Asian Research Thesis Index

Abstract

Use of genomic technology for engineering crops to combat various stresses has been witnessed in early 1980s. For example, “Bt”, coined with genes (Cry1Ac, Cry2Ab, etc.)— provide protection to lepidopteron insect pests, excised from a soil bacterium, were introduced in multiple crops including corn, cotton, soybean, rice, potato and canola. In Pakistan, work on introduction of Cry1Ac gene from a source cotton material (containing Cry1Ac gene) to local cotton cultivars through backcrossing breeding scheme has been started at the start of this 21st century, resulted in the development of more than 20 Btcotton varieties. Since the gene was new to our environment, was the compelling factor for studying various aspects including yield performance, expression of Bt gene under various environmental conditions and its impact on NTOs. In the present study, we tested the efficacy and the impact of Bt-cotton in Pakistani environment, which paved the way for approval of Bt-cotton varieties. Performance of 20 Bt-cotton genotypes (called as IR-cotton genotypes in the dissertation) along with 5 non-Bt conventional counterparts were evaluated in 10 different locations all over the Pakistan, of which most commonly, IR-cotton out yielded their non-IR cotton genotypes. On average, IR-cotton genotypes-cultivars produced almost 24.8% more seed cotton yield (SCY) than their non-IR counterparts for four years (2005-08) at all experimental sites and the yield advantage ranged from 21 to 30%. Likewise, mean values for the number of boll plant-1 were also found substantially higher (19-25%) in IR-cotton than that of non-IR conventional cultivars at 10 different locations. Furthermore, average boll weight was also significantly higher in IR-cotton (8.81%) than the conventional cultivars, which is primarily because of the selections made for high boll weight in developing IR-cotton. However, this advantage was not as higher as observed in case of SCY and number of bolls plant-1. IR-NIBGE-3701 was identified as the most adapted genotype, and recommended for cultivation. The present study was also aimed to examine the impact of drought on the expression of Cry1Ac gene in a set of 25 cotton genotypes-cultivars including five conventional counterparts. This study was conducted during the three normal cotton growing seasons (2005-2007). These genotypes-cultivars were grown under well-watered and water-limited conditions in NIBGE cotton field. Seed cotton yield and its components were markedly affected under the water-limited regime. Mean reduction in SCY due to water deficit was 19, 22 and 27% in 2005, 2006 and 2007, respectively. Moreover, genotypes-cultivars were also substantially differed for SCY ranging from 12.65 to 35% during the three consecutive years under stress conditions. Seed cotton yield was sustainability affected under waterlimited regime mainly due to fluctuation in number of bolls plant-1 rather than average boll weight. Similarly, the water stress significantly depressed the expression of Bt gene, i.e. ranging from 19 to 32% as cumulative for three years (2005-2007). Remarkably, no change was observed towards the efficacy of transgene against the Helicoverpa armigera. Another important abiotic factor is the problem of elevated temperature during the cotton growing season in Pakistan, and it significantly depresses the cotton production. Thus we tested the expression of Cry1Ac gene under normal and high temperature regimes for three years. In total 20 IR-cotton genotypes were exposed to high temperature (37±2oC) under glasshouse conditions, and the Bt expression level along with the efficacy was measured at 35, 60, 90 and 120 DAS. Our results revealed that after exposing cotton plants to high temperature, expression of Cry protein was decreased from 3.28-41.65% at different time intervals without effecting the biological activity (efficacy toward controlling the Helicoverpa armigera). However, the response of Cry protein expression under high temperature was significant among the genotypes-cultivars studied at different growth stages. Genotypic variation regarding the expression levels of Cry1Ac in normal as well as CLCuD infected cotton plants were found in the studies conducted for three years (2006-2008). The disease significantly reduced the expression of Cry1Ac, fluctuating between 26% (IRNIBGE- 3701 and IR-NIBGE-2422) to 64% (IR-NIBGE-2457) with a mean reduction of 47% between the IR and non-IR-cotton genotypes-cultivars. Though we have found significant reduction in expression of Cry 1Ac gene between the asymptomatic and symptomatic cotton plants but we could not establish any correlation between the disease incidence percentage and relative reduction in expression of Cry1Ac gene. The potential impact of IR-cotton on non-target organisms (NTOs) have also been studied independently for three and four consecutive years for soil microorganisms and non-target insects (jassids, thrips and whitefly), respectively. Statistically insignificant results were found for soil microorganisms (bacteria including actinomycetes and fungi) collected from IR or non-IR cotton. However, significant variations were observed for plant growth stages (30, 60, 90, 120 and 150 DAS) for microbial population. Similarly potential impact on NTOs (Jassid, whitefly and thrips) was demonstrated significance among the genotypescultivars, but non significant differences were observed for the Bt trait in four years of experimentation. Findings of the present studies paved the way for the approval of Bt-cotton varieties in Pakistan. Cotton cultivars IR-NIBGE-3701, IR-NIBGE-1524 and IR-NIBGE-901 identified from these experiments helped in sustaining cotton production in Pakistan. All these efforts have been admired by the Govt of Pakistan (bestowed Pride of Performance by the President of Pakistan on August 14, 2011) and International Cotton Community. These findings suggest that the introduction of Bt-cotton in the farming system of Pakistan is the best alternative to conventional non-Bt cotton which be useful in increasing the cotton production in Pakistan. The less capital intensive nature of this system may be particularly interesting for resource poor cotton farming communities and also to the ecologists. It is extremely important to enhance protection against the bollworm complex by introducing new genes in cotton as the single gene based protection can be broken down at any time. These efforts together would be another step in the door towards sustaining cotton production in the country till 2020.

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