TRENDS IN REGIONAL AND CHRONOLOGICAL DIVERSITY OF MAIZE (ZEA MAYS L.) GERMPLASM IN PAKISTAN

Maize germplasm was exclusively collected across Pakistan to probe the trends in genetic variability at regional levels and chronological periods. A total of 290 accessions were collected from 6 different regions. These were comprised of the following chronological order: 1980-1984, 1985-1990, 1991-2000, 2001-2007 and 2008-2016. These accessions represents maize growing provinces of Pakistan except Sindh. The performance of these entries were compared in the field and the data for different agronomic and yield related traits were subjected to statistical analysis. Mean comparison showed that Punjab region has highest mean grain yield followed by Azad Jammu & Kashmir (AJK). Regional differences in genetic diversity of maize germplasm were evident; AJK and Punjab possessed comparatively high genetic differences for various traits. Differences in the genetic variability across the region showed that various variability changing forces worked differently in different regions. Chronological studies showed that grain yield had been improving in Pakistan since 1980s. Highest grain yield was observed during the recent period (2008-2016) compared to earlier periods. Genetic diversity among available maize germplasm did not continuously reduce during the last 36 years based on the findings of this study. In the earlier years diversity showed increasing trend followed by declining trend. Highest genetic diversity was observed in the genotypes collected during 1980-1984 whereas, again there was boost in diversity during 1991-2000. It has been observed that addition of newly developed and better performing genotypes into informal seed system initially increased the diversity followed by substitution of traditional accessions which led to change in genetic variation in Pakistan. The gradual change in patterns of genetic variability in maize at regional and chronological levels in Pakistan emphasizes the importance of conserving genetic resources to avoid genetic vulnerability and depletion.