22 PEANUT SCIENCE Pathways for Introgression of Pest Resistance into Arachis hypogaea L.' Charles E. Simpson! ABSTRACT Four pathways for gene introgression into Arachis hypogaea L. were studied. Two "hexaploid routes" involved direct crosses of diploid Arachis species and diploid species hybrids with A.hypogaea (Pathways 1 and 2, respectively) and were followed by chromosome doubling with colchicine. A third pathway, a tetraploid route, involved chromosome doubling of a diploid hybrid before crossing with A. hypogaea. These first three routes involved only the A genome species, and all were unsuccessful because of lack of fertility. The fourth pathway, also a tetraploid route, utilized the B genome A. batizocoi Krap, et Greg. as a bridge species and brought about a successful (fertile) introgression. Genes from A. cardenasii Krap. et Greg. nom. nud. andA. chacoensis Krap et Greg. nom. nud. were combined into a hybrid and incorporated into A. hypogaea by using the B genome bridge species. Introgression of additional characters from these and other species through this pathway should be possible. Key Words: Peanut, groundnut, Arachis hypogaea L., interspecific hybrids, introgression, leafspot, nematode, resistance, wild species. "Texas Agricultural Experiment Station, Texas A&M UniversityTA No. 25605. 2Professor, Texas Agricultural Experiment Station, Texas A&M University, Stephenville, TX 76401. Peanut Science (1991) 18:22-26 The search for variability for use in improvement of the cultivated peanut, Arachis hypogaea L. (called groundnut in much of the world), has focused on plant introductions since the early stages of peanut breeding in the USA. In the mid1940's the possibility of finding needed variability in other species came to the attention of Gregory (5, 6, 7) and Krapovickas (12). Considerable attention has been given to searching for, collecting, introducing, preserving, and evaluatinggermplasm in the form of wild Arachis species (8, 25), and effort has been directed toward utilization of the wild species in improvement of the cultigen (1, 2, 14, 28, 30, 31,40,42). In Arachis, the most devastating diseases world wide include the leafspots, early (Cercospora arachidicola Hori) and late [Cercosporidium personatum (Berk. and Curt.) Deighton] (21, 41). Thousands of A. hypogaea lines have been evaluated for resistance to these two organisms, and some lines with resistance have been identified (13, 21, 35, 41). Attempts to utilize this resistance have been made by numerous breeders [13, and see reviews by Gregory (7), Norden (18), Norden et al. (19) Stalker and Moss (40), and Wynne and Halward (42)], with limited success. Recently the first cultivar with resistance to late leafspot was released by Gorbet and co-workers (3). 23 INTROGRESSION IN ARACHIS Abdou et al. (1) determined that A. chacoensis Krap et Greg. nom. nud. (GKP-I0602, PI-276235) had a high level of resistance to early leafspot, and A. cardenasii Krap et Greg. nom. nud. (GKP-I0017, PI-262141) was immune to late leafspot. The results of Sharief et al. (22) indicated that the genes for the resistance to these two diseases were not at the same loci; thus, providing a possibilitythat the resistances could be combined into one genotype, as suggested by Smartt et al. (34). Recently, Nelson et al. (15) identified high levels of resistance to root-knot nematode, Meloidogyne arenaria (Neal) Chitwood in twenty-one Arachis species. Within this group, the best resistance to M. arenaria was identified in A. cardenasii (GKP-I0017) andA. batizocoi Krap. et. Greg. (K9484) (PI -298639). These two species represent two different resistance mechanisms (15). Smartt et al. (33) identified two genomes (A and B) in the section Arachis, both of which occur in the tetraploid