportedTaxon
Verbatim
e0“The estimation accuracy for all mineral elements was low, and weak relationships existed between the mineral elements and the spectral indices.”
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Claims are grouped by organism, treatment and what was measured or targeted. A paper counts as positive when any of its claims in the group is positive.