Introgressing cry1Ac for Pod Borer Resistance in Chickpea Through Marker-Assisted Backcross Breeding

The gram pod borer Helicoverpa armigera is a major constraint to chickpea (Cicer arietinum L.) production worldwide, reducing crop yield by up to 90%. The constraint is difficult to overcome as chickpea germplasm including wild species either lacks pod borer resistance or if possessing resistance is cross-incompatible. This study describes conversion of elite but pod borer-susceptible commercial chickpea cultivars into resistant cultivars through introgression of cry1Ac using marker-assisted backcross breeding. The chickpea cultivars (PBG7 and L552) were crossed with pod borer-resistant transgenic lines (BS 100B and BS 100E) carrying cry1Ac that led to the development of BC₁F₁, BC₁F₂, BC₁F₃, BC₂F₁, BC₂F₂, and BC₂F₃ populations from three cross combinations. The foreground selection revealed that 35.38% BC₁F₁ and 8.4% BC₁F₂ plants obtained from Cross A (PBG7 × BS 100B), 50% BC₁F₁ and 76.5% BC₁F₂ plants from Cross B (L552 × BS 100E), and 12.05% BC₂F₂ and 82.81% (average) BC₂F₃ plants derived from Cross C (PBG7 × BS 100E) carried the cry1Ac gene. The bioassay of backcross populations for toxicity to H. armigera displayed up to 100% larval mortality. BC₁F₁ and BC₁F₂ populations derived from Cross B and BC₂F₃ population from Cross C segregated in the Mendelian ratio for cry1Ac confirmed inheritance of a single copy of transgene, whereas BC₁F₁ and BC₁F₂ populations obtained from Cross A and BC₂F₂ population from Cross C exhibited distorted segregation ratios. BC₁F₁ plants of Cross A and Cross B accumulated Cry1Ac protein ranging from 11.03 to 11.71 µgg^-1 in leaf tissue. Cry1Ac-positive BC₂F₂ plants from Cross C demonstrated high recurrent parent genome recovery (91.3%) through background selection using SSR markers and phenome recovery of 90.94%, amongst these 30% plants, were homozygous for transgene. The performance of BC₂F₃ progenies derived from homozygous plants was similar to that of the recurrent parent for main agronomic traits, such as number of pods and seed yield per plant. These progenies are a valuable source for H. armigera resistance in chickpea breeding programs.