STANDARDIZATION OF OPTIMUM ISOLATION DISTANCE FOR GENETIC PURITY MAINTENANCE IN PIGEONPEA (CAJANUS CAJAN L. MILLSP.) HYBRID SEED PRODUCTION

Abstract

Hybrid technology has opened a new route to breaking the yield plateau in Pigeonpea (Cajanus cajan (L.) Millsp.), but its commercial success depends on producing seed of high genetic purity, which is difficult in an often-cross-pollinated crop where insects carry pollen over considerable distances. Establishing an optimum isolation distance is therefore essential to limit pollen-mediated contamination and ensure genetic purity of hybrid seed. This study was undertaken to validate and optimize the isolation distance for hybrid Pigeonpea seed production under field conditions. Cytoplasmic male sterile (CMS) line served as the female parent, with its fertility restorer (R-line) as the pollen source. Field experiments were conducted during Kharif 2020-21 and 2021-22 at the Central Research Station, Dr. Panjabrao Deshmukh Krishi Vidyapeeth, Akola, Maharashtra, India. In 2020-21, the CMS line was planted at nine distances from the pollen source (200 to 600 m at 50 m intervals), and the observations were validated in 2021-22 at five distances (200 to 400 m). Seed set, seed yield per plant and test weight were recorded at different isolation distances. Flowering synchronization between parental lines the activity of insect pollinators at different times of the day were also monitored to assess their association with pollen-mediated seed set. Seed set from pollen-mediated outcrossing declined sharply with distance and was negligible beyond 350-400 m, while seed quality (test weight) remained unaffected. A 400 m isolation distance is effective for maintaining genetic purity in hybrid Pigeonpea seed production, providing a practical standard for breeders and commercial seed producers to minimize unwanted pollen contamination and ensure genetic purity.