A. hypogaea. Chromosome analyses by Stalker and Dalmacio (39) and by Singh and Moss (26) strongly support the two genome theory. Most diploid wild species which have been identified as section Arachis have the A genome, including A. cardenasii andA. chacoensis. Progeny from crosses within the A genome have varying levels offertility (4,26,27,32,36, 38). Arachis batizocoi is the only diploid B genome species which has been identified to date. When wild diploid Arachis species are crossed directly with the cultigen, A. hypogaea, triploids are produced which are essentially sterile. However, several studies have shown that triploids between many A genome diploids and A. hypogaea produce varying degrees ofpeg, pod, and seed set (22,24,27,32,34,38). Wild Arachis genes have been introgressed into A. hypogaea. See the review by Stalker and Moss (40) for a complete description ofthese reports. The objective ofthese studies was to develop a consistent pathway for introgressing wildArachis genes for pest resistance into A. hypogaea. This paper reports on four attempted procedures. The efforts began in 1970 (Table 1), and have continued to the present (Table 2). as described by Banks (2). Pollen was stained in a 1:1 mixture of acetocarmine/glycerin. Pollen counts were made by placing the pollen from one flower under a 22 mm" coverslip with acetocarmine/glycerin, taking the mean of five 100-grain counts made from random fields (maximum of ten grains per field), and making three flower counts per plant on separate days. These pollen counts were made on all plants which flowered, with the exceptions noted in Table 1. Plants were grown in deep soil benches, clay pots, or lined fruit baskets. In the short days of winter, daylength was extended to 12 h by using incandescent plant growth bulbs. Plants were inoculated with a commerical Rhizobium inoculum. The soil was a mix of fine sandy loam top soil and builders sand or washed river sand mixed in a 1:1 ratio. Final sand content of the soil mix was approximately 92%. Leafspot resistance was determined in laboratory experiments by using a modification of the detached leaf technique described by Melouk and Banks (13). Field screening was accomplished by using the ICRISATscale (41) or the Florida scale (11) for late leafspot. Nematode studies were described by Nelson et al. (15). Parent numbers used in these studies correspond to parent numbers cited by Gregory and Gregory (4) for parents 19,34, and 37. However, parents 82 and 83 were not the same germplasm as those used by Gregory and Gregory (4). The four pathways studied are outlined in Tables 1 and 2. Results and Discussion Pathway 1 My first attempts to transfer leafspot resistance were made by crossing parents 34 and 37 directly to parent 82. Triploids from A. hypogaea X 34 and 37 were produced and treated with colchicine to obtain hexaploids, Table 1 shows the pollen counts and ploidy ofthese hybrids and amphiploids. Meiotic behavior ofthe triploids was similar to that reported for other triploids (14, 24, 29, 30, 32, 37). The hexaploids were backcrossed to the A. hypogaea parent to produce pentaploid progeny (Table 1); however, a high level of sterility was encountered in the subsequent backcross and the pentaploids produced no seed (Table 1). This pathway has been used with some success by others (40,42). Table 1. Four pathways in attempts to introgress wild Arachis genes into A. hypogaea. Pollen Counts" se !