Evolution of resistance by insect pests can reduce the benefits of insecticidal proteins from Bacillus thuringiensis (Bt) that are used extensively in sprays and transgenic crops. Despite considerable knowledge of the genes conferring insect resistance to Bt toxins in laboratory-selected strains and in field populations exposed to Bt sprays, understanding of the genetic basis of field-evolved resistance to Bt crops remains limited. In particular, previous work has not identified the genes conferring resistance in any cases where field-evolved resistance has reduced the efficacy of a Bt crop. Here we report that mutations in a gene encoding a cadherin protein that binds Bt toxin Cry1Ac are associated with field-evolved resistance of pink bollworm (Pectinophora gossypiella) in India to Cry1Ac produced by transgenic cotton. We conducted laboratory bioassays that confirmed previously reported resistance to Cry1Ac in pink bollworm from the state of Gujarat, where Bt cotton producing Cry1Ac has been grown extensively. Analysis of DNA from 436 pink bollworm from seven populations in India detected none of the four cadherin resistance alleles previously reported to be linked with resistance to Cry1Ac in laboratory-selected strains of pink bollworm from Arizona. However, DNA sequencing of pink bollworm derived from resistant and susceptible field populations in India revealed eight novel, severely disrupted cadherin alleles associated with resistance to Cry1Ac. For these eight alleles, analysis of complementary DNA (cDNA) revealed a total of 19 transcript isoforms, each containing a premature stop codon, a deletion of at least 99 base pairs, or both. Seven of the eight disrupted alleles each produced two or more different transcript isoforms, which implicates alternative splicing of messenger RNA (mRNA). This represents the first example of alternative splicing associated with field-evolved resistance that reduced the efficacy of a Bt crop.

Savanna regions of Nigeria are deficient in nitrogen and phosphorus, which retard the growth and yield of crops. Therefore, a study was conducted in the wet season of 2006 at the Dry Land Teaching and Research Farm of Usmanu Danfodiyo University, Sokoto to evaluate the effect of phosphorus on the growth and yield of two cowpea varieties sourced from Republic of Niger. Treatment consisted of four (4) rates of phosphorus (0, 20, 40, 60 kg.ha^–1) factorialy combined with (2) varieties of cowpea (kvx303096G and TN5-78) and laid out in a randomized complete block design (RCBD) replicated three (3) times. Results showed significant response to applied P on pods per plant, grain and stover yield and 100-seed weight with highest response to the application of 60 kg.P.ha^–1. From this study it can be concluded that KVX303096G and TN5-78 could both be sown under Sokoto condition to obtain reasonable yield of about 1 t.ha^–1 of grain and 1.6 t.ha^–1 of stover. Irrespective of the varieties, application of 60 kg P₂O₅ ha^–1 could be recommended for higher yield of cowpea (1.4 t.ha^–1) relative to 0 kg.P.ha^–1 that yielded 1.0 t.ha^–1

Terrestrial field studies were conducted with endosulfan during the 1989–90 Kharif season in bare cotton soil, to investigate the fate of endosulfan and its downward movement under sub‐tropical conditions of northern India. Field experiments consisted of spray application of endosulfan at 875 g ha‐1 42 and 63 days after the assumed date of sowing in two separate treatments. Soil samples drawn periodically from different depths were analysed by GC‐ECD (Ni63) for endosulfan and its breakdown products. Dissipation of the total endosulfan residues occurred to an extent of 92–97% in the first four‐week period and by about 99% in 238 days in two distinct phases in first‐order kinetics. Residue half life (T1/2) varied from 39 to 42 days. The parent compound metabolized to endosulfan‐diol and endosulfan sulfate. Endosulfan‐diol remained confined in the upper 5‐cm layer and dissipated completely in 28 days whereas endosulfan sulfate was first detectable seven days after treatment and persisted until the end of the experiment, remaining confined in the upper 0–10 cm soil layer. The β‐isomer also did not leach down beyond 10 cm depth. © 1997 SCI.

No abstract