Relationship Between Damage by Cotton Bollworm Helicoverpa armigera (Hübner) and Different Plant Characteristics of Bt and Non-Bt Cotton Varieties in Pakistan
Relationship Between Damage by Cotton Bollworm Helicoverpa armigera (Hübner) and Different Plant Characteristics of Bt and Non-Bt Cotton Varieties in Pakistan
Muhammad Fahad1, Muhammad Asam Riaz1, Muhammad Zeeshan Majeed1*, Saba Tabasum2, Saeed Rauf2, Saba Tahseen3, Abdul Munim Farooq4 and Idrees Ahmad Nasir4
ABSTRACT
Helicoverpa armigera (Hübner) is one of the notorious lepidopterous pests of cotton (Gossypium hirsutum L.). Transgenic cotton varieties expressing Bacillus thuringiensis (Bt) induced insecticidal toxin (Cry1Ac) have been a key tool combating infestations of H. armigera and other cotton bollworms. However, the development of resistance in H. armigera to Bt transgenic cotton varieties is of major concern. This study assessed the H. armigera resistance to Cry1Ac expressing cotton varieties and association of plant biochemical, physico-morphic and physiological traits with boll damage by H. armigera. ELISA results revealed significantly high toxin (Cry1Ac) contents in Bt varieties particularly in PB-38, CRS-456 and PB-896 at 30-day post-germination. Moreover, toxin level in leaves decreased after 30 days of germination in most varieties except CRS-456 and PB-896. Bt varieties PB-896, CRS-456, PB-38 and VH-57 had the highest yield with low to moderate bollworm damage and exhibited a high and stable leaf Cry1Ac toxin level. The net photosynthesis rate, stomatal conductance, CO2 emission and absorption were positively, while Bt toxin level, gossypol glands density and yield were negatively and significantly correlated with the boll damage by H. armigera. All Bt cotton varieties exhibited a differential level of Cry1Ac toxin and none of them was found bollworm free, suggesting that H. armigera is able to infest most of the Bt cotton varieties though the level of infestation varied from variety to variety. Overall study findings recommend the cultivation of three Bt (VH-57, CRS-456 and PB-38) and one non-Bt (L.A Fragobract) cotton varieties by indigenous cotton growers to diminish bollworm infestations.
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