This study investigates the impact of different levels of potash (K2O) application on the gene expression of Cry1Ac and Cry2Ab2 endotoxins in Bt cotton hybrid G. Cot. Hy. 8 BG II. A field experiment was conducted at the Main Cotton Research Station, Surat, with 12 treatments, including varying potash levels (0, 40, and 80 kg ha-1), the application of potash mobilizing bacteria (KMB), and foliar sprays of potassium nitrate (KNO3). Potash application significantly influenced the incidence of pink bollworm (PBW), reducing larval populations and flower damage in Bt cotton. Cry1Ac and Cry2Ab2 expression levels in different plant parts remained above critical thresholds for bollworm management, with higher expressions in treatments with potash application. The study indicates that potash supplementation can enhance bollworm resistance by stabilizing Bt gene expression in cotton hybrids.

cotton, potash, bollworm, Cry1Ac and Cry2Ac.

Cotton (Gossypium spp.) is a major economic crop with high demand in textile industries worldwide. Bt cotton hybrids expressing Cry1Ac and Cry2Ab2 have proven to be effective against lepidopteran pests, particularly bollworms. However, various environmental factors, including nutrient availability, influence the efficacy of gene expression. Potassium (K), essential for plant growth and fiber quality, has been shown to affect transgene expression and pest resistance in cotton. This study explores the effect of K2O application on Cry1Ac and Cry2Ab2 gene expression in Bt cotton hybrid G. Cot. Hy. 8 BG II and its impact on bollworm incidence. Cotton is cultivated in varied climate and soil type with mono-cropping approach in Gujarat state due to economic cash crop. As per the soil type, texture and structure, nutrient up-take by plant is differed in rain fed and irrigated cotton. Based on regional suitability balanced fertilizer use is recommended in cotton. Though, Gujarat soil is rich in K content (Bhambhaneeya et al., 2017), the availability may be increased through the use of such organic amendments, foliar applications or potash mobilizing bacteria with supplementation of the K in deficient soils. The balanced use of fertilizers does not affect much the gene expression but the lower dose of nitrogen reduced the expression of gene in Bt cotton. Further, cotton appears to be more sensitive to K deficiencies than other crops, as root system of cotton is less dense than that of other crops (Mithaiwala et al., 1981). It has been found that potash application enhanced protein synthesis resulting in reduced amino acid content of the plant sap, may stabilize expression of genes in transgenic crop and reduced the development and multiplication of insect pests especially of bollworms.

A split-plot field experiment was conducted using Bt cotton hybrid G. Cot. Hy. 8 BG II, with 12 treatments including three K2O application rates (0, 40, and 80 kg ha-1), two levels of KMB, and two foliar spray treatments of KNO3. The study was designed to measure bollworm incidence, larval populations, flower damage, and gene expression levels of Cry1Ac and Cry2Ab2 across different plant parts at various growth stages. The incidence of bollworms was monitored, and Cry1Ac and Cry2Ab2 gene expression in different plant tissues were quantified using ELISA.

Experimental Details:

Table 1: Incidence of pink bollworm larvae (big) on G. Cot. Hy. 8 BG II during 2018-19.

The application of K2O significantly reduced PBW damage, with the highest potash application (80 kg ha-1) showing the lowest flower and boll damage. Cry1Ac and Cry2Ab2 expression levels were well above critical thresholds in all treatments but showed increased levels in treatments with potash application. Potassium mobilizing bacteria and KNO3 sprays further enhanced gene expression, though differences between treatments were marginal. In the present study, the pink bollworm infestation and damage was found above ETL on G. Cot. Hy. 8 BG II as the technology of Bt cotton lost its effectiveness against pink bollworm. Similar results were aslo found in potash application populations of pink bollworm to Cry1Ac (Dhurua and Gujar 2011) and Cry2Ab2 (Fabrick et al., 2015; Malthankar and Gujar 2016; Gao et al., 2018) or both the genes (Fabrick et al., 2014).

Gene Expression: The expression of Cry1Ac and Cry2Ab2 in leaves, squares, and boll rinds was significantly higher in potash-treated plots, particularly at 80 kg/ha. Potash mobilizing bacteria did not have a significant impact on gene expression, while foliar sprays of KNO3 further reduced bollworm incidence.

- Seed Cotton Yield: The highest yield (2692.90 kg/ha) was recorded in plots treated with 80 kg/ha of potash, followed by the 40 kg/ha treatment. KMB application marginally improved yields, but the interaction between treatments was not significant. Bhambhaneeya et al. (2017) studied the soil available nutrient status and their indexing in cotton growing areas of south Gujarat and reported high status of K(>280 kg ha-1 ) both in irrigated and rain fed regions in selected samples.

The findings suggest that potash enhances the expression of Cry genes in Bt cotton, leading to reduced bollworm damage and improved yields. This aligns with previous studies showing the role of potassium in plant resistance and gene expression stability. While KMB application did not significantly impact bollworm incidence, foliar sprays of KNO3 were effective in reducing larval populations, especially of pink bollworm. Application of hormone and micro-nutrient did not affect the population bollworms (Abro et al., 2004). With respect to synthetic and organic source of nutrition, some workers did not find any marked effect on whitefly, jassid, thrips and spotted bollworms (Ahmed et al., 2003) whereas less infestation of all three bollworms and sucking pests was noticed in organic source of nutrition (Kedar et al., 2010).

Table 2: Open bolls and locule damage by pink bollworm at harvest.

Note: TV= Transformed mean (Arc sine) whereas, OV= Original Values,

NS= Non- Significant, GM= General Mean

Table 3: Effect of potash application on gene expression of square tissue in Bt cotton hybrid.

Note: OV= Original Values, NS= Non-Significant, GM= General Mean, P= Period

This study demonstrates that potash application can significantly influence the efficacy of Bt genes in controlling bollworm populations by enhancing Cry1Ac and Cry2Ab2 expression in Bt cotton. These findings suggest that optimal K2O application can improve Bt cotton's resistance to bollworm pests and should be considered in pest management strategies.

Karan H. Parmar, H.R. Desai, B.K. Rajkumar, N.D. Makwana  and R.D. Patel (2024). Effect of Potash Application on Gene Expression of Cry1Ac and Cry2Ab2 in Bt Cotton Hybrid. Biological Forum – An International Journal, 16(12): 56-60.