~ l Year Number" Ploidy of Path· ways 82X34' 82X37 (82X34)C2 (82X37)c 82X(82X34) c 82X(82X37) c Materials and Methods The cultigens used in this research came from two of the four market classes. Spantex and .Tamnut 74 (parent 82) represented the spanish market type, and UF-439-16-1O-3-2 (parent 83), one of three sister lines comprising 'Flo runner' (9, 16), represented the runner market type. Spantex was used as parent 82 until 1973, then Tamnut 74 was substituted for the old "landrace" variety. Tamnut 74 was derived from a crossing scheme which involved A. rrwnticola Krap. et Rig., but the cuItivar is classified as subspecies fastigiata var. vulgare (23). Florunner has some spanish germplasm in its pedigree but is classified as subspecies hypogaea var. hypogaea (16). The wild species used in this program were collected in South America during the 1950's. Arachis batizocoi (K-9484)(parent 19) was collected in Southeast Bolivia and is thought by many to be one of the original parents of A. hypogaea (33). Arachis cardenasii (GKP-10017) (parent 34) was found near Robore in Eastern Bolivia and has been proposed as one of the parents of A. hypogaea (33). Arachis chacoensis (GKP-10602) (parent 37) was collected in north central Paraguay. All three species are diploid; A. batizocoi is annual and the other two are perennials. Standard cross pollination techniques were used in hybridization work as described by Norden (17). Cytological material was fixed in 1:1 alcohol/ acetic acid, modified (95% alcohol instead of 100%) Carney's or modified (added 5 mL chloroform/Inn mL) FAA solutions (10). Chromosomes were stained in acetocarmine or aceto-orcein. Chromosome numbers were doubled by treating cuttings with 0.02% colchicine or by treating seedlings CROSS 3 3 4 4 4 4 4 4 4 4 4 sx sx 6x ex 5x sx 2x observed yes/no average range % 5 6 23 7 % 2to 7 .OSto 12 14 to 37 4to 12 sterile" sterile" N N 53 to 62 1 to 93 6to 12 V V V 1970 1970 1971 1971 1972 1972 7(P) 16(P) 10(P) 10(P) 14(F) 56(P) 5(F) O· 59 V V V V 5x 1973 1974 1974 1975 (34X37)° 82X(34X37) 0 82X[82X{34X37) c] 4x 4x 4x 1975 1975 1976 61(P) 6(P) 27'(P) 68 19X(34X37) [19X(34X37)] 0 82X[19X(34X37)] 0 82X[19X(34X37)] e 83X[19X(34X37)) C 83X[19X(34X37)]c 83X[19X(34X37)) C 82X[82X(19X(34X37» oJ' 83X[83X(19X(34X37» oJ' 2x 1976 1976 1977 1978 1977 1977 1978 1979 1979 29(P) 5(P) 8 group 1(P) group 2(P) group 1(P) group 2(P) group 3(P) 17(P) 37(P) 0.6 78 7 29 15 19 32 30 OtoO.8 70 to 92 Oto 24 27 to 32 2t031 8t037 29 to 35 14 to 68 N 4x 4x 4x 4x 4x 4x 4x 40 9t079 Y 34X37 82X(34X37) [82X(34X37)] c 82X[82X(34X37)] C 3 hybrid 3x ex 4x 18 10 N 31 01099 17 to 42 V V N • Number of flowers (F) on one plant. or number of plants (P) observed. "Percentage of stained (viable) pollen, rounded to whole numbers. 1 Parental numbers used to identify parents in program. 19=~ (K-9484). 34=.A. ~ (GKP-10017). (GKP-10602). 37=.A. ~ 82=h. ~ var. .l!l.!!gm (Spantex through 1973). 82=h. ~ var. .l!l.!!gm (Tamnut 74 after 1973). var. ~ (UF-439-16-1C-3-2. component line of Florunner). 83=1>. ~ 2 Treated with colchicine to double the chromosome number. 3 The only flowers produced were used for crossing attempts. 4 All embryos aborted. 5 All plants were weak, none produced viable seeds. 6 A group represents from 4 to 7 plants from one F,. 7 Backcross one. V V V V V V y 24 PEANUT SCIENCE Pathway 2 Attempts to hybridize A. cardenasii (parent 34) and A. chacoensis (parent 37) to combine the two leafspot resistances met with complete failure when pollinations were made inside the greenhouse. Success was achieved by growing the female parent (parent 34) outdoors, where one seed was obtained after making 3500 pollinations. The resulting diploid hybrid plant was crossed (as a male parent) with Tamnut 74 (parent 82), producing triploids, Colchicine treatment of triploid seeds resulted in one partially fertile hexaploid (Table 1). The first backcross to parent 82 produced a pentaploid that closely resembled the A. hypogaeaparent in phenotype. Pollen staining (Table 1) indicated no male fertility, selfed seed were not obtained, and no seed were produced from backcross