Identification Of Maintainer Lines Research Articles

Successful deployment of marker assisted selection (MAS) for inbred and hybrid development in long-day onion (Allium cepaL.)

In the present investigation, male sterile and maintainer lines were identified using molecular markers in three long day onion populations. Molecular markers, 5’cob and orfA501 were able to distinguish effectively normal (N) and sterile (S) cytoplasm in all the three populations. The observed frequency of S cytoplasm in VL Piaz 67 (100%),VL Piaz3 (86.4%) and KR1 (90%) was higher than N cytoplasm. Out of the two PCR markers viz., OPT and PsaO used to determine the nuclear fertility restorer locus (Ms locus), OPT was found better than PsaO. Increased frequency of dominant homozygous alleles (87.4%) followed by heterozygous alleles (8.6%) and homozygous recessive alleles (4.0%) was observed. Fertility/sterility of plants were validated by acetocarmine staining of the pollens and correlated with observations made using molecular markers. Out of the three populations studied, only 12 plants (2.15%) happened to be completely male sterile in VL Piaz-3 and KR1 population, whereas there was no male sterile plant observed among the population in VL Piaz 67. Selfing and test crossing of plants having normal (N) cytoplasm led to the development and identification of maintainer lines in VL Piaz3 and KR1 population. This is the first example of deploying DNA markers for identification and purification of male sterility and hybrid development in long day onion in Indian population.

Single Nucleotide Polymorphisms in Linkage Disequilibrium with the Male-fertility Restoration (Ms) Locus in Open-pollinated and Inbred Populations of Onion

Maintainer lines are used to seed propagate male-sterile lines for the development of hybrid onion (Allium cepa L.) cultivars. The identification of maintainer lines would be more efficient with molecular markers distinguishing genotypes at the nuclear male-fertility restoration (Ms) locus. Ms has been mapped to chromosome 2 of onion and linked genetic markers identified. However, linkages between these markers and Ms were detected using F2 or BC1 families at maximum linkage disequilibrium and, for many markers, their efficacy to predict genotypes at Ms in onion populations at or near linkage equilibrium remains unknown. In this research, near isogenic lines homozygous-dominant and -recessive at Ms were developed and screened for 930 single nucleotide polymorphisms (SNPs). Three SNPs tightly linked on chromosome 2 remained in linkage disequilibrium with genotypes at Ms among randomly selected plants from three open-pollinated populations of onion as well as among a collection of inbred lines. These SNPs should be useful for selection of the recessive ms allele to aid in the development of maintainer lines for hybrid onion development.

Practical Application of PCR-based Technology to Screen Texas Onion Breeding Lines for Cytoplasmic Male Sterility

Identification and production of onion male-sterile and maintainer lines by conventional breeding takes between 4 to 8 years, due in part to the biennial nature of onion. In addition, male sterile plants and maintainer genotypes occur at a very low frequency in onion populations (Pike, 1986). A significantly shorter and more efficient alternative involves the screening of breeding lines for cytoplasmic male sterility using PCR-based technology. Thirty short-day onion breeding lines from the Texas A&M onion program were screened for type of cytoplasm (normal or sterile). Specific amplification of a fragment of chloroplast genome was achieved using the polymerase chain reaction according to Havey (1991). Forty-eight individual onion plants were screened per line. Out of thirty lines evaluated, 13 showed 100% sterile cytoplasm, 6 showed 100% normal cytoplasm, and 11 showed both types of cytoplasm. Lines showing normal cytoplasm or both cytoplasmic types were kept and reanalyzed. Only plants presenting normal cytoplasm were grown to maturity to help in the identification of maintainer lines as part of the Texas A&M onion breeding program.

Fertility Restoration in Male Sterille ✕ Maintainer Hybrids of Pearl Millet

Effects of environment and parental nuclear genotype may cause considerable difficulties in the identification of maintainer lines (Blines) and in the classification of different sources of cytoplasmic male‐sterility (cms) in pearl millet [Pennisetum glaucum (L.) R. Br.]. We studied the pollen shedding pattern as a measure of fertility restoration in A ✕ B hybrids of pearl millet by crossing seven cytoplasmic male‐sterile lines (A‐lines) with the B‐lines of each of the A‐lines at the ICRISAT Center in the dry and rainy seasons for 2 yr. Five of the A, system A‐lines (i.e. A ✕ B parental crosses) were stable for male‐sterility, whereas one was sterile in the dry season but produced a low frequency of pollen shedders in the rainy season. The non‐Al system A‐line (PT 732A) produced a low frequency of pollen shedders in both dry and rainy seasons. In comparison, almost all the non parental A ✕ B hybrids were uniformly or predominantly fertile across all the tests. The seed set data under selfing were generally supportive of the pollen fertility pattern. These results indicate that isonuclear lines or hybrids should be used for the reliable classification of cms sources in pearl millet. Fertility restoration pattern of hybrids in our study does not provide adequate evidence for differentiating the cytoplasm of PT 732A from that of Tift 23A1. A higher proportion of B‐lines produced sterile hybrids on 81A than on other A‐lines, indicating that 81A is a more efficient tester than other A‐lines used in this study for identifying B‐line sources.