Heritability and Early-Generation Selection for Resistance to Early and Late Leafspot in Peanut

The genetic nature of resistance to early (Cercospora arachidicola Hori) and late [Cercosporidiumpersonatum (Berk. &Curt.) Deightonl eafspot oi peanut (Arachis hypogaea L.) is quantitative, making selection for resistance difficult in segregating populations. In many areas of peanut production, without fungicide application one or both diseases may significantly reduce yields. A study was conducted to obtain heritability estimates, responses to selection, and relationship of resistance of two peanut populations for early and late leafspot resistance. Selection based on F2 family means in the F, generation via defoliation, infection, and sporulation Aas performed for early and late leafspot in North Carolina and Georgia, respectively, within populations of P] 314817/[TG3/EC 76446 (292)l and (FIl 314817/ ICGS 4). Divergent selections for each disease were evaluated in the F, generation at the same locations the following year for resistance by visual rating of infection and defoliation. Broad-sense heritability estimates ranged from to" to high (0.12-0.88) for components of resistance to each leaf-spot disease. Narron-sense heritability estimates from parent-otfspring regression (0.18-0.74) and realized heritability (0.60-1.41) were significant for late leafspot resistance and early leafspot resistance in the 1 314817/ITG3/EC 76446 (292)1 population. Results indicated that selection based on family means would be successful. Seiection of individual plants within families did not significantly improve genetic progress. NIoderate to high correlations (0.41-0.86) existed between early and late leafspot disease components indicating possible genetic linkage or host-plant physiology that conferred resistance to both diseases in one population. A MONG foliar fungal disease of peanut, early and late leafspot are the most widespread and destructive. Leafspots, if not controlled, can cause extensive defoliation and necrosis that significantly reduce yields (8,13[p. 7-15]). Chemical controls can increase production costs by 10% (7). The development of resistant breeding lines with high yield would increase net income for peanut farmers and reduce dependence on chemical control. Effectivc selection in early generations of segregat­ ing material can be achieved only when additive genetic effects are substantial and heritability is high. Additive gene action has been reported to be significant fer both early (9,10) and late ( 14,16,2 1) leafspot resistance. Green and Wynne (9) determined that nonadditive effects are also important for early leafspot resistance. Dominance was significant for the resistance components lesion size, latent period, and sporulation from a generation means analysis on late leafspot by ,Jogloy (14). Nevill (16) concluded from F. W.F. Anderson and J.C. Wsnnc. )ep. of 'rop Science. North Carolina State tUniv. Raleigh. NC 27695-7629: and (.(. Holbrook, USI)A-ARS. Coastal Plain Exp. Sin. Tifton. (VA 3179,-074,. North ('aolina Agric. Res. Scr. Paper no. 12571. The insestigaton was partialiy supported by the Peanut (ollaboratlie Research Sup­ port Program. t .S. Agencs for Int. Development grant No. )AN4048-(6-SS-2(65-(0). Reconimmendat ions do not represent an official position or policy tfUS.AD) or tS)A. Received I Mar. 1990. *Corresponding author. Published in Crop Sci. 31:588-593 (1991). populations skewed toward the susceptible parents that resistance to both leafspot diseases is polygenic and recessive. Estimates of narrow-sense heritabilities (12,14,15) have ranged from low to high for compo­ nents of resistance. Jogloy (14) found that heritability estimates were variable among crosses tested and among components of resistance within crosses. In general, broad-sense heritab;lity estimates for com­ ponents of resistance have been higher than narrow­ sense estimates (2,3, 15), substantiating the evidence that nonadditive gene effects add to the total genetic variance. Resistances to the two leafspot diseases on peanut is thought to be genetically independent (2). Through tandem selection in diverse populations, se­ lection of individual families with resistance to both leafspot diseases should be possibhc. Effective early generation selection for leafspot reEiftancewoul be angeon for pre­ sistance would b advantageous and allow for proce­ dures such as independent culling, tandem selection or index selection involving other traits such as yield. seed quality, and multip! ': pest resistance. Iroume and Knauft (12) recommended that selection among cross­ es be performed in early generation for late leafspot resistance, but they concluded that within-family se­ lection would not be effective because of low herita­ bility. Reports of response to selection or of realized heritability for resistance to leafspot are lacking in the literature. The objectives of this study were to (i) evaluate the response of peanut genotypes to selection within and among F2-derived families; (ii) determine realized her­ itabilities from family selections for early and late leaf­ spot; (iii) compL. ,, oroad-sense, narrow-sense, and realized heritability estimates in the populations; and (iv) determine the relationship of resistance to early and late leafspot through correlated response to selection. MATERIALS AND METHODS Two biparental populations from a 10-parent diallel cross were chosen for this study based on general and specific corn­ bining abilities for components of resistance to early leafspot and late leafspot tested in "_ hybrid (F) generation (I). Two of the parents IPI 314817 and [TG3/EC 76446(292)11 were identified as being highly resistant to late leafspot and mod­ crately resistant to early leafspot by the International Crops Research Institute for ote Semi-Arid Tropics (ICRISAT) (20). The other parent (ICGS 4) is a high-yielding, snmll-s,'cdcd Virginia peanut from ICRISAT. The F, seed from the two crosses JPI 3l4817/[TG3/E(" 76446(292)1 and ! 11314817/ ICGS 4) and parents were grown in the greenhouse during the winter of 1986-1987. Plants were harvested and F seed from the 50 and 40 highest yielding F. plants in ('ross , I PIf 314817/[TG3/EC 76446(292)]] and Cross 2 [P1 314817/1('GS 41, respectively, wre used Im lea'spot assessment during the