Bt Cotton issues, remedies related to Irrigation

Bt Cotton (Gossypium hirsutum) belongs to malvaceae family. Important cash crop (White gold, Queen of fiber). Source of clothes, feed and edible oil in more than 80 countries.

Production 11.581m bales in 2017-18 in Pakistan. 4^th in production, 3^rd in export and 4^th in consumption in world

Bt Cotton

Botanical name is Bacillus thuringiensis. Strains of the bacterium Bacillus thuringiensis produce different Bt toxins. Bt toxins are insecticidal to the larvae of moths and butterflies, beetles, cotton bollworms. But are harmless to other forms of life. Bt cotton is ineffective against many cotton pests such as plant bugs, stink bugs, and aphids.

Status of Bt cotton in Pakistan

It Commercialized in 2010 in Pakistan. Now more than 70% area. 47 Bt cotton varieties until 2016 (Govt. and Private sector).  33% farmers growing non-Bt in believing Bt cotton. 7% growing Bt cotton in believing non-Bt.

Benefits

• Decrease the use of pesticides.
• Insects of Lepidoptera are sensitive to crystalline endotoxic protein.
• Farmers spend 3 billion dollar annually to control insect pests.
• BT cotton halves the grower’s costs to Rs1500/acre.
• Decrease overall cost of production.
• 30% increase in cotton production was observed.

Issues

• High cost of Bt cotton seeds as compared to non Bt cotton seeds.
• Effectiveness up to 120 days.
• Toxin producing efficiency of the Bt gene drastically reduces.
• Declining concentration of Bt toxin with the passage of plant growth.
• Non effective for sucking insect pests (White fly, Aphid and Jassid).
• Bt expression is affected by high temperature, drought and salinity.

Reasons

• Cotton plant is delicate and sensitive to changing climate altering the sowing patterns and flowering sequences.
• Change in weather conditions has also enhanced the attack of sucking insects in cotton crop.
• Unpredicted weather promoted resistance in harmful insects even against resilient Bt varieties.
• Pink bollworm is also a major factor behind the poor performance of cotton.
• Current situation is demanding the introduction of new resistant cotton germplasm.
• There are many other factors which can contribute to regaining good cotton production.
• Among these, timely sowing, availability of good quality seed, control of insects and diseases.
• Balanced use of fertilizers and timely application of irrigation are the most important.
• Cotton has moderate irrigation requirements. Excessive rainfall or irrigation is harmful for cotton at any stage.

Effects on cotton production

Insect’s resistance against Bt cotton is one of major cause of declining cotton production in Pakistan (Mostly bollworms). The lowest cotton production in 2015-16 was due to outbreak of Pink bollworm. Yield loss by bollworms is 30-40%

Reasons

• Water use efficiency in cotton defined as measure of total yield (lint) produced per unit of water supplied.
• Excess of water, negative impact on cotton plants and leads to yield loss.
• Water logging in cotton is estimated to cause annual yield losses of approximately 1 bale/ha or 11%.
• Water logging occurs mainly when heavy rain follows a scheduled irrigation.
• Especially when combined with poorly draining soils and inadequate field slope.
• Research in the early 1980’s showed that a 32 hour waterlogging treatment of cotton could lead to yield losses of 42%
• Water logging damages plants due to low oxygen concentrations (hypoxia) around the roots.
• Because water displaces the oxygen in the soil, and cannot be replaced by diffusion of atmospheric oxygen.
• The low oxygen conditions inhibit energy production in the plant roots and other oxygen-dependent pathways.
• The visual symptoms of water logging are initially wilting.
• Leaf chlorosis and reduced boll number, leading to lint yield loss.
• Damage to crop yields occurred once leaf yellowing is observed.
• Impact of water logging early in crop growth has a far greater influence on yield than water logging at mid-flowering or later.
• Yield loss due to water logging can be sustained at all stages of crop growth.
• Uptake of potassium, phosphorus is impaired in waterlogged cotton.
• First 3-4 days of water logging most of the yield loss is due to less nitrogen being absorbed from the soil.

Remedies

• Bt varieties of cotton sustain for a longer time in the field and give greater yield.
• Accordingly balanced use of fertilizers not only maintains soil fertility but also assures good yield.
• 1^st irrigation of cotton sown by drill should be applied after 30 to 35 days.
• Cotton requires 18 to 20 acre-inches water collectively which can be fulfilled by 5 to 6 times irrigating the crop in case of drill sowing.
• With the improvement of cotton crop production, the agriculture sector will contribute to the country’s economy.
• This can be achieved with the mutual cooperation of the agriculture department and farmer community
• Through adopting improved agronomic practices, wise use of agricultural inputs and shifting to advanced technology.

References

• Akhtar, Z. R., M. Majid, U. Irshad, Z. Saeed, J. Khalid, H. Khan, A. A. Anjum, A. Noreen and Easha. 2018. Resistance development of lepidopteran pests against insecticides in Pakistan: A case study of pink boll worm against different insecticides. J. Ent. Zoo. 6(2): 97-101.
• de Oliveira, R. S., B. Osmundo, N. Oliveira, F. N. Hudson, L. Moura, L. Leonardo, P. de Macedo, B. Fabricio, M. Arraes, A. Wagner, I. Lucena, T. Lourenço, A. Aulus, C. Maria and F. Maria. 2017. Transgenic Cotton Plants Expressing Cry1Ia12 Toxin Confer Resistance to Fall Armyworm (Spodoptera frugiperda) and Cotton Boll Weevil (Anthonomus grandis). J. Front. Plant Sci. 7(165): 2321-2332.
• Wan, P., D. Xu, S. Cong, Y. Jiang, Y. Huang, J. Wang, H. Wu, L. Wang, K. Wu, Y. Carrieri, A. Mathias, X. Li and B. E. Tabashnik. 2017. Hybridizing transgenic Bt cotton with non-Bt cotton counters resistance in pink bollworm. J. PNAS. 114(21): 5413–5418.

Authors: Muhammad Umer Hameed and Muhammad Sajjad

University of Agriculture, Faisalabad