pollination with parent 82, even though pegs and pods developed. No attempts were made to culture the aborted embryos. Use of this pathway for germplasm enhancement has not been reported. Pathway 3 Cuttings and seeds from the 34 X 37 hybrid plant were treated with colchicine. Some of the resulting tetraploids had high levels of stainable pollen (Table 1), so crosses were attempted with parent 82. Resulting progenywere tetraploid with varying levels ofpollen stainability (Table 1). The plants appeared somewhat intermediate between wild and cultivated peanuts in early growth stages, but as they grew they became progressively more like the wild type in appearance. Fertility was low on all plants and no seed were produced (Table 1). These results on pathways 1 to 3 differ from those reported by others (40,42). The difference is most likely due to the use of different A. hypogaea parents, although location (latitude, elevation, climate) may have more effect than realized at the time these crosses were made. Existence of effects of differences in location were pointed out by Stalker and Moss (40). Pathway 4 The above approaches did not appear promising for the introgression of characters due to lack of fertility, so the 34 X 37 diploid hybrid was crossed with A. batizocoi. This approach (Pathway 4) had been proposed by Smartt et al (34) as a solution to overcoming the sterility barrier between A. hypogaea and diploid species. They hypothesized that use of the B genome parent might make the complex amphiploids more cross-compatible with A. hypogaea. The diploid threeway hybrid [19 X (34 X 37)] was sterile (anticipated), an ideal situation for colchicine doubling. The induced tetraploid expressed elevated hybrid vigor, had 92% pollen stainability (Table 1), and was highly female fertile. The complex amphiploid was hybridized with Tamnut 74 and the Florunner component line. The progeny expressed considerable hybrid vigor, a moderate level ofpollen stained (Table 1) and a low level of seed set. Backcrosses to the two A. hypogaea parents were accomplished readily. At this stage, the first backcross F l'S were evaluated for early and late leafspot resistance. High levels of resistance to both diseases were present in all plants evaluated, indicating that the gene groups can be combined into one plant. Others have confirmed this conclusion (14, 37, 38, 40, 42). Recombination of the genes for resistance into the A. hypogaea cytoplasm has been confirmed by Ouedraogo (20) in BCsF 4's derived from these lines. In an attempt to accelerate the introgression of disease resistance into A. hypogaea, the subsequent testing and backcrossing after the BC l generation was all done using greenhouse and laboratory techniques, whereby BCnFl's were tested for leafspot resistance and plants identified as resistant were again backcrossed to A. hypogaea (Table 2). The stainable pollen count data presented in Table 2 for the sixbackcross generations show that the stainablilityofpollen increased from BC l to BC 4' The data for BCs and BC6 do not appear to reflect increases; however, this may not be the case. Beginning in 1985 (last halfofBC4 cycle, i.e., parent 82 backcross) and continuing to date, an over-all suppression of pollen quality has been noted in our program. The reduction in stainable pollen (7 to 12%) was suspected at first, but has now been confirmed on cultivars, species, and hybrids analyzed before and after 1985. The reason for the lower counts has been identified and is being verified, but will not be presented here. If a conditions-induced reduction of7 to 12% is assumed on the BC s and BC pollen counts a continuous increase in pollen stain for the six backcrosses was observed. Although pollen stain counts are not necessarily the same as plant