Use of haploids and isozyme markers for genetic analysis in the polysomic polyploid potato

Hapluids (sporophytes with lhe gametic chrom06(Jme number) f,um polysomk: p(.Jlyploid~ represem a random gameti'c sample from the parenl and can be used 10 map genes that affect quantltat,ve trai! vmiation (OTV) with the aid of moleculm' markers (isozymes or RFLPs). The objel;ljvc: of (his work was to analyze QTV using isozyme markers in four potato (tetrasomic p0lyploid) haploid populations, Almost 200 haploids from lhe cvs. "Atlantic", "Chippewa'", "M,TrimRck'" and the advanced S('kction "W-231" were: evaluated ph~notypicaJJy for eight different agronomic traits and scored for 13 isozyme nll\rkers distributed in the 12 different linkage groups ot potatO, Eighl (lIZLI!,US "ere linked 10 quanlolatilJ(' trait loci (QT~) affecting QTV on the traits evaluated, HOW(;:lcT, lhere welt: difference" between haploid pupuJations for QTLs a... paren/. Three out of four QTLs for tuber yield and two out or lour QTLs tor avcrage tuber wci~ht, linked (0 isozyme markers in tht' Atlantic haploid population, had overdOnlmance as the main lypt: 01 g'.:Jjt' ;, ~osity on the phenotype and explains why the loss of parental heterozygosity, 01' the CliltiviJf Atlantic, results in lower than o.pcded tuber yield in its haploid progen)'. Key \\'()rds: Double reduction, Linkage maps, Molecular markers, QTLs, Solallum Il,beroswrl. INTRODUCTION the segregation ratios in the haploid population, DOUCHES el al. (1990) studied the segregation of 13 Haploids (sporophytes with the gametic isozyme loci in SOO haploids derived from six chromosome number) from poly~omic polyploids clones of the cultivated tetraploid potato (Gp. have been used for both genetic research and Tuberosum). In most families the gametic segrega­ breeding (JANSKY el ai., 1990; PELOQUIN el aZ" tion ratios fit expectations based upon the 4x geno­ 1990). Matemal haploids (211'-' 2x' 24) are easily type being diallelic, i.e" 31 3. a2 a2 . obtained in potato from 4x parents (2n= 48) via There always has been interest in mapping interploidy 'I x x 2x crosses (PELOOUIN el at., 1966). genes that affect quantitative traits, SAX (1923) was The 4x clones are crossed with pollen from 2x the first to find linkage between genes that influ­ clones of Gp. Phureja (e .g. 1. 22 or IvP 35). The ence quantitative traits and major genl,Cc;. With the haploids develop parthenogenetically C'pseudo­ development of molecuJar markers (isozymes and gamy") witn both male gametes feJiiJizing the restriction fragment length polymorph isms), gen­ central cell of the female gametophyte. Seeds with etic maps have been constructed for nUJllerOUS a 2x embryo and 6x endosperm are produced. crops (TANKS! TY ef ai., 1989), Thus, it is possible to Haploids must represent a random gametic identify chromosome segments which are associ­ sample from their polyploid parent to be valuable ated with quantitative variation (THODAY, 1961, in genetic studies. The use of genetic markers 1979), This can be clone by correlation bel ween ~ he allows this assumption to be tested by evaluating level of phenotypic expression of the trait and ~hc * Paper from the LaboratOly of Genel ics. Rcsc:arch supponccl by the Co)k~'c 01 AgriculturaJ and Life Sciences; Intcrnational Potato C~nter; USDA-CRCO-88-37234 3619, and Flito-I.ay, Inc , Correspollding author. Present addrt:' f1TA c/o Lambourn & Co., CaI'olyn H()~t<;f;, 26 Dingwall Road, Croydon, CR9 3FF.., England. b Present Address': AY;row Setd Comp:H1\ Idaho, USA,