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Abstract
ICRISAT’s pearl millet (Pennisetum glaucum (L.) R. Br.) breeding program at Patancheru, India, has developed genetically diverse hybrid parents since 1980s. The present study investigated genetic diversity pattern between two groups of parents in this program, bred till 2004 and developed during 2004-2010. Combined analysis of 379 hybrid parents (current 166 parents and 213 previously developed hybrid parents) carried out using a set of highly polymorphic 28 SSRs detected 12.7 alleles per locus. An average of 8.5 and 8.7 SSR alleles per locus were found in previously developed and current parents, respectively, indicating marginal improvement in the levels of genetic diversity of hybrid parents in this program. Distance matrix differentiated these current and previously developed hybrid parents into 2 separate clusters, indicating infusion of new genetic variability over time as reflected by development of more genotype-specific alleles. Also, the seed and restorer parents were found clearly separated from each other in both the sets with few crossovers, indicating existence of two diverse and broad-based pools in hybrid parents of pearl millet. Restorer parents (R-lines) were found more diverse than seed parents (B-lines), as higher average gene diversity was detected among R-lines (0.70) than B-lines (0.56), though variation between B- and R-lines was found reduced in newly developed lines to 9.22% from 16.98% in previously developed lines. Results suggested that newly developed lines were as much divergent when compared with previously developed lines, indicating that current ICRISAT pearl millet breeding program was moving towards development of diverse new hybrid parental lines. The study suggested use of trait-specific donors in B- and R-lines separately to maintain sufficient genetic distance between seed and restorer breeding lines. It was pointed out to cross parents having higher genetic distance within the seed (B-lines) and restorer (R-lines) breeding programs to derive diverse and productive hybrid parental lines in future.
Highlights
In the combined set of 379 hybrid parents, comprising of both previously designated as well as current pearl millet hybrid parents, 355 alleles were detected by 28 simple sequence repeat (SSR) loci, with an average of 12.68 alleles per locus
ICMB 96666, B-23, B-24, B-57, B-65, B-6, B-45 and B-46 among B-line cluster had presence of seed parents (B-lines); and ICMP 451, IPC 337, IPC 492, IPC 962, IPC 997, IPC 1018, IPC 1027, IPC 1078, IPC 1307, IPC 1503, IPC 1617, R-118, R-125, R-128, R-131, R-144, R-148, R-155, R-159, R-160, and R-166 among Restorer lines (R-lines) were genetically more variable than other lines, with heterozygosity at four to eight SSR loci detected each in the B-lines and in the R-lines
The present study identified 15 B- and 37 R-lines from both the sets of lines with unique alleles (1 to 2 alleles) not present in other lines that can be used as genetic tags to supplement distinctness, uniformity, and stability (DUS) tests, enabling ICRISAT to protect these from possible infringement by multiple users who have received these lines for use in their hybrid breeding programs
Summary
Br.) is cultivated on about 30 million ha in more than 30 countries with the majority of this area in Asia (>10 million ha), Africa (about 18 million ha), and >2 million ha in the Americas It is important as a high temperature and drought tolerant grain crop in Africa and Asia, on low-fertility soils with limited water and nutrient holding capacity and is important as a hot season forage crop in semi-arid and arid parts of the world [1]. Based on the expected significant contribution of hybrids to pearl millet productivity enhancement in India, in the 1980s ICRISAT-Patancheru re-aligned its research strategy to better complement those of the Indian national program and private seed industry, and so focused on genetic diversification of hybrid parents. A recently conducted study found that private seed companies developed 103 hybrids in India during 2000-2010, and 62 (60%) were directly or indirectly based on ICRISAT bred hybrid parents [5]
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