fertility, if used properly, they can be a relative measure ofmale fertility. In these studies the absolute percentage of pollen stained was not important because the fertility levels were high enough after the BC 3 generation to allow the germplasm to be used as a parent with A. hypogaea for introgression of desirable traits. After five cycles of testinglbackcrossing in the above manner, seeds of BC sF 2 families were increased for field Table 2. A successful pathway for introgression from Arachis species to A hypogaea. Cross or Backcross Parent Number Number Plants observed Pollen Coynts· average range % Seed set yes/no % Pathway 4 82X[19X(34X37)] c1.2 83X[19X(34X37)] c 4 (group 3)3 27 24-32 Y 4 (group 4) 30 27-31 Y BC 1 82 17 30 14-68 Y (1979-1982) 83 37 40 09-79 Y BC 2 82 3 46 18-80 Y (1982-1983) 83 14 48 11-95 Y BC 3 82 18 74 59-85 Y (1983-1984) 83 56 72 32-96 Y BC 4 82 12 73 64-84 Y (1984-1985) 83 70 82 13-92 Y BC s 82 18 69 54-77 Y (1985-1986) 83 68 78 63-88 Y BC e 82 20 75 68-80 y (1986-1987) 83 44 74 65-84 y • Percentage of stained (viable) pollen, rounded to whole numbers. 1 Parental numbers used to identify parents in program. 19=~ (K-9484). 34=,8. ~ (GKP-10017). 37=,8. chacoensis (GKP-10602). 82=,8. ~ var. ~ (Spantex through 1973). 82=,8. ~ var. ~ (Tamnut 74 after 1973). 83=,8. ~ var. ~ (UF-439-16-10-3-2, component line of Florunner). 2 Plant treated with colchicine to double the chromosome number. 3 A group represents 4 plants from one F1 • INTROGRESSION IN ARACHIS testing. Field evaluation ofthe BCsF 2 families indicated that resistance to leafspot had been introgressed into A. hypogaea. Further evaluation of six of these lines (20) has confirmed introgression ofleafspot resistance greaterthan that expressed by the C. personatum resistant cultivar, 'Southern Runner' (3). Evaluating this program in light ofthe available literature (e.g., 40, 42) points out the reason for lack of high levels of leafspot resistance. The characters of early and late leafspot are apparently multigenic with the strong possibility that each character is controlled by two or more genes. Thus the testing and backcrossing should have been conducted on BC nF2's or BC F 's rather than BCnF1's.The characters can be introgressed through pathway 4 (20), but the time factor will be important because selections for backcrossing will have to be made after testing and from later generations. Cuttings were maintained ofalmost all generations (some cuttings died), and retesting ofthese materials indicated that the resistance to three diseases (early and late leafspot and southern root-knot nematode) was contained in the BC F 1 material (15,20 and unpublished data). Backcrossing to that generation followed by testing of BC nF2's (or later generations) should result in development of leafspot resistant/root-knot nematode resistant germplasm that is highly compatible with A. hypogaea. Conclusions Conclusions drawn from these and the related studies are as follows: 1. Hybrids between A and B genome Arachis parents appear to be useful for introgressing characters into A. hypogaea from wild Arachis species. 2. B genome A. batizocoi can serve as an effective bridge species between A genome wild Arachis and A. hypogaea. 3. The results support the hypothesis that leafspot resistance is multigenic. 4. Leafspot resistant/root-knot nematode resistant cultivars of peanut should be possible by introgression of genes from wild peanut species into A. hypogaea. Acknowledgments The author thanks W.e. Gregory and M.P. Gregory for stimulating his interest in this program, and he gratefully acknowledges the technical assistance of Wm. H. Higgins, Jr., K.E. Woodard, D.L. Higgins, K.S. Davis, and numerous Tarleton State University students. Also, the encouragement and adviseofO.D. SmithandJ.S. Newman isacknowledged. Literature Cited 1. Abdou, Y. A-M., W. e. Gregory, W. E. Cooper. 1974. Sources and Nature of resistance to Cercospora arachidicola Hori. and Cercosporidium personatum (Beck and Curtis) Deighton in Arachis species. Peanut Sci. 1:6-11. 2. Banks, D. J. 1977. A colchicine method which achieves fertility in interspecific peanut hybrids. Proc. Amer. Peanut Res. and Educ. Assoc. 9:30 (Abstr.). 3. Gorbet, D. W., A. J. Norden, and F. M. Shokes. 1987. Registration of 'Southern Runner' peanut. Crop Sci. 27:817. 4. Gregory, M. P., and W. e. Gregory. 1979. Exotic germ plasm of Arachis L. interspecific hybrids.]. Hered. 70:185-193. 5. Gregory, W. C. 1945. Research and Farming. pp. 33-35. 68th Ann. Rpt. N. e. Agric. Exp. Stn. N. C. State Univ. Raleigh, N. C. USA. 6. Gregory, W. C. 1946. Peanut Breeding Program underway. pp. 42-44. Research and Farming. 69th Ann. Rpt. N. e. Agric. Exp. Stn. N. C. State Univ. Raleigh, N. C. USA. 25 7. Gregory, W. C., B. W. Smith, and T. A. Yarbrough. 1951. Morphology, Genetics, and Breeding. pp. 28-88. in The peanut-the unpredictable legume. The Nat. Fertilizer Assoc. Washington, D. e. 8. Gregory, W. C., M. P. Gregory, A. Krapovickas, B. W. Smith, and J. A. Yarbrough. 1973. Structures and genetic resources of peanuts. pp. 47133. in e. T. Wilson (ed.), Peanuts-Culture and Uses. Amer. Peanut Res. and Educ. Assoc., Inc. Stillwater, OK. USA. 9. Jackson, L. F. 1983. Relative susceptibilities of component lines of peanut cultivars Early Bunch and Florunnerto early and late leafspots. Peanut Sci. 10:3-5. 10. Johansen, D. A. 1940. Plant Microtechnique. McGraw-Hill Book Co., Inc. New York and London. 11. Knauft, D. A., D. W. Gorbet, andA. J. Norden. 1988. Yieldand market quality of seven peanut genotypes as affected by leafspot disease and harvest date. Peanut Sci. 15:9-13. 12. Krapovickas,A.1969.The origin,variabilityandspreadofthegroundnut (Arachis hypogaea). pp. 427-440. in P. J. Ucko and G. W. Dimbelby (eds.), The domestication and exploitation of plants and animals. Duckworth. London. 13. Melouk, H. A.,and D. J. Banks. 1978. A method for screening peanut genotypes for resistance to Cercospora leafspot. Peanut Sci. 5:112114. 14. Moss, J. P., 1. V. Spielman, A. P. Burge, A. K. Singh, and R. W. Gibbons. 1981. Utilization of wild Arachis species as a source of Cercospora leafspot resistance in groundnut breeding. pp. 673-677. in G. K. Marna and U. Sinha (eds.), Perspectives in cytologyand genetics. Hindasia Publ. Delhi, India. 15. Nelson, S. c., e. E. Simpson, and J. L. Starr. 1989. Resistance to Meloidogyne arenaria in Arachis spp. germplasm. Supp. J. of Nematology 21:654-660. 16. Norden, A. J., R. W. Lipscomb, and W. A. Carver. 1969. Registration of Florunner peanuts. Crop Sci. 9:850. 17. Norden, A. J. 1980. Chapter 31 - Peanut. pp. 443-453. in W. R. Fehr and H. H. Hadley (eds.), Hybridization of Crop Plants. Amer. Soc. of Agron. Crop. Sci. Soc. of Amer. Madison, WI. USA. 18. Norden, A. J. 1973. Breeding of the cultivated peanut (Arachis hypogaea L.). pp. 175-208. in e. T. Wilson (ed.), Peanuts-Culture and Uses. Amer. Peanut Res. and Educ. Assoc., Inc. Stillwater, OK. USA. 19. Norden, A. J., O. D. Smith, and D. W. Gorbet. 1982. Breeding of the cultivated peanut. pp. 95-122. in H. E. Pattee and e. T. Young (eds.), Peanut Science and Technology. Amer. Peanut Res. and Educ. Soc. Yoakum, TX. USA. 20. Ouedraogo, M. 1990.Yield,grade, and leafspot reaction ofinterspecific derived peanut lines. M. S. Thesis 92 pp. Soil and Crop Sci. Dept. Texas A&M Univ., College Station, TX 77843. 21. Porter, D. M., D. H. Smith, and R. Rodriguez-Kabana. 1982. Peanut diseases. pp. 326-410. in H. E. Pattee and C. T. Young (eds.), Peanut Science and Technology. Amer. Peanut Res. and Educ. Soc. Yoakum, TX. USA. 22. Sharief, Y., J. O. Rawlings, and W. C. Gregory. 1978. Estimates of leafspot resistance in three interspecific hybrids of Arachis. Euphytica 27:741-751. 23. Simpson, C. E. and O. D. Smith. 1975. Registration of Tamnut 74 Peanut. Crop Sci. 15:603-604. 24. Simpson, C. E. and K. S. Davis. 1983. Meiotic behavior of a malefertile triploid Arachis L. hybrid. Crop Sci. 23:581-584. 25. Simpson, C. E. 1984. Plant Exploration: planning, organization, and implementation with special emphasis on Arachis. pp. 1-20. in W. L. Brown,T. T. Chang, M. M. Goodman, and Q.Jones (eds.),Conservation of Crop Germplasm-An International Perspective. Crop Sci. Soc. of Amer. Madison WI. USA. 26. Singh, A. K. and J. P. Moss. 1982. Utilization of wild relatives in genetic improvement of Arachis hypogaea L. Part 2. Chromosome complements of species in section Arachis. Theor. Appl. Genet. 61:305-314. 27. Singh, A. K. and J. P. Moss. 1984. Utilization ofwild relatives in genetic improvement of Arachis hypogaea L. VI. Fertility in Triploids: Cytological basis and breeding implications. Peanut Sci. 11:17-21. 28. Singh, A.K. 1986a. Alien gene transfer in groundnut by ploidy and genome Manipulations. pp. 207-209. in Horn, Jensen, Odenbach, and Schieder (eds.), Genetic Manipulation in Plant Breeding. Walter de Gruyter and Co. Berline , New York. 29. Singh, A. K. 1986b. Utilization of wild relatives in the genetic improvement of Arachis hypogaea L. 7. Autotetraploid production and prospects in inter-specific breeding. Theor. Appl. Genet. 72:164- 26 PEANUT SCIENCE 169. 30. Singh, A. K. 1986c. Utilization of wild relatives in the genetic improvement of Arachis hypogaea L. 8. Synthetic amphidiploids and their importance in interspecific breeding. Theor. Appl. Genet. 72:433439. 31. Singh, A. K. 1988. Putative genome donors of Arachis hypogaea (Fabaceae), evidence from crossess with synthetic amphidipolids. Plant Syst. and Evol, 160:143-151. 32. Smartt, J. 1965. Cross-compatibility relationships between the cultivated peanut Arachis hypogaea L. and other species of the genus Arachis. Ph.D Thesis, North Carolina State Univ., Raleigh. Univ. Microfilms Int. Ann Arbor Mich. (Diss. Abstr. 65:8968). 33. Smartt, J.W. C. Gregory, and M. P. Gregory. 1978. The genomes of Arachis hypogaea 1. Cytogenetic studies of putative genome donors. Euphytica 27:665-675. 34. Smartt, J., W. C. Gregroy, and M. P. Gregory. 1978. The genomes of Arachis hypogaea 2. The implications in interspecific breeding. Euphytica 27:677-680. 35. Sowell, G., Jr., D. H. Smith, and R. O. Hammons. 1976. Resistance of peanut plant introductions to Cercospora arachidicola. Plant Disease Peanut Science (1991) 18:26-30 Reporter 60:494-498. 36. Spielman, I. V., A.P. Burge, and J.P. Moss. 1979. Chromosome loss and meiotic behaviour in interspecific hybrids in the genus Arachis L. and their implications in breeding for disease resistance. Z. Pflanzenzuchtg 83:236-250. 37. Stalker, H. T. andJ. C. Wynne. 1979. Cytology ofinterspecific hybrids in section Arachis of peanuts. Peanut Sci. 6:110-114. 38. Stalker, H. T, J. C. Wynne, and M. Company. 1979. Variation in progenies of an Arachis hypogaea X diploid wild species hybrid. Euphytica 28:675-684. 39. Stalker, H. T and R. D. Dalmacio. 1981. Chromosomes of Arachis species, section Arachis. J. Hered. 72:403-408. 40. Stalker, H. T and J. P. Moss. 1987. Speciation, Cytogenetics, and Utilization of Arachis Species. Adv. in Agron. 41:1-40. 41. Subrahmanyam, P., D. McDonald, R. W. Gibbons, S. N. Nigam, and D. J. Nevill. 1982. Resistance to rust and late leafspot diseases in some genotypes of Arachis hypogaea. Peanut Sci. 9:6-10. 42. Wynne, J. C. and T. Halward. 1989. Cytogenetics and Genetics of Arachis. Critical Reviews in Plant Sciences 8:189-220. Accepted February 8,1991